Double Shocks Research Articles

Verification of Buckley-Leverett three-phase theory using computerized tomography

The mathematical extension of the Buckley-Leverett (B-L) theory to three immiscible fluids was presented by Grader and O'Meara (1988). However, the three-phase flow extension of the theory has not previously been experimentally demonstrated. Fluid flow experiments are conducted through uniform glass bead packs using three immiscible liquids: water, benzyl alcohol and decane. In some experiments decane is injected into a core saturated with water and benzyl alcohol and in other experiments water is injected into a core saturated with all three phases. The recovered fluid volumes are used to calculate the in-situ saturations by applying the three-phase extension of the B-L theory. These saturations are then compared against in-situ saturations determined using X-ray computerized tomography (CT). The results show good agreement between the phase saturations determined by these two independent methods even for cases when double shocks are formed during the displacement process. They also show that the measurement of three-phase relative permeabilities using the extension of the B-L theory has both sound theoretical and experimental bases.

Navier-Stokes analysis of Korn aerofoil

Two-dimensional Reynolds-averaged Navier-Stokes equations with algebraic turbulence model have been solved using a vertex-based finite-volume space discretization and an explicit five-stage Runge-Kutta time steps. A modified artificial dissipation based on the time-step limit for convective and diffusive equation has been used for numerical stability. The off-design behaviour of the supercritical Korn aerofoil in viscous transonic flow has been considered a good test case because the numerical scheme needs more accuracy to predict the appearance of double shocks. Results have been compared with experiments and the general behaviour of the aerofoil has been studied.

Double sequential external shocks for refractory ventricular fibrillation

Objectives. A technique for terminating refractory ventricular fibrillation is described.Background. Refractory ventricular fibrillation can occur in up to 0.1% of electrophysiologic studies. Animal studies have shown that rapid sequential shocks may reduce ventricular fibrillation threshold.Methods. Five patients of 2,990 consecutive patients in a 3-year period experienced refractory ventricular fibrillation during 5,450 routine electrophysiologic studies. Multiple shocks were delivered by means of a single defibrillator. Double sequential shocks were delivered externally 0.5 to 4.5 s apart by means of two defibrillators with separate pairs of electrodes.Results. In all patients, standard defibrillation was unsuccessful, but all were successfully resuscitated using the double sequential shocks.Conclusions. This report stresses the importance of an additional defibrillator being readily available during electrophysiologic testing. This technique of rapid, double sequential external shocks may have general applicability, providing a simple and potentially lifesaving approach to refractory ventricular fibrillation.

Monosynaptic and disynaptic connections in the utriculo-ocular reflex arc of the cat.

1. Connections from the utricular (UT) nerve to motoneurons and interneurons in the ipsilateral abducens (AB) nucleus were studied in anesthetized and decerebrated cats. Bipolar electrodes were fixed on the left UT nerve under visual observation. The other branches of the vestibular nerve and the facial nerve were transected in the left inner ear. 2. Stimulation of the UT nerve evoked a small positive-negative (P/N) deflection and a negative (N1) potential in the vestibular nuclei, with mean latencies of 0.56 and 0.84 ms, respectively. In the AB nucleus a small P/N deflection with a mean latency of 0.72 ms was recorded, which was considered as a incoming volley of the UT nerve. 3. Excitatory postsynaptic potentials (EPSPs) were recorded from AB motoneurons with short latencies after UT nerve stimulation. They were classified into two types, M and D. M-type EPSPs, which followed repetitive high-frequency stimuli and were recorded from the majority of AB motoneurons, had latencies ranging from 0.9 to 1.2 ms. Double shocks to the UT nerve evoked EPSPs that had the same latency. It was suggested that the AB motoneurons had monosynaptic connections with the UT nerve. D-type EPSPs, which were recorded from most of the AB motoneurons, had slightly longer latencies ranging from 1.2 to 1.8 ms. They showed temporal facilitation when double shocks were provided to the UT nerve. They did not follow repetitive high-frequency stimuli (< or = 2.5-ms interval). It was suggested that D-type EPSPs were di-synaptically evoked via secondary vestibular neurons. Interneurons in the AB nucleus had the same characteristics as AB motoneurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Solar energetic particles in the intermediate region of the heliosphere

Energetic particle increases in the energy range 4 to 130 MeV observed by the Kiel Electron Telescope (KET) during the in-ecliptic part of the ULYSSES mission between 1 and 5.4 AU differ distinctly from their appearance in the inner heliosphere inside 1 AU. Prompt events are rare, and for most of the events velocity dispersion is lacking. The observed intensity-time profiles show poor time relations with optical solar flares. The data is far better organized by the structure of the interplanetary medium with its shocks, tangential discontinuities, corotating interaction regions, heliospheric current sheet crossings (sector boundaries), and coronal mass ejections. Nine particle events are discussed in detail. Spectral information as well as composition measurements are used to determine the source of the particle increases: solar, interplanetary, and Jovian. The few prompt events can be fitted with diffusive interplanetary propagation models, yielding radial mean free paths in the range λr = 0.05 to 0.15 AU. The shock related events are dominant at these intermediate distances, with particularly high intensities of MeV-electrons and > 30 MeV protons at merged or double shocks. A new feature are slowly-varying populations (SVP) with long time scales neither related to prompt events nor to local shock effects.

Factors predicting success in DC catheter ablation of accessory pathways.

In a series of 33 patients with accessory pathways, 26 had successful catheter ablation (fulguration [23 patients] or modification [3 patients]) of their accessory pathway conduction, and could be considered as a clinical success. One hundred thirteen single discharge or double discharge shocks were delivered, and each shock was studied to reveal which parameters were important to predict the success or failure of catheter ablation. Double discharge shocks resulted in successful accessory pathway modification or ablation twice as often as single discharge shocks (32% vs 16%). This effect was more pronounced in left lateral accessory pathways (48% vs 4%). Shocks in the electrophysiologically defined ventricular zone were more likely to be successful (33%) than shocks delivered in the atrial zone (14%), irrespective of accessory pathway location. The presence of a probable Kent potential was the parameter most strongly associated with success. The parameter most strongly associated with failure, with a 100% negative predictive value, was the absence of earliest activation recorded on the ablating catheter prior to shock delivery. An AV interval of < 60 msec significantly divided the successful from the unsuccessful shocks (P = 0.01). The VA interval during orthodromic reciprocating tachycardia or right ventricular stimulation did not allow for significant division into successful and unsuccessful attempts in this relatively short series. VA intervals, when longer, were predictive of failure but, when shorter, had low positive predictive value. Mean follow-up in 25 successful patients was 15 +/- 6 months. All patients did well in the follow-up period. Neither those patients with ablation nor modification of the accessory pathway had recurrent episodes of tachycardia or required pharmacological treatment for control of arrhythmias.

Solar energetic and shock‐accelerated particles observed between 1 and 4 AU by the Kiel Electron Telescope (KET) on board Ulysses

We present observations of solar energetic particles and shock‐accelerated particles observed by the Kiel Electron Telescope (KET) on board the Ulysses spacecraft in the time interval 26 October 1990 to mid November 1991. Prompt events with diffusive propagation were observed mainly at small radial distances while at larger distances shock‐related events became dominant. Particularly high intensities of high energy electrons and &gt;30 MeV/n nuclei are observed at merged or double shocks. Slowly‐varying populations (SVP) with long time scales neither related to prompt events nor to local shock effects are a new feature at these intermediate distances.

Spinal input to thalamic VL neurons: evidence for direct spinothalamic effects.

1. The postsynaptic actions of afferents ascending in the ventrolateral quadrant and dorsal columns of the spinal cord were studied in neurons in the ventrolateral nucleus of the thalamus (VL) (n = 138) by use of intracellular recording procedures. Neurons were identified by their monosynaptic input from the cerebellum and, when possible, their antidromic activation from the motor cortex. The possible occurrence of monosynaptic transmission along spinothalamic fibers was investigated by estimating the intrathalamic delay time of postsynaptic responses and by examining the occurrence of temporal facilitation to double-shock stimulation. The experiments were performed in cats anesthetized with alpha-chloralose. 2. The majority of neurons (86%) responded with excitatory or inhibitory postsynaptic potentials to stimulation of the ascending paths. The response latencies of excitation on stimulation of the ventral quadrants at C3 ranged from 2.9 to 18 ms. Evidence for monosynaptic excitation after stimulation of (spinothalamic) afferents ascending in the ventrolateral quadrants was obtained for a number of neurons (n = 30). For these neurons, estimated intrathalamic delays were less than 1 ms and/or the neurons did not display temporal facilitation to double shocks. All the shortest latency responses (from C3) showed evidence of monosynaptic transmission. It is estimated that approximately 19-39% of neurons sampled may receive monosynaptic input. The spinal conduction velocities of the direct projections ranged from 10 to 35 m/s (median 20 m/s). 3. Much of the ascending input was mediated polysynaptically. For afferents ascending in the ventrolateral quadrant, estimated intrathalamic delays were greater than 1.5 ms and/or the postsynaptic responses displayed temporal facilitation to double shocks. The shortest latency from C3 of a polysynaptic response was 5 ms. Spatial interactions were observed between polysynaptic inputs from the ventrolateral quadrants and the dorsal columns, indicating that at least some of the pathways to VL are shared. 4. The data show that many neurons in the VL receive input ascending from the spinal cord via direct and indirect routes. Somatosensory information reaching VL could serve to adjust, during the course of movement execution, the cerebellar commands relayed by VL to the motor cortex.

Mixed nonlinearity and double shocks in superfluid helium

We examine weak second-sound waves in He II at temperatures and pressures near one of the zeros of the Khalatnikov steepening parameter Γ. An extension of the reductive perturbation scheme of Taniuti &amp; Wei is employed to derive the cubic Burgers’ equation governing these waves. It is shown that mixed nonlinearity may occur in disturbances in which the local value of Γ remains strictly positive or strictly negative. Further new results include expressions for the shock speed, shock structure and the conditions under which the shock thickness increases, rather than decreases, with strength. The fundamental existence conditions for temperature shocks are also delineated and related to the shock disintegration process observed in experimental studies.

Better Predictors of Successful His‐Bundle Ablation Analysis of First Shocks

We have reported here that a longer HV interval in association with a larger His amplitude yields a high rate of success when used to position the ablating catheter for His-bundle ablation. Additionally, we have shown that double discharge shocks are more effective than single discharge shocks, and that negative polarity is more effective than positive polarity. The use of bipolar or tripolar, and not quadripolar catheters, was also associated with a higher success rate. In our institution, using a bipolar catheter, we attempt to record an HV interval greater than 55 msec and a His amplitude greater than 0.35 mV. When both of these criteria are fulfilled, we use 3 to 4 joules per kg, and a single discharge shock. When one or the other of these criteria are not fulfilled, we use the double discharge shock method. Using these techniques, we have achieved successful His-bundle ablation with only one shock in all but one of the most recent 21 consecutive patients.

Ionospheric modification ‐ An outdoor laboratory for plasma and atmospheric science

With the ability to induce large‐scale changes in the ionosphere by high‐power ground‐based HF transmitters, laboratory‐like experiments can be performed repetitively in space plasmas. Using satellites and rockets, as well as ground‐based magnetometers, optical and radar diagnostics, this large‐scale plasma has been investigated. The absence of walls and the long confinement time make this plasma distinctively different from conventional laboratory plasmas. Particle and energy transports can be studied in this large‐scale well‐confined plasma. Significant changes in density profiles and velocity distributions can be brought about by modest incident EM wave intensity because the wave fields are resonantly enhanced and the perturbations are cumulative in the same plasma over a long time. Free energy sources can further enhance the excitation of waves. Experimental methods are reviewed together with major experiments performed at the Platteville, Arecibo, Max Planck, and HIPAS observatories. The ionospheric plasma with a rich source of free energy is highly variable especially in the auroral zone, and fast temporal resolution techniques used in laboratory experiments have been introduced to these outdoor experiments to observe caviton collapse and other fast processes. High‐frequency and low‐frequency wave phenomena are observed to be excitable simultaneously and coupled by non‐linear processes. Laboratory experiments, computer simulation, and analytic theories are used to interpret and to guide field experiments. Future experiments include the studies of the formation of potential double layers and ion acoustic shocks from density cavities and their coupling to free energy sources in the ionosphere. Active experiments are desirable in the atmosphere whose response to a known perturbation such as the controlled heating of electrons and neutrals and the formation of negative ions can be quantified. With higher focusing of the available power, there is the exciting possibility of generating a steady state ionospheric plasma and an opening to a new era in controlled atmospheric experiments and long‐range communications.

Killing of drosophila larvae by the fields of an electrohydraulic lithotripter

Drosophila larvae contain small gas bodies stabilized within their respiratory system. Because these bubbles are inhibited in their capacity to expand by the surrounding tissues, it is probable that they do not respond to acoustic fields in the manner described by classical cavitation theory that assumes a spherical bubble in an infinite fluid. However, just because of this inhibited expansion, they may serve as reasonable models for the gas bodies in mammalian tissues. Approximately one half of a population of Drosophila larvae is killed by exposure to 3 to 10 double lithotripter shocks with a positive pressure of 2–3 MPa. In contrast with the predictions of classical cavitation theory, adding a negative pressure to the exposure has little influence on the killing rate or its threshold pressure. The available evidence suggests that interaction of gas bodies in tissues with pressure fields and the resultant biological effects may be qualitatively different than predicted by classical cavitation theory and that positive rather than negative pressure may be a predictor of these effects.

Particle Acceleration Processes in the Solar Corona

Theoretical ideas on particle acceleration associated with solar flares are reviewed. A historical outline is used to introduce the various acceleration mechanisms. These are stochastic acceleration in its various forms, diffusive acceleration at shock fronts, shock drift acceleration, resonant acceleration, acceleration during magnetic reconnection and acceleration by parallel electric fields in double layers or electrostatic shocks. Particular emphasis is placed on so-called first phase acceleration of electrons in solar flares, which is conventionally attributed to bulk energisation of electrons (Ramaty et al. 1980). There is no widely accepted theory for bulk energisation, which may be regarded as an enhanced form of heating. Ideas on bulk energisation are discussed critically. It is argued that the dissipation cannot be due to classical resistivity and involves anomalous resistivity or hyperresistivity, e.g., in multiple double layers. The dissipation must occur in very many localised regions. Bulk energisation due to magnetic reconnection is discussed briefly. A model for bulk energisation due to the continual formation and decay of weak double layers is outlined

The effect of temperature on electrical interactions between antidromically stimulated frog motoneurons and dorsal root afferent axons

The effect of temperature on electrical interactions between antidromically stimulated motoneruons and dorsal root afferents was studied in the isolated and hemisected spinal cord of the frog, superfused with Ringer in which Ca 2+ was equimolarly replaced by Co 2+ or Mn 2+ to suppress chemical synaptic transmission. Suction electrodes were used for stimulating and/or recorcling from dorsal and ventral roots from segments IX or X. Intrafibre recorclings from sensory fibres were made at their point of entry into the spinal cord. Supramaximal ventral root stimuli elicited two distinct responses in the segmental dorsal root. First a brief short-latency depolarizing potential. Second, at temperatures below 11°C, a second depolarizing root potential appeared following the short-latency depolarizing potential-I. Amplitude and duration of short-latency depolarizing potential-II reversibly increased as the bath temperature was decreased, reaching a maximum at 3°C. Between 8 and 3°C, short-latency depolarizing potential-II increased in amplitude by 20%/°C. In contrast short-latency depolarizing potential-I did not show substantial changes with temperature. The short-latency depolarizing potential-II, unlike shortlatency depolarizing potential-I showed stepped fluctuations in amplitude, and appeared to be composed of unitary events. Intrafibre records revealed that the unitary events corresponded to action potentials on individual dorsal root fibres. Double shocks applied to the ventral root, at constant bath temperatures (below 11°C), revealed facilitation of the short-latency depolarizing potential-II, which was maximal between 50 and 80 ms and lasted about 200 ms. Neither the antidromic motoneurone field potential nor the short-latency depolarizing potential-I were facilitated. The results show that the short-latency depolarizing potential-II reflects the relatively synchronous antidromic firing of action potentials in some sensory axons in response to ventral root stimuli. It is proposed that the short-latency depolarizing potential-II results from electrical coupling between some afferent terminals encling monosynaptically on distal motoneuron dendrites. The unmasking and apparent enhancement of electrical coupling when lowering the temperature is likely to result from changes in the electrical properties of non-junctional membranes.

The role of periodontal receptors in the jaw-opening reflex in the cat.

1. In anaesthetized cats, graded electrical stimulation of the inferior alveolar nerve at just above threshold for the largest afferent fibres caused inhibition of jaw-closer motoneurones. Stimulus strength had to be increased to 1.5 times threshold with double shocks to cause reflex contraction of the digastric muscle. 2. Inhibition of jaw-closer muscles and excitation of digastric muscle resulted from transients of force applied to the upper canine tooth. However, the threshold for the digastric response was approximately 11 times higher than that of the periodontal afferent units recorded in the mesencephalic nucleus of the fifth nerve (MesV). Vibration of the upper canine at 50 Hz, with amplitude adequate to excite periodontal afferents, caused no digastric contraction. 3. Stimulation in the caudal part of the MesV so as to excite periodontal afferents caused no digastric reflex, provided that the stimulus did not spread to other parts of the fifth nerve nuclei. 4. It is concluded that under these conditions the low-threshold periodontal mechanoreceptors cause inhibition of jaw-closer muscles, but no significant excitation of jaw-opener muscles. 5. These findings are discussed from the point of view of the control which periodontal mechanoreceptors may exert over the biting force during mastication.

Effect of a tachykinin antagonist on a nociceptive reflex in the isolated spinal cord‐tail preparation of the newborn rat.

1. The pharmacological profile of Spantide, [D-Arg1, D-Trp7,9, Leu11] substance P, as a substance P (SP) antagonist was examined in isolated spinal cords of newborn rats. Potential changes were recorded extracellularly from a lumbar ventral root (L1-L5). Application of SP to the perfusion bath with a brief pressure pulse of 0.05-0.8 s duration produced a dose-dependent depolarization of the ventral root. Spantide in concentrations of 2-16 microM depressed the depolarizing responses of the ventral root to SP in a concentration-dependent manner. The log dose-response curve of SP was shifted to the right in the presence of 16 microM-Spantide by log 5. The responses to neurokinin A (NKA) and bombesin were similarly depressed by 16 microM-Spantide whereas the responses to noradrenaline, gamma-aminobutyric acid (GABA), neurotensin and thyrotrophin-releasing hormone were not affected by 16 microM-Spantide. 2. In an isolated spinal cord-tail preparation of the newborn rat, brief pulse injection of capsaicin into the perfusion solution of the tail induced a depolarizing response in a lumbar ventral root (L3-L5). This response probably represents a nociceptive C fibre reflex. 3. The capsaicin-induced nociceptive reflex was markedly depressed by 16 microM-Spantide and the reflex recovered its original amplitude and shape 30-60 min after removal of Spantide. 4. The capsaicin-induced nociceptive reflex was depressed by morphine (2 microM) and dynorphin (1-13) (0.2 microM), and these effects were reversed by 1 microM-naloxone. 5. In an isolated spinal cord preparation of the newborn rat, stimulation of a dorsal root with single or double shocks induced depolarizing responses of slow time course in both ipsilateral and contralateral ventral roots of the same segment. These slow depolarizing responses were also depressed by 16 microM-Spantide. In contrast the monosynaptic reflex was not affected by 16 microM-Spantide. 6. The present results suggest that SP and NKA are involved as neurotransmitters in the capsaicin-induced nociceptive reflex in the isolated spinal cord-tail preparation of the newborn rat.

Sequential or Single Pulse Defibrillation? Investigations towards Energy Reduction in Experimental Animals

With introduction of the automatic implantable cardioverter-defibrillator for treatment of medically refractory ventricular arrhythmias, many investigations are focussing on possibilities of reducing the energy necessary for defibrillating the heart to obtain a more adequate size and a longer durability of the generator. Several studies favour the sequential pulse delivery, using three electrodes, either endocardial, epicardial or subcutaneous plates, to improve defibrillation performance of low energy shocks. However, the validity of this conclusion remains equivocal since two different electrode configurations were used for single and sequential defibrillation. In the present study the influence of sequential pulse delivery, pulse sequence and resultant current pathways on defibrillation energy requirements were examined in comparison with single-shocks between the same epicardial electrode configuration as well as four orthogonally positioned patches. The energy requirement for 100% efficiency could be reduced by sequential pulsing with a time interval of 1 msec thus yielding significant superiority compared to single pulse defibrillation using three electrodes. The same reliable defibrillation and reduced threshold has been obtained by using four electrodes and one single shock. The addition of a third electrode alone had no influence on the energy requirements. Therefore, we have to discuss a different electrophysiological mechanism for sequential defibrillation than for single shocks with an extended current distribution over the heart using four electrodes. Possibly the action potential of the single cell of the fibrillating heart is of interest in reflecting the efficiency of sequential pulse defibrillation. By influencing the action potential pharmacologically in some animals, the optimal time interval for double shocks could be extended up to 7 msec.(ABSTRACT TRUNCATED AT 250 WORDS)

Exact solutions for sonic shocks in van der Waals gases

Exact closed-form solutions for finite amplitude sonic shocks are presented for the case of a van der Waals gas having a constant specific heat. Solutions are provided for both single and double sonic shocks. Sample calculations are presented that include sonic shocks embedded in smooth inviscid flows.

Double and triple sequential shocks reduce ventricular defibrillation threshold in dogs with and without myocardial infarction

The role of optimal placement of electrodes and mode of shock delivery from a defibrillator was examined in dogs with and without myocardial infarction. Single, double and triple truncated exponential shocks separated by 1 ms were delivered through various electrode combinations and cardiac vectors after electrical induction of ventricular fibrillation. A single shock through a pathway not incorporating the interventricular septum (catheter electrodes or epicardial patches between anterior and posterior left ventricle) required the highest total energy (22.6 and greater than 26.4 J, respectively) and peak voltage (1,004 and greater than 1,094 V, respectively) to terminate ventricular fibrillation. A single shock through a pathway including the interventricular septum required lower total energy and peak voltage to defibrillate. Combinations of two sequential shocks between an intracardiac catheter electrode and anterior left ventricular epicardial patch, between the catheter electrode and subcutaneous extrathoracic plate and between three ventricular epicardial patches all significantly reduced total energy (7.7, 8.7 and 7.8 J, respectively) and peak voltage (424, 436 and 424 V, respectively) needed to defibrillate. Three sequential shocks exerted no significant additional reduction in total energy of the defibrillation threshold than did two sequential shocks. Infarcted canine heart required less peak voltage but not total energy to terminate ventricular fibrillation than did noninfarcted heart. Therefore, two sequential shocks over different pathways reduce both total energy and peak voltage required to terminate ventricular fibrillation.

Properties of postsynaptic potentials evoked in hypoglossal motoneurons by inferior alveolar nerve stimulation

The properties of excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs) produced in cat hypoglossal motoneurons by inferior alveolar nerve stimulation were studied. The percentage magnitude of a short- and a long-lasting component in inferior alveolar-induced IPSPs was measured by application of double shocks separated by 80- to 90-ms intervals to the inferior alveolar nerve. As a result, the protruder motoneurons received synaptic input primarily from the afferent fibers in both the ipsilateral and the contralateral inferior alveolar nerve generating the long-lasting IPSP. In addition, the retractor motoneurons received afferent fibers from the bilateral inferior alveolar nerves to generate the short- and the long-lasting IPSP. With respect to the properties of EPSPs, we have demonstrated that the amplitude of inferior alveolar-induced EPSPs decreased greatly with depolarization.