Shock Amplitude Research Articles

A Novel Low-Energy Electrotherapy That Terminates Ventricular Tachycardia With Lower Energy Than a Biphasic Shock When Antitachycardia Pacing Fails

The authors sought to develop a low-energy electrotherapy that terminates ventricular tachycardia (VT) when antitachycardia pacing (ATP) fails. High-energy implantable cardioverter-defibrillator (ICD) shocks are associated with device failure, significant morbidity, and increased mortality. A low-energy alternative to ICD shocks is desirable. Myocardial infarction was created in 25 dogs. Sustained, monomorphic VT was induced by programmed stimulation. Defibrillation electrodes were placed in the right ventricular apex, and coronary sinus and left ventricular epicardium. If ATP failed to terminate sustained VT, the defibrillation thresholds (DFTs) of standard versus experimental electrotherapies were measured. Sustained VT ranged from 276 to 438 beats/min (mean 339 beats/min). The right ventricular-coronary sinus shock vector had lower impedance than the right ventricular-left ventricular patch (54.4 ± 18.1 Ω versus 109.8 ± 16.9 Ω; p < 0.001). A single shock required between 0.3 ± 0.2 J to 5.9 ± 2.5 J (mean 2.64 ± 3.22 J; p = 0.008) to terminate VT, and varied depending upon the phase of the VT cycle in which it was delivered. By contrast, multiple shocks delivered within 1 VT cycle length were not phase dependent and achieved lower DFT compared with a single shock (0.13 ± 0.09 J for 3 shocks, 0.08 ± 0.04 J for 5 shocks, and 0.09 ± 0.07 J for 7 shocks; p < 0.001). Finally, a multistage electrotherapy (MSE) achieved significantly lower DFT compared with a single biphasic shock (0.03 ± 0.05 J versus 2.37 ± 1.20 J; respectively, p < 0.001). At a peak shock amplitude of 20 V, MSE achieved 91.3% of terminations versus 10.5% for a biphasic shock (p < 0.001). MSE achieved a major reduction in DFT compared with a single biphasic shock for ATP-refractory monomorphic VT, and represents a novel electrotherapy to reduce high-energy ICD shocks.

AN INVESTIGATION INTO THE CHARACTER OF PRE-EXPLOSION CORE-COLLAPSE SUPERNOVA SHOCK MOTION

We investigate the structure of the stalled supernova shock in both 2D and 3D and explore the differences in the effects of neutrino heating and the standing accretion shock instability (SASI). We find that early on the amplitude of the dipolar mode of the shock is factors of 2 to 3 smaller in 3D than in 2D. However, later in both 3D and 2D the monopole and dipole modes start to grow until explosion. Whereas in 2D the (l,m) = (1,0) mode changes sign quasi-periodically, producing the "up-and-down" motion always seen in modern 2D simulations, in 3D this almost never happens. Rather, in 3D when the dipolar mode starts to grow, it grows in magnitude and wanders stochastically in direction until settling before explosion to a particular patch of solid angle. In 2D we find that the amplitude of the dipolar shock deformation separates into two classes. For the first, identified with the SASI and for a wide range of "low" neutrino luminosities, this amplitude remains small and roughly constant. For the other, identified with higher luminosities and neutrino-driven convection, the dipolar amplitude grows sharply. Importantly, it is only for this higher luminosity class that we see neutrino-driven explosions within ~1 second of bounce. Moreover, for the "low" luminosity runs, the power spectra of these dipolar oscillations peak in the 30-50 Hz range associated with advection timescales, while for the high-luminosity runs the power spectra at lower frequencies are significantly more prominent. We associate this enhanced power at lower frequencies with slower convective effects and the secular growth of the dipolar shock amplitude. On the basis of our study, we hypothesize that neutrino-driven buoyant convection should almost always dominate the SASI when the supernova explosion is neutrino-driven.

Laser compression of monocrystalline tantalum

Monocrystalline tantalum with orientations [100] and [111] was subjected to laser-driven compression at energies of 350–684J, generating shock amplitudes varying from 10 to 110GPa. A stagnating reservoir driven by a laser beam with a spot radius of ∼800μm created a crater of significant depth (∼80 to ∼200μm) on the drive side of the Ta sample. The defects generated by the laser pulse were characterized by transmission and scanning electron microscopy, and are composed of dislocations at low pressures, and mechanical twins and a displacive phase transformation at higher pressures. The defect substructure is a function of distance from the energy deposition surface and correlates directly with the pressure. Directly under the bottom of the crater is an isentropic layer, approximately 40μm thick, which shows few deformation markings. Lattice rotation was observed immediately beneath this layer. Further below this regime, a high density of twins and dislocations was observed. As the shock amplitude decayed to below ∼40GPa, the incidence of twinning decreased dramatically, suggesting a critical threshold pressure. The twinning planes were primarily {112}, although some {123} twins were also observed. Body-centered cubic to hexagonal close-packed pressure induced-transformation was observed at high pressures (∼68GPa).The experimentally measured dislocation densities and threshold stress for twinning are compared with predictions using analyses based on the constitutive response, and the similarities and differences are discussed in terms of the mechanisms of defect generation.

Thin-foil expansion into a vacuum with a two-temperature electron distribution function

A kinetic theory of the expansion into a vacuum of a plasma thin foil with initially a hot and a cold Maxwellian electron population is examined with a one-dimensional kinetic code. Whereas hot electrons always lose energy to expanding ions, cold electrons can either gain or lose energy depending on the initial temperature and density ratios and on time. When the cold electrons' density is not too large, they experience initially an adiabatic compression by the electric field associated with the rarefaction wave. The corresponding temperature increase can be as large as a factor of a few tens. Later on, as expected, the cold electrons eventually lose energy to the expansion. When cold electrons are numerically dominant, a rarefaction shock appears during the first phase of the expansion. Hot electrons cool down faster than cold electrons, thus reducing the effective temperature ratio. Furthermore, the amplitude of the rarefaction shock and the dip that it causes on the ion velocity spectrum tend to be smoothed out by the expansion.

Dynamic response of an electrostatically actuated microbeam to drop-table test

In this paper, we present a theoretical and experimental investigation into the dynamic response of an electrostatically actuated microbeam when subjected to drop-table test. For the theoretical part, a reduced-order model based on an Euler–Bernoulli beam model is utilized. The model accounts for the electrostatic bias on the microbeam and the shock pulse of the drop-table test. Simulation results are presented showing the combined effect of electrostatic force and mechanical shock in triggering early pull-in instability of the cantilever microbeams. The analytical simulation results are validated by finite-element results for the static response. Dynamic pull-in threshold as a function of the mechanical shock amplitude is shown over a wide range of shock spanning hundreds of thousands of g up to zero g. For the experimental part, a micromachined cantilever beam made of gold of length 50 µm is subjected to drop-table tests while being biased by electrostatic loads. Several experimental data are shown demonstrating the phenomenon of collapse due to the combined shock and electrostatic forces. It is also demonstrated that by biasing short and too stiff microbeams with electrostatic voltages, their stiffness is weakened. This lowers their threshold of collapse considerably to the range of acceleration that enables testing them with in-house shock testing equipments, such as drop-table tests.

Shock waves in random viscoelastic media

Determining the effects of material spatial randomness on the evolution of shocks is the objective of this study. Considering a linear viscoelastic-type material, a very general class of random media is modeled by a three-component random vector field: the instantaneous relaxation function (E), its derivative (E � ), and the mass density (ρ). The reason for considering the randomness of the said material coefficients is the fact that a wavefront's length scale (thickness) is most likely smaller than the Representative Volume Element, thus contradicting a "separation of scales" condition tacitly assumed in deterministic continuum mechanics, even in the context of wavefront analyses. In effect, the wavefront is an object much more appropriately analyzed as a Statistical Volume Element and therefore to be treated via a stochastic dynamical system rather than a deterministic one. Various cases of the random vector field (E, E � ,ρ )x are examined: white versus correlated noises as well as the independence versus coupling of these random fields to the shock amplitude.

Ion acoustic shock waves in presence of superthermal electrons and interaction of classical positron beam

The effect of positron beam on the ion-acoustic shock wave is studied. The plasma system under-consideration consists of inertial ions and superthermal electrons and the positron beam with classical streaming velocities. Kinematic viscosity of the ions component is responsible of the dissipation in plasma system. The Burgers equation has been derived by employing the reductive perturbation method. It is noticed that both the amplitude and steepness of the ion-acoustic shock wave accrue, as the spectral index of the superthermal electrons, and concentration of impinging positron beam are enhanced. However, the shock amplitude is found to diminish as the beam streaming velocity and temperature ratio of positrons to electrons are increased in the plasma system. Our findings may be helpful in the understanding of laboratory beam plasma interaction experiments as well as the space and astrophysical plasmas with effects of superthermality and interacting beam.

Polymorphic transition of tin under shock wave compression: Experimental results

In this work, the β-bct polymorphic transition in tin is investigated by means of plate impact experiments. The Sn target surface is observed in a partially released state obtained thanks to a transparent lithium fluoride (LiF) anvil. We report both measurements of interface velocity and temperature obtained using Photon Doppler Velocimetry and IR optical pyrometer on shock-loaded tin from 8 to 16 GPa. We show that the Mabire Model EOS associated to the SCG plasticity model provides an overall good estimate of the velocity profiles. However, depnding on the shock amplitude, its prediction of the temperature profile may be less satisfactory, hence underlining the need for future improvements in terms of phase transition kinetics description.

Transmission of vibration and energy through layered and jointed plates subjected to shock excitation

In this article, the vibration and energy transmission characteristics at the multiple interfaces of layered and jointed plates associated with friction are studied as a function of the shock loading amplitude using the established ‘sphere-joint assembled multi-layered plates’ model. The dynamic responses at the multiple interfaces under shock excitation are calculated using finite element analysis. The transmissions of vibration and energy through the multiple interfaces are characterized by the defined vibration and energy transmission ratios. Results show that the acceleration amplitudes at different interfaces increase nonlinearly with the shock amplitude and they are approximated by a third-order polynomial function. The acceleration amplitude nonlinearly decreases along the transmitting interfaces and the maximum attenuation occurs between the first and second transmitting interfaces. A minimum vibration transmission ratio is observed for the range of shock amplitude considered and the value of shock amplitude leading to the minimum is identical for different transmitting interfaces. It is also shown that the energy transmission ratio exhibits a nonlinear behaviour similar to that of the vibration transmission ratio. The expression for determining the shock amplitude resulting in peak energy transmission ratio at the input interface is also presented. Experimental validation is performed, which shows good agreement with numerical results.

The characteristics of ion acoustic shock waves in non-Maxwellian plasmas with (G′/G)-expansion method

Korteweg-de-Vries-Burger (K-dVB) equation is derived for ion acoustic shock waves in electron-positron-ion plasmas. Electrons and positrons are considered superthermal and are effectively modeled by a kappa distribution in which ions are as cold fluid. The analytical traveling wave solutions of the K-dVB equation investigated, through the (G′/G)-expansion method. These traveling wave solutions are expressed by hyperbolic function, trigonometric functions are rational functions. When the parameters are taken special values, the shock waves are derived from the traveling waves. It is observed that the amplitude ion acoustic shock waves increase as spectral index κ and kinematic viscosity ηi,0 increases in which with increasing positron density β and electron temperature σ the shock amplitude decreases. Also, numerically the effect different parameters on the nonlinearity A and dispersive B terms and wave velocity V investigated.

Controlled tissue emulsification produced by high intensity focused ultrasound shock waves and millisecond boiling

In high intensity focused ultrasound (HIFU) applications, tissue may be thermally necrosed by heating, emulsified by cavitation, or, as was recently discovered, emulsified using repetitive millisecond boiling caused by shock wave heating. Here, this last approach was further investigated. Experiments were performed in transparent gels and ex vivo bovine heart tissue using 1, 2, and 3 MHz focused transducers and different pulsing schemes in which the pressure, duty factor, and pulse duration were varied. A previously developed derating procedure to determine in situ shock amplitudes and the time-to-boil was refined. Treatments were monitored using B-mode ultrasound. Both inertial cavitation and boiling were observed during exposures, but emulsification occurred only when shocks and boiling were present. Emulsified lesions without thermal denaturation were produced with shock amplitudes sufficient to induce boiling in less than 20 ms, duty factors of less than 0.02, and pulse lengths shorter than 30 ms. Higher duty factors or longer pulses produced varying degrees of thermal denaturation combined with mechanical emulsification. Larger lesions were obtained using lower ultrasound frequencies. The results show that shock wave heating and millisecond boiling is an effective and reliable way to emulsify tissue while monitoring the treatment with ultrasound.

Shear strength measurements in a shock loaded commercial silastomer

The shock-induced shear strength of a commercial silastomer, trade name Sylgard 184™, has been determined using laterally mounted manganin stress gauges. Shear strength has been observed to increase with increasing shock amplitude, in common with many other materials. Shear strength has also been observed to increase slightly behind the shock front as well. It is believed that a combination of polymer chain entanglement and cross linking between chains is responsible. Finally, a ramp on the leading edge of the lower amplitude stress traces has been observed. It has been suggested that this is due to shock-induced collapse of free space between the polymer chains. Similar explanations have been used to explain the apparent non-linearity of the shock velocity with particle velocity at low shock amplitudes.

In vivo tissue emulsification using millisecond boiling induced by high intensity focused ultrasound.

Shock-wave heating and millisecond boiling in high intensity focused ultrasound fields have been shown to result in mechanical emulsification of ex-vivo tissue. In this work, the same in situ exposures were applied in vivo in pig liver and in mice bearing 5–7 mm subcutaneous tumors (B16 melanoma) on the hind limb. Lesions were produced using a 2-MHz annular array in the case of pig liver (shock amplitudes up to 98 MPa) and a 3.4-MHz single-element transducer in the case of mouse tumors (shock amplitude of 67 MPa). The parameters of the pulsing protocol (1–500 ms pulse durations and 0.01–0.1 duty factor) were varied depending on the extent of desired thermal effect. All exposures were monitored using B-mode ultrasound. Mechanical and thermal tissue damage in the lesions was evaluated histologically using H&amp;E and NADH-diphorase staining. The size and shape of emulsified lesions obtained in-vivo agreed well with those obtained in ex-vivo tissue samples using the same exposure parameters. The lesions were successfully produced both in bulk liver tissue at depths of 1–2 cm and in superficial tumors at depths less than 1 mm without damaging the skin. [Work supported by NIH (DK070618, EB007643, and DK007742) and NSBRI through NASA NCC 9-58.]

The effects of hydrostatic pressure on conditions in and near a collapsing cavitation bubble.

It has long been understood that the conditions within a collapsing cavitation bubble become more extreme as hydrostatic pressure increases, but quantification of these conditions requires estimating the temperature, pressure, and density of the plasma in the bubble, a difficult task. To provide this information, we conducted numerical simulations using the plasma physics hydrocode HYADES, a 1-D, three-temperature, Lagrangean hydrodynamics, and energy transport code. The contents of a bubble at the center of a sphere of water at 1–3000 bars were specified at time = 0, and the bubble was driven by a spherically converging pressure wave of various frequencies (2.5–26 kHz) and amplitudes (10–3000 bars). Results were obtained for temperature, pressure, and density within and immediately outside the bubble. Calculations for bubble radius and the velocity and amplitude of the radiated shock wave compared well with experimental measurements at modest hydrostatic pressures (1–300 bars). At higher pressures, the maximum temperature within the bubble increases above 100 eV, the shock amplitude becomes greater than 1 Gbar, and its propagation speed is up to Mach 100. Also, the shock front heats the fluid, stimulating photon emissions in the liquid [Impulse ACPT contract No. W9113M-07-C-0178.]

Histological and biochemical analysis of emulsified lesions in tissue induced by high intensity focused ultrasound.

As recently shown, shock wave heating and millisecond boiling can be used to obtain mechanical emulsification of tissue with or without evident thermal damage, which can be controlled by varying the parameters of the high intensity focused ultrasound exposure. The goal of this work was to examine these bioeffects using histological and biochemical analysis. Lesions were created in ex vivo bovine heart and liver using a 2-MHz transducer and pulsing scheme with 71 MPa in situ shock amplitude, 0.01 duty factor, and 5–500 ms pulse duration. Mechanical tissue damage and viability of cells in the lesions were evaluated histologically using conventional staining techniques (H&amp;E and NADH-diaphorase). Thermal effects were quantified by measuring denaturation of salt soluble proteins in the treated area and confirmed by histology. By visual observation, the liquefied lesions obtained with shorter pulses (&amp;lt; 15 ms) did not show any thermal damage that correlated well with the results of both histology and protein analysis. Increasing the pulse duration resulted in an increase in thermal damage; both protein analysis and NADH-diaphorase staining showed denaturation that was visually observed as whitening of the lesion content. [Work supported by NSBRI through NASA NCC 9-58, NIH EB007643 and DK007742.]

SINGLE OR DOUBLE DEGENERATE PROGENITORS? SEARCHING FOR SHOCK EMISSION IN THE SDSS-II TYPE Ia SUPERNOVAE

From the set of nearly 500 spectroscopically confirmed type~Ia supernovae and around 10,000 unconfirmed candidates from SDSS-II, we select a subset of 108 confirmed SNe Ia with well-observed early-time light curves to search for signatures from shock interaction of the supernova with a companion star. No evidence for shock emission is seen; however, the cadence and photometric noise could hide a weak shock signal. We simulate shocked light curves using SN Ia templates and a simple, Gaussian shock model to emulate the noise properties of the SDSS-II sample and estimate the detectability of the shock interaction signal as a function of shock amplitude, shock width, and shock fraction. We find no direct evidence for shock interaction in the rest-frame $B$-band, but place an upper limit on the shock amplitude at 9% of supernova peak flux ($M_B > -16.6$ mag). If the single degenerate channel dominates type~Ia progenitors, this result constrains the companion stars to be less than about 6 $M_{\odot}$ on the main sequence, and strongly disfavors red giant companions.

Numerical simulation of long-duration blast wave evolution in confined facilities

The objective of this research effort was to investigate the quasi-steady flow field produced by explosives in confined facilities. In this effort we modeled tests in which a high explosive (HE) cylindrical charge was hung in the center of a room and detonated. The HEs used for the tests were C-4 and AFX 757. While C-4 is just slightly under-oxidized and is typically modeled as an ideal explosive, AFX 757 includes a significant percentage of aluminum particles, so long-time afterburning and energy release must be considered. The Lawrence Livermore National Laboratory (LLNL)-produced thermo-chemical equilibrium algorithm, “Cheetah”, was used to estimate the remaining burnable detonation products. From these remaining species, the afterburning energy was computed and added to the flow field. Computations of the detonation and afterburn of two HEs in the confined multi-room facility were performed. The results demonstrate excellent agreement with available experimental data in terms of blast wave time of arrival, peak shock amplitude, reverberation, and total impulse (and hence, total energy release, via either the detonation or afterburn processes.

One-dimensional stability of parallel shock layers in isentropic magnetohydrodynamics

Extending investigations of Barker, Humpherys, Lafitte, Rudd, and Zumbrun for compressible gas dynamics and Freistühler and Trakhinin for compressible magnetohydrodynamics, we study by a combination of asymptotic ODE estimates and numerical Evans function computations the one-dimensional stability of parallel isentropic magnetohydrodynamic shock layers over the full range of physical parameters (shock amplitude, strength of imposed magnetic field, viscosity, magnetic permeability, and electrical resistivity) for a γ-law gas with γ ∈ [ 1 , 3 ] . Other γ-values may be treated similarly, but were not checked numerically. Depending on magnetic field strength, these shocks may be of fast Lax, intermediate (overcompressive), or slow Lax type; however, the shock layer is independent of magnetic field, consisting of a purely gas-dynamical profile. In each case, our results indicate stability. Interesting features of the analysis are the need to renormalize the Evans function in order to pass continuously across parameter values where the shock changes type or toward the large-amplitude limit at frequency λ = 0 and the systematic use of winding number computations on Riemann surfaces.

Transient cavitation in high-quality-factor resonators at high static pressures

It is well known that cavitation collapse can generate intense concentrations of mechanical energy, sufficient to erode even the hardest metals and to generate light emissions visible to the naked eye [sonoluminescence (SL)]. Considerable attention has been devoted to the phenomenon of "single bubble sonoluminescence" (SBSL) in which a single stable cavitation bubble radiates light flashes each and every acoustic cycle. Most of these studies involve acoustic resonators in which the ambient pressure is near 0.1 MPa (1 bar), and with acoustic driving pressures on the order of 0.1 MPa. This study describes a high-quality factor, spherical resonator capable of achieving acoustic cavitation at ambient pressures in excess of 30 MPa (300 bars). This system generates bursts of violent inertial cavitation events lasting only a few milliseconds (hundreds of acoustic cycles), in contrast with the repetitive cavitation events (lasting several minutes) observed in SBSL; accordingly, these events are described as "inertial transient cavitation." Cavitation observed in this high pressure resonator is characterized by flashes of light with intensities up to 1000 times brighter than SBSL flashes, as well as spherical shock waves with amplitudes exceeding 30 MPa at the resonator wall. Both SL and shock amplitudes increase with static pressure.

Shock-Induced Heating and Millisecond Boiling in Gels and Tissue Due to High Intensity Focused Ultrasound

Nonlinear propagation causes high-intensity ultrasound waves to distort and generate higher harmonics, which are more readily absorbed and converted to heat than the fundamental frequency. Although such nonlinear effects have been investigated previously and found to not significantly alter high-intensity focused ultrasound (HIFU) treatments, two results reported here change this paradigm. One is that at clinically relevant intensity levels, HIFU waves not only become distorted but form shock waves in tissue. The other is that the generated shock waves heat the tissue to boiling in much less time than predicted for undistorted or weakly distorted waves. In this study, a 2-MHz HIFU source operating at peak intensities up to 25,000 W/cm 2 was used to heat transparent tissue-mimicking phantoms and ex vivo bovine liver samples. Initiation of boiling was detected using high-speed photography, a 20-MHz passive cavitation detector and fluctuation of the drive voltage at the HIFU source. The time to boil obtained experimentally was used to quantify heating rates and was compared with calculations using weak shock theory and the shock amplitudes obtained from nonlinear modeling and measurements with a fiber optic hydrophone. As observed experimentally and predicted by calculations, shocked focal waveforms produced boiling in as little as 3 ms and the time to initiate boiling was sensitive to small changes in HIFU output. Nonlinear heating as a result of shock waves is therefore important to HIFU, and clinicians should be aware of the potential for very rapid boiling because it alters treatments. (E-mail: mcanney@u.washington.edu).