Impulse Duration Research Articles

A Measurement Technique for Shock Wave-Loaded Structures and Its Applications

In engineering problems it is necessary to predict the deformations of structural elements subjected to shock waves. In the literature a wide range of structural theories, constitutive equations and simulation techniques is available in order to simulate the occurring deformations. However, an objective statement about the accuracy of calculated structural deformations is only possible by comparing these results to experiments. In the present work a measurement technique with shock tubes is introduced which was especially developed to measure fast deections of plates during the impulse duration. This technique provides a possibility to validate and to improve constitutive and structural theories. Furthermore, very precise measurements can be performed in order to observe limit states and buckling of repeatedly loaded plates. These applications are shown in this study.

Paraspinal Muscle Spindle Responses to the Duration of A Spinal Manipulation Under Force Control

More than 90% of chiropractic patients receive high-velocity, low-amplitude spinal manipulation (HVLA-SM) as part of their chiropractic care. The purpose of the current study was determine how the duration of a lumbar HVLA-SM given under force control affects the discharge of paraspinal muscle spindle afferents. Experiments were performed on deeply anesthetized adult cats treated in accordance with the Guiding Principles in the Care and Use of Animals approved by the American Physiological Society. Muscle spindle afferents were identified in the dorsal roots. Neural activity was recorded from individual spindles located in the low back predominately from multifidus and longissimus muscles. Spinal manipulative loads were applied to the L6 vertebra. Force-time profiles were half-sine waves with impulse durations of 25, 50, 100, 200, 400, and 800 milliseconds, delivered at constant magnitudes of 33%, 66%, or 100% body weight. The relationships between spinal manipulation duration and muscle spindle responses were determined using a randomized block design. Mean instantaneous discharge frequency increased with decreasing impulse duration. There appeared to be a threshold effect for impulse duration below which the increase in muscle spindle discharge changed greatly with decreasing impulse duration and above which the discharge did not substantially change with decreasing impulse duration. This threshold was in the vicinity of the duration of an HVLA-SM applied clinically (<or=200 milliseconds). After the manipulation, muscle spindle afferents often became silent, but manipulation duration had little effect on this duration and also had little effect on the time it took for the afferents to recover their initial resting discharge. The findings suggest that one biomechanical characteristic of an HVLA-SM is its capacity to load paraspinal muscle spindles at a rate where their velocity sensitivity predominates over their length sensitivity.

Long-term assessment of auditory changes resulting from a single noise exposure associated with non-occupational activities

We examined the long-term sequelae in both ears of 42 patients who reported the occurrence of auditory changes resulting from a single exposure to intense sound levels during non-occupational activities. We divided these patients into two groups, based upon noise exposures of either continuous duration or single high-energy impulse. Audiometric data were available for each of these subjects shortly after their noise-exposure events and follow-up examinations took place more than one year after the noise occurrence (range: 1–16 years). The initial median hearing loss for the continuous-type noise exposure group at 3–8 kHz was found to be 9 dB, relative to the age-appropriate norms, in the more affected ears, and hearing function was found to have returned to normal levels at follow-up. The same initial hearing loss was measured for the impulse-type noise group, but a residual hearing loss of 4 dB was measured at follow-up. Furthermore, the majority of the subjects from both groups reported tinnitus and hypersensitivity to sound at follow-up, but with minimal impact on their lives.SumarioExaminamos en ambos oídos las secuelas a largo plazo en 42 pacientes que reportaban cambios auditivos como resultado de una exposición única a ruido intenso durante actividades no laborales. Dividimos a los pacientes en dos grupos, dependiendo de la exposición a ruido, ya fuera de duración continua o debida a un impulso de gran energía. Los datos audiométricos estuvieron disponibles para cada uno de estos sujetos poco después de su evento de exposición sonora y el seguimiento se llevó a cabo durante más de un año después de la exposición a ruido (rango de 1 a 16 años). El promedio de hipoacusia inicial entre 3 y 8 kHz para el grupo de exposición continua fue de 9dB, con relación a las normas adecuadas por edad en el oído más afectado, y la función auditiva había regresado a los niveles normales en el seguimiento. La misma pérdida auditiva fue medida en el grupo de ruido tipo impulso, pero en el seguimiento se detectó una pérdida de 4dB. Incluso la mayoría de los sujetos de ambos grupos reportaron acúfeno e hipersensibilidad al sonido en el seguimiento, pero con un impacto mínimo en sus vidas.

Buckling and damage of dynamically loaded plates in shock tubes

AbstractIn this study circular metal plates are subjected alternately to impulsive loadings in shock tubes. The aim is to develop an experimental method to measure the buckling shapes of shock wave‐loaded plates during the impulse duration. Furthermore, the measurements are used to validate failure modes predicted in finite element simulations. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Determinants and Effects of Electrical Stimulation of the Inferior Interatrial Parasympathetic Plexus During Atrial Fibrillation

Catheter stimulation of the inferior interatrial ganglionated parasympathetic plexus decreases the ventricular rate during atrial fibrillation (AF) in humans. However, the relatively high stimulation voltages might prevent implementation of neurostimulation in chronic implantable devices. From myocardial electrostimulation it is known that the required impulse energy and charge is lowest at the chronaxie time. In order to lower energy requirements for cardiac neurostimulation, the present study evaluates the impulse-strength versus impulse-duration relationship for a neurostimulation lead that was implanted into the inferior interatrial ganglionated plexus. In nine dogs, permanent epicardial bipolar screw-in electrodes were fixed in the inferior interatrial ganglionated plexus. AF was maintained via rapid atrial pacing. During AF, neural stimulation was performed at various frequencies (1-100 Hz), impulse durations (0.05-2 msec), and voltages (0.02-11.5 V). There was a linear correlation between R-R interval lengthening and stimulus voltage (R = 0.99; P < 0.001) and a bell-shaped relationship between stimulation frequency and negative dromotropic effect with maximum rate slowing at 30-50 Hz. The rheobase for a 50% R-R interval prolongation during AF was 1.81 V and 2.72 V for high-grade AVB yielding a chronaxie time of 0.14 msec and 0.18 msec, respectively. The impulse energy (charge) at the chronaxie time was 4-6 microJ (6-8 microC). Cardiac neurostimulation follows a chronaxie/rheobase behavior. Energy, charge, and voltage values needed to achieve significant negative dromotropic effects are within the limits of conventional cardiac pacemaker outputs, which may allow implementation of neurostimulation capabilities in current pacemaker technology.

A Non-Dissipative Reflex Charging Circuit

A novel circuit is proposed to implement Reflex charging for rechargeable batteries. The required asymmetrical bilateral pulses for Reflex charging are generated controlling the only one active power switch with pulse-width-modulation (PWM) control. The pulse width of the charging current is regulated simply by controlling the duty ratio of the active power switch, while the amplitude and duration of the negative impulse can be determined by the designed circuit parameters. Experimental tests are carried out to verify the theoretical analyses.

Long current impulses may be required for nerve stimulation in patients with ischemic pain

To report on the efficacy of peripheral plexus catheters in the treatment of ischemic pain in spite of nerve stimulation with long current impulses.Two patients with severe neuropathic ischemic foot pain are described. A 56-yr-old man with diabetes, renal failure, and autonomic neuropathy presented with severe ischemic foot pain. Opioids produced excess sedation and hypotension. A 62-yr-old woman was admitted after femoral-popliteal bypass and developed a reperfusion pain syndrome not relieved with opioids, gabapentin, amitryptiline, and clonidine. In both patients, a sciatic plexus catheter was placed with resolution of pain. Conventional nerve stimulation, which uses a pulse duration of 0.1 msec, did not result in muscle contraction. However, by using a nerve stimulator capable of delivering a 1.0 msec impulse duration, a muscle twitch or paresthesia endpoint ensued allowing for successful catheter placement.Peripheral plexus catheters provide a safe alter-native to systemic analgesics for pain relief in patients with ischemic foot pain. However, conventional nerve stimulation techniques may not elicit a motor response in patients with underlying neuropathy, and the use of nerve stimulators capable of delivering long current impulses is recommended.

Electric-field generated by the combustion of titanium in nitrogen

A short temporal electrical impulse (duration of 30–150ms) was generated during the nitridation of mixtures of titanium and titanium nitride by a high temperature moving reaction front. The maximum voltage and current were generated in the combustion front region, in which the conversion of Ti to TiN was incomplete. The electric field (voltage up to 2V and current up to 60mA) decayed and vanished before the maximum combustion temperature was attained. The generation of an electric field during a rapid high-temperature nitridation is most probably due to the different diffusion velocities of charge carriers through the growing titanium nitride shell during the initial stage of the reaction. When the reactant mixture contained a high percentage of pure titanium (larger than 60wt%), partial melting led to irreproducibility in the amplitude and duration of the electrical signal.

Influence of laser pulse shape both on temperature profile and hardened layer depth

This paper presents a mathematical modelling and numerical calculations of heat conduction problems where laser generated heat is assumed as a surface heat source. Also the effect of a laser time structure on a hardened layer depth is examined. Temperature profiles for different laser pulse shapes are determined from the solution of a linear one-dimensional heat conduction equation for semi-infinite medium and discussed in terms of the parameters evolution such as dimensionless: temperature, heat flux, hardening depth, laser impulse duration and increasing time of triangular pulse shape.

Wear resistance of 3Cr2W8V rough surfaces

Three types of rough surface were processed by laser irradiation on the 3Cr2W8V material hot-work die steel surface. The wear experiments with smooth surface and rough surface samples were repeated on the pin-tray wear machine. According to the wear results, we studied the regularity of wear resistance of different rough surface samples. The results indicated that bionic rough surface can improve the wear resistance of the material and the wear resistance can be increased 1 – 2 times, compared with the smooth surface. Also, the wear resistance of the rough surface was affected by laser current and duration of impulse. The bigger the laser current or the impulse duration, the better is the wear resistance. When the distance between the same kind of units which are distributed on the surfaces is changed, the wear resistance changes. The wear resistance of a bionic rough surface on which the grid units were distributed at spacing of 1 mm was the best. And we designed the wear models.

Prediction of Blast Loads Based on the Expected Damage Level by Using Displacement Based Method

This paper describes how the equivalent viscous damping (EVD) ratio is a crucial parameter in the application of the displacement based method. Previous works have correlated the EVD ratio as a function of the displacement ductility level based on the hysteric response of reinforced concrete members subjected to blast loads. Furthermore, the displacement response factor (DRF) for blast loads was proved as a function of the EVD ratio and the ratio of impulse duration to the natural period. The explosive charge weight and stand-off distance required to impose a given damage level were predicted by the DBD method based on these research results. In order to examine the feasibility of assessing the blast-resistant capacity of concrete (RC) slabs using the displacement based design (DBD) method. A RC slab was tested under real blast loads in the out-of-plane direction. Test results have shown that the blast loads were effectively estimated and the damage levels observed from the field tests correlated well with the predicted levels.

Leg Stiffness and Expertise in Men Jumping

The aim of the present study is to investigate: a) the leg spring behavior in the one-leg vertical jump, b) the contribution of impulse parameters to this behavior, and c) the effect of jumping expertise on leg stiffness. Four categories of experts (handball, basketball, volleyball players, and Fosbury athletes), as well as novice subjects performed a run-and-jump test to touch a ball with the head. Five experimental conditions were tested from 55 to 95% of the maximum jump height. Kinematic and kinetic data were collected using six cameras and a force plate. The mechanical behavior of the musculoskeleton component of the human body can be modeled as a simple mass-spring system, from which leg stiffness values can be extracted to better understand energy transfer during running or jumping. The results indicate that leg stiffness (mean value of 11.5 kN.m) decreased with jumping height. Leg shortening at takeoff also increased with jumping height, whereas contact time decreased (-18%). No difference was found between experts and novices for leg stiffness. However, a principal components analysis (PCA) indicated the contribution of two main factors to the performance. The first factor emerged out of vertical force, stiffness, and duration of impulse. The second factor included leg shortening and jumping height. Differences between experts and novices were observed in terms of the contribution of leg stiffness to jump height, and more importantly, clear differences existed between experts in jumping parameters. The analysis performed on the sport categories indeed revealed different jumping profiles, characterized by specific, sport-related impulse parameters.

Elastoplastic Deformation of a Compound Disk under Impulsive Loading

The small elastoplastic deformation theory and the finite-element method are used to analyze the behavior of a compound disk under axisymmetric impulsive loading. Numerical results are presented, which describe the development of plastic deformation, the effect of hardening and the duration of the loading impulse on the oscillatory elastoplastic deformation of the disk

Impulsive control and synchronization of spatiotemporal chaos

Abstract The impulsive control of spatiotemporal chaos of a particular type of non-linear partial differential equations has been investigated. A criterion for the solutions of these partial differential equations to be equi-attractive in the large is determined and an estimate for the basin of attraction is given in terms of the impulse durations and the magnitude of the impulses. Extending these results to impulsively synchronize spatiotemporal chaos of the same type of partial differential equations is explored. A proof for the existence of a certain kind of impulses for synchronization such that the error dynamics is equi-attractive in the large, is established. A comparison of the developed theoretical model with other existent numerical models available in the literature has been studied. Several simulation results are given to confirm the theoretical results. Moreover, an investigation of the Lyapunov exponents of the error dynamics between impulsively synchronized spatiotemporal chaotic systems, is done to further confirm the theoretical results.

Excitability of chronic hemiparetic muscles: determination of chronaxie values and strength-duration curves and its implication in functional electrical stimulation

Central nervous system disorders affect the anatomy and physiology of the lower motoneuron. This fact has an impact on the stimulation parameters, especially on the duration of the stimulating impulses, for functional electrical stimulation in chronic hemiparetic patients. The aim of this study was thus to test the excitability and to determine chronaxie values and strength-duration curves of weak wrist and finger extensor muscles and spastic finger and wrist flexor muscles in the hemiparetic arm. Twelve patients with chronic hemiplegia (>6 months after the onset of the cerebral lesion) participated in the study. A constant current stimulator was used. As to chronaxie values no significant differences were found between the extensor muscles (mean+/-SD: 0.44+/-0.16 ms) and flexor muscles (mean+/-SD: 0.36+/-0.22 ms). A moderate variability was seen for both extensor muscles (0.2-0.8 ms) and flexor muscles (0.1-0.9 ms). These values are well within the normal range determined for innervated muscles. All strength-duration curves were completely normal for each muscle. We conclude that in chronic hemiparetic muscles, impulses of the same duration can be used as in muscles of healthy subjects.

Ground reaction forces and limb function in tölting Icelandic horses

Gaited horses employ 4-beat stepping (singlefoot) gaits that extend into speeds typical of trots. Ground reaction force (GRF) patterns of these specialised gaits have not been reported; therefore, appraisal of these gaits using nongaited horse kinetics may lead to clinical misjudgements. GRFs of tölting Icelandic horses will be comparable in profile and magnitude with those of trotting horses. Forelimb and hindlimb GRFs were obtained for 10 Icelandic horses ridden at a tölt. These data were evaluated across 3 speed ranges: <2, 2.5-5 and >5 m/sec. Virtually all vertical force tracings were single-peaked. Forelimbs typically had greater peak vertical forces and impulses compared with hindlimbs. Support duration and forelimb vertical impulse were correlated negatively with speed, whereas peak vertical, braking and propulsive forces and hindlimb braking and propulsive impulses were correlated positively with speed. GRF profiles of tölting Icelandic horses are more similar to profiles of trots than walks, suggesting that tölts follow bouncing mechanics. Greater overlap of limb support in 4-beat gaits (even at high speeds) is associated with lower peak vertical force magnitudes of tölts compared with those reported for trots at comparable speeds, which may help limit the occurrence of overloading injuries in Icelandic horses.

Compensatory load redistribution of horses with induced weightbearing hindlimb lameness trotting on a treadmill

The compensatory mechanisms of horses with weightbearing hindlimb lameness are still not fully understood. That weightbearing, unilateral hindlimb lameness would not only alter stride characteristics to diminish structural stress in the affected limb but also induce compensatory load adjustments in the other supporting limbs. To document the load and time shifting mechanisms of horses with unilateral weightbearing hindlimb lameness. Reversible lameness was induced in 8 clinically sound horses by applying a solar pressure model. Three degrees of lameness (subtle, mild and moderate) were induced and compared with the nonlame (sound) control measurement. Vertical ground reaction forces were recorded for all 4 limbs simultaneously on an instrumented treadmill. Compared to the sound situation, moderate hindlimb hoof lameness induced a decrease in stride duration (-3.3%) and stride impulse (-3.1%). Diagonal impulse decreased selectively in the lame diagonal stance (-7.7%). Within the diagonal limb pair, vertical impulse was shifted to the forelimb during the lame diagonal stance (+6.5%) and to the hindlimb during the sound diagonal stance (+3.2%). Peak vertical force and vertical impulse decreased in the lame limb (-15%), but only vertical impulse increased in the contralateral hindlimb (+5.7%). Stance duration was prolonged in both hindlimbs (+2.5%). Suspension duration was reduced to a greater extent after push-off of the lame diagonal limb pair (-21%) than after the sound diagonal limb pair (-9.2%). Four compensatory mechanisms could be identified that served to reduce structural stress, i.e. peak vertical force on the affected limb: 1) reduction of the total vertical impulse per stride; 2) diagonal impulse decreased selectively in the lame diagonal; 3) impulse was shifted within the lame diagonal to the forelimb and in the sound diagonal to the hindlimb; and 4) the rate of loading and peak forces were reduced by prolonging the stance duration. Load shifting mechanisms are not only effective in diminishing peak forces in the affected limb, but also suppress compensatory overload in other limbs. Selected force and time parameters allow the unequivocal identification of the lame limb. Future studies have to examine how far these compensatory mechanisms may be generalised for other defined orthopaedic problems in the hindlimb.

Nonlinear Time Series Analysis of Volcanic Tremor Events Recorded at Sangay Volcano, Ecuador

The assumption that volcanic tremor may be generated by deterministic nonlinear source processes is now supported by a number of studies at different volcanoes worldwide that clearly demonstrate the low-dimensional nature of the phenomenon. We applied methods based on the theory of nonlinear dynamics to volcanic tremor events recorded at Sangay volcano, Ecuador in order to obtain more information regarding the physics of their source mechanism. The data were acquired during 21–26 April 1998 and were recorded using a sampling interval of 125 samples s−1 by two broadband seismometers installed near the active vent of the volcano. In a previous study Johnson and Lees (2000) classified the signals into three groups: (1) short duration (<1 min) impulses generated by degassing explosions at the vent; (2) extended degassing ‘chugging’ events with a duration 2–5 min containing well-defined integer overtones (1–5 Hz) and variable higher frequency content; (3) extended degassing events that contain significant energy above 5 Hz. We selected 12 events from groups 2 and 3 for our analysis that had a duration of at least 90 s and high signal-to-noise ratios. The phase space, which describes the evolution of the behavior of a nonlinear system, was reconstructed using the delay embedding theorem suggested by Takens. The delay time used for the reconstruction was chosen after examining the first zero crossing of the autocorrelation function and the first minimum of the Average Mutual Information (AMI) of the data. In most cases it was found that both methods yielded a delay time of 14–18 samples (0.112–0.144 s) for group 2 and 5 samples (0.04 s) for group 3 events. The sufficient embedding dimension was estimated using the false nearest neighbors method which had a value of 4 for events in group 2 and was in the range 5–7 for events in group 3. Based on these embedding parameters it was possible to calculate the correlation dimension of the resulting attractor, as well as the average divergence rate of nearby orbits given by the largest Lyapunov exponent. Events in group 2 exhibited lower values of both the correlation dimension (1.8–2.6) and largest Lyapunov exponent (0.013–0.022) in comparison with the events in group 3 where the values of these quantities were in the range 2.4–3.5 and 0.029–0.043, respectively. Theoretically, a nonlinear oscillation described by the equation +β+γg(x)=fcosωt can generate deterministic signals with characteristics similar to those observed in groups 2 and 3 as the values of the parameters β,γ,f,ω are drifting, causing instability of orbits in the phase space.

ENDOVENOUS OBLITERATION OF LONG SAPHENOUS VEIN. A NEW MINIMAL INVASIVE METHOD OF TREATMENT FOR VARICOSE VEINS – PRELIMINARY REPORT

Background. Minimally invasive treatment of varicose veins is becoming more and more important as it represents less burden to the patient and health system. The success of the different methods depends on their capability to eliminate the reflux at the sapheno-femoral junction (SFJ) and the incompetent greater saphenous vein (GSV). In achieving these only three methods are successful: ultrasound (US) guided catheter sclerosation, radiofrequency or laser endovenous obliteration of GSV. Aims. To demonstrate a novel way to use a laser energy through an endoluminal laser fiber for the minimally invasive treatment of truncal varicosities and the elimination of SFJ reflux. Methods. The patients with US detected reflux in the SFJ and GSV were treated on the outpatient basis under local anaesthesia with laser mediated heat energy in the GSV 2–3 cm from SFJ with the laser of wave length of 980 nm with the power 15 W and the impulse duration of 1 sek. We used 20–40 impulses along the treated segment of GSV. The exact position of the laser fiber was determined by the US. The smaller branch varices were removed by mini phlebectomies. Patients tolerated well the procedure and they were dismissed from the hospital with applied compression stockings (CCL II) immediately after the completion of the procedure. The control US was done one week, four weeks and three months later. At one week one out of 16 patients presented with no occlusion of the GSV. At four weeks another patient had recanalisation of GSV but without the reflux. All other patients had the short GSV stump in which the patent epigastric vein was draining while the remaning part of the GSV was obliterated by the thrombus. Except for some skin ecchymosis and mild induration in the but patients did not have any other problems. The unsuccessful treatment in two patients is probably due to insufficient applied energy. Conclusions. Endovenous laser obliteration of GSV is an effective method that can be performed on the outpatient basis under local anaesthesia. Patients tolerate well the intervention. The preliminary results promise that the method, after additional experiences, could become in some patients an adequate alternative to classical surgical treatment of the varicosities of GSV, which remains the »the gold standard«.

Sur la réponse transitoire d'une couche solidaire d'un milieu semi-infini ; application à un impact sur le thorax

The theory of generalized rays is dedicated to the investigation of the transient response of elastic layered media. It yields exact solutions, whatever the duration of the applied impulse (i.e., for any frequency content of the excitation). This Note is part of a research project on the modeling of non-penetrating impact on thorax. We investigate a simplified model of the thoracic wall – a layer welded to a semi-infinite medium – submitted to an impulse of variable duration. Among other things, it is found that the response computed for a “long” impulse is consistent with a result of the classical plate theory. To cite this article: Q. Grimal et al., C. R. Mecanique 331 (2003).