Brown, N.J.; Fuchs, B.A.
1989-04-24
The thesis of this paper is that shear mode grinding of glass (1) occurs with abrasive particle sizes less than 1/mu/m, (2) that it is the mechanical limit of the the more common mechanical-chemical glass polishing, and (3) that the debris is insufficient in size to perform the function of eroding the binder in the grinding wheel and thus necessitates the addition of an abrasive and/or chemical additions to the coolant to effect wheel-dressing. 13 refs.
Ke, Jie; King, P J; George, Michael W; Poliakoff, Martyn
2005-01-01
A new approach to locating the critical point of fluid mixtures is reported, utilizing a shear mode piezoelectric sensor. This technique employs a single piece of quartz crystal that is installed at the bottom of a strongly stirred high-pressure vessel. The sensor response indicates whether liquid or gas is in contact with its surfaces. Thus, the sensor is able to identify vapor-liquid phase separation by registering a discontinuity in the impedance minimum of the sensor as a function of pressure. Two systems (methanol + CO2 and H2 + CO2) have been investigated using this method. The critical point data of the methanol + CO2 system were chosen to validate the approach against a wealth of literature data, and good agreement was obtained. The sensor behavior in the two-phase region, as well as the effect of stirring, is discussed. The method is general and can be used with other sensors.
NASA Astrophysics Data System (ADS)
Jin, Hyung-Ha; Ko, Eunsol; Kwon, Junhyun; Hwang, Seong Sik; Shin, Chansun
2016-03-01
Micro-compression tests were applied to evaluate the changes in the strength and deformation mode of proton-irradiated commercial austenitic stainless steel. Proton irradiation generated small dots at low dose levels and Frank loops at high dose levels. The increase in critical resolved shear stresses (CRSS) was measured from micro-compression of pillars and the Schmid factor calculated from the measured loading direction. The magnitudes of the CRSS increase were in good agreement with the values calculated from the barrier hardening model using the measured size and density of radiation defects. The deformation mode changed upon increasing the irradiation dose level. At a low radiation dose level, work hardening and smooth flow behavior were observed. Increasing the dose level resulted in the flow behavior changing to a distinct heterogeneous flow, yielding a few large strain bursts in the stress-strain curves. The change in the deformation mode was related to the formation and propagation of defect-free slip bands. The effect of the orientation of the pillar or loading direction on the strengths is discussed.
Oag, Robert M; King, Peter J; Mellor, Christopher J; George, Michael W; Ke, Jie; Poliakoff, Martyn
2003-02-01
With the rapidly expanding industrial and research applications of near-critical and supercritical technology there is a pressing need for a simple and inexpensive sensor that may be used to determine the phase coexistence regions of fluid mixtures and to establish whether a fluid system is below, at, or above, a critical point. Mechanically vibrating AT-cut quartz plates may be used to determine the product of the fluid density and viscosity of a fluid in which it is immersed, through measurement of the impedance minimum of the electrical equivalent circuit or of the corresponding frequency. The density-viscosity product changes abruptly between fluid phases and rapidly along the isotherm corresponding to the critical temperature, enabling such a plate to act as a sensor of these fluid features. We consider the limitations and linearity of such a sensor and its behavior when a liquid-gas meniscus crosses its surface. We demonstrate for the first time the effective use of an AT-cut quartz sensor in mapping the phase behavior of fluids, using measurements made on carbon dioxide and ethane for calibration and then investigating an ethane-carbon dioxide mixture. The advantages of this experimental approach are that (i) piezoelectric sensors are available for operation up to 1,000 degrees C and at extremely high pressures and (ii) the measurement of the density-viscosity product of supercritical fluids is inherently simpler than traditional techniques for determining phase behavior.
Sheared-flow Modes in Toroidal Geometry
J.L.V. Lewandowski; T.S. Hahm; W.W. Lee; Z. Lin
1999-10-01
Using a Fourier-Bessel representation for the fluctuating (turbulent) electrostatic potential, an equation governing the sheared-flow modes in toroidal geometry is derived from the gyrokinetic Poisson equation, where both the adiabatic and non-adiabatic responses of the electrons are taken into account. It is shown that the principal geometrical effect on sheared-flow modes of the electrostatic potential is due to the flux-surface average of 1/B, where B is the magnetic field strength.
Shear horizontal guided wave modes to infer the shear stiffness of adhesive bond layers.
Le Crom, Bénédicte; Castaings, Michel
2010-04-01
This paper presents a non-destructive, ultrasonic technique to evaluate the quality of bonds between substrates. Shear-horizontally polarized (SH) wave modes are investigated to infer the shear stiffness of bonds, which is necessarily linked to the shear resistance that is a critical parameter for bonded structures. Numerical simulations are run for selecting the most appropriate SH wave modes, i.e., with higher sensitivity to the bond than to other components, and experiments are made for generating-detecting pre-selected SH wave modes and for measuring their phase velocities. An inverse problem is finally solved, consisting of the evaluation of the shear stiffness modulus of a bond layer at different curing times between a metallic plate and a composite patch, such assembly being investigated in the context of repair of aeronautical structures.
Wave packet critical layers in stratified shear flows
NASA Astrophysics Data System (ADS)
Maslowe, S. A.
1996-01-01
In the inviscid theory of shear flow stability, the eigenvalue problem for a neutral or weakly amplified mode revolves around possible discontinuities in the eigenfunction as the singular critical point is crossed. Extensions of the linear normal mode approach to include nonlinearity and/or wave packets lead to amplitude evolution equations whose coefficients generally involve singular integrals. In the past, viscosity, nonlinearity or time dependence has been introduced in a critical layer centered upon the singular point to resolve these integrals. The form of the amplitude evolution equation is greatly influenced by which choice is made. In this paper, a new approach is proposed in which wave packet effects are dominant in the critical layer, and it is argued that in many applications this is the appropriate choice. The theory is applied here to two-dimensional wave propagation in stratified shear flows.
Tearing Mode Stability with Sheared Toroidal Flows
NASA Astrophysics Data System (ADS)
White, Ryan; Coppi, Bruno
2016-10-01
Toroidal plasma flow induced by neutral beam heating has been found to increase the stability of tearing modes in tokamak plasmas. The need to extrapolate current (experimentally-based) knowledge of tearing mode onset to future machines, requiresa better understanding of the essential physics. We consider the physics of flow near the rational surfaces. For realistic flow profiles, the velocity shear near the rational surface can be treated as a perturbation, and is found to amplify the dominant stabilizing effect of magnetic curvature. This effect can be seen using a cylindrical model if large-aspect-ratio corrections to the magnetic curvature are incorporated. On the other hand, the physical effects of toroidal rotation are completely absent in a cylinder, and require a fully-toroidal calculation to study. The toroidal rotation near the rational surface is found to couple to a geometrical parameter which vanishes for up-down symmetric profiles. Physically, the dominant effects of rotation arise from a Coriolis force, leading to flow directional dependence. This work is supported by the US DOE.
Lapping: Polishing and shear mode grinding
Brown, N.J.
1990-02-01
It is the thesis of this paper that shear mode grinding (SMG), (ductile grinding, nanogrinding, fractureless grinding) is just a particular form of polishing. It may be unique in that it can involve a hard wheel of very precise dimensions compared to the soft laps usually used in polishing. Such a wheel would permit the fabrication of a precision surface on a brittle material such as glass at a precisely located and oriented position on a part. The technological and economic consequences of such a process seem important but the technical obstacles to implementing the technique are for the moment formidable. It is in production in Japan. This paper provides a bit of understanding of that process obtained by making an end run around the obstacles to view the process from the vantage point of lapping. The paper will lay out some of the concepts and terminology necessary to understand the papers that have supplied the real labor to get us to this point. It will refer to parts of this work briefly in passing so the reader who needs the details knows where to look, and for what, in the bibliography appended. 32 refs., 5 figs.
Dynamic modes of red blood cells in oscillatory shear flow.
Noguchi, Hiroshi
2010-06-01
The dynamics of red blood cells (RBCs) in oscillatory shear flow was studied using differential equations of three variables: a shape parameter, the inclination angle θ, and phase angle ϕ of the membrane rotation. In steady shear flow, three types of dynamics occur depending on the shear rate and viscosity ratio. (i) tank-treading (TT): ϕ rotates while the shape and θ oscillate. (ii) tumbling (TB): θ rotates while the shape and ϕ oscillate. (iii) intermediate motion: both ϕ and θ rotate synchronously or intermittently. In oscillatory shear flow, RBCs show various dynamics based on these three motions. For a low shear frequency with zero mean shear rate, a limit-cycle oscillation occurs, based on the TT or TB rotation at a high or low shear amplitude, respectively. This TT-based oscillation well explains recent experiments. In the middle shear amplitude, RBCs show an intermittent or synchronized oscillation. As shear frequency increases, the vesicle oscillation becomes delayed with respect to the shear oscillation. At a high frequency, multiple limit-cycle oscillations coexist. The thermal fluctuations can induce transitions between two orbits at very low shear amplitudes. For a high mean shear rate with small shear oscillation, the shape and θ oscillate in the TT motion but only one attractor exists even at high shear frequencies. The measurement of these oscillatory modes is a promising tool for quantifying the viscoelasticity of RBCs, synthetic capsules, and lipid vesicles.
Dynamic modes of red blood cells in oscillatory shear flow
NASA Astrophysics Data System (ADS)
Noguchi, Hiroshi
2010-06-01
The dynamics of red blood cells (RBCs) in oscillatory shear flow was studied using differential equations of three variables: a shape parameter, the inclination angle θ , and phase angle ϕ of the membrane rotation. In steady shear flow, three types of dynamics occur depending on the shear rate and viscosity ratio. (i) tank-treading (TT): ϕ rotates while the shape and θ oscillate. (ii) tumbling (TB): θ rotates while the shape and ϕ oscillate. (iii) intermediate motion: both ϕ and θ rotate synchronously or intermittently. In oscillatory shear flow, RBCs show various dynamics based on these three motions. For a low shear frequency with zero mean shear rate, a limit-cycle oscillation occurs, based on the TT or TB rotation at a high or low shear amplitude, respectively. This TT-based oscillation well explains recent experiments. In the middle shear amplitude, RBCs show an intermittent or synchronized oscillation. As shear frequency increases, the vesicle oscillation becomes delayed with respect to the shear oscillation. At a high frequency, multiple limit-cycle oscillations coexist. The thermal fluctuations can induce transitions between two orbits at very low shear amplitudes. For a high mean shear rate with small shear oscillation, the shape and θ oscillate in the TT motion but only one attractor exists even at high shear frequencies. The measurement of these oscillatory modes is a promising tool for quantifying the viscoelasticity of RBCs, synthetic capsules, and lipid vesicles.
The nonlinear evolution of modes on unstable stratified shear layers
NASA Technical Reports Server (NTRS)
Blackaby, Nicholas; Dando, Andrew; Hall, Philip
1993-01-01
The nonlinear development of disturbances in stratified shear flows (having a local Richardson number of value less than one quarter) is considered. Such modes are initially fast growing but, like related studies, we assume that the viscous, non-parallel spreading of the shear layer results in them evolving in a linear fashion until they reach a position where their amplitudes are large enough and their growth rates have diminished sufficiently so that amplitude equations can be derived using weakly nonlinear and non-equilibrium critical-layer theories. Four different basic integro-differential amplitude equations are possible, including one due to a novel mechanism; the relevant choice of amplitude equation, at a particular instance, being dependent on the relative sizes of the disturbance amplitude, the growth rate of the disturbance, its wavenumber, and the viscosity of the fluid. This richness of choice of possible nonlinearities arises mathematically from the indicial Frobenius roots of the governing linear inviscid equation (the Taylor-Goldstein equation) not, in general, differing by an integer. The initial nonlinear evolution of a mode will be governed by an integro-differential amplitude equations with a cubic nonlinearity but the resulting significant increase in the size of the disturbance's amplitude leads on to the next stage of the evolution process where the evolution of the mode is governed by an integro-differential amplitude equations with a quintic nonlinearity. Continued growth of the disturbance amplitude is expected during this stage, resulting in the effects of nonlinearity spreading to outside the critical level, by which time the flow has become fully nonlinear.
Shear Thinning Near the Critical Point of Xenon
NASA Technical Reports Server (NTRS)
Zimmerli, Gregory A.; Berg, Robert F.; Moldover, Michael R.; Yao, Minwu
2008-01-01
We measured shear thinning, a viscosity decrease ordinarily associated with complex liquids, near the critical point of xenon. The data span a wide range of reduced shear rate: 10(exp -3) < gamma-dot tau < 700, where gamma-dot tau is the shear rate scaled by the relaxation time tau of critical fluctuations. The measurements had a temperature resolution of 0.01 mK and were conducted in microgravity aboard the Space Shuttle Columbia to avoid the density stratification caused by Earth's gravity. The viscometer measured the drag on a delicate nickel screen as it oscillated in the xenon at amplitudes 3 mu,m < chi (sub 0) >430 mu, and frequencies 1 Hz < omega/2 pi < 5 Hz. To separate shear thinning from other nonlinearities, we computed the ratio of the viscous force on the screen at gamma-dot tau to the force at gamma-dot tau approximates 0: C(sub gamma) is identical with F(chi(sub 0), omega tau, gamma-dot tau )/F)(chi(sub 0, omega tau, 0). At low frequencies, (omega tau)(exp 2) < gamma-dot tau, C(sub gamma) depends only on gamma-dot tau, as predicted by dynamic critical scaling. At high frequencies, (omega tau)(exp 2) > gamma-dot tau, C(sub gamma) depends also on both x(sub 0) and omega. The data were compared with numerical calculations based on the Carreau-Yasuda relation for complex fluids: eta(gamma-dot)/eta(0)=[1+A(sub gamma)|gamma-dot tau|](exp - chi(sub eta)/3+chi(sub eta)), where chi(sub eta) =0.069 is the critical exponent for viscosity and mode-coupling theory predicts A(sub gamma) =0.121. For xenon we find A(sub gamma) =0.137 +/- 0.029, in agreement with the mode coupling value. Remarkably, the xenon data close to the critical temperature T(sub c) were independent of the cooling rate (both above and below T(sub c) and these data were symmetric about T(sub c) to within a temperature scale factor. The scale factors for the magnitude of the oscillator s response differed from those for the oscillator's phase; this suggests that the surface tension of the two
Shear Thinning Near the Critical Point of Xenon
NASA Technical Reports Server (NTRS)
Zimmerli, Gregory A.; Berg, Robert F.; Moldover, Michael R.; Yao, Minwu
2008-01-01
We measured shear thinning, a viscosity decrease ordinarily associated with complex liquids, near the critical point of xenon. The data span a wide range of reduced shear rate: 10(exp -3) < gamma-dot tau < 700, where gamma-dot tau is the shear rate scaled by the relaxation time tau of critical fluctuations. The measurements had a temperature resolution of 0.01 mK and were conducted in microgravity aboard the Space Shuttle Columbia to avoid the density stratification caused by Earth's gravity. The viscometer measured the drag on a delicate nickel screen as it oscillated in the xenon at amplitudes 3 mu,m < chi (sub 0) >430 mu, and frequencies 1 Hz < omega/2 pi < 5 Hz. To separate shear thinning from other nonlinearities, we computed the ratio of the viscous force on the screen at gamma-dot tau to the force at gamma-dot tau approximates 0: C(sub gamma) is identical with F(chi(sub 0), omega tau, gamma-dot tau )/F)(chi(sub 0, omega tau, 0). At low frequencies, (omega tau)(exp 2) < gamma-dot tau, C(sub gamma) depends only on gamma-dot tau, as predicted by dynamic critical scaling. At high frequencies, (omega tau)(exp 2) > gamma-dot tau, C(sub gamma) depends also on both x(sub 0) and omega. The data were compared with numerical calculations based on the Carreau-Yasuda relation for complex fluids: eta(gamma-dot)/eta(0)=[1+A(sub gamma)|gamma-dot tau|](exp - chi(sub eta)/3+chi(sub eta)), where chi(sub eta) =0.069 is the critical exponent for viscosity and mode-coupling theory predicts A(sub gamma) =0.121. For xenon we find A(sub gamma) =0.137 +/- 0.029, in agreement with the mode coupling value. Remarkably, the xenon data close to the critical temperature T(sub c) were independent of the cooling rate (both above and below T(sub c) and these data were symmetric about T(sub c) to within a temperature scale factor. The scale factors for the magnitude of the oscillator s response differed from those for the oscillator's phase; this suggests that the surface tension of the two
Longitudinal and shear mode ultrasound propagation in human skull bone
White, P.J.; Clement, G.T.; Hynynen, K.
2006-01-01
Recent studies have attempted to dispel the idea of the longitudinal mode being the only significant mode of ultrasound energy transport through the skull bone. The inclusion of shear waves in propagation models has been largely ignored because of an assumption that shear mode conversions from the skull interfaces to the surrounding media rendered the resulting acoustic field insignificant in amplitude and overly distorted. Experimental investigations with isotropic phantom materials and ex vivo human skulls demonstrated that, in certain cases, a shear mode propagation scenario not only can be less distorted, but at times allowed for a substantial (as much as 36% of the longitudinal pressure amplitude) transmission of energy. The phase speed of 1.0-MHz shear mode propagation through ex vivo human skull specimens has been measured to be nearly half of that of the longitudinal mode (shear sound speed = 1500±140 m/s, longitudinal sound speed = 2820±40 m/s), demonstrating that a closer match in impedance can be achieved between the skull and surrounding soft tissues with shear mode transmission. By comparing propagation model results with measurements of transcranial ultrasound transmission obtained by a radiation force method, the attenuation coefficient for the longitudinal mode of propagation was determined to between 14 Np/m and 70 Np/m for the frequency range studied while the same for shear waves was found to be between 94 Np/m and 213 Np/m. This study was performed within the frequency range of 0.2–0.9 MHz. (E-mail: white@bwh.harvard.edu) PMID:16829322
Enhanced ultra-low-frequency interlayer shear modes in folded graphene layers
NASA Astrophysics Data System (ADS)
Cong, Chunxiao; Yu, Ting
2014-08-01
Few-layer graphene has attracted tremendous attention owing to its exceptional electronic properties inherited from single-layer graphene and new features led by introducing extra freedoms such as interlayer stacking sequences or rotations. Effectively probing interlayer shear modes are critical for unravelling mechanical and electrical properties of few-layer graphene and further developing its practical potential. Unfortunately, shear modes are extremely weak and almost fully blocked by a Rayleigh rejecter in Raman measurements. This greatly hinders investigations of shear modes in few-layer graphene. Here, we demonstrate enhancing of shear modes by properly folding few-layer graphene. As a direct benefit of the strong signal, enhancement mechanism, vibrational symmetry, anharmonicity and electron-phonon coupling of the shear modes are uncovered through studies of Raman mapping, polarization- and temperature-dependent Raman spectroscopy. This work complements Raman studies of graphene layers, and paves an efficient way to exploit low-frequency shear modes of few-layer graphene and other two-dimensional layered materials.
Contained Modes In Mirrors With Sheared Rotation
Abraham J. Fetterman and Nathaniel J. Fisch
2010-10-08
In mirrors with E × B rotation, a fixed azimuthal perturbation in the lab frame can appear as a wave in the rotating frame. If the rotation frequency varies with radius, the plasma-frame wave frequency will also vary radially due to the Doppler shift. A wave that propagates in the high rotation plasma region might therefore be evanescent at the plasma edge. This can lead to radially localized Alfven eigenmodes with high azimuthal mode numbers. Contained Alfven modes are found both for peaked and non-peaked rotation profiles. These modes might be useful for alpha channeling or ion heating, as the high azimuthal wave number allows the plasma wave frequency in the rotating frame to exceed the ion cyclotron frequency. __________________________________________________
Material characterization of structural adhesives in the lap shear mode
NASA Technical Reports Server (NTRS)
Sancaktar, E.; Schenck, S. C.
1983-01-01
A general method for characterizing structual adhesives in the bonded lap shear mode is proposed. Two approaches in the form of semiempirical and theoretical approaches are used. The semiempirical approach includes Ludwik's and Zhurkov's equations to describe respectively, the failure stresses in the constant strain rate and constant stress loading modes with the inclusion of the temperature effects. The theoretical approach is used to describe adhesive shear stress-strain behavior with the use of viscoelastic or nonlinear elastic constitutive equations. Two different model adhesives are used in the single lap shear mode with titanium adherends. These adhesives (one of which was developed at NASA Langley Research Center) are currently considered by NASA for possible aerospace applications. Use of different model adhesives helps in assessment of the generality of the method.
Shear-mode scanning capacitance microscope
NASA Astrophysics Data System (ADS)
Naitou, Yuichi; Ookubo, Norio
2001-05-01
Scanning capacitance microscope (SCM) is developed using an all-metallic probe, whose distance from the sample is controlled by detecting the shear-force drag on the laterally oscillating probe. The oscillatory motion of the probe is electromechanically excited and detected. Using this SCM, a set of images of topography, dC/dV, and dC/dX is simultaneously obtained, where C and V are, respectively, capacitance and applied voltage between the probe and the sample, and X is the coordinate along probe tip oscillation. The SCM developed shows sensitivity for dC/dV higher than the conventional SCM. The dC/dX image clearly indicates the built-in depletion region due to the p-n junction.
Stabilization of ballooning modes with sheared toroidal rotation
Miller, R.L.; Waelbroeck, F.L.; Hassam, A.B.; Waltz, R.E.
1995-10-01
Stabilization of magnetohydrodynamic ballooning modes by sheared toroidal rotation is demonstrated using a shifted circle equilibrium model. A generalized ballooning mode representation is used to eliminate the fast Alfven wave, and an initial value code solves the resulting equations. The {ital s}{minus}{alpha} diagram (magnetic shear versus pressure gradient) of ballooning mode theory is extended to include rotational shear. In the ballooning representation, the modes shift periodically along the field line to the next point of unfavorable curvature. The shift frequency ({ital d}{Omega}/{ital dq}, where {Omega} is the angular toroidal velocity and {ital q} is the safety factor) is proportional to the rotation shear and inversely proportional to the magnetic shear. Stability improves with increasing shift frequency and direct stable access to the second stability regime occurs when this frequency is approximately one-quarter to one-half the Alfven frequency, {omega}{sub A}={ital V}{sub A}/{ital qR}. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Zonal flow dynamics in the double tearing mode with antisymmetric shear flows
Mao, Aohua; Li, Jiquan; Liu, Jinyuan; Kishimoto, Yasuaki
2014-05-15
The generation dynamics and the structural characteristics of zonal flows are investigated in the double tearing mode (DTM) with antisymmetric shear flows. Two kinds of zonal flow oscillations are revealed based on reduced resistive magnetohydrodynamics simulations, which depend on the shear flow amplitudes corresponding to different DTM eigen mode states, elaborated by Mao et al. [Phys. Plasmas 20, 022114 (2013)]. For the weak shear flows below an amplitude threshold, v{sub c}, at which two DTM eigen states with antisymmetric or symmetric magnetic island structure are degenerated, the zonal flows grow oscillatorily in the Rutherford regime during the nonlinear evolution of the DTMs. It is identified that the oscillation mechanism results from the nonlinear interaction between the distorted islands and the zonal flows through the modification of shear flows. However, for the medium shear flows above v{sub c} but below the critical threshold of the Kelvin-Helmholtz instability, an oscillatory growing zonal flow occurs in the linear phase of the DTM evolution. It is demonstrated that the zonal flow oscillation originates from the three-wave mode coupling or a modulation instability pumped by two DTM eigen modes with the same frequency but opposite propagating direction. With the shear flows increasing, the amplitude of zonal flow oscillation increases first and then decreases, whilst the oscillation frequency as twice of the Doppler frequency shift increases. Furthermore, impacts of the oscillatory zonal flows on the nonlinear evolution of DTM islands and the global reconnection are also discussed briefly.
Self-organized criticality of plastic shear bands in rocks
Poliakov, A.N.B.; Herrmann, H.J.
1994-09-01
We show that the shear bands that appear during the pure shear numerical simulations of rocks with a non-associated plastic flow rule form fractal networks. The system drives spontaneously into a state in which the length distribution of shear bands follows a power law (self-organized criticality) with exponent 2.07. The distribution of local gradients in deviatoric strain rate has different scaling exponents for each moment, in particular the geometrical fractal dimension is 1.7. Samples of granodiorite sheared under high confining pressure from the Pyrenees are analyzed and their properties compared with the numerical results.
Breakup modes of fluid drops in confined shear flows
NASA Astrophysics Data System (ADS)
Barai, Nilkamal; Mandal, Nibir
2016-07-01
Using a conservative level set method we investigate the deformation behavior of isolated spherical fluid drops in a fluid channel subjected to simple shear flows, accounting the following three non-dimensional parameters: (1) degree of confinement (Wc = 2a/h, where a is the drop radius and h is the channel thickness); (2) viscosity ratio between the two fluids (λ = μd/μm, where μd is the drop viscosity and μm is the matrix viscosity); and (3) capillary number (Ca). For a given Wc, a drop steadily deforms to attain a stable geometry (Taylor number and inclination of its long axis to the shear direction) when Ca < 0.3. For Ca > 0.3, the deformation behavior turns to be unsteady, leading to oscillatory variations of both its shape and orientation with progressive shear. This kind of unsteady deformation also occurs in a condition of high viscosity ratios (λ > 2). Here we present a detailed parametric analysis of the drop geometry with increasing shear as a function of Wc, Ca, and λ. Under a threshold condition, deforming drops become unstable, resulting in their breakup into smaller droplets. We recognize three principal modes of breakup: Mode I (mid-point pinching), Mode II (edge breakup), and Mode III (homogeneous breakup). Each of these modes is shown to be most effective in the specific field defined by Ca and λ. Our study also demonstrates the role of channel confinement (Wc) in controlling the transition of Mode I to III. Finally, we discuss implications of the three modes in determining characteristic drop size distributions in multiphase flows.
Asymptotic persistence of collective modes in shear flows
Mahajan, S.M. |; Rogava, A.D. |
1998-03-31
A new nonasymptotic method is presented that reveals an unexpected richness in the spectrum of fluctuations sustained by a shear flow with nontrivial arbitrary mean kinematics. The vigor of the method is illustrated by analyzing a two-dimensional, compressible hydrodynamic shear flow. The temporal evolution of perturbations spans a wide range of nonexponential behavior from growth-cum oscillations to monotonic growth. The principal characteristic of the revealed exotic collective modes in their asymptotic persistence. {open_quotes}Echoing{close_quotes} as well as unstable (including parametrically-driven) solutions are displayed. Further areas of application, for both the method and the new physics, are outlined.
Vibrational modes identify soft spots in a sheared disordered packing.
Manning, M L; Liu, A J
2011-09-02
We analyze low-frequency vibrational modes in a two-dimensional, zero-temperature, quasistatically sheared model glass to identify a population of structural "soft spots" where particle rearrangements are initiated. The population of spots evolves slowly compared to the interval between particle rearrangements, and the soft spots are structurally different from the rest of the system. Our results suggest that disordered solids flow via localized rearrangements that tend to occur at soft spots, which are analogous to dislocations in crystalline solids.
The Critical Criterion on Runaway Shear Banding in Metallic Glasses
NASA Astrophysics Data System (ADS)
Sun, B. A.; Yang, Y.; Wang, W. H.; Liu, C. T.
2016-02-01
The plastic flow of metallic glasses (MGs) in bulk is mediated by nanoscale shear bands, which is known to proceed in a stick-slip manner until reaching a transition state causing catastrophic failures. Such a slip-to-failure transition controls the plasticity of MGs and resembles many important phenomena in natural science and engineering, such as friction, lubrication and earthquake, therefore has attracted tremendous research interest over past decades. However, despite the fundamental and practical importance, the physical origin of this slip-to-failure transition is still poorly understood. By tracking the behavior of a single shear band, here we discover that the final fracture of various MGs during compression is triggered as the velocity of the dominant shear band rises to a critical value, the magnitude of which is independent of alloy composition, sample size, strain rate and testing frame stiffness. The critical shear band velocity is rationalized with the continuum theory of liquid instability, physically originating from a shear-induced cavitation process inside the shear band. Our current finding sheds a quantitative insight into deformation and fracture in disordered solids and, more importantly, is useful to the design of plastic/tough MG-based materials and structures.
The Critical Criterion on Runaway Shear Banding in Metallic Glasses.
Sun, B A; Yang, Y; Wang, W H; Liu, C T
2016-02-19
The plastic flow of metallic glasses (MGs) in bulk is mediated by nanoscale shear bands, which is known to proceed in a stick-slip manner until reaching a transition state causing catastrophic failures. Such a slip-to-failure transition controls the plasticity of MGs and resembles many important phenomena in natural science and engineering, such as friction, lubrication and earthquake, therefore has attracted tremendous research interest over past decades. However, despite the fundamental and practical importance, the physical origin of this slip-to-failure transition is still poorly understood. By tracking the behavior of a single shear band, here we discover that the final fracture of various MGs during compression is triggered as the velocity of the dominant shear band rises to a critical value, the magnitude of which is independent of alloy composition, sample size, strain rate and testing frame stiffness. The critical shear band velocity is rationalized with the continuum theory of liquid instability, physically originating from a shear-induced cavitation process inside the shear band. Our current finding sheds a quantitative insight into deformation and fracture in disordered solids and, more importantly, is useful to the design of plastic/tough MG-based materials and structures.
The Critical Criterion on Runaway Shear Banding in Metallic Glasses
Sun, B. A.; Yang, Y.; Wang, W. H.; Liu, C. T.
2016-01-01
The plastic flow of metallic glasses (MGs) in bulk is mediated by nanoscale shear bands, which is known to proceed in a stick-slip manner until reaching a transition state causing catastrophic failures. Such a slip-to-failure transition controls the plasticity of MGs and resembles many important phenomena in natural science and engineering, such as friction, lubrication and earthquake, therefore has attracted tremendous research interest over past decades. However, despite the fundamental and practical importance, the physical origin of this slip-to-failure transition is still poorly understood. By tracking the behavior of a single shear band, here we discover that the final fracture of various MGs during compression is triggered as the velocity of the dominant shear band rises to a critical value, the magnitude of which is independent of alloy composition, sample size, strain rate and testing frame stiffness. The critical shear band velocity is rationalized with the continuum theory of liquid instability, physically originating from a shear-induced cavitation process inside the shear band. Our current finding sheds a quantitative insight into deformation and fracture in disordered solids and, more importantly, is useful to the design of plastic/tough MG-based materials and structures. PMID:26893196
Coupling of damped and growing modes in unstable shear flow
NASA Astrophysics Data System (ADS)
Fraser, A. E.; Terry, P. W.; Zweibel, E. G.; Pueschel, M. J.
2017-06-01
Analysis of the saturation of the Kelvin-Helmholtz instability is undertaken to determine the extent to which the conjugate linearly stable mode plays a role. For a piecewise-continuous mean flow profile with constant shear in a fixed layer, it is shown that the stable mode is nonlinearly excited, providing an injection-scale sink of the fluctuation energy similar to what has been found for gyroradius-scale drift-wave turbulence. Quantitative evaluation of the contribution of the stable mode to the energy balance at the onset of saturation shows that nonlinear energy transfer to the stable mode is as significant as energy transfer to small scales in balancing energy injected into the spectrum by the instability. The effect of the stable mode on momentum transport is quantified by expressing the Reynolds stress in terms of stable and unstable mode amplitudes at saturation, from which it is found that the stable mode can produce a sizable reduction in the momentum flux.
A fluidized bed technique for estimating soil critical shear stress
USDA-ARS?s Scientific Manuscript database
Soil erosion models, depending on how they are formulated, always have erodibilitiy parameters in the erosion equations. For a process-based model like the Water Erosion Prediction Project (WEPP) model, the erodibility parameters include rill and interrill erodibility and critical shear stress. Thes...
Dynamic growth of mixed-mode shear cracks
Andrews, D.J.
1994-01-01
A pure mode II (in-plane) shear crack cannot propagate spontaneously at a speed between the Rayleigh and S-wave speeds, but a three-dimensional (3D) or two-dimensional (2D) mixed-mode shear crack can propagate in this range, being driven by the mode III (antiplane) component. Two different analytic solutions have been proposed for the mode II component in this case. The first is the solution valid for crack speed less than the Rayleigh speed. When applied above the Rayleigh speed, it predicts a negative stress intensity factor, which implies that energy is generated at the crack tip. Burridge proposed a second solution, which is continuous at the crack tip, but has a singularity in slip velocity at the Rayleigh wave. Spontaneous propagation of a mixed-mode rupture has been calculated with a slip-weakening friction law, in which the slip velocity vector is colinear with the total traction vector. Spontaneous trans-Rayleigh rupture speed has been found. The solution depends on the absolute stress level. The solution for the in-plane component appears to be a superposition of smeared-out versions of the two analytic solutions. The proportion of the first solution increases with increasing absolute stress. The amplitude of the negative in-plane traction pulse is less than the absolute final sliding traction, so that total in-plane traction does not reverse. The azimuth of the slip velocity vector varies rapidly between the onset of slip and the arrival of the Rayleigh wave. The variation is larger at smaller absolute stress.
Critical scaling with strain rate in overdamped sheared disordered solids
NASA Astrophysics Data System (ADS)
Clemmer, Joel; Salerno, Kenneth; Robbins, Mark
In the limit of quasistatic shear, disordered solids demonstrate non-equilibrium critical behavior including power-law distributions of avalanches. Using molecular dynamics simulations of 2D and 3D overdamped binary LJ glasses, we explore the critical behavior in the limit of finite strain rate. We use finite-size scaling to find the critical exponents characterizing shear stress, kinetic energy, and measures of temporal and spatial correlations. The shear stress of the system rises as a power β of the strain rate. Larger system size extends this power law to lower rates. This behavior is governed by a power law drop of the dynamic correlation length with increasing shear stress defined by the exponent ν. This finite-size effect also impacts the scaling of the RMS kinetic energy with strain rate as avalanches begin nucleating simultaneously leading to continuous deformation of the solid. As system size increases, avalanches begin overlapping at lower rates. The correlation function of non-affine displacement exhibits novel anisotropic power law scaling with the magnitude of the wave vector. Its strain rate dependence is used to determine the scaling of the dynamic correlation length. Support provided by: DMR-1006805; NSF IGERT-0801471; OCI-0963185; CMMI-0923018.
Nonequilibrium mode-coupling theory for uniformly sheared underdamped systems.
Suzuki, Koshiro; Hayakawa, Hisao
2013-01-01
Nonequilibrium mode-coupling theory (MCT) for uniformly sheared underdamped systems is developed, starting from the microscopic thermostated Sllod equation and the corresponding Liouville equation. Special attention is paid to the translational invariance in the sheared frame, which requires an appropriate definition of the transient time correlators. The derived MCT equation satisfies the alignment of the wave vectors and is manifestly translationally invariant. Isothermal condition is implemented by the introduction of current fluctuation in the dissipative coupling to the thermostat. This current fluctuation grows in the α relaxation regime, which generates a pronounced relaxation of the yield stress compared to the overdamped case. This result fills the gap between the molecular dynamics simulation and the overdamped MCT reported previously. The response to a perturbation of the shear rate demonstrates an inertia effect which is not observed in the overdamped case. Our theory turns out to be a nontrivial extension of the theory by Fuchs and Cates [J. Rheol. 53, 957 (2009)] to underdamped systems. Since our starting point is identical to that of Chong and Kim [Phys. Rev. E 79, 021203 (2009)], the contradictions between Fuchs-Cates and Chong-Kim are resolved.
New instability modes for bounded, free shear flows
NASA Technical Reports Server (NTRS)
Macaraeg, Michele G.; Streett, Craig L.
1989-01-01
A class of highly amplified supersonic disturbances are found for high-speed, bounded mixing layers at high values of streamwise wavenumber. Their amplification is an order of magnitude greater than the most amplified modes, which occur at 60-65 deg at low streamwise wavenumber. These disturbances are stabilized by increasing Mach number, viscosity, and sweep; however, the effect of sweep on the most amplified mode is not significant until the wave propagation angle reaches 30 deg. The maximum growth rate of the unstable disturbances decreases as the temperature of the higher Mach number stream is increased. The structure of these disturbances is such that the phase speed with respect to the mean flow is subsonic in a small region in the center of the shear layer, and supersonic on either side of this region.
Active Head Slider with Piezoelectric Actuator Using Shear Mode Deformation
NASA Astrophysics Data System (ADS)
Naniwa, Irizo; Sato, Kazuo; Nakamura, Shigeo; Sato, Kazutaka
The rapid increase in the recording density of hard disk drive (HDD) has required a significant decrease in the flying height of sliders. The active-head slider technology for HDD is one of the most promising means to decrease flying height. This paper describes a piezoelectric flying height control (PFC) slider which has a faster dynamic response compared with conventional active-head sliders. This slider can be also adapted to the conventional slider-fabrication process. PZT layer located near the magnetic head has shear mode deformation by applying electric voltage between the upper and lower electrodes when the flying height of magnetic head needs to be decreased or increased. We fabricated a prototype with single crystal Si substrate for feasibility study. Our evaluation of the prototype revealed that the piezoelectric constant of the shear mode deformation was 0.88 nm/V, and the first resonant frequency was 50 kHz. The shape of the air bearing surface (ABS) was optimized by simulations using a robust design method. We found that the stroke was 8 nm for an applied voltage of 11 V if the flying height was 11nm.
Influence of equilibrium shear flow on peeling-ballooning instability and edge localized mode crash
Xi, P. W.; Xu, X. Q.; Wang, X. G.; Xia, T. Y.
2012-09-15
The E Multiplication-Sign B shear flow plays a dual role on peeling-ballooning modes and their subsequently triggered edge localized mode (ELM) crashes. On one hand, the flow shear can stabilize high-n modes and twist the mode in the poloidal direction, constraining the mode's radial extent and reducing the size of the corresponding ELM. On the other hand, the shear flow also introduces the Kelvin-Helmholtz drive, which can destabilize peeling-ballooning modes. The overall effect of equilibrium shear flow on peeling-ballooning modes and ELM crashes depends on the competition between these two effects. When the flow shear is either small or very large, it can reduce ELM size. However, for moderate values of flow shear, the destabilizing effect from the Kelvin-Helmholtz term is dominant and leads to larger ELM crashes.
Observation of critical modes in quasiperiodic systems
NASA Astrophysics Data System (ADS)
Desideri, Jean-Pierre; Macon, Louis; Sornette, Didier
1989-07-01
We present experimental results and their interpretation on the propagation of surface acoustic waves on a quasiperiodically corrugated solid. The surface is made of a thousand grooves engraved according to a Fibonacci sequence. For the first time, we observe the spatial structure of the critical proper modes obtained from an optical diffraction experiment. These special modes are characteristic of quasiperiodic systems and exhibit remarkable scaling features.
About the Possibility Of Transformation Of Shear Deformation Modes.
NASA Astrophysics Data System (ADS)
Ostapchuk, Aleksey; Kocharyan, Gevorg; Pavlov, Dmitriy; Markov, Vadim
2014-05-01
In this study we present the results of laboratory experiments aimed to investigate the effect of material properties, filling a discontinuity, on transformation of deformation modes from stable creep to regular stick-slip. Qualitative correspondence between experimental results and natural phenomena is detected. The experiments were carried out in the classical 'slider model' statement. A small granite block slid under shear load on a bigger granite block. The contact between rough surfaces of the blocks was filled with a discrete material, which simulated the fault zone. Quartz sand, granite crumb, glass balls and rock salt were used as the filling material. The normal load was applied to the sliding block through a special device excluding origination of tangential forces. Shear load was applied to the block through a spring. The sliding block position was controlled by laser sensors that recorded relative displacement of blocks at the frequency up to 4 kHz with the accuracy of 0.1 micron. A full spectrum of possible deformation regimes was obtained in experiments - from stable slip to low-velocity motion and to regular stick-slip, with various seismic moments realized per one act of instability. The deformation regime can transform into another one due to a slight change of the filling material structure and humidity. Experimental data can be divided into three groups, which, speaking in terms of seismology, correspond to aseismic creep, slow earthquakes and normal earthquakes with various magnitudes. Laboratory experiments allowed to determine the main factor that controlls realization of deformation regime of the model fault and to develop the phenomenological model of the process based on assumption that some force mesostructures were forming across the model fault in shearing. The mode of deformation regime is completely controlled by the length and amount of these mesostructures. At the same time narrow particle-size distribution, high degree of order of
Linear and nonlinear effect of sheared plasma flow on resistive tearing modes
Hu, Qiming Hu, Xiwei; Yu, Q.
2014-12-15
The effect of sheared plasma flow on the m/n = 2/1 tearing mode is studied numerically (m and n are the poloidal and toroidal mode numbers). It is found that in the linear phase the plasma flow with a weak or moderate shear plays a stabilizing effect on tearing mode. However, the mode is driven to be more unstable by sufficiently strong sheared flow when approaching the shear Alfvén resonance (AR). In the nonlinear phase, a moderate (strong) sheared flow leads to a smaller (larger) saturated island width. The stabilization of tearing modes by moderate shear plasma flow is enhanced for a larger plasma viscosity and a lower Alfvén velocity. It is also found that in the nonlinear phase AR accelerates the plasma rotation around the 2/1 rational surface but decelerates it at the AR location, and the radial location satisfying AR spreads inwards towards the magnetic axis.
A face-shear mode single crystal ultrasonic motor
NASA Astrophysics Data System (ADS)
Li, Shiyang; Jiang, Wenhua; Zheng, Limei; Cao, Wenwu
2013-05-01
We report a face-shear mode ultrasonic motor (USM) made of [011]c poled Zt ± 45° cut 0.24Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 single crystal, which takes advantage of the extremely large d36 = 2368 pC/N. This motor has a maximum no-load linear velocity of 182.5 mm/s and a maximum output force of 1.03 N under the drive of Vp = 50 V, f = 72 kHz. Compared with the k31 mode USM made of Pb(Zr,Ti)O3 (PZT), our USM has simpler structure, lower driving frequency, much higher electromechanical coupling factor, and twice power density. This USM can be used for low frequency operation as well as cryogenic actuation with a large torque.
Integral eigenmode analysis of shear flow effects on the ion temperature gradient mode
Artun, M.; Reynders, J.V.M.; Tang, W.M.
1993-07-01
Previous numerical and analytic kinetic studies have investigated the influence of velocity shear on the ion temperature gradient (ITG) mode. These studies relied on a differential approximation to study mode structures with k[sub [perpendicular
Neoclassical tearing mode seeding by coupling with infernal modes in low-shear tokamaks
NASA Astrophysics Data System (ADS)
Kleiner, A.; Graves, J. P.; Brunetti, D.; Cooper, W. A.; Halpern, F. D.; Luciani, J.-F.; Lütjens, H.
2016-09-01
A numerical and an analytical study of the triggering of resistive MHD modes in tokamak plasmas with low magnetic shear core is presented. Flat q profiles give rise to fast growing pressure driven MHD modes, such as infernal modes. It has been shown that infernal modes drive fast growing islands on neighbouring rational surfaces. Numerical simulations of such instabilities in a MAST-like configuration are performed with the initial value stability code XTOR-2F in the resistive frame. The evolution of magnetic islands are computed from XTOR-2F simulations and an analytical model is developed based on Rutherford’s theory in combination with a model of resistive infernal modes. The parameter {{Δ }\\prime} is extended from the linear phase to the non-linear phase. Additionally, the destabilising contribution due to a helically perturbed bootstrap current is considered. Comparing the numerical XTOR-2F simulations to the model, we find that coupling has a strong destabilising effect on (neoclassical) tearing modes and is able to seed 2/1 magnetic islands in situations when the standard NTM theory predicts stability.
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
Fuzzy control of shear-mode MR damper under impact force
NASA Astrophysics Data System (ADS)
Cho, Jeongmok; Kim, Hyoun Young; Jung, Taegeun; Joh, Joongseon
2007-01-01
Recently, a number of researches about linear magnetorheological(MR) damper using valve-mode characteristics of MR fluid have sufficiently undertaken, but researches about rotary MR damper using shear-mode characteristics of MR fluid are not enough. In this paper, we performed vibration control of shear-mode MR damper for unlimited rotating actuator of mobile robot. Also fuzzy logic based vibration control for shear-mode MR damper is suggested. The parameters, like scaling factor of input/output and center of the triangular membership functions associated with the different linguistic variables, are tuned by genetic algorithm. Experimental results demonstrate the effectiveness of the fuzzy-skyhook controller for vibration control of shear-mode MR damper under impact force.
Spectrum of shear modes in the neutron-star crust: Estimating the nuclear-physics uncertainties
NASA Astrophysics Data System (ADS)
Tews, I.
2017-01-01
I construct a model of the inner crust of neutron stars using interactions from chiral effective field theory (EFT) in order to calculate its equation of state (EOS), shear properties, and the spectrum of crustal shear modes. I systematically study uncertainties associated with the nuclear physics input, the crust composition, and neutron entrainment, and estimate their impact on crustal shear properties and the shear-mode spectrum. I find that the uncertainties originate mainly in two sources: The neutron-matter EOS and neutron entrainment. I compare the spectrum of crustal shear modes to observed frequencies of quasiperiodic oscillations in the afterglow of giant γ -ray bursts and find that all of these frequencies could be described within uncertainties, which are, however, at present too sizable to infer neutron-star properties from observations.
Determining critical points in organizational learning modes
NASA Astrophysics Data System (ADS)
Hamner, Marvine P.
2002-07-01
It has been postulated that organizations can be categorized into one of three perspectives that represent the mind-set of managers within organizations with respect to their organization and organizational learning. These are the normative, the developmental and the capability perspectives. Each of these reflects variations among organizational features such as the source of organizational learning, the timeframe for organizational learning and the relationship between organizational learning and organizational culture. However, much like the dynamics experienced by teams, i.e. various stages such as forming, norming, storming and performing, organizations can move through various learning stages, i.e. the three 'perspectives,' often stopping and restarting at different points in their cycles. This means that the three perspectives can be simply viewed as different modes of organizational learning. All organizations operate within one of the three perspectives all the time. And, the perspective through which the organization is best viewed at any point in time changes over time. Because organizations are complex, adaptive systems these modes can be mathematically represented using the output from a neural network model of complex, adaptive systems. This paper briefly describes the organizational science, the neural network model, and the mathematics required to determine critical points in these modes.
Bingham and Response Characteristics of ER Fluids in Shear and Flow Modes
NASA Astrophysics Data System (ADS)
Lee, H. G.; Choi, S. B.; Han, S. S.; Kim, J. H.; Suh, M. S.
This paper presents field-dependent Bingham and response characteristics of ER fluid under shear and flow modes. Two different types of electroviscometers are designed and manufactured for the shear mode and flow mode, respectively. An ER fluid consisting of soluble chemical starches (particles) and silicon oil is made and its field-dependent yield stress is experimentally distilled at two different temperatures using the electroviscometers. Time responses of the ER fluid to step electric fields are also evaluated under two operating modes. In addition, a cylindrical ER damper, which is operated under the flow mode, is adopted and its measured damping force is compared with predicted one obtained from Bingham model of the shear and flow mode, respectively.
Demonstration of Shear Waves, Lamb Waves, and Rayleigh Waves by Mode Conversion.
ERIC Educational Resources Information Center
Leung, W. P.
1980-01-01
Introduces an experiment that can be demonstrated in the classroom to show that shear waves, Rayleigh waves, and Lamb waves can be easily generated and observed by means of mode conversion. (Author/CS)
The interaction between fishbone modes and shear Alfvén waves in tokamak plasmas
NASA Astrophysics Data System (ADS)
He, Hongda; Liu, Yueqiang; Dong, J. Q.; Hao, G. Z.; Wu, Tingting; He, Zhixiong; Zhao, K.
2016-05-01
The resonant interaction between the energetic particle triggered fishbone mode and the shear Alfvén waves is computationally investigated and firmly demonstrated based on a tokamak plasma equilibrium, using the self-consistent MHD-kinetic hybrid code MARS-K (Liu et al 2008 Phys. Plasmas 15 112503). This type of continuum resonance, occurring critically due to the mode’s toroidal rotation in the plasma frame, significantly modifies the eigenmode structure of the fishbone instability, by introducing two large peaks of the perturbed parallel current density near but offside the q = 1 rational surface (q is the safety factor). The self-consistently computed radial plasma displacement substantially differs from that being assumed in the conventional fishbone theory.
Kinetic ballooning modes at the tokamak transport barrier with negative magnetic shear
Yamagiwa, M.; Hirose, A.; Elia, M.
1997-11-01
Stability of the kinetic ballooning modes is investigated for plasma parameters at the internal transport barrier in tokamak discharges with negative magnetic shear employing a kinetic shooting code with long shooting distance. It is found that the second stability regime with respect to the pressure gradient parameter, which was predicted for negative shear [A. Hirose and M. Elia, Phys. Rev. Lett. {bold 76}, 628 (1996)], can possibly disappear. The mode with comparatively low toroidal mode number and mode frequency below 100 kHz is found to be destabilized marginally only around the transport barrier characterized by steep pressure and density gradients. {copyright} {ital 1997 American Institute of Physics.}
Garai, S.; Banerjee, D.; Janaki, M. S.; Chakrabarti, N.
2014-02-11
In strongly coupled limit the general hydrodynamic (GH) model shows that the dusty plasma, acquiring significant rigidity, is able to support the 'shear' like mode [P. K. Kaw and A. Sen, Phys. Plasmas 5, 3552 (1998)]. In presence of velocity shear, this shear like mode is coupled with the dust acoustic mode which is generated by the compressibility effect of the dust fluid due to the finite temperature of the dust, electron and ion fluids. Local dispersion shows the velocity shear is also responsible for the instabilities of the shear mode, acoustic mode, as well as the shear-acoustic coupled mode. The present work, carried out in GH visco-elastic formalism, also gives the clear insight of the instabilities of the coupled mode in non local regime with a hyperbolic tangent velocity shear profile over a finite width.
Influence of equilibrium shear flow in the parallel magnetic direction on edge localized mode crash
Luo, Y.; Xiong, Y. Y.; Chen, S. Y.; Huang, J.; Tang, C. J.
2016-04-15
The influence of the parallel shear flow on the evolution of peeling-ballooning (P-B) modes is studied with the BOUT++ four-field code in this paper. The parallel shear flow has different effects in linear simulation and nonlinear simulation. In the linear simulations, the growth rate of edge localized mode (ELM) can be increased by Kelvin-Helmholtz term, which can be caused by the parallel shear flow. In the nonlinear simulations, the results accord with the linear simulations in the linear phase. However, the ELM size is reduced by the parallel shear flow in the beginning of the turbulence phase, which is recognized as the P-B filaments' structure. Then during the turbulence phase, the ELM size is decreased by the shear flow.
Modeling changes in rill erodibility and critical shear stress on native surface roads
Randy B. Foltz; Hakjun Rhee; William J. Elliot
2008-01-01
This study investigated the effect of cumulative overland flow on rill erodibility and critical shear stress on native surface roads in central Idaho. Rill erodibility decreased exponentially with increasing cumulative overland flow depth; however, critical shear stress did not change. The study demonstrated that road erodibility on the studied road changes over the...
Designing of a Testing Machine for Shear-Mode Fatigue Crack Growth
NASA Astrophysics Data System (ADS)
Kusaba, A.; Okazaki, S.; Endo, M.; Yanase, K.
As recognized, flaking-type failure is one of the serious problems for railroad tracks and bearings. In essence, flaking-type failure is closely related to the growth of the shear-mode (Mode-II and Mode-III) fatigue crack. In our research group, it is demonstrated that a shear-mode fatigue crack can be reproduced for cylindrical specimens by applying the cyclic torsion in the presence of the static axial compressive stress. However, a biaxial servo-hydraulic fatigue testing machine is quite expensive to purchase and costly to maintain. The low testing speed (about 10Hz) of the testing machine further aggravates the situation. As a result, study on shear-mode fatigue crack growth is still in the nascent stage. To overcome the difficulties mentioned above, in this research activity, we developed a high-performance and cost-effective testing machine to reproduce the shear-mode fatigue crack growth by improving the available resonance-type torsion fatigue testing machine. The primary advantage of using the resonance-type torsion fatigue testing machine is cost-efficiency. In addition, the testing speed effectively can be improved, in comparison with that of a biaxial servo-hydraulic fatigue testing machine. By utilizing the newly-designed testing machine, we have demonstrated that we can successfully reproduce the shear-mode fatigue crack.
Ideal MHD stability properties of pressure-driven modes in low shear tokamaks
Manickam, J.; Pomphrey, N.; Todd, A.M.M.
1987-03-01
The role of shear in determining the ideal MHD stability properties of tokamaks is discussed. In particular, we assess the effects of low shear within the plasma upon pressure-driven modes. The standard ballooning theory is shown to break down, as the shear is reduced and the growth rate is shown to be an oscillatory function of n, the toroidal mode number, treated as a continuous parameter. The oscillations are shown to depend on both the pressure and safety-factor profiles. When the shear is sufficiently weak, the oscillations can result in bands of unstable n values which are present even when the standard ballooning theory predicts complete stability. These instabilities are named ''infernal modes.'' The occurrence of these instabilities at integer n is shown to be a sensitive function of q-axis, raising the possibility of a sharp onset as plasma parameters evolve. 20 refs., 31 figs.
The barotropic normal modes in certain shear flows and the traveling waves in the atmosphere
NASA Technical Reports Server (NTRS)
Chen, Ping
1993-01-01
It is shown analytically and numerically that in certain shear flows the linearized nondivergent barotropic vorticity equation has a limited number of neutral normal modes. The latitudinal structures of these shear flows can be expressed as polynomials of the sine of latitude. The first few such shear flows resemble the gross features of the zonal winds in the atmosphere of the earth at different times and altitudes. The spatial structures of the neutral normal modes in these shear flows are spherical harmonics, and, as a consequence, these modes are also the exact solutions of the fully nonlinear equation because the nonlinear interaction term vanishes identically. The spatial structures of the observed 5-, 4-, 2-, and 16-day free traveling waves in the atmosphere are often identified with the spherical harmonics with indices of (m, n) = ( 1, 2), (2, 3), (3, 3), and ( 1, 4), which are known previously as the neutral normal modes of the nondivergent barotropic vorticity equation in a motionless background state. Our results could explain why these free traveling waves can survive the shearing effects of zonal flows that are far different from rest because these spherical harmonics are also normal modes in certain shear flows that resemble the observations of the atmosphere.
Surface modes in sheared boundary layers over impedance linings
NASA Astrophysics Data System (ADS)
Brambley, E. J.
2013-08-01
Surface modes, being duct modes localized close to the duct wall, are analysed within a lined cylindrical duct with uniform flow apart from a thin boundary layer. As well as full numerical solutions of the Pridmore-Brown equation, simplified mathematical models are given where the duct lining and boundary layer are lumped together and modelled using a single boundary condition (a modification of the Myers boundary condition previously proposed by the author), from which a surface mode dispersion relation is derived. For a given frequency, up to six surface modes are shown to exist, rather than the maximum of four for uniform slipping flow. Not only is the different number and behaviour of surface modes important for frequency-domain mode-matching techniques, which depend on having found all relevant modes during matching, but the thin boundary layer is also shown to lead to different convective and absolute stability than for uniform slipping flow. Numerical examples are given comparing the predictions of the surface mode dispersion relation to full solutions of the Pridmore-Brown equation, and the accuracy with which surface modes are predicted is shown to be significantly increased compared with the uniform slipping flow assumption. The importance of not only the boundary layer thickness but also its profile (tanh or linear) is demonstrated. A Briggs-Bers stability analysis is also performed under the assumption of a mass-spring-damper or Helmholtz resonator impedance model.
Theoretical analysis of a ceramic plate thickness-shear mode piezoelectric transformer.
Xu, Limei; Zhang, Ying; Fan, Hui; Hu, Junhui; Yang, Jiashi
2009-03-01
We perform a theoretical analysis on a ceramic plate piezoelectric transformer operating with thickness-shear modes. Mindlin's first-order theory of piezoelectric plates is employed, and a forced vibration solution is obtained. Transforming ratio, resonant frequencies, and vibration mode shapes are calculated, and the effects of plate thickness and electrode dimension are examined.
Critical Phenomenon Analysis of Shear-Banding Flow in Polymer-Like Micellar Solutions
NASA Astrophysics Data System (ADS)
Bautista, F.; Pérez-López, J. H.; Puig, J. E.; Manero, O.
2008-07-01
We examined the shear-banding flow phenomenon in polymer-like micellar solutions with the Bautista-Manero-Puig (BMP) model, which predicts that upon decreasing the shear banding intensity parameter of this model, which correspond to increasing temperature, concentration or varying salt-to-surfactant concentration, a non-equilibrium critical line is reached. By using non-equilibrium critical theory, which we obtain a set of symmetrical curves which are the normalized stress versus normalized shear rate flow curves, similar to gas-liquid transitions around the critical point. In addition, we derived the non-equilibrium critical exponents and found that them are no classic values.
Amann, Christian P. Fuchs, Matthias; Denisov, Dmitry; Dang, Minh Triet; Schall, Peter; Struth, Bernd
2015-07-21
We employ x-ray scattering on sheared colloidal suspensions and mode coupling theory to study structure factor distortions of glass-forming systems under shear. We find a transition from quadrupolar elastic distortion at small strains to quadrupolar and hexadecupolar modes in the stationary state. The latter are interpreted as signatures of plastic rearrangements in homogeneous, thermalized systems. From their transient evolution with strain, we identify characteristic strain and length-scale values where these plastic rearrangements dominate. This characteristic strain coincides with the maximum of the shear stress versus strain curve, indicating the proliferation of plastic flow. The hexadecupolar modes dominate at the wavevector of the principal peak of the equilibrium structure factor that is related to the cage-effect in mode coupling theory. We hence identify the structural signature of plastic flow of glasses.
NASA Astrophysics Data System (ADS)
Krishna Swamy, Aditya; Verma, Deepak; Ganesh, Rajaraman; Brunner, Stephan; Villard, Laurent
2016-10-01
Turbulent transport of energy, particles and momentum is one of the important limiting factors for long time plasma confinement. Modern study using gyrokinetic formalism and simulation has progressed to identify several microinstabilities that cause ion and electron thermal transport. Typically, these have been ballooning parity modes (φ is even and Ã∥ is odd) such as Ion Temperature Gradient mode (ITG), Kinetic Ballooning Mode (KBM) and Electron Temperature Gradient mode (ETG) which cause transport through fluctuations or tearing parity modes (φ is odd and Ã∥ is even) such as Microtearing modes (MTM) which change the local magnetic topology and cause transport through stochastization of the magnetic field. Here, the role of global safety factor profile variation on the MTM instability and global mode structure is studied in large aspect ratio tokamaks. Multiple subdominant branches of MTM are linearly unstable in several shear profiles. At lower shear, linearly unstable Mixed Parity Modes are found to exist. The growth rate spectrum, β-scaling in reverse shear profiles and the role of equilibrium flow on the stability and global mode structures of these modes will be presented.
NASA Astrophysics Data System (ADS)
Boschetto, Davide; Hung, Chung; Malard Moreira, Leandro; Mak, Kin Fai; Yan, Hugen; Heinz, Tony F.
2010-03-01
Raman spectroscopy is one of the key methods for the characterization of single and multilayer graphene. In the bulk limit, the lateral motion of adjacent graphene planes gives rise to a Raman active low-frequency mode, the so-called interlayer shearing mode. Coherent excitation of this mode has been observed by femtosecond time-resolved reflectivity [1]. For the case of few-layer graphene, related modes are predicted to be present and to exhibit different properties as a function of layer thickness [2]. Here we report the observation of coherent oscillation of such shearing mode phonons in multilayer graphene. The experiments are performed on mechanically exfoliated graphene samples using femtosecond laser excitation pulses and time-delayed femtosecond probe pulses in a transient reflectivity measurement. The coherent shearing-mode phonons exhibit a period of 800 fs, with a lifetime exceeding 10 ps. We will discuss the characteristics of shearing mode phonons as a function of the thickness of multilayer graphene. [1] T. Mishina et al., Phys. Rev. B 62, 2908 (2000) [2] S. K. Saha et al., Phys Rev. B 78, 165421 (2008)
Resonant mode characterisation of a cylindrical Helmholtz cavity excited by a shear layer.
Bennett, Gareth J; Stephens, David B; Rodriguez Verdugo, Francisco
2017-01-01
This paper investigates the interaction between the shear-layer over a circular cavity with a relatively small opening and the flow-excited acoustic response of the volume within to shear-layer instability modes. Within the fluid-resonant category of cavity oscillation, most research has been conducted on rectangular geometries: generally restricted to longitudinal standing waves, or when cylindrical: to Helmholtz resonance. In practical situations, however, where the cavity is subject to a range of flow speeds, many different resonant mode types may be excited. The current work presents a cylindrical cavity design where Helmholtz oscillation, longitudinal resonance, and azimuthal acoustic modes may all be excited upon varying the flow speed. Experiments performed show how lock-on between each of the three fluid-resonances and shear-layer instability modes can be generated. A circumferential array of microphones flush-mounted with the internal surface of the cavity wall was used to decompose the acoustic pressure field into acoustic modes and has verified the excitation of higher order azimuthal modes by the shear-layer. For azimuthal modes especially, the location of the cavity opening affects the pressure response. A numerical solution is validated and provides additional insight and will be applied to more complex aeronautical and automotive geometries in the future.
Nonlinear evolution of resistive tearing mode instability with shear flow and viscosity
NASA Technical Reports Server (NTRS)
Ofman, L.; Morrison, P. J.; Steinolfson, R. S.
1993-01-01
The effect of shear flow on the nonlinear evolution of the tearing mode is investigated via numerical solutions of the resistive MHD equations in slab geometry, using a finite-difference alternative-direction implicit method. It was found that, when the shear flow is small (V less than 0.3), the tearing mode saturates within one resistive time, whereas for larger flows the nonlinear saturation develops on longer time scales. The magnetic energy release decreases and the saturation time increases with increasing values of V for both small and large resistivity. Shear flow was found to decrease the saturated magnetic island width and to generate currents far from the tearing layer. Results suggest that equilibrium shear flow may improve the confinement of tokamak plasma.
Nonlinear evolution of resistive tearing mode instability with shear flow and viscosity
NASA Technical Reports Server (NTRS)
Ofman, L.; Morrison, P. J.; Steinolfson, R. S.
1993-01-01
The effect of shear flow on the nonlinear evolution of the tearing mode is investigated via numerical solutions of the resistive MHD equations in slab geometry, using a finite-difference alternative-direction implicit method. It was found that, when the shear flow is small (V less than 0.3), the tearing mode saturates within one resistive time, whereas for larger flows the nonlinear saturation develops on longer time scales. The magnetic energy release decreases and the saturation time increases with increasing values of V for both small and large resistivity. Shear flow was found to decrease the saturated magnetic island width and to generate currents far from the tearing layer. Results suggest that equilibrium shear flow may improve the confinement of tokamak plasma.
Smith, D. R.; Kaye, S. M.; Lee, W.; Mazzucato, E.; Park, H. K.; Bell, R. E.; Domier, C. W.; LeBlanc, B. P.; Levinton, F. M.; Luhmann, Jr., N. C.; Menard, J. E.; Yu, H.
2009-02-13
Electron gyro-scale fluctuation measurements in National Spherical Torus Experiment (NSTX) H-mode plasmas with large toroidal rotation reveal fluctuations consistent with electron temper- ature gradient (ETG) turbulence. Large toroidal rotation in NSTX plasmas with neutral beam injection generates E × B flow shear rates comparable to ETG linear growth rates. Enhanced fluctuations occur when the electron temperature gradient is marginally stable with respect to the ETG linear critical gradient. Fluctuation amplitudes decrease when the E × B flow shear rate exceeds ETG linear growth rates. The observations indicate E × B flow shear can be an effective suppression mechanism for ETG turbulence.
Nonlinear shearing modes approach to the diocotron instability of a planar electron strip
Mikhailenko, V. V. Mikhailenko, V. S.; Jo, Younghyun; Lee, Hae June
2015-09-15
The nonlinear evolution of the diocotron instability of a planar electron strip is investigated analytically by means of the nonlinear shearing mode for the solution of the initial and boundary value problems. The method is based on the sheared spatial coordinates which account for the motion of electron flow in the electrostatic field of the unstable diocotron modes in addition to the unperturbed sheared motion of the electron flow on the transformed shear coordinates. The time evolutions are studied by the solution of the initial and boundary value problems. The obtained solutions for the perturbed electrostatic potential include two nonlinear effects—the effect of the distortion of the boundaries of the planar electron strip and the effect of the coupling of the sheared nonmodal diocotron modes. It was proved by a two-dimensional particle-in-cell simulation that the developed theory is valid as long as the distortion of the boundaries of the basic shear flow does not change the frequency and growth rate of the linear diocotron instability in the transformed coordinates.
NASA Astrophysics Data System (ADS)
Krishna Swamy, Aditya; Ganesh, Rajaraman; Brunner, Stephan; Vaclavik, Jan; Villard, Laurent
2015-11-01
Gyrokinetic simulations have found Collisionless Microtearing Modes (MTM) to be linearly unstable in sharp temperature gradient regions of tokamaks, typically with high magnetic shear. The collisionless MTM is driven by the magnetic drift resonance of passing electrons, aided by the closeness of Mode Rational Surfaces (MRS) arising due to the high shear. Here, the role of global safety factor profile variation on the MTM instability and global mode structure is studied, in particular in weak reverse shear (WRS) configurations in large aspect ratio tokamaks. At lower shear profiles, multiple MTM branches are found with tearing parity as well as mixed parity. The linear growth rates of MTM is found to be weakened and linearly unstable modes are found whose global mode structures of φ~ and Ã∥ exhibit Mixed Parity. For the same equilibrium profiles and parameters, AITG instability is also studied and global mode structures are compared with MTM. The growth rate spectrum is found to extend to shorter/mesoscale wavelengths in WRS. Several other characteristics of MTMs and AITG are recovered in the WRS configuration, such as the dependency on free energy source and on plasma β.
Material characterization of structural adhesives in the lap shear mode. M.S. Thesis
NASA Technical Reports Server (NTRS)
Schenck, S. C.; Sancaktar, E.
1983-01-01
A general method for characterizing structural adhesives in the bonded lap shear mode is proposed. Two approaches in the form of semi-empirical and theoretical approaches are used. The semi-empirical approach includes Ludwik's and Zhurkov's equations to describe respectively, the failure stresses in the constant strain rate and constant stress loading modes with the inclusion of the temperature effects. The theoretical approach is used to describe adhesive shear stress-strain behavior with the use of viscoelastic or nonlinear elastic constitutive equations. Three different model adhesives are used in the simple lap shear mode with titanium adherends. These adhesives (one of which was developed at NASA Langley Research Center) are currently considered by NASA for possible aerospace applications. Use of different model adhesives helps in assessment of the generality of the method.
Normal force for static and steady shear mode in magnetorheological fluid
NASA Astrophysics Data System (ADS)
Liu, Xuhui; Ye, Dun; Gao, Xiaoli; Li, Fang; Sun, Meng; Zhang, Hui; Tu, Tiangang; Yu, Hao
2016-01-01
This paper presents the normal force phenomena for static and steady shear mode in magnetorheological (MR) fluid. The results of the study show that, in the static mode, with the magnetic flux density increasing, the normal force will increase until the maximum, and then reduce to a steady value, and during the increasing stage, it can be expressed as FN=4667*B2.48 approximately; however, in the steady shear mode, only when the magnetic flux density achieves a certain value, the normal force phenomena will be observed clearly, and with the increasing of magnetic field, the normal force reaches the maximum, and then also decreases to a steady value. Besides, by defining the time parameters of dynamic response, the dynamic response of normal force is studied. If the shear plate is stationary, from the magnetic field on to a stable normal force produced, the response time is about 25.11 ms.
Fourier band-power E/B-mode estimators for cosmic shear
Becker, Matthew R.; Rozo, Eduardo
2016-01-20
We introduce new Fourier band-power estimators for cosmic shear data analysis and E/B-mode separation. We consider both the case where one performs E/B-mode separation and the case where one does not. The resulting estimators have several nice properties which make them ideal for cosmic shear data analysis. First, they can be written as linear combinations of the binned cosmic shear correlation functions. Secondly, they account for the survey window function in real-space. Thirdly, they are unbiased by shape noise since they do not use correlation function data at zero separation. Fourthly, the band-power window functions in Fourier space are compact and largely non-oscillatory. Fifthly, they can be used to construct band-power estimators with very efficient data compression properties. In particular, we find that all of the information on the parameters Ωm, σ8 and ns in the shear correlation functions in the range of ~10–400 arcmin for single tomographic bin can be compressed into only three band-power estimates. Finally, we can achieve these rates of data compression while excluding small-scale information where the modelling of the shear correlation functions and power spectra is very difficult. Given these desirable properties, these estimators will be very useful for cosmic shear data analysis.
Characteristics of a current sheet shear mode in collisionless magnetic reconnection
NASA Astrophysics Data System (ADS)
Fujimoto, Keizo
2016-05-01
The current study shows the characteristics of the kink-type electromagnetic mode excited in the thin current layer formed around the x-line during the quasi-steady phase of magnetic reconnection. The linear wave analyses are carried out for the realistic current sheet profile which differs significantly from the Harris current sheet. It is found that the peak growth rate is very sensitive to the current sheet width even though the relative drift velocity at the center of the current sheet is fixed. This indicates that the mode is excited by the velocity shear rather than the relative drift velocity. Thus, the mode is termed here a current sheet shear mode. It is also shown that the wavenumber ky has a clear mass ratio dependency as ky λi ∝ (mi /me )1/4, implying the coupling of the ion and electron dynamics, where λi is the ion inertia length.
Critical combinations of shear and direct axial stress for curved rectangular panels
NASA Technical Reports Server (NTRS)
Schildcrout, Murry; Stein, Manuel
1949-01-01
A solution is presented for the problem of the buckling of curved rectangular panels subjected to combined shear and direct axial stress. Charts giving theoretical critical combinations of shear and direct axial stress are presented for panels having five different length-width ratios. Because the actual critical compressive stress of rectangular panels having substantial curvature is known to be much lower than the theoretical value, a semiempirical method of analysis of curved panels subjected to combined shear and direct axial stress is presented for use in design. (author
Non-resonant fishbone-like modes in tokamak plasmas with reversed magnetic shear
NASA Astrophysics Data System (ADS)
Wang, Xian-Qu; Wang, Xiao-Gang
2016-03-01
Energetic ion excited non-resonant fishbone-like modes (FLMs) of m / n > 1 is investigated for reversed magnetic shear configurations. It is found that the mode can be destabilized by trapped fast ions with a similar excitation mechanism as m / n = 1 fishbones but with a local interchange-like mode structure, which is in agreement with previous experiments (Toi et al 1999 Nucl. Fusion 39 1929). The dispersion relation of the mode is derived for m / n > 1. The radial mode structure is then studied by numerically solving the eigenvalue equation. Effects of on/off-axis heating, the width of the particle distribution, the beam energy and the energy distribution on the mode are discussed in detail. Nonlinear analysis of the mode is also carried out by a modified predator-prey model.
Long-lasting energetic particle modes in tokamak plasmas with low magnetic shear
NASA Astrophysics Data System (ADS)
Zhang, Rui-Bin; Wang, Xian-Qu; Xiao, Chi-Jie; Wang, Xiao-Gang; Liu, Yi; Deng, Wei; Chen, Wei; Ding, Xuan-Tong; Duan, Xu-Ru; the HL-2 A Team
2014-09-01
A long-lasting (for hundreds of milliseconds) m/n = 1 energetic particle mode driven by trapped fast ions, other than conventional fishbone bursts, is studied theoretically and in comparison with HL-2A experimental results. The mode can be observed in weak shear tokamak plasmas during neutral beam injection with a mostly steady amplitude envelope of long-lasting magnetic perturbation signals. The dispersion relation and radial structure of the mode are calculated with a weak shear q-profile. Both the m/n = 1/1 component and its higher frequency m/n = 2/2 harmonics are found to be unstable, in good agreement with experimental observations on HL-2A. On the other hand, due to the feature of weak magnetic shear, the mode is also significantly different from bursty fishbones, especially the mode structure, temporal behavior, instability threshold and growth rate dependence on the fast ion gradient. The nonlinear evolution of the mode and the comparison with fishbone bursts are also further investigated.
A theoretical study on critical phenomena of magnetic soft modes
NASA Astrophysics Data System (ADS)
Zeng, Xiaoyan; Yang, Guohong; Yan, Ming
2017-02-01
Below a threshold magnetic field, domain structures in ferromagnetic samples may start to nucleate from the initially saturated state via either continuous or discontinuous phase transitions. Such processes are usually accompanied by the occurrence of soft spin-wave modes at the critical point. In this paper, we present a theoretical study on the critical phenomena of uniform soft modes in a macrospin model and spatially non-uniform ones in ferromagnetic thin films. The critical exponents of the mode frequency and its polarization are derived. The value is found to be equal to one half, which is directly related to the breaking of a reflection-symmetry in the phase transition. At the critical point, the soft mode becomes linearly polarized, which provides an additional measurable effect of the critical phenomena.
Rotational shear effects on edge harmonic oscillations in DIII-D quiescent H-mode discharges
NASA Astrophysics Data System (ADS)
Chen, Xi; Burrell, K. H.; Ferraro, N. M.; Osborne, T. H.; Austin, M. E.; Garofalo, A. M.; Groebner, R. J.; Kramer, G. J.; Luhmann, N. C., Jr.; McKee, G. R.; Muscatello, C. M.; Nazikian, R.; Ren, X.; Snyder, P. B.; Solomon, W. M.; Tobias, B. J.; Yan, Z.
2016-07-01
In the quiescent H-mode (QH-mode) regime, edge harmonic oscillations (EHOs) play an important role in avoiding transient edge localized mode (ELM) power fluxes by providing benign and continuous edge particle transport. A detailed theoretical, experimental and modeling comparison has been made of low-n (n ⩽ 5) EHO in DIII-D QH-mode plasmas. The calculated linear eigenmode structure from the extended magentoohydrodynamics (MHD) code M3D-C1 matches closely the coherent EHO properties from external magnetics data and internal measurements using the ECE, BES, ECE-Imaging and microwave imaging reflectometer (MIR) diagnostics, as well as the kink/peeling mode properties found by the ideal MHD code ELITE. Numerical investigations indicate that the low-n EHO-like solutions from M3D-C1 are destabilized by rotation and/or rotational shear while high-n modes are stabilized. This effect is independent of the rotation direction, suggesting that EHOs can be destabilized in principle with rotation in either direction. The modeling results are consistent with observations of EHO, support the proposed theory of the EHO as a low-n kink/peeling mode destabilized by edge E × B rotational shear, and improve our understanding and confidence in creating and sustaining QH-mode in present and future devices.
Rotational shear effects on edge harmonic oscillations in DIII-D quiescent H-mode discharges
Chen, Xi; Burrell, Keith H.; Ferraro, Nathaniel M.; Osborne, Thomas H.; Austin, Max E.; Garofalo, Andrea M.; Groebner, Richard J.; Kramer, Gerrit J.; Luhmann, Jr., Neville C.; McKee, George R.; Muscatello, C. M.; Nazikian, R.; Ren, X.; Snyder, P. B.; Solomon, W. M.; Tobias, B. J.; Yan, Z.
2016-06-21
In the quiescent H-mode (QH-mode) regime, edge harmonic oscillations (EHO) play an important role in avoiding transient edge localized mode (ELM) power fluxes by providing benign and continuous edge particle transport. A detailed theoretical, experimental and modeling comparison has been made of low-n (n ≤ 5) EHO in DIII-D QH-mode plasmas. The calculated linear eigenmode structure from the extended MHD code M3D-C1 matches closely the coherent EHO properties from external magnetics data and internal measurements using the ECE, BES, ECE-Imaging and microwave imaging reflectometer (MIR) diagnostics, as well as the kink/peeling mode properties found by the ideal MHD code ELITE. Numerical investigations indicate that the low-n EHO-like solutions from M3D-C1 are destabilized by the rotational shear while high-n modes are stabilized. This effect is independent of the rotation direction, suggesting that EHO can be destabilized in principle with rotation in either direction. Furthermore, the modeling results are consistent with observations of the EHO, support the proposed theory of the EHO as a rotational shear driven kink/peeling mode, and improve our understanding and confidence in creating and sustaining QH-mode in present and future devices.
Rotational shear effects on edge harmonic oscillations in DIII-D quiescent H-mode discharges
Chen, Xi; Burrell, Keith H.; Ferraro, Nathaniel M.; Osborne, Thomas H.; Austin, Max E.; Garofalo, Andrea M.; Groebner, Richard J.; Kramer, Gerrit J.; Luhmann, Jr., Neville C.; McKee, George R.; Muscatello, C. M.; Nazikian, R.; Ren, X.; Snyder, P. B.; Solomon, W. M.; Tobias, B. J.; Yan, Z.
2016-06-21
In the quiescent H-mode (QH-mode) regime, edge harmonic oscillations (EHO) play an important role in avoiding transient edge localized mode (ELM) power fluxes by providing benign and continuous edge particle transport. A detailed theoretical, experimental and modeling comparison has been made of low-n (n ≤ 5) EHO in DIII-D QH-mode plasmas. The calculated linear eigenmode structure from the extended MHD code M3D-C1 matches closely the coherent EHO properties from external magnetics data and internal measurements using the ECE, BES, ECE-Imaging and microwave imaging reflectometer (MIR) diagnostics, as well as the kink/peeling mode properties found by the ideal MHD code ELITE. Numerical investigations indicate that the low-n EHO-like solutions from M3D-C1 are destabilized by the rotational shear while high-n modes are stabilized. This effect is independent of the rotation direction, suggesting that EHO can be destabilized in principle with rotation in either direction. Furthermore, the modeling results are consistent with observations of the EHO, support the proposed theory of the EHO as a rotational shear driven kink/peeling mode, and improve our understanding and confidence in creating and sustaining QH-mode in present and future devices.
Rotational shear effects on edge harmonic oscillations in DIII-D quiescent H-mode discharges
Chen, Xi; Burrell, Keith H.; Ferraro, Nathaniel M.; ...
2016-06-21
In the quiescent H-mode (QH-mode) regime, edge harmonic oscillations (EHO) play an important role in avoiding transient edge localized mode (ELM) power fluxes by providing benign and continuous edge particle transport. A detailed theoretical, experimental and modeling comparison has been made of low-n (n ≤ 5) EHO in DIII-D QH-mode plasmas. The calculated linear eigenmode structure from the extended MHD code M3D-C1 matches closely the coherent EHO properties from external magnetics data and internal measurements using the ECE, BES, ECE-Imaging and microwave imaging reflectometer (MIR) diagnostics, as well as the kink/peeling mode properties found by the ideal MHD code ELITE.more » Numerical investigations indicate that the low-n EHO-like solutions from M3D-C1 are destabilized by the rotational shear while high-n modes are stabilized. This effect is independent of the rotation direction, suggesting that EHO can be destabilized in principle with rotation in either direction. Furthermore, the modeling results are consistent with observations of the EHO, support the proposed theory of the EHO as a rotational shear driven kink/peeling mode, and improve our understanding and confidence in creating and sustaining QH-mode in present and future devices.« less
NASA Astrophysics Data System (ADS)
Chalioris, Constantin E.; Papadopoulos, Nikos A.; Angeli, Georgia M.; Karayannis, Chris G.; Liolios, Asterios A.; Providakis, Costas P.
2015-10-01
Damage detection at early cracking stages in shear-critical reinforced concrete beams, before further deterioration and their inevitable brittle shear failure is crucial for structural safety and integrity. The effectiveness of a structural health monitoring technique using the admittance measurements of piezoelectric transducers mounted on a reinforced concrete beam without shear reinforcement is experimentally investigated. Embedded "smart aggregate" transducers and externally bonded piezoelectric patches have been placed in arrays at both shear spans of the beam. Beam were tested till total shear failure and monitored at three different states; healthy, flexural cracking and diagonal cracking. Test results showed that transducers close to the critical diagonal crack provided sound and graduated discrepancies between the admittance responses at the healthy state and thedamage levels.Damage assessment using statistical indices calculated from the measurements of all transducers was also attempted. Rational changes of the index values were obtained with respect to the increase of the damage. Admittance responses and index values of the transducers located on the shear span where the critical diagonal crack formed provided cogent evidence of damage. On the contrary, negligible indication of damage was yielded by the responses of the transducers located on the other shear span, where no diagonal cracking occurred.
Shear Alfv'en spectrum and mode structures for 3D configurations
NASA Astrophysics Data System (ADS)
Spong, D. A.; Todo, Y.
2007-11-01
Energetic particle destabilized Alfv'en modes are observed in a wide range of stellarator experiments. We have developed a code (AE3D) to calculate the full shear Alfv'en frequency spectrum and associated mode structures for arbitrary stellarator equilibria. This is based on a Galerkin approach using a combined Fourier mode (poloidal/toroidal angle) finite element (radial) representation. It has been applied to an LHD case where Alfv'en activity and enhanced ion losses were seen. Applications also are underway to other experiments, such as HSX, where ECH-driven Alfv'en modes were observed. This model can form the basis for stellarator optimization targets, synthetic diagnostics, and reduced linear/nonlinear stability models. It is also applicable to tokamaks with symmetry-breaking effects. By matching observed frequencies with calculated mode structures, improved understanding of the physics mechanisms of AE modes, such as sideband coupling, damping, and enhanced fast particle losses can be developed.
Effects of energetic ions on double tearing modes in reversed shear plasmas
NASA Astrophysics Data System (ADS)
Wang, Xian-Qu; Wang, Xiao-Gang
2017-01-01
The modified dispersion relation of q s = m/n double tearing modes (DTMs) with trapped energetic ions is derived by the matching procedure of mode structures in the ideal region and resistive layer. It is found that a mode transition between the DTM and the fishbone-like mode can be triggered, depending on fast ion driving, which provides a possible explanation for the observation of experiments (Günter et al 1999 Nucl. Fusion 39 1793; Maget et al 2006 Nucl. Fusion 46 797). The resistivity scaling of DTMs is changed significantly by on/off-axis heating beams. The effects of beam energy, electron inertia, magnetic shear and plasma resistivity on the stability of the mode and mode transition are discussed in detail.
NASA Astrophysics Data System (ADS)
Ming, Yue; Zhou, Deng
2017-01-01
The effect of the poloidal equilibrium flow and flow shear on the tearing mode instabilities for tokamak plasmas is investigated. The vorticity equation is derived and approximately solved for large poloidal mode numbers (m). Asymptotic matching of the inner solution to the outer solution can approximately give the classical tearing mode stability index Δ' . For typical plasma parameters with positive flow shear, we notice that the poloidal mean flows have a beneficial effect on the classical tearing mode and vice versa. To study the modes with arbitrary poloidal mode numbers, we numerically solve the vorticity equation for delta prime ( Δ' ) for typical plasma parameters with positive flow shear at the rational surface and the resulting Δ' with large m also decreases with increasing poloidal flow velocity, consistent with the approximate analytical large m results. Our numerical calculations indicate that the poloidal mean flow with positive flow shear has beneficial influence on the stabilization of classical tearing modes in tokamak plasmas.
Rapid repair of severely earthquake-damaged bridge piers with flexural-shear failure mode
NASA Astrophysics Data System (ADS)
Sun, Zhiguo; Wang, Dongsheng; Du, Xiuli; Si, Bingjun
2011-12-01
An experimental study was conducted to investigate the feasibility of a proposed rapid repair technique for severely earthquake-damaged bridge piers with flexural-shear failure mode. Six circular pier specimens were first tested to severe damage in flexural-shear mode and repaired using early-strength concrete with high-fluidity and carbon fiber reinforced polymers (CFRP). After about four days, the repaired specimens were tested to failure again. The seismic behavior of the repaired specimens was evaluated and compared to the original specimens. Test results indicate that the proposed repair technique is highly effective. Both shear strength and lateral displacement of the repaired piers increased when compared to the original specimens, and the failure mechanism of the piers shifted from flexural-shear failure to ductile flexural failure. Finally, a simple design model based on the Seible formulation for post-earthquake repair design was compared to the experimental results. It is concluded that the design equation for bridge pier strengthening before an earthquake could be applicable to seismic repairs after an earthquake if the shear strength contribution of the spiral bars in the repaired piers is disregarded and 1.5 times more FRP sheets is provided.
Gyrokinetic analysis of ion temperature gradient modes in the presence of sheared flows
NASA Astrophysics Data System (ADS)
Artun, M.; Tang, W. M.
1992-05-01
The linearized gyrokinetic equation governing electrostatic microinstabilities in the presence of sheared equilibrium flows in both the ẑ and ŷ directions has been systematically derived for a sheared slab geometry, where in the large-aspect-ratio limit ẑ and ŷ directions correspond to the toroidal and poloidal directions, respectively. In the familiar long perpendicular wavelength regime (k⊥ρi<1), the analysis leads to a comprehensive kinetic differential eigenmode equation that is solved numerically. The numerical results have been successfully cross-checked against analytic estimates in the fluid limit. For typical conditions, the ion temperature gradient (ηi) modes are found to be stabilized for ŷ direction flows with a velocity shear scale comparable to that of the ion temperature gradient and velocities of a few percent of the sound speed. Sheared flows in the ẑ direction taken alone are usually destabilizing, with the effect being independent of the sign of the flow. However, when both types are simultaneously considered, it is found that in the presence of sheared ẑ-direction flow, sheared ŷ-direction flow can be either stabilizing or destabilizing depending on the relative sign of these flows. However, for sufficiently large values of v'y the mode is completely stabilized regardless of the sign of vzv'y. The importance of a proper kinetic treatment of this problem is supported by comparisons with fluid estimates. In particular, when such effects are favorable, significantly smaller values of sheared ŷ-direction flow are required for stability than fluid estimates would indicate.
Experimental research and finite element analysis of bridge piers failed in flexure-shear modes
NASA Astrophysics Data System (ADS)
Sun, Zhiguo; Si, Bingjun; Wang, Dongsheng; Guo, Xun
2008-12-01
In recent earthquakes, a large number of reinforced concrete (RC) bridges were severely damaged due to mixed flexure-shear failure modes of the bridge piers. An integrated experimental and finite element (FE) analysis study is described in this paper to study the seismic performance of the bridge piers that failed in flexure-shear modes. In the first part, a nonlinear cyclic loading test on six RC bridge piers with circular cross sections is carried out experimentally. The damage states, ductility and energy dissipation parameters, stiffness degradation and shear strength of the piers are studied and compared with each other. The experimental results suggest that all the piers exhibit stable flexural response at displacement ductilities up to four before exhibiting brittle shear failure. The ultimate performance of the piers is dominated by shear capacity due to significant shear cracking, and in some cases, rupturing of spiral bars. In the second part, modeling approaches describing the hysteretic behavior of the piers are investigated by using ANSYS software. A set of models with different parameters is selected and evaluated through comparison with experimental results. The influences of the shear retention coefficients between concrete cracks, the Bauschinger effect in longitudinal reinforcement, the bond-slip relationship between the longitudinal reinforcement and the concrete and the concrete failure surface on the simulated hysteretic curves are discussed. Then, a modified analysis model is presented and its accuracy is verified by comparing the simulated results with experimental ones. This research uses models available in commercial FE codes and is intended for researchers and engineers interested in using ANSYS software to predict the hysteretic behavior of reinforced concrete structures.
J Squire, A Bhattacharjee
2014-07-01
We study the magnetorotational instability (MRI) (Balbus & Hawley 1998) using non-modal stability techniques.Despite the spectral instability of many forms of the MRI, this proves to be a natural method of analysis that is well-suited to deal with the non-self-adjoint nature of the linear MRI equations. We find that the fastest growing linear MRI structures on both local and global domains can look very diff erent to the eigenmodes, invariably resembling waves shearing with the background flow (shear waves). In addition, such structures can grow many times faster than the least stable eigenmode over long time periods, and be localized in a completely di fferent region of space. These ideas lead – for both axisymmetric and non-axisymmetric modes – to a natural connection between the global MRI and the local shearing box approximation. By illustrating that the fastest growing global structure is well described by the ordinary diff erential equations (ODEs) governing a single shear wave, we find that the shearing box is a very sensible approximation for the linear MRI, contrary to many previous claims. Since the shear wave ODEs are most naturally understood using non-modal analysis techniques, we conclude by analyzing local MRI growth over finite time-scales using these methods. The strong growth over a wide range of wave-numbers suggests that non-modal linear physics could be of fundamental importance in MRI turbulence (Squire & Bhattacharjee 2014).
NASA Astrophysics Data System (ADS)
Wang, Jialei; Wang, Zheng-Xiong; Wei, Lai; Liu, Yue
2017-04-01
The control of neo-classical tearing modes (NTMs) by the differential rotation in the reversed magnetic shear (RMS) configuration with different separations Δ {{r}\\text{s}} between two rational surfaces is numerically studied by means of reduced magnetohydrodynamic (MHD) simulations. It is found that the differential rotation with a strong shear at the outer resonant surface can effectively suppress the explosive burst of double tearing modes (DTMs)/NTMs. Critical values of the strength of rotation to suppress the burst are also presented for different bootstrap current fractions {{f}\\text{b}} . Furthermore, a couple of measurable parameters ≤ft(δ, κ \\right) , corresponding respectively to the triangularity and elongation of the magnetic islands at the outer resonant surface, are introduced to characterize the deformation of islands in the nonlinear phase. It is found that the triangularity δ is more likely to precisely predict the onset of burst than the island width w and elongation κ . For a given Δ {{r}\\text{s}} , the critical value of triangularity {δ\\text{crit}} is obtained by scanning different plasma parameters. Establishing such a database of ≤ft(δ,κ \\right) is helpful to effectively control the development of NTMs in the RMS experimental discharges.
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.
Integral eigenmode analysis of shear flow effects on the ion temperature gradient mode
Artun, M.; Reynders, J.V.M.; Tang, W.M.
1993-07-01
Previous numerical and analytic kinetic studies have investigated the influence of velocity shear on the ion temperature gradient (ITG) mode. These studies relied on a differential approximation to study mode structures with k{sub {perpendicular}}{rho}{sub i} {much_lt} 1. A recently developed gyrokinetic integral code is here used to explore the effects of sheared flows on the ITG mode for arbitrary values of k{sub {perpendicular}}{rho}{sub i}. It is found that both the mode structure and eigenfrequencies predicted by the integral code can differ from the results obtained by the differential approach, even in the k{sub y}{rho}{sub i} {much_lt} 1 limit. Although some trends predicted by the differential approximation are recovered by the integral approach, there are some significant differences. For example, the slight destabilizing effect observed for small values of the perpendicular velocity shear at k{sub {perpendicular}}{rho}{sub i} {much_lt} 1 is amplified when the integral approach is applied. In dealing with the higher radial eigenmodes, which can often exhibit the largest growth rates, it is emphasized that their finer radial structure usually dictates that the integral equation analysis is required. Results from the integral code are presented together with comparisons with results from the differential approach.
Critical bed shear stress and threshold of motion of maerl biogenic gravel
NASA Astrophysics Data System (ADS)
Joshi, Siddhi; Duffy, Garret Patrick; Brown, Colin
2017-07-01
A determination of the critical bed shear stress of maerl is a prerequisite for quantifying its mobility, rate of erosion and deposition in conservation management. The critical bed shear stress for incipient motion has been determined for the first time for samples from biogenic free-living maerl beds in three contrasting environments (open marine, intertidal and beach) in Galway Bay, west of Ireland. The bed shear stress was determined using two methods, Law of the Wall and Turbulent Kinetic Energy, in a rotating annular flume and in a linear flume. The velocity profile of flowing water above a bed of natural maerl grains was measured in four runs of progressively increasing flow velocity until the flow exceeded the critical shear stress of grains on the bed. The critical Shields parameter and the mobility number are estimated and compared with the equivalent curves for natural quartz sand. The critical Shields parameters for the maerl particles from all three environments fall below the Shields curve. Along with a previously reported correlation between maerl grain shape and settling velocity, these results suggest that the highly irregular shapes also allow maerl grains to be mobilised more easily than quartz grains with the same sieve diameter. The intertidal beds with the roughest particles exhibit the greatest critical shear stress because the particle thalli interlock and resist entrainment. In samples with a high percentage of maerl and low percentage of siliciclastic sand, the lower density, lower settling velocity and lower critical bed shear stress of maerl results in its preferential transport over the siliciclastic sediment. At velocities ∼10 cm s-1 higher than the threshold velocity of grain motion, rarely-documented subaqueous maerl dunes formed in the annular flume.
Gyrokinetic analysis of ion temperature gradient modes in the presence of sheared flows
Artun, M.; Tang, W.M.
1992-01-01
The linearized gyrokinetic equation governing electrostatic microinstabilities in the presence of sheared equilibrium flow in both the {cflx z} and {cflx y} directions has been systematically derived for a sheared slab geometry, where in the large aspect ratio limit {cflx z} and {cflx y} directions correspond to the toroidal and poloidal directions respectively. In the familiar long perpendicular wavelength regime ({kappa}{perpendicular}{rho}i > 1), the analysis leads to a comprehensive kinetic differential eigenmode equation which is solved numerically. The numerical results have been successfully cross-checked against analytic estimates in the fluid limit. For typical conditions, the Ion Temperature Gradient ({eta}i) modes are found to be stabilized for {cflx y}-direction flows with a velocity shear scale comparable to that of the ion temperature gradient and velocities of a few percent of the sound speed. Sheared flows in the {cflx z}-direction taken along are usually destabilizing, with the effect being independent of the sign of the flow. However, when both types are simultaneously considered, it is found that in the presence of shared {cflx z}-direction flow, sheared {cflx y}-direction flow can be either stabilizing or destabilizing depending on the relative sign of these flows. However, for sufficiently large values of {upsilon}{prime}{sub y} the mode is completely stabilized regardless of the sign of {upsilon}{prime}{sub z} {upsilon}{prime}{sub y}. The importance of a proper kinetic treatment of this problem is supported by comparisons with fluid estimates. In particular, when such effects are favorable, significantly smaller values of sheared {cflx y}-direction flow are required for stability than fluid estimates would indicate.
A Study of the Unstable Modes in High Mach Number Gaseous Jets and Shear Layers
NASA Astrophysics Data System (ADS)
Bassett, Gene Marcel
1993-01-01
Instabilities affecting the propagation of supersonic gaseous jets have been studied using high resolution computer simulations with the Piecewise-Parabolic-Method (PPM). These results are discussed in relation to jets from galactic nuclei. These studies involve a detailed treatment of a single section of a very long jet, approximating the dynamics by using periodic boundary conditions. Shear layer simulations have explored the effects of shear layers on the growth of nonlinear instabilities. Convergence of the numerical approximations has been tested by comparing jet simulations with different grid resolutions. The effects of initial conditions and geometry on the dominant disruptive instabilities have also been explored. Simulations of shear layers with a variety of thicknesses, Mach numbers and densities perturbed by incident sound waves imply that the time for the excited kink modes to grow large in amplitude and disrupt the shear layer is taug = (546 +/- 24) (M/4)^{1.7 } (Apert/0.02) ^{-0.4} delta/c, where M is the jet Mach number, delta is the half-width of the shear layer, and A_ {pert} is the perturbation amplitude. For simulations of periodic jets, the initial velocity perturbations set up zig-zag shock patterns inside the jet. In each case a single zig-zag shock pattern (an odd mode) or a double zig-zag shock pattern (an even mode) grows to dominate the flow. The dominant kink instability responsible for these shock patterns moves approximately at the linear resonance velocity, nu_ {mode} = cextnu_ {relative}/(cjet + c_ {ext}). For high resolution simulations (those with 150 or more computational zones across the jet width), the even mode dominates if the even penetration is higher in amplitude initially than the odd perturbation. For low resolution simulations, the odd mode dominates even for a stronger even mode perturbation. In high resolution simulations the jet boundary rolls up and large amounts of external gas are entrained into the jet. In low
Critical Property in Relaxor-PbTiO3 Single Crystals --- Shear Piezoelectric Response
Xu, Zhuo; Wei, Xiaoyong; Shrout, Thomas R.
2011-01-01
The shear piezoelectric behavior in relaxor-PbTiO3 (PT) single crystals is investigated in regard to crystal phase. High levels of shear piezoelectric activity, d15 or d24 >2000 pC N−1, has been observed for single domain rhombohedral (R), orthorhombic (O) and tetragonal (T) relaxor-PT crystals. The high piezoelectric response is attributed to a flattening of the Gibbs free energy at compositions proximate to the morphotropic phase boundaries, where the polarization rotation is easy with applying perpendicular electric field. The shear piezoelectric behavior of pervoskite ferroelectric crystals was discussed with respect to ferroelectric-ferroelectric phase transitions and dc bias field using phenomenological approach. The relationship between single domain shear piezoelectric response and piezoelectric activities in domain engineered configurations were given in this paper. From an application viewpoint, the temperature and ac field drive stability for shear piezoelectric responses are investigated. A temperature independent shear piezoelectric response (d24, in the range of −50°C to O-T phase transition temperature) is thermodynamically expected and experimentally confirmed in orthorhombic relaxor-PT crystals; relatively high ac field drive stability (5 kV cm−1) is obtained in manganese modified relaxor-PT crystals. For all thickness shear vibration modes, the mechanical quality factor Qs are less than 50, corresponding to the facilitated polarization rotation. PMID:21960942
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.
Critical Thinking and EFL Learners' Performance on Different Writing Modes
ERIC Educational Resources Information Center
Golpour, Farhad
2014-01-01
The essential function of critical thinking in education is obvious by many studies done in this field. The main purpose of this article is to find the relationship between critical thinking levels of Iranian EFL learners and their performance on different modes of writing. The sample of the study selected among those who studying English at the…
Critical Thinking and EFL Learners' Performance on Different Writing Modes
ERIC Educational Resources Information Center
Golpour, Farhad
2014-01-01
The essential function of critical thinking in education is obvious by many studies done in this field. The main purpose of this article is to find the relationship between critical thinking levels of Iranian EFL learners and their performance on different modes of writing. The sample of the study selected among those who studying English at the…
Shear-Mode Piezoelectric Properties of KNbO3-Based Ferroelectric Ceramics
NASA Astrophysics Data System (ADS)
Hikita, Kouhei; Hiruma, Yuji; Nagata, Hajime; Takenaka, Tadashi
2009-07-01
Potassium niobate, KNbO3, (KN)-based ceramics were prepared by a modified conventional ceramic fabrication process to characterize their piezoelectric properties. The KN-MnCO3 0.1 wt % (KN-Mn0.1) ceramic used in this study showed a high density ratio >96% and a high resistivity, ρ, of about 1013 Ω·cm without deliquescent properties. The shear mode of the KN-Mn0.1 ceramic showed excellent resonance and antiresonance characteristics with tiny spurious peaks upon optimization of the sample dimensions. The electromechanical coupling factor, k15, and piezoelectric strain constant, d15, of KN-Mn0.1 showed relatively large values of 0.55 and 207 pC/N, respectively. The shear-mode vibration of KN-based ceramics appears to be a very promising candidate for actuators and high-power applications.
Anesthesia and critical care ventilator modes: past, present, and future.
Bristle, Timothy J; Collins, Shawn; Hewer, Ian; Hollifield, Kevin
2014-10-01
Mechanical ventilators have evolved from basic machines to complicated, electronic, microprocessing engines. Over the last 2 decades, ventilator capabilities and options for critical care and anesthesia ventilators have rapidly advanced. These advances in ventilator modalities--in conjunction with a better understanding of patient physiology and the effects of positive pressure ventilation on the body--have revolutionized the mechanical ventilation process. Clinicians today have a vast array of mechanical ventilator mode options designed to match the pulmonary needs of the critically ill and anesthetized patient. Modes of mechanical ventilation continue to be based on 1 of 2 variances: volume-based or pressure-based. The wording describing the standard ventilatory modes on select present-day ventilators has changed, yet the basic principles of operation have not changed compared with older ventilators. Anesthesia providers need to understand these ventilator modes to best care for patients. This literature review encompasses a brief history of mechanical ventilation and current modes available for anesthesia and critical care ventilators, including definitions of each mode, definitions of the various descriptive labels given each mode, and techniques for optimizing and meeting the ventilator needs of the patient while avoiding complications in the surgical and critical care patient.
Critical shear stress for erosion of cohesive soils subjected to temperatures typical of wildfires
Moody, J.A.; Dungan, Smith J.; Ragan, B.W.
2005-01-01
[1] Increased erosion is a well-known response after wildfire. To predict and to model erosion on a landscape scale requires knowledge of the critical shear stress for the initiation of motion of soil particles. As this soil property is temperature-dependent, a quantitative relation between critical shear stress and the temperatures to which the soils have been subjected during a wildfire is required. In this study the critical shear stress was measured in a recirculating flume using samples of forest soil exposed to different temperatures (40??-550??C) for 1 hour. Results were obtained for four replicates of soils derived from three different types of parent material (granitic bedrock, sandstone, and volcanic tuffs). In general, the relation between critical shear stress and temperature can be separated into three different temperature ranges (275??C), which are similar to those for water repellency and temperature. The critical shear stress was most variable (1.0-2.0 N m-2) for temperatures 2.0 N m-2) between 175?? and 275??C, and was essentially constant (0.5-0.8 N m-2) for temperatures >275??C. The changes in critical shear stress with temperature were found to be essentially independent of soil type and suggest that erosion processes in burned watersheds can be modeled more simply than erosion processes in unburned watersheds. Wildfire reduces the spatial variability of soil erodibility associated with unburned watersheds by eliminating the complex effects of vegetation in protecting soils and by reducing the range of cohesion associated with different types of unburned soils. Our results indicate that modeling the erosional response after a wildfire depends primarily on determining the spatial distribution of the maximum soil temperatures that were reached during the wildfire. Copyright 2005 by the American Geophysical Union.
Peterson, J. L.; Hammet, G. W.; Mikkelsen, D. R.; Yuh, H. Y.; Candy, J.; Guttenfelder, W.; Kaye, S. M.; LeBlanc, B.
2011-05-11
The first nonlinear gyrokinetic simulations of electron internal transport barriers (e-ITBs) in the National Spherical Torus Experiment show that reversed magnetic shear can suppress thermal transport by increasing the nonlinear critical gradient for electron-temperature-gradient-driven turbulence to three times its linear critical value. An interesting feature of this turbulence is non- linearly driven off-midplane radial streamers. This work reinforces the experimental observation that magnetic shear is likely an effective way of triggering and sustaining e-ITBs in magnetic fusion devices.
Pressure-induced softening of shear modes in ZnO
Decremps, Frederic; Zhang, Jianzhong; Li, Baosheng; Liebermann, Robert C.
2001-06-01
The room-temperature elastic moduli C{sub IJ} corresponding to the pure longitudinal and transverse modes in single crystals of the wurtzite phase of ZnO have been determined from ultrasonic wave velocities measurements as a function of pressure up to 10 GPa. All the moduli exhibit a linear dependence on pressure, with positive values for the longitudinal moduli (dC{sub 11}/dP=5.32 and dC{sub 33}/dP=3.78) but negative values for the shear moduli (dC{sub 44}/dP={minus}0.35 and dC{sub 66}/dP={minus}0.30). All modes exhibit anomalous travel time above P{sub Tr}=7.5GPa, indicating the onset of a transition to the rocksalt (B1) phase. Using recent improvements for ultrasonic measurements in multianvil apparatus, this experimental study on the phase-transformation mechanism is extended to simultaneous high pressures and high temperatures. At high temperatures, P{sub Tr} decrease and the pressure derivatives of the elastic shear modes become more negative. Thus, the elastic shear softening observed at room temperature is enhanced at elevated temperatures.
NASA Astrophysics Data System (ADS)
Vuong, T. Q. P.; Cassabois, G.; Valvin, P.; Jacques, V.; Cuscó, R.; Artús, L.; Gil, B.
2017-01-01
We address the intrinsic optical properties of hexagonal boron nitride in deep ultraviolet. We show that the fine structure of the phonon replicas arises from overtones involving up to six low-energy interlayer shear modes. These lattice vibrations are specific to layered compounds since they correspond to the shear rigid motion between adjacent layers, with a characteristic energy of about 6-7 meV. We obtain a quantitative interpretation of the multiplet observed in each phonon replica under the assumption of a cumulative Gaussian broadening as a function of the overtone index, and with a phenomenological line broadening taken identical for all phonon types. We show from our quantitative interpretation of the full emission spectrum above 5.7 eV that the energy of the involved phonon mode is 6.8 ±0.5 meV, in excellent agreement with temperature-dependent Raman measurements of the low-energy interlayer shear mode in hexagonal boron nitride. We highlight the unusual properties of this material where the optical response is tailored by the phonon group velocities in the middle of the Brillouin zone.
Comparison of shear flow formation between resonant and non-resonant resistive interchange modes
NASA Astrophysics Data System (ADS)
Unemura, T.; Hamaguchi, S.; Wakatani, M.
1999-11-01
It is known that the poloidal shear flow is produced from the nonlinear resistive interchange modes(A. Hasegawa and M. Wakatani, Phys. Rev. Lett. 59) 1581 (1987)(B.A. Carreras and V. E. Lynch, Phys. Fluids B 5) 1795 (1993). Since the non-resonant resistive modes also become unstable(K. Ichiguchi, Y. Nakamura and M. Wakatani, Nucl. Fusion 31) 2073 (1991), the nonlinear behavior is compared between the resonant and non-resonant modes from the point of view of poloidal flow formation. For understanding the difference, we studied single helicity (m,n)=(3,2) mode in a cylindrical geometry.Rotational transform profile, ι(r), was changed. First, we assumed ι(r)=0.51+0.39r^2, and increased ι(0). This change represents a finite beta effect in currentless stellarators. When the resonant surface exists with ι(r_s)=2/3, the poloidal flow are created near the resonant surface. And, in the case when no resonant surface exists but ι_min ~ 2/3, the non-resonant (3,2) mode grows and poloidal shear flow is also generated; however, the magnitude decreases sharply with the increase of ι_min.
Rotational Shear Effects on Edge Harmonic Oscillations in DIII-D Quiescent H-mode Discharges
NASA Astrophysics Data System (ADS)
Chen, Xi; Burrell, K. H.; Ferraro, N. M.; Osborne, T. H.; Austin, M. E.; Garofalo, A. M.; Groebner, R. J.; Kramer, G. J.; Luhmann, N. C., Jr.; McKee, G. R.; Muscatello, C. M.; Nazikian, R.; Ren, X.; Snyder, P. B.; Solomon, Wm.; Tobias, B. J.; Yan, Z.
2015-11-01
In quiescent H-mode (QH) regime, the edge harmonic oscillations (EHO) play an important role in avoiding the transient ELM power fluxes by providing benign and continuous edge particle transport. A detailed theoretical, experimental and modeling comparison has been made of low-n (n <= 5) EHO in DIII-D QH-mode plasmas. The calculated linear eigenmode structure from the extended MHD code M3D-C1 matches closely the coherent EHO properties from external magnetics data and internal measurements using the ECE, BES, ECE-I and MIR diagnostics, as well as the kink/peeling mode properties of the ideal MHD code ELITE. The numerical investigations indicate that the low-n EHO-like solutions from M3D-C1 are destabilized by the toroidal rotational shear while high-n modes are stabilized. This effect is independent of the rotation direction, suggesting that the low-n EHO can be destabilized in principle with rotation in both directions. These modeling results are consistent with experimental observations of the EHO and support the proposed theory of the EHO as a rotational shear driven kink/peeling mode.
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.
Deuterium-Tritium Simulations of the Enhanced Reversed Shear Mode in the Tokamak Fusion Test Reactor
Mikkelsen, D.R.; Manickam, J.; Scott, S.D.; Zarnstorff
1997-04-01
The potential performance, in deuterium-tritium plasmas, of a new enhanced con nement regime with reversed magnetic shear (ERS mode) is assessed. The equilibrium conditions for an ERS mode plasma are estimated by solving the plasma transport equations using the thermal and particle dif- fusivities measured in a short duration ERS mode discharge in the Tokamak Fusion Test Reactor [F. M. Levinton, et al., Phys. Rev. Letters, 75, 4417, (1995)]. The plasma performance depends strongly on Zeff and neutral beam penetration to the core. The steady state projections typically have a central electron density of {approx}2:5x10 20 m{sup -3} and nearly equal central electron and ion temperatures of {approx}10 keV. In time dependent simulations the peak fusion power, {approx} 25 MW, is twice the steady state level. Peak performance occurs during the density rise when the central ion temperature is close to the optimal value of {approx} 15 keV. The simulated pressure profiles can be stable to ideal MHD instabilities with toroidal mode number n = 1, 2, 3, 4 and {infinity} for {beta}{sub norm} up to 2.5; the simulations have {beta}{sub norm} {le} 2.1. The enhanced reversed shear mode may thus provide an opportunity to conduct alpha physics experiments in conditions imilar to those proposed for advanced tokamak reactors.
Lao, L.L.; Burrell, K.H.; Casper, T.S.
1996-08-01
The confinement and the stability properties of the DIII-D tokamak high performance discharges are evaluated in terms of rotational and magnetic shear with emphasis on the recent experimental results obtained from the negative central magnetic shear (NCS) experiments. In NCS discharges, a core transport barrier is often observed to form inside the NCS region accompanied by a reduction in core fluctuation amplitudes. Increasing negative magnetic shear contributes to the formation of this core transport barrier, but by itself is not sufficient to fully stabilize the toroidal drift mode (trapped- electron-{eta}{sub i}mode) to explain this formation. Comparison of the Doppler shift shear rate to the growth rate of the {eta}{sub i} mode suggests that the large core {bold E x B} flow shear can stabilize this mode and broaden the region of reduced core transport . Ideal and resistive stability analysis indicates the performance of NCS discharges with strongly peaked pressure profiles is limited by the resistive interchange mode to low {Beta}{sub N} {lt} 2.3. This mode is insensitive to the details of the rotational and the magnetic shear profiles. A new class of discharges which has a broad region of weak or slightly negative magnetic shear (WNS) is described. The WNS discharges have broader pressure profiles and higher values than the NCS discharges together with high confinement and high fusion reactivity.
NASA Astrophysics Data System (ADS)
Akaki, Y.; Matsuo, T.; Nishimura, Y.; Miyakawa, S.; Endo, M.
2017-05-01
Ball bearing is widely used in a variety of machines including the transportation equipments of the automobiles and airplanes. Flaking failure is a common problem for ball bearing and it is caused by shear-mode fatigue crack growth under cyclic shear stress. Further, it is known that the premature flaking is attributed to the combined effect of hydrogen penetration into the material and cyclic shear stress during the operation. Therefore, in order to ensure the integrity of ball bearing, it is necessary to clarify the effect of hydrogen on shear-mode fatigue crack growth behavior, in particular, the threshold behavior. The evaluation of the shear-mode crack growth behavior is not easy because mode I crack branching occurs easily. Our previous studies revealed that it is required to apply static compression in the direction of specimen axis to attain a stable shear-mode fatigue crack growth. In addition, successive hydrogen supply to the specimen is essential for the evaluation of hydrogen effect on the fatigue threshold because hydrogen emits from the specimen during the fatigue test. In other words, the hydrogen-precharging method, commonly used for the research on hydrogen embrittlement, is not appropriate for the evaluation of fatigue threshold. In this study, to solve these problems, we have developed a novel, easy-to-use experimental method to evaluate the threshold behavior of shear-mode fatigue crack in the presence of hydrogen. The fundamental principle of the method is introduced in this paper.
Fundamental-mode sources in approach-to-critical experiments
Goda, J.; Busch, R.
2000-05-01
The 1/M method is commonly used in approach-to-critical experiments to ensure criticality safety. Ideally, a plot of 1/M versus amount of nuclear material or separation distance will be linear. However, the result is usually a curve. If the curve is concave up it is said to be conservative, since the critical mass is underestimated. However, it is possible for the curve to be non-conservative and overestimate the critical mass. This paper discusses one of the factors contributing to the shape of the 1/M curve and how it can be predicted and measured. Two source distributions, producing the same number of spontaneous fission neutrons, will not necessarily contribute equally towards the multiplication of a given system. For this reason equally sized units added during an approach-to-critical will have different effects on the multiplication of the system. A method of denoting the relative importance of source distributions is needed. One method is to compare any given source distribution to its equivalent fundamental-mode source distribution. An equivalent fundamental-mode source is an imaginary source distributed identically in space, energy, and angle to the fundamental-mode fission source that would produce the same neutron multiplication as the given source distribution. A factor, denoted as g* and defined as the ratio of the fixed-source multiplication to the fundamental-mode multiplication, is used to relate a given source strength to its equivalent fundamental-mode source strength (Spriggs, et al., 1999).
Critical behavior of a passively mode-locked laser: rational harmonic mode locking.
Zhan, Li; Gu, Zhaochang; Zhang, Jianwen; Xia, Yuxing
2007-08-15
The critical behavior of passive mode locking has been demonstrated in a figure-eight fiber laser that performs rational harmonic mode locking (RHML). On both the repetition rate and the pulse amplitude distribution, the observed pulse trains near the threshold exhibit the same regulations as the rational harmonic mode-locked ones. The theory also shows that there should be a middle status of RHML before achieving normal mode locking. It is important to note that the results provide what we believe to be the first confirmed attempt to address a fundamental question: how does a laser become mode locking with an increase of pump power?
Switching from pure- into simple-shear mode during uplift of the Altiplano plateau (Central Andes)
NASA Astrophysics Data System (ADS)
Babeyko, A. Yu.; Sobolev, S. V.
2003-04-01
The Altiplano plateau of the Central Andes is the second greatest plateau in the world after Tibet with an average elevation of about 4 km formed as a result of ocean-continent collision between subducting Nasca plate on the west and Brazilian shield on the east. According to the well known Isacks (1988) scenario, the Cenozoic evolution of the plateau started ca. 30 Ma in response to the retreat of the flat-subducted Nasca plate. Astenospheric material, which replaced the retreated plate, thermally thinned and softened the overlying lithosphere. The Altiplano crust, being pushed by the Brazilian shield from the east, was first shortened in a pure-shear mode and reached 60-70 km in thickness. At ca. 8-10 Ma deformation changed to a simple-shear mode: it was ceased in the upper crust of the plateau and migrated eastwards, into the Subandean, while the plateau itself continued to grow due to ongoing shortening in the lower crust. We employ numerical 2D thermomechanical modelling to test the above scenario and to evaluate the key parameters, which account for the transition from pure- to simple- shear style of the lithosphere-scale deformation under pure-shear boundary condition. As a numerical tool we use explicit finite difference/finite element lagrangian code with markers tracking material properties. The model contains rheologically different layers representing sediments, felsic and mafic crust, lithospheric mantle, and astenosphere. Rheological laws are Mohr-Coloumb elasto-plastic with softening and Maxwell visco-elastic with nonlinear power-law creep. Initial and boundary conditions simulate thermal activation of the Altiplano lithosphere by upwelling astenosphere as well as its westward pushing by the cold Brazilian shield with constant velocity. We found that model shortening always occurs in a pure-shear mode unless the uppermost crust of the Brazilian shield becomes during the deformation considerably weaker than the Altiplano upper crust (drop of friction
Sun, Xin; Stephens, Elizabeth V.; Khaleel, Mohammad A.
2008-06-01
This paper examines the effects of fusion zone size on failure modes, static strength and energy absorption of resistance spot welds (RSW) of advanced high strength steels (AHSS) under lap shear loading condition. DP800 and TRIP800 spot welds are considered. The main failure modes for spot welds are nugget pullout and interfacial fracture. Partial interfacial fracture is also observed. Static weld strength tests using lap shear samples were performed on the joint populations with various fusion zone sizes. The resulted peak load and energy absorption levels associated with each failure mode were studied for all the weld populations using statistical data analysis tools. The results in this study show that AHSS spot welds with conventionally required fusion zone size of can not produce nugget pullout mode for both the DP800 and TRIP800 welds under lap shear loading. Moreover, failure mode has strong influence on weld peak load and energy absorption for all the DP800 welds and the TRIP800 small welds: welds failed in pullout mode have statistically higher strength and energy absorption than those failed in interfacial fracture mode. For TRIP800 welds above the critical fusion zone level, the influence of weld failure modes on peak load and energy absorption diminishes. Scatter plots of peak load and energy absorption versus weld fusion zone size were then constructed, and the results indicate that fusion zone size is the most critical factor in weld quality in terms of peak load and energy absorption for both DP800 and TRIP800 spot welds.
Understanding the approximations of mode-coupling theory for sheared steady states of colloids.
Nandi, Saroj Kumar
2015-10-01
The lack of clarity of various mode-coupling theory (MCT) approximations, even in equilibrium, makes it hard to understand the relation between various MCT approaches for sheared steady states as well as their regime of validity. Here we try to understand these approximations indirectly by deriving the MCT equations through two different approaches for a colloidal system under shear, first through a microscopic approach, as suggested by Zaccarelli et al., and second through fluctuating hydrodynamics, where the approximations used in the derivation are quite clear. The qualitative similarity of our theory with a number of existing theories show that linear response theory might play a role in various approximations employed in deriving those theories and one needs to be careful while applying them for systems arbitrarily far away from equilibrium, such as a granular system or when shear is very strong. As a by-product of our calculation, we obtain the extension of the Yvon-Born-Green (YBG) equation for a sheared system and under the assumption of random-phase approximation, the YBG equation yields the distorted structure factor that was earlier obtained through different approaches.
Understanding the approximations of mode-coupling theory for sheared steady states of colloids
NASA Astrophysics Data System (ADS)
Nandi, Saroj Kumar
2015-10-01
The lack of clarity of various mode-coupling theory (MCT) approximations, even in equilibrium, makes it hard to understand the relation between various MCT approaches for sheared steady states as well as their regime of validity. Here we try to understand these approximations indirectly by deriving the MCT equations through two different approaches for a colloidal system under shear, first through a microscopic approach, as suggested by Zaccarelli et al., and second through fluctuating hydrodynamics, where the approximations used in the derivation are quite clear. The qualitative similarity of our theory with a number of existing theories show that linear response theory might play a role in various approximations employed in deriving those theories and one needs to be careful while applying them for systems arbitrarily far away from equilibrium, such as a granular system or when shear is very strong. As a by-product of our calculation, we obtain the extension of the Yvon-Born-Green (YBG) equation for a sheared system and under the assumption of random-phase approximation, the YBG equation yields the distorted structure factor that was earlier obtained through different approaches.
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.
High-order face-shear modes of relaxor-PbTiO3 crystals for piezoelectric motor applications
NASA Astrophysics Data System (ADS)
Ci, Penghong; Liu, Guoxi; Chen, Zhijiang; Zhang, Shujun; Dong, Shuxiang
2014-06-01
The face-shear vibration modes of [011] poled Zt ± 45° cut relaxor-PT crystals and their applications for linear piezoelectric motors were investigated. Unlike piezoelectric ceramics, the rotated crystal was found to exhibit asymmetric face-shear deformations, and its two high-order face-shear modes degraded into two non-isomorphic modes. As an application example, a standing wave ultrasonic linear motor (10 × 10 × 2 mm3) operating in high-order face-shear vibration modes was developed. The motor exhibits a large driving force (1.5 N) under a low driving voltage (22 Vpp). These findings could provide guidance for design of crystal resonance devices.
Wavelet reconstruction of E and B modes for CMB polarization and cosmic shear analyses
NASA Astrophysics Data System (ADS)
Leistedt, Boris; McEwen, Jason D.; Büttner, Martin; Peiris, Hiranya V.
2017-04-01
We present new methods for mapping the curl-free (E-mode) and divergence-free (B-mode) components of spin 2 signals using spin directional wavelets. Our methods are equally applicable to measurements of the polarization of the cosmic microwave background (CMB) and the shear of galaxy shapes due to weak gravitational lensing. We derive pseudo- and pure wavelet estimators, where E-B mixing arising due to incomplete sky coverage is suppressed in wavelet space using scale- and orientation-dependent masking and weighting schemes. In the case of the pure estimator, ambiguous modes (which have vanishing curl and divergence simultaneously on the incomplete sky) are also cancelled. On simulations, we demonstrate the improvement (i.e. reduction in leakage) provided by our wavelet space estimators over standard harmonic space approaches. Our new methods can be directly interfaced in a coherent and computationally efficient manner with component separation or feature extraction techniques that also exploit wavelets.
Line-tied kink modes in cylindrical equilibria with magnetic shear
Delzanno, G. L.; Evstatiev, E. G.; Finn, J. M.
2007-07-15
The method described by Evstatiev et al. [Phys. Plasmas 13, 072902 (2006)] to study the linear stability of line-tied modes in cylindrical geometry is applied to screw pinch equilibria with magnetic shear. The method is based on an expansion in eigenfunctions which depend on radius, and for ideal magnetohydrodynamics (MHD) the inclusion in the expansion of singular eigenfunctions (originating from a continuum) is necessary. The method is also applied to study scaling laws for large cylinder lengths L. It is found that the width of the internal layer of the radial displacement for the line-tied mode scales asymptotically as L{sup -2}, consistent with the so-called two-mode approximation. This result is valid in the context of both ideal and resistive MHD and is obtained both analytically and numerically.
Effect of Curing Mode on Shear Bond Strength of Self-Adhesive Cement to Composite Blocks
Kim, Jin-Young; Cho, Ga-Young; Roh, Byoung-Duck; Shin, Yooseok
2016-01-01
To overcome the disadvantages of computer-aided design/computer-aided manufacturing (CAD/CAM) processed indirect restorations using glass-ceramics and other ceramics, resin nano ceramic, which has high strength and wear resistance with improved polish retention and optical properties, was introduced. The purpose of this study was to evaluate the shear bond strength and fracture pattern of indirect CAD/CAM composite blocks cemented with two self-etch adhesive cements with different curing modes. Sand-blasted CAD/CAM composite blocks were cemented using conventional resin cement, Rely X Ultimate Clicker (RXC, 3M ESPE, St. Paul, MN, USA) with Single Bond Universal (SB, 3M ESPE, St. Paul, MN, USA) for the control group or two self-adhesive resin cements: Rely X U200 (RXU, 3M ESPE, St. Paul, MN, USA) and G-CEM Cerasmart (GC, GC corporation, Tokyo, Japan). RXU and GC groups included different curing modes (light-curing (L) and auto-curing (A)). Shear bond strength (SBS) analyses were performed on all the specimens. The RXC group revealed the highest SBS and the GC A group revealed the lowest SBS. According to Tukey’s post hoc test, the RXC group showed a significant difference compared to the GC A group (p < 0.05). For the curing mode, RXU A and RXU L did not show any significant difference between groups and GC A and GC L did not show any significant difference either. Most of the groups except RXC and RXU L revealed adhesive failure patterns predominantly. The RXC group showed a predominant cohesive failure pattern in their CAD/CAM composite, LavaTM Ultimate (LU, 3M ESPE, St. Paul, MN, USA). Within the limitations of this study, no significant difference was found regarding curing modes but more mixed fracture patterns were showed when using the light-curing mode than when using the self-curing mode. PMID:28773334
Dean, David W.; Wentzcovitch, Renata M.; Keskar, N.; Chelikowsky, James R.; Binggeli, N.
2000-02-01
Quartz and closely related materials will transform under pressure from crystalline states to amorphous forms. Here we examine coesite, a high-pressure form of silica which also undergoes pressure induced amorphization. We find that coesite, like quartz, possesses a shear instability closely coupled to a zone-edge phonon softening at pressures comparable to the amorphization transformation. The commonality of these features strongly suggests that a coupling between a shear and a phonon soft mode plays an important role in pressure induced amorphization. This mechanism is similar to that observed in martensitic transformations. The densities for the phases produced at high pressures, as calculated from variable cell shape molecular dynamics, follow the experimental glassy region joining coesite to stishovite. (c) 2000 The American Physical Society.
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
Measurement of shear-wave velocity by ultrasound critical-angle reflectometry (UCR)
NASA Technical Reports Server (NTRS)
Mehta, S.; Antich, P.; Blomqvist, C. G. (Principal Investigator)
1997-01-01
There exists a growing body of research that relates the measurement of pressure-wave velocity in bone to different physiological conditions and treatment modalities. The shear-wave velocity has been less studied, although it is necessary for a more complete understanding of the mechanical properties of bone. Ultrasound critical-angle reflectometry (UCR) is a noninvasive and nondestructive technique previously used to measure pressure-wave velocities both in vitro and in vivo. This note describes its application to the measurement of shear-wave velocity in bone, whether directly accessible or covered by soft tissue.
Mixed-mode static and fatigue crack growth in central notched and compact tension shear specimens
Shlyannikov, V.N.
1999-07-01
Elastic-plastic crack growth under mixed Mode I and 2 in six types of aluminum alloys and three types of steel were investigated. The experimental study of fatigue crack growth in six types of the aluminum alloys and one type of the steel is performed on biaxially loaded eight-petal specimens (EPS). All specimens for biaxial loading contained inclined through thickness central cracks. Mixed Mode I/2 static and fatigue crack growth experiments on the three types of steels and one type of the aluminum alloy used compact tension shear (CTS) specimens. Two approaches are developed for geometrical modeling of crack growth trajectories for the central notched and compact tension shear specimens respectively. The principal feature of such modeling is the determination of crack growth direction and the definition of crack length increment in this direction. On the basis of the analysis of the experimental data for the aluminum alloys and the steels an empirical crack reorientation criterion is suggested for both brittle and ductile materials. The damage process zone size concept is used for calculations and mixed-mode crack path. The influence of specimen geometry, biaxial loading and properties of the aluminum alloys and the steels on both crack growth direction and crack path at the macroscopic scale is discussed.
A global shear velocity model of the mantle from normal modes and surface waves
NASA Astrophysics Data System (ADS)
durand, S.; Debayle, E.; Ricard, Y. R.; Lambotte, S.
2013-12-01
We present a new global shear wave velocity model of the mantle based on the inversion of all published normal mode splitting functions and the large surface wave dataset measured by Debayle & Ricard (2012). Normal mode splitting functions and surface wave phase velocity maps are sensitive to lateral heterogeneities of elastic parameters (Vs, Vp, xi, phi, eta) and density. We first only consider spheroidal modes and Rayleigh waves and restrict the inversion to Vs, Vp and the density. Although it is well known that Vs is the best resolved parameter, we also investigate whether our dataset allows to extract additional information on density and/or Vp. We check whether the determination of the shear wave velocity is affected by the a priori choice of the crustal model (CRUST2.0 or 3SMAC) or by neglecting/coupling poorly resolved parameters. We include the major discontinuities, at 400 and 670 km. Vertical smoothing is imposed through an a priori gaussian covariance matrix on the model and we discuss the effect of coupling/decoupling the inverted structure above and below the discontinuities. We finally discuss the large scale structure of our model and its geodynamical implications regarding the amount of mass exchange between the upper and lower mantle.
Interlayer breathing and shear modes in few-trilayer MoS2 and WSe2.
Zhao, Yanyuan; Luo, Xin; Li, Hai; Zhang, Jun; Araujo, Paulo T; Gan, Chee Kwan; Wu, Jumiati; Zhang, Hua; Quek, Su Ying; Dresselhaus, Mildred S; Xiong, Qihua
2013-03-13
Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have recently attracted tremendous interest as potential valleytronic and nanoelectronic materials, in addition to being well-known as excellent lubricants in the bulk. The interlayer van der Waals (vdW) coupling and low-frequency phonon modes and how they evolve with the number of layers are important for both the mechanical and the electrical properties of 2D TMDs. Here we uncover the ultralow frequency interlayer breathing and shear modes in few-layer MoS2 and WSe2, prototypical layered TMDs, using both Raman spectroscopy and first principles calculations. Remarkably, the frequencies of these modes can be perfectly described using a simple linear chain model with only nearest-neighbor interactions. We show that the derived in-plane (shear) and out-of-plane (breathing) force constants from experiment remain the same from two-layer 2D crystals to the bulk materials, suggesting that the nanoscale interlayer frictional characteristics of these excellent lubricants should be independent of the number of layers.
Procedure for Failure Mode, Effects, and Criticality Analysis (FMECA)
NASA Technical Reports Server (NTRS)
1966-01-01
This document provides guidelines for the accomplishment of Failure Mode, Effects, and Criticality Analysis (FMECA) on the Apollo program. It is a procedure for analysis of hardware items to determine those items contributing most to system unreliability and crew safety problems.
Effects of a sheared ion velocity on the linear stability of ITG modes
Lontano, M.; Lazzaro, E.; Varischetti, M. C.
2006-11-30
The linear dispersion of the ion temperature gradient (ITG) modes, in the presence of a non uniform background ion velocity U(parallel sign) U(parallel sign)(x) ez, in the direction of the sheared equilibrium magnetic field B0 = B0(x) ez, has been studied in the frame of the two-fluid guiding center approximation, in slab geometry. Generally speaking, the presence of an ion flow destabilizes the oscillations. The role of the excited K-H instability is discussed.
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.
One-step thickness shear mode acoustic assay for plasminogen activators.
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%.
Tunable rejection filters with ultra-wideband using zeroth shear mode plate wave resonators
NASA Astrophysics Data System (ADS)
Kadota, Michio; Sannomiya, Toshio; Tanaka, Shuji
2017-07-01
This paper reports wide band rejection filters and tunable rejection filters using ultra-wideband zeroth shear mode (SH0) plate wave resonators. The frequency range covers the digital TV band in Japan that runs from 470 to 710 MHz. This range has been chosen to meet the TV white space cognitive radio requirements of rejection filters. Wide rejection bands were obtained using several resonators with different frequencies. Tunable rejection filters were demonstrated using Si diodes connected to the band rejection filters. Wide tunable ranges as high as 31% were measured by applying a DC voltage to the Si diodes.
E × B flow shear drive of the linear low-n modes of EHO in the QH-mode regime
NASA Astrophysics Data System (ADS)
Xu, G. S.; Wan, B. N.; Wang, Y. F.; Wu, X. Q.; Chen, Xi; Peng, Y.-K. Martin; Guo, H. Y.; Burrell, K. H.; Garofalo, A. M.; Osborne, T. H.; Groebner, R. J.; Wang, H. Q.; Chen, R.; Yan, N.; Wang, L.; Ding, S. Y.; Shao, L. M.; Hu, G. H.; Li, Y. L.; Lan, H.; Yang, Q. Q.; Chen, L.; Ye, Y.; Xu, J. C.; Li, J.
2017-08-01
A new model for the edge harmonic oscillations (EHOs) in the quiescent H-mode regime has been developed, which successfully reproduces the recent observations in the DIII-D tokamak. In particular, at high E × B flow shear only a few low-n kink modes remain unstable at the plasma edge, consistent with the EHO behavior, while at low E × B flow shear, the unstable mode spectrum is significantly broadened, consistent with the low-n broadband electromagnetic turbulence behavior. The model is based on a new mechanism for destabilizing low-n kink/peeling modes by the E × B flow shear, which underlies the EHOs, separately from the previously found Kelvin-Helmholtz drive. We find that the differential advection of mode vorticity by sheared E × B flows modifies the 2D pattern of mode electrostatic potential perpendicular to the magnetic field lines, which in turn causes a radial expansion of the mode structure, an increase of field line bending away from the mode rational surface, and a reduction of inertial stabilization. This enhances the kink drive as the parallel wavenumber increases significantly away from the rational surface at the plasma edge where the magnetic shear is also strong. This destabilization is also shown to be independent of the sign of the flow shear, as observed experimentally, and has not been taken into account in previous pedestal linear stability analyses. Verification of the veracity of this EHO mechanism will require analysis of the nonlinear evolution of low-n kink/peeling modes so destabilized in the linear regime.
Embolization: critical thrombus height, shear rates, and pulsatility. Patency of blood vessels.
Basmadjian, D
1989-11-01
The present article builds on elementary fluid dynamics and previous analyses by the author to delineate approximate boundaries of mural thrombus height Hp, maximum shear rate gamma Max, and flow pulsatility beyond which thrombi are subject to either very high or very low probabilities of embolization. A thrombus height of approximately 0.1 mm emerges as a critical dividing line: Below it, the maximum embolizing shear stress tau s is independent of thrombus height and varies only linearly with shear rate. Above it, tau s quickly approaches a strong quadratic dependence on both thrombus height and shear rate: tau s approximately (Hp gamma)2, significantly increasing the likelihood of an embolizing event. By contrast, convective-diffusive removal of blood components during the initial stages of thrombus formation varies only weakly with gamma 1/3 in all but the smallest vessels. These maximum embolizing stresses are due principally to fluid drag. Acceleration (pulsatile) forces only begin to make their presence felt at gamma less than 500 s-1 and reach parity with fluid drag at gamma approximately 10 s-1, i.e., at a level where the presence of pulsatility is questionable. The results are used to provide maps of domains with high and low probabilities of an embolytic event and of vessel patency. The maps reveal that relatively modest changes in shear rate and/or vessel lumen can cause shifts from high to low likelihood of vessel patency, opening up possible ways of controlling blockage by manipulation of these variables.
Force Transmission Modes of Non-Cohesive and Cohesive Materials at the Critical State
2017-01-01
This paper investigates the force transmission modes, mainly described by probability density distributions, in non-cohesive dry and cohesive wet granular materials by discrete element modeling. The critical state force transmission patterns are focused on with the contact model effect being analyzed. By shearing relatively dense and loose dry specimens to the critical state in the conventional triaxial loading path, it is observed that there is a unique critical state force transmission mode. There is a universe critical state force distribution pattern for both the normal contact forces and tangential contact forces. Furthermore, it is found that using either the linear Hooke or the non-linear Hertz model does not affect the universe force transmission mode, and it is only related to the grain size distribution. Wet granular materials are also simulated by incorporating a water bridge model. Dense and loose wet granular materials are tested, and the critical state behavior for the wet material is also observed. The critical state strength and void ratio of wet granular materials are higher than those of a non-cohesive material. The critical state inter-particle distribution is altered from that of a non-cohesive material with higher probability in relatively weak forces. Grains in non-cohesive materials are under compressive stresses, and their principal directions are mainly in the axial loading direction. However, for cohesive wet granular materials, some particles are in tension, and the tensile stresses are in the horizontal direction on which the confinement is applied. The additional confinement by the tensile stress explains the macro strength and dilatancy increase in wet samples. PMID:28858238
Investigation of supersonic modes and three-dimensionality in bounded, free shear flows
NASA Technical Reports Server (NTRS)
Macaraeg, Michele G.
1991-01-01
It is found through two-dimensional temporal simulations of high-speed free shear layers that mean flow distortion is significantly increased when supersonic disturbances are introduced as initial conditions. The shear layer exhibits no subharmonic growth or roll-up, but rather a spectral broadening as energy is distributed into higher harmonics. Increasing the velocity of one side of the mixing layer (u2) to roughly 1/5 the speed of the high speed side (u1), allows a slight subharmonic growth at a very slow rate for two-dimensional modes. A first look at three-dimensional free shear flows is also presented for M = 2. No effect is seen for incompressible flow; however, stabilization is seen with respect to maximum temporal growth rates as the transverse velocity is increased. A much stronger, but similar effect is seen if u2 is increased. The wave direction of maximum growth for u2 is greater than 0.4 is found to be the direction of the faster stream (u1) over a broad range of transverse velocities.
Chen, Jianguo; Liu, Guoxi; Cheng, Jinrong; Dong, Shuxiang
2016-08-01
The actuation performance, strain hysteresis, and heat generation of the shear-bending mode actuators based on soft and hard BiScO3-PbTiO3 (BS-PT) ceramics were investigated under different thermal (from room temperature to 300 °C) and electrical loadings (from 2 to 10 kV/cm and from 1 to 1000 Hz). The actuator based on both soft and hard BS-PT ceramics worked stably at the temperature as high as 300 °C. The maximum working temperature of this shear-bending actuators is 150 °C higher than those of the traditional piezoelectric actuators based on commercial Pb(Zr, Ti)O3 materials. Furthermore, although the piezoelectric properties of soft-type ceramics based on BS-PT ceramics were superior to those of hard ceramics, the maximum displacement of the actuator based on hard ceramics was larger than that fabricated by soft ceramics at high temperature. The maximum displacement of the actuator based on hard ceramics was [Formula: see text] under an applied electric field of 10 kV/cm at 300 °C. The strain hysteresis and heat generation of the actuator based on hard ceramics was smaller than those of the actuator based on soft ceramics in the wide temperature range. These results indicated that the shear-bending actuator based on hard piezoelectric ceramics was more suitable for high-temperature piezoelectric applications.
NASA Astrophysics Data System (ADS)
Sarkar, C.; Hirani, H.
2013-11-01
The torque characteristics of magnetorheological brakes, consisting of rotating disks immersed in a MR fluid and enclosed in an electromagnetic casing, are controlled by regulating the yield stress of the MR fluid. An increase in yield stress increases the braking torque, which means that the higher the yield strength of the MR fluid, the better the performance of the MR brake will be. In the present research an application of compressive force on MR fluid has been proposed to increase the torque capacity of MR brakes. The mathematical expressions to estimate the torque values for MR brake, operating under compression plus shear mode accounting Herschel-Bulkley shear thinning model, have been detailed. The required compressive force on MR fluid of the proposed brake has been applied using an electromagnetic actuator. The development of a single-plate MR disk brake and an experimental test rig are described. Experiments have been performed to illustrate braking torque under different control currents (0.0-2.0 A). The torque results have been plotted and compared with theoretical study. Experimental results as well as theoretical calculations indicate that the braking torque of the proposed MR brake is higher than that of the MR brake operating only under shear.
Properties of shear horizontal acoustic plate modes in BT-cut quartz.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Ehlers, F. J. H.; Seydou, M.; Tingaud, D.; Maurel, F.; Queyreau, S.; Charles, Y.
2017-09-01
Using the framework of density functional theory, the structural and energetic response of two face-centred cubic (fcc) Al grain boundaries (GBs) to combined tension and shear loadings has been examined. It is shown that tension will serve to inhibit the Σ5 [100] 36.87° twist GB response to shear in a mixed-mode loading scenario, by increasing the difference in structural environments for inequivalent atoms at the GB plane. We propose that the presence of such atoms, rather than the full structural details of the GB structure, is instrumental in triggering this tension-shear interplay. As support for this hypothesis, we compute the Σ3 [-110] (111) 60° symmetric tilt GB mixed-mode loading response. Here, all atoms at the GB plane are equivalent, and the qualitative shear energy variation is unaffected by tension. Our findings indicate that general fcc Al GBs may display a stronger shear energy variation at larger levels of tension, contrasting general expectations. The implications to GB breakage are discussed.
Pichardo, Samuel; Hynynen, Kullervo
2007-12-21
Shear mode transmission through the skull has been previously proposed as a new trans-skull propagation technique for noninvasive therapeutic ultrasound (Clement 2004 J. Acoust. Soc. Am. 115 1356-64). The main advantage of choosing shear over longitudinal mode resides on the fact that there is less wavefront distortion with the former. In the present study, the regions of the brain suitable for shear-mode transmission were established for a simple focused ultrasound device. The device consists of a spherically curved transducer that has a focal length of 10 cm, an aperture between 30 degrees and 60 degrees and operates at 0.74 MHz. The regions suitable for shear-mode transmission were determined by the shear wave acoustic windows that matched the shape of the device acoustic field. The acoustic windows were calculated using segmentation and triangulation of outer and inner faces of skull from 3D-MRI head datasets. Nine heads of healthy adults were analyzed. The surface considered for the calculations was the head region found above the supra-orbital margin. For every inspected point in the brain volume, the axis of the device was determined by the vector between this inspection point and a point located in the center of the brain. Numerical predictions of the acoustic field, where shear-mode conversion through the skull was considered, were obtained and compared to the case of water-only conditions. The brain tissue that is close to the skull showed suitable acoustic windows for shear waves. The central region of the brain seems to be unreachable using shear-mode. Analysis of the acoustic fields showed a proportional relation between the acoustic window for shear mode and the effective degree of focusing. However, this relation showed significant differences among specimens. In general, highly focused fields were obtained when the acoustic window for shear waves (A(SW)) intersected more than 67% of the entering acoustic window (A(TX)) of the device. The average
Notch strengthening or weakening governed by transition of shear failure to normal mode fracture.
Lei, Xianqi; Li, Congling; Shi, Xinghua; Xu, Xianghong; Wei, Yujie
2015-05-29
It is generally observed that the existence of geometrical discontinuity like notches in materials will lead to strength weakening, as a resultant of local stress concentration. By comparing the influence of notches to the strength of three typical materials, aluminum alloys with intermediate tensile ductility, metallic glasses with no tensile ductility, and brittle ceramics, we observed strengthening in aluminum alloys and metallic glasses: Tensile strength of the net section in circumferentially notched cylinders increases with the constraint quantified by the ratio of notch depth over notch root radius; in contrast, the ceramic exhibit notch weakening. The strengthening in the former two is due to resultant deformation transition: Shear failure occurs in intact samples while samples with deep notches break in normal mode fracture. No such deformation transition was observed in the ceramic, and stress concentration leads to its notch weakening. The experimental results are confirmed by theoretical analyses and numerical simulation. The results reported here suggest that the conventional criterion to use brittleness and/or ductility to differentiate notch strengthening or weakening is not physically sound. Notch strengthening or weakening relies on the existence of failure mode transition and materials exhibiting shear failure while subjected to tension will notch strengthen.
Notch strengthening or weakening governed by transition of shear failure to normal mode fracture
Lei, Xianqi; Li, Congling; Shi, Xinghua; Xu, Xianghong; Wei, Yujie
2015-01-01
It is generally observed that the existence of geometrical discontinuity like notches in materials will lead to strength weakening, as a resultant of local stress concentration. By comparing the influence of notches to the strength of three typical materials, aluminum alloys with intermediate tensile ductility, metallic glasses with no tensile ductility, and brittle ceramics, we observed strengthening in aluminum alloys and metallic glasses: Tensile strength of the net section in circumferentially notched cylinders increases with the constraint quantified by the ratio of notch depth over notch root radius; in contrast, the ceramic exhibit notch weakening. The strengthening in the former two is due to resultant deformation transition: Shear failure occurs in intact samples while samples with deep notches break in normal mode fracture. No such deformation transition was observed in the ceramic, and stress concentration leads to its notch weakening. The experimental results are confirmed by theoretical analyses and numerical simulation. The results reported here suggest that the conventional criterion to use brittleness and/or ductility to differentiate notch strengthening or weakening is not physically sound. Notch strengthening or weakening relies on the existence of failure mode transition and materials exhibiting shear failure while subjected to tension will notch strengthen. PMID:26022892
A Self-consistent Simulation of KSTAR Reverse-shear Operation Mode using ASTRA Code
NASA Astrophysics Data System (ADS)
Kim, J. Y.; Jhang, Hogun
2001-10-01
A simulation study is presented on the reverse-shear operation mode of KSTAR (Korea Superconducting Tokamak Advanced Research) device, using the ASTRA (Automatic System of TRansport Analysis in a tokamak) code. The heat deposition and the current profile evolution are modeled self-consistently from the ASTRA code into which several heating and current-drive modules of NBI, ICRH/FWCD, and LHCD have been implemented. The anomalous transport is modeled more elaborately by using the theory-based models, such as IFS/PPPL one, rather than conventional empirical or artificial formulas. The effect of equilibrium flow shear and its time evolution are also included in the modeling for a more realistic description of the formation of ITB and its spatial and temporal evolution. Finally, based on the simulation results we will discuss the possible way to get an AT mode plasma with high-beta and high bootstrap current fraction, avoiding a steep pressure gradient and related local MHD instabilities.
NASA Astrophysics Data System (ADS)
Shi, Yang; Gao, Yuanwen
2017-08-01
In this study, a novel functionally graded cylindrical magnetoelectric (ME) composite based on d15 shear-mode response is analyzed theoretical by using the elastic mechanics model and equivalent circuit model. The composite is mounted around AC current-carrying power lines to scavenge AC magnetic field energy. For different sensing configurations, the generated magnetic fields are calculated, respectively. Then, based on the theoretical models, the dependences of the ME performances, i.e., the ME voltage and power, upon the type of the material gradation, the material constants, and geometrical parameters of the cylindrical ME composite are numerically evaluated. The results show that the ME coupling effect in the functionally graded cylindrical ME composite with special gradation is stronger than that in the homogeneous structure. The ME performance can be improved by geometrical parameters as well. The presented two models can be synthesized under the open-circuit condition, which provide a theoretical basis to understand and improve the ME property of the d15 shear-mode cylindrical ME composites operating at resonant frequency and off-resonance frequency.
NASA Astrophysics Data System (ADS)
Sund, Richard; Scharer, John
2002-11-01
We examine a new method for generating sheared flows in advanced tokamak D-T reactors with the goal of creating and controlling internal transport barriers. Ion-Bernstein waves (IBWs) have the recognized capacity to create internal transport barriers through sheared plasma flows resulting from ion absorption. Under reactor conditions, the IBW can be generated by mode conversion of a fast magnetosonic wave incident from the high-field side (HFS) on the second harmonic resonance of a minority hydrogen component, with near 100200 MHz) minimizes parasitic absorption and permits the converted IBW to approach the fifth tritium harmonic. It also facilitates compact antennas and feeds, and efficient fast wave launch. Placement of the 5T absorption layer on the HFS is advantageous for shear production. The scheme is applicable to reactors with aspect ratio < 3 such that the conversion and absorption layers are both on the high field side of the magnetic axis. Various factors (adequate separation of the mode conversion layer from the magnetic axis, concentration of the fast wave near the midplane, large machine size, and plasma elongation) minimize poloidal field effects in the conversion zone and permit a slab analysis. We use a 1-D full-wave code to analyze the conversion and absorption. A 2-D ray-tracing code incorporating poloidal magnetic fields is used to follow the IBW for various equilibria. Within this analysis a weak bean shape appears most favorable. This is an attractive scheme for future advanced tokamak reactors. *Research supported by the Univ. of Wisconsin, Madison
NASA Astrophysics Data System (ADS)
Miao, Hongchen; Huan, Qiang; Li, Faxin
2016-11-01
The fundamental shear horizontal (SH0) wave in plate-like structures is of great importance in non-destructive testing (NDT) and structural health monitoring (SHM) as it is non-dispersive, while excitation or reception of SH0 waves using piezoelectrics is always a challenge. In this work, we firstly demonstrate via finite element simulations that face-shear piezoelectrics is superior to thickness-shear piezoelectrics in driving SH waves. Next, by using a newly defined face-shear d24 PZT wafer as an actuator and face-shear d36 PMN-PT wafers as sensors, pure SH0 wave was successfully excited in an aluminum plate from 130 to 180 kHz. Then, it was shown that the face-shear d24 PZT wafer could receive the SH0 wave only and filter the Lamb waves over a wide frequency range (120-230 kHz). The directionality of the excited SH0 wave was also investigated using face-shear d24 PZT wafers as both actuators and sensors. Results show that pure SH0 wave can be excited symmetrically along two orthogonal directions (0° and 90°) and the amplitude of the excited SH0 wave can keep over 90% of the maximum amplitude when the deviate angle is within 30°. This work could greatly promote the applications of SH0 wave in NDT and SHM.
Shear viscosity at the Ising-nematic quantum critical point in two-dimensional metals
NASA Astrophysics Data System (ADS)
Eberlein, Andreas; Patel, Aavishkar A.; Sachdev, Subir
2017-02-01
In an isotropic strongly interacting quantum liquid without quasiparticles, general scaling arguments imply that the dimensionless ratio (kB/ℏ )η /s , where η is the shear viscosity and s is the entropy density, is a universal number. We compute the shear viscosity of the Ising-nematic critical point of metals in spatial dimension d =2 by an expansion below d =5 /2 . The anisotropy associated with directions parallel and normal to the Fermi surface leads to a violation of the scaling expectations: η scales in the same manner as a chiral conductivity, and the ratio η /s diverges at low temperature (T ) as T-2 /z, where z is the dynamic critical exponent for fermionic excitations dispersing normal to the Fermi surface.
Diocotron Mode Damping from a Flux through the Critical Layer
NASA Astrophysics Data System (ADS)
Driscoll, C. Fred
2014-10-01
Experiments and theory characterize a novel type of spatial Landau damping of diocotron modes which is algebraic rather than exponential in time; this damping is caused by a flux of particles through the wave/rotation critical layer. These kz = 0 diocotron (drift) modes with azimuthal mode numbers mθ = 1 , 2 . . . are dominant features in the dynamics of non-neutral plasmas in cylindrical and toroidal traps; and they are directly analogous to Kelvin waves on 2D fluid vortices. Spatial Landau damping is the resonant interaction between a mode at frequency fm and the plasma rotation fE (r) , at the critical radius Rc where fm =mθfE (Rc) . This is mathematically analogous to velocity-space Landau damping with fk = kv / 2 π . Experimentally, diocotron modes on pure electron plasmas exhibit exponential Landau damping when the initial plasma density is non-zero at Rc. Here, we demonstrate that a steady outward flux of particles through Rc causes diocotron modes to damp algebraically to zero amplitude, as D (t) =D0 -γm t . The outward flux is controlled and measured experimentally, and the damping rates γm are proportional to the flux. In general, any weak non-ideal process which causes outward flux may cause this damping. Analytics and simulations have developed a simple model of this damping, treating the transfer of canonical angular momentum from the mode to particles transiting the nonlinear trapping region at Rc. The model qualitatively agrees with experiments for mθ = 1 , but nominally predicts a discrepant algebraic exponent for mθ = 2 , perhaps due to the amplitude dependence of the trapping structure. Overall, this novel flux-driven damping is determined by the present magnitudes of the wave and outward flux, in contrast to the Landau analysis of phase mixing of the initial density. Supported by NSF/DOE Partnership Grants PHY-0903877 and DE-SC0002451.
Lao, L.L.; Burrell, K.H.; Casper, T.S.; Chan, V.S.; Chu, M.S.; DeBoo, J.C.; Doyle, E.J.; Durst, R.D.; Forest, C.B.; Greenfield, C.M.; Groebner, R.J.; Hinton, F.L.; Kawano, Y.; Lazarus, E.A.; Lin-Liu, Y.R.; Mauel, M.E.; Meyer, W.H.; Miller, R.L.; Navratil, G.A.; Osborne, T.H.; Peng, Q.; Rettig, C.L.; Rewoldt, G.; Rhodes, T.L.; Rice, B.W.; Schissel, D.P.; Stallard, B.W.; Strait, E.J.; Tang, W.M.; Taylor, T.S.; Turnbull, A.D.; Waltz, R.E.; the DIII-D Team
1996-05-01
The confinement and the stability properties of the DIII-D tokamak [{ital Plasma} {ital Physics} {ital and} {ital Controlled} {ital Nuclear} {ital Fusion} {ital Research} 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] high-performance discharges are evaluated in terms of rotational and magnetic shear, with an emphasis on the recent experimental results obtained from the negative central magnetic shear (NCS) experiments. In NCS discharges, a core transport barrier is often observed to form inside the NCS region accompanied by a reduction in core fluctuation amplitudes. Increasing negative magnetic shear contributes to the formation of this core transport barrier, but by itself is not sufficient to fully stabilize the toroidal drift mode (trapped-electron-{eta}{sub {ital i}} mode) to explain this formation. Comparison of the Doppler shift shear rate to the growth rate of the {eta}{sub {ital i}} mode suggests that the large core {ital E}{times}{ital B} flow shear can stabilize this mode and broaden the region of reduced core transport. Ideal and resistive stability analysis indicates the performance of NCS discharges with strongly peaked pressure profiles is limited by the resistive interchange mode to low {beta}{sub {ital N}}{le}2.3. This mode is insensitive to the details of the rotational and the magnetic shear profiles. A new class of discharges, which has a broad region of weak or slightly negative magnetic shear (WNS), is described. The WNS discharges have broader pressure profiles and higher {beta} values than the NCS discharges, together with high confinement and high fusion reactivity. {copyright} {ital 1996 American Institute of Physics.}
Clustered frequency analysis of shear Alfvén modes in stellarators
NASA Astrophysics Data System (ADS)
Spong, D. A.; D'Azevedo, E.; Todo, Y.
2010-02-01
The shear Alfvén spectrum in three-dimensional configurations, such as stellarators and rippled tokamaks, is more densely populated due to the larger number of mode couplings caused by the variation in the magnetic field in the toroidal dimension. This implies more significant computational requirements that can rapidly become prohibitive as more resolution is requested. Alfvén eigenfrequencies and mode structures are a primary point of contact between theory and experiment. A new algorithm based on the Jacobi-Davidson method is developed here and applied for a reduced magnetohydrodynamics model to several stellarator configurations. This technique focuses on finding a subset of eigenmodes clustered about a specified input frequency. This approach can be especially useful in modeling experimental observations, where the mode frequency can generally be measured with good accuracy and several different simultaneous frequency lines may be of interest. For cases considered in this paper, it can be a factor of 102-103 times faster than more conventional methods.
Interlayer breathing and shear modes in NbSe2 atomic layers
NASA Astrophysics Data System (ADS)
He, Rui; van Baren, Jeremiah; Yan, Jia-An; Xi, Xiaoxiang; Ye, Zhipeng; Ye, Gaihua; Lu, I.-Hsi; Leong, S. M.; Lui, C. H.
2016-09-01
Atomically thin NbSe2 is a metallic layered transition metal dichalcogenide with novel charge-density-wave (CDW) and superconductive phases. Properties of NbSe2 atomic layers are sensitive to interlayer coupling. Here we investigate the interlayer phonons of few-layer NbSe2 by ultralow-frequency Raman spectroscopy. We observe both the interlayer breathing modes and shear modes at frequencies below 40 cm-1 for samples of 2-15 layers. Their frequency, Raman activity, and environmental instability depend systematically on the layer number. We account for these results by a combination of linear-chain model, group theory and first-principles calculations. We find that, although NbSe2 has different stacking order from MoS2, MoSe2, WS2 and WSe2, they share the same crystal symmetry groups and exhibit similar Raman selection rules for interlayer phonons. In addition, the interlayer phonon modes evolve smoothly from T = 300 to 8 K, with no observable response to the CDW formation in NbSe2. This finding indicates that the atomic registry between adjacent NbSe2 layers is well preserved in the CDW transition.
Scaling of the critical slip distance for seismic faulting with shear strain in fault zones
Marone, C.; Kilgore, B.
1993-01-01
THEORETICAL and experimentally based laws for seismic faulting contain a critical slip distance1-5, Dc, which is the slip over which strength breaks down during earthquake nucleation. On an earthquake-generating fault, this distance plays a key role in determining the rupture nucleation dimension6, the amount of premonitory and post-seismic slip7-10, and the maximum seismic ground acceleration1,11. In laboratory friction experiments, Dc has been related to the size of surface contact junctions2,5,12; thus, the discrepancy between laboratory measurements of Dc (??? 10-5 m) and values obtained from modelling earthquakes (??? 10-2 m) has been attributed to differences in roughness between laboratory surfaces and natural faults5. This interpretation predicts a dependence of Dc on the particle size of fault gouge 2 (breccia and wear material) but not on shear strain. Here we present experimental results showing that Dc scales with shear strain in simulated fault gouge. Our data suggest a new physical interpretation for the critical slip distance, in which Dc is controlled by the thickness of the zone of localized shear strain. As gouge zones of mature faults are commonly 102-103 m thick13-17, whereas laboratory gouge layers are 1-10 mm thick, our data offer an alternative interpretation of the discrepancy between laboratory and field-based estimates of Dc.
Rohrer, C A; Roesner, L A
2006-01-01
Hydrologic and hydraulic modeling in the USEPA Stormwater Management Model (SWMM) were used to examine the effectiveness of typical stormwater management practices in reducing the potential for stream erosion. Fifty-year continuous simulations were used to produce flow duration curves and stream erosion rates for a variety of critical shear stress values representative of both cohesive and non-cohesive sediments. An excess shear stress erosion potential index was used to evaluate changes in erosion between undeveloped conditions of a 10 hectare watershed and four variations of post-development stormwater control. Evaluation of flow duration curves showed that when development takes place, the duration of mid- to low-range discharges increase significantly, especially when detention practices are applied. In channels with low entrainment thresholds for bed and bank materials, e.g. sands and highly erodible clays, the significant increase of the duration of mid- to low-range discharges results in erosion potential index values greater than two regardless of the detention practices used. Overcontrol detention resulted in erosion potential index values of less than one, indicating a loss of erosion potential for bed materials such as most gravels (d(s) > 6 mm) and resistant clays that have critical shear stress values greater than four Pa.
NASA Astrophysics Data System (ADS)
Mukherjee, Soumyajit; Koyi, Hemin A.
2010-09-01
The Higher Himalayan Shear Zone (HHSZ) in the Sutlej section reveals (1) top-to-SW ductile shearing, (2) top-to-NE ductile shearing in the upper- and the lower strands of the South Tibetan Detachment System (STDSU, STDSL), and (3) top-to-SW brittle shearing corroborated by trapezoid-shaped minerals in micro-scale. In the proposed extrusion model of the HHSZ, the E1-phase during 25-19 Ma is marked by simple shearing of the upper sub-channel defined by the upper strand of the Main Central Thrust (MCTU) and the top of STDSU as the lower- and the upper boundaries, respectively. Subsequently, the E2a-pulse during 15-14 Ma was characterized by simple shear, pure shear, and channel flow of the entire HHSZ. Finally, the E2b-pulse during 14-12 Ma observed simple shearing and channel flow of the lower sub-channel defined by the lower strand of the Main Central Thrust (MCTL) and the top of the STDSL as the lower- and the upper boundaries, respectively. The model explains the constraints of thicknesses of the STDSU and the STDSL along with spatially variable extrusion rate and the inverted metamorphism of the HHSZ. The model predicts (1) shear strain after ductile extrusion to be maximum at the boundaries of the HHSZ, which crudely matches with the existing data. The other speculations that cannot be checked are (2) uniform shear strain from the MCTU to the top of the HHSZ in the E1-phase; (3) fastest rates of extrusion of the lower boundaries of the STDSU and the STDSL during the E2a- and E2b-pulses, respectively; and (4) variable thickness of the STDSL and rare absence of the STDSU. Non-parabolic shear fabrics of the HHSZ possibly indicate heterogeneous strain. The top-to-SW brittle shearing around 12 Ma augmented the ductile extruded rocks to arrive a shallower depth. The brittle-ductile extension leading to boudinage possibly did not enhance the extrusion.
Optimization Of Shear Modes To Produce Enhanced Bandwidth In Ghz GaP Bragg Cells
NASA Astrophysics Data System (ADS)
Soos, J., I.; Rosemeier, R. G.; Rosenbaum, J.
1988-02-01
Applications of Gallium Phosphide (GaP) acousto-optic devices, at wavelengths from 570nm - 1.06um seem to be ideal for fiber optic modulators, scanners, deflectors, frequency shifters, Q-switches and mode lockers. One of the major applications are for RF spectrometers in early warning radar receivers and auto-correlators. Longitudinal GaP acousto-optic Bragg cells which have respectively operational frequencies in the range of 200 MHz - 3 GHz and diffraction efficiencies in the range of 120%/RF watt to 1%/RF watt have recently been fabricated. Comparatively, shear GaP devices which have operational frequencies in the range of 200 MHz to 2 GHz and diffraction efficiencies from 80%/RF watt to 7%/RF watt have also been constructed.
A global shear velocity model of the mantle from normal modes, surface waves and body waves
NASA Astrophysics Data System (ADS)
Durand, S.; Debayle, E.; Ricard, Y. R.; Lambotte, S.; Zaroli, C.
2014-12-01
We present SEISGLOB2, a new global shear-wave velocity model of the mantle. SEISGLOB 2 results from the inversion of all published spheroidal mode splitting and coupling coefficients, completed with new measurements made in Strasbourg, of a large Rayleigh wave dataset measured by Debayle & Ricard (2012) and extended to long periods by Durand et al. (2014), and of a global dataset of S, SS and ScS travel times measured at ≈30 s period by Zaroli et al. (2010). These seismic data are sensitive to 3D heterogeneities of elastic parameters (Vs, Vp, ζ, φ, η in a transversly isotropic medium) and density. We discuss the depth and lateral resolution of our model and compare our results with other global tomographies. Although it is well known that Vs is the best resolved parameter, we also investigate whether our dataset allows to extract additional information on density and/or Vp.
Continuous monitoring of bacterial biofilm growth using uncoated Thickness-Shear Mode resonators
NASA Astrophysics Data System (ADS)
Castro, P.; Resa, P.; Durán, C.; Maestre, J. R.; Mateo, M.; Elvira, L.
2012-12-01
Quartz Crystal Microbalances (QCM) were used to nondestructively monitor in real time the microbial growth of the bacteria Staphylococcus epidermidis (S. epidermidis) in a liquid broth. QCM, sometimes referred to as Thickness-Shear Mode (TSM) resonators, are highly sensitive sensors not only able to measure very small mass, but also non-gravimetric contributions of viscoelastic media. These devices can be used as biosensors for bacterial detection and are employed in many applications including their use in the food industry, water and environment monitoring, pharmaceutical sciences and clinical diagnosis. In this work, three strains of S. epidermidis (which differ in the ability to produce biofilm) have been continuously monitored using an array of piezoelectric TSM resonators, at 37 °C in a selective culturing media. Microbial growth was followed by measuring the changes in the crystal resonant frequency and bandwidth at several harmonics. It was shown that microbial growth can be monitored in real time using multichannel and multiparametric QCM sensors.
Shear flows at the tokamak edge and their interaction with edge-localized modes
Aydemir, A. Y.
2007-05-15
Shear flows in the scrape-off layer (SOL) and the edge pedestal region of tokamaks are shown to arise naturally out of transport processes in a magnetohydrodynamic model. In quasi-steady-state conditions, collisional resistivity coupled with a simple bootstrap current model necessarily leads to poloidal and toroidal flows, mainly localized to the edge and SOL. The role of these flows in the grad-B drift direction dependence of the power threshold for the L (low) to H (high) transition, and their effect on core rotation, are discussed. Theoretical predictions based on symmetries of the underlying equations, coupled with computational results, are found to be in agreement with observations in Alcator C-Mod [Phys. Plasmas 12, 056111 (2005)]. The effects of these self-consistent flows on linear peeling/ballooning modes and their nonlinear consequences are also examined.
Field measurement of critical shear stress for erosion and deposition of fine muddy sediments
NASA Astrophysics Data System (ADS)
Salehi, M.; Strom, K. B.; Field Study
2010-12-01
The movement of muddy sediment from one region to another is linked to the fate and transport of pollutants that can be attached to this sediment. Important in understanding this movement is the need to know the critical conditions for erosion and deposition of the fine muddy sediment. For non-cohesion sediment, such as sands and gravels, reasonable estimates for the critical conditions can often be made theoretically without in situ measurements of the critical fluid condition or sediment transport rate. However, the shear stress needed for the incipient motion of the mud (cohesive sediments) is inherently difficult to calculate theoretically or in research flumes due to the influence of (1) flow history; (2) local sediment composition; (3) biological activity within the bed; (4) water content of the bed; and (5) salinity of the water column. The complexity of the combination of these factors makes the field measurement necessary. A field experiment was conducted under tidal flow in the region surrounding the Houston Ship Channel (near Houston, TX) to determine these conditions. Observations were made using single point, simultaneous, in situ measurement of turbulent flow and suspended sediment concentration within bottom boundary layer. Measurements were primarily made with a 6 MHz Nortek Vector velocimeter (ADV). The ADV was programmed to record 3-minute turbulent velocity with 32 Hz frequency every 10 minute. The suspended sediment concentration (SSC) was measured using the calibration of acoustic backscatter recorded by ADV against sample derived SSC. Different methods such as turbulent kinetic energy (TKE), TKEw and direct covariance method (COV) are compared together. TKE showed much more reasonable estimation on bed shear stress. Combination of time varying SSC, distance from the bed to the sampling volume recorded by ADV and calculation of shear stress made the determination of critical conditions for erosion and deposition possible.
Biosensor for human IgE detection using shear-mode FBAR devices
NASA Astrophysics Data System (ADS)
Chen, Ying-Chung; Shih, Wei-Che; Chang, Wei-Tsai; Yang, Chun-Hung; Kao, Kuo-Sheng; Cheng, Chien-Chuan
2015-02-01
Film bulk acoustic resonators (FBARs) have been evaluated for use as biosensors because of their high sensitivity and small size. This study fabricated a novel human IgE biosensor using shear-mode FBAR devices with c-axis 23°-tilted AlN thin films. Off-axis radio frequency (RF) magnetron sputtering method was used for deposition of c-axis 23°-tilted AlN thin films. The deposition parameters were adopted as working pressure of 5 mTorr, substrate temperature of 300°C, sputtering power of 250 W, and 50 mm distance between off-axis and on-axis. The characteristics of the AlN thin films were investigated by X-ray diffraction and scanning electron microscopy. The frequency response was measured with an HP8720 network analyzer with a CASCADE probe station. The X-ray diffraction revealed (002) preferred wurtzite structure, and the cross-sectional image showed columnar structure with 23°-tilted AlN thin films. In the biosensor, an Au/Cr layer in the FBAR backside cavity was used as the detection layer and the Au surface was modified using self-assembly monolayers (SAMs) method. Then, the antigen and antibody were coated on biosensor through their high specificity property. Finally, the shear-mode FBAR device with k t 2 of 3.18% was obtained, and the average sensitivity for human IgE detection of about 1.425 × 105 cm2/g was achieved.
Ambiguity of the critical load for spherical shells with shear damageability of the material
NASA Astrophysics Data System (ADS)
Babich, D. V.; Dorodnykh, T. I.
2016-06-01
The structural-probabilistic approach to the modeling of combined crack formation and material deformation processes is used to develop a technique for solving bifurcation stability problems for thin-walled structural members made of damageable materials under single and repeated loadings. The example of a uniformly compressed spherical shell is used to show that, under repeated loading, thin-walled structural members made of shear damageable materials can lose stability under loads smaller than the upper critical loads. The ambiguity of the critical loads for various damage accumulation processes in the material of thin-walled structures depends on the level and character of loading. This phenomenon can be one possible cause of the experimental data spread and the discrepancy between theoretical and experimental results used to determine the critical loads for spherical and cylindrical shells.
Zhang, Jian-ning; Bergeron, Angela L; Yu, Qinghua; Sun, Carol; McBride, Latresha; Bray, Paul F; Dong, Jing-fei
2003-10-01
Platelet functions are increasingly measured under flow conditions to account for blood hydrodynamic effects. Typically, these studies involve exposing platelets to high shear stress for periods significantly longer than would occur in vivo. In the current study, we demonstrate that the platelet response to high shear depends on the duration of shear exposure. In response to a 100 dyn/cm2 shear stress for periods less than 10-20 sec, platelets in PRP or washed platelets were aggregated, but minimally activated as demonstrated by P-selectin expression and binding of the activation-dependent alphaIIbbeta3 antibody PAC-1 to sheared platelets. Furthermore, platelet aggregation under such short pulses of high shear was subjected to rapid disaggregation. The disaggregated platelets could be re-aggregated by ADP in a pattern similar to unsheared platelets. In comparison, platelets that are exposed to high shear for longer than 20 sec are activated and aggregated irreversibly. In contrast, platelet activation and aggregation were significantly greater in whole blood with significantly less disaggregation. The enhancement is likely via increased collision frequency of platelet-platelet interaction and duration of platelet-platelet association due to high cell density. It may also be attributed to the ADP release from other cells such as red blood cells because increased platelet aggregation in whole blood was partially inhibited by ADP blockage. These studies demonstrate that platelets have a higher threshold for shear stress than previously believed. In a pathologically relevant timeframe, high shear alone is likely to be insufficient in inducing platelet activation and aggregation, but acts synergistically with other stimuli.
Viscosity of a sheared correlated (near-critical) model fluid in confinement
NASA Astrophysics Data System (ADS)
Rohwer, Christian M.; Gambassi, Andrea; Krüger, Matthias
2017-08-01
Second-order phase transitions are characterized by a divergence of the spatial correlation length of the order parameter fluctuations. For confined systems, this is known to lead to remarkable equilibrium physical phenomena, including finite-size effects and critical Casimir forces. We explore here some non-equilibrium aspects of these effects in the stationary state resulting from the action of external forces: by analyzing a model of a correlated fluid under shear, spatially confined by two parallel plates, we study the resulting viscosity within the setting of (Gaussian) Landau-Ginzburg theory. Specifically, we introduce a model in which the hydrodynamic velocity field (obeying the Stokes equation) is coupled to an order parameter with dissipative dynamics. The well-known Green-Kubo relation for bulk systems is generalized for confined systems. This is shown to result in a non-local Stokes equation for the fluid flow, due to the correlated fluctuations. The resulting effective shear viscosity shows universal as well as non-universal contributions, which we study in detail. In particular, the deviation from the bulk behavior is universal, depending on the ratio of the correlation length and the film thickness L. In addition, at the critical point the viscosity is proportional to \\ell /L , where \\ell is a dynamic length scale. These findings are expected to be experimentally observable, especially for systems where the bulk viscosity is affected by critical fluctuations.
On the correlation between creep rate and critical shear stress of irradiated metals
NASA Astrophysics Data System (ADS)
Ibragimov, Sh. Sh.; Kamshilin, D. V.; Pyatiletov, Yu. S.; Tyupkina, O. G.
1989-02-01
The critical shear stress τcr and the creep rate /.ɛ of irradiated metals for different values of density and strength of radiation defects being barriers for gliding dislocations are calculated with the help of a computer simulation method. Correlation between /.ɛ and τcr has been established on the basis of these data. The regression line /.ɛ on τcr has been determined. The correlation ration η characterizing binding force between /.ɛ and τcr has been defined. Good agreement with experimental data for correlation between irradiation creep rate and yield strength σ0.2 in some fcc metals and alloys is obtained.
Nonlinear saturation of ideal interchange modes in a sheared magnetic field
Beklemishev, A.D.
1990-09-01
Pressure-driven ideal modes cannot completely interchange flux tubes of a sheared magnetic field; instead, they saturate, forming new helical equilibria. These equilibria are studied both analytically and numerically with reduced MHD equations in a flux-conserving Lagrangian representation. For unstable localized modes, the structure of the nonlinear layer generated around the resonant flux surface depends on the value of Mercier parameter D{sub M}. Its width is found to be proportional to the position of the inflection point on the linear eigenfunction. Perturbed surfaces in equilibrium always have folds, i.e., areas where the direction of the original reduced magnetic field is reserved. But only far from the instability threshold does the internal structure of the nonlinear layer resemble bubble' formation. The appearance of sheet currents and island-like structures along the resonant flux surface may be of interest for the description of forced reconnection in models with finite resistivity. Analytic results are found to be in agreement with 2-D numerical simulations. This study also includes the case of ballooning instability by representing nonlocal driving terms through the matching parameter {Delta}{prime}, which defines the outer boundary conditions for the interchange layer. 12 refs., 9 figs.
NASA Astrophysics Data System (ADS)
Li, Enzhu; Sasaki, Ryo; Hoshina, Takuya; Takeda, Hiroaki; Tsurumi, Takaaki
2009-09-01
A miniature piezoelectric ultrasonic motor (USM) using the shear mode of (K,Na)NbO3 (KNN)-based lead-free piezoelectric ceramics was developed. The motor can be driven in the shearing and bending vibration modes. By using the finite-element method, the motor vibration modes and driving mechanism were modeled. Both the “soft-type” (high-d USM) and “hard-type” (high-Qm USM) KNN-based lead-free piezoelectric ceramics were employed to clarify the characteristics of USMs. The experimental results reveal that the high-d USM widens the band of operational frequency in both vibration modes. In the shearing vibration mode, the high-d USM showed a revolution speed of 416 rpm, a torque of 41.5 µN m, and an efficiency of 0.6%, whereas the high-Qm USM showed the same characteristics of 313 rpm, 19.6 µN m and 1.6%, respectively. In the bending vibration mode, the characteristics of the high-Qm USM were 376 rpm, 51.4 µN m and 0.4%; however, the characters of the high-d USM deteriorated owing to the shift in resonance frequency caused by heat generation.
High-Power Characteristics of Thickness Shear Mode for Textured SrBi2Nb2O9 Ceramics
NASA Astrophysics Data System (ADS)
Ogawa, Hirozumi; Kawada, Shinichiro; Kimura, Masahiko; Higuchi, Yukio; Takagi, Hiroshi
2009-09-01
The high-power piezoelectric characteristics of the thickness shear mode for <00l> oriented ceramics of bismuth layer structured ferroelectrics (BLSF), SrBi2Nb2O9 (SBN), were studied by the constant current driving method. These textured ceramics were fabricated by the templated grain growth (TGG) method, and the Lotgering factor was 95%. The vibration of the thickness shear mode in the textured SBN ceramics was stable at the vibration velocity of 2.0 m/s. The resonant frequency was almost constant with increasing vibration velocity in the textured SBN ceramics, however, it decreased with increasing vibration velocity in the randomly oriented SBN ceramics. In the case of Pb(Mn,Nb)O3-Pb(Zr,Ti)O3 ceramics, the vibration velocity of the thickness shear mode was saturated at more than 0.3 m/s, and the resonant frequency decreased at lower vibration velocity than in the case of SBN ceramics. The dissipation power density of the textured SBN ceramics was the lowest among those of the randomly oriented SBN and Pb(Mn,Nb)O3-PZT ceramics. The thickness shear mode of textured SBN ceramics is a good candidate for high-power piezoelectric applications.
Effect of activation mode on shear bond strength of metallic brackets.
Correr, Américo Bortolazzo; Costa, Ana Rosa; Lucato, Adriana Simoni; Vedovello, Silvia Amélia; Valdrighi, Heloísa Cristina; Vedovello Filho, Mário; Correr-Sobrinho, Lourenço
2013-01-01
The aim of this study was to evaluate the shear bond strength (SBS) of metallic orthodontic brackets bonded to bovine teeth using light-activated or chemically activated composite resins. One hundred and twenty bovine mandibular incisors were divided into 6 groups (n=20), according to the bonding materials: Transbond XT (T); Enforce Dual (ED); Enforce chemical (EC); Enforce Light-activated (EL); Concise Orthodontic (C); and RelyX Unicem Capsule (UN). Metallic brackets were positioned and firmly bonded to the teeth. Light-activation for T, ED, EL and UN was carried out with four exposures on each side of the bracket with 20 s total exposure times using XL2500 (3M ESPE). EC and C were chemically cured. Next, all specimens were stored in deionized water at 37 °C for 24 h. The shear bond strength was carried out at a crosshead speed of 1.0 mm/min. Data were subjected to one-way ANOVA and Tukey's test (α=0.05). The adhesive remnant index (ARI) was evaluated at 8× magnification. C (17.72 ± 4.45) presented significantly higher SBS means (in MPa) than the other groups (p<0.05), followed by EC (11.97 ± 5.77) and ED (10.57 ± 1.32). EL (5.39 ± 1.06) and UN (4.32 ± 1.98) showed the lowest SBS means, while T (9.09 ± 2.56) showed intermediate values. For ARI, there was a predominance of score 0 for EC, C and UN, and score 3 for T, ED and EL. In conclusion, the activation mode influenced the SBS.
Jayakumar, R.J.; Austin, M.E.; Brennan, D.P.; Chu, M.S.; Luce, T.C.; Strait, E.J.; Turnbull, A.D.
2002-07-01
In DIII-D plasmas with L-mode edge and negative central shear (q{sub axis}-q{sub min} {approx}0.3 to 0.5), an interchange-like instability has been observed [1]. The instability and a subsequent tearing mode cause reduction of the core electron temperature and plasma rotation, and therefore the instability affects discharge evolution and the desired high performance is not achieved. Stability analyses indicate robust ideal stability, while the Resistive Interchange Mode criterion is marginal and the instability appears to be localized initially. Based on this, we believe that the mode is, most likely, a Resistive Interchange Mode. The amplitude of the instability is correlated with the location of the q{sub min} surface and inversely with the fast-ion pressure. There is indication that the interchange-like instability may be ''seeding'' the tearing mode that sometimes follows the interchange-like instability.
NASA Astrophysics Data System (ADS)
Aydin, A.
2012-12-01
Two common opening-mode fracture patterns include those comprising one set (Figure 1a) and two orthogonal sets (Figure 1b). It is also possible to have three mutually orthogonal opening-mode fractures, but this situation is rare. The prediction of the orientation and dimensional attributes of these simple systems requires a basic knowledge of the medium in which they occur (lithology, bedding, shape and distribution of initial flaws, elastic modulus, subcritical index and other environmental conditions) and the driving stresses or strains responsible for their formation. The issues related to fracture patterns become more complex when initial patterns of predominantly opening-mode fractures were later subjected to shearing. Shearing of a single set of opening-mode fractures (Figure 1c) produces splay fractures whose orientations and lengths show a significant variation. Given the attributes of the initial set and the orientation and relative magnitudes of the new stress components responsible for the shearing, and the mechanical behavoir of the fractures, it is possible to constrain the splay geometry. It turns out that the natural progression of the system is such that the new splays are sheared in a sequential manner to form remarkably consistent fracture domain patterns, which may be called "apparent conjugate." Well-documented case studies, some of which will be used in this presentation as templates, indicate that these fracture domain patterns can be visualized, but mapping their variation (local orientation and geometry of the individual components) is not a trivial task and may require knowledge both of some of the parameters referred to above and of the stress distribution about larger regional structures such as folds and faults. The shearing of orthogonal arrays of opening-mode fractures produces splay fractures diagonal to both orthogonal sets (Figure 1d). New through-going shear fractures, again in apparent conjugate patterns, utilize both members of
Behrends, R; Iwanowski, I; Kosmowska, M; Szala, A; Kaatze, U
2004-09-22
The shear viscosity eta(s), mutual diffusion coefficient D, and ultrasonic attenuation spectra of the nitroethane-cyclohexane mixture of critical composition have been measured at various temperatures near the critical temperature T(c). The relaxation rate of order parameter fluctuations resulting from a combined evaluation of the eta(s) and D data follows power law behavior with the theoretical exponent and with the large amplitude Gamma(o)=(156+/-2)x10(9) s(-1). The ultrasonic spectra have been evaluated in terms of a critical contribution and a noncritical background contribution. The amplitude of the former exhibits a temperature dependence, in conformity with a temperature dependence in the adiabatic coupling constant (|g| = 0.064 near T(c) and 0.1 at T-T(c)=3 K). If the variation of the critical amplitude with T is taken into account the experimental attenuation coefficient data display a scaling function which nicely fits to the theoretical prediction from the Bhattacharjee-Ferrell dynamic scaling model [R. A. Ferrell and J. K. Bhattacharjee, Phys. Rev. A 31, 1788 (1985)].
Critical shear stress for mass erosion of organic-rich fine sediments
NASA Astrophysics Data System (ADS)
Mehta, Ashish J.; Hwang, Kyu-Nam; Khare, Yogesh P.
2015-11-01
In shallow lakes of Florida laden with low-strength organic-rich sediments, wind-induced water movement is believed to actuate bed surface erosion as well as mass erosion. Experiments in hydraulic flumes to measure the critical shear stress for mass erosion tend to be lengthy and require large quantities of sediment. For bottom sediment from Lake Okeechobee at naturally occurring values of the floc volume fraction, a comparison of the viscoplastic yield stress, readily obtained from rheometry, with the mass erosion critical stress from flume tests indicates that it may be permissible to consider the yield stress as a surrogate for the critical stress. This inference appears to be supported by ancillary observations from Lake Apopka and Newnans Lake. Interestingly enough, the variation of yield stress with the floc volume fraction of the organic-rich bed is found to conform to fractal characterization commonly invoked for mineral sediment flocs, consistent with a representative constant value of 2.55 of the fractal dimension. Pending fuller investigations with a wide range of organic-rich sediments, recourse to rheometry in lieu of flume experiments holds promise as a means to simplify testing requirements for estimating the mass erosion critical stress.
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.
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.
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.
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.
Real-time analysis of cell-surface adhesive interactions using thickness shear mode resonator.
Hong, Soonjin; Ergezen, Ertan; Lec, Ryszard; Barbee, Kenneth A
2006-12-01
The cell adhesion process and the molecular interactions that determine its kinetics were investigated using a thickness shear mode (TSM) sensor. The goal of this study was to correlate sensor readings with the progression of cell adhesion. In particular, the specific effects of receptor-mediated adhesion, the glycocalyx, and surface charge on initial cell-surface attachment and steady-state adhesion of endothelial cells were investigated. We found a strong correlation between resistance changes (DeltaR) and the development of cell adhesion strength by comparing the sensor readings with independently assessed cell adhesion. The result showed that integrin binding determines the kinetics of initial cell attachment while heparan sulfate proteoglycan (HSPG) modulates steady-state adhesion strength. Coating the sensor surface with the positively charged poly-d-lysine (PDL) enhanced the initial interaction with substratum. These data confirm our current understanding of the contribution of these three phenomena to the adhesion process. The real-time monitoring capability of this technique with high temporal resolution provides more detailed information on the kinetics of the different stages of the adhesion process. This technique has the potential to facilitate the evaluation of biomaterials and surface treatments used for implants and tissue-engineering scaffolds for their bioactive effects on the cell adhesion process.
NASA Astrophysics Data System (ADS)
Hu, Ji-Ying; Li, Zhao-Hui; Sun, Yang; Li, Qi-Hu
2016-12-01
Shear-mode piezoelectric materials have been widely used to shunt the damping of vibrations where utilizing surface or interface shear stresses. The thick-shear mode (TSM) elastic constant and the mechanical loss factor can change correspondingly when piezoelectric materials are shunted to different electrical circuits. This phenomenon makes it possible to control the performance of a shear-mode piezoelectric damping system through designing the shunt circuit. However, due to the difficulties in directly measuring the TSM elastic constant and the mechanical loss factor of piezoelectric materials, the relationships between those parameters and the shunt circuits have rarely been investigated. In this paper, a coupling TSM electro-mechanical resonant system is proposed to indirectly measure the variations of the TSM elastic constant and the mechanical loss factor of piezoelectric materials. The main idea is to transform the variations of the TSM elastic constant and the mechanical loss factor into the changes of the easily observed resonant frequency and electrical quality factor of the coupling electro-mechanical resonator. Based on this model, the formular relationships are set up theoretically with Mason equivalent circuit method and they are validated with finite element (FE) analyses. Finally, a prototype of the coupling electro-mechanical resonator is fabricated with two shear-mode PZT5A plates to investigate the TSM elastic constants and the mechanical loss factors of different circuit-shunted cases of the piezoelectric plate. Both the resonant frequency shifts and the bandwidth changes observed in experiments are in good consistence with the theoretical and FE analyses under the same shunt conditions. The proposed coupling resonator and the obtained relationships are validated with but not limited to PZT5A. Project supported by the National Defense Foundation of China (Grant No. 9149A12050414JW02180).
NASA Astrophysics Data System (ADS)
Ge, Jianzhong; Shen, Fang; Guo, Wenyun; Chen, Changsheng; Ding, Pingxing
2015-12-01
Simulating the sediment transport in a high-turbidity region with spatially varying bed properties is challenging. A comprehensive strategy that integrates multiple methods is applied here to retrieve the critical shear stress for erosion, which plays a major role in suspended sediment dynamics in the Changjiang Estuary (CE). Time-series of sea surface suspended sediment concentration (SSC) were retrieved from the Geostationary Ocean Color Imager (GOCI) satellite data at hourly intervals (for 8 h each day) and combined with hydrodynamic modeling of high-resolution CE Finite-Volume Community Ocean Model (CE-FVCOM) to estimate the near-bed critical shear stress in the clay-dominated bed region (plasticity index > 7%). An experimental algorithm to determine the in situ critical shear stress via the plasticity index method was also used to verify the GOCI-derived critical shear stress. Implemented with this new critical shear stress, the sediment transport model significantly improved the simulation of the distribution and spatial variability of the SSC during the spring and neap tidal cycles in the CE. The results suggest that a significant lateral water exchange between channels and shoals occurred during the spring flood tide, which led to a broader high-SSC area in the CE throughout the water column.
NASA Astrophysics Data System (ADS)
Miao, Hongchen; Li, Faxin
2017-04-01
The non-dispersive fundamental shear horizontal (SH0) and torsional [T(0,1)] waves are extremely useful in guidedwave-based inspection techniques. However, excitation of SH0 and T(0,1) waves using piezoelectrics is always a challenge. In this work, firstly, a newly defined face-shear d24 PZT wafer is proposed to excite and receive SH0 wave mode. The d24 wafer is in-plane poled and its working electric field is applied along another orthogonal in-plane direction. Both finite element simulations and experiments show that single SH0 mode can be excited by using the d24 wafer along two orthogonal directions (0° and 90°). Then an omnidirectional SH0 wave piezoelectric transducer (OSHPT) is developed which consists of a circular array of twelve face-shear d24 trapezoidal PZT elements. Results show that the proposed OSH-PT exhibits good omnidirectional properties, no matter it is used as a SH0 wave transmitter or receiver. Finally, the development of a T(0,1) wave transducer for pipes based on a ring array of d24 PZT elements is described. Both finite element simulations and experiments show that the d24 elements ring can excite single T(0,1) mode and suppress all the unwanted non-axisymmetric modes. This work may greatly promote the applications of SH0 and T(0,1) waves in nondestructive testing (NDT) and structural health monitoring (SHM).
Lee, Byoung-Kwon; Ko, Jae-yong; Lim, Hyun-jung; Nam, Jeong-Hun; Shin, Sehyun
2012-01-01
Recent electrical investigation of hemorheology provided useful information on the kinetics of red blood cell (RBC) aggregation. However, because of the inconsistent results in the electrical measurements, we need to understand the electrical characteristics of RBC aggregation at various flow conditions. In the present study, AC electrical-capacitance (EC) and -impedance (EI) and light backscattering (LB) were simultaneously measured for transient shear-decreasing blood flow in a microchannel. EI, EC and LB signals of RBCs in plasma show similar time-varying curves, both yielding either a peak or a minimal point in the optimal frequency range (10~500 kHz). Critical shear stress (CSS) determined from EC showed the nearly same results as that determined from LB, with yielding hematocrits-independence and dextran-concentration dependence. However, the high concentration of fibrinogen caused electrical saturation, which resulted in different results of CSS determined from between LB and EC. These results suggest that electrical properties of RBC suspensions should be further examined to replace the optical method of measurement of RBC aggregation.
NASA Astrophysics Data System (ADS)
Li, Faxin; Miao, Hongchen
2016-10-01
The non-dispersive fundamental shear horizontal (SH0) wave is extremely useful in guided-wave-based inspection techniques. However, the generation or reception of the SH0 wave by using a piezoelectric transducer is always a challenge. In this work, first, we realized the apparent face-shear (d36) mode in PbZr1-xTixO3 (PZT) ceramics via two-dimensional antiparallel poling. Then, we demonstrated via finite element simulations that the apparent d36 mode PZT wafer can behave as both a SH0 wave actuator and a SH0 wave sensor. Next, by using the apparent d36 PZT wafer as an actuator and a face-shear d36 0.72[Pb(Mg1/3Nb2/3)O3]-0.28[PbTiO3] crystal as the sensor, almost a pure SH0 wave with a high signal-to-noise ratio was successfully excited in an aluminum plate from 180 kHz to 200 kHz. Later, experiments showed that the proposed apparent d36 PZT wafer can also serve as a sensor to detect the SH0 wave over a wide frequency range (160 kHz to 230 kHz). Finally, the amplitude directivity of the SH0 wave generated by the apparent d36 PZT wafer was also investigated. The wave amplitude reaches its maxima at the main direction (0° and 90°) and then decreases monotonically when the propagation direction deviates from the main directions, with the symmetric axis along the 45° direction. The proposed apparent d36 PZT wafer is very suitable for severing as SH0 wave actuators and sensors in structural health monitoring systems.
NASA Astrophysics Data System (ADS)
Xiong, Juan; Guo, Peng; Sun, Xi-Liang; Wang, Sheng-Fu; Hu, Ming-Zhe; Gu, Hao-Shuang
2014-02-01
AlN solidly mounted resonators with silicone microfluidic systems vibrating in shear mode are fabricated and characterized. The fabrication process is compatible with integrated circuits and the c-axis tilted AlN films are deposited, which allow in-liquid operation through excitation of the shear mode. The silicone microfluidic system is mounted on top of the sensor chip to transport the analyses and confine the flow to the active area. The properties of sensor operation in air, deionized water, ethanol, isopropanol, 80% glycol aqueous solution, glycol, and olive oil are characterized. The effects of different viscosities on the resonance frequency shift and Q-factor of the sensor have been discussed. The sensitivity and Q value in glycol of the sensor are 1.52 MHz cm2/μg and around 60, respectively. The results indicate the potential of a highly sensitive microfluidic sensor system for the applications in viscous media.
Patil, Narendra P; Dandekar, Minal; Nadiger, Ramesh K; Guttal, Satyabodh S
2010-09-01
The aim of this study was to evaluate the shear bond strength of porcelain to laser welded titanium surface and to determine the mode of bond failure through scanning electron microscopy (SEM) and energy dispersive spectrophotometry (EDS). Forty five cast rectangular titanium specimens with the dimension of 10 mm x 8 mm x 1 mm were tested. Thirty specimens had a perforation of 2 mm diameter in the centre. These were randomly divided into Group A and B. The perforations in the Group B specimens were repaired by laser welding using Cp Grade II titanium wire. The remaining 15 specimens were taken as control group. All the test specimens were layered with low fusing porcelain and tested for shear bond strength. The debonded specimens were subjected to SEM and EDS. Data were analysed with 1-way analysis of variance and Student's t-test for comparison among the different groups. One-way analysis of variance (ANOVA) showed no statistically significant difference in shear bond strength values at a 5% level of confidence. The mean shear bond strength values for control group, Group A and B was 8.4 +/- 0.5 Mpa, 8.1 +/- 0.4 Mpa and 8.3 +/- 0.3 Mpa respectively. SEM/EDS analysis of the specimens showed mixed and cohesive type of bond failure. Within the limitations of the study laser welding did not have any effect on the shear bond strength of porcelain bonded to titanium.
Nondimensional scaling of magnetorheological rotary shear mode devices using the Mason number
NASA Astrophysics Data System (ADS)
Becnel, Andrew C.; Sherman, Stephen; Hu, Wei; Wereley, Norman M.
2015-04-01
Magnetorheological fluids (MRFs) exhibit rapidly adjustable viscosity in the presence of a magnetic field, and are increasingly used in adaptive shock absorbers for high speed impacts, corresponding to high fluid shear rates. However, the MRF properties are typically measured at very low (γ ˙<1000 s-1) shear rates due to limited commercial rheometer capabilities. A custom high shear rate (γ ˙>10,000 s-1) Searle cell magnetorheometer, along with a full scale rotary-vane magnetorheological energy absorber (γ ˙>25,000 s-1) are employed to analyze MRF property scaling across shear rates using a nondimensional Mason number to generate an MRF master curve. Incorporating a Reynolds temperature correction factor, data from both experiments is shown to collapse to a single master curve, supporting the use of Mason number to correlate low- and high-shear rate characterization data.
NASA Astrophysics Data System (ADS)
Luo, Xin; Lu, Xin; Cong, Chunxiao; Yu, Ting; Xiong, Qihua; Ying Quek, Su
2015-10-01
2D layered materials have recently attracted tremendous interest due to their fascinating properties and potential applications. The interlayer interactions are much weaker than the intralayer bonds, allowing the as-synthesized materials to exhibit different stacking sequences, leading to different physical properties. Here, we show that regardless of the space group of the 2D materials, the Raman frequencies of the interlayer shear modes observed under the typical configuration blue shift for AB stacked materials, and red shift for ABC stacked materials, as the number of layers increases. Our predictions are made using an intuitive bond polarizability model which shows that stacking sequence plays a key role in determining which interlayer shear modes lead to the largest change in polarizability (Raman intensity); the modes with the largest Raman intensity determining the frequency trends. We present direct evidence for these conclusions by studying the Raman modes in few layer graphene, MoS2, MoSe2, WSe2 and Bi2Se3, using both first principles calculations and Raman spectroscopy. This study sheds light on the influence of stacking sequence on the Raman intensities of intrinsic interlayer modes in 2D layered materials in general, and leads to a practical way of identifying the stacking sequence in these materials.
A Critical Review of Mode of Action (MOA) Assignment ...
There are various structure-based classification schemes to categorize chemicals based on mode of action (MOA) which have been applied for both eco and human health toxicology. With increasing calls to assess thousands of chemicals, some of which have little available information other than structure, clear understanding how each of these MOA schemes was devised, what information they are based on, and the limitations of each approach is critical. Several groups are developing low-tier methods to more easily classify or assess chemicals, using approaches such as the ecological threshold of concern (eco-TTC) and chemical-activity. Evaluation of these approaches and determination of their domain of applicability is partly dependent on the MOA classification that is used. The most commonly used MOA classification schemes for ecotoxicology include Verhaar and Russom (included in ASTER), both of which are used to predict acute aquatic toxicity MOA. Verhaar is a QSAR-based system that classifies chemicals into one of 4 classes, with a 5th class specified for those chemicals that are not classified in the other 4. ASTER/Russom includes 8 classifications: narcotics (3 groups), oxidative phosphorylation uncouplers, respiratory inhibitors, electrophiles/proelectrophiles, AChE inhibitors, or CNS seizure agents. Other methodologies include TEST (Toxicity Estimation Software Tool), a computational chemistry-based application that allows prediction to one of 5 broad MOA
A Critical Review of Mode of Action (MOA) Assignment ...
There are various structure-based classification schemes to categorize chemicals based on mode of action (MOA) which have been applied for both eco and human health toxicology. With increasing calls to assess thousands of chemicals, some of which have little available information other than structure, clear understanding how each of these MOA schemes was devised, what information they are based on, and the limitations of each approach is critical. Several groups are developing low-tier methods to more easily classify or assess chemicals, using approaches such as the ecological threshold of concern (eco-TTC) and chemical-activity. Evaluation of these approaches and determination of their domain of applicability is partly dependent on the MOA classification that is used. The most commonly used MOA classification schemes for ecotoxicology include Verhaar and Russom (included in ASTER), both of which are used to predict acute aquatic toxicity MOA. Verhaar is a QSAR-based system that classifies chemicals into one of 4 classes, with a 5th class specified for those chemicals that are not classified in the other 4. ASTER/Russom includes 8 classifications: narcotics (3 groups), oxidative phosphorylation uncouplers, respiratory inhibitors, electrophiles/proelectrophiles, AChE inhibitors, or CNS seizure agents. Other methodologies include TEST (Toxicity Estimation Software Tool), a computational chemistry-based application that allows prediction to one of 5 broad MOA
NASA Astrophysics Data System (ADS)
Yoshizawa, K.
2014-10-01
A new radially anisotropic shear wave speed model for the Australasian region is constructed from multi-mode phase dispersion of Love and Rayleigh waves. An automated waveform fitting technique based on a global optimization with the Neighbourhood Algorithm allows the exploitation of large numbers of three-component broad-band seismograms to extract path-specific dispersion curves covering the entire continent. A 3-D shear wave model is constructed including radial anisotropy from a set of multi-mode phase speed maps for both Love and Rayleigh waves. These maps are derived from an iterative inversion scheme incorporating the effects of ray-path bending due to lateral heterogeneity, as well as the finite frequency of the surface waves for each mode. The new S wave speed model exhibits major tectonic features of this region that are in good agreement with earlier shear wave models derived primarily from Rayleigh waves. The lateral variations of depth and thickness of the lithosphere-asthenosphere transition (LAT) are estimated from the isotropic (Voigt average) S wave speed model and its vertical gradient, which reveals correlations between the lateral variations of the LAT and radial anisotropy. The thickness of the LAT is very large beneath the Archean cratons in western Australia, whereas that in south Australia is thinner. The radial anisotropy model shows faster SH wave speed than SV beneath eastern Australia and the Coral Sea at the lithospheric depth. The faster SH anomaly in the lithosphere is also seen in the suture zone between the three cratonic blocks of Australia. One of the most conspicuous features of fast SH anisotropy is found in the asthenosphere beneath the central Australia, suggesting anisotropy induced by shear flow in the asthenosphere beneath the fast drifting Australian continent.
Squire, J.; Bhattacharjee, A.
2014-12-10
We study magnetorotational instability (MRI) using nonmodal stability techniques. Despite the spectral instability of many forms of MRI, this proves to be a natural method of analysis that is well-suited to deal with the non-self-adjoint nature of the linear MRI equations. We find that the fastest growing linear MRI structures on both local and global domains can look very different from the eigenmodes, invariably resembling waves shearing with the background flow (shear waves). In addition, such structures can grow many times faster than the least stable eigenmode over long time periods, and be localized in a completely different region of space. These ideas lead—for both axisymmetric and non-axisymmetric modes—to a natural connection between the global MRI and the local shearing box approximation. By illustrating that the fastest growing global structure is well described by the ordinary differential equations (ODEs) governing a single shear wave, we find that the shearing box is a very sensible approximation for the linear MRI, contrary to many previous claims. Since the shear wave ODEs are most naturally understood using nonmodal analysis techniques, we conclude by analyzing local MRI growth over finite timescales using these methods. The strong growth over a wide range of wave-numbers suggests that nonmodal linear physics could be of fundamental importance in MRI turbulence.
Surface and Shear Wave Analysis of the Critical Zone in Betasso Catchment, Colorado
NASA Astrophysics Data System (ADS)
Andrus, A. B.; Befus, K. M.; Sheehan, A. F.
2009-12-01
Seismic surface waves, once considered an inhibitor to the interpretation of active source seismic data, have become useful in determining shear wave velocity (Vs) structure of the shallow subsurface. We employed three seismic methods to characterize the shallow subsurface of the Betasso catchment, west of Boulder, Colorado. As part of a multidisciplinary study of the weathered and weathering hydrologically active near surface environment, shallow geophysical data provide an essential, noninvasive subsurface image of the critical zone. In general, weathered rock (saprolite) overlies granitic bedrock with soils and transported material above. Shear wave-derived velocity structure offer an independent confirmation of compressional wave (Vp) profiles and allow us to calculate Poisson's ratio and Vp/Vs as indicators of material properties, porosity, and water content. We obtained Vs structure using three seismic collection methods: (1) S-refraction with horizontal component geophones, (2) Multichannel Analysis of Surface Waves (MASW), and (3) Refraction Microtremor (ReMi) surface wave analysis. Based upon this field test, the S-refraction method is preferred based on data quality. The MASW technique produces Vs images with lower resolution than S-refraction, but has the distinct advantage that MASW data can be collected simultaneously with our standard P-refraction data acquisition. The Vs techniques all result in similar velocity structures to the Vp profile with roughly half the velocity for corresponding layers. Bedrock Vp values appear in the 2400-4400 m/s range while Vs values are 1200-2000 m/s. S-refraction yields bedrock Vs values 0-40% higher than MASW. Additionally, the depth to layer interfaces remains generally within 1 m (approx. 2-5%) between results from each survey method. Profiles showing Poisson's ratio and Vp/Vs across each survey line show reasonable values for the expected subsurface materials. In general, for the three-layer structure of soil
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.
NASA Astrophysics Data System (ADS)
Bastrukov, Sergey; Chang, Hsiang-Kuang; Mişicu, Şerban; Molodtsova, Irina; Podgainy, Dima
The past three decades of investigation on nuclear physics and pulsar astrophysics have seen gradual recognition that elastodynamic approach to the continuum mechanics of nuclear matter provides proper account of macroscopic motions of degenerate Fermi-matter constituting interior of the nuclear material objects, the densest of all known today. This paper focuses on one theoretical issue of this development which is concerned with oscillatory behavior of a viscoelastic solid globe in the regime of quasistatic, force-free, noncompressional oscillations less investigated in the literature compared to oscillations in the regime of standing shear waves. We show that in this case the problem of computing frequency and lifetime of spheroidal and torsional modes of nonradial shear vibrations damped by viscosity can be unambiguously resolved by working from the energy balance equation and taking advantage of the Rayleigh's variational method. The efficiency of this method is demonstrated by solid globe models of nuclear physics and pulsar astrophysics dealing with oscillations of a spherical mass of a viscoelastic Fermi-solid with homogeneous and nonhomogeneous profiles of the bulk density, the shear modulus, and the shear viscosity.
Yamaguchi, Tsuyoshi; Faraone, Antonio
2017-06-28
The role of the prepeak structure of liquid methanol in determining its shear viscosity was studied by means of molecular dynamics (MD) simulation and mode-coupling theory (MCT). The autocorrelation function of the shear stress and the intermediate scattering functions at both the prepeak and the main peak were calculated from the MD trajectories. Their comparison based on MCT suggests that the viscoelastic relaxation in the ps regime is affected by the slow structural dynamics at the prepeak. On the other hand, the MCT for molecular liquids based on the interaction-site model (site-site MCT) fails to describe the coupling between the prepeak dynamics and shear stress. The direct evaluation of the coupling between the two-body density and the shear stress reveals that the viscoelastic relaxation is actually affected by the prepeak dynamics, although the coupling is not captured by the site-site MCT. The site-site MCT works well for a model methanol without partial charges, suggesting that the failure of the site-site MCT originates from the existence of a hydrogen-bonding network structure.
Critical transition for the edge shear layer formation: Comparison of model and experiment
Carreras, B. A.; Garcia, L.; Pedrosa, M. A.; Hidalgo, C.
2006-12-15
The experimental results for the emergence of the plasma edge shear flow layer in TJ-II [C. Alehaldre et al.Fusion Technol. 17, 131 (1990)] can be explained using a simple model for a second-order transition based on the sheared flow amplification by Reynolds stress and turbulence suppression by shearing. In the dynamics of the model, the resistive interchange instability is used. This model gives power dependence on density gradients before and after the transition, consistent with experiment.
Hollweg, Joseph V.; Chandran, Benjamin D. G.; Kaghashvili, Edisher Kh. E-mail: ekaghash@aer.com
2013-06-01
We analytically consider how velocity shear in the corona and solar wind can cause an initial Alfven wave to drive up other propagating signals. The process is similar to the familiar coupling into other modes induced by non-WKB refraction in an inhomogeneous plasma, except here the refraction is a consequence of velocity shear. We limit our discussion to a low-beta plasma, and ignore couplings into signals resembling the slow mode. If the initial Alfven wave is propagating nearly parallel to the background magnetic field, then the induced signals are mainly a forward-going (i.e., propagating in the same sense as the original Alfven wave) fast mode, and a driven signal propagating like a forward-going Alfven wave but polarized like the fast mode; both signals are compressive and subject to damping by the Landau resonance. For an initial Alfven wave propagating obliquely with respect to the magnetic field, the induced signals are mainly forward- and backward-going fast modes, and a driven signal propagating like a forward-going Alfven wave but polarized like the fast mode; these signals are all compressive and subject to damping by the Landau resonance. A backward-going Alfven wave, thought to be important in the development of MHD turbulence, is also produced, but it is very weak. However, we suggest that for oblique propagation of the initial Alfven wave the induced fast-polarized signal propagating like a forward-going Alfven wave may interact coherently with the initial Alfven wave and distort it at a strong-turbulence-like rate.
Briguglio, S. Vlad, G.; Fogaccia, G.; Di Troia, C.; Fusco, V.; Wang, X.; Zonca, F.
2014-11-15
We present a series of numerical simulation experiments set up to illustrate the fundamental physics processes underlying the nonlinear dynamics of Alfvénic modes resonantly excited by energetic particles in tokamak plasmas and of the ensuing energetic particle transports. These phenomena are investigated by following the evolution of a test particle population in the electromagnetic fields computed in self-consistent MHD-particle simulation performed by the HMGC code. Hamiltonian mapping techniques are used to extract and illustrate several features of wave-particle dynamics. The universal structure of resonant particle phase space near an isolated resonance is recovered and analyzed, showing that bounded orbits and untrapped trajectories, divided by the instantaneous separatrix, form phase space zonal structures, whose characteristic non-adiabatic evolution time is the same as the nonlinear time of the underlying fluctuations. Bounded orbits correspond to a net outward resonant particle flux, which produces a flattening and/or gradient inversion of the fast ion density profile around the peak of the linear wave-particle resonance. The connection of this phenomenon to the mode saturation is analyzed with reference to two different cases: a Toroidal Alfvén eigenmode in a low shear magnetic equilibrium and a weakly unstable energetic particle mode for stronger magnetic shear. It is shown that, in the former case, saturation is reached because of radial decoupling (resonant particle redistribution matching the mode radial width) and is characterized by a weak dependence of the mode amplitude on the growth rate. In the latter case, saturation is due to resonance detuning (resonant particle redistribution matching the resonance width) with a stronger dependence of the mode amplitude on the growth rate.
Rost, Jon C.; Porkolab, Miklos; Dorris, James R.; Burrell, Keith H.
2014-06-17
A region of turbulence with large radial wavenumber (k_{r}ρ_{s} > 1) is found in the high-shear portion of the plasma edge in Quiescent H-mode (QH-mode) on DIII{D using the Phase Contrast Imaging (PCI) diagnostic. At its peak outside the minimum of the E_{r} well, the turbulence exhibits large amplitude $\\tilde{n}$/n ~ 40%, with large radial wavenumber |$\\bar{k}$_{r}/ $\\bar{k}$_{θ}| ~ 11 and short radial correlation length L_{r}/ρ _{i} ~ 0.2. The turbulence inside the E_{r} well minimum is characterized by the opposite sign in radial wavenumber from that of turbulence outside the minimum, consistent with the expected effects of velocity shear. The PCI diagnostic provides a line-integrated measurement of density uctuations, so data is taken during a scan of plasma position at constant parameters to allow the PCI to sample a range in k_{r}/k_{θ} . Analysis of the Doppler Shift and plasma geometry allows the turbulence to be localized to a narrow region 3 mm inside the last closed flux surface (LCFS), outside the minimum of the E_{r} well. The turbulence amplitude and radial wavenumber and correlation length are determined by fitting the PCI results with a simple non-isotropic turbulence model with two regions of turbulence. Finally, these PCI observations, made in QH-mode, are qualitatively similar to those made in standard ELM-free H-mode and between edge localized modes (ELMs), suggesting a similar role for large k_{r} turbulence there.
Rost, Jon C.; Porkolab, Miklos; Dorris, James R.; ...
2014-06-17
A region of turbulence with large radial wavenumber (krρs > 1) is found in the high-shear portion of the plasma edge in Quiescent H-mode (QH-mode) on DIII{D using the Phase Contrast Imaging (PCI) diagnostic. At its peak outside the minimum of the Er well, the turbulence exhibits large amplitudemore » $$\\tilde{n}$$/n ~ 40%, with large radial wavenumber |$$\\bar{k}$$r/ $$\\bar{k}$$θ| ~ 11 and short radial correlation length Lr/ρ i ~ 0.2. The turbulence inside the Er well minimum is characterized by the opposite sign in radial wavenumber from that of turbulence outside the minimum, consistent with the expected effects of velocity shear. The PCI diagnostic provides a line-integrated measurement of density uctuations, so data is taken during a scan of plasma position at constant parameters to allow the PCI to sample a range in kr/kθ . Analysis of the Doppler Shift and plasma geometry allows the turbulence to be localized to a narrow region 3 mm inside the last closed flux surface (LCFS), outside the minimum of the Er well. The turbulence amplitude and radial wavenumber and correlation length are determined by fitting the PCI results with a simple non-isotropic turbulence model with two regions of turbulence. Finally, these PCI observations, made in QH-mode, are qualitatively similar to those made in standard ELM-free H-mode and between edge localized modes (ELMs), suggesting a similar role for large kr turbulence there.« less
Nishimura, A.
2008-03-03
A short beam test is useful to evaluate interlaminar shear strength of glass fiber reinforced plastics, especially for material selection. However, effect of test fixture configuration on interlaminar shear strength has not been clarified. This paper describes dependence of fracture mode and interlaminar shear strength on the fixture radius using the same materials and procedure. In addition, global understanding of the role of the fixture is discussed. When small loading nose and supports are used for the tests, bending fracture or translaminar fracture happens and the interlaminar shear strength would become smaller. By adopting the large radius loading nose and supports (6 mm radius is recommended), it is newly recognized that some stress concentration is able to be reduced, and the interlaminar fracture tends to occur and the other fracture modes will be suppressed. The interlaminar shear strength of 2.5 mm thick GFRP plate of G-10CR is evaluated as 130-150 MPa at 77 K.
Tsujimoto, Akimasa; Barkmeier, Wayne W; Erickson, Robert L; Takamizawa, Toshiki; Latta, Mark A; Miyazaki, Masashi
2017-09-28
The influence of the number of cycles on shear fatigue strength to enamel and dentin using dental adhesives in self-etch mode was investigated. A two-step self-etch adhesive and two universal adhesives were used to bond to enamel and dentin in self-etch mode. Initial shear bond strength and shear fatigue strength to enamel and dentin using the adhesive in self-etch mode were determined. Fatigue testing was used with 20 Hz frequency and cycling periods of 50,000, 100,000 and 1,000,000 cycles, or until failure occurred. For each of the cycling periods, there was no significant difference in shear fatigue strength across the cycling periods for the individual adhesives. Differences in shear fatigue strength were found between the adhesives within the cycling periods. Regardless of the adhesive used in self-etch mode for bonding to enamel or dentin, shear fatigue strength was not influenced by the number of cycles used for shear fatigue strength testing.
Short wavelength turbulence generated by shear in the quiescent H-mode edge on DIII-D
NASA Astrophysics Data System (ADS)
Rost, J. C.; Porkolab, M.; Dorris, J.; Burrell, K. H.
2014-06-01
A region of turbulence with large radial wavenumber (krρs>1) is found in the high-shear portion of the plasma edge in Quiescent H-mode (QH-mode) on DIII-D using the Phase Contrast Imaging (PCI) diagnostic. At its peak outside the minimum of the Er well, the turbulence exhibits large amplitude n ˜/n˜40%, with large radial wavenumber |k¯r/k¯θ|˜11 and short radial correlation length Lr/ρi˜0.2. The turbulence inside the Er well minimum is characterized by the opposite sign in radial wavenumber from that of turbulence outside the minimum, consistent with the expected effects of velocity shear. The PCI diagnostic provides a line-integrated measurement of density fluctuations, so data are taken during a scan of plasma position at constant parameters to allow the PCI to sample a range in kr/kθ. Analysis of the Doppler shift and plasma geometry allows the turbulence to be localized to a narrow region 3 mm inside the last closed flux surface, outside the minimum of the Er well. The turbulence amplitude and radial wavenumber and correlation length are determined by fitting the PCI results with a simple non-isotropic turbulence model with two regions of turbulence. These PCI observations, made in QH-mode, are qualitatively similar to those made in standard edge localized modes (ELM)-free H-mode and between ELMs, suggesting a similar role for large kr turbulence there.
Short wavelength turbulence generated by shear in the quiescent H-mode edge on DIII–D
Rost, J. C.; Porkolab, M.; Dorris, J.; Burrell, K. H.
2014-06-15
A region of turbulence with large radial wavenumber (k{sub r}ρ{sub s}>1) is found in the high-shear portion of the plasma edge in Quiescent H-mode (QH-mode) on DIII–D using the Phase Contrast Imaging (PCI) diagnostic. At its peak outside the minimum of the E{sub r} well, the turbulence exhibits large amplitude n{sup ~}/n∼40%, with large radial wavenumber |k{sup ¯}{sub r}/k{sup ¯}{sub θ}|∼11 and short radial correlation length L{sub r}/ρ{sub i}∼0.2. The turbulence inside the E{sub r} well minimum is characterized by the opposite sign in radial wavenumber from that of turbulence outside the minimum, consistent with the expected effects of velocity shear. The PCI diagnostic provides a line-integrated measurement of density fluctuations, so data are taken during a scan of plasma position at constant parameters to allow the PCI to sample a range in k{sub r}/k{sub θ}. Analysis of the Doppler shift and plasma geometry allows the turbulence to be localized to a narrow region 3 mm inside the last closed flux surface, outside the minimum of the E{sub r} well. The turbulence amplitude and radial wavenumber and correlation length are determined by fitting the PCI results with a simple non-isotropic turbulence model with two regions of turbulence. These PCI observations, made in QH-mode, are qualitatively similar to those made in standard edge localized modes (ELM)-free H-mode and between ELMs, suggesting a similar role for large k{sub r} turbulence there.
Undamped critical speeds of rotor systems using assumed modes
NASA Astrophysics Data System (ADS)
Nelson, H. D.; Chen, W. J.
1993-07-01
A procedure is presented to reduce the DOF of a discrete rotordynamics model by utilizing an assumed-modes Rayleigh-Ritz approximation. Many possibilities exist for the assumed modes and any reasonable choice will yield a reduced-order model with adequate accuracy for most applications. The procedure provides an option which can be implemented with relative ease and may prove beneficial for many applications where computational efficiency is particularly important.
Characteristic modes and evolution processes of shear-layer vortices in an elevated transverse jet
NASA Astrophysics Data System (ADS)
Huang, Rong F.; Lan, Jen
2005-03-01
Characteristics and evolution processes of the traveling coherent flow structure in the shear layer of an elevated round jet in crossflow are studied experimentally in an open-loop wind tunnel. Streak pictures of the smoke flow patterns illuminated by the laser-light sheet in the median and horizontal planes are recorded with a high speed digital camera. Time histories of the instantaneous velocity of the vortical flows in the shear layer are digitized by a hot-wire anemometer through a high-speed data acquisition system. By analyzing the streak pictures of the smoke flow visualization, five characteristic flow structures, mixing-layer type vortices, backward-rolling vortices, forward-rolling vortices, swing-induced mushroom vortices, and jet-type vortices, are identified in the shear layer evolving from the up-wind edge of the jet exit. The behaviors and mechanisms of the vortical flow structure in the bent shear layer are prominently distinct in different flow regimes. The frequency characteristics, Strouhal number, power-spectrum density functions, autocorrelation coefficient, as well as the time and length scales of the coherent structure and the Lagrangian integral scales are obtained by processing the measured instantaneous velocity data. The Strouhal number is found to decay exponentially with the increase of the jet-to-crossflow momentum flux ratio. The autocorrelation coefficients provide the information for calculating the statistical time scales of the coherent structure and the integral time scales of turbulence fluctuations. The corresponding length scales of the vortical structure and the integral length scales of turbulence in the shear layer are therefore obtained and discussed.
NASA Astrophysics Data System (ADS)
Wang, Wurong; Wei, Xicheng; Yang, Jun; Shi, Gang
2011-08-01
Due to its excellent strength and formability combinations, dual phase (DP) steels offer the potential to improve the vehicle crashworthiness performance without increasing car body weight and have been increasingly used into new vehicles. However, a new type of crack mode termed as shear fracture is accompanied with the application of these high strength DP steel sheets. With the cup drawing experiment to identify the limit drawing ratio (LDR) of three DP AHSS with strength level from 600 MPa to 1000 MPa, the study compared and categorized the macroscopic failure mode of these three types of materials. The metallographical observation along the direction of crack was conducted for the DP steels to discover the micro-level propagation mechanism of the fracture.
Ghizzo, A.; Palermo, F.
2015-08-15
We address the mechanisms underlying low-frequency zonal flow generation in turbulent system and the associated intermittent regime of ion-temperature-gradient (ITG) turbulence. This model is in connection with the recent observation of quasi periodic zonal flow oscillation at a frequency close to 2 kHz, at the low-high transition, observed in the ASDEX Upgrade [Conway et al., Phys. Rev. Lett. 106, 065001 (2011)] and EAST tokamak [Xu et al., Phys. Rev. Lett 107, 125001 (2011)]. Turbulent bursts caused by the coupling of Kelvin-Helmholtz (KH) driven shear flows with trapped ion modes (TIMs) were investigated by means of reduced gyrokinetic simulations. It was found that ITG turbulence can be regulated by low-frequency meso-scale zonal flows driven by resonant collisionless trapped ion modes (CTIMs), through parametric-type scattering, a process in competition with the usual KH instability.
NASA Astrophysics Data System (ADS)
Huang, Hongbo; Chen, Jiujiu; Huo, Shaoyong
2017-07-01
In this paper, we realize the topological edge modes of a shear horizontal (SH) guided wave in the one-dimensional (1D) composite structure that exist at the phononic band gaps opened at the center of the Brillouin zone (BZ), or at the zone boundary, or both. Furthermore, we investigate the topological edge modes in periodic acoustic systems result from both Bragg scattering and local resonances. In particular, we find and demonstrate that, in our system where topological and trivial defect states coexist, these results provide a new paradigm for manipulating the existence of the interface states in a set of prescribed band gaps that can have potential applications in the design of novel acoustic devices.
Seismicity, shear failure and modes of deformation in deep subduction zones
NASA Technical Reports Server (NTRS)
Lundgren, Paul R.; Giardini, Domenico
1992-01-01
The joint hypocentral determination method is used to relocate deep seismicity reported in the International Seismological Center catalog for earthquakes deeper than 400 km in the Honshu, Bonin, Mariannas, Java, Banda, and South America subduction zones. Each deep seismic zone is found to display planar features of seismicity parallel to the Harvard centroid-moment tensor nodal planes, which are identified as planes of shear failure. The sense of displacement on these planes is one of resistance to deeper penetration.
Seismicity, shear failure and modes of deformation in deep subduction zones
NASA Technical Reports Server (NTRS)
Lundgren, Paul R.; Giardini, Domenico
1992-01-01
The joint hypocentral determination method is used to relocate deep seismicity reported in the International Seismological Center catalog for earthquakes deeper than 400 km in the Honshu, Bonin, Mariannas, Java, Banda, and South America subduction zones. Each deep seismic zone is found to display planar features of seismicity parallel to the Harvard centroid-moment tensor nodal planes, which are identified as planes of shear failure. The sense of displacement on these planes is one of resistance to deeper penetration.
NASA Astrophysics Data System (ADS)
Mahalder, B.; Schwartz, J. S.; Palomino, A.; Papanicolaou, T.
2016-12-01
Cohesive soil erodibility and threshold shear stress for stream bed and bank are dependent on both soil physical and geochemical properties in association with the channel vegetative conditions. These properties can be spatially variable therefore making critical shear stress measurement in cohesive soil challenging and leads to a need for a more comprehensive understanding of the erosional processes in streams. Several in-situ and flume-type test devices for estimating critical shear stress have been introduced by different researchers; however reported shear stress estimates per device vary widely in orders of magnitude. Advantages and disadvantages exist between these devices. Development of in-situ test devices leave the bed and/or bank material relatively undisturbed and can capture the variable nature of field soil conditions. However, laboratory flumes provide a means to control environmental conditions that can be quantify and tested. This study was conducted to observe differences in critical shear stress using jet tester and a well-controlled conduit flume. Soil samples were collected from the jet test locations and tested in a pressurized flume following standard operational procedure to calculate the critical shear stress. The results were compared using statistical data analysis (mean-separation ANOVA procedure) to identify possible differences. In addition to the device comparison, the mini jet device was used to measure critical shear stress across geologically diverse regions of Tennessee, USA. Statistical correlation between critical shear stress and the soil physical, and geochemical properties were completed identifying that geological origin plays a significant role in critical shear stress prediction for cohesive soils. Finally, the critical shear stress prediction equations using the jet test data were examined with possible suggestions to modify based on the flume test results.
A critical review of the experimental data for developed free turbulent shear layers
NASA Technical Reports Server (NTRS)
Birch, S. F.; Eggers, J. M.
1973-01-01
Experimental shear layer data are reviewed and the results are compared to numerical predictions for three test cases. It was concluded from the study that many, if not most, of the apparent inconsistencies which exist in the interpretation of the experimental data for free shear layers result from confusing data taken in developed turbulent flows with those taken in transitional or developing flows. Other conclusions drawn from the study include the following: (1) The effects of Mach number are more uncertain primarily because of limited data and the absence of any turbulence measurements for supersonic shear layers. (2) The data available for heterogeneous shear layers are not sufficient to clearly establish the effect of density ratio on mixing rate.
NASA Astrophysics Data System (ADS)
Rubina, A. L.; Krashakov, Yu. F.
The problem of determining the critical buckling stress of symmetric and nonsymmetric sandwich panels loaded in two-sided compression and shear is investigated analytically. The governing equation is obtained by solving equations of balance of forces and moments for an element of a sandwich structure in the case of buckling. The solution is based on the general assumptions of the theory of thin shallow shells. The results of the study can be used to optimize the structure of sandwich panels.
Castro, Pedro; Elvira, Luis; Maestre, Juan Ramón; Montero de Espinosa, Francisco
2017-01-01
This work analyzes some key aspects of the behavior of sensors based on piezoelectric Thickness Shear Mode (TSM) resonators to study and monitor microbial biofilms. The operation of these sensors is based on the analysis of their resonance properties (both resonance frequency and dissipation factor) that vary in contact with the analyzed sample. This work shows that different variations during the microorganism growth can be detected by the sensors and highlights which of these changes are indicative of biofilm formation. TSM sensors have been used to monitor in real time the development of Staphylococcus epidermidis and Escherichia coli biofilms, formed on the gold electrode of the quartz crystal resonators, without any coating. Strains with different ability to produce biofilm have been tested. It was shown that, once a first homogeneous adhesion of bacteria was produced on the substrate, the biofilm can be considered as a semi-infinite layer and the quartz sensor reflects only the viscoelastic properties of the region immediately adjacent to the resonator, not being sensitive to upper layers of the biofilm. The experiments allow the microrheological evaluation of the complex shear modulus (G* = G′ + jG″) of the biofilm at 5 MHz and at 15 MHz, showing that the characteristic parameter that indicates the adhesion of a biofilm for the case of S. epidermidis and E. coli, is an increase in the resonance frequency shift of the quartz crystal sensor, which is connected with an increase of the real shear modulus, related to the elasticity or stiffness of the layer. In addition both the real and the imaginary shear modulus are frequency dependent at these high frequencies in biofilms. PMID:28617343
Castro, Pedro; Elvira, Luis; Maestre, Juan Ramón; Montero de Espinosa, Francisco
2017-06-15
This work analyzes some key aspects of the behavior of sensors based on piezoelectric Thickness Shear Mode (TSM) resonators to study and monitor microbial biofilms. The operation of these sensors is based on the analysis of their resonance properties (both resonance frequency and dissipation factor) that vary in contact with the analyzed sample. This work shows that different variations during the microorganism growth can be detected by the sensors and highlights which of these changes are indicative of biofilm formation. TSM sensors have been used to monitor in real time the development of Staphylococcus epidermidis and Escherichia coli biofilms, formed on the gold electrode of the quartz crystal resonators, without any coating. Strains with different ability to produce biofilm have been tested. It was shown that, once a first homogeneous adhesion of bacteria was produced on the substrate, the biofilm can be considered as a semi-infinite layer and the quartz sensor reflects only the viscoelastic properties of the region immediately adjacent to the resonator, not being sensitive to upper layers of the biofilm. The experiments allow the microrheological evaluation of the complex shear modulus (G* = G' + jG″) of the biofilm at 5 MHz and at 15 MHz, showing that the characteristic parameter that indicates the adhesion of a biofilm for the case of S. epidermidis and E. coli, is an increase in the resonance frequency shift of the quartz crystal sensor, which is connected with an increase of the real shear modulus, related to the elasticity or stiffness of the layer. In addition both the real and the imaginary shear modulus are frequency dependent at these high frequencies in biofilms.
NASA Astrophysics Data System (ADS)
Li, Enzhu; Kakemoto, Hirofumi; Hoshina, Takuya; Tsurumi, Takaaki
2008-09-01
(K,Na)NbO3-LiNbO3-CuO lead-free piezoelectric ceramics that show a high mechanical quality factor Qm were synthesized and used as a drive element of an ultrasonic motor. The Qm of the (K,Na)NbO3 ceramic could be enhanced by chemical modification using Li and Cu as well as microstructure control to obtain ceramics with fine grains. The grain size dependence of the Qm was consistent with a model based on the formation of internal bias field to stabilize the domain structure. A shear mode was used to drive the ultrasonic motor because the piezoelectric d31 and d33 constants of the ceramics were not sufficient for the motor applications. A shear-mode motor driven with four piezoelectric ceramic plates was developed using the lead-free ceramics with a high Qm of 1400, a high d15 of 207 pC/N, and a high k15 of 0.72. The highest revolution speed of 486 rpm was achieved at 34.5 kHz with the input voltage of approximately 180 Vp-p (peak to peak).
Room temperature sputtering of inclined c-axis ZnO for shear mode solidly mounted resonators
NASA Astrophysics Data System (ADS)
Rughoobur, G.; DeMiguel-Ramos, M.; Mirea, T.; Clement, M.; Olivares, J.; Díaz-Durán, B.; Sangrador, J.; Miele, I.; Milne, W. I.; Iborra, E.; Flewitt, A. J.
2016-01-01
ZnO films with a c-axis significantly inclined away from the surface normal were grown by a remote plasma sputtering technique at room temperature. The films were used to make solidly mounted resonators (SMRs) operating in shear mode at a resonant frequency of 1.35 GHz. Control of the ZnO microstructure was achieved using a polycrystalline AlN seed layer which can be added on top of a sputtered acoustic mirror to give a complete SMR device. The ZnO was reactively sputtered in an atmosphere of argon and oxygen from a zinc target. The c-axis of the ZnO was estimated to be at an angle of ˜45° to the surface normal. SMRs were measured to have quality factors (Q) of up to 140 and effective electromechanical coupling coefficients of up to 2.2% in air. Although an inclined c-axis can be achieved with direct growth onto the acoustic mirror, it is shown that the AlN seed layer provides higher coupling coefficients and narrower inclination angular distribution. The responses of the devices in liquids of different viscosities (acetone, water, and AZ5214E photoresist) were measured. The shear mode Q decreased by 45% in acetone, 72% in water, and 92% in AZ5214E.
NASA Astrophysics Data System (ADS)
Wang, Xian-Qu; Wang, Xiao-Gang
2015-10-01
The nonlinear properties of q ≳ 1 non-resonant fishbone (NRF) instabilities excited by energetic ions are analyzed theoretically for weakly reversed shear in this work. Nonlinear radial displacement of the NRF mode ξ0 is derived by the method of matched asymptotic expansions. It is found that ξ0 depends on the energetic ion beta in a power law of ˜βhα with α=1 /3 , α=1 /7 , and α≪1 , corresponding to a finite qs″ , qs″=0 , and an extremely flattened q-profile, respectively. The scaling dependence of ξ0 on the linear growth rate ˜γ1/4 is also different from that of ˜γ in a conventional positive shear configuration. The scaling suggests that ξ0 weakly depends on βh and γ when the q-profile is flattened. Nonlinear saturation amplitude of the mode for an ITER-like plasma is also estimated by numerical analysis.
NASA Astrophysics Data System (ADS)
Park, Hyungkwon; Kim, Jinyoung; Lee, Sung Bo; Lee, Changhee
2017-02-01
Vacuum kinetic spraying (VKS) is a promising room-temperature process to fabricate dense ceramic films. However, unfortunately, the deposition mechanism is still not clearly understood. In this respect, the critical conditions for successful deposition were investigated. Based on simulation and microstructural analysis, it was found that as the particle velocity increased, fracture mode transition from tensile fracture to shear fracture occurred and particle did not bounce off anymore above a certain velocity. Simultaneously, particle underwent shock-induced plasticity and dynamic fragmentation. The plasticity assisted to prevent the fragments from rebounding by spending the excessive kinetic energy and fragmentation is essential for fragment bonding and film growth considering that the deposition rate increased as the fraction of fragmentation increased. Accordingly, plasticity and fragmentation take a crucial role for particle deposition. In this respect, the velocity that fracture mode transition occurs is newly defined as critical velocity. Consequently, for successful deposition, the particle should at least exceed the critical velocity and thus it is very crucial for film fabrication in VKS process at room temperature.
NASA Astrophysics Data System (ADS)
Park, Hyungkwon; Kim, Jinyoung; Lee, Sung Bo; Lee, Changhee
2016-12-01
Vacuum kinetic spraying (VKS) is a promising room-temperature process to fabricate dense ceramic films. However, unfortunately, the deposition mechanism is still not clearly understood. In this respect, the critical conditions for successful deposition were investigated. Based on simulation and microstructural analysis, it was found that as the particle velocity increased, fracture mode transition from tensile fracture to shear fracture occurred and particle did not bounce off anymore above a certain velocity. Simultaneously, particle underwent shock-induced plasticity and dynamic fragmentation. The plasticity assisted to prevent the fragments from rebounding by spending the excessive kinetic energy and fragmentation is essential for fragment bonding and film growth considering that the deposition rate increased as the fraction of fragmentation increased. Accordingly, plasticity and fragmentation take a crucial role for particle deposition. In this respect, the velocity that fracture mode transition occurs is newly defined as critical velocity. Consequently, for successful deposition, the particle should at least exceed the critical velocity and thus it is very crucial for film fabrication in VKS process at room temperature.
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.
NASA Astrophysics Data System (ADS)
Ghorbanirenani, Iman
This thesis presents two experimental programs together with companion numerical studies that were carried out on reinforced concrete shear walls: static tests and dynamic (shake table) tests. The first series of experiments were monotonic and cyclic quasi-static testing on ductile reinforced concrete shear wall specimens designed and detailed according to the seismic provisions of NBCC 2005 and CSA-A23.3-04 standard. The tests were carried out on full-scale and 1:2.37 reduced scale wall specimens to evaluate the seismic design provisions and similitude law and determine the appropriate scaling factor that could be applied for further studies such as dynamic tests. The second series of experiments were shake table tests conducted on two identical 1:2.33 scaled, 8-storey moderately ductile reinforced concrete shear wall specimens to investigate the effects of higher modes on the inelastic response of slender walls under high frequency ground motions expected in Eastern North America. The walls were designed and detailed according to the seismic provisions of NBCC 2005 and CSA-A23.3-04 standard. The objectives were to validate and understand the inelastic response and interaction of shear, flexure and axial loads in plastic hinge zones of the walls considering the higher mode effects and to investigate the formation of second hinge in upper part of the wall due to higher mode responses. Second mode response significantly affected the response of the walls. This caused inelastic flexural response to develop at the 6th level with approximately the same rotation ductility compared to that observed at the base. Dynamic amplification of the base shear forces was also observed in both walls. Numerical modeling of these two shake table tests was performed to evaluate the test results and validate current modeling approaches. Nonlinear time history analyses were carried out by the reinforced concrete fibre element (OpenSees program) and finite element (VecTor2 program
Wang, L.; Zheng, Z.; Phukan, H.; ...
2017-05-07
Knowledge of the critical resolved shear stress (CRSS) values of different slip modes is important for accurately modeling plastic deformation of hexagonal materials. Here, we demonstrate that CRSS can be directly measured with an in-situ high energy X-ray diffraction microscopy (HEDM) experiment. A commercially pure Ti tensile specimen was deformed up to 2.6% strain. In-situ far-field HEDM experiments were carried out to track the evolution of crystallographic orientations, centers of masses, and stress states of 1153 grains in a material volume of 1.1mm×1mm×1mm. Predominant prismatic slip was identified in 18 grains, where the orientation change occurred primarily by rotation aroundmore » the c-axis during specimen deformation. By analyzing the resolved shear stress on individual slip systems, the estimated CRSS for prismatic slip is 96±18 MPa. Predominant basal slip was identified in 22 other grains, where the 2 orientation change occurred primarily by tilting the c-axis about an axis in the basal plane. The estimated CRSS for basal slip is 127±33 MPa. The ratio of CRSSbasal/CRSSprismatic is in the range of 1.7-2.1. From indirect assessment, the CRSS for pyramidal < c+a > slip is likely greater than 240MPa. Lastly, grain size and free surface effects on the CRSS value in different grains are also examined.« less
Mirzaev, S Z; Behrends, R; Heimburg, T; Haller, J; Kaatze, U
2006-04-14
The specific heat C(p) at constant pressure, the shear viscosity eta(s), and the mutual diffusion coefficient D of the 2,6-dimethylpyridine-water mixture of critical composition have been measured in the homogeneous phase at various temperatures near the lower critical demixing temperature T(c). The amplitude of the fluctuation correlation length xi(0)=(0.198+/-0.004) nm has been derived from a combined evaluation of the eta(s) and D data. This value is in reasonable agreement with the one obtained from the amplitude A(+)=(0.26+/-0.01) J(g K) of the critical term in the specific heat, using the two-scale-factor universality relation. Within the limits of error the relaxation rate Gamma of order parameter fluctuations follows power law with the theoretical universal exponent and with the amplitude Gamma=(25+/-1)x10(9) s(-1). No indications of interferences of the critical fluctuations with other elementary chemical reactions have been found. A noteworthy result is the agreement of the background viscosity eta(b), resulting from the treatment of eta(s) and D data, with the viscosity eta(s)(nu=0) extrapolated from high-frequency viscosity data. The latter have been measured in the frequency range of 5-130 MHz using a novel shear impedance spectrometer.
NASA Astrophysics Data System (ADS)
Debayle, E.; Ricard, Y. R.
2011-12-01
We present a global SV-wave tomographic model of the upper mantle, built from a new dataset of fundamental and higher mode Rayleigh waveforms. We use an extension of the automated waveform inversion approach of Debayle (1999) designed to improve the extraction of fundamental and higher mode information from a single surface wave seismogram. The improvement is shown to be significant in the transition zone structure which is constrained by the higher modes. The new approach is fully automated and can be run on a Beowulf computer to process massive surface wave dataset. It has been used to match successfully over 350 000 fundamental and higher mode Rayleigh waveforms, corresponding to about 20 millions of new measurements extracted from the seismograms. For each seismogram, we obtain a path average shear velocity and quality factor model, and a set of fundamental and higher mode dispersion and attenuation curves compatible with the recorded waveform. The set of dispersion curves provides a global database for future finite frequency inversion. Our new 3D SV-wave tomographic model takes into account the effect of azimuthal anisotropy and is constrained with a lateral resolution of several hundred kilometers and a vertical resolution of a few tens of kilometers. In the uppermost 200 km, our model shows a very strong correlation with surface tectonics. The slow velocity signature of mid-oceanic ridges extend down to ~100 km depth while the high velocity signature of cratons vanishes below 200 km depth. At depth greater than 400 km, the pattern of seismic velocities appear relatively homogeneous at large scale, except for high velocity slabs which produce broad high velocity regions within the transition zone. Although resolution is still good, the region between 200 and 400 km is associated with a complex pattern of seismic heterogeneities showing no simple correlation with the shallower or deeper structure.
NASA Astrophysics Data System (ADS)
Simpson Chen, Abraham; Bergbreiter, Sarah
2017-02-01
Elastomer-based electroadhesion can be an effective method to provide tunable adhesion between robots and grasped objects or surfaces. However, there has been little work to develop models of electroadhesion and characterization of adhesive performance relative to these models. In this paper, a basic friction model is proposed to describe the critical shear force for a single electrode electroadhesive fabricated from conductive PDMS encased in parylene. The use of parylene results in thin dielectrics that require only tens of Volts to achieve shear pressures greater than 100 kPa. The experimental results gathered by characterizing voltage, dielectric thickness, adhesive area, and adhesive thickness follow the trends predicted by theory with some important deviations that are studied using high speed video capture of the soft adhesive failure.
Critical Delocalization of Chiral Zero Energy Modes in Graphene
NASA Astrophysics Data System (ADS)
Ferreira, Aires; Mucciolo, Eduardo R.
2015-09-01
Graphene subjected to chiral-symmetric disorder is believed to host zero energy modes (ZEMs) resilient to localization, as suggested by the renormalization group analysis of the underlying nonlinear sigma model. We report accurate quantum transport calculations in honeycomb lattices with in excess of 109 sites and fine meV resolutions. The Kubo dc conductivity of ZEMs induced by vacancy defects (chiral BDI class) is found to match 4 e2/π h within 1% accuracy, over a parametrically wide window of energy level broadenings and vacancy concentrations. Our results disclose an unprecedentedly robust metallic regime in graphene, providing strong evidence that the early field-theoretical picture for the BDI class is valid well beyond its controlled weak-coupling regime.
Critical Delocalization of Chiral Zero Energy Modes in Graphene
NASA Astrophysics Data System (ADS)
Ferreira, Aires; Mucciolo, Eduardo
Graphene subjected to chiral-symmetric disorder is believed to host zero energy modes (ZEMs) resilient to localization, as suggested by the renormalization group analysis of the underlying nonlinear sigma model. We report accurate quantum transport calculations in honeycomb lattices with in excess of 109sites and fine meV resolutions. The Kubo dc conductivity of ZEMs induced by vacancy defects (chiral BDI class) is found to match 4e2 / (πh) within 1 % accuracy, over a parametrically wide window of energy level broadenings and vacancy concentrations. Our results disclose an unprecedentedly robust metallic regime in graphene, providing strong evidence that the early field-theoretical picture for the BDI class is valid well beyond its controlled weak-coupling regime. A.F. acknowledges the financial support of the Royal Society, UK.
Wu, Huiyan; Zhao, Guangyi; Zu, Hongfei; Wang, James H.-C.; Wang, Qing-Ming
2015-01-01
Aging not only affects the whole body performance but also alters cellular biological properties, including cell proliferation and differentiation. This study was designed to determine the effect of aging on the mechanical properties of tendon stem cells (TSCs), a newly discovered stem cell type in tendons, using quartz thickness shear mode (TSM) resonators. TSCs were isolated from both old and young rats, and allowed to grow to confluency on the surface of TSM resonators. The admittance spectrums of TSM with TSC monolayer were acquired, and a series of complex shear modulus G′ + jG″ as well as average thickness hTSC were calculated based on a two-layer-loading transmission line model (TLM) for TSM resonator sensor. The results showed an overall increase in G′, G″ and hTSC during aging process. Specifically, the storage modulus G′ of aging TSCs was over ten times than that of young, revealing an important increase in stiffness of aging TSCs. Additionally, through phase-contrast and scanning electronic microscopy, it was shown that aging TSCs were large, flat and heterogeneous in morphologies while young TSCs were uniformly elongated. Increased cell size and irregular cell shape might be associated with the dense cytoskeleton organization, which could lead to an increase in both stiffness and viscosity. These results are in agreement with previously published data using different measurement methods, indicating TSM resonator sensor as a promising tool to measure the mechanical properties of cells. PMID:26251564
Wu, Huiyan; Zhao, Guangyi; Zu, Hongfei; Wang, James H-C; Wang, Qing-Ming
2015-04-01
Aging not only affects the whole body performance but also alters cellular biological properties, including cell proliferation and differentiation. This study was designed to determine the effect of aging on the mechanical properties of tendon stem cells (TSCs), a newly discovered stem cell type in tendons, using quartz thickness shear mode (TSM) resonators. TSCs were isolated from both old and young rats, and allowed to grow to confluency on the surface of TSM resonators. The admittance spectrums of TSM with TSC monolayer were acquired, and a series of complex shear modulus G' + jG″ as well as average thickness hTSC were calculated based on a two-layer-loading transmission line model (TLM) for TSM resonator sensor. The results showed an overall increase in G', G″ and hTSC during aging process. Specifically, the storage modulus G' of aging TSCs was over ten times than that of young, revealing an important increase in stiffness of aging TSCs. Additionally, through phase-contrast and scanning electronic microscopy, it was shown that aging TSCs were large, flat and heterogeneous in morphologies while young TSCs were uniformly elongated. Increased cell size and irregular cell shape might be associated with the dense cytoskeleton organization, which could lead to an increase in both stiffness and viscosity. These results are in agreement with previously published data using different measurement methods, indicating TSM resonator sensor as a promising tool to measure the mechanical properties of cells.
A scanning-mode 2D shear wave imaging (s2D-SWI) system for ultrasound elastography.
Qiu, Weibao; Wang, Congzhi; Li, Yongchuan; Zhou, Juan; Yang, Ge; Xiao, Yang; Feng, Ge; Jin, Qiaofeng; Mu, Peitian; Qian, Ming; Zheng, Hairong
2015-09-01
Ultrasound elastography is widely used for the non-invasive measurement of tissue elasticity properties. Shear wave imaging (SWI) is a quantitative method for assessing tissue stiffness. SWI has been demonstrated to be less operator dependent than quasi-static elastography, and has the ability to acquire quantitative elasticity information in contrast with acoustic radiation force impulse (ARFI) imaging. However, traditional SWI implementations cannot acquire two dimensional (2D) quantitative images of the tissue elasticity distribution. This study proposes and evaluates a scanning-mode 2D SWI (s2D-SWI) system. The hardware and image processing algorithms are presented in detail. Programmable devices are used to support flexible control of the system and the image processing algorithms. An analytic signal based cross-correlation method and a Radon transformation based shear wave speed determination method are proposed, which can be implemented using parallel computation. Imaging of tissue mimicking phantoms, and in vitro, and in vivo imaging test are conducted to demonstrate the performance of the proposed system. The s2D-SWI system represents a new choice for the quantitative mapping of tissue elasticity, and has great potential for implementation in commercial ultrasound scanners.
The effects of green infrastructure on exceedance of critical shear stress in Blunn Creek watershed
NASA Astrophysics Data System (ADS)
Shannak, Sa'd.
2017-09-01
Green infrastructure (GI) has attracted city planners and watershed management professional as a new approach to control urban stormwater runoff. Several regulatory enforcements of GI implementation created an urgent need for quantitative information on GI practice effectiveness, namely for sediment and stream erosion. This study aims at investigating the capability and performance of GI in reducing stream bank erosion in the Blackland Prairie ecosystem. To achieve the goal of this study, we developed a methodology to represent two types of GI (bioretention and permeable pavement) into the Soil Water Assessment Tool, we also evaluated the shear stress and excess shear stress for stream flows in conjunction with different levels of adoption of GI, and estimated potential stream bank erosion for different median soil particle sizes using real and design storms. The results provided various configurations of GI schemes in reducing the negative impact of urban stormwater runoff on stream banks. Results showed that combining permeable pavement and bioretention resulted in the greatest reduction in runoff volumes, peak flows, and excess shear stress under both real and design storms. Bioretention as a stand-alone resulted in the second greatest reduction, while the installation of detention pond only had the least reduction percentages. Lastly, results showed that the soil particle with median diameter equals to 64 mm (small cobbles) had the least excess shear stress across all design storms, while 0.5 mm (medium sand) soil particle size had the largest magnitude of excess shear stress. The current study provides several insights into a watershed scale for GI planning and watershed management to effectively reduce the negative impact of urban stormwater runoff and control streambank erosion.
Cluster observations of Shear-mode surface waves diverging from Geomagnetic Tail reconnection
NASA Astrophysics Data System (ADS)
Dai, L.; Wygant, J. R.; Dombeck, J. P.; Cattell, C. A.; Thaller, S. A.; Mouikis, C.; Balogh, A.; Reme, H.
2010-12-01
We present the first Cluster spacecraft study of the intense (δB/B~0.5, δE/VAB~0.5) equatorial plane surface waves diverging from magnetic reconnection in the geomagnetic tail at ~17 Re. Using phase lag analysis with multi-spacecraft measurements, we quantitatively determine the wavelength and phase velocity of the waves with spacecraft frame frequencies from 0.03 Hz to 1 Hz and wavelengths from much larger (4Re) than to comparable to the H+ gyroradius (~300km). The phase velocities track the strong variations in the equatorial plane projection of the reconnection outflow velocity perpendicular to the magnetic field. The propagation direction and wavelength of the observed surface waves resemble those of flapping waves of the magnetotail current sheet, suggesting a same origin shared by both of these waves. The observed waves appear ubiquitous in the outflows near magnetotail reconnection. Evidence is found that the observed waves are associated with velocity shear in reconnection outflows. Analysis shows that observed waves are associated with strong field-aligned Alfvenic Poynting flux directed away from the reconnection region toward Earth. These observations present a scenario in which the observed surface waves are driven and convected through a velocity-shear type instability by high-speed (~1000km) reconnection outflows tending to slow down due to power dissipation through Poynting flux. The mapped Poynting flux (100ergs/cm2s) and longitudinal scales (10-100 km) to 100km altitude suggest that the observed waves and their motions are an important boundary condition for night-side aurora. Figure: a) The BX-GSM in the geomagnetic tail current sheet. b) The phase difference wavelet spectrum between Bz_GSM from SC2 and SC3, used to determine the wave phase velocity, is correlated with the reconnection outflow velocity (represented by H+ VX-GSM) c) The spacecraft trajectory through magnetotail reconnection. d) The observed equatorial plane surface wave
Palermo, F.; Garbet, X.; Cartier-Michaud, T.; Ghendrih, P.; Grandgirard, V.; Sarazin, Y.; Ghizzo, A.
2015-04-15
One important issue in turbulence self-organization is the interplay between the Kelvin–Helmholtz (KH) instability and streamers and/or zonal flows. This question has been debated for a long time. The effects of the KH instability and its position in the sequence of events between streamers, turbulence, and zonal flows have been investigated with a reduced gyro-bounce averaged kinetic code devoted to study the primary ion temperature gradient (ITG) instability linked to trapped ion modes (TIM). In toroidal geometry, the specific dynamics of TIM linked to trapped particles becomes important when the frequency of ITG modes falls below the ion bounce frequency, allowing one to average on both the cyclotron and bounce motion fast time scales. This reduction of the number of degrees of freedom leads to a strong reduction of computer resources (memory and computation time). Bounce-averaged gyrokinetic code can be considered as a toy model able to describe basic structures of turbulent transport in tokamak devices. In particular, by means of this code, we have observed that the energy injected in the system by the TIM instability is exchanged between streamers and zonal flows by means of KH vortices that grow along these structures in the nonlinear phase. The energy transfer occurs throughout the relaxation phase of the streamer growth leading to a modification of the KH modes and to the generation of the zonal flows.
Ma, Tingfeng; Wang, Ji; Du, Jianke; Yang, Jiashi
2015-05-01
We analyze coupled thickness-shear and extensional vibrations of a piezoelectric resonator of AT-cut quartz. Different from most of the AT-cut quartz resonators studied in the literature which are based on the slow shear mode excited by a thickness electric field, the resonator in this paper operates with the fast shear mode driven by a lateral electric field produced by a pair of electrodes on the top surface of the resonator. Mindlin's first-order theory of piezoelectric plates is used. Dispersion relations of the relevant waves in unelectroded and electroded plates are presented and compared. The motional capacitance, resonant frequencies and mode shapes near resonances are obtained from an electrically forced vibration analysis. Trapped modes without vibration near the resonator edges are identified. The effects of various structural parameters on energy trapping are examined and the mechanisms are discussed. The results can provide important bases for the parameters design of new resonators operating with the fast shear mode with new excitation schemes. Copyright © 2015 Elsevier B.V. All rights reserved.
ENRICO FERMI FAST REACTOR SPENT NUCLEAR FUEL CRITICALLY CALCULATIONS: INTACT MODE
A.S. Mobasheran
1999-04-12
The purpose of this calculation is to perform intact mode and partially degraded mode criticality evaluations of the Department of Energy's (DOE) Enrico Fermi (EF) Spent Nuclear Fuel (SNF) co-disposed in a 5 Defense High-Level Waste (5-DHLW) Waste Package (WP) and emplaced in a Monitored Geologic Repository (MGR). The criticality evaluations estimate the values of the effective neutron multiplication factor, k{sub eff}, a measure of nuclear criticality potential, for the 5-DHLW/DOE SNF WP with intact or partially degraded internal configurations. These evaluations contribute to the WP design.
A mode-coupling theory of vibrational line broadening in near-critical fluids.
Egorov, S A; Lawrence, C P; Skinner, J L
2005-04-14
We present a fully microscopic mode-coupling theory of near-critical line broadening. All the structural and dynamical input required by the theory is calculated directly from intermolecular potentials. We compute vibrational frequency time-correlation functions and line shapes as the critical point is approached along both the critical isochore and the liquid-gas coexistence curve. Theory is shown to be in good agreement with simulation.
Acevedo, Nuria C; Block, Jane M; Marangoni, Alejandro G
2012-01-01
This article reports on the effect of laminar shear on structural and mechanical properties of physical mixtures of fully hydrogenated soybean oil (FHSO) in soybean oil (SO). Blends were crystallized statically and under laminar shear rates of 30 and 240 s(-1) at different wall temperatures (-10, 0, 20 degrees C). The micro- and nanocrystalline structures were characterized using Polarized Light Microscopy (PLM), and Cryogenic Transmission Electron Microscopy (Cryo-TEM). Rheological analysis was used to determine changes in mechanical properties. Oil-binding capacity was analyzed through the measurement of the oil lost from the fat samples (OL). Shearing greatly affected the structure at the nano- and mesoscale. At low shear rates, blends displayed the largest increase in crystal size with an increase in wall temperature at both the nano- and mesoscale. On the other hand, at shear rates of 240 s(-1), the effect of crystallization temperature was observed only at the nanoscale since no changes in meso-crystal sizes were observed at different temperatures. Crystallization under laminar shear promoted the growth of spherical crystalline particles at the mesoscale, called here "solid-lipid meso-particles". Crystallization under higher shear rates led to the formation of a weak network with low oil-binding capacity and promoted the asymmetric growth of nanoplatelets. In statically crystallized blends, nanoplatelets had an aspect ratio of -2, while in sheared blends this value increased significantly. These results revealed the existence of critical shear rate values above which strong alterations in the structure of the solid crystalline network took place. Shearing also affected the material's strength. Laminar shear induced a decrease in elastic modulus and yield stress values which was more pronounced at higher shear rate-temperature combinations. Shear-temperature combinations were successfully used to structure fats at the nano and mesoscale.
NASA Astrophysics Data System (ADS)
Adrjanowicz, K.; Jakobsen, B.; Hecksher, T.; Kaminski, K.; Dulski, M.; Paluch, M.; Niss, K.
2015-11-01
In this paper, we present results of dielectric and shear-mechanical studies for amine (2-ethyl-1-hexylamine) and thiol (2-ethyl-1-hexanethiol) derivatives of the monohydroxy alcohol, 2-ethyl-1-hexanol. The amine and thiol can form hydrogen bonds weaker in strength than those of the alcohol. The combination of dielectric and shear-mechanical data enables us to reveal the presence of a relaxation mode slower than the α-relaxation. This mode is analogous to the Debye mode seen in monohydroxy alcohols and demonstrates that supramolecular structures are present for systems with lower hydrogen bonding strength. We report some key features accompanying the decrease in the strength of the hydrogen bonding interactions on the relaxation dynamics close to the glass-transition. This includes changes (i) in the amplitude of the Debye and α-relaxations and (ii) the separation between primary and secondary modes.
NASA Astrophysics Data System (ADS)
Heap, M. J.; Lavallee, Y.; David, E. C.; Petrakova, L.; Baud, P.; Dingwell, D. B.; Reuschle, T.
2011-12-01
Andesite is an extrusive volcanic rock of intermediate composition (i.e., SiO2 varies between 52-63%). Andesitic volcanoes, typical of convergent plate margin settings, represent about 25% of volcanoes worldwide. However, our understanding of the physical and mechanical properties of andesites, important for volcanic hazard mitigation, remains sparse. We have therefore embarked on a systematic study on the mechanical properties of a suite of andesites collected from Volcán de Colima, one of the most active volcanoes on the Trans-Mexican volcanic belt, Mexico. Our andesite samples (ranging from 8 to 18% porosity) had high initial crack densities (as inferred from both a newly-devised sliding crack model and from more traditional stereological techniques), corroborated by low ultrasonic wave velocities (P-wave velocities were about 2.5 km/s for all samples). Bulk geochemical analysis showed that all samples were compositionally identical. Compressive strength experiments, performed at room temperature and under a constant strain rate of 10-5 s-1, were performed under a range of effective confining pressures (representative of those within a volcanic edifice). When rock is exposed to an applied differential stress, it can react in two different ways. The void space (a combination of cracks and pores) within the rock can either demonstrate net dilatation or net compaction. The resultant behaviour of the rock is governed by the competition between micromechanical processes, namely dilatational microcracking versus grain crushing and pore collapse. The potency of these competing processes is dependent on both the initial physical properties of the rock, such as porosity and grain size, and the conditions under which the rock deforms. In our experiments, all of the andesites displayed dilatancy and/or dilatant modes of failure, either axial splitting (restricted to the uniaxial experiments) or shear faulting at low effective confining pressures. Under uniaxial conditions
NASA Astrophysics Data System (ADS)
Calamita, F.; Satolli, S.; Turtù, A.
2012-11-01
This work reports the results of our analysis of the brittle-ductile shear zone associated with the Olevano-Antrodoco-Sibillini (OAS) curved-shape thrust in the Central/Northern Apennines of Italy. Its southern sector is characterized by NNW-SSE trending footwall anticlines, which also affect the OAS thrust surface. S tectonites in the NNE-SSW trending sector are crenulated by conjugate extensional surfaces (extensional crenulation cleavage). The NW-SE trending segment of the OAS thrust is characterized by SC tectonites developed along the thrust-related shear zone. Both the SC and S tectonites are consistent with a top-to-the N60-70°E direction of tectonic transport. The SC tectonites are associated with a simple-shear-dominated deformation (Wn = 0.86-0.98). On the other hand, the S tectonites and their related extensional shear planes document two stages of strain: (i) sub-simple shear (Wn = 0.34-0.50, related to OAS thrusting contemporaneous to growing incipient footwall anticlines, and (ii) pure-shear-dominated deformation (Wn = 0.17-0.00), subsequent to the OAS thrusting and caused by the definitive growth of footwall anticlines within an in-sequence deformation context. The present study proposes the analysis of shear zones to: (i) discriminate in-sequence against out-of-sequence evolution, and (ii) use as a tool to constrain the modes and timing of the curved belt's development.
Nanocharacterization of Soft Biological Samples in Shear Mode with Quartz Tuning Fork Probes
Otero, Jorge; Gonzalez, Laura; Puig-Vidal, Manel
2012-01-01
Quartz tuning forks are extremely good resonators and their use is growing in scanning probe microscopy. Nevertheless, only a few studies on soft biological samples have been reported using these probes. In this work, we present the methodology to develop and use these nanosensors to properly work with biological samples. The working principles, fabrication and experimental setup are presented. The results in the nanocharacterization of different samples in different ambients are presented by using different working modes: amplitude modulation with and without the use of a Phase-Locked Loop (PLL) and frequency modulation. Pseudomonas aeruginosa bacteria are imaged in nitrogen using amplitude modulation. Microcontact printed antibodies are imaged in buffer using amplitude modulation with a PLL. Finally, metastatic cells are imaged in air using frequency modulation. PMID:22666059
Nanocharacterization of soft biological samples in shear mode with quartz tuning fork probes.
Otero, Jorge; Gonzalez, Laura; Puig-Vidal, Manel
2012-01-01
Quartz tuning forks are extremely good resonators and their use is growing in scanning probe microscopy. Nevertheless, only a few studies on soft biological samples have been reported using these probes. In this work, we present the methodology to develop and use these nanosensors to properly work with biological samples. The working principles, fabrication and experimental setup are presented. The results in the nanocharacterization of different samples in different ambients are presented by using different working modes: amplitude modulation with and without the use of a Phase-Locked Loop (PLL) and frequency modulation. Pseudomonas aeruginosa bacteria are imaged in nitrogen using amplitude modulation. Microcontact printed antibodies are imaged in buffer using amplitude modulation with a PLL. Finally, metastatic cells are imaged in air using frequency modulation.
NASA Astrophysics Data System (ADS)
Miao, Hongchen; Huan, Qiang; Wang, Qiangzhong; Li, Faxin
2017-02-01
Excitation of single fundamental torsional wave T(0, 1) mode is of practical importance in inspecting or monitoring the structural integrity of pipelines, as T(0, 1) wave is the only non-dispersive mode in pipe-like structures. This work presents a piezoelectric ring array to excite and receive single T(0, 1) mode which is made up of a series of equally-spaced face-shear d24 PZT elements around the pipe. Firstly, we proposed that single T(0, 1) mode can be excited by the piezoelectric ring, when the number of d24 PZT elements is slightly greater than n, where F(n, 2) is the highest circumferential order flexural torsional mode within the frequency bandwidth of the drive signal. Then this proposed principle was confirmed by finite element simulations. Later, experimental testing was conducted on a 100 mm outer diameter, 3 mm thick aluminum pipe. Results show that the ring of 24 face-shear d24 PZT elements can suppress all the non-axisymmetric flexural modes at the excitation frequency of 150 kHz so that single T(0, 1) mode is generated. Moreover, such a piezoelectric ring transducer can also filter flexural modes and receive the T(0, 1) mode only at 150 kHz. Note that here the highest circumferential order flexural torsional mode within the frequency bandwidth is F(20, 2), so the experimental results are in good agreement with the proposed principle. The presented ring of face-shear d24 PZT elements is very suitable for severing as the T(0, 1) wave transducer in structural health monitoring system, as it is cost-effective and no external load is required for operation.
NASA Astrophysics Data System (ADS)
Wang, Meng; Huerre, Patrick; Jiang, Chung-Hsiang; Pei, Suyang; Rui, Maryann; Marcus, Philip
2015-11-01
It has been found recently that baroclinic critical layers are responsible for a new finite-amplitude instability, called the Zombie Vortex Instability (ZVI), in stratified (with Brunt-Väisälä frequency N) flows, rotating with angular velocity Ω and shear σ. ZVI occurs via baroclinic critical layers that create linearly unstable vortex layers, which roll-up into vortices. Those vortices excite new baroclinic critical layers, which form new generations of vortices, resulting in ``vortex self-replication'' that fills the fluid with turbulent vortices. To understand the role of baroclinic critical layers in ZVI, we analyze their structures with matched asymptotic expansions, assuming viscosity determines the magnitude and thickness of the critical layer. We verify our analytically obtained leading order inner and outer layer solutions with numerical simulations. In addition, maps of the control parameter space (Reynolds number, N/ Ω and σ/ Ω) are presented that show two regimes where ZVI occurs, and the physics that determines the boundaries of the two regimes is interpreted. The parameter map and its underlying physics provide guidance for designing practical laboratory experiments in which ZVI could be observed.
Piscaglia, F; Salvatore, V; Mulazzani, L; Cantisani, V; Schiavone, C
2016-02-01
elastography, pSWE and 2D-SWE), leading to a bidimensional assessment of liver stiffness in real time up to 5 Hz and in larger regions; thus this technique is also termed real-time 2 D SWE. It has been available on the market for a few years 19 20, and many articles have been published showing stiffness values quite similar to those of Fibroscan(®) 21; likewise, defined thresholds based on histological findings have appeared in several articles 19 20 21.After this brief summary of the technological state of the art we would like to mention the following critical issues that we believe every user should note prior to providing liver stiffness reports. · The thresholds obtained from the "oldest" techniques for the various fibrosis stages based on hundreds of patients with histology as reference standard cannot be straightforwardly applied to the new ultrasound elastography techniques, even if based on the same principle (e. g. pSWE). In fact, the different manufacturers apply proprietary patented calculation modes, which might result in slightly to moderately different values. It should be kept in mind that the range for intermediate fibrosis stages (F1 to F3) is quite narrow, in the order of 2 - 3 kilopascal (over a total range spanning 2 to 75 kPa with Fibroscan), so that slightly different differences in outputs could shift the assessment of patients from one stage to another. Comparative studies using phantoms and healthy volunteers, as well as patients, are eagerly awaited. In fact, the equipment might not produce linear correlations of measurements at different degrees of severity of fibrosis. As a theoretical example, some equipment might well correlate in their values with an older technique, such as transient elastography, at low levels of liver fibrosis, but not as well in cases of more advanced fibrosis or vice versa. Consequentely, when elastography data are included in a report, the equipment utilized for the measurement should be clearly specified, and
Salerno, K Michael; Robbins, Mark O
2013-12-01
Molecular dynamics simulations with varying damping are used to examine the effects of inertia and spatial dimension on sheared disordered solids in the athermal quasistatic limit. In all cases the distribution of avalanche sizes follows a power law over at least three orders of magnitude in dissipated energy or stress drop. Scaling exponents are determined using finite-size scaling for systems with 10(3)-10(6) particles. Three distinct universality classes are identified corresponding to overdamped and underdamped limits, as well as a crossover damping that separates the two regimes. For each universality class, the exponent describing the avalanche distributions is the same in two and three dimensions. The spatial extent of plastic deformation is proportional to the energy dissipated in an avalanche. Both rise much more rapidly with system size in the underdamped limit where inertia is important. Inertia also lowers the mean energy of configurations sampled by the system and leads to an excess of large events like that seen in earthquake distributions for individual faults. The distribution of stress values during shear narrows to zero with increasing system size and may provide useful information about the size of elemental events in experimental systems. For overdamped and crossover systems the stress variation scales inversely with the square root of the system size. For underdamped systems the variation is determined by the size of the largest events.
Totem-Pole Power-Factor-Correction Converter under Critical-Conduction-Mode Interleaved Operation
NASA Astrophysics Data System (ADS)
Firmansyah, Eka; Tomioka, Satoshi; Abe, Seiya; Shoyama, Masahito; Ninomiya, Tamotsu
This paper proposes a new power-factor-correction (PFC) topology, and explains its operation principle, its control mechanism, related application problems followed by experimental results. In this proposed topology, critical-conduction-mode (CRM) interleaved technique is applied to a bridgeless PFC in order to achieve high efficiency by combining benefits of each topology. This application is targeted toward low to middle power applications that normally employs continuous-conduction-mode boost converter.
Specific Energy as an Index to Identify the Critical Failure Mode Transition Depth in Rock Cutting
NASA Astrophysics Data System (ADS)
He, Xianqun; Xu, Chaoshui
2016-04-01
Rock cutting typically involves driving a rigid cutter across the rock surface at certain depth of cut and is used to remove rock material in various engineering applications. It has been established that there exist two distinct failure modes in rock cutting, i.e. ductile mode and brittle mode. The ductile mode takes precedence when the cut is shallow and the increase in the depth of cut leads to rock failure gradually shifted to brittle-dominant mode. The threshold depth or the critical transition depth, at which rock failure under cutting changes from the ductile to the brittle mode, is associated with not only the rock properties but also the cutting operational parameters and the understanding of this threshold is important to optimise the tool design and operational parameters. In this study, a new method termed the specific cutting energy transition model is proposed from an energy perspective which is demonstrated to be much more effective in identifying the critical transition depth compared with existing approaches. In the ductile failure cutting mode, the specific cutting energy is found to be independent of the depth of cut; but in the brittle failure cutting mode, the specific cutting energy is found to be dependent on the depth of cut following a power-law relationship. The critical transition depth is identified as the intersection point between these two relationships. Experimental tests on two types of rocks with different combinations of cutting velocity, depth of cut and back rake angle are conducted and the application of the proposed model on these cutting datasets has demonstrated that the model can provide a very effective tool to analyse the cutting mechanism and to identify the critical transition depth.
A strategy for minimizing common mode human error in executing critical functions and tasks
Beltracchi, L.; Lindsay, R.W.
1992-05-01
Human error in execution of critical functions and tasks can be costly. The Three Mile Island and the Chernobyl Accidents are examples of results from human error in the nuclear industry. There are similar errors that could no doubt be cited from other industries. This paper discusses a strategy to minimize common mode human error in the execution of critical functions and tasks. The strategy consists of the use of human redundancy, and also diversity in human cognitive behavior: skill-, rule-, and knowledge-based behavior. The authors contend that the use of diversity in human cognitive behavior is possible, and it minimizes common mode error.
A strategy for minimizing common mode human error in executing critical functions and tasks
Beltracchi, L. ); Lindsay, R.W. )
1992-01-01
Human error in execution of critical functions and tasks can be costly. The Three Mile Island and the Chernobyl Accidents are examples of results from human error in the nuclear industry. There are similar errors that could no doubt be cited from other industries. This paper discusses a strategy to minimize common mode human error in the execution of critical functions and tasks. The strategy consists of the use of human redundancy, and also diversity in human cognitive behavior: skill-, rule-, and knowledge-based behavior. The authors contend that the use of diversity in human cognitive behavior is possible, and it minimizes common mode error.
Simulations of granular bed erosion due to laminar shear flow near the critical Shields number
NASA Astrophysics Data System (ADS)
Derksen, J. J.
2011-11-01
Direct numerical simulations of granular beds consisting of uniformly sized spherical particles being eroded by a shear flow of Newtonian liquid have been performed. The lattice-Boltzmann method has been used for resolving the flow of the interstitial liquid. Fluid and solid dynamics are fully coupled with the particles having finite size and undergoing hard-sphere collisions. Only laminar flow has been considered with particle-based Reynolds numbers in the range 0.02 to 0.6. The parameter range of the simulations covers the transition between static and mobilized beds. The transition occurs for 0.10<θ<0.15 with θ the Shields number. The transition is insensitive of the Reynolds number and the solid-over-liquid density ratio. Incipient bed motion has been interpreted in terms of the probability density functions of the hydrodynamic forces acting on the spheres in the upper layer of the bed.
NASA Astrophysics Data System (ADS)
Parker, Jacob; Longcope, Dana
2017-08-01
On April 18, 2014 (SOL2014-04-18T13:03) an M-class flare was observed by IRIS. The associated flare ribbon contained a quasi-periodic sawtooth pattern that was observed to propagate perpendicular the the IRIS spectral slit with a phase velocity of approximately 15 km/s (Brannon et al. 2015). This motion resulted in periodicities in both intensity and Doppler velocity along the slit. These periodicities were reported by Brannon et al. (2015) to be approximately plus-minus .5 arcseconds in position and plus-minus 20 km/s in velocity and were measured to be approximately 180 degrees out of phase with one another. This quasi-periodic behavior has been attributed by others to bursty or patchy reconnection (Brosius & Daw 2015; Brosius et al. 2016) and slipping occurring during three-dimensional magnetic reconnection (Li & Zhang 2015; Li et al. 2016). While able to account for periodicities in both intensity and Doppler velocity these suggestions do not explicitly account for the phase velocity of the entire sawtooth structure, or for the relative phasing of the oscillations. Here we propose that the observations can be explained by a tearing mode instability occurring at a current sheet across which there is also a velocity shear. We suggest a geometry and local plasma parameters for the April 18 flare which would support our hypothesis. Under this proposal the IRIS observations of this flare may provide the most compelling evidence to date of a tearing mode occurring in the solar magnetic field.
Functional renormalization group analysis of the soft mode at the QCD critical point
NASA Astrophysics Data System (ADS)
Yokota, Takeru; Kunihiro, Teiji; Morita, Kenji
2016-07-01
We make an intensive investigation of the soft mode at the quantum chromodynamics (QCD) critical point on the basis of the functional renormalization group (FRG) method in the local potential approximation. We calculate the spectral functions ρ_{σ, π}(ω, p) in the scalar (σ) and pseudoscalar (π) channels beyond the random phase approximation in the quark-meson model. At finite baryon chemical potential μ with a finite quark mass, the baryon-number fluctuation is coupled to the scalar channel and the spectral function in the σ channel has a support not only in the time-like (ω > p) but also in the space-like (ω < p) regions, which correspond to the mesonic and the particle-hole phonon excitations, respectively. We find that the energy of the peak position of the latter becomes vanishingly small with the height being enhanced as the system approaches the QCD critical point, which is a manifestation of the fact that the phonon mode is the soft mode associated with the second-order transition at the QCD critical point, as has been suggested by some authors. Moreover, our extensive calculation of the spectral function in the (ω, p) plane enables us to see that the mesonic and phonon modes have the respective definite dispersion relations ω_{σ.ph}(p), and it turns out that ω_{σ}(p) crosses the light-cone line into the space-like region, and then eventually merges into the phonon mode as the system approaches the critical point more closely. This implies that the sigma-mesonic mode also becomes soft at the critical point. We also provide numerical stability conditions that are necessary for obtaining the accurate effective potential from the flow equation.
NASA Astrophysics Data System (ADS)
Goodarzi, Mohammad Saeed; Hosseini-Toudeshky, Hossein
2017-02-01
In this paper a formulation of a viscoelastic-damage interface model with friction in mode-II is presented. The cohesive constitutive law contains elastic and damage regimes. It has been assumed that the shear stress in the elastic regime follows the viscoelastic properties of the matrix material. The three element Voigt model has been used for the formulation of relaxation modulus of the material. Damage evolution proceeds according to the bilinear cohesive constitutive law combined with friction stress consideration. Combination of damage and friction is based on the presumption that the damaged area, related to an integration point, can be dismembered into the un-cracked area with the cohesive damage and cracked area with friction. Samples of a one element model have been presented to see the effect of parameters on the cohesive constitutive law. A comparison between the predicted results with available results of end-notched flexure specimens in the literature is also presented to verify the model. Transverse crack tension specimens are also simulated for different applied displacement velocities.
Martin, S J; Bandey, H L; Cernosek, R W; Hillman, A R; Brown, M J
2000-01-01
We derive a lumped-element, equivalent-circuit model for the thickness-shear mode (TSM) resonator with a viscoelastic film. This modified Butterworth-Van Dyke model includes in the motional branch a series LCR resonator, representing the quartz resonance, and a parallel LCR resonator, representing the film resonance. This model is valid in the vicinity of film resonance, which occurs when the acoustic phase shift across the film is an odd multiple of pi/2 rad. For low-loss films, this model accurately predicts the frequency changes and damping that arise at resonance and is a reasonable approximation away from resonance. Elements of the parallel LCR resonator are explicitly related to film properties and can be interpreted in terms of elastic energy storage and viscous power dissipation. The model leads to a simple graphical interpretation of the coupling between the quartz and film resonances and facilitates understanding of the resulting responses. These responses are compared with predictions from the transmission-line and Sauerbrey models.
Rodriguez-Gonzalez, Carmen Guadalupe; Martin-Barbero, Maria Luisa; Herranz-Alonso, Ana; Durango-Limarquez, Maria Isabel; Hernandez-Sampelayo, Paloma; Sanjurjo-Saez, Maria
2015-08-01
To critically evaluate the causes of preventable adverse drug events during the nurse medication administration process in inpatient units with computerized prescription order entry and profiled automated dispensing cabinets in order to prioritize interventions that need to be implemented and to evaluate the impact of specific interventions on the criticality index. This is a failure mode, effects and criticality analysis (FMECA) study. A multidisciplinary consensus committee composed of pharmacists, nurses and doctors evaluated the process of administering medications in a hospital setting in Spain. By analysing the process, all failure modes were identified and criticality was determined by rating severity, frequency and likelihood of failure detection on a scale of 1 to 10, using adapted versions of already published scales. Safety strategies were identified and prioritized. Through consensus, the committee identified eight processes and 40 failure modes, of which 20 were classified as high risk. The sum of the criticality indices was 5254. For the potential high-risk failure modes, 21 different potential causes were found resulting in 24 recommendations. Thirteen recommendations were prioritized and developed over a 24-month period, reducing total criticality from 5254 to 3572 (a 32.0% reduction). The recommendations with a greater impact on criticality were the development of an electronic medication administration record (-582) and the standardization of intravenous drug compounding in the unit (-168). Other improvements, such as barcode medication administration technology (-1033), were scheduled for a longer period of time because of lower feasibility. FMECA is a useful approach that can improve the medication administration process. © 2015 John Wiley & Sons, Ltd.
NASA Astrophysics Data System (ADS)
Sawant, M.; Christou, A.
2012-12-01
While use of LEDs in Fiber Optics and lighting applications is common, their use in medical diagnostic applications is not very extensive. Since the precise value of light intensity will be used to interpret patient results, understanding failure modes [1-4] is very important. We used the Failure Modes and Effects Criticality Analysis (FMECA) tool to identify the critical failure modes of the LEDs. FMECA involves identification of various failure modes, their effects on the system (LED optical output in this context), their frequency of occurrence, severity and the criticality of the failure modes. The competing failure modes/mechanisms were degradation of: active layer (where electron-hole recombination occurs to emit light), electrodes (provides electrical contact to the semiconductor chip), Indium Tin Oxide (ITO) surface layer (used to improve current spreading and light extraction), plastic encapsulation (protective polymer layer) and packaging failures (bond wires, heat sink separation). A FMECA table is constructed and the criticality is calculated by estimating the failure effect probability (β), failure mode ratio (α), failure rate (λ) and the operating time. Once the critical failure modes were identified, the next steps were generation of prior time to failure distribution and comparing with our accelerated life test data. To generate the prior distributions, data and results from previous investigations were utilized [5-33] where reliability test results of similar LEDs were reported. From the graphs or tabular data, we extracted the time required for the optical power output to reach 80% of its initial value. This is our failure criterion for the medical diagnostic application. Analysis of published data for different LED materials (AlGaInP, GaN, AlGaAs), the Semiconductor Structures (DH, MQW) and the mode of testing (DC, Pulsed) was carried out. The data was categorized according to the materials system and LED structure such as AlGaInP-DH-DC, Al
Piezoelectric d36 in-plane shear-mode of lead-free BZT-BCT single crystals for torsion actuation
NASA Astrophysics Data System (ADS)
Berik, P.; Chang, W.-Y.; Jiang, X.
2017-01-01
We report the study of piezoelectric direct torsion actuation mechanism using lead-free piezoelectric d36 in-plane shear-mode BZT-BCT single crystals. The generated angle of twist of the piezoelectric torsion actuator was obtained from the transverse deflection measurement using a laser vibrometer. The bi-morph torsional actuator, consisting of two lead-free piezoelectric BZT-BCT in-plane shear-mode single crystals with a giant piezoelectric d36 shear strain coefficient of 1590 pC/N, provided a rate of twist of 34.12 mm/m under a quasi-static 15 V drive. The experimental benchmark was further modelled and verified by the ANSYS software using three dimensional (3D) piezoelectric finite elements. The experimental results revealed that lead-free piezoelectric BZT-BCT d36-mode single crystal is a superior candidate for piezoelectric torsion actuation. This lead-free piezoelectric BZT-BCT d36-mode torsion actuator can be effectively applied in torsional deformation control by taking into account the environmental considerations.
Higgs amplitude mode in a two-dimensional quantum antiferromagnet near the quantum critical point
NASA Astrophysics Data System (ADS)
Hong, Tao; Matsumoto, Masashige; Qiu, Yiming; Chen, Wangchun; Gentile, Thomas R.; Watson, Shannon; Awwadi, Firas F.; Turnbull, Mark M.; Dissanayake, Sachith E.; Agrawal, Harish; Toft-Petersen, Rasmus; Klemke, Bastian; Coester, Kris; Schmidt, Kai P.; Tennant, David A.
2017-07-01
Spontaneous symmetry-breaking quantum phase transitions play an essential role in condensed-matter physics. The collective excitations in the broken-symmetry phase near the quantum critical point can be characterized by fluctuations of phase and amplitude of the order parameter. The phase oscillations correspond to the massless Nambu-Goldstone modes whereas the massive amplitude mode, analogous to the Higgs boson in particle physics, is prone to decay into a pair of low-energy Nambu-Goldstone modes in low dimensions. Especially, observation of a Higgs amplitude mode in two dimensions is an outstanding experimental challenge. Here, using inelastic neutron scattering and applying the bond-operator theory, we directly and unambiguously identify the Higgs amplitude mode in a two-dimensional S = 1/2 quantum antiferromagnet C9H18N2CuBr4 near a quantum critical point in two dimensions. Owing to an anisotropic energy gap, it kinematically prevents such decay and the Higgs amplitude mode acquires an infinite lifetime.
Cantor set spectra and self-similar critical modes in a 1D-quasicrystal
NASA Astrophysics Data System (ADS)
Desideri, J. P.; Legrand, O.; Macon, L.; Sornette, D.
1989-09-01
Specific properties of the propagation of surface acoustic waves on quasiperiodically corrugated solids are reviewed. This problem is shown to correspond to the critical regime of the Anderson localization transition, characterized by critical proper modes which are neither extended nor localized and which exhibit remarkable scaling features. The spectrum is also predicted to have a Cantor-like structure. The experimental system is made of a thousand grooves engraved according to a Fibonacci sequence. For the first time, the self-similar spatial structure of the critical proper modes is observed through an optical diffraction experiment. Signatures of the fractal spectrum are also reported. These results are explained in terms of the asymptotic approximation of the quasicrystal by periodic systems of increasing periods.
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.
Yang, Q. Q. Zhong, F. C. E-mail: fczhong@dhu.edu.cn; Jia, M. N.; Xu, G. S. E-mail: fczhong@dhu.edu.cn; Wang, L.; Wang, H. Q.; Chen, R.; Yan, N.; Liu, S. C.; Chen, L.; Li, Y. L.; Liu, J. B.
2015-06-15
The power fall-off width in the H-mode scrape-off layer (SOL) in tokamaks shows a strong inverse dependence on the plasma current, which was noticed by both previous multi-machine scaling work [T. Eich et al., Nucl. Fusion 53, 093031 (2013)] and more recent work [L. Wang et al., Nucl. Fusion 54, 114002 (2014)] on the Experimental Advanced Superconducting Tokamak. To understand the underlying physics, probe measurements of three H-mode discharges with different plasma currents have been studied in this work. The results suggest that a higher plasma current is accompanied by a stronger E×B shear and a shorter radial correlation length of turbulence in the SOL, thus resulting in a narrower power fall-off width. A simple model has also been applied to demonstrate the suppression effect of E×B shear on turbulence in the SOL and shows relatively good agreement with the experimental observations.
NASA Astrophysics Data System (ADS)
Parker, Jacob; Longcope, Dana
2017-09-01
On 2014 April 18 (SOL2014-04-18T13:03), an M-class flare was observed by IRIS. The associated flare ribbon contained a quasi-periodic sawtooth pattern that was observed to propagate along the ribbon, perpendicular to the IRIS spectral slit, with a phase velocity of ∼15 km s‑1. This motion resulted in periodicities in both intensity and Doppler velocity along the slit. These periodicities were reported by Brannon et al. to be approximately ±0.″5 in position and ±20 km s‑1 in velocity and were measured to be ∼180° out of phase with one another. This quasi-periodic behavior has been attributed by others to bursty or patchy reconnection and slipping occurring during three-dimensional magnetic reconnection. Though able to account for periodicities in both intensity and Doppler velocity, these suggestions do not explicitly account for the phase velocity of the entire sawtooth structure or the relative phasing of the oscillations. Here we propose that the observations can be explained by a tearing mode (TM) instability occurring at a current sheet across which there is also a velocity shear. Using a linear model of this instability, we reproduce the relative phase of the oscillations, as well as the phase velocity of the sawtooth structure. We suggest a geometry and local plasma parameters for the April 18 flare that would support our hypothesis. Under this proposal, the combined spectral and spatial IRIS observations of this flare may provide the most compelling evidence to date of a TM occurring in the solar magnetic field.
NASA Astrophysics Data System (ADS)
Madraki, Yasaman; Hormozi, Sarah; Ovarlez, Guillaume; Guazzelli, Élisabeth; Pouliquen, Olivier
2017-03-01
A cornstarch suspension is the quintessential particulate system that exhibits shear thickening. By adding large non-Brownian spheres to a cornstarch suspension, we show that shear thickening can be significantly enhanced. More precisely, the shear-thickening transition is found to be increasingly shifted to lower critical shear rates. This influence of the large particles on the discontinuous shear-thickening transition is shown to be more dramatic than that on the viscosity or the yield stress of the suspension.
Herle, V; Manneville, S; Fischer, P
2008-01-01
We carried out pointwise local velocity measurements on 40 mM cetylpyridinium chloride-sodium salicylate (CPyCl-NaSal) wormlike micellar solution using high-frequency ultrasound velocimetry in a Couette shear cell. The studied wormlike solution exhibits Newtonian, shear-thinning and shear-thickening rheological behavior in a stress-controlled environment. Previous rheology, flow visualization and small-angle light/neutron scattering experiments in the shear-thickening regime of this system showed the presence of stress-driven alternating transparent and turbid rings or vorticity bands along the axis of the Couette geometry. Through local velocity measurements we observe a homogeneous flow inside the 1mm gap of the Couette cell in the shear-thinning (stress-plateau) region. Only when the solution is sheared beyond the critical shear stress (shear-thickening regime) in a stress-controlled experiment, we observe inhomogeneous flow characterized by radial or velocity gradient shear bands with a highly sheared band near the rotor and a weakly sheared band near the stator of the Couette geometry. Furthermore, fast measurements performed in the shear-thickening regime to capture the temporal evolution of local velocities indicate coexistence of both radial and vorticity shear bands. However the same measurements carried out in shear rate controlled mode of the rheometer do not show such rheological complexity.
Diffusion in a Metallic Melt at the Critical Temperature of Mode Coupling Theory
NASA Astrophysics Data System (ADS)
Zöllmer, Volker; Rätzke, Klaus; Faupel, Franz; Meyer, Andreas
2003-05-01
According to mode coupling theory, liquidlike motion becomes frozen at a critical temperature Tc well above the caloric glass transition temperature Tg. Here, for the first time, we report on radiotracer diffusion in a supercooled Pd43Cu27Ni10P20 alloy from Tg to the equilibrium melt. Liquidlike motion is seen to set in exactly above Tc as evidenced by a gradual drop of the effective activation energy. This strongly supports the mode coupling scenario. Isotope effect measurements, which have never been carried out near Tc in any material, show atomic transport up to the equilibrium melt to be far away from the hydrodynamic regime of uncorrelated binary collisions.
Porenczuk, Alicja; Firlej, Piotr; Szczepańska, Grażyna; Kolenda, Adam; Olczak-Kowalczyk, Dorota
2016-01-01
More than half of the cavity restorations are replaced due to bacterial microleakage. A need for disinfection agents arises. Application of silver nanoparticles (AgNPs) may be beneficial, yet their impact on the adhesives' shear bond strength to dentin remains unknown. The aim was to assess the shear bond strength to dentin of different dental materials combined with AgNPs. Failure modes were also examined using SEM/FIB, SEM/EDS and endodontic microscopes. The results showed no impact of AgNPs addition to dental materials in terms of shear bond strength to dentin. A change of the failure mode of the self-etch bonding system, Clearfil SE Bond, combined with AgNPs was observed. The new failure modes depended upon the order of application of the materials onto dentin. The microscopic evaluation of the samples showed the presence of AgNPs agglomerations gathered on the dentin's surface. AgNPs connection with self-etching dentin bonding system may have a serious clinical impact.
Luo, Xin; Lu, Xin; Cong, Chunxiao; Yu, Ting; Xiong, Qihua; Quek, Su Ying
2015-10-15
2D layered materials have recently attracted tremendous interest due to their fascinating properties and potential applications. The interlayer interactions are much weaker than the intralayer bonds, allowing the as-synthesized materials to exhibit different stacking sequences, leading to different physical properties. Here, we show that regardless of the space group of the 2D materials, the Raman frequencies of the interlayer shear modes observed under the typical z(xx)z configuration blue shift for AB stacked materials, and red shift for ABC stacked materials, as the number of layers increases. Our predictions are made using an intuitive bond polarizability model which shows that stacking sequence plays a key role in determining which interlayer shear modes lead to the largest change in polarizability (Raman intensity); the modes with the largest Raman intensity determining the frequency trends. We present direct evidence for these conclusions by studying the Raman modes in few layer graphene, MoS2, MoSe2, WSe2 and Bi2Se3, using both first principles calculations and Raman spectroscopy. This study sheds light on the influence of stacking sequence on the Raman intensities of intrinsic interlayer modes in 2D layered materials in general, and leads to a practical way of identifying the stacking sequence in these materials.
Lorchat, Etienne; Froehlicher, Guillaume; Berciaud, Stéphane
2016-02-23
We investigate the interlayer phonon modes in N-layer rhenium diselenide (ReSe2) and rhenium disulfide (ReS2) by means of ultralow-frequency micro-Raman spectroscopy. These transition metal dichalcogenides exhibit a stable distorted octahedral (1T') phase with significant in-plane anisotropy, leading to sizable splitting of the (in-plane) layer shear modes. The fan-diagrams associated with the measured frequencies of the interlayer shear modes and the (out-of-plane) interlayer breathing modes are perfectly described by a finite linear chain model and allow the determination of the interlayer force constants. Nearly identical values are found for ReSe2 and ReS2. The latter are appreciably smaller than but on the same order of magnitude as the interlayer force constants reported in graphite and in trigonal prismatic (2Hc) transition metal dichalcogenides (such as MoS2, MoSe2, MoTe2, WS2, WSe2), demonstrating the importance of van der Waals interactions in N-layer ReSe2 and ReS2. In-plane anisotropy results in a complex angular dependence of the intensity of all Raman modes, which can be empirically utilized to determine the crystal orientation. However, we also demonstrate that the angular dependence of the Raman response drastically depends on the incoming photon energy, shedding light on the importance of resonant exciton-phonon coupling in ReSe2 and ReS2.
On the mode-coupling theory of vibrational line broadening in near-critical fluids.
Lawrence, C P; Skinner, J L
2004-05-08
Molecular-dynamics simulations of a neat atomic fluid, coupled with a simple model for vibrational frequency perturbations, are used to investigate vibrational line broadening near the liquid-gas critical point. All features of our simulations are in qualitative agreement with recent Raman experiments on nitrogen. We also use our simulation results to assess the validity of the mode-coupling theories that have been used to analyze experiment. We find that the theoretical results are not in good agreement with simulation, both for the temperature dependence of the linewidth, and for the frequency time-correlation functions. However, the mode-coupling prediction that critical line broadening is due to the diverging correlation time of the frequency fluctuations is shown to be correct.
Sechrest, Y.; Munsat, T.; D’Ippolito, D. A.; ...
2011-01-01
Fluctuations in the edge and scrape-off layer (SOL) of L-mode plasmas in the National Spherical Torus Experiment (NSTX) as observed by the gas puff imaging (GPI) diagnostic are studied. Calculation of local, time resolved velocity maps using the Hybrid Optical Flow and Pattern Matching Velocimetry (HOP-V) code enables analysis of turbulent flow and shear behavior. Periodic reversals in the direction of the poloidal flow near the separatrix are observed. Also, poloidal velocities and their radial shearing rate are found to be well correlated with the fraction of Dα light contained in the SOL, which acts as a measure of turbulentmore » bursts. The spectra of GPI intensity and poloidal velocity both have a strong feature near 3 kHz, which appears to correspond with turbulent bursts. This mode exhibits a poloidal structure with poloidal wavenumber of 7.7 m-1 for GPI intensity and 3.4 m-1 for poloidal velocity, and the poloidal velocity fluctuations near 3 kHz remain coherent over length scales in excess of the turbulent scales. Furthermore, recent SOL Turbulence (SOLT) simulations find a parameter regime that exhibits periodic bursty transport and shares many qualitative similarities with the experimental data. Strong correlations between the shearing rate and the turbulent bursts are observed for time periods of ~ 2 ms, but the relationship is complicated by several factors. Finally, measurements of the radial profiles of the Reynolds shear stresses are reported. These radial profiles exhibit many similarities for several shots, and a region with positive radial gradient is seen to be coincident with local flow shear.« less
The use of failure mode effect and criticality analysis in a medication error subcommittee.
Williams, E; Talley, R
1994-04-01
Failure Mode Effect and Criticality Analysis (FMECA) is the systematic assessment of a process or product that enables one to determine the location and mechanism of potential failures. It has been used by engineers, particularly in the aerospace industry, to identify and prioritize potential failures during product development when there is a lack of data but an abundance of expertise. The Institute for Safe Medication Practices has recommended its use in analyzing the medication administration process in hospitals and in drug product development in the pharamceutical industry. A medication error subcommittee adopted and modified FMECA to identify and prioritize significant failure modes in its specific medication administration process. Based on this analysis, the subcommittee implemented solutions to four of the five highest ranked failure modes. FMECA provided a method for a multidisciplinary group to address the most important medication error concerns based upon the expertise of the group members. It also facilitated consensus building in a group with varied perceptions.
Dimensionless scaling of the critical beta for onset of a neoclassical tearing mode
La Haye, R. J.; Buttery, R. J.; Huysmans, G. T. A.; Maraschek, M.; Wilson, H. R.
2000-08-01
The islands from tearing modes driven unstable and sustained by the helically perturbed neoclassical bootstrap current often provide the practical limit to long-pulse, high confinement tokamak operation. The destabilization of such ''metastable'' plasmas depends on a ''seed'' island exceeding a threshold. A database from similar regimes [high confinement H-mode with periodic edge localized modes (ELMs) and periodic central sawteeth] was compiled from the tokamaks ASDEX Upgrade (AUG) [Plasma Phys. Controlled Fusion 41, 767 (1999)], DIII-D [Nucl. Fusion 38, 987 (1998)], and JET (Joint European Torus) [Plasma Phys. Controlled Fusion 41, B1 (1999)]. A comparison is made of the measured critical beta for onset of the m/n=3/2 mode (m and n being the poloidal and toroidal Fourier harmonics, respectively) to a model in terms of dimensionless parameters for the seed and threshold islands. This modeling is then used for extrapolation to a reactor-grade tokamak design such as ITER/FDR (International Thermonuclear Experimental Reactor/Final Design Report) [Nucl. Fusion 39, 2137 (1999)]; this indicates that the seed island from sawteeth could be too small to sufficiently disturb the metastable plasma and excite the m/n=3/2 neoclassical tearing mode. (c) 2000 American Institute of Physics.
Critical angle effects and their treatment using ray theory and mode theory
NASA Astrophysics Data System (ADS)
Westwood, Evan K.; Penrod, Clark S.
2005-09-01
The interaction of the acoustic field from a point source with a fluid half-space is examined in terms of ray theory and mode theory. For ray theory, a complex ray approach [E. K. Westwood, J. Acoust. Soc. Am. 85, 1872-1884 (1989)] is used to find the reflected and transmitted fields as the sum of one or two eigenrays. The approach uses the method of steepest descent to solve the plane-wave integral for the fields, where the reflection and transmission coefficients are allowed to influence the locations of the saddle points and their steepest descent paths. As a consequence, saddle points are complex, and complicated processes such as the reflected lateral wave, beam displacement, and the transmitted evanescent field are included. For mode theory, the ORCA normal mode model [Westwood et al., J. Acoust. Soc. Am. 100, 3631-3645 (1996)] is used to illustrate the effects of the critical angle on the mode structure in a Pekeris waveguide. The Pekeris branch cut is shown to correspond to the lateral wave, and a method for replacing its branch line integral with a series of modes is described.
NASA Astrophysics Data System (ADS)
Alkan, Engin
It is essential to understand natural fracture systems embedded in shale-gas reservoirs and the stress fields that influence how induced fractures form in targeted shale units. Multicomponent seismic technology and elastic seismic stratigraphy allow geologic formations to be better images through analysis of different S-wave modes as well as the P-wave mode. Significant amounts of energy produced by P-wave sources radiate through the Earth as downgoing SV-wave energy. A vertical-force source is an effective source for direct SV radiation and provides a pure shear-wave mode (SV-SV) that should reveal crucial information about geologic surfaces located in anisotropic media. SV-SV shear wave modes should carry important information about petrophysical characteristics of hydrocarbon systems that cannot be obtained using other elastic-wave modes. Regardless of the difficulties of extracting good-quality SV-SV signal, direct shear waves as well as direct P and converted S energy should be accounted for in 3C seismic studies. Acquisition of full-azimuth seismic data and sampling data at small intervals over long offsets are required for detailed anisotropy analysis. If 3C3D data can be acquired with improved signal-to-noise ratio, more uniform illumination of targets, increased lateral resolution, more accurate amplitude attributes, and better multiple attenuation, such data will have strong interest by the industry. The objectives of this research are: (1) determine the feasibility of extracting direct SV-SV common-mid-point sections from 3-C seismic surveys, (2) improve the exploration for stratigraphic traps by developing systematic relationship between petrophysical properties and combinations of P and S wave modes, (3) create compelling examples illustrating how hydrocarbon-bearing reservoirs in low-permeable rocks (particularly anisotropic shale formations) can be better characterized using different Swave modes (P-SV, SV-SV) in addition to the conventional P
Intermittent Transport Associated with the Geodesic Acoustic Mode near the Critical Gradient Regime
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.
NASA Astrophysics Data System (ADS)
Kireeva, I. V.; Chumlyakov, Yu. I.; Pobedennaya, Z. V.; Vyrodova, A. V.; Kuksgauzen, I. V.; Poklonov, V. V.; Kuksgauzen, D. A.
2017-07-01
It is established that the critical shear stresses under tensile strain of Al0.3CoCrFeNi high-entropy alloy single crystals are independent of crystal orientation. It is shown that the development of the planar dislocation structure in Al0.3CoCrFeNi single crystals at T = 296 K leads to a decrease in the ratio between the strain-hardening coefficient and shear modulus relative to that the value for Cu single crystals, where the cellular dislocation structure is developed at the similar staking fault energy.
Role of Fourier Modes in Finite-Size Scaling above the Upper Critical Dimension
NASA Astrophysics Data System (ADS)
Flores-Sola, Emilio; Berche, Bertrand; Kenna, Ralph; Weigel, Martin
2016-03-01
Renormalization-group theory has stood, for over 40 years, as one of the pillars of modern physics. As such, there should be no remaining doubt regarding its validity. However, finite-size scaling, which derives from it, has long been poorly understood above the upper critical dimension dc in models with free boundary conditions. In addition to its fundamental significance for scaling theories, the issue is important at a practical level because finite-size, statistical-physics systems with free boundaries and above dc are experimentally relevant for long-range interactions. Here, we address the roles played by Fourier modes for such systems and show that the current phenomenological picture is not supported for all thermodynamic observables with either free or periodic boundaries. In particular, the expectation that dangerous irrelevant variables cause Gaussian-fixed-point scaling indices to be replaced by Landau mean-field exponents for all Fourier modes is incorrect. Instead, the Gaussian-fixed-point exponents have a direct physical manifestation for some modes above the upper critical dimension.
Critical test of the mode-coupling theory of the glass transition.
Berthier, Ludovic; Tarjus, Gilles
2010-09-01
In its common implementation, the mode-coupling theory of the glass transition predicts the time evolution of the intermediate scattering functions in viscous liquids on the sole basis of the structural information encoded in two-point density correlations. We provide a critical test of this property and show that the theory fails to describe the strong differences of dynamical behavior seen in two model liquids characterized by very similar pair-correlation functions. Because we use "exact" static information provided by numerical simulations, our results are a direct indication that some important information about the dynamics of viscous liquids is not captured by pair correlations and is thus not described by the mode-coupling theory, even in the temperature regime where the theory is usually applied.
NASA Technical Reports Server (NTRS)
Ghosh, P.; Abramowicz, M. A.
1991-01-01
The role of the internal gravity modes in mediating the growth of nonaxisymmetric instabilities is investigated by studying the instability of stratified incompressible differentially rotating fluid cylinders to global nonaxisymmetric modes. The results indicate that, in addition to a modified version of the well-known principal branch mediated by surface modes of the system (analogous to f-modes of stars), there exist unstable branches of the dispersion relation mediated by internal gravity modes of the system (similar to the g-modes of stars). These branches arise due to the interaction between the g-modes. It is shown that the maximum growth rate on one of the new branches can sometimes equal or exceed that on the principal branch, thus modifying the principal branch.
NASA Astrophysics Data System (ADS)
Chen, W.; Yu, L. M.; Ding, X. T.; Xie, H. S.; Shi, Z. B.; Ji, X. Q.; Yu, D. L.; Zhang, Y. P.; Shi, P. W.; Li, Y. G.; Feng, B. B.; Jiang, M.; Zhong, W. L.; Cao, J. Y.; Song, X. M.; Xu, M.; Xu, Y. H.; Yan, L. W.; Liu, Yi; Yang, Q. W.; Duan, X. R.; HL-2A Team
2016-03-01
Recent experimental results that are associated with the core-localized (i.e. normalized radius ρ =r/a<0.5 ) Alfvénic modes in HL-2A neutral beam injection (NBI) plasmas with weak magnetic shears are reported. In the different plasma parameter regions, the energetic ions produced by the NBI drive multiple Alfvénic instabilities, such as the toroidal Alfvén eigenmode (TAE), beta-induced Alfvén eigenmode, reversed shear Alfvén eigenmode (RSAE) and fishbone and energetic particle mode (EPM). Here, we focus on the high-frequency RSAE (HFRSAE) and resonant kinetic ballooning mode (rKBM). A group of downward-sweeping frequency coherent modes (HFRSAEs) with 100 < f < 500 kHz and n = 3-7 are often observed with an increase in the edge safety factor, q a . Their measured frequency is more than that of the TAEs, and {{f}\\text{min}}˜ {{f}\\text{TAE}} . The analysis suggests that these modes localize inside the high-order Alfvén eigenmode (AE) gap of the Alfvénic continuum, and their eigenfrequency and eigenfunction depend on the {{q}\\text{min}} and q-profile. When the core plasma density is more than {{n}e0}>3.0× {{10}19} m-3 and the impurity or supersonic molecular beam enters the bulk plasma, the profiles of the plasma density/pressure peak, and the magnetic shear is weak or negative. In this case, a group of multi-harmonic coherent modes (rKBMs) with 30 < f < 150 kHz and n = 2-9 are observed through multiple diagnostic techniques, and {{f}\\ast pi}/2<{{f}\\text{MHD}}={{f}\\text{lab}}-n{{f}vφ}<{{f}\\ast pi} , where {{f}\\ast pi}={ω\\ast pi}/2π is the diamagnetic drift frequency of the thermal ion. It is found that the HFRSAEs can transit into the rKBMs when the density profile suddenly peaks. Neutron monitoring outside the vacuum chamber demonstrates that the HFRSAE and rKBM both degrade the confinement of the energetic ions. The rKBM instabilities also affect the bulk plasma performance.
Yang, J
2008-05-01
A set of nonlinear two-dimensional equations for thin electroelastic shells in vibrations with moderately large shear deformation in the tangent plane are obtained from the three-dimensional equations of nonlinear electroelasticity. As an example for application, the equations are used to study nonlinear torsional vibration of a circular cylindrical piezoelectric shell. It is shown that torsion is nonlinearly coupled to axial extension and circumferential extension. The results of this paper emphasize the need for further study of mode coupling induced by nonlinearity.
Ghizzo, A.; Palermo, F.
2015-08-15
Collisionless trapped ion modes (CTIMs) turbulence exhibits a rich variety of zonal flow physics. The coupling of CTIMs with shear flow driven by the Kelvin-Helmholtz (KH) instability has been investigated. The work explores the parametric excitation of zonal flow modified by wave-particle interactions leading to a new type of resonant low-frequency zonal flow. The KH-CTIM interaction on zonal flow growth and its feedback on turbulence is investigated using semi-Lagrangian gyrokinetic Vlasov simulations based on a Hamiltonian reduction technique, where both fast scales (cyclotron plus bounce motions) are gyro-averaged.
Xu, Y.; Jachmich, S.; Weynants, R. R.; Schoor, M. van; Vergote, M.; Kraemer-Flecken, A.; Schmitz, O.; Unterberg, B.
2009-11-15
Long-distance toroidal correlations of potential and density fluctuations have been investigated at the TEXTOR tokamak [H. Soltwisch et al., Plasma Phys. Controlled Fusion 26, 23 (1984)] in edge electrode-biasing experiments. During the biasing-induced H-mode, the dc ExB shear flow triggers a zonal flow structure and hence long-distance correlation in potential fluctuations, whereas for density fluctuations there is nearly no correlation. These results indicate an intimate interaction between the mean and zonal flows, and the significance of long range correlations in improved-confinement regimes.
Kumar, Ashish; Gernaey, Krist V; De Beer, Thomas; Nopens, Ingmar
2013-11-01
The manufacturing of pharmaceutical dosage forms, which has traditionally been a batch-wise process, is now also transformed into a series of continuous operations. Some operations such as tabletting and milling are already performed in continuous mode, while the adaptation towards a complete continuous production line is still hampered by complex steps such as granulation and drying which are considered to be too inflexible to handle potential product change-overs. Granulation is necessary in order to achieve good flowability properties and better control of drug content uniformity. This paper reviews modelling and supporting measurement tools for the high shear wet granulation (HSWG) process, which is an important granulation technique due to the inherent benefits and the suitability of this unit operation for the desired switch to continuous mode. For gaining improved insight into the complete system, particle-level mechanisms are required to be better understood, and linked with an appropriate meso- or macro-scale model. A brief review has been provided to understand the mechanisms of the granulation process at micro- or particle-level such as those involving wetting and nucleation, aggregation, breakage and consolidation. Further, population balance modelling (PBM) and the discrete element method (DEM), which are the current state-of-the-art methods for granulation modelling at micro- to meso-scale, are discussed. The DEM approach has a major role to play in future research as it bridges the gap between micro- and meso-scales. Furthermore, interesting developments in the measurement technologies are discussed with a focus towards inline measurements of the granulation process to obtain experimental data which are required for developing good models. Based on the current state of the developments, the review focuses on the twin-screw granulator as a device for continuous HSWG and attempts to critically evaluate the current process. As a result, a set of open
NASA Astrophysics Data System (ADS)
Kadota, Michio; Tanaka, Shuji
2016-07-01
There are two kinds of plate waves propagating in a thin plate, Lamb and shear horizontal (SH) waves. The former has a velocity higher than 15,000 m/s when the plate is very thin. On the contrary, 0th SH (SH0) mode plate wave in an ultrathin LiNbO3 plate has an electro-mechanical coupling factor larger than 50%. Authors fabricated an ultra-wideband T-type ladder filter with a relative bandwidth (BW) of 41% using the SH0 mode plate wave. Although the BW of the filter fully covers the digital TV band in Japan, it does not have sufficient margin at the lower and higher end of BW. Besides, periodic small ripples due to transverse mode in pass-band of the filter were observed. In this study π-type ladder filters were fabricated by changing the pitch ratio of interdigital transducer (IDT) of parallel and series arm resonators (PR(IDT)) to control the BW, and by apodizing IDTs to improve the periodic small ripples due to transverse mode. Ultra-wideband filters without periodic small transverse mode with ultrawide bandwidth from 41 to 49% were fabricated. The BWs fully cover ultrawide digital television bands in Japan and U.S.A. These filters with an ultrawide BW and a steep characteristic show the possibility to be applied to a reported cognitive radio system and other communication systems requiring an ultrawide BW.
NASA Astrophysics Data System (ADS)
Zillinger, Christian
2016-09-01
In a previous article (Zillinger, Linear inviscid damping for monotone shear flows, 2014), we have established linear inviscid damping for a large class of monotone shear flows in a finite periodic channel and have further shown that boundary effects asymptotically lead to the formation of singularities of derivatives of the solution as {t → infty}. As the main results of this article, we provide a detailed description of the singularity formation and establish stability in all sub-critical fractional Sobolev spaces and blow-up in all super-critical spaces. Furthermore, we discuss the implications of the blow-up to the problem of nonlinear inviscid damping in a finite periodic channel, where high regularity would be essential to control nonlinear effects.
Risk Management in Magnetic Resonance: Failure Mode, Effects, and Criticality Analysis
Granata, Vincenza; Filice, Salvatore; Raiano, Nicola; Amato, Daniela Maria; Zirpoli, Maria; di Finizio, Alessandro; Sansone, Mario; Russo, Anna; Covelli, Eugenio Maria; Pedicini, Tonino; Triassi, Maria
2013-01-01
The aim of the study was to perform a risk management procedure in “Magnetic Resonance Examination” process in order to identify the critical phases and sources of radiological errors and to identify potential improvement projects including procedures, tests, and checks to reduce the error occurrence risk. In this study we used the proactive analysis “Failure Mode Effects Criticality Analysis,” a qualitative and quantitative risk management procedure; has calculated Priority Risk Index (PRI) for each activity of the process; have identified, on the PRI basis, the most critical activities and, for them, have defined improvement projects; and have recalculated the PRI after implementation of improvement projects for each activity. Time stop and audits are performed in order to control the new procedures. The results showed that the most critical tasks of “Magnetic Resonance Examination” process were the reception of the patient, the patient schedule drafting, the closing examination, and the organization of activities. Four improvement projects have been defined and executed. PRI evaluation after improvement projects implementation has shown that the risk decreased significantly following the implementation of procedures and controls defined in improvement projects, resulting in a reduction of the PRI between 43% and 100%. PMID:24171173
Iwanowski, I; Behrends, R; Kaatze, U
2004-05-15
Ultrasonic attenuation spectra, the shear viscosity, and the mutual diffusion coefficient of the n-pentanol-nitromethane mixture of critical composition have been measured at different temperatures near the critical temperature. The noncritical background contribution, proportional to frequency, to the acoustical attenuation-per-wavelength spectra has been determined and subtracted from the total attenuation to yield the critical contribution. When plotted versus the reduced frequency, with the relaxation rate of order-parameter fluctuations from the shear viscosity and diffusion coefficient measurements, the critical part in the sonic attenuation coefficient displays a scaling function which nicely fits to the data for the critical system 3-methylpentane-nitromethane and also to the empirical scaling function of the Bhattacharjee-Ferrell dynamic scaling theory. The scaled half-attenuation frequency follows from the experimental data as Omega(1/2)emp= 1.8+/-0.1. The relaxation rate of order-parameter fluctuation shows power-law behavior with the theoretically predicted universal exponent and the extraordinary high amplitude Gammao= (187+/-2) x 10(9) s(-1). The amount of the adiabatic coupling constant /g/= 0.03, as estimated from the amplitude of the critical contribution to the acoustical spectra, is unusually small.
NASA Astrophysics Data System (ADS)
Stark, N.; Hay, A. E.; Cheel, R.; Lake, C. B.
2013-12-01
The impact of particle shape on the friction angle, and the resulting critical shear stress on sediment dynamics, is still poorly understood. In areas characterized by sediments of specific shape, particularly non-rounded particles, this can lead to large departures from the expected sediment dynamics. The steep slope (1:10) of the mixed sand-gravel beach at Advocate Harbour was found stable in large-scale morphology over decades, despite a high tidal range of ten meters or more, and strong shorebreak action during storms. The Advocate sand (d < 2 mm) was found to have an elliptic, plate-like shape. Exceptionally high friction angles of the material were determined using direct shear, ranging from φ ≈ 41-46°, while the round to angular gravel was characterized by φ = 33°. The addition of 25% of the elliptic sand to the gravel led to an immediate increase of the friction angle to φ = 38°. Furthermore, re-organization of the particles occurred during shearing, being characterized by a short phase of settling and compaction, followed by a pronounced strong dilatory behavior and an accompanying strong increase of shear stress. Long-term shearing (24 h) using a ring shear apparatus led to destruction of the particles without re-compaction. Finally, submerged particle mobilization was simulated using a tilted tray in a tank. Despite a smooth tray surface, particle motion was not initiated until reaching tray tilt angles of 31° and more, being 7° steeper than the latest gravel motion initiation. In conclusion, geotechnical laboratory experiments quantified the important impact of the elliptic, plate-like shape of Advocate Beach sand on the friction angles of both pure sand and sand-gravel mixtures. The resulting effect on initiation of particle motion was confirmed in tilting tray experiments. This makes it a vivid example of how particle shape can contribute to the stabilization of the beachface.
NASA Astrophysics Data System (ADS)
Asgari, Marika; Heymans, Catherine; Blake, Chris; Harnois-Deraps, Joachim; Schneider, Peter; Van Waerbeke, Ludovic
2017-01-01
We present a re-analysis of the CFHTLenS weak gravitational lensing survey using Complete Orthogonal Sets of E/B-mode Integrals, known as COSEBIs. COSEBIs provide a complete set of functions to efficiently separate E-modes from B-modes and hence allow for robust and stringent tests for systematic errors in the data. This analysis reveals significant B-modes on large angular scales that were not previously seen using the standard E/B decomposition analyses. We find that the significance of the B-modes is enhanced when the data are split by galaxy type and analysed in tomographic redshift bins. Adding tomographic bins to the analysis increases the number of COSEBIs modes, which results in a less-accurate estimation of the covariance matrix from a set of simulations. We therefore also present the first compressed COSEBIs analysis of survey data, where the COSEBIs modes are optimally combined based on their sensitivity to cosmological parameters. In this tomographic CCOSEBIs analysis, we find the B-modes to be consistent with zero when the full range of angular scales are considered.
Singular eigenfunctions for shearing fluids I
Balmforth, N.J.; Morrison, P.J.
1995-02-01
The authors construct singular eigenfunctions corresponding to the continuous spectrum of eigenvalues for shear flow in a channel. These modes are irregular as a result of a singularity in the eigenvalue problem at the critical layer of each mode. They consider flows with monotonic shear, so there is only a single critical layer for each mode. They then solve the initial-value problem to establish that these continuum modes, together with any discrete, growing/decaying pairs of modes, comprise a complete basis. They also view the problem within the framework of Hamiltonian theory. In that context, the singular solutions can be viewed as the kernel of an integral, canonical transformation that allows us to write the fluid system, an infinite-dimensional Hamiltonian system, in action-angle form. This yields an expression for the energy in terms of the continuum modes and provides a means for attaching a characteristic signature (sign) to the energy associate with each eigenfunction. They follow on to consider shear-flow stability within the Hamiltonian framework. Next, the authors show the equivalence of integral superpositions of the singular eigenfunctions with the solution derived with Laplace transform techniques. In the long-time limit, such superpositions have decaying integral averages across the channel, revealing phase mixing or continuum damping. Under some conditions, this decay is exponential and is then the fluid analogue of Landau damping. Finally, the authors discuss the energetics of continuum damping.
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.
Cavitation study of a pump-turbine at turbine mode with critical cavitation coefficient condition
NASA Astrophysics Data System (ADS)
Wang, J.; Yang, D.; Xu, J. W.; Liu, J. T.; Jiao, L.
2016-05-01
To study the cavitation phenomenon of a pump-turbine at turbine mode when it ran at the critical cavitation coefficient condition, a high-head model pump-turbine was disperse using hexahedron grid. Three dimensional, steady cavitating flow was numerically studied using SST k-ω model. It is confirmed that ZGB cavitation model and SST k-ω model are useful ways to study the two-phase cavitation flow in pump-turbine. Mass flow inlet and pressure outlet were specified at the casing inlet and draft tube outlet, respectively. The static pressure was set according to the cavitation coefficient. The steady cavitating flows at critical cavitation coefficient condition were analysed. The cavitation area in the runner was investigated. It was found that the pressure of the suction on the blade surface was decreasing gradually with the decrease of the cavitation coefficient. In addition, the vortex flow in the draft tube was observed at the critical cavitation coefficient. It was found that the vortex flow appeared at the center of the draft tube inlet with the decreasing of the cavitation coefficient. Compared with the experimental data, the simulation results show reasonable agreement with the experimental data.
Youk, Ji Hyun; Son, Eun Ju; Gweon, Hye Mi; Kim, Hana; Park, Yun Joo; Kim, Jeong-Ah
2014-10-01
Our aim was to compare the diagnostic performance of strain elastography (SE) and shear-wave elastography (SWE), combined with B-mode ultrasonography (US), in breast cancer. For 79 breast lesions that underwent SE and SWE, two radiologists reviewed five data sets (B-mode US, SWE, SE and two combined sets). Qualitative and quantitative elastographic data and Breast Imaging Reporting and Data System (BI-RADS) categories were recorded. The area under the receiver operating characteristic curve (AUC) was evaluated. No significant difference in the AUC between the two elastography methods was noted. After subjective assessment by reviewers, the AUC for the combined sets was improved (SWE, 0.987; SE, 0.982; B-mode US, 0.970; p < 0.05). When SE and SWE were added, 38% and 56% of benign BI-RADS category 4a lesions with a low suspicion of cancer were downgraded without false-negative results, respectively. SE and SWE performed similarly. Therefore, addition of SE or SWE improved the diagnostic performance of B-mode US, potentially reducing unnecessary biopsies. Copyright © 2014 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.
Ren, Zhen-Zhen; Wang, Feng; Fu, G. Y.; ...
2017-04-24
Linear and nonlinear simulations of high-order harmonics q=1 energetic particle modes excited by trapped energetic particles in tokamaks are carried out using kinetic/magnetohydrodynamic hybrid code M3D-K. It is found that with a flat safety factor profile in the core region, the linear growth rate of high-order harmonics (m=n>1) driven by energetic trapped particles can be higher than the m/n=1/1 component. The high m=n>1 modes become more unstable when the pressure of energetic particles becomes higher. Moreover, it is shown that there exist multiple resonant locations satisfying different resonant conditions in the phase space of energetic particles for the high-order harmonicsmore » modes, whereas there is only one precessional resonance for the m/n=1/1 harmonics. The fluid nonlinearity reduces the saturation level of the n=1 component, while it hardly affects those of the high n components, especially the modes with m=n=3,4. The frequency of these modes does not chirp significantly, which is different with the typical fishbone driven by trapped particles. Lastly, in addition, the flattening region of energetic particle distribution due to high-order harmonics excitation is wider than that due to m/n=1/1 component, although the m/n=1/1 component has a higher saturation amplitude.« less
NASA Astrophysics Data System (ADS)
Ren, Zhen-Zhen; Wang, Feng; Fu, G. Y.; Shen, Wei; Wang, Zheng-Xiong
2017-05-01
Linear and nonlinear simulations of high-order harmonics q = 1 energetic particle modes excited by trapped energetic particles in tokamaks are carried out using kinetic/magnetohydrodynamic hybrid code M3D-K. It is found that with a flat safety factor profile in the core region, the linear growth rate of high-order harmonics ( m = n > 1 ) driven by energetic trapped particles can be higher than the m / n = 1 / 1 component. The high m = n > 1 modes become more unstable when the pressure of energetic particles becomes higher. Moreover, it is shown that there exist multiple resonant locations satisfying different resonant conditions in the phase space of energetic particles for the high-order harmonics modes, whereas there is only one precessional resonance for the m / n = 1 / 1 harmonics. The fluid nonlinearity reduces the saturation level of the n = 1 component, while it hardly affects those of the high n components, especially the modes with m = n = 3 , 4 . The frequency of these modes does not chirp significantly, which is different with the typical fishbone driven by trapped particles. In addition, the flattening region of energetic particle distribution due to high-order harmonics excitation is wider than that due to m / n = 1 / 1 component, although the m / n = 1 / 1 component has a higher saturation amplitude.
NASA Technical Reports Server (NTRS)
Bergm Robert F.; Moldover, Michael R.; Yao, Minwu; Zimmerli, Gregory A.
2009-01-01
We measured shear thinning, a viscosity decrease ordinarily associated with complex liquids such as molten plastics or ketchup, near the critical point of xenon. The data span a wide range of dimensionless shear rate: the product of the shear rate and the relaxation time of critical fluctuations was greater than 0.001 and was less than 700. As predicted by theory, shear thinning occurred when this product was greater than 1. The measurements were conducted aboard the Space Shuttle Columbia to avoid the density stratification caused by Earth's gravity.
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.
A Note on the Wave Action Density of a Viscous Instability Mode on a Laminar Free-shear Flow
NASA Technical Reports Server (NTRS)
Balsa, Thomas F.
1994-01-01
Using the assumptions of an incompressible and viscous flow at large Reynolds number, we derive the evolution equation for the wave action density of an instability wave traveling on top of a laminar free-shear flow. The instability is considered to be viscous; the purpose of the present work is to include the cumulative effect of the (locally) small viscous correction to the wave, over length and time scales on which the underlying base flow appears inhomogeneous owing to its viscous diffusion. As such, we generalize our previous work for inviscid waves. This generalization appears as an additional (but usually non-negligible) term in the equation for the wave action. The basic structure of the equation remains unaltered.
NASA Astrophysics Data System (ADS)
Peel, David J.; Bullough, William A.
1998-04-01
A general technique providing effective but approximate characterization of electro-rheological fluids as continua (as against their apparent device specific performance) is extended by relating data from cylindrical, sliding electrode induced shear flow, and fixed, plane electrode, pressure induced linear flow types of test rigs. The motion being laminar, use is made of the well known Buckingham relationships: the yield stress in the fluid is taken to vary at constant excitation whilst the well defined unexcited viscosity remains fixed. On the basis of experimental data, and within an acceptable error band (for engineering design purposes) the two modes of operation are shown to share common fluid characteristics in terms of Hedstrom and Reynolds Numbers at constant excitation, and when these are related to a Friction Coefficient, a technique of using `fluid alone' data is made available. This technique allows small sample, low shear rate fluid test results from Couette-type apparatus to be applied in user friendly fashion to the prediction of performance of parallel plate valves and cylindrical clutches operating in the engineering scale.
Thoman, R.W.; Niezgoda, S.L.
2008-12-15
The continuous discharge of coalbed natural gas-produced (CBNG-produced) water within ephemeral, cohesive channels in the Powder River Basin (PRB) of Wyoming can result in significant erosion. A study was completed to investigate channel stability in an attempt to correlate cohesive soil properties to critical shear stress. An in situ jet device was used to determine critical shear stress (tau{sub c}) and erodibility (k{sub d}); cohesive soil properties were determined following ASTM procedures for 25 reaches. The study sites were comprised of erodible to moderately resistant clays with tau{sub c} ranging from 0.11 to 15.35 Pa and k{sub d} ranging from 0.27 to 2.38 cm{sup 3}/N s. A relationship between five cohesive soil characteristics and tau{sub c} was developed and presented for use in deriving tau{sub c} for similar sites. Allowable discharges for CBNG-produced water were also derived using tau{sub c} and the tractive force method. An increase in the allowable discharge was found for channels in which vegetation was maintained. The information from this case study is critical to the development of a conservative methodology to establish allowable discharges while minimizing flow-induced instability.
NASA Technical Reports Server (NTRS)
Dahl, Milo D.; Sutliff, Daniel L.
2007-01-01
A technique is presented for the analysis of measured data obtained from a rotating microphone rake system. The system is designed to measure the interaction modes of ducted fans. A Fourier analysis of the data from the rotating system results in a set of circumferential mode levels at each radial location of a microphone inside the duct. Radial basis functions are then least-squares fit to this data to obtain the radial mode amplitudes. For ducts with soft walls and mean flow, the radial basis functions must be numerically computed. The linear companion matrix method is used to obtain both the eigenvalues of interest, without an initial guess, and the radial basis functions. The governing equations allow for the mean flow to have a boundary layer at the wall. In addition, a nonlinear least-squares method is used to adjust the wall impedance to best fit the data in an attempt to use the rotating system as an in-duct wall impedance measurement tool. Simulated and measured data are used to show the effects of wall impedance and mean flow on the computed results.
NASA Astrophysics Data System (ADS)
Chambers, Jennifer; Parrish, Randall; Argles, Tom; Harris, Nigel; Horstwood, Matthew
2011-04-01
In easternmost Bhutan the South Tibetan detachment (STD) is a ductile shear zone that juxtaposes the Radi (or Sakteng) klippe of the Tethyan Sedimentary Series from underlying high-grade Greater Himalayan rocks. In situ LA-ICPMS U-Th-Pb analysis of metamorphic monazite from the immediate footwall and hanging wall of the STD within the shear zone at the base of the klippe, constrains north vergent normal shear to between 25 and 20 Ma. Coeval thrusting on the Main Central Thrust during this time supports a phase of channel flow-viscous wedge model activity, lasting only ˜3 Ma. Geochronologic data from the eastern Himalaya indicate alternating mechanisms for extrusion of the metamorphic core of the orogen from the Late Oligocene through to the Late Miocene, switching from channel flow-viscous wedge behavior to critical taper-frictional wedge behavior, each phase lasting approximately only 2 to 5 Ma. The tectonic evolution of the eastern Himalaya is comparable to central and western Himalayan tectonics during the Early Miocene, but during the Middle Miocene metamorphism and magmatism in the eastern Himalaya migrated toward the orogenic hinterland, a process not widely documented elsewhere in the Himalaya, thus highlighting the need for an orogenic model in three spatial dimensions.
NASA Astrophysics Data System (ADS)
Chemenda, A. I.; Jorand, C.; Petit, J.; Nguyen, S.
2011-12-01
Dilatancy bands were recently obtained in conventional axisymmetric extension tests on a synthetic physical rock analogue (granular, frictional, cohesive and dilatant) material GRAM1 at a relatively low mean stress σ within range σd < σ < σs , where σd and σs are experimentally constrained values (Chemenda et al., JGR, 2011). The walls of the opened bands have plumose morphology defined by the decohesion pattern of the material within the band, which have a complex 3-D structure. At σ < σd , the sample rupture occurs through mode I cracking and results in smooth fracture surfaces. With σ increase at σ > σs , the bands become inclined to σ1 , resulting in dilatant shear and then in compactive shear bands that have an irregular structure and geometry at a micro-scale. Pure compaction bands were not obtained (at least not evidenced) in the extension tests, but they were generated in the GRAM1 compression tests as previously in the porous rocks. At lower pressure in the compression tests were obtained compactive shear and dilatant shear bands as well as axial splitting fractures that could be originated as dilatancy bands. We also present results from poly-axial tests conducted with material GRAM2 that have slightly different properties than GRAM1. The parallelepiped GRAM2 samples are first subject to the isotropic stress σ0 and then to the uniaxial unloading under plane-strain conditions. At some stage of this process, the sample loses stability and is affected by regular networks of localization bands/fractures whose spacing depends on the loading conditions. The band type changes with the initial mean stress σ0 in the same way as in the above axisymmetric tests where normally only one band is formed. The angle ψ between the bands and σ1 direction continuously increases with σ0 . At sufficiently low σ0 , ψ = 0, which corresponds to the dilatancy bands. Their borders bear plumose features very similar to those on natural joint surfaces. Different
Fan, Quan-Yong; Yang, Guang-Hong
2016-01-01
This paper is concerned with the problem of integral sliding-mode control for a class of nonlinear systems with input disturbances and unknown nonlinear terms through the adaptive actor-critic (AC) control method. The main objective is to design a sliding-mode control methodology based on the adaptive dynamic programming (ADP) method, so that the closed-loop system with time-varying disturbances is stable and the nearly optimal performance of the sliding-mode dynamics can be guaranteed. In the first step, a neural network (NN)-based observer and a disturbance observer are designed to approximate the unknown nonlinear terms and estimate the input disturbances, respectively. Based on the NN approximations and disturbance estimations, the discontinuous part of the sliding-mode control is constructed to eliminate the effect of the disturbances and attain the expected equivalent sliding-mode dynamics. Then, the ADP method with AC structure is presented to learn the optimal control for the sliding-mode dynamics online. Reconstructed tuning laws are developed to guarantee the stability of the sliding-mode dynamics and the convergence of the weights of critic and actor NNs. Finally, the simulation results are presented to illustrate the effectiveness of the proposed method.
NASA Astrophysics Data System (ADS)
Mullin, Daniel Richard
2013-09-01
The majority of space programs whether manned or unmanned for science or exploration require that a Failure Modes Effects and Criticality Analysis (FMECA) be performed as part of their safety and reliability activities. This comes as no surprise given that FMECAs have been an integral part of the reliability engineer's toolkit since the 1950s. The reasons for performing a FMECA are well known including fleshing out system single point failures, system hazards and critical components and functions. However, in the author's ten years' experience as a space systems safety and reliability engineer, findings demonstrate that the FMECA is often performed as an afterthought, simply to meet contract deliverable requirements and is often started long after the system requirements allocation and preliminary design have been completed. There are also important qualitative and quantitative components often missing which can provide useful data to all of project stakeholders. These include; probability of occurrence, probability of detection, time to effect and time to detect and, finally, the Risk Priority Number. This is unfortunate as the FMECA is a powerful system design tool that when used effectively, can help optimize system function while minimizing the risk of failure. When performed as early as possible in conjunction with writing the top level system requirements, the FMECA can provide instant feedback on the viability of the requirements while providing a valuable sanity check early in the design process. It can indicate which areas of the system will require redundancy and which areas are inherently the most risky from the onset. Based on historical and practical examples, it is this author's contention that FMECAs are an immense source of important information for all involved stakeholders in a given project and can provide several benefits including, efficient project management with respect to cost and schedule, system engineering and requirements management
NASA Astrophysics Data System (ADS)
Rost, J. C.; Porkolab, M.; Dorris, J. R.; Marinoni, A.; Burrell, K. H.
2012-10-01
The Phase Contrast Imaging (PCI) diagnostic on DIII-D provides a line-integrated measurement of density fluctuations covering wavenumbers 2 to 30 cm-1. An outer gap scan during QH-mode with stationary plasma parameters allowed the PCI to sample a large range in kr/kθ. A narrow peak in turbulence amplitude is seen near the LCFS. The ExB Doppler shift allows the location to be determined precisely, showing two distinct regions of turbulence at 0.5 and 0.2 cm inside the LCFS with kr>0 and kr<0 respectively, consistent with the expected effects of shear in the Er well. PCI measurements at 200 kHz show that kθ=0.8 cm-1 with poloidal correlation length Lθ=6 cm. Using a simple non-isotropic turbulence model, we find that kr=3 cm-1 and Lr=0.5 cm, with n/n˜25% in the pedestal for this high-kr turbulence. These fluctuations, which are outside the parameter range accessible to most turbulence diagnostics, are large enough in amplitude to play a role in setting the pedestal structure. These PCI observations are qualitatively similar to those made in ELM-free H-mode and between ELMs suggesting that similar large kr turbulence may be important.
Coles, Garill A.; Fuller, Becky; Nordquist, Kathleen; Kongslie, Anita
2005-03-01
The staff at three Washington State hospitals and Battelle Pacific Northwest Division have been collaborating to apply Failure Mode Effects and Criticality Analysis (FMECA) to assess several hospital processes. The staff from Kadlec Medical Center (KMC), located in Richland, Washington; Kennewick General Hospital (KGH), located in Kennewick, Washington; and Lourdes Medical Center (LMC), located in Pasco, Washington, along with staff from Battelle, which is located in Richland, Washington have been working together successfully for two and a half years. Tri-Cities Shared Services, a local organization which implements shared hospital services, has provided the forum for joint activity. This effort was initiated in response to the new JCAHO patient safety standards implemented in July 2001, and the hospitals’ desire to be more proactive in improving patient safety. As a result of performing FMECAs the weaknesses of six medical processes have been characterized and corresponding system improvements implemented. Based on this collective experience, insights about the benefits of applying FMECAs to healthcare processes have been identified.
A study of self organized criticality in ion temperature gradient mode driven gyrokinetic turbulence
Mavridis, M.; Isliker, H.; Vlahos, L.; Görler, T.; Jenko, F.; Told, D.
2014-10-15
An investigation on the characteristics of self organized criticality (Soc) in ITG mode driven turbulence is made, with the use of various statistical tools (histograms, power spectra, Hurst exponents estimated with the rescaled range analysis, and the structure function method). For this purpose, local non-linear gyrokinetic simulations of the cyclone base case scenario are performed with the GENE software package. Although most authors concentrate on global simulations, which seem to be a better choice for such an investigation, we use local simulations in an attempt to study the locally underlying mechanisms of Soc. We also study the structural properties of radially extended structures, with several tools (fractal dimension estimate, cluster analysis, and two dimensional autocorrelation function), in order to explore whether they can be characterized as avalanches. We find that, for large enough driving temperature gradients, the local simulations exhibit most of the features of Soc, with the exception of the probability distribution of observables, which show a tail, yet they are not of power-law form. The radial structures have the same radial extent at all temperature gradients examined; radial motion (transport) though appears only at large temperature gradients, in which case the radial structures can be interpreted as avalanches.
Isliker, H.; Pisokas, Th.; Vlahos, L.; Strintzi, D.
2010-08-15
A new self-organized criticality (SOC) model is introduced in the form of a cellular automaton (CA) for ion temperature gradient (ITG) mode driven turbulence in fusion plasmas. Main characteristics of the model are that it is constructed in terms of the actual physical variable, the ion temperature, and that the temporal evolution of the CA, which necessarily is in the form of rules, mimics actual physical processes as they are considered to be active in the system, i.e., a heating process and a local diffusive process that sets on if a threshold in the normalized ITG R/L{sub T} is exceeded. The model reaches the SOC state and yields ion temperature profiles of exponential shape, which exhibit very high stiffness, in that they basically are independent of the loading pattern applied. This implies that there is anomalous heat transport present in the system, despite the fact that diffusion at the local level is imposed to be of a normal kind. The distributions of the heat fluxes in the system and of the heat out-fluxes are of power-law shape. The basic properties of the model are in good qualitative agreement with experimental results.
Nonlinear Upshift of Trapped Electron Mode Critical Density Gradient: Simulation and Experiment
NASA Astrophysics Data System (ADS)
Ernst, D. R.
2012-10-01
A new nonlinear critical density gradient for pure trapped electron mode (TEM) turbulence increases strongly with collisionality, saturating at several times the linear threshold. The nonlinear TEM threshold appears to limit the density gradient in new experiments subjecting Alcator C-Mod internal transport barriers to modulated radio-frequency heating. Gyrokinetic simulations show the nonlinear upshift of the TEM critical density gradient is associated with long-lived zonal flow dominated states [1]. This introduces a strong temperature dependence that allows external RF heating to control TEM turbulent transport. During pulsed on-axis heating of ITB discharges, core electron temperature modulations of 50% were produced. Bursts of line-integrated density fluctuations, observed on phase contrast imaging, closely follow modulations of core electron temperature inside the ITB foot. Multiple edge fluctuation measurements show the edge response to modulated heating is out of phase with the core response. A new limit cycle stability diagram shows the density gradient appears to be clamped during on-axis heating by the nonlinear TEM critical density gradient, rather than by the much lower linear threshold. Fluctuation wavelength spectra will be quantitatively compared with nonlinear TRINITY/GS2 gyrokinetic transport simulations, using an improved synthetic diagnostic. In related work, we are implementing the first gyrokinetic exact linearized Fokker Planck collision operator [2]. Initial results show short wavelength TEMs are fully stabilized by finite-gyroradius collisional effects for realistic collisionalities. The nonlinear TEM threshold and its collisionality dependence may impact predictions of density peaking based on quasilinear theory, which excludes zonal flows.[4pt] In collaboration with M. Churchill, A. Dominguez, C. L. Fiore, Y. Podpaly, M. L. Reinke, J. Rice, J. L. Terry, N. Tsujii, M. A. Barnes, I. Bespamyatnov, R. Granetz, M. Greenwald, A. Hubbard, J. W
Zeng, Zhou; Ren, Bo; Gai, Linlin; Zhao, Xiangyong; Luo, Haosu; Wang, Dong
2016-08-01
Energy harvesting from external mechanical excitation has become a hot interest area, and relaxor piezoelectric single crystal ( 1 - x )Pb(Mg1/3Nb2/3)O3- x PbTiO3 (PMN- x PT or PMN-PT) has attracted continuous attention due to the well-known ultrahigh shear-mode electromechanical response. To exploit the low-frequency application of excellent shear-mode performance of the PMN-PT single crystal, we proposed a Shear-mode-based CANtilever Driving Low-frequency Energy harvester. The device is composed of two symmetrically assembled sandwich structures and a cantilever, in which sandwich structures can be driven by the cantilever. An analytical method was used to illustrate the high output mechanism, and a finite-element method model of the device was also established to optimize the generated electric energy in this device. The electrical properties of the device under different excitation frequencies and load resistances were studied systematically. The maximum voltage and power density at resonance frequency (43.8 Hz) were measured to be 60.8 V and 10.8 mW/cm(3) under a proof mass of 13.5 g, respectively. Both theoretical and experimental results demonstrate the considerable potential of the resonance-excited shear-mode energy harvester applied to wireless sensors and low-power portable electronics.
Knarr, Matthias; Bayer, Roland
2014-10-13
The gelation temperature of methylcellulose (MC) in aqueous solutions as well as in aqueous ceramic paste depends on the applied shear. Rheological investigations in oscillation vs. shear mode show lower gelation temperature at low shear rates as for the corresponding angular frequencies. Above a critical shear rate the gelation temperature is shifted to higher temperatures. The paste extrusion process uses MC as a plasticizer and runs under high shear conditions. When extruding close to the gelation temperature of the MC in the paste, crack formation and other defects can occur. The upwards shift of the gelation temperature with increasing applied shear gives a larger temperature window during the extrusion process. The understanding of the shear influence on the gelation temperature is important to design the optimal process conditions. Copyright © 2014 Elsevier Ltd. All rights reserved.
Shear-banding Induced Indentation Size Effect in Metallic Glasses
Lu, Y. M.; Sun, B. A.; Zhao, L. Z.; Wang, W. H.; Pan, M. X.; Liu, C. T.; Yang, Y.
2016-01-01
Shear-banding is commonly regarded as the “plasticity carrier” of metallic glasses (MGs), which usually causes severe strain localization and catastrophic failure if unhindered. However, through the use of the high-throughput dynamic nanoindentation technique, here we reveal that nano-scale shear-banding in different MGs evolves from a “distributed” fashion to a “localized” mode when the resultant plastic flow extends over a critical length scale. Consequently, a pronounced indentation size effect arises from the distributed shear-banding but vanishes when shear-banding becomes localized. Based on the critical length scales obtained for a variety of MGs, we unveil an intrinsic interplay between elasticity and fragility that governs the nanoscale plasticity transition in MGs. Our current findings provide a quantitative insight into the indentation size effect and transition mechanisms of nano-scale plasticity in MGs. PMID:27324835
Ergezen, E; Hong, S; Barbee, K A; Lec, R
2007-04-15
The effects of Heparan Sulfate Proteoglycan (HSPG) and surface charge on the cellular interactions of the cell membrane with different substrates to determine the kinetics of cell adhesion was studied using thickness shear mode (TSM) sensor. The TSM sensor was operated at its first, third, fifth and seventh harmonics. Since the penetration depth of the shear wave decreases with increases in frequency, the multi-resonance operation of the TSM sensor was used to monitor the changes in the kinetics of the cell-substrate interaction at different distances from the sensor surface. During the sedimentation and the initial attachment of the cells on the sensor surface, the changes in the sensor resonant frequency and the magnitude response were monitored. First, HSPGs were partially digested with the enzyme Heparinase III to evaluate the effect of HSPG on the cell adhesion process. The results indicated that HSPG did not have any effect on the kinetics of the initial attachment, but it did reduce the strength of steady-state cell adhesion. Next, we investigated the effect of the electrostatic interactions of the cell membrane with the substrate on the cell adhesion. In this case, the sensor surface was coated with positively charged Poly-D-Lysine (PDL). It was observed that electrostatic interaction of the negatively charged cell membrane with the PDL surface promoted the initial cell adhesion but did not support long-term cell adhesion. The multi-resonant TSM technique was shown to be a very promising method for monitoring specific interfacial effects involving in cell adhesion process in real-time.
NASA Astrophysics Data System (ADS)
Madraki, Fatemeh; Hormozi, Sarah; Ovarlez, Guillaume; Guazzelli, Elisabeth; Pouliquen, Olivier
2016-11-01
A cornstarch suspension is the quintessential particulate system that exhibits shear thickening. By adding large non-Brownian spheres to a cornstarch suspension, we show that shear thickening can be significantly enhanced. More precisely, the shear thickening transition is found to be increasingly shifted to lower critical shear rates. This enhancement is found to be mainly controlled by the concentration of the large particles. ANR(ANR-13-IS09-0005-01), ANR(ANR-11-LABX-0092), MIDEX (ANR-11-IDEX-0001-02), NSF (CBET-1554044-CAREER).
NASA Astrophysics Data System (ADS)
James, E.; Dalton, C. A.; Gaherty, J. B.
2014-12-01
We investigate the three-dimensional (3-D) shear-velocity structure of the upper mantle beneath the Atlantic Ocean. Phase velocity in the period range 30-130 seconds is measured for approximately 10,000 fundamental-mode Rayleigh waves traversing the Atlantic basin. In order to isolate the signal of the oceanic upper mantle, paths with >30% of their length through continental upper mantle are excluded. The lateral distribution of Rayleigh wave phase velocity in the Atlantic upper mantle is explored with two approaches. One, phase velocity is allowed to vary only as a function of seafloor age. Two, a general two-dimensional parameterization is utilized in order to capture perturbations to age-dependent structure. In both scenarios, phase velocity shows a strong dependence on seafloor age at all periods, with higher velocity associated with older seafloor. Removing age-dependent velocity from the 2-D phase-velocity maps highlights areas of anomalously low velocity, almost all of which are proximal to locations of hotspot volcanism. The age-dependent phase velocities for the Atlantic are not consistent with a half-space cooling model and are best explained by a plate cooling model with thickness of 75 km and mantle temperature of 1400oC. In contrast, age-dependent phase velocities for the Pacific basin determined by Nishimura and Forsyth [1989] can be fit reasonably well by a half-space cooling model with mantle temperature approximately 50oC warmer than the Atlantic. Comparison of Rayleigh wave phase velocity and fractionation-corrected Na concentrations in mid-ocean-ridge basalts erupted at 87 axial ridge segments reveals a positive correlation coefficient that increases with period, as expected if along-ridge variations in mantle potential temperature are controlling both quantities. Depth-dependent variations in vertically-polarized shear velocity are explored with a 3-D model and allow for comparison to previous whole-basin studies of the Atlantic [e.g., Moquet
Hardage, Bob
2013-07-01
This 3-year project was terminated at the end of Year 1 because the DOE Geothermal project-evaluation committee decided one Milestone was not met and also concluded that our technology would not be successful. The Review Panel recommended a ?no-go? decision be implemented by DOE. The Principal Investigator and his research team disagreed with the conclusions reached by the DOE evaluation committee and wrote a scientifically based rebuttal to the erroneous claims made by the evaluators. We were not told if our arguments were presented to the people who evaluated our work and made the ?no-go? decision. Whatever the case regarding the information we supplied in rebuttal, we received an official letter from Laura Merrick, Contracting Officer at the Golden Field Office, dated June 11, 2013 in which we were informed that project funding would cease and instructed us to prepare a final report before September 5, 2013. In spite of the rebuttal arguments we presented to DOE, this official letter repeated the conclusions of the Review Panel that we had already proven to be incorrect. This is the final report that we are expected to deliver. The theme of this report will be another rebuttal of the technical deficiencies claimed by the DOE Geothermal Review Panel about the value and accomplishments of the work we did in Phase 1 of the project. The material in this report will present images made from direct-S modes produced by vertical-force sources using the software and research findings we developed in Phase 1 that the DOE Review Panel said would not be successful. We made these images in great haste when we were informed that DOE Geothermal rejected our rebuttal arguments and still regarded our technical work to be substandard. We thought it was more important to respond quickly rather than to take additional time to create better quality images than what we present in this Final Report.
NASA Astrophysics Data System (ADS)
Moulik, P.; Ekström, G.
2014-12-01
We use normal-mode splitting functions in addition to surface wave phase anomalies, body wave traveltimes and long-period waveforms to construct a 3-D model of anisotropic shear wave velocity in the Earth's mantle. Our modelling approach inverts for mantle velocity and anisotropy as well as transition-zone discontinuity topographies, and incorporates new crustal corrections for the splitting functions that are consistent with the non-linear corrections we employ for the waveforms. Our preferred anisotropic model, S362ANI+M, is an update to the earlier model S362ANI, which did not include normal-mode splitting functions in its derivation. The new model has stronger isotropic velocity anomalies in the transition zone and slightly smaller anomalies in the lowermost mantle, as compared with S362ANI. The differences in the mid- to lowermost mantle are primarily restricted to features in the Southern Hemisphere. We compare the isotropic part of S362ANI+M with other recent global tomographic models and show that the level of agreement is higher now than in the earlier generation of models, especially in the transition zone and the lower mantle. The anisotropic part of S362ANI+M is restricted to the upper 300 km in the mantle and is similar to S362ANI. When radial anisotropy is allowed throughout the mantle, large-scale anisotropic patterns are observed in the lowermost mantle with vSV > vSH beneath Africa and South Pacific and vSH > vSV beneath several circum-Pacific regions. The transition zone exhibits localized anisotropic anomalies of ˜3 per cent vSH > vSV beneath North America and the Northwest Pacific and ˜2 per cent vSV > vSH beneath South America. However, small improvements in fits to the data on adding anisotropy at depth leave the question open on whether large-scale radial anisotropy is required in the transition zone and in the lower mantle. We demonstrate the potential of mode-splitting data in reducing the trade-offs between isotropic velocity and
Simon, Andrew; Thorne, Colin R.
1996-01-01
Channel adjustments in the North Fork Toutle River and the Toutle River main stem were initiated by deposition of a 2.5km3 debris avalanche and associated lahars that accompanied the catastrophic eruption of Mount St. Helens, Washington on 18 May 1980. Channel widening was the dominant process. In combination, adjustments caused average boundary shear stress to decrease non-linearly with time and critical shear stress to increase non-linearly with time. At the discharge that is equalled or exceeded 1 per cent of the time, these trends converged by 1991-1992 so that excess shear stress approached minimum values. Extremal hypotheses, such as minimization of unit stream power and minimization of the rate of energy dissipation (minimum stream power), are shown to be applicable to dynamic adjustments of the Toutle River system. Maximization of the Darcy-Weisbach friction factor did not occur, but increases in relative bed roughness, caused by the concomitant reduction in hydraulic depths and bed-material coarsening, were documented. Predictions of stable channel geometries using the minimum stream power approach were unsuccessful when compared to the 1991-1992 geometries and bed-material characteristics measured in the field. It is concluded that the predictions are not applicable because the study reaches are not truly stable and cannot become so until a new floodplain has been formed by renewed channel incision, retreat of stream-side hummocks, and establishment of riparian vegetation to limit the destabilizing effects of large floods. Further, prediction of energy slope (and consequently stream power) by the sediment transport equations is inaccurate because of the inability of the equations to account for significant contributions of finer grained (sand and gravel) bank materials (relative to the coarsened channel bed) from bank retreat and from upstream terrace erosion.
NASA Astrophysics Data System (ADS)
La Haye, R. J.; Petty, C. C.; Strait, E. J.
2000-10-01
While m/n=3/2 NTMs have been observed and studied in detail,(R.J. La Haye et al.), to be in the August 2000 Phys. Plasmas. their consequences are small compared to the m/n=2/1 mode which tends to lock, destroy the H-Mode and cause disruption. The 2/1 modes in DIII-D H-Mode discharges appear to be NTMs in that they are excited as beta is rising, are triggered by a sawtooth crash, ELM or both and have a nearly linear critical beta with rhoistar (the ion gyroradius normalized to the plasma minor radius). Analysis of a 2/1 database in DIII-D will be presented. Preliminary comparison to the polarization/ inertial theory,(H.R. Wilson et al.), Phys. Plasmas 3, 248 (1996). particularly of the key issue of island propagation in the local (q=2) E_r=0 quasi-neutrality frame, shows consistency with a stabilizing effect, i.e., a threshold.
NASA Astrophysics Data System (ADS)
Okamoto, Norihiko L.; Fujimoto, Shu; Kambara, Yuki; Kawamura, Marino; Chen, Zhenghao M. T.; Matsunoshita, Hirotaka; Tanaka, Katsushi; Inui, Haruyuki; George, Easo P.
2016-10-01
High-entropy alloys (HEAs) comprise a novel class of scientifically and technologically interesting materials. Among these, equatomic CrMnFeCoNi with the face-centered cubic (FCC) structure is noteworthy because its ductility and strength increase with decreasing temperature while maintaining outstanding fracture toughness at cryogenic temperatures. Here we report for the first time by single-crystal micropillar compression that its bulk room temperature critical resolved shear stress (CRSS) is ~33–43 MPa, ~10 times higher than that of pure nickel. CRSS depends on pillar size with an inverse power-law scaling exponent of –0.63 independent of orientation. Planar ½ < 110 > {111} dislocations dissociate into Shockley partials whose separations range from ~3.5–4.5 nm near the screw orientation to ~5–8 nm near the edge, yielding a stacking fault energy of 30 ± 5 mJ/m2. Dislocations are smoothly curved without any preferred line orientation indicating no significant anisotropy in mobilities of edge and screw segments. The shear-modulus-normalized CRSS of the HEA is not exceptionally high compared to those of certain concentrated binary FCC solid solutions. Its rough magnitude calculated using the Fleischer/Labusch models corresponds to that of a hypothetical binary with the elastic constants of our HEA, solute concentrations of 20–50 at.%, and atomic size misfit of ~4%.
Okamoto, Norihiko L; Fujimoto, Shu; Kambara, Yuki; Kawamura, Marino; Chen, Zhenghao M T; Matsunoshita, Hirotaka; Tanaka, Katsushi; Inui, Haruyuki; George, Easo P
2016-10-24
High-entropy alloys (HEAs) comprise a novel class of scientifically and technologically interesting materials. Among these, equatomic CrMnFeCoNi with the face-centered cubic (FCC) structure is noteworthy because its ductility and strength increase with decreasing temperature while maintaining outstanding fracture toughness at cryogenic temperatures. Here we report for the first time by single-crystal micropillar compression that its bulk room temperature critical resolved shear stress (CRSS) is ~33-43 MPa, ~10 times higher than that of pure nickel. CRSS depends on pillar size with an inverse power-law scaling exponent of -0.63 independent of orientation. Planar ½ < 110 > {111} dislocations dissociate into Shockley partials whose separations range from ~3.5-4.5 nm near the screw orientation to ~5-8 nm near the edge, yielding a stacking fault energy of 30 ± 5 mJ/m(2). Dislocations are smoothly curved without any preferred line orientation indicating no significant anisotropy in mobilities of edge and screw segments. The shear-modulus-normalized CRSS of the HEA is not exceptionally high compared to those of certain concentrated binary FCC solid solutions. Its rough magnitude calculated using the Fleischer/Labusch models corresponds to that of a hypothetical binary with the elastic constants of our HEA, solute concentrations of 20-50 at.%, and atomic size misfit of ~4%.
Okamoto, Norihiko L.; Fujimoto, Shu; Kambara, Yuki; Kawamura, Marino; Chen, Zhenghao M. T.; Matsunoshita, Hirotaka; Tanaka, Katsushi; Inui, Haruyuki; George, Easo P.
2016-01-01
High-entropy alloys (HEAs) comprise a novel class of scientifically and technologically interesting materials. Among these, equatomic CrMnFeCoNi with the face-centered cubic (FCC) structure is noteworthy because its ductility and strength increase with decreasing temperature while maintaining outstanding fracture toughness at cryogenic temperatures. Here we report for the first time by single-crystal micropillar compression that its bulk room temperature critical resolved shear stress (CRSS) is ~33–43 MPa, ~10 times higher than that of pure nickel. CRSS depends on pillar size with an inverse power-law scaling exponent of –0.63 independent of orientation. Planar ½ < 110 > {111} dislocations dissociate into Shockley partials whose separations range from ~3.5–4.5 nm near the screw orientation to ~5–8 nm near the edge, yielding a stacking fault energy of 30 ± 5 mJ/m2. Dislocations are smoothly curved without any preferred line orientation indicating no significant anisotropy in mobilities of edge and screw segments. The shear-modulus-normalized CRSS of the HEA is not exceptionally high compared to those of certain concentrated binary FCC solid solutions. Its rough magnitude calculated using the Fleischer/Labusch models corresponds to that of a hypothetical binary with the elastic constants of our HEA, solute concentrations of 20–50 at.%, and atomic size misfit of ~4%. PMID:27775026
NASA Astrophysics Data System (ADS)
Antonov, N. V.; Ignatieva, A. A.
2006-11-01
Critical behaviour of a fluid (binary mixture or liquid crystal), subjected to strongly anisotropic turbulent mixing, is studied by means of the field theoretic renormalization group. As a simplified model, relaxational stochastic dynamics of a non-conserved scalar order parameter, coupled to a random velocity field with prescribed statistics, is considered. The velocity is taken Gaussian, white in time, with a correlation function of the form ~δ(t - t')/|kbottom|d+ξ, where kbottom is the component of the wave vector, perpendicular to the distinguished direction ('direction of the flow')—the d-dimensional generalization of the ensemble introduced by Avellaneda and Majda (1990 Commun. Math. Phys. 131 381) within the context of passive scalar advection. It is shown that, depending on the relation between the exponent ξ and the space dimensionality d, the system exhibits various types of large-scale self-similar behaviour, associated with different infrared attractive fixed points of the renormalization group equations. In addition to well-known asymptotic regimes (model A of equilibrium critical dynamics and a passively advected scalar with no self-interaction), the existence of a new, non-equilibrium and strongly anisotropic type of critical behaviour (universality class) is established, and the corresponding critical dimensions are calculated to the second order of the double expansion in ξ and ɛ = 4 - d (two-loop approximation). The most realistic values of the model parameters (for example, d = 3 and the Kolmogorov exponent ξ = 4/3) belong to this class. The scaling behaviour appears anisotropic in the sense that the critical dimensions related to the directions parallel and perpendicular to the flow are essentially different. The results are in qualitative agreement with the results, obtained in experiments and simulations of fluid systems subjected to various kinds of regular and chaotic anisotropic flows.
Linear Feedback Stabilization of Nonlinear Systems with an Uncontrollable Critical Mode
1992-11-17
mode that is uncontrollable. The results complement previous work on the synthesis of nonlinear stabilizing control laws. The present work addresses...analysis and stabilizing control design employ results on stability of bifurcations of parametrized systems.
Composite Interlaminar Shear Fracture Toughness, G(sub 2c): Shear Measurement of Sheer Myth?
NASA Technical Reports Server (NTRS)
OBrien, T. Kevin
1997-01-01
The concept of G2c as a measure of the interlaminar shear fracture toughness of a composite material is critically examined. In particular, it is argued that the apparent G2c as typically measured is inconsistent with the original definition of shear fracture. It is shown that interlaminar shear failure actually consists of tension failures in the resin rich layers between plies followed by the coalescence of ligaments created by these failures and not the sliding of two planes relative to one another that is assumed in fracture mechanics theory. Several strain energy release rate solutions are reviewed for delamination in composite laminates and structural components where failures have been experimentally documented. Failures typically occur at a location where the mode 1 component accounts for at least one half of the total G at failure. Hence, it is the mode I and mixed-mode interlaminar fracture toughness data that will be most useful in predicting delamination failure in composite components in service. Although apparent G2c measurements may prove useful for completeness of generating mixed-mode criteria, the accuracy of these measurements may have very little influence on the prediction of mixed-mode failures in most structural components.
Federspiel, L.; Labit, B.; Ricci, P.; Fasoli, A.; Furno, I.; Theiler, C.
2009-09-15
The existence of a critical pressure gradient needed to drive the interchange instability is experimentally demonstrated in the simple magnetized torus TORoidal Plasma EXperiment [A. Fasoli et al., Phys. Plasmas 13, 055902 (2006)]. This gradient is reached during a scan in the neutral gas pressure p{sub n}. Around a critical value for p{sub n}, depending on the magnetic configuration and on the injected rf power, a small increase in the neutral gas pressure triggers a transition in the plasma behavior. The pressure profile is locally flattened, stabilizing the interchange mode observed at lower neutral gas densities. The measured value for the critical gradient is close to the linear theory estimate.
Multi Resonance Shear Mode Transducers
2016-11-21
1 ~~ 140 Q,j @ Oil> t:-:0! ..... Q.. 130 - = ~-: .-::: ~ 120 • ALUMINUM1 6::!- "’ D TUNGSTEN = • Alumina eo : 110 ~ • PIN241ow I ~ f-J...ALUMINUM1 ..... = 120 8::!. D TUNGSTEN "’ = eo : 11 0 • Alumina ’"’ ~ • PIN24 1ow 100 0 5 10 15 20 25 30 Frequency (kHz) Figure 15...ALUMINUM1 s:::. "’ • PIN24 LOWK SH = eo :: ~ 100 ~ l/ ’I\\ N I~ .... ’¥ ___.1’ I I I 90 l 0 5 10 15 20 25 30 35 Frequency (kHz) Figure 21
NASA Astrophysics Data System (ADS)
Callahan, R. P.; Taylor, N. J.; Pasquet, S.; Dueker, K. G.; Riebe, C. S.; Holbrook, W. S.
2016-12-01
Geophysical imaging is rapidly becoming popular for quantifying subsurface critical zone (CZ) architecture. However, a diverse array of measurements and measurement techniques are available, raising the question of which are appropriate for specific study goals. Here we compare two techniques for measuring S-wave velocities (Vs) in the near surface. The first approach quantifies Vs in three dimensions using a passive source and an iterative residual least-squares tomographic inversion. The second approach uses a more traditional active-source seismic survey to quantify Vs in two dimensions via a Monte Carlo surface-wave dispersion inversion. Our analysis focuses on three 0.01 km2 study plots on weathered granitic bedrock in the Southern Sierra Critical Zone Observatory. Preliminary results indicate that depth-averaged velocities from the two methods agree over the scales of resolution of the techniques. While the passive- and active-source techniques both quantify Vs, each method has distinct advantages and disadvantages during data acquisition and analysis. The passive-source method has the advantage of generating a three dimensional distribution of subsurface Vs structure across a broad area. Because this method relies on the ambient seismic field as a source, which varies unpredictably across space and time, data quality and depth of investigation are outside the control of the user. Meanwhile, traditional active-source surveys can be designed around a desired depth of investigation. However, they only generate a two dimensional image of Vs structure. Whereas traditional active-source surveys can be inverted quickly on a personal computer in the field, passive source surveys require significantly more computations, and are best conducted in a high-performance computing environment. We use data from our study sites to compare these methods across different scales and to explore how these methods can be used to better understand subsurface CZ architecture.
May, Lennart; Granhag, Pär Anders; Tekin, Serra
2017-01-01
This study examines how different evidence disclosure modes affect the elicitation of new critical information. Two modes derived from the Strategic Use of Evidence (SUE) framework were compared against an early disclosure mode (i.e., the evidence was disclosed at the outset of the interview). Participants (N = 88) performed a mock crime consisting of several actions before they were interviewed as suspects. In both SUE conditions the interviewer elicited and disclosed statement-evidence inconsistencies in two phases after an introductory phase. For the SUE-Confrontation (SUE-C) condition, the interview was introduced in a business-like manner, and the interviewer confronted the suspects with the in/consistencies without giving them a chance to comment on these. For the SUE-Introduce-Present-Respond (SUE-IPR) condition, the interviewer introduced the interview in a non-guilt-presumptive way, presented the in/consistencies and allowed the suspects to comment on these, and then responded to their comments; at all times in a non-judgmental manner. Both SUE conditions generated comparatively more statement-evidence inconsistencies. The SUE-IPR condition resulted in more new critical information about the phase of the crime for which the interviewer lacked information, compared to the Early disclosure condition. A likely explanation for this was that (for the SUE-IPR condition) the interviewer used the inconsistencies to create a fostering interview atmosphere and made the suspects overestimate the interviewer's knowledge about the critical phase of the crime. In essence, this study shows that in order to win the game (i.e., obtaining new critical information), the interviewer needs to keep the suspect in the game (i.e., by not being too confrontational and judgmental). PMID:28769829
A Critical Review of Mode of Action (MOA) Assignment Classifications for Ecotoxicology
There are various structure-based classification schemes to categorize chemicals based on mode of action (MOA) which have been applied for both eco and human health toxicology. With increasing calls to assess thousands of chemicals, some of which have little available informatio...
A Critical Review of Mode of Action (MOA) Assignment Classifications for Ecotoxicology
There are various structure-based classification schemes to categorize chemicals based on mode of action (MOA) which have been applied for both eco and human health toxicology. With increasing calls to assess thousands of chemicals, some of which have little available informatio...
Wave propagation in carbon nanotubes under shear deformation
NASA Astrophysics Data System (ADS)
Dong, K.; Wang, X.
2006-06-01
This paper reports the results of an investigation on the effect of shear deformations on wave propagation in carbon nanotubes embedded in an elastic matrix. A multi-walled carbon nanotube is considered as a multiple shell coupled together through van der Waals forces between two adjacent tubes. The surrounding matrix is considered as a spring element defined by the Winkler model. Using the variational calculus of Hamilton's principle, dynamic governing equations considering the shear deformation and rotary inertia terms are derived. Numerical examples describe the effects of shear deformation, rotary inertia and elastic matrix on the velocity, the critical frequency, the cut-off frequency and the amplitude ratio of wave propagation in multi-walled carbon nanotubes embedded in an elastic matrix, respectively. The results obtained show that wave propagation in carbon nanotubes appears in a critical frequency or a cut-off frequency for different wave modes; the effect of shear deformation decreases the value of critical frequency; the critical frequency increases as the matrix stiffness increases; the inertia rotary has an obvious influence on the wave velocity for some wave modes in the higher frequency region.
NASA Astrophysics Data System (ADS)
Rose, F.; Léonard, F.; Dupuis, N.
2015-06-01
We study the "Higgs" amplitude mode in the relativistic quantum O (N ) model in two space dimensions. Using the nonperturbative renormalization group and the Blaizot-Méndez-Galain-Wschebor approximation (which we generalize to compute four-point correlation functions), we compute the O (N ) -invariant scalar susceptibility at zero temperature in the vicinity of the quantum critical point. In the ordered phase, we find a well-defined Higgs resonance for N =2 and 3 and determine its universal properties. No resonance is found for N ≥4 . In the disordered phase, the spectral function exhibits a threshold behavior with no Higgs-like peak. We also show that for N =2 , the Higgs mode manifests itself as a very broad peak in the longitudinal susceptibility in spite of the infrared divergence of the latter. We compare our findings with results from quantum Monte Carlo simulations and ɛ =4 -(d +1 ) expansion near d =3 .
Rosakis, A.J.
1995-12-31
The phenomenon of dynamic initiation and propagation of two-dimensional adiabatic shear bands is experimentally and numerically investigated. Prenotched metal plates are subjected to asymmetric impact load histories (dynamic mode-II loading). Dynamic shear bands emanate from the notch-tip and propagate rapidly in a direction nearly parallel to the direction of impact. Real time temperature histories along a line intersecting and perpendicular to the shear band paths are recorded by means of a high speed infrared detector system. The materials studied are C-300 (a maraging steel), HY-100 steel and Ti-6Al-4V. Experiments show that the peak temperatures inside the propagating shear bands are approaching 90% of the melting point for C-300 and are significantly lower for the titanium alloy (up to 6000C). Additionally, measured distances of shear band propagation indicate stronger resistance to shear banding by HY-100 steel and Ti-6Al-4V. Deformation fields around the propagating shear band are recorded using high speed photography. Shear band speeds are found to strongly depend on impact velocity are as high as 1200 m/s for C-300 steel. Finite element simulations of the experiment are carried out under the context of plane strain, considering finite deformations, inertia, heat conduction, thermal softening, strain hardening and strain-rate hardening. In the simulations, the shear band propagation is assumed to be governed by a critical plastic strain criterion. The results are compared with experimental measurements obtained using the high speed infrared detectors and high speed photography. Finally, the numerical calculations are used to investigate motions of shear band toughness. The shear band driving force is calculated as a function of shear band velocity and compared to the crack driving force versus velocity relations for mode-I, opening cracks in the same material.
Meek, M E Bette; Klaunig, James E
2010-03-19
Mode of action is defined as a series of key biological events leading to an observed toxicological effect (for example, metabolism to a toxic entity, cell death, regenerative repair and tumors). It contrasts with mechanism of action, which generally involves a detailed understanding of the molecular basis for an effect. A framework to consider the weight of evidence for hypothesized modes of action in animals and their relevance to humans, has been widely adopted and used by government agencies and international organizations. The framework, developed and refined through its application in case studies for principally non-DNA-reactive carcinogens, has more recently been extended to DNA-reactive carcinogens, non-cancer endpoints and different life stages. In addition to increasing transparency, use of the framework promotes consistency in decision-making concerning adequacy of weight of evidence, facilitates peer input and review and identifies critical research needs. The framework provides an effective tool to facilitate discussion between the research and risk assessment communities on critical data gaps, which if filled, would permit more refined estimates of risk. As a basis for additionally coordinating and focusing research on critical data gaps in a risk assessment context, five key events in the mode of action for benzene-induced leukemia are proposed: (1) benzene metabolism via Cytochrome P450, (2) the interaction of benzene metabolites with target cells in the bone marrow, (3) formation of initiated, mutated target cells, (4) selective proliferation of the mutated cells and (5) production of leukemia. These key events are considered in a framework analysis of human relevance as a basis to consider appropriate next steps in developing research strategies.
Arts Activism: Praxis in Social Justice, Critical Discourse, and Radical Modes of Engagement
ERIC Educational Resources Information Center
Frostig, Karen
2011-01-01
How does arts activism relate to concepts of voice, issues of social justice, and ideas about sustainable change and transformative processes? Does arts activism imply a particular set of values? This article describes an arts activism course that is designed to raise critical discourse on these and other questions and to provide a structure for…
NASA Astrophysics Data System (ADS)
Ghose-Hajra, M.; McCorquodale, A.; Mattson, G.; Jerolleman, D.; Filostrat, J.
2015-03-01
Sea-level rise, the increasing number and intensity of storms, oil and groundwater extraction, and coastal land subsidence are putting people and property at risk along Louisiana's coast, with major implications for human safety and economic health of coastal areas. A major goal towards re-establishing a healthy and sustainable coastal ecosystem has been to rebuild Louisiana's disappearing wetlands with fine grained sediments that are dredged or diverted from nearby rivers, channels and lakes to build land in open water areas. A thorough geo-hydrodynamic characterization of the deposited sediments is important in the correct design and a more realistic outcome assessment of the long-term performance measures for ongoing coastal restoration projects. This paper evaluates the effects of salinity and solid particle concentration on the re-suspension characteristics of fine-grained dredged sediments obtained from multiple geographic locations along the Gulf coast. The critical bed-shear-stress for erosion has been evaluated as a function of sedimentation time. The sediment hydrodynamic properties obtained from the laboratory testing were used in a numerical coastal sediment distribution model to aid in evaluating sediment diversions from the Mississippi River into Breton Sound and Barataria Bay.
Shear Yielding and Shear Jamming of Dense Hard Sphere Glasses
NASA Astrophysics Data System (ADS)
Urbani, Pierfrancesco; Zamponi, Francesco
2017-01-01
We investigate the response of dense hard sphere glasses to a shear strain in a wide range of pressures ranging from the glass transition to the infinite-pressure jamming point. The phase diagram in the density-shear strain plane is calculated analytically using the mean-field infinite-dimensional solution. We find that just above the glass transition, the glass generically yields at a finite shear strain. The yielding transition in the mean-field picture is a spinodal point in presence of disorder. At higher densities, instead, we find that the glass generically jams at a finite shear strain: the jamming transition prevents yielding. The shear yielding and shear jamming lines merge in a critical point, close to which the system yields at extremely large shear stress. Around this point, highly nontrivial yielding dynamics, characterized by system-spanning disordered fractures, is expected.
Features of sound propagation through and stability of a finite shear layer
NASA Technical Reports Server (NTRS)
Koutsoyannis, S. P.
1976-01-01
The plane wave propagation, the stability and the rectangular duct mode problems of a compressible inviscid linearly sheared parallel, but otherwise homogeneous flow, are shown to be governed by Whittaker's equation. The exact solutions for the perturbation quantities are essentially Whittaker M-functions. A number of known results are obtained as limiting cases of exact solutions. For the compressible finite thickness shear layer it is shown that no resonances and no critical angles exist for all Mach numbers, frequencies and shear layer velocity profile slopes except in the singular case of the vortex sheet.
Geometric aspects of shear jamming induced by deformation of frictionless sphere packings
NASA Astrophysics Data System (ADS)
Vinutha, H. A.; Sastry, Srikanth
2016-09-01
It has recently been demonstrated that shear deformation of frictionless sphere packings leads to structures that will undergo jamming in the presence of friction, at densities well below the isotropic jamming point {φj}≈ 0.64 , and at high enough strains. Here, we show that the geometric features induced by strain are robust with respect to finite size effects, and include the feature of hyperuniformity, previously studied in the context of jamming, and more recently in driven systems. We study the approach to jamming as strain is increased, by evolving frictionless sheared configurations through frictional dynamics, and thereby identify a critical, or jamming, strain for each density, for a chosen value of the coefficient of friction. In the presence of friction above a certain strain value the sheared frictionless packings begin to develop finite stresses, which marks the onset of shear jamming. At a higher strain value, the shear stress reaches a saturation value after rising rapidly above the onset of shear jamming, which permits identification of the shear jamming transition. The onset of shear jamming and shear jamming are found to occur when the coordination number Z reaches values of Z = 3 and Z = 4 respectively. By considering percolation probabilities for the contact network, clusters of four coordinated and six coordinated spheres, we show that the percolation of four coordinated spheres corresponds to the onset of shear jamming behaviour, whereas the percolation of six coordinated spheres corresponds to shear jamming, for the chosen friction coefficients. At the onset of shear jamming, the force distribution begins to develop a peak at finite value and the force network is anisotropic and heterogeneous. And at the shear jamming transition, the force distribution has a well defined peak close to < f> and the force network is less anisotropic and homogeneous. We briefly discuss mechanical aspects of the jamming behaviour by
Penttinen, O.P.; Kukkonen, J.
1995-12-31
The toxicity of organic chemicals with different mode of toxic action was evaluated by determining their effect on the metabolic rate of two common benthic invertebrates, midge larva (Chironomus riparius) and oligochate worm (Lumbriculus variegatus). The rate of metabolism was monitored by direct microcalorimetry and the change of heat output was related to the body residue of chemicals. The expected response of 2,4,5-trichlorophenol (TCP), known as an uncoupler of oxidative phosphorylation, was an increase of metabolic rate. The animals were exposed 24 h to water spiked with TCP (10 to 1,200 {micro}g/L) and they received the body residues of TCP in the range of 8.8 to 336 {micro}g/g wet wt (0.04 to 1.75 {micro}mol/g). The threshold concentration was 0.7 {micro}mol/g wet wt. (C. riparius) or 1.0 {micro}mol/g wet wt. (L. variegatus) above which the rate of heat dissipation increased in direct proportion to the concentration of TCP in tissue. At maximum, the metabolic rate increased by a factor of three. At the highest water concentration animals were dying and the metabolic rate was low. The energetic responses obtained with TCP are compared to those of a non-polar narcotic compound 1,2,4-trichlorobenzene and an other uncoupling agent, 2,4-dinitrophenol.
Vachon, Vincent; Laprade, Raynald; Schwartz, Jean-Louis
2012-09-15
Bacillus thuringiensis (Bt) Cry toxins constitute the active ingredient in the most widely used biological insecticides and insect-resistant transgenic crops. A clear understanding of their mode of action is necessary for improving these products and ensuring their continued use. Accordingly, a long history of intensive research has established that their toxic effect is due primarily to their ability to form pores in the plasma membrane of the midgut epithelial cells of susceptible insects. In recent years, a rather elaborate model involving the sequential binding of the toxins to different membrane receptors has been developed to describe the events leading to membrane insertion and pore formation. However, it was also proposed recently that, in contradiction with this mechanism, Bt toxins function by activating certain intracellular signaling pathways which lead to the necrotic death of their target cells without the need for pore formation. Because work in this field has largely focused, for several years, on the elaboration and promotion of these two models, the present revue examines in detail the experimental evidence on which they are based. It is concluded that the presently available information still supports the notion that Bt Cry toxins act by forming pores, but most events leading to their formation, following binding of the activated toxins to their receptors, remain relatively poorly understood.
NASA Astrophysics Data System (ADS)
Sharma, Maya; Madras, Giridhar; Bose, Suryasarathi
2016-06-01
In situ reduction of graphene oxide (GO) during the preparation of conducting polymeric nanocomposites has been explored recently. In this study, the in situ reduction of GO in poly (vinylidene fluoride) (PVDF) under different conditions like quiescent, high and low shear, pre-shear has been investigated in detail. To accomplish this, PVDF/GO composites were prepared by both melt and solution blending. The bulk electrical conductivity of melt mixed composites, which had undergone extensive shear during preparation, was monitored by a rheo-dielectric setup and compared with the composites which experienced low shear. In addition, the bulk electric conductivity was also measured in situ for the composites that had undergone quiescent compositing. Comprehensive characterization of the composites reveals that GO is in situ reducing under all processes but the improvement in conductivity is dependent on the adopted process. Compression molded samples, which were annealed for 45 min, showed highest melt conductivity among all the adopted processes. The intense shearing of composites at high temperature in melt extrusion led to re-stacking of graphene sheets and resulted in decreased bulk electrical conductivity. Surprisingly, melt conductivity decreases with shear and time in all composites. This study can help in understanding the reduction of GO during intense shearing of composites.
Shear fatigue crack growth - A literature survey
NASA Technical Reports Server (NTRS)
Liu, H. W.
1985-01-01
Recent studies of shear crack growth are reviewed, emphasizing test methods and data analyses. The combined mode I and mode II elastic crack tip stress fields are considered. The development and design of the compact shear specimen are described, and the results of fatigue crack growth tests using compact shear specimens are reviewed. The fatigue crack growth tests are discussed and the results of inclined cracks in tensile panels, center cracks in plates under biaxial loading, cracked beam specimens with combined bending and shear loading, center-cracked panels and double edge-cracked plates under cyclic shear loading are examined and analyzed in detail.
A Critical Interpersonal Distance Switches between Two Coordination Modes in Kendo Matches
Okumura, Motoki; Kijima, Akifumi; Kadota, Koji; Yokoyama, Keiko; Suzuki, Hiroo; Yamamoto, Yuji
2012-01-01
In many competitive sports, players need to quickly and continuously execute movements that co-adapt to various movements executed by their opponents and physical objects. In a martial art such as kendo, players must be able to skillfully change interpersonal distance in order to win. However, very little information about the task and expertise properties of the maneuvers affecting interpersonal distance is available. This study investigated behavioral dynamics underlying opponent tasks by analyzing changes in interpersonal distance made by expert players in kendo matches. Analysis of preferred interpersonal distances indicated that players tended to step toward and away from their opponents based on two distances. The most preferred distance enabled the players to execute both striking and defensive movements immediately. The relative phase analysis of the velocities at which players executed steps toward and away revealed that players developed anti-phase synchronizations at near distances to maintain safe distances from their opponents. Alternatively, players shifted to in-phase synchronization to approach their opponents from far distances. This abrupt phase-transition phenomenon constitutes a characteristic bifurcation dynamics that regularly and instantaneously occurs between in- and anti-phase synchronizations at a critical interpersonal distance. These dynamics are profoundly affected by the task constraints of kendo and the physical constraints of the players. Thus, the current study identifies the clear behavioral dynamics that emerge in a sport setting. PMID:23284799
The 3-min test does not provide a valid measure of critical power using the SRM isokinetic mode.
Karsten, B; Jobson, S A; Hopker, J; Passfield, L; Beedie, C
2014-04-01
Recent datas suggest that the mean power over the final 30 s of a 3-min all-out test is equivalent to Critical Power (CP) using the linear ergometer mode. The purpose of the present study was to identify whether this is also true using an "isokinetic mode". 13 cyclists performed: 1) a ramp test; 2) three 3-min all-out trials to establish End Power (EP) and work done above EP (WEP); and 3) 3 constant work rate trials to determine CP and the work done above CP (W') using the work-time (=CP1/W'1) and 1/time (=CP2/W'2) models. Coefficient of variation in EP was 4.45% between trials 1 and 2, and 4.29% between trials 2 and 3. Limits of Agreement for trials 1-2 and trials 2-3 were -2±38 W. Significant differences were observed between EP and CP1 (+37 W, P<0.001), between WEP and W'1(-6.2 kJ, P=0.001), between EP and CP2 (+31 W, P<0.001) and between WEP and W'2 (-4.2 kJ, P=0.006). Average SEE values for EP-CP1 and EP-CP2 of 7.1% and 6.6% respectively were identified. Data suggest that using an isokinetic mode 3-min all-out test, while yielding a reliable measure of EP, does not provide a valid measure of CP.
NASA Astrophysics Data System (ADS)
Gorospe, Alking; Bautista, Zhierwinjay; Shin, Hyung-Seop
2016-10-01
Coated conductor (CC) tapes utilized in high-current-density superconducting cables are commonly subjected to different loading modes, primarily torsion and tension especially in the case of twisted stacked-tape cable. Torsion load can occur due to twisting along the length or when winding the CC tapes around a former, while tension load can occur due to pre-tension when coiled and as a hoop stress when the coil is energized. In this study, electromechanical properties of single CC tapes under torsion load were investigated using a new test apparatus. The results could provide basic information for cable designers to fully characterize stacked cables. Copper-electroplated and brass-laminated CC tapes fabricated with different deposition techniques were subjected to pure torsion and combined tension-torsion loading. The critical current, I c degradation behaviours of CC tapes under torsional deformation were examined. Also, the effect of further external lamination on the I c degradation behaviour of the CC tapes under such loading conditions was investigated. In the case of the combined tension-torsion test, short samples were subjected to twist pitches of 200 mm and 100 mm. Critical parameters including reversible axial stress and strain in such twist pitch conditions were also investigated.
Feng, Z
1997-09-01
The fracture toughness at crack initiation was determined for bovine cortical bone under tension (mode I), shear (mode II), and tear (mode III). A total of 130 compact tension specimens, compact shear specimens and triple pantleg specimens were used for the measurement of fracture toughness under tension, shear, and tear, respectively. Multiple-sample compliance method was utilized to measure the critical strain energy release rate (Gc) at the a/W = 0.55 (crack length, a, to specimen width, W, ratio). The critical stress intensity factor (Kc) was also calculated from the critical loading (PQ) of the specimens at the a/W = 0.55. The effect of the anisotropy of bone on its resistance to crack initiation under shear and tear loading was investigated as well. The fracture toughness of bone with precrack orientations parallel(designed as longitudinal fracture) to and that with precrack orientations normal (designed as transverse fracture) to the longitudinal axis of bone were compared. In longitudinal fracture, the critical strain energy release rates(Gc) of cortical bone under tension, shear, and tear were 644 +/- 102, 2430 +/- 836, and 1723 +/- 486 N/m, respectively. In transverse fracture, the critical strain energy release rates(Gc) of cortical bone under tesion, shear, and tear were 1374 +/- 183, 4710 +/- 1284, and 4016 +/- 948 N/m, respectively. An analysis of variance demonstrated that the crack initiation fracture toughness of bone under shear and tear loading is significantly greater than that under tensile loading in both longitudinal and transverse fracture. Our results also suggest that cortical bone has been "designed" to prevent crack initiation in transverse fracture under tension, shear, and tesar.
NASA Astrophysics Data System (ADS)
Zhang, Yaoyao; Garland, Philip P.; Adamson, Robert B. A.; Brown, Jeremy A.
2014-06-01
We present results of investigations into a low-frequency vibration mode (LVM) in [001] poled Pb(Mg1/3Nb2/3)O3-PbTiO3 crystal. Through a series of impedance measurement and polarization microscopy observations of domain structure, we find that the LVM is a shear mode arising from a polarization component lying in the (001) plane. Through quenching, a metastable state can be reached where the LVM is greatly enhanced and the thickness vibration mode of the typical poled state is highly suppressed. Measurements on the transverse vibration modes of differently oriented crystal samples show that the LVM state possesses a macroscopic orthorhombic symmetry (mm2) with its polarization vector along the [110] direction. The structural differences between the LVM-enhanced state and the usual poled state are discussed in detail. The two states have the same crystalline phase but different ferroelectric domain structures. When heated above the rhombohedral-to-tetragonal transition temperature, Trt, a tetragonal phase with (110) domain walls is formed. This domain structure can be frozen by the rapid quenching through the Trt. Based on compatibility of ferroelectric polarizations at domain walls, and observed polarization microscopy results, we are able to infer the possible arrangement of domain structures in rhombohedral and tetragonal phases. The [110] polarization component associated with LVM originates from the domain structure with well-organized (110) domain walls.
Aita, Kaoruko; Kai, Ichiro
2010-02-01
Despite a number of guidelines issued in Anglo-American countries over the past few decades for forgoing treatment stating that there is no ethically relevant difference between withholding and withdrawing life-sustaining treatments (LST), it is recognized that many healthcare professionals in Japan as well as some of their western counterparts do not agree with this statement. This research was conducted to investigate the barriers that prevent physicians from withdrawing specific LST in critical care settings, focusing mainly on the modes of withdrawal of LST, in what the authors believe was the first study of its kind anywhere in the world. In 2006-2007, in-depth, face-to-face, semistructured interviews were conducted with 35 physicians working at emergency and critical care facilities across Japan. We elicited their experiences, attitudes, and perceptions regarding withdrawal of mechanical ventilation and other LST. The process of data analysis followed the grounded theory approach. We found that the psychosocial resistance of physicians to withdrawal of artificial devices varied according to the modes of withdrawal, showing a strong resistance to withdrawal of mechanical ventilation that requires physicians to halt the treatment when continuation of its mechanical operation is possible. However, there was little resistance to the withdrawal of percutaneous cardiopulmonary support and artificial liver support when their continuation was mechanically or physiologically impossible. The physicians shared a desire for a "soft landing" of the patient, that is, a slow and gradual death without drastic and immediate changes, which serves the psychosocial needs of the people surrounding the patient. For that purpose, vasopressors were often withheld and withdrawn. The findings suggest what the Japanese physicians avoid is not what they call a life-shortening act but an act that would not lead to a soft landing, or a slow death that looks 'natural' in the eyes of those
Dobruch-Sobczak, Katarzyna; Zalewska, Elwira Bakuła; Gumińska, Anna; Słapa, Rafał Zenon; Mlosek, Krzysztof; Wareluk, Paweł; Jakubowski, Wiesław; Dedecjus, Marek
2016-12-01
The aims of our study were to determine whether shear wave elastography (SWE) can improve the conventional B-mode differentiation of thyroid lesions, determine the most accurate SWE parameter for differentiation and assess the influence of microcalcifications and chronic autoimmune thyroiditis on SWE values. We examined 119 patients with 169 thyroid nodules who prospectively underwent B-mode ultrasound and SWE using the same ultrasound machine. The parameters assessed using SWE were: mean elasticity within the entire lesion (SWE-whole) and mean (SWE-mean) and maximum (SWE-max) elasticity for a 2-mm-diameter region of interest in the stiffest portion of the lesion, excluding microcalcifications. The discriminant powers of a generalized estimating equation model including B-mode parameters only and a generalized estimation equation model including both B-mode and SWE parameters were assessed and compared using the area under the receiver operating characteristic curve, in association with pathologic verification. In total, 50 and 119 malignant and benign lesions were detected. In generalized estimated equation regression, the B-mode parameters associated with higher odds ratios (ORs) for malignant lesions were microcalcifications (OR = 4.3), hypo-echogenicity (OR = 3.13) and irregular margins (OR = 10.82). SWE-max was the only SWE independent parameter in differentiating between malignant and benign tumors (OR = 2.95). The area under the curve for the B-mode model was 0.85, whereas that for the model combining B-mode and SWE parameters was 0.87. There was no significant difference in mean SWE values between patients with and without chronic autoimmune thyroiditis. The results of the present study suggest that SWE is a valuable tool for the characterization of thyroid nodules, with SWE-max being a significant parameter in differentiating benign and malignant lesions, independent of conventional B-mode parameters. The combination of SWE parameters and
NASA Technical Reports Server (NTRS)
2001-01-01
Whipped cream and the filling for pumpkin pie are two familiar materials that exhibit the shear-thinning effect seen in a range of industrial applications. It is thick enough to stand on its own atop a piece of pie, yet flows readily when pushed through a tube. This demonstrates the shear-thinning effect that was studied with the Critical Viscosity of Xenon Experiment (CVX-2) on the STS-107 Research 1 mission in 2002. CVX observed the behavior of xenon, a heavy inert gas used in flash lamps and ion rocket engines, at its critical point. The principal investigator was Dr. Robert Berg of the National Institutes of Standards and Technology in Gaithersburg, MD.
NASA Technical Reports Server (NTRS)
2001-01-01
Whipped cream and the filling for pumpkin pie are two familiar materials that exhibit the shear-thinning effect seen in a range of industrial applications. It is thick enough to stand on its own atop a piece of pie, yet flows readily when pushed through a tube. This demonstrates the shear-thinning effect that was studied with the Critical Viscosity of Xenon Experiment (CVX-2) on the STS-107 Research 1 mission in 2002. CVX observed the behavior of xenon, a heavy inert gas used in flash lamps and ion rocket engines, at its critical point. The principal investigator was Dr. Robert Berg of the National Institutes of Standards and Technology in Gaithersburg, MD.
Hanasaki, Itsuo; Walther, Jens H; Kawano, Satoyuki; Koumoutsakos, Petros
2010-11-01
We study shear-induced instabilities of lipid bilayers immersed in water using coarse-grained molecular dynamics simulations. The shear imposed by the flow of the water induces initially microscopic structural changes of the membrane, starting with tilting of the molecules in the direction of the shear. The tilting propagates in the spanwise direction when the shear rate exceeds a critical value and the membrane undergoes a bucklinglike deformation in the direction perpendicular to the shear. The bucklinglike undulation continues until a localized Kelvin-Helmholtz-like instability leads to membrane rupture. We study the different modes of membrane undulation using membranes of different geometries and quantify the relative importance of the bucklinglike bending and the Kelvin-Helmholtz-like instability of the membrane.
NASA Astrophysics Data System (ADS)
Hanasaki, Itsuo; Walther, Jens H.; Kawano, Satoyuki; Koumoutsakos, Petros
2010-11-01
We study shear-induced instabilities of lipid bilayers immersed in water using coarse-grained molecular dynamics simulations. The shear imposed by the flow of the water induces initially microscopic structural changes of the membrane, starting with tilting of the molecules in the direction of the shear. The tilting propagates in the spanwise direction when the shear rate exceeds a critical value and the membrane undergoes a bucklinglike deformation in the direction perpendicular to the shear. The bucklinglike undulation continues until a localized Kelvin-Helmholtz-like instability leads to membrane rupture. We study the different modes of membrane undulation using membranes of different geometries and quantify the relative importance of the bucklinglike bending and the Kelvin-Helmholtz-like instability of the membrane.
Shear jamming in highly strained granular system without shear banding
NASA Astrophysics Data System (ADS)
Zhao, Yiqiu; Barés, Jonathan; Zheng, Hu; Behringer, Robert
2016-11-01
Bi et al. have shown that, if sheared, a granular material can jam even if its packing fraction (ϕ) is lower than the critical isotropic jamming point ϕJ. They have introduced a new critical packing fraction value ϕS such that for ϕS< ϕ< ϕJ the system jams if sheared. Nevertheless, the value of ϕS as a function of the shear profile or the strain necessary to observe jamming remain poorly understood because of the experimental complexity to access high strain without shear band. We present a novel 2D periodic shear apparatus made of 21 independent, aligned and mirrored glass rings. Each ring can be moved independently which permits us to impose any desired shear profile. The circular geometry allows access to any strain value. The forces between grains are measured using reflective photoelasticity. By performing different shear profiles for different packing fractions we explored the details of jamming diagram including the location of the yield surface. This work is supported by NSF No.DMR1206351, NASA No.NNX15AD38G and W. M. Keck Foundation.
Ren, Bo; Or, Siu Wing; Wang, Feifei; Zhao, Xiangyong; Luo, Haosu; Li, Xiaobing; Zhang, Qinhui; Di, Wenning; Zhang, Yaoyao
2010-06-01
In this paper we theoretically and experimentally present a nonresonant vibration energy harvesting device based on the shear mode of 0.71Pb(Mg(1/3)Nb(2/3))O3-0.29PbTiO3 single crystals. The electrical properties of the energy harvesting device were evaluated using an analytical method. Good consistency was obtained between the analytical and experimental results. Under a mass load of 200 g, a peak voltage of 11.3 V and maximum power of 0.70 mW were obtained at 500 Hz when connecting a matching load resistance of 91 komega. A high output could always be obtained within a very wide frequency range. The results demonstrate the potential of the device in energy harvesting applied to low-power portable electronics and wireless sensors.
Khare, Rahul K; Nannicelli, Anna P; Powell, Emilie S; Seivert, Nicholas P; Adams, James G; Holl, Jane L
2013-10-01
The Centers for Medicare & Medicaid Services currently endorses a door-to-balloon time of 90 minutes or less for patients presenting to the emergency department (ED) with ST-segment elevation myocardial infarction. Recent evidence shows that a door-to-balloon time of 60 minutes significantly decreases inhospital mortality. We seek to use a proactive risk assessment method of failure mode, effects, and criticality analysis (FMECA) to evaluate door-to-balloon time process, to investigate how each component failure may affect the performance of a system, and to evaluate the frequency and the potential severity of harm of each failure. We conducted a 2-part study: FMECA of the door-to-balloon time system and process of care, and evaluation of a single institution's door-to-balloon time operational data using a retrospective observational cohort design. A multidisciplinary group of FMECA participants described the door-to-balloon time process to then create a comprehensive map and table listing all process steps and identified process failures, including their frequency, consequence, and causes. Door-to-balloon time operational data were assessed by "on" versus "off" hours. Fifty-one failure points were identified across 4 door-to-balloon time phases. Of the 12 high-risk failures, 58% occurred between ECG and catheterization laboratory activation. Total door-to-balloon time during on hours had a median time of 55 minutes (95% confidence interval 46 to 60 minutes) compared with 77 minutes (95% confidence interval 68 to 83 minutes) during off hours. The FMECA revealed clear areas of potential delay and vulnerability that can be addressed to decrease door-to-balloon time from 90 to 60 minutes. FMECAs can provide a robust assessment of potential risks and can serve as the platform for significant process improvement and system redesign for door-to-balloon time. Copyright © 2013 American College of Emergency Physicians. Published by Mosby, Inc. All rights reserved.
Nadir Ayrilmis; Jerrold E. Winandy
2007-01-01
The influence of four fire-retardant systems on the planar (rolling) shear properties of structural hardwood plywood is evaluated using two possible ASTM D2718 test methodologies: the plate-shear method and the five-point flexural shear method. Knowing the planar shear properties and the potential of the various fire-retardant systems to affect properties is critical...
NASA Technical Reports Server (NTRS)
1996-01-01
This Failure Modes and Effects Analysis (FMEA) is for the Advanced Microwave Sounding Unit-A (AMSU-A) instruments that are being designed and manufactured for the Meteorological Satellites Project (METSAT) and the Earth Observing System (EOS) integrated programs. The FMEA analyzes the design of the METSAT and EOS instruments as they currently exist. This FMEA is intended to identify METSAT and EOS failure modes and their effect on spacecraft-instrument and instrument-component interfaces. The prime objective of this FMEA is to identify potential catastrophic and critical failures so that susceptibility to the failures and their effects can be eliminated from the METSAT/EOS instruments.
ERIC Educational Resources Information Center
Akhlaq, Muhammad; Sulehri, Shazia Munawar
2010-01-01
The premise of this article is to analyze the managerial skills competencies of secondary schools heads trained through distance mode of education in Pakistan. For this purpose a sample 300 secondary school teachers and 100 secondary schools head-teachers trained through distance mode and working in the Federal Government Educational Institutions…
1988-04-01
DEVELOP GROuE RULES AND ASSUMPTIONS) ITK/FUN ITEM ACRONYMS: FMlA - FAILURE MODE AND EFFECT ANALYSIS FUNCTION L8AR - LOGISTIC SUPPORT ANALYSIS RECORD...Fiu/BLK/DIA FUNCTIONAL ACRONM: FMLA ...FAILURE MODE AND EFFECTS ANALYSIS BLOCK DIAGRAM PURPOSE OF DATA: ALLOW TUE ANALYST ACCESS TO THE FUNCTIONAL BLOCK DIAGRAMS NEEDED TO COPLETE TUE FMlA
ERIC Educational Resources Information Center
Ruddock, Ivan S.
2009-01-01
The derivation and description of the modes in optical waveguides and fibres are reviewed. The version frequently found in undergraduate textbooks is shown to be incorrect and misleading due to the assumption of an axial ray of light corresponding to the lowest order mode. It is pointed out that even the lowest order must still be represented in…
ERIC Educational Resources Information Center
Ruddock, Ivan S.
2009-01-01
The derivation and description of the modes in optical waveguides and fibres are reviewed. The version frequently found in undergraduate textbooks is shown to be incorrect and misleading due to the assumption of an axial ray of light corresponding to the lowest order mode. It is pointed out that even the lowest order must still be represented in…
NASA Astrophysics Data System (ADS)
Fusseis, Florian; Gilgannon, James; Burns, Thomas; Menegon, Luca
2017-04-01
Mid-crustal shear zones host deep slow slip events and play a critical role in transferring stress from viscously deforming lower-crustal domains to the frictional, seismogenic upper crust. At the same time, these shear zones act as conduits for trans-crustal fluid transfer. Deformation in shear zones at the frictional-viscous transition is accommodated by a complex combination of deformation mechanisms that is dominated by grain-size sensitive creep in fine-grained ultramylonites. Over the past years, the significance of synkinematic creep cavitation in the deformation of these ultramylonites has been established, and Fusseis et al. (2009) have formulated the dynamic granular fluid pump model to consider this form of porosity in models of fluid transfer through the middle crust. In this presentation we analyse amphibolite-facies ultramylonitic samples from the Redbank Shear Zone (Australia) that have been exhumed from the frictional-viscous transition without any significant retrograde overprint. The ultramylonites, which were derived from a granitic protolith, appear compositionally layered, with alternating layers of extremely fine-grained ( 1-2 um) polymineralic mixtures of feldspar, quartz, mica, epidote and ilmenite and mono-mineralic quartz layers. The latter exhibit abundant creep cavities, which are the focus of this contribution. A hierarchy of creep cavities are found to exists in the quartz domains. This porosity can be considered to have formed synkinematically by two distinct mechanisms: Zener-Stroh cracking and superplastic void growth. The porosity is shown to have evolved with the disaggregation of the dynamically recrystallising quartz ribbons during ultramylonitisation. In initially thick and coherent quartz ribbons, pores generated by Zener-Stroh cracking emerge on grain-boundaries aligned with the YZ plane of finite strain. With decreasing quartz domain thickness and increasing quartz dispersion into the fine-grained ( 1-2 μm) polyphase
Meng, Wei; Kotamarthy, Lalith; Panikar, Savitha; Sen, Maitraye; Pradhan, Shankali; Marc, Michaelis; Litster, James D; Muzzio, Fernando J; Ramachandran, Rohit
2016-11-20
This study is concerned with identifying the design space of two different continuous granulators and their respective granulation mechanisms. Performance of a continuous high shear granulator and a twin screw granulator with paracetamol formulations were examined by face-centered cubic design, which focused on investigating key performance metrics, namely, granule size, porosity, flowability and particle morphology of granules as a function of essential input process parameters (liquid content, throughput and rotation speed). Liquid and residence time distribution tests were also performed to gain insights into the liquid-powder mixing and flow behavior. The results indicated that continuous high shear granulation was more sensitive to process variation and produced spherical granules with monomodal size distribution and distinct internal structure and strength variation. Twin screw granulation with such a particular screw configuration showed narrower design space and granules were featured with multimodal size distribution, irregular shape, less detectible porosity difference and tighter range of strength. Granulation mechanisms explored on the basis of nucleation and growth regime maps revealed that for most cases liquid binder was uniformly distributed with fast droplet penetration into the powder bed and that granule consolidation and coalescence mainly took place in the nucleation, steady growth and rapid growth regimes.
Avalanches in strained amorphous solids: does inertia destroy critical behavior?
Salerno, K Michael; Maloney, Craig E; Robbins, Mark O
2012-09-07
Simulations are used to determine the effect of inertia on athermal shear of amorphous two-dimensional solids. In the quasistatic limit, shear occurs through a series of rapid avalanches. The distribution of avalanches is analyzed using finite-size scaling with thousands to millions of disks. Inertia takes the system to a new underdamped universality class rather than driving the system away from criticality as previously thought. Scaling exponents are determined for the underdamped and overdamped limits and a critical damping that separates the two regimes. Systems are in the overdamped universality class even when most vibrational modes are underdamped.
Nguyen, Christina; Côté, Justine; Lebel, Denis; Caron, Elaine; Genest, Christine; Mallet, Monia; Phan, Véronique; Bussières, Jean-François
2013-02-01
The objective of this article was to critically evaluate the causes of adverse drug events during the nurse medication administration process in paediatric care units in order to identify and prioritize interventions that need to be implemented. This is a failure mode, effects and criticality analysis (FMECA) study. A multidisciplinary committee composed of nurses, pharmacists, physicians and risk managers evaluated through consensus the process of administering medications at the Centre hospitalier universitaire de Sainte-Justine. By mapping the process, all the failure modes were identified and associated with at least one cause each. Using a summary grid, each failure mode was evaluated by rating frequency (from 1 to 9), likelihood of failure detection (from 0 to 100%) and severity (from 1 to 9) using adapted versions of already published scales. A 10-member committee was set up, and it met eight times between January and April 2010. In the two specialized paediatric units selected (n = 38 beds), an average number of approximately 20 000 drug doses was administered monthly from about 400 non-proprietary names. Through consensus, the committee identified 16 processes and 53 failure modes. While frequency and severity were based on perceptions that could be objectivized with local data and scientific documentation, the likelihood of detection was mainly based on individual perception. FMECA is a useful approach to improve the medication process. © 2011 Blackwell Publishing Ltd.
Shear shocks in fragile networks.
Ulrich, Stephan; Upadhyaya, Nitin; van Opheusden, Bas; Vitelli, Vincenzo
2013-12-24
A minimal model for studying the mechanical properties of amorphous solids is a disordered network of point masses connected by unbreakable springs. At a critical value of its mean connectivity, such a network becomes fragile: it undergoes a rigidity transition signaled by a vanishing shear modulus and transverse sound speed. We investigate analytically and numerically the linear and nonlinear visco-elastic response of these fragile solids by probing how shear fronts propagate through them. Our approach, which we tentatively label shear front rheology, provides an alternative route to standard oscillatory rheology. In the linear regime, we observe at late times a diffusive broadening of the fronts controlled by an effective shear viscosity that diverges at the critical point. No matter how small the microscopic coefficient of dissipation, strongly disordered networks behave as if they were overdamped because energy is irreversibly leaked into diverging nonaffine fluctuations. Close to the transition, the regime of linear response becomes vanishingly small: the tiniest shear strains generate strongly nonlinear shear shock waves qualitatively different from their compressional counterparts in granular media. The inherent nonlinearities trigger an energy cascade from low to high frequency components that keep the network away from attaining the quasi-static limit. This mechanism, reminiscent of acoustic turbulence, causes a superdiffusive broadening of the shock width.
Plasma pressure effect on the multiple low-shear toroidal Alfven eigenmodes
Marchenko, V. S.
2009-04-15
It is shown that there is a critical thermal pressure gradient at which the polarizations of the multiple low-shear toroidal Alfven eigenmodes (TAEs) are reversed. Below the critical value, the TAE spectrum consists of two bands of the even (odd) modes located in the upper (lower) part of the toroidal Alfven gap, which is consistent with the zero-pressure limit [J. Candy, B. N. Breizman, J. W. Van Dam, and T. Ozeki, Phys. Lett. A 215, 299 (1996)]. Above the critical pressure, the odd (even) TAEs appear in the upper (lower) part of the gap.
Coherent motion in excited free shear flows
NASA Technical Reports Server (NTRS)
Wygnanski, Israel J.; Petersen, Robert A.
1987-01-01
The application of the inviscid instability approach to externally excited turbulent free shear flows at high Reynolds numbers is explored. Attention is given to the cases of a small-deficit plane turbulent wake, a plane turbulent jet, an axisymmetric jet, the nonlinear evolution of instabilities in free shear flows, the concept of the 'preferred mode', vortex pairing in turbulent mixing layers, and experimental results for the control of free turbulent shear layers. The special features often attributed to pairing or to the preferred mode are found to be difficult to comprehend; the concept of feedback requires further substantiation in the case of incompressible flow.
Superstrings in Sheared Polymer Blends
NASA Astrophysics Data System (ADS)
Migler, Kalman
2000-03-01
We report the discovery of a droplet-string-ribbon transition in concentrated polymer blends which occurs when the droplet size of the dispersed component becomes comparable to the gap between the boundary plates. Above a critical shear rate (or gap width), dispersed droplets continuously coalescence and breakup; the upper limit on their size is set by the Taylor length. Below this critical shear rate, droplets coalesce into strings and then ribbons in a four stage kinetic process. The mass ratio of string / droplet can be as large as 10^4. The transition is sharp, occurring over a shear interval of 2droplet-string transition is a manifestation of the weakening of the Rayleigh-Tomatika instability which occurs when the system becomes quasi two-dimensional. Possible applications of this technology are ultra-thin materials of high one-dimensional strength, polymer blend wires, and novel polymeric scaffolds.
Molecular friction dissipation and mode coupling in organic monolayers and polymer films
NASA Astrophysics Data System (ADS)
Knorr, Daniel B.; Widjaja, Peggy; Acton, Orb; Overney, René M.
2011-03-01
The impact of thermally active molecular rotational and translational relaxation modes on the friction dissipation process involving smooth nano-asperity contacts has been studied by atomic force microscopy, using the widely known Eyring analysis and a recently introduced method, dubbed intrinsic friction analysis. Two distinctly different model systems, i.e., monolayers of octadecyl-phosphonic acid (ODPA) and thin films of poly(tert-butyl acrylate) (PtBA) were investigated regarding shear-rate critical dissipation phenomena originating from diverging mode coupling behaviors between the external shear perturbation and the internal molecular modes of relaxation. Rapidly (ODPA) versus slowly (PtBA) relaxing systems, in comparison to the sliding rate, revealed monotonous logarithmic and nonmonotonous spectral shear rate dependences, respectively. Shear coupled, enthalpic activation energies of 46 kJ/mol for ODPA and of 35 and ˜65 kJ/mol for PtBA (below and above the glass transition) were found that could be attributed to intrinsic modes of relaxations. Also, entropic energies involved in the cooperative backbone mobility of PtBA could be quantified, dwarfing the activation energy by more than a factor of five. This study provides (i) a material specific understanding of the molecular scale dissipation process in shear compliant substances, (ii) analyses of material intrinsic shear-rate mode coupling, shear coordination and energetics, (iii) a verification of Eyring's model applied to tribological systems toward material intrinsic specificity, and (iv) a valuable extension of the Eyring analysis for complex macromolecular systems that are slowly relaxing, and thus, exhibit shear-rate mode coupling.
Molecular friction dissipation and mode coupling in organic monolayers and polymer films.
Knorr, Daniel B; Widjaja, Peggy; Acton, Orb; Overney, René M
2011-03-14
The impact of thermally active molecular rotational and translational relaxation modes on the friction dissipation process involving smooth nano-asperity contacts has been studied by atomic force microscopy, using the widely known Eyring analysis and a recently introduced method, dubbed intrinsic friction analysis. Two distinctly different model systems, i.e., monolayers of octadecyl-phosphonic acid (ODPA) and thin films of poly(tert-butyl acrylate) (PtBA) were investigated regarding shear-rate critical dissipation phenomena originating from diverging mode coupling behaviors between the external shear perturbation and the internal molecular modes of relaxation. Rapidly (ODPA) versus slowly (PtBA) relaxing systems, in comparison to the sliding rate, revealed monotonous logarithmic and nonmonotonous spectral shear rate dependences, respectively. Shear coupled, enthalpic activation energies of 46 kJ∕mol for ODPA and of 35 and ∼65 kJ∕mol for PtBA (below and above the glass transition) were found that could be attributed to intrinsic modes of relaxations. Also, entropic energies involved in the cooperative backbone mobility of PtBA could be quantified, dwarfing the activation energy by more than a factor of five. This study provides (i) a material specific understanding of the molecular scale dissipation process in shear compliant substances, (ii) analyses of material intrinsic shear-rate mode coupling, shear coordination and energetics, (iii) a verification of Eyring's model applied to tribological systems toward material intrinsic specificity, and (iv) a valuable extension of the Eyring analysis for complex macromolecular systems that are slowly relaxing, and thus, exhibit shear-rate mode coupling.
Physics of the L-mode to H-mode transition in tokamaks
Burrell, K.H.; Carlstrom, T.N.; Gohil, P.; Groebner, R.J.; Kim, J.; Osborne, T.H.; St. John, H.; Stambaugh, R.D. ); Doyle, E.J.; Moyer, R.A.; Rettig, C.L.; Peebles, W.A.; Rhodes, T.L. ); Finkenthal, D. ); Hillis, D.L.; Wade, M.R. (Oak Ridge National Lab., TN (United
1992-07-01
Combined theoretical and experimental work has resulted in the creation of a paradigm which has allowed semi-quantitative understanding of the edge confinement improvement that occurs in the H-mode. Shear in the E {times} B flow of the fluctuations in the plasma edge can lead to decorrelation of the fluctuations, decreased radial correlation lengths and reduced turbulent transport. Changes in the radial electric field, the density fluctuations and the edge transport consistent with shear stabilization of turbulence have been seen in several tokamaks. The purpose of this paper is to discuss the most recent data in the light of the basic paradigm of electric field shear stabilization and to critically compare the experimental results with various theories.
NASA Technical Reports Server (NTRS)
Milligan, Walter W.; Antolovich, Stephen D.
1989-01-01
The PWA 1480 nickel-base superalloy is known to exhibit a unique minimum in the critical resolved shear stress (CRSS) at about 400 C. This paper reports an observation of a deformation mechanism whose temperature dependence correlates exactly with the reduction in the CRSS. It was found that, after monotonic or cyclic deformation of PWA 1480 at 20 C, the deformation substructures typically contain high density of superlattice-intrinsic stacking faults (S-ISFs) within the gamma-prime precipitates. As the temperature of deformation is increased, the density of S-ISFs is reduced, until finally no faults are observed after deformation in the range from 400 to 705 C. The reduction in the fault density corresponds exactly to the reduction in the CRSS, and the temperature at which the fault density is zero corresponds with the minimum in the CRRS. Two possible mechanisms related to the presence of the S-ISFs in the alloy are considered.
ERIC Educational Resources Information Center
Kendrick, Maureen; Mutonyi, Harriet
2007-01-01
This article seeks to better understand the relation between local and traditional modes of communication and health literacy within the context of a rural West Nile community in Northern Uganda. Drawing on social semiotics (multimodality) and Bakhtin's notion of the carnival, the focus is on a group of women participating in a grassroots literacy…
ERIC Educational Resources Information Center
Kendrick, Maureen; Mutonyi, Harriet
2007-01-01
This article seeks to better understand the relation between local and traditional modes of communication and health literacy within the context of a rural West Nile community in Northern Uganda. Drawing on social semiotics (multimodality) and Bakhtin's notion of the carnival, the focus is on a group of women participating in a grassroots literacy…
NASA Technical Reports Server (NTRS)
2001-01-01
The Critical Viscosity of Xenon Experiment (CVX-2) on the STS-107 Research 1 mission in 2002 will measure the viscous behavior of xenon, a heavy inert gas used in flash lamps and ion rocket engines, at its critical point. Shear thirning will cause a normally viscous fluid -- such as pie filling or whipped cream -- to deform and flow more readily under high shear conditions. In shear thinning, a pocket of fluid will deform and move one edge forward, as depicted here.
NASA Technical Reports Server (NTRS)
2001-01-01
The Critical Viscosity of Xenon Experiment (CVX-2) on the STS-107 Research 1 mission in 2002 will measure the viscous behavior of xenon, a heavy inert gas used in flash lamps and ion rocket engines, at its critical point. Shear thirning will cause a normally viscous fluid -- such as pie filling or whipped cream -- to deform and flow more readily under high shear conditions. In shear thinning, a pocket of fluid will deform and move one edge forward, as depicted here.
Viejo Moreno, R; Sánchez-Izquierdo Riera, J Á; Molano Álvarez, E; Barea Mendoza, J A; Temprano Vázquez, S; Díaz Castellano, L; Montejo González, J C
2016-11-01
To improve critical patient safety in the prevention of venous thromboembolic disease, using failure mode and effects analysis as safety tool. A contemporaneous cohort study covering the period January 2014-March 2015 was made in 4 phases: phase 1) prior to failure mode and effects analysis; phase 2) conduction of mode analysis and implementation of the detected improvements; phase 3) evaluation of outcomes, and phase 4) (post-checklist introduction impact. Patients admitted to the adult polyvalent ICU of a third-level hospital center. A total of 196 patients, older than 18 years, without thromboembolic disease upon admission to the ICU and with no prior anticoagulant treatment. A series of interventions were implemented following mode analysis: training, and introduction of a protocol and checklist to increase preventive measures in relation to thromboembolic disease. Indication and prescription of venous thrombosis prevention measures before and after introduction of the measures derived from the failure mode and effects analysis. A total of 59, 97 and 40 patients were included in phase 1, 3 and 4, respectively, with an analysis of the percentage of subjects who received thromboprophylaxis. The failure mode and effects analysis was used to detect potential errors associated to a lack of training and protocols referred to thromboembolic disease. An awareness-enhancing campaign was developed, with staff training and the adoption of a protocol for the prevention of venous thromboembolic disease. The prescription of preventive measures increased in the phase 3 group (91.7 vs. 71.2%, P=.001). In the post-checklist group, prophylaxis was prescribed in 97.5% of the patients, with an increase in the indication of dual prophylactic measures (4.7, 6.7 and 41%; P<.05). There were no differences in complications rate associated to the increase in prophylactic measures. The failure mode and effects analysis allowed us to identify improvements in the prevention of
Chang, R.F.; Doiron, T.; Pegg, I.L.; Hanley, H.J.M.; Cezairliyan, A.
1986-03-01
Using the technique of photon correlation spectroscopy we have measured the decay rate of critical fluctuations in mixtures of ethane and carbon dioxide of various compositions including a near-azeotropic mixture. Our experimental data indicate that there is only one dominant mode of fluctuations and the decay rate is well described by the predictions of the mode-coupling theory with the exponent v=0.63 for all compositions. The decay rate, its background contributions, the shear viscosity, and the correlation length for the mixtures appear to interpolate simply between those of ethane and carbon dioxide.
Nucleation of shear bands in amorphous alloys
Perepezko, John H.; Imhoff, Seth D.; Chen, Ming-Wei; Wang, Jun-Qiang; Gonzalez, Sergio
2014-01-01
The initiation and propagation of shear bands is an important mode of localized inhomogeneous deformation that occurs in a wide range of materials. In metallic glasses, shear band development is considered to center on a structural heterogeneity, a shear transformation zone that evolves into a rapidly propagating shear band under a shear stress above a threshold. Deformation by shear bands is a nucleation-controlled process, but the initiation process is unclear. Here we use nanoindentation to probe shear band nucleation during loading by measuring the first pop-in event in the load–depth curve which is demonstrated to be associated with shear band formation. We analyze a large number of independent measurements on four different bulk metallic glasses (BMGs) alloys and reveal the operation of a bimodal distribution of the first pop-in loads that are associated with different shear band nucleation sites that operate at different stress levels below the glass transition temperature, Tg. The nucleation kinetics, the nucleation barriers, and the density for each site type have been determined. The discovery of multiple shear band nucleation sites challenges the current view of nucleation at a single type of site and offers opportunities for controlling the ductility of BMG alloys. PMID:24594599
Critical dynamic viscosities in a binary mixture
NASA Astrophysics Data System (ADS)
Izumi, Y.; Sawano, H.; Sato, H.; Miyake, Y.; Kono, R.; Yoshizaki, H.
1989-03-01
Ultrasonic shear measurements were conducted on polystyrene-cyclohexane solutions at 3, 51, and 252 kHz using the crystal fork and torsion methods. The real and imaginary parts of the complex shear modulus above the critical point are compared with modified theoretical expressions derived within the framework of the decoupled-mode theory. For this comparison, a background part was assumed to be described by a scaling form proposed by de Gennes. Numerical analysis of the data shows a satisfactory agreement between the theory and the experiments for ultrasonic shear data over a wide range of reduced frequency ω ... In addition, it is shown that the description of the simple viscosity dynamical scaling function is broken at a high-frequency limit.
Rosakis, A.J.; Ravichandran, G.; Zhou, M.
1995-12-31
The phenomenon of dynamic initiation and propagation of adiabatic shear bands is experimentally and numerically investigated. Pre-notched metal plates are subjected to asymmetric impact load histories (dynamic mode-II loading). Dynamic shear bands emanate from the notch tip and propagate rapidly in a direction nearly parallel to the direction of the impact. Real time temperature histories along a line intersecting and perpendicular to the shear band paths are recorded by means of a high-speed infrared detector system. The materials studied are C-300 (a maraging steel) and Ti - 6 Al - 4 V alloy. Experiments show that the peak temperatures inside the propagating shear bands are approaching 90% of the melting point for C-300 and are significantly lower for the titanium alloy (up to 600{degrees}C). Additionally, measured distances of shear band propagation indicate stronger resistance to shear banding by the Ti - 6Al - 4V alloy. Deformation fields around the propagating shear bands are recorded using high-speed photography. Shear band speeds are found to strongly depend on impact velocities, and are as high as 1200 m/s for C-300 steels. Finite Element simulations of the experiments are carried out under the context of plane strain, considering finite deformations, inertia, heat conduction, thermal softening, strain hardening and strain-rate hardening. In the simulations, the shear band propagation is assumed to be governed by a critical plastic strain criterion. The results are compared with experimental measurements obtained using the high-speed infrared detectors and high-speed photography.
NASA Astrophysics Data System (ADS)
Kitching, Thomas D.; Alsing, Justin; Heavens, Alan F.; Jimenez, Raul; McEwen, Jason D.; Verde, Licia
2017-08-01
In this paper, we discuss the commonly used limiting cases, or approximations, for two-point cosmic-shear statistics. We discuss the most prominent assumptions in this statistic: the flat-sky (small angle limit), the Limber (Bessel-to-delta function limit) and the Hankel transform (large ℓ-mode limit) approximations; that the vast majority of cosmic-shear results to date have used simultaneously. We find that the combined effect of these approximations can suppress power by ≳ 1 per cent on scales of ℓ ≲ 40. A fully non-approximated cosmic-shear study should use a spherical-sky, non-Limber-approximated power spectrum analysis and a transform involving Wigner small-d matrices in place of the Hankel transform. These effects, unaccounted for, would constitute at least 11 per cent of the total budget for systematic effects for a power spectrum analysis of a Euclid-like experiment; but they are unnecessary.
Bouzidi, Laziz; Narine, Suresh S
2010-03-16
The isoconversional method, a model-free analysis of the kinetics of liquid-solid transformations, was used to determine the effective activation energy of the nonisothermal crystallization of melts of pure and complex systems of triacylglycerols (TAGs). The method was applied to data from differential scanning calorimetry (DSC) measurements of the heat of crystallization of purified 1,3-dilauroyl-2-stearoyl-sn-glycerol (LSL) and commercially available cocoa butter melts. The method conclusively demonstrated the existence of specific growth modes and critical rates of cooling at specific degrees of conversion. The existence of critical rates suggests that the crystallization mechanism is composed of growth modes that can be effectively treated as mutually exclusive, each being predominant for one range of cooling rates and extent of conversion. Importantly, the data suggests that knowledge of the critical cooling rates at specific rates of conversion can be exploited to select preferred growth modes for lipid networks, with concomitant benefits of structural organization and resultant physical functionality. Differences in transport phenomena induced by different cooling rates suggest the existence of thresholds for particular growth mechanisms and help to explain the overall complexity of lipid crystallization. The results of this model-free analysis may be attributed to the relative importance of nucleation and growth at different stages of crystallization. A mechanistic explanation based on the competing effects of the thermodynamic driving force and limiting heat and transport phenomena is provided to explain the observed behavior. This work, furthermore, offers satisfactory explanations for the noted effect of cooling-rate-induced changes in the physical functionality of lipid networks.
NASA Astrophysics Data System (ADS)
Anastasiadi, G. P.; Kondrat'ev, S. Yu.; Malyshevskii, V. A.; Sil'nikov, M. V.
2017-03-01
The role of plotting of diagrams of isothermal and thermokinetic transformations of supercooled austenite in the development of heat treatment processes of steels is discussed. Specific examples of the necessity of plotting of thermokinetic diagrams of transformations in steels for solving critical production problems are considered.
NASA Technical Reports Server (NTRS)
Bonavito, N. L.; Nagai, O.; Tanaka, T.
1975-01-01
Previous spin wave theories of the antiferromagnet hematite were extended. The behavior of thermodynamic quantities around the Morin transition temperature was studied, and the latent heat of the Morin transition was calculated. The temperature dependence of the antiferromagnetic resonance frequency and the parallel and perpendicular critical spin-flop magnetic fields were calculated. It was found that the theory agrees well with experiment.
Effect of rotation and velocity shear on tearing layer stability in tokamak plasmas
NASA Astrophysics Data System (ADS)
White, Ryan L.; Fitzpatrick, Richard
2015-10-01
Using a resistive generalization of the Frieman-Rotenberg formalism, the leading-order effects of velocity shear and rotation on linear tearing layer stability are studied for tokamak equilibria. The layer equations for resistive interchange modes are derived for arbitrary equilibrium rotation and velocity shear. The resulting layer equations do not conserve parity and are not simplified by Fourier transform. Thus, many standard numerical techniques cannot be implemented in a straightforward manner. Layer equations are also derived in the constant- Ψ limit. The constant- Ψ dispersion relation is obtained and is used to study the leading-order effects of rotation and velocity shear on the critical value of Δ' required for tearing instability. It is found that rotation and velocity shear can couple with the parallel current and the current gradient in the layer to reduce Δ'crit . If parallel currents are sufficiently weak to compete with second-order effects, velocity shear can be stabilizing, while rotation is found to have a destabilizing effect. Second-order coupling of velocity shear and rotation can have either sign, and thus can affect stability in either direction.
Hierarchical cosmic shear power spectrum inference
NASA Astrophysics Data System (ADS)
Alsing, Justin; Heavens, Alan; Jaffe, Andrew H.; Kiessling, Alina; Wandelt, Benjamin; Hoffmann, Till
2016-02-01
We develop a Bayesian hierarchical modelling approach for cosmic shear power spectrum inference, jointly sampling from the posterior distribution of the cosmic shear field and its (tomographic) power spectra. Inference of the shear power spectrum is a powerful intermediate product for a cosmic shear analysis, since it requires very few model assumptions and can be used to perform inference on a wide range of cosmological models a posteriori without loss of information. We show that joint posterior for the shear map and power spectrum can be sampled effectively by Gibbs sampling, iteratively drawing samples from the map and power spectrum, each conditional on the other. This approach neatly circumvents difficulties associated with complicated survey geometry and masks that plague frequentist power spectrum estimators, since the power spectrum inference provides prior information about the field in masked regions at every sampling step. We demonstrate this approach for inference of tomographic shear E-mode, B-mode and EB-cross power spectra from a simulated galaxy shear catalogue with a number of important features; galaxies distributed on the sky and in redshift with photometric redshift uncertainties, realistic random ellipticity noise for every galaxy and a complicated survey mask. The obtained posterior distributions for the tomographic power spectrum coefficients recover the underlying simulated power spectra for both E- and B-modes.
Stability of an accelerated shear layer
Mjolsness, R.C.; Ruppel, H.M.
1986-07-01
A fluid shear layer with free boundary conditions is subject to a Kelvin--Helmholtz-like instability. When the shear layer is accelerated by a difference in applied pressures it is also subject to a Rayleigh--Taylor-like instability. The combined action of these instabilities leads to at most one unstable mode at each wavelength, whose behavior depends in detail on fluid parameters, the fluid acceleration and the perturbation wavelength. Typically, at longest wavelengths the instability is essentially of Rayleigh--Taylor form; its behavior resembles the Kelvin--Helmholtz-like mode at shorter wavelengths, near the thickness of the shear layer, cutting off when the Kelvin--Helmholtz-like mode does. At still shorter wavelengths, the shear layer is subject to a Rayleigh--Taylor-like instability. Careful control of fluid parameters could place the most unstable wavelength for Rayleigh--Taylor instability, calculated from viscous theory, in the range of wavelengths where the accelerated shear layer has no unstable mode. However, this may be difficult to achieve in practice. If this can be realized, the most unstable growth rate may be reduced by about an order of magnitude by the presence of shear.
Yield shear stress and disaggregating shear stress of human blood
NASA Astrophysics Data System (ADS)
Jung, Jinmu; Lee, Byoung-Kwon; Shin, Sehyun
2014-05-01
This review presents two distinct rheological parameters of blood that have the potential to indicate blood circulation adequacy: yield shear stress (YSS) and disaggregating shear stress (DSS). YSS and DSS reflect the strength of red blood cell (RBC) aggregation in suspension under static and dynamic conditions, respectively. YSS, defined as the critical stress to disperse RBC aggregates under static conditions, was found to be dependent upon hematocrit, fibrinogen, and red cell deformability, but not temperature. DSS, defined as the minimum shear stress to disperse RBC aggregates under dynamic conditions, is dependent upon fibrinogen, red cell deformability, and temperature but not hematocrit. Owing to recent advances in measurement technology, these two parameters can be easily measured, and thus, their clinical significance in blood circulation can be verified.
Miyamoto, Naokazu; Hirata, Kosuke; Kanehisa, Hiroaki; Yoshitake, Yasuhide
2015-01-01
Ultrasound shear wave elastography is becoming a valuable tool for measuring mechanical properties of individual muscles. Since ultrasound shear wave elastography measures shear modulus along the principal axis of the probe (i.e., along the transverse axis of the imaging plane), the measured shear modulus most accurately represents the mechanical property of the muscle along the fascicle direction when the probe’s principal axis is parallel to the fascicle direction in the plane of the ultrasound image. However, it is unclear how the measured shear modulus is affected by the probe angle relative to the fascicle direction in the same plane. The purpose of the present study was therefore to examine whether the angle between the principal axis of the probe and the fascicle direction in the same plane affects the measured shear modulus. Shear modulus in seven specially-designed tissue-mimicking phantoms, and in eleven human in-vivo biceps brachii and medial gastrocnemius were determined by using ultrasound shear wave elastography. The probe was positioned parallel or 20° obliquely to the fascicle across the B-mode images. The reproducibility of shear modulus measurements was high for both parallel and oblique conditions. Although there was a significant effect of the probe angle relative to the fascicle on the shear modulus in human experiment, the magnitude was negligibly small. These findings indicate that the ultrasound shear wave elastography is a valid tool for evaluating the mechanical property of pennate muscles along the fascicle direction. PMID:25853777
NASA Astrophysics Data System (ADS)
Baud, Patrick; Vajdova, Veronika; Wong, Teng-Fong
2006-12-01
We studied the mechanics of compactant failure in four sandstones associated with a broad range of failure modes in the brittle-ductile transition. While Berea and Bentheim sandstones can fail by compaction localization, homogeneous cataclastic flow dominates failure modes in Adamswiller and Darley Dale sandstones at high effective pressures. We acquired new experimental data to complement previous studies, focusing on the strain hardening behavior in samples under drained conditions. The initial yield stresses were identified as the critical stresses at the onset of shear-enhanced compaction, subsequent yield stresses were considered to depend on hardening given by plastic volumetric strain. The yield stresses were described by elliptical yield caps in the stress space, and we compared the cap evolution with two constitutive models: the critical state model and the cap model. Bentheim sandstone showed the best agreement with both models to relatively large strains. Darley Dale sandstone showed the best agreement with the associated flow rule as prescribed by the normality condition, which is implicitly assumed in both constitutive models. Shear-enhanced compaction in Bentheim and Berea sandstones was appreciably more than that predicted for an associative flow rule, with the implication that a nonassociative model is necessary for capturing the inelastic and failure behavior of these sandstones over a broad range of effective pressures. With reference to the nonassociative model formulated by Rudnicki and Rice, bifurcation analysis would predict the transition of failure mode from shear band to compaction band and ultimately to cataclastic flow, in qualitative agreement with the experimental observations.
Role of a MHD mode crash in triggering H-mode at marginal heating power on the HL-2A tokamak
NASA Astrophysics Data System (ADS)
Cheng, J.; Xu, Y.; Hidalgo, C.; Yan, L. W.; Liu, Yi; Jiang, M.; Li, Y. G.; Yu, L. M.; Dong, Y. B.; Li, D.; Liu, L.; Zhong, W. L.; Xu, J. Q.; Huang, Z. H.; Ji, X. Q.; Song, S. D.; Yu, D. L.; Xu, M.; Shi, Z. B.; Pan, O.; Yang, Q. W.; Ding, X. T.; Duan, X. R.; Liu, Yong
2016-12-01
The impact of a low frequency MHD mode crash on triggering the H-mode has been studied in detail on the HL-2A tokamak. The mode manifests fishbone characteristics with a precession frequency f ≈ 14- 19 kHz. The abrupt mode crash evokes substantial energy release from the core to the plasma boundary and hence increases the edge pressure gradient and Er × B flow shear, which further suppresses turbulence and leads to confinement improvement into the H-mode. Under the same NBI heating (∼1 MW), the I-phase plasma transits into H-mode with a rapid MHD mode crash while it returns to the L-mode without the presence of the mode in the I-phase. With increasing heating power by the ECRH added to the NBI, the MHD mode disappears. The statistical result shows that with the MHD mode crash the heating power for accessing the H-mode is significantly lower than that without the mode crash. All these facts reveal that the MHD mode crash in the I-phase plays a critical role in trigging the I → H transition at marginal heating power. In addition, it has been found that with the same NBI power heating, the magnitude of the mode (crash) increases with increasing plasma density, implying larger energy release being needed to access the H-mode for higher density plasmas.
Development of a low frequency omnidirectional piezoelectric shear horizontal wave transducer
NASA Astrophysics Data System (ADS)
Belanger, Pierre; Boivin, Guillaume
2016-04-01
Structural health monitoring (SHM) may offer an alternative to time based maintenance of safety critical components. Ultrasonic guided waves have recently emerged as a prominent option because their propagation carries information regarding the location, severity and types of damage. The fundamental shear horizontal ultrasonic guided wave mode has recently attracted interest in SHM because of its unique properties. This mode is not dispersive and has no attenuation due to fluid loading. In order to cover large areas using an SHM system, omnidirectional transduction is desired. Omnidirectional transduction of SH0 is challenging because of the required torsional surface stress. This paper presents a concept based on the discretisation of a torsional surface stress source using shear piezoelectric trapezoidal elements. Finite element simulation and experimental results are used to demonstrate the performance of this concept. The experimental modal selectivity is 17 dB and the transducer has a true omnidirectional behaviour.
Lawler, Karen; Foran, Eilis; O'Sullivan, Gerald; Long, Aideen; Kenny, Dermot
2006-10-01
To metastasize, tumor cells must adopt different morphological responses to resist shear forces encountered in circulating blood and invade through basement membranes. The Rho and Ras GTPases play a critical role in regulating this dynamic behavior. Recently, we demonstrated shear-induced activation of adherent esophageal metastatic cells, characterized by formation of dynamic membrane blebs. Although membrane blebbing has only recently been characterized as a rounded mode of cellular invasion promoted through Rho kinase (ROCK), the role of shear forces in modulating membrane blebbing activity is unknown. To further characterize membrane blebbing in esophageal metastatic cells (OC-1 cell line), we investigated the role of shear in cytoskeletal remodeling and signaling through ROCK and Ras. Our results show that actin and tubulin colocalize to the cortical ring of the OC-1 cell under static conditions. However, under shear, actin acquires a punctuate distribution and tubulin localizes to the leading edge of the OC-1 cell. We show for the first time that dynamic bleb formation is induced by shear alone independent of integrin-mediated adhesion (P < 0.001, compared with OC-1 cells). Y-27632, a specific inhibitor of ROCK, causes a significant reduction in shear-induced bleb formation and inhibits integrin alpha(v)beta(3)-Ras colocalization at the leading edge of the cell. Direct measurement of Ras activation shows that the level of GTP-bound Ras is elevated in sheared OC-1 cells and that the shear-induced increase in Ras activity is inhibited by Y-27632. Finally, we show that shear stress significantly increases OC-1 cell invasion (P < 0.007), an effect negated by the presence of Y-27632. Together our findings suggest a novel physiological role for ROCK and Ras in metastatic cell behavior.
Critical Layers and Protoplanetary Disk Turbulence
NASA Astrophysics Data System (ADS)
Umurhan, Orkan M.; Shariff, Karim; Cuzzi, Jeffrey N.
2016-10-01
A linear analysis of the zombie vortex instability (ZVI) is performed in a stratified shearing sheet setting for three model barotropic shear flows. The linear analysis is done by utilizing a Green’s function formulation to resolve the critical layers of the associated normal-mode problem. The instability is the result of a resonant interaction between a Rossby wave and a gravity wave that we refer to as Z-modes. The associated critical layer is the location where the Doppler-shifted frequency of a distant Rossby wave equals the local Brunt-Väisälä frequency. The minimum required Rossby number for instability, {\\mathtt{Ro}}=0.2, is confirmed for parameter values reported in the literature. It is also found that the shear layer supports the instability in the limit where stratification vanishes. The ZVI is examined in a jet model, finding that the instability can occur for {\\mathtt{Ro}}=0.05. Nonlinear vorticity forcing due to unstable Z-modes is shown to result in the creation of a jet flow at the critical layer emerging as the result of the competition between the vertical lifting of perturbation radial vorticity and the radial transport of perturbation vertical vorticity. We find that the picture of this instability leading to a form of nonlinearly driven self-replicating pattern of creation and destruction is warranted: a parent jet spawns a growing child jet at associated critical layers. A mature child jet creates a next generation of child jets at associated critical layers of the former while simultaneously contributing to its own destruction via the Rossby wave instability.
A dynamic jamming point for shear thickening suspensions
NASA Astrophysics Data System (ADS)
Brown, Eric; Jaeger, Heinrich
2008-11-01
Densely packed suspensions can shear thicken, in which the viscosity increases with shear rate. We performed rheometry measurements on two model systems: corn starch in water and glass spheres in oils. In both systems we observed shear thickening up to a critical packing fraction φc (=0.55 for spherical grains) above which the flow abruptly transitions to shear thinning. The viscosity and yield stress diverge as power laws at φc. Extrapolating the dynamic ranges of shear rate and stress in the shear thickening regime up to φc suggests a finite change in shear stress with zero change in shear rate. This is a dynamic analog to the jamming point with a yield stress at zero shear rate.
Study of shear-stiffened elastomers
NASA Astrophysics Data System (ADS)
Tian, Tongfei; Li, Weihua; Ding, Jie; Alici, Gursel; Du, Haiping
2013-06-01
Shear thickening fluids, which are usually concentrated colloidal suspensions composed of non-aggregating solid particles suspended in fluids, exhibit a marked increase in viscosity beyond a critical shear rate. This increased viscosity is seen as being both 'field-activated', due to the dependence on shearing rate, as well as reversible. Shear thickening fluids have found good applications as protection materials, such as in liquid body armor, vibration absorber or dampers. This research aims to expand the protection material family by developing a novel solid status shear thickening material, called shear-stiffened elastomers. These new shear-stiffened elastomers were fabricated with the mixture of silicone rubber and silicone oil. A total of four SSE samples were fabricated in this study. Their mechanical and rheological properties under both steady-state and dynamic loading conditions were tested with a parallel-plate. The effects of silicone oil composition and angular frequency were summarized. When raising the angular frequency in dynamic shear test, the storage modulus of conventional silicone rubber shows a small increasing trend with the frequency. However, if silicone oil is selected to be mixed with silicone rubber, the storage modulus increases dramatically when the frequency and strain are both beyond the critical values.
Dynamic shear deformation in high purity Fe
Cerreta, Ellen K; Bingert, John F; Trujillo, Carl P; Lopez, Mike F; Gray, George T
2009-01-01
The forced shear test specimen, first developed by Meyer et al. [Meyer L. et al., Critical Adiabatic Shear Strength of Low Alloyed Steel Under Compressive Loading, Metallurgical Applications of Shock Wave and High Strain Rate Phenomena (Marcel Decker, 1986), 657; Hartmann K. et al., Metallurgical Effects on Impact Loaded Materials, Shock Waves and High Strain rate Phenomena in Metals (Plenum, 1981), 325-337.], has been utilized in a number of studies. While the geometry of this specimen does not allow for the microstructure to exactly define the location of shear band formation and the overall mechanical response of a specimen is highly sensitive to the geometry utilized, the forced shear specimen is useful for characterizing the influence of parameters such as strain rate, temperature, strain, and load on the microstructural evolution within a shear band. Additionally, many studies have utilized this geometry to advance the understanding of shear band development. In this study, by varying the geometry, specifically the ratio of the inner hole to the outer hat diameter, the dynamic shear localization response of high purity Fe was examined. Post mortem characterization was performed to quantify the width of the localizations and examine the microstructural and textural evolution of shear deformation in a bcc metal. Increased instability in mechanical response is strongly linked with development of enhanced intergranular misorientations, high angle boundaries, and classical shear textures characterized through orientation distribution functions.
Origins of Shear Jamming for Frictional Grains
NASA Astrophysics Data System (ADS)
Wang, Dong; Zheng, Hu; Ren, Jie; Dijksman, Joshua; Bares, Jonathan; Behringer, Robert
2016-11-01
Granular systems have been shown to be able to behave like solids, under shear, even when their densities are below the critical packing fraction for frictionless isotropic jamming. To understand such a phenomena, called shear jamming, the question we address here is: how does shear bring a system from a unjammed state to a jammed state, where the coordination number, Z, is no less than 3, the isotropic jamming point for frictional grains? Since Z can be used to distinguish jammed states from unjammed ones, it is vital to understand how shear increases Z. We here propose a set of three particles in contact, denoted as a trimer, as the basic unit to characterize the deformation of the system. Trimers, stabilized by inter-grain friction, fail under a certain amount of shear and bend to make extra contacts to regain stability. By defining a projection operator of the opening angle of the trimer to the compression direction in the shear, O, we see a systematically linear decrease of this quantity with respect to shear strain, demonstrating the bending of trimers as expected. In addition, the average change of O from one shear step to the next shows a good collapse when plotted against Z, indicating a universal behavior in the process of shear jamming. We acknowledge support from NSF DMR1206351, NASA NNX15AD38G, the William M. Keck Foundation and a RT-MRSEC Fellowship.
a Critical Test of the Galactic Escape Velocity at R(sun): Cycle 1 Observations; Pos Mode Only
NASA Astrophysics Data System (ADS)
MacConnell, D.
1991-07-01
We propose to measure the trigonometric parallaxes and proper motions of the three high-proper motion stars which Carney, Latham, and Laird (1988) identify as having the most extreme velocities known in the galactic rest frame. Using these stars, they conclude that the local value of the escape velocity, V(esc), is at least 500 k/s, and this leads them to draw other important conclusions regarding the distribution of mass in the galactic disk. However, their assigned distances, and hence the tangential velocities and V(esc) value, depend on uncertain photometric corrections and reddening estimates. The photometric distances they find are in the range 400-550 pc, so the parallaxes are expected to be of the order of 2 milliarcsec. If these distances are approximately correct, it will be possible to measure them at the 4-sigma level using an FGS on the HST. It will be of great interest if the parallaxes are smaller than the estimates of Carney, et al., since this would lead to a higher value for the escape velocity and a larger mass for the galaxy. Alternatively, if the parallaxes are found to be larger than they adopted, either V(esc) is considerably smaller than 500 k/s or these three stars are not the most app- ropriate for setting a limit on V(esc). NOTE added 16-Apr-1991: Three targets changed to two, G166-37 and G233-27. This is Cycle 1 POS mode only. NOTE added 09-Mar-1992: Target G233-27 dropped after TRANS obs. failed due to spoiler 4" away. New target, G16-25, was substituted and is included here.
a Critical Test of the Galactic Escape Velocity at R(sun): Cycle 1 Observations; Trans Mode Only
NASA Astrophysics Data System (ADS)
MacConnell, D.
1990-12-01
We propose to measure the trigonometric parallaxes and proper motions of the three high-proper motion stars which Carney, Latham, and Laird (1988) identify as having the most extreme velocities known in the galactic rest frame. Using these stars, they conclude that the local value of the escape velocity, V(esc), is at least 500 k/s, and this leads them to draw other important conclusions regarding the distribution of mass in the galactic disk. However, their assigned distances, and hence the tangential velocities and V(esc) value, depend on uncertain photometric corrections and reddening estimates. The photometric distances they find are in the range 400-550 pc, so the parallaxes are expected to be of the order of 2 milliarcsec. If these distances are approximately correct, it will be possible to measure them at the 4-sigma level using an FGS on the HST. It will be of great interest if the parallaxes are smaller than the estimates of Carney, et al., since this would lead to a higher value for the escape velocity and a larger mass for the galaxy. Alternatively, if the parallaxes are found to be larger than they adopted, either V(esc) is considerably smaller than 500 k/s or these three stars are not the most app- ropriate for setting a limit on V(esc). NOTE added 16-Apr-1991: Three targets changed to two, G166-37 and G233-27. This is Cycle 1 POS mode only. NOTE added 09-Mar-1992: Target G233-27 dropped after TRANS obs. failed due to spoiler 4" away. New target, G16-25, was substituted and is included here.
NASA Astrophysics Data System (ADS)
MacConnell, D.
1991-07-01
We propose to measure the trigonometric parallaxes and proper motions of the three high-proper motion stars which Carney, Latham, and Laird (1988) identify as having the most extreme velocities known in the galactic rest frame. Using these stars, they conclude that the local value of the escape velocity, V(esc), is at least 500 k/s, and this leads them to draw other important conclusions regarding the distribution of mass in the galactic disk. However, their assigned distances, and hence the tangential velocities and V(esc) value, depend on uncertain photometric corrections and reddening estimates. The photometric distances they find are in the range 400-550 pc, so the parallaxes are expected to be of the order of 2 milliarcsec. If these distances are approximately correct, it will be possible to measure them at the 4-sigma level using an FGS on the HST. It will be of great interest if the parallaxes are smaller than the estimates of Carney, et al., since this would lead to a higher value for the escape velocity and a larger mass for the galaxy. Alternatively, if the parallaxes are found to be larger than they adopted, either V(esc) is considerably smaller than 500 k/s or these three stars are not the most app- ropriate for setting a limit on V(esc). NOTE added 16-Apr-1991: Three targets changed to two, G166-37 and G233-27. This is Cycle 1 POS mode only. NOTE added 09-Mar-1992: Target G233-27 dropped after TRANS obs. failed due to spoiler 4" away. New target, G16-25, was substituted and is included here.
Daverio, Marco; Fino, Giuliana; Luca, Brugnaro; Zaggia, Cristina; Pettenazzo, Andrea; Parpaiola, Antonella; Lago, Paola; Amigoni, Angela
2015-12-01
Errors in are estimated to occur with an incidence of 3.7-16.6% in hospitalized patients. The application of systems for detection of adverse events is becoming a widespread reality in healthcare. Incident reporting (IR) and failure mode and effective analysis (FMEA) are strategies widely used to detect errors, but no studies have combined them in the setting of a pediatric intensive care unit (PICU). The aim of our study was to describe the trend of IR in a PICU and evaluate the effect of FMEA application on the number and severity of the errors detected. With this prospective observational study, we evaluated the frequency IR documented in standard IR forms completed from January 2009 to December 2012 in the PICU of Woman's and Child's Health Department of Padova. On the basis of their severity, errors were classified as: without outcome (55%), with minor outcome (16%), with moderate outcome (10%), and with major outcome (3%); 16% of reported incidents were 'near misses'. We compared the data before and after the introduction of FMEA. Sixty-nine errors were registered, 59 (86%) concerning drug therapy (83% during prescription). Compared to 2009-2010, in 2011-2012, we noted an increase of reported errors (43 vs 26) with a reduction of their severity (21% vs 8% 'near misses' and 65% vs 38% errors with no outcome). With the introduction of FMEA, we obtained an increased awareness in error reporting. Application of these systems will improve the quality of healthcare services. © 2015 John Wiley & Sons Ltd.
NASA Technical Reports Server (NTRS)
Miner, R. V.
1997-01-01
Prototypical single-crystal NiAlCrX superalloys were studied to examine the effects of the common major alloying elements, Co, Mo, Nb, Ta, Ti, and W, on yielding behavior. The alloys contained about 10 at. pct Cr, 60 vol pct of the gamma' phase, and about 3 at. pct of X in the gamma'. The critical resolved shear stresses (CRSSs) for octahedral and primary cube slip were measured at 760 C, which is about the peak strength temperature. The CRSS(sub oct) and CRSS(sub cube) are discussed in relation to those of Ni, (Al, X) gamma' alloys taken from the literature and the gamma'/gamma lattice mismatch. The CRSS(sub oct) of the gamma + gamma' alloys reflected a similar compositional dependence to that of both the CRSS(sub cube) of the gamma' phase and the gamma'/gamma lattice parameter mismatch. The CRSS(sub cube) of the gamma + gamma' alloys also reflected the compositional dependence of the gamma'/gamma mismatch, but bore no similarity to that of CRSS(sub cube) for gamma' alloys since it is controlled by the gamma matrix. The ratio of CRSS(sub cube)/CRSS(sub oct) was decreased by all alloying elements except Co, which increased the ratio. The decrease in CRSS(sub cube)/CRSS(sub oct) was related to the degree in which elements partition to the gamma' rather than the gamma phase.
NASA Technical Reports Server (NTRS)
Miner, R. V.
1997-01-01
Prototypical single-crystal NiAlCrX superalloys were studied to examine the effects of the common major alloying elements, Co, Mo, Nb, Ta, Ti, and W, on yielding behavior. The alloys contained about 10 at. pct Cr, 60 vol pct of the gamma' phase, and about 3 at. pct of X in the gamma'. The critical resolved shear stresses (CRSSs) for octahedral and primary cube slip were measured at 760 C, which is about the peak strength temperature. The CRSS(sub oct) and CRSS(sub cube) are discussed in relation to those of Ni, (Al, X) gamma' alloys taken from the literature and the gamma'/gamma lattice mismatch. The CRSS(sub oct) of the gamma + gamma' alloys reflected a similar compositional dependence to that of both the CRSS(sub cube) of the gamma' phase and the gamma'/gamma lattice parameter mismatch. The CRSS(sub cube) of the gamma + gamma' alloys also reflected the compositional dependence of the gamma'/gamma mismatch, but bore no similarity to that of CRSS(sub cube) for gamma' alloys since it is controlled by the gamma matrix. The ratio of CRSS(sub cube)/CRSS(sub oct) was decreased by all alloying elements except Co, which increased the ratio. The decrease in CRSS(sub cube)/CRSS(sub oct) was related to the degree in which elements partition to the gamma' rather than the gamma phase.
From Phase Locking to Phase Slips: A Mechanism for a Quiescent H mode
NASA Astrophysics Data System (ADS)
Guo, Z. B.; Diamond, P. H.
2015-04-01
We demonstrate that E ×B shear, VE×B ' , governs the dynamics of the cross phase of the peeling-ballooning-(PB-)mode-driven heat flux, and so determines the evolution from the edge-localized (ELMy) H mode to the quiescent (Q ) H mode. A physics-based scaling of the critical E ×B shearing rate (VE×B ,c r ' ) for accessing the Q H mode is predicted. The ELMy H mode to the Q H -mode evolution is shown to follow from the conversion from a phase locked state to a phase slip state. In the phase locked state, PB modes are pumped continuously, so bursts occur. In the slip state, the PB activity is a coherent oscillation. Stronger E ×B shearing implies a higher phase slip frequency. This finding predicts a new state of cross phase dynamics and shows a new way to understand the physics mechanism for ELMy to the Q H -mode evolution.
Measurement of the temperature-dependent threshold shear-stress of red blood cell aggregation
NASA Astrophysics Data System (ADS)
Lim, Hyun-Jung; Nam, Jeong-Hun; Lee, Yong-Jin; Shin, Sehyun
2009-09-01
Red blood cell (RBC) aggregation is becoming an important hemorheological parameter, which typically exhibits temperature dependence. Quite recently, a critical shear-stress was proposed as a new dimensional index to represent the aggregative and disaggregative behaviors of RBCs. The present study investigated the effect of the temperature on the critical shear-stress that is required to keep RBC aggregates dispersed. The critical shear-stress was measured at various temperatures (4, 10, 20, 30, and 37 °C) through the use of a transient microfluidic aggregometry. The critical shear-stress significantly increased as the blood temperature lowered, which accorded with the increase in the low-shear blood viscosity with the lowering of the temperature. Furthermore, the critical shear-stress also showed good agreement with the threshold shear-stress, as measured in a rotational Couette flow. These findings assist in rheologically validating the critical shear-stress, as defined in the microfluidic aggregometry.
Acoustic measurements in sheared granular materials
NASA Astrophysics Data System (ADS)
Brzinski, Theodore; Daniels, Karen
2014-03-01
Acoustic measurements in static, jammed granular materials have revealed an excess of low-frequency vibrational modes which decreases as the confining pressure is increased. This behavior may be analogous to the excess in low-frequency modes associated with the loss of rigidity in molecular and colloidal glasses. To test this analogy, we measure the acoustic emissions from jammed, quasi-2D granular packings under shear. In contrast to static experiments, shear enables direct comparison of acoustic properties as a packing approaches failure. We use a split-bottom geometry with flexible boundaries held under controlled tension, allowing experiments to be conducted at a set confining pressure.
Shear accommodation in dirty grain boundaries
NASA Astrophysics Data System (ADS)
Wang, C.; Upmanyu, M.
2014-04-01
The effect of solutes (dirt) on the mechanics of crystalline interfaces remains unexplored. Here, we perform atomic-scale simulations to study the effect of carbon segregation on the shear accommodation at select grain boundaries in the classical α-Fe/C system. For shear velocities larger than the solute diffusion rate, we observe a transition from coupled motion to sliding. Below a critical solute excess, the boundaries break away from the solute cloud and exhibit in a coupled motion. At smaller shear velocities, the extrinsic coupled motion is jerky, occurs at relatively small shear stresses, and is aided by fast convective solute diffusion along the boundary. Our studies underscore the combined effect of energetics and kinetics of solutes in modifying the bicrystallography, temperature and rate dependence of shear accommodation at grain boundaries.
Visualization of shear banding in colloidal glasses
NASA Astrophysics Data System (ADS)
Chikkadi, Vijayakumar; Schofield, Andrew; Nienhuis, Bernard; Schall, Peter
2010-03-01
Shear banding, i.e. the localization of shear flow, occurs in a manifold of systems ranging from hard materials such as metallic glasses to soft materials such as clays, shaving cream or mayonnaise. We investigate this phenomenon in a dense colloidal system using confocal microscopy that enables to track individual particles in 3D space and time. The particle motions reveal a transition from homogeneous flow to shear localization above a critical shear rate. We elucidate this transition using spatial correlations in the displacement of the particles. The diffusive motion of the particles is correlated over large length, and shows intermittent, scale-free behavior, reminiscent of crystal plasticity. Further, we associate an order parameter with the mobility of particles and demonstrate that shear banding is phase coexistence of regions differing in mobilities.
Linear stability of thermocapillary liquid layers of a shear-thinning fluid
NASA Astrophysics Data System (ADS)
Hu, Kai-Xin; He, Meng; Chen, Qi-Sheng; Liu, Rong
2017-07-01
The linear stability analysis has been performed for the thermocapillary liquid layers of a shear-thinning fluid. The Carreau fluid model is applied to describe the rheological property. The critical parameters are determined as a function of Prandtl number (Pr), degree of shear-thinning, and gravity level. For linear flow, the shear-thinning effect is destabilizing for small and moderate Pr but increases the stability slightly for large Pr. For return flow, the perturbation kinetic energy concentrates near the surface, and the flow is stabilized when the surface viscosity is used. The streamwise wave is excited at large Pr, and a new mechanism is found at moderate Pr, where the hot spots appear at the bottom of the layer. In the presence of gravity, the viscosity stratification is enhanced and more kinds of different modes are excited. The preferred mode changes to downstream at large Pr while the gravity becomes an important perturbation energy source at small Pr. The shear-thinning effect for the instability mechanism is discussed and the comparisons are made with channel flows.
Failure Mode of the Water-filled Fractures under Hydraulic Pressure in Karst Tunnels
NASA Astrophysics Data System (ADS)
Dong, Xin; Lu, Hao; Huang, Houxu; Hao, Yiqing; Xia, Yuanpu
2017-06-01
Water-filled fractures continue to grow after the excavation of karst tunnels, and the hydraulic pressure in these fractures changes along with such growth. This paper simplifies the fractures in the surrounding rock as flat ellipses and then identifies the critical hydraulic pressure values required for the occurrence of tensile-shear and compression-shear failures in water-filled fractures in the case of plane stress. The occurrence of tensile-shear fracture requires a larger critical hydraulic pressure than compression-shear failure in the same fracture. This paper examines the effects of fracture strike and lateral pressure coefficient on critical hydraulic pressure, and identifies compression-shear failure as the main failure mode of water-filled fractures. This paper also analyses the hydraulic pressure distribution in fractures with different extensions, and reveals that hydraulic pressure decreases along with the continuous growth of fractures and cannot completely fill a newly formed fracture with water. Fracture growth may be interrupted under the effect of hydraulic tensile shear.
Nonlinear Instability of a Uni-directional Transversely Sheared Mean Flow
NASA Technical Reports Server (NTRS)
Wundrow, David W.; Goldstein, Marvin E.
1994-01-01
It is well known that the presence of a weak cross flow in an otherwise two-dimensional shear flow results in a spanwise variation in the mean streamwise velocity profile that can lead to an amplification of certain three-dimensional disturbances through a kind of resonant-interaction mechanism (Goldstein and Wundrow 1994). The spatial evolution of an initially linear, finite-growth-rate, instability wave in such a spanwise-varying shear flow is considered, The base flow, which is governed by the three-dimensional parabolized Navier-Stokes equations, is initiated by imposing a spanwise- periodic cross-flow velocity on an otherwise two-dimensional shear flow at some fixed streamwise location. The resulting mean-flow distortion initially grows with increasing streamwise distance, reaches a maximum and eventually decays through the action of viscosity. This decay, which coincides with the viscous spread of of the shear layer, means that the local growth rate of the instability wave will eventually decrease as the wave propagates downstream. Nonlinear effects can then become important within a thin spanwise-modulated critical layer once the local instability-wave amplitude and growth rate become sufficiently large and small, respectively. The amplitude equation that describes this stage of evolution is shown to be a generalization of the one obtained by Goldstein and Choi (1989) who considered the related problem of the interaction of two oblique modes in a two-dimensional shear layer.
Dodelson, Scott; Shapiro, Charles; White, Martin J.; /UC, Berkeley, Astron. Dept. /UC, Berkeley
2005-08-01
Measurements of ellipticities of background galaxies are sensitive to the reduced shear, the cosmic shear divided by (1-{kappa}) where {kappa} is the projected density field. They compute the difference between shear and reduced shear both analytically and with simulations. The difference becomes more important an smaller scales, and will impact cosmological parameter estimation from upcoming experiments. A simple recipe is presented to carry out the required correction.
Hydrodynamic lubrication in nanoscale bearings under high shear velocity
NASA Astrophysics Data System (ADS)
Chen, Yunfei; Li, Deyu; Jiang, Kai; Yang, Juekuan; Wang, Xiaohui; Wang, Yujuan
2006-08-01
The setting up process in a nanoscale bearing has been modeled by molecular dynamics simulation. Contrary to the prediction from the classical Reynolds' theory, simulation results show that the load capacity of the nanoscale bearing does not increase monotonically with the operation speed. This is attributed to the change of the local shear rate, which will decrease with the shear velocity of the bearing as the shear velocity exceeds a critical value, i.e., the local shear rate has an upper limit. A simple nonlinear dynamic model indicates that the momentum exchange between the liquid and the solid wall is reduced with the shear velocity when the shear velocity is above a critical value. The weak momentum exchange results in a decrease of the local shear rate, which in turn causes a sharp increase of the slip length.
Experimental study of shear rate dependence in perpetually sheared granular matter
NASA Astrophysics Data System (ADS)
Liu, Sophie Yang; Guillard, François; Marks, Benjy; Rognon, Pierre; Einav, Itai
2017-06-01
We study the shear behaviour of various granular materials by conducting novel perpetual simple shear experiments over four orders of magnitude of relatively low shear rates. The newly developed experimental apparatus employed is called "3D Stadium Shear Device" which is an extended version of the 2D Stadium Shear Device [1]. This device is able to provide a non-radial dependent perpetual shear flow and a nearly linear velocity profile between two oppositely moving shear walls. Using this device, we are able to test a large variety of granular materials. Here, we demonstrate the applicability of the device on glass beads (diameter 1 mm, 3 mm, and 14 mm) and rice. We particularly focus on studying these materials at very low inertial number I ranging from 10-6 to 10-2. We find that, within this range of I, the friction coefficient μ of glass beads has no shear rate dependence. A particularly appealing observation comes from testing rice, where the attainment of critical state develops under much longer duration than in other materials. Initially during shear we find a value of μ similar to that found for glass beads, but with time this value decreases gradually towards the asymptotic critical state value. The reason, we believe, lies in the fact that rice grains are strongly elongated; hence the time to achieve the stable μ is primarily controlled by the time for particles to align themselves with respect to the shear walls. Furthermore, the initial packing conditions of samples also plays a role in the evolution of μ when the shear strain is small, but that impact will eventually be erased after sufficient shear strain.
Rotatable shear plate interferometer
Duffus, Richard C.
1988-01-01
A rotatable shear plate interferometer comprises a transparent shear plate mounted obliquely in a tubular supporting member at 45.degree. with respect to its horizontal center axis. This tubular supporting member is supported rotatably around its center axis and a collimated laser beam is made incident on the shear plate along this center axis such that defocus in different directions can be easily measured.
Derivation of Path Independent Coupled Mix Mode Cohesive Laws from Fracture Resistance Curves
NASA Astrophysics Data System (ADS)
Goutianos, Stergios
2017-08-01
A generalised approach is presented to derive coupled mixed mode cohesive laws described with physical parameters such as peak traction, critical opening, fracture energy and cohesive shape. The approach is based on deriving mix mode fracture resistance curves from an effective mix mode cohesive law at different mode mixities. From the fracture resistance curves, the normal and shear stresses of the cohesive laws can be obtained by differentiation. Since, the mixed mode cohesive laws are obtained from a fracture resistance curve (potential function), path independence is automatically satisfied. The effective mix mode cohesive law can have different shape and cohesive law parameters at different mode mixities so that the approach can be applied to various material failure models.
Interlaminar shear fracture toughness and fatigue thresholds for composite materials
NASA Technical Reports Server (NTRS)
Obrien, T. Kevin; Murri, Gretchen B.; Salpekar, Satish A.
1987-01-01
Static and cyclic end notched flexure tests were conducted on a graphite epoxy, a glass epoxy, and graphite thermoplastic to determine their interlaminar shear fracture toughness and fatigue thresholds for delamination in terms of limiting values of the mode II strain energy release rate, G-II, for delamination growth. The influence of precracking and data reduction schemes are discussed. Finite element analysis indicated that the beam theory calculation for G-II with the transverse shear contribution included was reasonably accurate over the entire range of crack lengths. Cyclic loading significantly reduced the critical G-II for delamination. A threshold value of the maximum cyclic G-II below which no delamination occurred after one million cycles was identified for each material. Also, residual static toughness tests were conducted on glass epoxy specimens that had undergone one million cycles without delamination. A linear mixed-mode delamination criteria was used to characterize the static toughness of several composite materials; however, a total G threshold criterion appears to characterize the fatigue delamination durability of composite materials with a wide range of static toughness.
Interlaminar shear fracture toughness and fatigue thresholds for composite materials
NASA Technical Reports Server (NTRS)
O'Brien, T. Kevin; Murri, Gretchen B.; Salpekar, Satish A.
1989-01-01
Static and cyclic end notched flexure tests were conducted on a graphite epoxy, a glass epoxy, and graphite thermoplastic to determine their interlaminar shear fracture toughness and fatigue thresholds for delamination in terms of limiting values of the mode II strain energy release rate, G-II, for delamination growth. The influence of precracking and data reduction schemes are discussed. Finite element analysis indicated that the beam theory calculation for G-II with the transverse shear contribution included was reasonably accurate over the entire range of crack lengths. Cyclic loading significantly reduced the critical G-II for delamination. A threshold value of the maximum cyclic G-II below which no delamination occurred after one million cycles was identified for each material. Also, residual static toughness tests were conducted on glass epoxy specimens that had undergone one million cycles without delamination. A linear mixed-mode delamination criteria was used to characterize the static toughness of several composite materials; however, a total G threshold criterion appears to characterize the fatigue delamination durability of composite materials with a wide range of static toughness.
Effects of shear coupling on shear properties of wood
Jen Y. Liu
2000-01-01
Under pure shear loading, an off-axis element of orthotropic material such as pure wood undergoes both shear and normal deformations. The ratio of the shear strain to a normal strain is defined as the shear coupling coefficient associated with the direction of the normal strain. The effects of shear coupling on shear properties of wood as predicted by the orthotropic...
Discontinuous Shear Thickening of Frictional Hard-Sphere Suspensions
NASA Astrophysics Data System (ADS)
Seto, Ryohei; Mari, Romain; Morris, Jeffrey F.; Denn, Morton M.
2013-11-01
Discontinuous shear thickening (DST) observed in many dense athermal suspensions has proven difficult to understand and to reproduce by numerical simulation. By introducing a numerical scheme including both relevant hydrodynamic interactions and granularlike contacts, we show that contact friction is essential for having DST. Above a critical volume fraction, we observe the existence of two states: a low viscosity, contactless (hence, frictionless) state, and a high viscosity frictional shear jammed state. These two states are separated by a critical shear stress, associated with a critical shear rate where DST occurs. The shear jammed state is reminiscent of the jamming phase of granular matter. Continuous shear thickening is seen as a lower volume fraction vestige of the jamming transition.
Ballooning mode second stability region for sequences of tokamak equilibria
Sugiyama, L.; Mark, J. W-K.
1980-01-01
A numerical study of several sequences of tokamak equilibria derived from two flux conserving sequences confirms the tendency of high n ideal MHD ballooning modes to stabilize for values of the plasma beta greater than a second critical beta, for sufficiently favorable equilibria. The major stabilizing effect of increasing the inverse rotational transform profile q(Psi) for equilibria with the same flux surface geometry is shown. The unstable region shifts toward larger shear d ln q/d ln ..gamma.. and the width of the region measured in terms of the poloidal beta or a pressure gradient parameter, for fixed shear, decreases. The smaller aspect ratio sequences are more sensitive to changes in q and have less stringent limits on the attainable value of the plasma beta in the high beta stable region. Finally, the disconnected mode approximation is shown to provide a reasonable description of the second high beta stability boundary.
A Controlled Shear Decorrelation Experiment (CSDX)
NASA Astrophysics Data System (ADS)
Tynan, George
1999-11-01
The controlled shear de-correlation experiment (CSDX) is being designed to study the effect of sheared flows on: (1) known linear pressure gradient-driven drift and/or effective gravity-driven flute eigenmodes; (2) the nonlinear three-wave coupling of a finite number of large amplitude coherent modes; and (3) on the rate of electrostatic turbulent fluctuation energy cascades. This research is motivated by magnetic confinement experiments and theory which suggest that sheared E x B shear flows lead to a nonlinear de-correlation of plasma turbulence. The plasma state (i.e. quiescent, single small-amplitude drift wave, nonlinearly coupled modes, or strongly turbulent) will be controlled by varying the magnetic field strength, collisionality, parallel current, and/or effective gravity due to solid-body plasma rotation driven by azimuthal ExB drifts. The radial electric field strength and shear rate will be controlled independently of the plasma state by the application of externally controlled voltages to concentric annular rings which will form the ends of the experimental region. Diagnostics include azimuthal, radial, and axial Langmuir probe arrays, laser induced flourescence (LIF) for ion temperature and equilibrium ExB flow velocities. Bi-spectral analysis techniques will be used to measure k-space resolved linear growth rates and nonlinear energy cascading due to three-wave coupling in the presence of flow shear. Designs and experimental plans will be presented and discussed.
Roles of nanoclusters in shear banding and plastic deformation of bulk metallic glasses
Nieh, T G
2012-07-31
During the course of this research we published 33 papers in various physics/material journals. We select four representing papers in this report and their results are summarized as follows. I. To study shear banding process, it is pertinent to know the intrinsic shear strain rate within a propagating shear band. To this aim, we used nanoindentation technique to probe the mechanical response of a Au49Ag5.5Pd2.3Cu26.9Si16.3 bulk metallic glass in locality and found notable pop-in events associated with shear band emission. Using a free volume model and under the situation when temperature and stress/hardness are fixed result in an equation, which predicts that hardness serration caused by pop-in decreases exponentially with the strain rate. Our data are in good agreement with the prediction. The result also predicts that, when strain rate is higher than a critical strain rate of 1700 s^-1, there will be no hardness serration, thereby no pop-in. In other words, multiple shear bandings will take place and material will flow homogeneously. The critical strain rate of 1700 s^-1 can be treated as the intrinsic strain rate within a shear band. We subsequently carried out a simulation study and showed that, if the imposed strain rate was over , the shear band spacing would become so small that the entire sample would virtually behave like one major shear band. Using the datum strain rate =1700 s^-1 and based on a shear band nucleation model proposed by us, the size of a shear-band nucleus in Au-BMG was estimated to be 3 10^6 atoms, or a sphere of ~30 nm in diameter. II. Inspired by the peculiar result published in a Science article Super Plastic Bulk Metallic Glasses at Room Temperature, we synthesized the Zr-based bulk metallic glass with a composition identical to that in the paper (Zr64.13Cu15.75Ni10.12Al10) and, subsequently, tested in compression at the same slow strain rate (~10^-4 s^-1). We found that the dominant deformation mode is always single shear. The stress
Shear induced orientation of edible fat and chocolate crystals
NASA Astrophysics Data System (ADS)
Mazzanti, Gianfranco; Welch, Sarah E.; Marangoni, Alejandro G.; Sirota, Eric B.; Idziak, Stefan H. J.
2003-03-01
Shear-induced orientation of fat crystallites was observed during crystallization of cocoa butter, milk fat, stripped milk fat and palm oil. This universal effect was observed in systems crystallized under high shear. The minor polar components naturally present in milk fat were found to decrease the shear-induced orientation effect in this system. The competition between Brownian and shear forces, described by the Peclet number, determines the crystallite orientation. The critical radius size, from the Gibbs-Thomson equation, provides a tool to understand the effect of shear at the onset stages of crystallization.
Transiently Jammed State in Shear Thickening Suspensions under Shear
NASA Astrophysics Data System (ADS)
Mukhopadhyay, Shomeek; Allen, Benjamin; Brown, Eric
2014-03-01
We examine the response of a suspension of cornstarch and water under normal impact at controlled velocities. This is a model system to understand why a person can run on the surface of a discontinuous shear thickening fluid. Using simultaneous high-speed imaging of the top and bottom surfaces along with normal force measurements allows us to investigate whether the force response is a result of system spanning structures. We observe a shear thickening transition where above a critical velocity the normal force increases by orders of magnitude. In the high force regime the force response is displacement dependent like a solid rather than velocity dependent like a liquid. The stresses are on the order of 106 Pa which is enough to hold up a person's weight. In this regime imaging shows the existence of a solid like structure that extends to the bottom interface.
Influence of magnetic shear on impurity transport
Nordman, H.; Fueloep, T.; Candy, J.; Strand, P.; Weiland, J.
2007-05-15
The magnetic shear dependence of impurity transport in tokamaks is studied using a quasilinear fluid model for ion temperature gradient (ITG) and trapped electron (TE) mode driven turbulence in the collisionless limit and the results are compared with nonlinear gyrokinetic results using GYRO [J. Candy and R. E. Waltz, J. Comput. Phys 186, 545 (2003)]. It is shown that the impurity transport is sensitive to the magnetic shear, in particular for weak, negative, and large positive shear where a strong reduction of the effective impurity diffusivity is obtained. The fluid and gyrokinetic results are in qualitative agreement, with the gyrokinetic diffusivities typically a factor 2 larger than the fluid diffusivities. The steady state impurity profiles in source-free plasmas are found to be considerably less peaked than the electron density profiles for moderate shear. Comparisons between anomalous and neoclassical transport predictions are performed for ITER-like profiles [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002)].
Sustained shear flows in Rayleigh-Bénard convection
NASA Astrophysics Data System (ADS)
Quist, Tayler; Anders, Evan; Brown, Benjamin; Oishi, Jeffrey
2016-11-01
Zonal shear flows play important roles in both the solar and geo dynamos. In two dimensional simulations, and at relatively narrow aspect ratios, Rayleigh-Bénard convection naturally achieves zonal shear flows. These zonal flows are driven by the convection and modify it, significantly altering the heat transport and convective structures. Here we study shear flows in two and three-dimensional simulations of Rayleigh-Bénard convection using the Dedalus pseudospectral framework. At small aspect ratios and at Prandtl number 1, a large horizontal shear naturally occurs. At larger aspect ratios, we find that shearing is naturally prevented unless manually induced; there is a bistability between states dominated by "flywheel" modes and states dominated by large scale shear. We explore these states and the possibilities of sustained large scale shear in 3-D simulations.
Mechanical shear and tensile characteristics of selected biomass stems
USDA-ARS?s Scientific Manuscript database
Mechanical characteristics (stress and energy of tensile and shear modes) of selected biomass stems, such as big bluestem, bromegrass, and Barlow wheat were determined. A high capacity MTI-100K universal testing machine attached with standard tensile clamps and designed fabricated double-shear devic...
Dynamics of High Pressure Reacting Shear Flows
2013-12-17
and supercritical acoustic-jet interactions to reacting flow in a canonical coaxial shear flow configuration – Emphasis on the flame holding region...unlimited. PA#13554 11 Coaxial Jets Initial...PA#13554 12 Forced Coaxial Jets 1. Transverse Acoustic mode from chamber
Shear forces enhance Toxoplasma gondii tachyzoite motility on vascular endothelium.
Harker, Katherine S; Jivan, Elizabeth; McWhorter, Frances Y; Liu, Wendy F; Lodoen, Melissa B
2014-04-01
Toxoplasma gondii is a highly successful parasite that infects approximately one-third of the human population and can cause fatal disease in immunocompromised individuals. Systemic parasite dissemination to organs such as the brain and eye is critical to pathogenesis. T. gondii can disseminate via the circulation, and both intracellular and extracellular modes of transport have been proposed. However, the processes by which extracellular tachyzoites adhere to and migrate across vascular endothelium under the conditions of rapidly flowing blood remain unknown. We used microfluidics and time-lapse fluorescence microscopy to examine the interactions between extracellular T. gondii and primary human endothelial cells under conditions of physiologic shear stress. Remarkably, tachyzoites adhered to and glided on human vascular endothelium under shear stress conditions. Compared to static conditions, shear stress enhanced T. gondii helical gliding, resulting in a significantly greater displacement, and increased the percentage of tachyzoites that invaded or migrated across the endothelium. The intensity of the shear forces (from 0.5 to 10 dynes/cm(2)) influenced both initial and sustained adhesion to endothelium. By examining tachyzoites deficient in the T. gondii adhesion protein MIC2, we found that MIC2 contributed to initial adhesion but was not required for adhesion strengthening. These data suggest that under fluidic conditions, T. gondii adhesion to endothelium may be mediated by a multistep cascade of interactions that is governed by unique combinations of adhesion molecules. This work provides novel information about tachyzoite interactions with vascular endothelium and contributes to our understanding of T. gondii dissemination in the infected host. IMPORTANCE Toxoplasma gondii is a global parasite pathogen that can cause fatal disease in immunocompromised individuals. An unresolved question is how the parasites circulate in the body to tissues to cause disease
Compact forced simple-shear sample for studying shear localization in materials
Gray, George Thompson; Vecchio, K. S.; Livescu, Veronica
2015-11-06
In this paper, a new specimen geometry, the compact forced-simple-shear specimen (CFSS), has been developed as a means to achieve simple shear testing of materials over a range of temperatures and strain rates. The stress and strain state in the gage section is designed to produce essentially “pure” simple shear, mode II in-plane shear, in a compact-sample geometry. The 2-D plane of shear can be directly aligned along specified directional aspects of a material's microstructure of interest; i.e., systematic shear loading parallel, at 45°, and orthogonal to anisotropic microstructural features in a material such as the pancake-shaped grains typical in many rolled structural metals, or to specified directions in fiber-reinforced composites. Finally, the shear-stress shear-strain response and the damage evolution parallel and orthogonal to the pancake grain morphology in 7039-Al are shown to vary significantly as a function of orientation to the microstructure.
Compact forced simple-shear sample for studying shear localization in materials
Gray, George Thompson; Vecchio, K. S.; Livescu, Veronica
2015-11-06
In this paper, a new specimen geometry, the compact forced-simple-shear specimen (CFSS), has been developed as a means to achieve simple shear testing of materials over a range of temperatures and strain rates. The stress and strain state in the gage section is designed to produce essentially “pure” simple shear, mode II in-plane shear, in a compact-sample geometry. The 2-D plane of shear can be directly aligned along specified directional aspects of a material's microstructure of interest; i.e., systematic shear loading parallel, at 45°, and orthogonal to anisotropic microstructural features in a material such as the pancake-shaped grains typical inmore » many rolled structural metals, or to specified directions in fiber-reinforced composites. Finally, the shear-stress shear-strain response and the damage evolution parallel and orthogonal to the pancake grain morphology in 7039-Al are shown to vary significantly as a function of orientation to the microstructure.« less
NASA Astrophysics Data System (ADS)
Kushnir, Alexandra R. L.; Martel, Caroline; Champallier, Rémi; Arbaret, Laurent
2017-01-01
The ferocity of volcanic eruptions - their penchant for either effusive or explosive behaviour - is to a large extent a matter of the ease with which volatiles are able to escape the volcanic system. Of particular importance are the mechanisms by which permeable networks within magma are fabricated and how they permit gas escape, thereby diffusing possibly calamitous explosions. Here, we present a series of experiments that confirms sample-scale fracture propagation and permeability development during shearing viscous flow of initially impermeable, bubble-bearing (<0.20 bubble fraction) magmas under conditions pertinent to volcanic conduits. These samples are deformed in torsion at constant shear strain rates until an applied differential pore fluid pressure across the sample equilibrates, confirming permeability development in situ. Permeability develops at moderate to high shear strain rates (γ ˙ > 2 ×10-4 s-1). At moderate shear strain rates (2 ×10-4 s-1 < γ ˙ < 4.5 ×10-4 s-1), permeability initiates at high strain (γ > 3) via en échelon Mode I fractures produced by repeated fracture events. At high shear strain rates (γ ˙ > 4.5 ×10-4 s-1), permeability develops shortly after the onset of inelastic deformation and is, again, established through a series of en échelon Mode I fractures. Critically, strain is not immediately localized on Mode I fractures, making them long-lived and efficient outgassing channels that are ideally oriented for directing volatiles from the central conduit upward and outward toward the conduit rim. Indeed, Mode I fracture arrays may prove necessary for dissipating gas overpressures in the central regions of the magma column, which are considered difficult to outgas. These experiments highlight mechanisms that are likely active along conduit margins and constrain previously postulated processes under truly applicable conditions.
Shearing stability of lubricants
NASA Technical Reports Server (NTRS)
Shiba, Y.; Gijyutsu, G.
1984-01-01
Shearing stabilities of lubricating oils containing a high mol. wt. polymer as a viscosity index improver were studied by use of ultrasound. The oils were degraded by cavitation and the degradation generally followed first order kinetics with the rate of degradation increasing with the intensity of the ultrasonic irradiation and the cumulative energy applied. The shear stability was mainly affected by the mol. wt. of the polymer additive and could be determined in a short time by mechanical shearing with ultrasound.
Improving Interlaminar Shear Strength
NASA Technical Reports Server (NTRS)
Jackson, Justin
2015-01-01
To achieve NASA's mission of space exploration, innovative manufacturing processes are being applied to the fabrication of complex propulsion elements.1 Use of fiber-reinforced, polymeric composite tanks are known to reduce weight while increasing performance of propulsion vehicles. Maximizing the performance of these materials is needed to reduce the hardware weight to result in increased performance in support of NASA's missions. NASA has partnered with the Mississippi State University (MSU) to utilize a unique scalable approach of locally improving the critical properties needed for composite structures. MSU is responsible for the primary development of the concept with material and engineering support provided by NASA. The all-composite tank shown in figure 1 is fabricated using a prepreg system of IM7 carbon fiber/CYCOM 5320-1 epoxy resin. This is a resin system developed for out-of-autoclave applications. This new technology is needed to support the fabrication of large, all composite structures and is currently being evaluated on a joint project with Boeing for the Space Launch System (SLS) program. In initial efforts to form an all composite pressure vessel using this prepreg system, a 60% decrease in properties was observed in scarf joint regions. Inspection of these areas identified interlaminar failure in the adjacent laminated structure as the main failure mechanism. This project seeks to improve the interlaminar shear strength (ILSS) within the prepreg layup by locally modifying the interply region shown in figure 2.2
An evaluation of mixed-mode delamination failure criteria
NASA Technical Reports Server (NTRS)
Reeder, J. R.
1992-01-01
Many different failure criteria have been suggested for mixed mode delamination toughness, but few sets of mixed mode data exist that are consistent over the full mode I opening to mode II shear load range. The mixed mode bending (MMB) test was used to measure the delamination toughness of a brittle epoxy composite, a state of the art toughened epoxy composite, and a tough thermoplastic composite over the full mixed mode range. To gain insight into the different failure responses of the different materials, the delamination fracture surfaces were also examined. An evaluation of several failure criteria which have been reported in the literature was performed, and the range of responses modeled by each criterion was analyzed. A new bilinear failure criterion was analyzed. A new bilinear failure criterion was developed based on a change in the failure mechanism observed from the delamination surfaces. The different criteria were compared to the failure criterion. The failure response of the tough thermoplastic composite could be modeled well with the bilinear criterion but could also be modeled with the more simple linear failure criterion. Since the materials differed in their mixed mode failure response, mixed mode delamination testing will be needed to characterize a composite material. A critical evaluation is provided of the mixed mode failure criteria and should provide general guidance for selecting an appropriate criterion for other materials.
Stability of coupled tearing and twisting modes in tokamaks
Fitzpatrick, R.
1994-03-01
A dispersion relation is derived for resistive modes of arbitrary parity in a tokamak plasma. At low mode amplitude, tearing and twisting modes which have nonideal MHD behavior at only one rational surface at a time in the plasma are decoupled via sheared rotation and diamagnetic flows. At higher amplitude, more unstable {open_quote}compound{close_quote} modes develop which have nonideal behavior simultaneously at many surfaces. Such modes possess tearing parity layers at some of the nonideal surfaces, and twisting parity layers at others, but mixed parity layers are generally disallowed. At low mode number, {open_quote}compound{close_quote} modes are likely to have tearing parity layers at all of the nonideal surfaces in a very low-{beta} plasma, but twisting parity layers become more probable as the plasma {beta} is increased. At high mode number, unstable twisting modes which exceed a critical amplitude drive conventional magnetic island chains on alternate rational surfaces, to form an interlocking structure in which the O-points and X-points of neighboring chains line up.
Electrical percolation networks of carbon nanotubes in a shear flow.
Kwon, Gyemin; Heo, Youhee; Shin, Kwanwoo; Sung, Bong June
2012-01-01
The effect of shear on the electrical percolation network of carbon nanotube (CNT)-polymer composites is investigated using computer simulations. Configurations of CNTs in a simple shear, obtained by using Monte Carlo simulations, are used to locate the electrical percolation network of CNTs and calculate the electric conductivity. When exposed to the shear, CNTs align parallel to the shear direction and the electrical percolation threshold CNT concentration decreases. Meanwhile, after a certain period of the shear imposition above a critical shear rate, CNTs begin to form an aggregate and the percolating network of CNTs is broken, thus decreasing the electric conductivity significantly. We also construct quasiphase diagrams for the aggregate formation and the electrical percolation network formation to investigate the effect of the shear rate and CNT concentration.
Plastic Collapse Localisation in Simple Shearing and Coaxial Deformations
NASA Astrophysics Data System (ADS)
Hobbs, B. E.; Ord, A.
2011-12-01
We explore, numerically, the evolution of localisation due to plastic collapse in both coaxial shortening and simple shearing deformations. These localisation features arise from plastic behaviour and hence differ from the formation of anticracks modelled by linear elastic behaviour (Fletcher and Pollard, 1990). The behaviour is close to that discussed by Rudnicki (2004) and Chemenda (2009) in that localisation consists of zones of plastic collapse separated by elastically unloaded regions. The constitutive behaviour assumed here comprises a Tresca yield with both strain-softening of the yield stress and of a cap that models plastic volumetric collapse during phase transformations, such as the olivine-spinel transition, with ΔV<0. The work builds on Detournay et al. (2003). An analysis similar to that of Issen and Rudnicki (2000) allows conditions for localisation to be specified. However critical softening of the cap is a necessary condition for collapse localisation to form. Localised collapse zones develop as tabular bodies oriented normal to the principal axis of compression and, within a shear zone, at approximately 45degrees to the boundaries of the shear zone. A different mode of localisation results from softening of the yield stress. This leads to shear localisation approximately parallel to the boundaries of a shear zone with zero plastic volume change. Whether one form of localisation or the other develops is a function of the constitutive parameters which are influenced by energy dissipation due to deformation and chemical reactions, and hence position, within a heterogeneously deforming zone. Localisation due to plastic collapse is followed by a stress drop and so is presumably seismic in nature as suggested by Green and Burnley (1989). The shear localisation mode of deformation is aseismic unless coupled to thermal or chemical effects. This study forms part of a broader study in which energy dissipation is coupled to constitutive behaviour similar to
Directional Shear in the Nocturnal Atmospheric Surface Layer
NASA Astrophysics Data System (ADS)
Mahrt, L.
2017-06-01
We examine the potential importance of wind-directional shear in the surface layer of the stable nocturnal boundary layer by analyzing two tower datasets with eddy-correlation measurements at multiple levels. Directional shear is a major contributor to the total vector shear for weak winds due primarily to frequent shallow drainage flows at one site and due primarily to non-stationary modes at the second site. For weak winds, the turbulence intensity is more related to the wind-directional shear than to the wind speed or stratification, at least for these two datasets.
Use of a fluid membrane in the observation of a shear instability caused by rotational motion
NASA Astrophysics Data System (ADS)
Couder, Y.
1981-07-01
An experiment to study the shear layer disturbances formed around a cylinder rotating in a fluid by means of a fluid film is presented. A cylinder with a large radius relative to its height was covered with a soapy film over the top, while motor driven disks with variable speed and radius were inserted from the bottom. Traces of HCl and NH3 were added to the top of the disk to form a smoke which was entrained on the inner side of the soapy film as the disk below turned and turbulent shear zones formed at certain critical speeds of the inner disks. A speed was eventually found with total oscillation of the vortexes. Replacement of the soap film with glass required much greater thickness of the transparency and higher speeds of the rotating disks, giving rise to unstable vortex formation. The method is effective in quantitative visualization of vortex formation and mode transitions.
Berendsen, Bjorn J A; Meijer, Thijs; Wegh, Robin; Mol, Hans G J; Smyth, Wesley G; Armstrong Hewitt, S; van Ginkel, Leen; Nielen, Michel W F
2016-05-01
Besides the identification point system to assure adequate set-up of instrumentation, European Commission Decision 2002/657/EC includes performance criteria regarding relative ion abundances in mass spectrometry and chromatographic retention time. In confirmatory analysis, the relative abundance of two product ions, acquired in selected reaction monitoring mode, the ion ratio should be within certain ranges for confirmation of the identity of a substance. The acceptable tolerance of the ion ratio varies with the relative abundance of the two product ions and for retention time, CD 2002/657/EC allows a tolerance of 5%. Because of rapid technical advances in analytical instruments and new approaches applied in the field of contaminant testing in food products (multi-compound and multi-class methods) a critical assessment of these criteria is justified. In this study a large number of representative, though challenging sample extracts were prepared, including muscle, urine, milk and liver, spiked with 100 registered and banned veterinary drugs at levels ranging from 0.5 to 100 µg/kg. These extracts were analysed using SRM mode using different chromatographic conditions and mass spectrometers from different vendors. In the initial study, robust data was collected using four different instrumental set-ups. Based on a unique and highly relevant data set, consisting of over 39 000 data points, the ion ratio and retention time criteria for applicability in confirmatory analysis were assessed. The outcomes were verified based on a collaborative trial including laboratories from all over the world. It was concluded that the ion ratio deviation is not related to the value of the ion ratio, but rather to the intensity of the lowest product ion. Therefore a fixed ion ratio deviation tolerance of 50% (relative) is proposed, which also is applicable for compounds present at sub-ppb levels or having poor ionisation efficiency. Furthermore, it was observed that retention time
High strength semi-active energy absorbers using shear- and mixedmode operation at high shear rates
NASA Astrophysics Data System (ADS)
Becnel, Andrew C.
This body of research expands the design space of semi-active energy absorbers for shock isolation and crash safety by investigating and characterizing magnetorheological fluids (MRFs) at high shear rates ( > 25,000 1/s) under shear and mixed-mode operation. Magnetorheological energy absorbers (MREAs) work well as adaptive isolators due to their ability to quickly and controllably adjust to changes in system mass or impact speed while providing fail-safe operation. However, typical linear stroking MREAs using pressure-driven flows have been shown to exhibit reduced controllability as impact speed (shear rate) increases. The objective of this work is to develop MREAs that improve controllability at high shear rates by using pure shear and mixed shear-squeeze modes of operation, and to present the fundamental theory and models of MR fluids under these conditions. A proof of concept instrument verified that the MR effect persists in shear mode devices at shear rates corresponding to low speed impacts. This instrument, a concentric cylinder Searle cell magnetorheometer, was then used to characterize three commercially available MRFs across a wide range of shear rates, applied magnetic fields, and temperatures. Characterization results are presented both as flow curves according to established practice, and as an alternate nondimensionalized analysis based on Mason number. The Mason number plots show that, with appropriate correction coefficients for operating temperature, the varied flow curve data can be collapsed to a single master curve. This work represents the first shear mode characterization of MRFs at shear rates over 10 times greater than available with commercial rheometers, as well as the first validation of Mason number analysis to high shear rate flows in MRFs. Using the results from the magnetorheometer, a full scale rotary vane MREA was developed as part of the Lightweight Magnetorheological Energy Absorber System (LMEAS) for an SH-60 Seahawk helicopter
NASA Astrophysics Data System (ADS)
Miles, John
2001-09-01
The eigenvalue problem for gravity waves on a shear flow of depth h and non-inflected velocity profile U(y) (typically parabolic) is revisited, following Burns (1953) and Yih (1972). Complementary variational formulations that provide upper and lower bounds to the Froude number F as a function of the wave speed c and wavenumber k are constructed. These formulations are used to improve Burns's long-wave approximation and to determine Yih's critical wavenumber k[low asterisk], for which the wave is stationary (c = 0) and to which k must be inferior for the existence of an upstream running wave.
Behavior of Tilted Angle Shear Connectors
Khorramian, Koosha; Maleki, Shervin; Shariati, Mahdi; Ramli Sulong, N. H.
2015-01-01
According to recent researches, angle shear connectors are appropriate to transfer longitudinal shear forces across the steel-concrete interface. Angle steel profile has been used in different positions as L-shaped or C-shaped shear connectors. The application of angle shear connectors in tilted positions is of interest in this study. This study investigates the behaviour of tilted-shaped angle shear connectors under monotonic loading using experimental push out tests. Eight push-out specimens are tested to investigate the effects of different angle parameters on the ultimate load capacity of connectors. Two different tilted angles of 112.5 and 135 degrees between the angle leg and steel beam are considered. In addition, angle sizes and lengths are varied. Two different failure modes were observed consisting of concrete crushing-splitting and connector fracture. By increasing the size of connector, the maximum load increased for most cases. In general, the 135 degrees tilted angle shear connectors have a higher strength and stiffness than the 112.5 degrees type. PMID:26642193
Shear waves in inhomogeneous, compressible fluids in a gravity field.
Godin, Oleg A
2014-03-01
While elastic solids support compressional and shear waves, waves in ideal compressible fluids are usually thought of as compressional waves. Here, a class of acoustic-gravity waves is studied in which the dilatation is identically zero, and the pressure and density remain constant in each fluid particle. These shear waves are described by an exact analytic solution of linearized hydrodynamics equations in inhomogeneous, quiescent, inviscid, compressible fluids with piecewise continuous parameters in a uniform gravity field. It is demonstrated that the shear acoustic-gravity waves also can be supported by moving fluids as well as quiescent, viscous fluids with and without thermal conductivity. Excitation of a shear-wave normal mode by a point source and the normal mode distortion in realistic environmental models are considered. The shear acoustic-gravity waves are likely to play a significant role in coupling wave processes in the ocean and atmosphere.
Opportunities for shear energy scaling in bulk acoustic wave resonators.
Jose, Sumy; Hueting, Raymond J E
2014-10-01
An important energy loss contribution in bulk acoustic wave resonators is formed by so-called shear waves, which are transversal waves that propagate vertically through the devices with a horizontal motion. In this work, we report for the first time scaling of the shear-confined spots, i.e., spots containing a high concentration of shear wave displacement, controlled by the frame region width at the edge of the resonator. We also demonstrate a novel methodology to arrive at an optimum frame region width for spurious mode suppression and shear wave confinement. This methodology makes use of dispersion curves obtained from finite-element method (FEM) eigenfrequency simulations for arriving at an optimum frame region width. The frame region optimization is demonstrated for solidly mounted resonators employing several shear wave optimized reflector stacks. Finally, the FEM simulation results are compared with measurements for resonators with Ta2O5/ SiO2 stacks showing suppression of the spurious modes.
Interlaminar shear stress effects on the postbuckling response of graphite-epoxy panels
NASA Technical Reports Server (NTRS)
Engelstad, S. P.; Knight, N. F., Jr.; Reddy, J. N.
1990-01-01
The influence of shear flexibility on overall postbuckling response was assessed, and transverse shear stress distributions in relation to panel failure were examined. Nonlinear postbuckling results are obtained for finite element models based on classical laminated plate theory and first-order shear deformation theory. Good correlation between test and analysis is obtained. The results presented analytically substantiate the experimentally observed failure mode.
Shear flexibility for structures
NASA Technical Reports Server (NTRS)
Stangeland, Maynard L. (Inventor)
1976-01-01
This device comprises a flexible sheet member having cross convolutions oriented 45.degree. to the shear vector with spherical reliefs at the convolution junctions. The spherical reliefs are essential to the shear flexibility by interrupting the principal stress lines that act along the ridges of the convolutions. The spherical reliefs provide convolutions in both directions in the plane of the cross-convolution ridges.
Shear flexibility for structures
NASA Technical Reports Server (NTRS)
Stangeland, Maynard L. (Inventor)
1977-01-01
This device comprises a flexible sheet member having cross convolutions oriented 45.degree. to the shear vector with spherical reliefs at the convolution junctions. The spherical reliefs are essential to the shear flexibility by interrupting the principal stress lines that act along the ridges of the convolutions. The spherical reliefs provide convolutions in both directions in the plane of the cross-convolution ridges.
Shear viscosity of nuclear matter
NASA Astrophysics Data System (ADS)
Magner, A. G.; Gorenstein, M. I.; Grygoriev, U. V.; Plujko, V. A.
2016-11-01
Shear viscosity η is calculated for the nuclear matter described as a system of interacting nucleons with the van der Waals (VDW) equation of state. The Boltzmann-Vlasov kinetic equation is solved in terms of the plane waves of the collective overdamped motion. In the frequent-collision regime, the shear viscosity depends on the particle-number density n through the mean-field parameter a , which describes attractive forces in the VDW equation. In the temperature region T =15 -40 MeV, a ratio of the shear viscosity to the entropy density s is smaller than 1 at the nucleon number density n =(0.5 -1.5 ) n0 , where n0=0.16 fm-3 is the particle density of equilibrium nuclear matter at zero temperature. A minimum of the η /s ratio takes place somewhere in a vicinity of the critical point of the VDW system. Large values of η /s ≫1 are, however, found in both the low-density, n ≪n0 , and high-density, n >2 n0 , regions. This makes the ideal hydrodynamic approach inapplicable for these densities.
Dense, inhomogeneous shearing flows of spheres
NASA Astrophysics Data System (ADS)
Berzi, Diego; Jenkins, James T.
2017-06-01
We make use of recent extensions of kinetic theory of granular gases to include the role of particle stiffness in collisions to deal with pressure-imposed shearing flows between bumpy planes in relative motion, in which the solid volume fraction and the intensity of the velocity fluctuations are not uniformly distributed in the domain. As in previous numerical simulations on the flow of disks in an annular shear cell, we obtain an exponential velocity profile in the region where the volume fraction exceeds the critical value at which a rate-independent contribution to the stresses arises. We also show that the thickness of the inertial region, where the solid volume fraction is less than the critical value, and the shear stress at the moving boundary are determined functions of the relative velocity of the boundaries.
Shear-flow Effects in Open Traps
Beklemishev, A. D.
2008-11-01
Interaction between shear flows and plasma instabilities and turbulence in open traps can lead to improved confinement both in experiments and in simulations. Shear flows, driven by biasing end-plates and limiters or by off-axis electron heating, in combination with the finite-larmor-radius (FLR) effects are shown to be efficient in confining plasmas even with unstable flute modes. Interpretation of the observed effects as the ''vortex confinement,'' i.e., confinement of the plasma core in the dead-flow zone of the driven vortex, is shown to agree well with simulations.
KELVIN-HELMHOLTZ INSTABILITY IN CORONAL MAGNETIC FLUX TUBES DUE TO AZIMUTHAL SHEAR FLOWS
Soler, R.; Terradas, J.; Oliver, R.; Ballester, J. L.; Goossens, M.
2010-04-01
Transverse oscillations of coronal loops are often observed and have been theoretically interpreted as kink magnetohydrodynamic (MHD) modes. Numerical simulations by Terradas et al. suggest that shear flows generated at the loop boundary during kink oscillations could give rise to a Kelvin-Helmholtz instability (KHI). Here, we investigate the linear stage of the KHI in a cylindrical magnetic flux tube in the presence of azimuthal shear motions. We consider the basic, linearized MHD equations in the beta = 0 approximation and apply them to a straight and homogeneous cylindrical flux tube model embedded in a coronal environment. Azimuthal shear flows with a sharp jump of the velocity at the cylinder boundary are included in the model. We obtain an analytical expression for the dispersion relation of the unstable MHD modes supported by the configuration, and compute analytical approximations of the critical velocity shear and the KHI growth rate in the thin tube limit. A parametric study of the KHI growth rates is performed by numerically solving the full dispersion relation. We find that fluting-like modes can develop a KHI in timescales comparable to the period of kink oscillations of the flux tube. The KHI growth rates increase with the value of the azimuthal wavenumber and decrease with the longitudinal wavenumber. However, the presence of a small azimuthal component of the magnetic field can suppress the KHI. Azimuthal motions related to kink oscillations of untwisted coronal loops may trigger a KHI, but this phenomenon has not been observed to date. We propose that the azimuthal component of the magnetic field is responsible for suppressing the KHI in a stable coronal loop. The required twist is small enough to prevent the development of the pinch instability.
Mixed mode fracture characterization of hydroxylapatite-titanium alloy interface.
Mann, K A; Edidin, A A; Kinoshita, R K; Manley, M T
1994-01-01
Cantilever beam and four-point bend specimen geometries were used to experimentally determine the critical energy release rates for a plasma sprayed hydroxylapatite-titanium alloy (HA-Ti alloy) interface. A locus of energy release rates as a function of crack tip phase angle was determined where a 0 degree phase angle represented tensile opening (mode I) loading and a 90 degree phase angle represented in-plane shear (mode II) loading. Energy release rates were found to increase substantially with an increase in phase angle. An energy release rate of 0.108 N/mm was determined for a phase angle of 0 degrees (mode I). Energy release rates of 0.221, 0.686, and 1.212 N/mm were determined for phase angles of 66 degrees, 69 degrees, and 72 degrees, respectively. The experimental data was matched to a phenomenological model for which crack propagation depended on mode I loading alone indicating that crack propagation at the Ha-Ti alloy interface is dominated by the mode I loading component. Therefore, regions of HA coated implants that experience compressive or shear loading across the HA-Ti alloy interface may be much less likely to debond than regions that experience tensile loading.
Estimation of seabed shear-wave velocity profiles using shear-wave source data.
Dong, Hefeng; Nguyen, Thanh-Duong; Duffaut, Kenneth
2013-07-01
This paper estimates seabed shear-wave velocity profiles and their uncertainties using interface-wave dispersion curves extracted from data generated by a shear-wave source. The shear-wave source generated a seismic signature over a frequency range between 2 and 60 Hz and was polarized in both in-line and cross-line orientations. Low-frequency Scholte- and Love-waves were recorded. Dispersion curves of the Scholte- and Love-waves for the fundamental mode and higher-order modes are extracted by three time-frequency analysis methods. Both the vertically and horizontally polarized shear-wave velocity profiles in the sediment are estimated by the Scholte- and Love-wave dispersion curves, respectively. A Bayesian approach is utilized for the inversion. Differential evolution, a global search algorithm is applied to estimate the most-probable shear-velocity models. Marginal posterior probability profiles are computed by Metropolis-Hastings sampling. The estimated vertically and horizontally polarized shear-wave velocity profiles fit well with the core and in situ measurements.
Experimental studies on behavior of fully grouted reinforced-concrete masonry shear walls
NASA Astrophysics Data System (ADS)
Zhao, Yan; Wang, Fenglai
2015-12-01
An experimental study is conducted on fully grouted reinforced masonry shear walls (RMSWs) made from concrete blocks with a new configuration. Ten RMSWs are tested under reversed cyclic lateral load to investigate the influence of different reinforcements and applied axial stress values on their seismic behavior. The results show that flexural strength increases with the applied axial stress, and shear strength dominated by diagonal cracking increases with both the amount of horizontal reinforcement and applied axial stress. Yield displacement, ductility, and energy dissipation capability can be improved substantially by increasing the amount of horizontal reinforcement. The critical parameters for the walls are derived from the experiment: displacement ductility values corresponding to 15% strength degradation of the walls reach up to 2.6 and 4.5 in the shear and flexure failure modes, respectively; stiffness values of flexure- and shear-dominated walls rapidly degrade to 17%-19% and 48%-57% of initial stiffness at 0.50 D max (displacement at peak load). The experiment suggests that RMSWs could be assigned a higher damping ratio (˜14%) for collapse prevention design and a lower damping value (˜7%) for a fully operational limit state or serviceability limit state.
Shear Strength Behavior of Human Trabecular Bone
Sanyal, Arnav; Gupta, Atul; Bayraktar, Harun H.; Kwon, Ronald Y.; Keaveny, Tony M.
2012-01-01
The shear strength of human trabecular bone may influence overall bone strength under fall loading conditions and failure at bone-implant interfaces. Here, we sought to compare shear and compressive yield strengths of human trabecular bone and elucidate the underlying failure mechanisms. We analyzed 54 specimens (5-mm cubes), all aligned with the main trabecular orientation and spanning four anatomic sites, 44 different cadavers, and a wide range of bone volume fraction (0.06–0.38). Micro-CT-based non-linear finite element analysis was used to assess the compressive and shear strengths and the spatial distribution of yielded tissue; the tissue-level constitutive model allowed for kinematic non-linearity and yielding with strength asymmetry. We found that the computed values of both the shear and compressive strengths depended on bone volume fraction via power law relations having an exponent of 1.7 (R2=0.95 shear; R2=0.97 compression). The ratio of shear to compressive strengths (mean ± SD, 0.44 ± 0.16) did not depend on bone volume fraction (p=0.24) but did depend on microarchitecture, most notably the intra-trabecular standard deviation in trabecular spacing (R2=0.23, p<0.005). For shear, the main tissue-level failure mode was tensile yield of the obliquely oriented trabeculae. By contrast, for compression, specimens having low bone volume fraction failed primarily by large-deformation-related tensile yield of horizontal trabeculae and those having high bone volume failed primarily by compressive yield of vertical trabeculae. We conclude that human trabecular bone is generally much weaker in shear than compression at the apparent level, reflecting different failure mechanisms at the tissue level. PMID:22884967
Overstability of acoustic waves in strongly magnetized anisotropic magnetohydrodynamic shear flows
Uchava, E. S.; Shergelashvili, B. M.; Tevzadze, A. G.; Poedts, S.
2014-08-15
We present a linear stability analysis of the perturbation modes in anisotropic magnetohydrodynamic (MHD) flows with velocity shear and strong magnetic field. Collisionless or weakly collisional plasma is described within the 16-momentum MHD fluid closure model that takes into account not only the effect of pressure anisotropy but also the effect of anisotropic heat fluxes. In this model, the low frequency acoustic wave is revealed into a standard acoustic mode and higher frequency fast thermo-acoustic and lower frequency slow thermo-acoustic waves. It is shown that thermo-acoustic waves become unstable and grow exponentially when the heat flux parameter exceeds some critical value. It seems that velocity shear makes thermo-acoustic waves overstable even at subcritical heat flux parameters. Thus, when the effect of heat fluxes is not profound acoustic waves will grow due to the velocity shear, while at supercritical heat fluxes the flow reveals compressible thermal instability. Anisotropic thermal instability should be also important in astrophysical environments, where it will limit the maximal value of magnetic field that a low density ionized anisotropic flow can sustain.
Beatty, Mark W; Hohl, Rebecca H; Nickel, Jeffrey C; Iwasaki, Laura R; Pidaparti, Ramana M
2008-05-01
The aim of this study was to assess the critical energy required to induce flaw propagation in the temporomandibular joint (TMJ) disc when tensile and shear stresses were applied. J-integrals were measured for Mode I and III fractures because excessive tensile and shear stresses promote disc failure. Single edge notch (Mode I) and trouser tear (Mode III) specimens were constructed with flaws oriented parallel to the predominant anteroposteriorly oriented collagen fibers of the TMJ disc. Disks with and without an impulsive pre-load of 3 N s were studied to compare impact-damaged and healthy tissues. Results demonstrated that impulsive loading stiffened the tissues and significantly increased the Mode I fracture energy (J (IC)) but not Mode III (J (IIIC)) (p < or = 0.05). J (IC) and J (IIIC) values were similar for undamaged tissues, but J (IC) values were 2.3 times higher for impulsively loaded tissues (p < or = 0.05). This suggests that when flaws are introduced through impact, the TMJ disc responds by requiring more energy for tensile flaw extension. This research is a first step towards characterizing the mechanical microenvironment that initiates joint disease. This characterization is essential for successful integration of engineered replacement tissues for damaged TMJs.
Dynamics of Sheared Granular Materials
NASA Technical Reports Server (NTRS)
Kondic, Lou; Utter, Brian; Behringer, Robert P.
2002-01-01
This work focuses on the properties of sheared granular materials near the jamming transition. The project currently involves two aspects. The first of these is an experiment that is a prototype for a planned ISS (International Space Station) flight. The second is discrete element simulations (DES) that can give insight into the behavior one might expect in a reduced-g environment. The experimental arrangement consists of an annular channel that contains the granular material. One surface, say the upper surface, rotates so as to shear the material contained in the annulus. The lower surface controls the mean density/mean stress on the sample through an actuator or other control system. A novel feature under development is the ability to 'thermalize' the layer, i.e. create a larger amount of random motion in the material, by using the actuating system to provide vibrations as well control the mean volume of the annulus. The stress states of the system are determined by transducers on the non-rotating wall. These measure both shear and normal components of the stress on different size scales. Here, the idea is to characterize the system as the density varies through values spanning dense almost solid to relatively mobile granular states. This transition regime encompasses the regime usually thought of as the glass transition, and/or the jamming transition. Motivation for this experiment springs from ideas of a granular glass transition, a related jamming transition, and from recent experiments. In particular, we note recent experiments carried out by our group to characterize this type of transition and also to demonstrate/ characterize fluctuations in slowly sheared systems. These experiments give key insights into what one might expect in near-zero g. In particular, they show that the compressibility of granular systems diverges at a transition or critical point. It is this divergence, coupled to gravity, that makes it extremely difficult if not impossible to
Design optimization of blood shearing instrument by computational fluid dynamics.
Wu, Jingchun; Antaki, James F; Snyder, Trevor A; Wagner, William R; Borovetz, Harvey S; Paden, Bradley E
2005-06-01
Rational design of blood-wetted devices requires a careful consideration of shear-induced trauma and activation of blood elements. Critical levels of shear exposure may be established in vitro through the use of devices specifically designed to prescribe both the magnitude and duration of shear exposure. However, it is exceptionally difficult to create a homogeneous shear-exposure history by conventional means. This study was undertaken to develop a Blood Shearing Instrument (BSI) with an optimized flow path which localized shear exposure within a rotating outer ring and a stationary conical spindle. By adjustment of the rotational speed and the gap dimension, the BSI is designed to generate shear stress magnitudes up to 1500 Pa for exposure time between 0.0015 and 0.20 s with a pressure drop of 100 mm Hg. Computational fluid dynamics (CFD) revealed that a flow path designed by first-order analysis and intuition exhibited unfavorable pressure gradient, vortices, and undesirable regions of reverse flow. An optimized design was evolved utilizing a parameterized geometric model and automatic mesh generation to eliminate vortices and reversal flow and to avoid unfavorable pressure gradients. Analysis of the flow and shear fields for the extreme limits of the shear gap demonstrated an improvement in homogeneity due to shape optimization and the limitations of an annular shear device for achieving completely uniform shear exposure.
Steady Shear Flow Behavior of Mixed Proteins
USDA-ARS?s Scientific Manuscript database
Knowledge of the fundamental flow behavior of protein gels is critical for creating food products using a combination of proteins. Because multiple protein gels are complex systems, many aspects of their flow behavior must be studied to fully understand what effects shear, time, and temperature hav...
Modern developments in shear flow control with swirl
NASA Technical Reports Server (NTRS)
Farokhi, Saeed; Taghavi, R.
1990-01-01
Passive and active control of swirling turbulent jets is experimentally investigated. Initial swirl distribution is shown to dominate the free jet evolution in the passive mode. Vortex breakdown, a manifestation of high intensity swirl, was achieved at below critical swirl number (S = 0.48) by reducing the vortex core diameter. The response of a swirling turbulent jet to single frequency, plane wave acoustic excitation was shown to depend strongly on the swirl number, excitation Strouhal number, amplitude of the excitation wave, and core turbulence in a low speed cold jet. A 10 percent reduction of the mean centerline velocity at x/D = 9.0 (and a corresponding increase in the shear layer momentum thickness) was achieved by large amplitude internal plane wave acoustic excitation. Helical instability waves of negative azimuthal wave numbers exhibit larger amplification rates than the plane waves in swirling free jets, according to hydrodynamic stability theory. Consequently, an active swirling shear layer control is proposed to include the generation of helical instability waves of arbitrary helicity and the promotion of modal interaction, through multifrequency forcing.
Excitation of fundamental shear horizontal wave by using face-shear (d36) piezoelectric ceramics
NASA Astrophysics Data System (ADS)
Miao, Hongchen; Dong, Shuxiang; Li, Faxin
2016-05-01
The fundamental shear horizontal (SH0) wave in plate-like structures is extremely useful for non-destructive testing (NDT) and structural health monitoring (SHM) as it is non-dispersive. However, currently, the SH0 wave is usually excited by electromagnetic acoustic transducers (EMAT) whose energy conversion efficiency is fairly low. The face-shear ( d 36 ) mode piezoelectrics is more promising for SH0 wave excitation, but this mode cannot appear in conventional piezoelectric ceramics. Recently, by modifying the symmetry of poled PbZr1-xTixO3 (PZT) ceramics via ferroelastic domain engineering, we realized the face-shear d 36 mode in both soft and hard PZT ceramics. In this work, we further improved the face-shear properties of PZT-4 and PZT-5H ceramics via lateral compression under elevated temperature. It was found that when bonded on a 1 mm-thick aluminum plate, the d 36 type PZT-4 exhibited better face-shear performance than PZT-5H. We then successfully excite SH0 wave in the aluminum plate using a face-shear PZT-4 square patch and receive the wave using a face-shear 0.72[Pb(Mg1/3Nb2/3)O3]-0.28[PbTiO3] (PMN-PT) patch. The frequency response and directionality of the excited SH0 wave were also investigated. The SH0 wave can be dominated over the Lamb waves (S0 and A0 waves) from 160 kHz to 280 kHz. The wave amplitude reaches its maxima along the two main directions (0° and 90°). The amplitude can keep over 80% of the maxima when the deviate angle is less than 30°, while it vanishes quickly at the 45° direction. The excited SH0 wave using piezoelectric ceramics could be very promising in the fields of NDT and SHM.
Wang, Jianbin; Heo, Jinseok; Hua, Susan Z
2010-01-21
Fluid shear stress has profound effects on cell physiology. Here we present a versatile microfluidic method capable of generating variable magnitudes, gradients, and different modes of shear flow, to study sensory and force transduction mechanisms in cells. The chip allows cell culture under spatially resolved shear flow conditions as well as study of cell response to shear flow in real-time. Using this chip, we studied the effects of chronic shear stress on cellular functions of Madin-Darby Canine Kidney (MDCK), renal epithelial cells. We show that shear stress causes reorganization of actin cytoskeleton, which suppresses flow-induced Ca(2+) response.
Formation of a sheared flow Z pinch
NASA Astrophysics Data System (ADS)
Golingo, R. P.; Shumlak, U.; Nelson, B. A.
2005-06-01
The ZaP Flow Z-Pinch project is experimentally studying the effect of sheared flows on Z-pinch stability. It has been shown theoretically that when dVz/dr exceeds 0.1kVA the kink (m =1) mode is stabilized. [U. Shumlak and C. W. Hartman, Phys. Rev. Lett. 75, 3285 (1995).] Z pinches with an embedded axial flow are formed in ZaP with a coaxial accelerator coupled with a 1m assembly region. Long-lived, quiescent Z pinches are generated throughout the first half cycle of the current. During the initial plasma acceleration phase, the axial motion of the current sheet is consistent with snowplow models. Magnetic probes in the assembly region measure the azimuthal modes of the magnetic field. The amplitude of the m =1 mode is proportional to the radial displacement of the Z-pinch plasma current. The magnetic mode levels show a quiescent period which is over 2000 times the growth time of a static Z pinch. The axial velocity is measured along 20 chords through the plasma and deconvolved to provide a radial profile. Using data from multiple pulses, the time evolution of the velocity profile is measured during formation, throughout the quiescent period, and into the transition to instability. The evolution shows that a sheared plasma flow develops as the Z pinch forms. Throughout the quiescent period, the flow shear is greater than the theoretically required threshold for stability. As the flow shear decreases, the magnetic mode fluctuations increase. The coaxial accelerator provides plasma throughout the quiescent period and may explain the evolution of the velocity profile and the sustainment of the flow Z pinch.
Internal hydraulic jumps with large upstream shear
NASA Astrophysics Data System (ADS)
Ogden, Kelly; Helfrich, Karl
2015-11-01
Internal hydraulic jumps in approximately two-layered flows with large upstream shear are investigated using numerical simulations. The simulations allow continuous density and velocity profiles, and a jump is forced to develop by downstream topography, similar to the experiments conducted by Wilkinson and Wood (1971). High shear jumps are found to exhibit significantly more entrainment than low shear jumps. Furthermore, the downstream structure of the flow has an important effect on the jump properties. Jumps with a slow upper (inactive) layer exhibit a velocity minimum downstream of the jump, resulting in a sub-critical downstream state, while flows with the same upstream vertical shear and a larger barotropic velocity remain super-critical downstream of the jump. A two-layer theory is modified to account for the vertical structure of the downstream density and velocity profiles and entrainment is allowed through a modification of the approach of Holland et al. (2002). The resulting theory can be matched reasonably well with the numerical simulations. However, the results are very sensitive to how the downstream vertical profiles of velocity and density are incorporated into the layered model, highlighting the difficulty of the two layer approximation when the shear is large.
Viscoelasticity and shear thinning of nanoconfined water
NASA Astrophysics Data System (ADS)
Kapoor, Karan; Amandeep, Patil, Shivprasad
2014-01-01
Understanding flow properties and phase behavior of water confined to nanometer-sized pores and slits is central to a wide range of problems in science, such as percolation in geology, lubrication of future nano-machines, self-assembly and interactions of biomolecules, and transport through porous media in filtration processes. Experiments with different techniques in the past have reported that viscosity of nanoconfined water increases, decreases, or remains close to bulk water. Here we show that water confined to less than 20-nm-thick films exhibits both viscoelasticity and shear thinning. Typically viscoelasticity and shear thinning appear due to shearing of complex non-Newtonian mixtures possessing a slowly relaxing microstructure. The shear response of nanoconfined water in a range of shear frequencies (5 to 25 KHz) reveals that relaxation time diverges with reducing film thickness. It suggests that slow relaxation under confinement possibly arises due to existence of a critical point with respect to slit width. This criticality is similar to the capillary condensation in porous media.
NASA Astrophysics Data System (ADS)
A “coherent and sustained program” of improved radar detection of weather, pilot training, and better communication between pilots and air controllers can greatly reduce the risk of wind shear to airplanes landing or taking off, according to a National Research Council (NRC) committee.Wind shear, characterized by winds rapidly changing direction and speed, has caused several serious accidents in recent years; among the most notable is the July 8, 1982, crash of a Pan American World Airlines jetliner at the New Orleans International Airport, which killed 153 persons. Following the accident, Congress directed the Federal Aviation Administration (FAA) to contract with the NRC to study wind shear.
Ruda, Mitchell C [Tucson, AZ; Greynolds, Alan W [Tucson, AZ; Stuhlinger, Tilman W [Tucson, AZ
2009-07-14
One or more disc-shaped angular shear plates each include a region thereon having a thickness that varies with a nonlinear function. For the case of two such shear plates, they are positioned in a facing relationship and rotated relative to each other. Light passing through the variable thickness regions in the angular plates is refracted. By properly timing the relative rotation of the plates and by the use of an appropriate polynomial function for the thickness of the shear plate, light passing therethrough can be focused at variable positions.
Strength of footing with punching shear preventers.
Lee, Sang-Sup; Moon, Jiho; Park, Keum-Sung; Bae, Kyu-Woong
2014-01-01
The punching shear failure often governs the strength of the footing-to-column connection. The punching shear failure is an undesirable failure mode, since it results in a brittle failure of the footing. In this study, a new method to increase the strength and ductility of the footing was proposed by inserting the punching shear preventers (PSPs) into the footing. The validation and effectiveness of PSP were verified through a series of experimental studies. The nonlinear finite element analysis was then performed to demonstrate the failure mechanism of the footing with PSPs in depth and to investigate the key parameters that affect the behavior of the footing with PSPs. Finally, the design recommendations for the footing with PSPs were suggested.
Strength of Footing with Punching Shear Preventers
Lee, Sang-Sup; Moon, Jiho; Park, Keum-Sung; Bae, Kyu-Woong
2014-01-01
The punching shear failure often governs the strength of the footing-to-column connection. The punching shear failure is an undesirable failure mode, since it results in a brittle failure of the footing. In this study, a new method to increase the strength and ductility of the footing was proposed by inserting the punching shear preventers (PSPs) into the footing. The validation and effectiveness of PSP were verified through a series of experimental studies. The nonlinear finite element analysis was then performed to demonstrate the failure mechanism of the footing with PSPs in depth and to investigate the key parameters that affect the behavior of the footing with PSPs. Finally, the design recommendations for the footing with PSPs were suggested. PMID:25401141
Shear Fractures of Extreme Dynamics
NASA Astrophysics Data System (ADS)
Tarasov, Boris
2016-10-01
Natural and laboratory observations show that shear ruptures (faults) can propagate with extreme dynamics (up to intersonic rupture velocities) through intact materials and along pre-existing faults with frictional and coherent (bonded) interfaces. The rupture propagation is accompanied by significant fault strength weakening in the rupture head. Although essential for understanding earthquakes, rock mechanics, tribology and fractures, the question of what physical processes determine how that weakening occurs is still unresolved. The general approach today to explain the fault weakening is based upon the strong velocity-weakening friction law according to which the fault strength drops rapidly with slip velocity. Different mechanisms of strength weakening caused by slip velocity have been proposed including thermal effect, high-frequency compressional waves, expansion of pore fluid, macroscopic melting and gel formation. This paper proposes that shear ruptures of extreme dynamics propagating in intact materials and in pre-existing frictional and coherent interfaces are governed by the same recently identified mechanism which is associated with an intensive microcracking process in the rupture tip observed for all types of extreme ruptures. The microcracking process creates, in certain conditions, a special fan-like microstructure shear resistance of which is extremely low (up to an order of magnitude less than the frictional strength). The fan-structure representing the rupture head provides strong interface weakening and causes high slip and rupture velocities. In contrast with the velocity-weakening dependency, this mechanism provides the opposite weakening-velocity effect. The fan-mechanism differs remarkably from all reported earlier mechanisms, and it can provide such important features observed in extreme ruptures as: extreme slip and rupture velocities, high slip velocity without heating, off-fault tensile cracking, transition from crack-like to pulse
NASA Astrophysics Data System (ADS)
Jacobson, William R.; Hooyer, Thomas S.
2015-12-01
Herein we present data on the shearing rate (glacier velocity) and effective pressure (difference between the ice-overburden pressure and pore-water pressure) in the development of magnetic fabric (anisotropy of magnetic susceptibility) using a rotary ring-shear device. A Wisconsin-age basal till was used in the experiments and deformed to its critical state at shear strains as high as 93. We also present data from hysteresis and high temperature susceptibility experiments to identify the magnetic carrier in the basal till. Results showed little change in fabric strength when varying the shearing rate in the speed range of 110-860 m year- 1. Moreover, the effective pressure tests also showed an inconsistency in fabric between 30 and 150 kPa; however, a slight strengthening effect was documented. Thus, the k1 magnetic fabric strength is independent of the shearing rate and effective pressure. This suggests that the fabric strength upon these variables cannot be used as a benchmark for estimating shear deformation to the geological record. The k1 fabric strength in this study; however, remained consistent with respect to other till particle fabric methods (e.g., sand and pebble) in which the same conclusion was drawn; all particles align parallel to the direction of shear and plunge mildly up glacier.
NASA Astrophysics Data System (ADS)
Rusconi, Roberto; Guasto, Jeffrey S.; Stocker, Roman
2012-11-01
Bacteria are ubiquitously exposed to flow, both in natural environments and artificial devices (e.g., catheters), where confining surfaces create non-uniform shear. While the effects of shear on passive particles are well understood, little is known about the consequences of shear on motile bacteria. We exposed bacteria having different motility strategies (e.g., run-and-tumble, run-and-reverse) to microfluidic Poiseuille flows and quantified the swimming kinematics and cell distribution in the channel using video-microscopy. We discovered that the coupling of motility and a spatially varying shear results in a dramatic trapping of motile cells in high-shear regions, and conversely a strong depletion in the low-shear portion of the channel. We demonstrate experimentally that this trapping process is robust across species such as Bacillus subtilis and Pseudomonas aeruginosa, and can have far-reaching consequences on bacterial transport, by (i) counteracting bacterial chemotactic responses; and (ii) enhancing surface attachment and thus biofilm formation by trapping cells near walls. More generally, this work shows that-despite the low Reynolds number-the coupling of flow and self-propulsion can be nonlinear and not simply a superposition of the two effects.
Radiative instabilities in sheared magnetic field
NASA Technical Reports Server (NTRS)
Drake, J. F.; Sparks, L.; Van Hoven, G.
1988-01-01
The structure and growth rate of the radiative instability in a sheared magnetic field B have been calculated analytically using the Braginskii fluid equations. In a shear layer, temperature and density perturbations are linked by the propagation of sound waves parallel to the local magnetic field. As a consequence, density clumping or condensation plays an important role in driving the instability. Parallel thermal conduction localizes the mode to a narrow layer where K(parallel) is small and stabilizes short wavelengths k larger-than(c) where k(c) depends on the local radiation and conduction rates. Thermal coupling to ions also limits the width of the unstable spectrum. It is shown that a broad spectrum of modes is typically unstable in tokamak edge plasmas and it is argued that this instability is sufficiently robust to drive the large-amplitude density fluctuations often measured there.
Electrostatic ion cyclotron velocity shear instability
Lemons, D.S.; Winske, D.; Gary, S.P. )
1992-12-01
An electrostatic ion cyclotron instability driven by sheared velocity flow perpendicular to a uniform magnetic field is investigated in the local approximation. The dispersion equation, which includes all kinetic effects and involves only one important parameter, is cast in the form of Gordeyev integrals and solved numerically. The instability occurs roughly at multiples of the ion cyclotron frequency (but modified by the shear) with the growth rate of the individual harmonics overlapping in wavenumber. At small values of the shear parameter, the instability exists in two branches, one at long wavelength, [kappa][rho][sub i] [approximately] 0.5, and one at short wavelength, [kappa][rho][sub i] > 1.5 ([kappa][rho][sub i] is the wavenumber normalized to the ion gyroradius). At larger values of the shear parameter only the longer wavelength branch persists. The growth rate of the long wavelength mode, maximized over wavenumber and frequency, increases monotonically with the shear parameter. Properties of the instability are compared to those of Ganguli et al. obtained in the nonlocal limit.
NASA Astrophysics Data System (ADS)
Liu, Pinzhi; Lu, Jie; Yu, Hualong; Ren, Ning; Lockwood, Frances E.; Wang, Q. Jane
2017-08-01
The shear thinning of a lubricant significantly affects lubrication film generation at high shear rates. The critical shear rate, defined at the onset of shear thinning, marks the transition of lubricant behaviors. It is challenging to capture the entire shear-thinning curve by means of molecular dynamics (MD) simulations owing to the low signal-to-noise ratio or long calculation time at comparatively low shear rates (104-106 s-1), which is likely coincident with the shear rates of interest for lubrication applications. This paper proposes an approach that correlates the shear-thinning phenomenon with the change in the molecular conformation characterized by the radius of gyration of the molecule. Such a correlation should be feasible to capture the major mechanism of shear thinning for small- to moderate-sized non-spherical molecules, which is shear-induced molecular alignment. The idea is demonstrated by analyzing the critical shear rate for squalane (C30H62) and 1-decene trimer (C30H62); it is then implemented to study the behaviors of different molecular weight poly-α-olefin (PAO) structures. Time-temperature-pressure superpositioning (TTPS) is demonstrated and it helps further extend the ranges of the temperature and pressure for shear-thinning behavior analyses. The research leads to a relationship between molecular weight and critical shear rate for PAO structures, and the results are compared with those from the Einstein-Debye equation.
Axisymmetric single shear element combustion instability experiment
NASA Technical Reports Server (NTRS)
Breisacher, Kevin J.
1993-01-01
The combustion stability characteristics of a combustor consisting of a single shear element and a cylindrical chamber utilizing LOX and gaseous hydrogen as propellants are presented. The combustor geometry and the resulting longitudinal mode instability are axisymmetric. Hydrogen injection temperature and pyrotechnic pulsing were used to determine stability boundaries. Mixture ratio, fuel annulus gap, and LOX post configuration were varied. Performance and stability data are presented for chamber pressures of 300 and 1000 psia.
Axisymmetric single shear element combustion instability experiment
NASA Technical Reports Server (NTRS)
Breisacher, Kevin J.
1993-01-01
The combustion stability characteristics of a combustor consisting of a single shear element and a cylindrical chamber utilizing LOX and gaseous hydrogen as propellants are presented. The combustor geometry and the resulting longitudinal mode instability are axisymmetric. Hydrogen injection temperature and pyrotechnic pulsing were used to determine stability boundaries. Mixture ratio, fuel annulus gap, and LOX post configuration were varied. Performance and stability data were obtained for chamber pressures of 300 and 1000 psia.
Crosscut shearing of roundwood bolts.
Rodger A. Arola
1971-01-01
Discusses results of study on crosscut shearing of aspen, basswood, spruce, hard maple, and yellow birch with numerous shear blade and anvil designs. Also includes effect of temperature, coated shear blades, dulling, wood properties, and very thin shear blades on force and splitting damage.
Multiple ion temperature gradient driven modes in transport barriers
NASA Astrophysics Data System (ADS)
Han, M. K.; Wang, Zheng-Xiong; Dong, J. Q.; Du, Huarong
2017-04-01
The ion temperature gradient (ITG) modes in transport barriers (TBs) of tokamak plasmas are numerically studied with a code solving gyrokinetic integral eigenvalue equations in toroidal configurations. It is found that multiple ITG modes with conventional and unconventional ballooning mode structures can be excited simultaneously in TBs with steep gradients of ion temperature and density. The characteristics of the modes, including the dependence of the mode frequencies, growth rate and structure on plasma parameters, are systematically investigated. Unconventional modes with large mode-number l (where l denotes a certain parity and peak number in ballooning space) dominate in the large {{k}θ}{ρs} region ({{k}θ}{ρs}≥slant 1.2 ), while the conventional mode with l=0 dominates in the medium {{k}θ}{ρs} region (0.4≤slant {{k}θ}{ρs}<1.2 ), and unconventional modes with small mode-number l dominate in the small {{k}θ}{ρs} region ({{k}θ}{ρs}<0.4 ). Thus, the {{k}θ}{ρs} spectra of these conventional and unconventional modes at steep gradients are qualitatively different from those of the conventional ITG modes at small or medium gradients, in which the growth rate of the only ITG mode with l=0 reaches maximum at the medium value {{k}θ}{ρs}=0.6 . Through scanning ion temperature gradient {{\\varepsilon}T\\text{i}} and density gradient {{\\varepsilon}n} separately, it is proven that the synergetic effect of {{\\varepsilon}T\\text{i}} and {{\\varepsilon}n} , rather than {{\\varepsilon}T\\text{i}} alone, drives the unconventional ITG modes in TBs. Moreover, it is found that the critical value of {{\\varepsilon}n} for driving the unconventional ITG modes with large l number increases with increasing {{k}θ}{ρs} . In addition, the effects of magnetic shear on conventional and unconventional ITG modes in the high confinement regime (H-mode) are analyzed in detail, and compared with equivalent effects on conventional modes in the low and intermediate gradient
Dynamics of flexible fibers in shear flow
Słowicka, Agnieszka M.; Wajnryb, Eligiusz; Ekiel-Jeżewska, Maria L.
2015-09-28
Dynamics of flexible non-Brownian fibers in shear flow at low-Reynolds-number are analyzed numerically for a wide range of the ratios A of the fiber bending force to the viscous drag force. Initially, the fibers are aligned with the flow, and later they move in the plane perpendicular to the flow vorticity. A surprisingly rich spectrum of different modes is observed when the value of A is systematically changed, with sharp transitions between coiled and straightening out modes, period-doubling bifurcations from periodic to migrating solutions, irregular dynamics, and chaos.
Waves in Turbulent Stably Stratified Shear Flow
NASA Technical Reports Server (NTRS)
Jacobitz, F. G.; Rogers, M. M.; Ferziger, J. H.; Parks, John W. (Technical Monitor)
2002-01-01
Two approaches for the identification of internal gravity waves in sheared and unsheared homogeneous stratified turbulence are investigated. First, the phase angle between the vertical velocity and density fluctuations is considered. It was found, however, that a continuous distribution of the phase angle is present in weakly and strongly stratified flow. Second, a projection onto the solution of the linearized inviscid equations of motion of unsheared stratified flow is investigated. It was found that a solution of the fully nonlinear viscous Navier-Stokes equations can be represented by the linearized inviscid solution. The projection yields a decomposition into vertical wave modes and horizontal vortical modes.
Sheared DNA fragment sizing: comparison of techniques.
Ordahl, C P; Johnson, T R; Caplan, A I
1976-01-01
DNA fragmented by conventional French press shearing procedures (30,000 lbs/in2) has a number-average fragment size of 230 base pairs. This is considerably smaller than the 450 base pairs typically reported for DNA sheared by this method. Comparison of 5 sizing techniques indicates that sheared DNA fragment size is overestimated by either measurement of velocity sedimentation or Kleinschmidt Electron Microscopic visualization. Both adsorption grid electron microscopic visualization and gel electrophoresis yield the most reliable estimates of the mean size of small DNA fragment populations. In addition, the assessment of fragment size distribution (not possible from sedimentation analysis) potentially allows more critical evaluation of DNA hybridization and reassociation kinetic and measurement parameters. Images PMID:1034292
Stiffener bond line monitoring using ultrasonic shear guided waves
NASA Astrophysics Data System (ADS)
Fan, Z.; Castaings, M.; Lowe, M. J. S.; Fromme, P.; Biateau, C.
2012-05-01
Adhesively bonded stiffeners are employed in aerospace applications to increase str