Mechanical Impulse Research Articles

On a Bone Vibration

At our previous study, we designed a device to add a mechanical impulse to clarify some dynamic mechanical properties of bones and demonstrated that a bone vibration in natural frequency with high and low-frequency components and with logarithmic decrement was developed.This report demonstrates that logarithmic decrement and natural frequency is constant every site of a femur, but its stress in a bone exerted by one mechanical impulse is varied every site.And differences of the logarithmic decrement between ages and between males and females is not clearly.We make sure them, using Desk-Top Analog Computor.Furthermore, we illustrate the distribution of stresses in one femur in the medial side in detail and in three femurs in both sides.

The Bone Vibration of the Lumbar Neural Arch

We have made this experiment to know the dynamic mechanical characteristics of the lumbar vertebra.Experimental approach1. Material: 4 lumbar vertebrae.2. The mechanical system of the pendulum: Mechanical impulse was exerted on the inferior articular process of the lumbar vertebra.3. An holder: It is made from cement, and hold the body of the lumbar vertebra.4. Desk-Top analog computor: simulated the vibration of the lumbar neural arch.5. Recording: Recorded by means of two channel oscilloscpoe. ResultsThe mechanical impulse response of the lumbar vertebrae seems to be will fitted by a simple underdamped second order equation.Approximate values found of the equivalent mechanical parameter are: Natural frequency: 1900 c. p. s. logarithmic decrement: O. 14.

Linear Momentum of Quasistatic Electromagnetic Fields

It is shown that the net mechanical impulse one must exert to change one static system of currents and charges slowly into another such system is independent of the method used, and is given by the change in ΣqiAT(xi,t), where AT(xi,t) is the transverse vector potential, evaluated at the position xi of the charge qi. The linear momentum stored in a quasistatic electromagnetic field is thus given by ΣqiAT(xi,t). These considerations show that it is possible to give the transverse vector potential AT of a static system a physical meaning. Namely, that AT(x) is the net mechanical impulse one must exert to bring a unit point charge slowly from infinity to the point x.

The Mechanical Impulse Method for Determining Dynamic Elastic Moduli and Internal Friction of Solids

The theory governing the excitation of a linear mechanical system by delta function impulse is summarized. In the case of a finite elastic rod excited by an impulse, the Fourier transform of the output function enables the frequency spectrum of the rod to be obtained. A spectrometer for accomplishing this operation is described and a comparative study is made between the impulse and resonance responses of a cylindrical rod

Integration of mechanical impulses of the heart

A simple integration method for quantitative measurement of the cardiac impulses is presented. This method was developed for measuring the cerebral and muscular biocurrents. Ballistic impulses of the heart are recorded by means of a special device—an integrator—and are expressed in conventional units.

Influence of sympathetic stimulation and catecholamines on ectopic impulse formation in the ventricles of the dog ∗

Ventricular tachycardia provoked by focal application of Hypertonic solutions of sodium chloride on the exposed heart of the dog is little influenced by the intravenous injection of 0.01 to 0.02 cc. per kg. of the commercial solution of epinephrine. Only a moderate acceleration of the rate is seen when epinephrine is injected in the same dosage after a ventricular tachycardia was obtained by focal application of sodium oxalate. In no experiment did epinephrine elicit ventricular fibrillation. These results and the experience that extrasystoles and tachycardias caused by administration of aconitine are abolished by administration of epinephrine or sympathetic stimulation encourage the use of the less stormily acting pressor amines in patients with ectopic arrhythmias and shock. Under the influence of nicotine or epinephrine applied focally, one mechanical impulse causes a long after-discharge in the form of chains of ectopic beats. The clinical implications of this finding are discussed.

Drop counter, photocell, amplifier, and counting down circuit for measurement of blood flow with pen-recorder

A hermetically sealed photoelectric drop impulse pickup has been constructed for measuring the volumetric blood flow in veins and arteries by means of the pen-recorder. A miniature semi-conductor photoresistance is used in this pickup. The wiring circuit of the electron amplifier which controls the pen-recorder is presented. The amplifier allows the internals to be registered either between each drop or after every drop and automatically controls the displacement of the recorder pen at regular intervals. The amplifier also registers the frequency of mechanical impulses (heartbeat, etc.) by means of the pen-recorder.

Elastic Waves in Lake Ice Produced by Impact of Falling Weights

Experimental studies of the propagation of elastic waves in lake ice were made at Lake Margrethe, Michigan, and Garrison Dam, North Dakota. These studies were designed to investigate, in particular, flexural waves in the ice-water system produced by hammer drops, cylinder drops, and sledge hammer impacts on lake ice and nearby land. A method similar to the standard seismic-refraction techniques was employed for the wave studies. Flexural wave dispersion curves obtained from records of mechanical impulses on ice are, in general, consistent with theoretical curves based on the “layer” theory of Press and Ewing (1951) for the observed ice thickness and elastic parameters. Three groups of points on the observed dispersion curves obtained from Lake Margrethe data are flexural waves with frequencies from 2 to 8 cps, 13 to 25 cps, and 40 to 140 cps. The first and third groups exhibit dispersion consistent with the combined thickness of a two-layer floating ice sheet. The second group follows dispersion for a wave path in the upper thin layer only. Hammer drops on land generate flexural waves in the layer of frozen ground in the frequency range 15 to 40 cps. These waves are transmitted across the lake-shore boundary and follow a wave path in the upper thin layer of lake ice. A continuous train of flexural waves in the frequency range 4 to 140 cps was observed on records of cylinder drops taken at Garrison Dam, North Dakota. (Parts of this work were supported by Tri-service Contract No. DA-36-039-sc-52654.)

Second Sound Propagation in liquid helium II

One of the strangest anomalies thus far exhibited by matter has been the special thermal wave property of liquid helium II, known as second sound. Characteristic of no other substance than helium II—that weird form adopted by liquid helium below the λ-temperature of 2.19°K—second sound is essentially an undamped thermal wave propagation. Such thermal waves display all the usual properties of wave phenomena, including resonance and reflection characteristics. This property of heat flow conforming to a wave equation, rather than to the classical diffusive heat flow equation, results in such seemingly paradoxical situations as heat flowing uphill against thermal gradients. Anomalous even in name, second sound never activates microphones and is generated by heat impulses rather than by mechanical impulses. Finally, its behaviour provides perhaps the most effective means for investigating and understanding the true nature of this so-called quantum liquid, helium II, and the associated quantum hydrodynamics.

Coincidence Circuit of Medium Resolution

A reliable coincidence circuit of medium resolution with resolving time adjustable between 0.4 and 0.01 microsecond is described. The circuit uses a biased-diode pulse level selector in either channel, followed by a triggered blocking oscillator. Narrow and constant shape pulses so produced in the channels actuate a coincidence tube, output from which keys a rectangular pulse generator for turning on a power tube connected to a mechanical impulse recorder. Preliminary applications to the study of time fluctuations and delays in proportional counters and to proton time of flight measurements are described.

Dip Measurement of Overhead Lines by Mechanical Impulse Waves

Dip Measurement of Overhead Lines by Mechanical Impulse Waves

Frequency Meter for Random or Uniformly Spaced Pulses

The instrument, designed primarily for the determination of average nuclear counting rates, incorporates the following circuit features: (1) biased diode for establishing the recording level; (2) frequency meter using a triggered blocking oscillator, the average plate current of which is proportional to the rate of arrival of pulses; (3) provisions for the operation of a mechanical impulse counter at low rates. A resolving time in the vicinity of 1 microsecond can be achieved.

The use of Artificially Produced Radio-active Elements as Tagged Atoms in Biological Research

ONE might expect that the carrying out of medical and biologic research involving the radio-active elements would be quite different in method and in the apparatus from that employed for biologic and clinical research. Unfortunately for those of us who are using the radio-isotopes in biologic work, this has not been so. Work carried out with experimental animals still involves metabolism cages, dissections, extractions, and all of the apparatus (mostly beakers, volumetrics and so forth) of the biochemical research laboratory. Also, clinical work still involves collecting and homogenizing urine and feces, taking occasional blood samples, working up operative and occasional autopsy material, and the various clinical chemistry procedures so well known to everyone. The only impressive or unique apparatus we use at Rochester is the Geiger-Muller counter, the use of which is, of course, by no mcans limited to measurements of radio-activity. Perhaps most of us know it instead as a sensitive means of detecting lost radium, or as a means for measuring weak x-radiation when r meters and other ionization chambers are not sensitive enough. Figure 1 shows the type of Geiger-Muller apparatus we are using at the present time (1). In most instances, radio-activity measurements are made on substances in solution. We have persuaded ourselves that this technic most easily leads to quantitative results. Two c.c. of the solution on which activity measurements are to be made are placed in a glass cup which has an inside diameter about two millimeters larger than the radio-sensitive plunger-shaped end of the Geiger counting tube. When the cup is brought up around the tube with a rack and pinion, the solution forms a 1-mm.-thick liquid film surrounding the counting tube. This thin film of liquid, together with the thin counter wall (about 0.003 of an inch thick), only slightly absorbs the beta rays of most of the radio-active elements. Most of the beta rays that are headed in the right direction penetrate into the inside of the counter tube where they give rise to electrical impulses that are amplified and eventually recorded on a mechanical impulse counter. After subtracting a constant background due largely to cosmic rays, the number of counts per minute is proportional to the radio-activity of the solution contained in the cup. Figure 2 shows better the actual construction of the Geiger-Muller tube and the method of mounting that is used. Radio-iron ejects very soft beta rays. For this dement the sensitivity of the apparatus can be increased about five times by electroplating the iron onto the inside surface of a tin foil cylinder that will just slip over the counting cylinder. This procedure eliminates the adsorption of the beta rays by the solution in which the iron is dissolved. The beta rays of radio-sulphur are so soft and non-penetrating that this type of apparatus is not suitable for their measurement.

III. An automatic method for the investigation of velocity of transmission of excitation in mimosa

The question whether the transmitted effect in Mimosa is due to a hydro mechanical or excitatory impulse is held to be of much interest in Plant Physiology. I shall therefore deal with the subject in some detail and adduce results of additional investigations that I have carried out recently. The general belief that the transmitted impulse in the plant is hydro-mechanical has been largely based on two well-known experiments of Pfeffer and Haberlandt. In the former of these the effect of strong stimulus was found to travel over chloroformed parts of the stem. Pfeffer assumed that the conductivity of this portion must have been abolished, since chloroform is known to abolish motile excitability. In the experiment of Haberlandt, an intervening tissue was killed by scalding; in spite of this, stimulus was found to be transmitted across the scalded area. From these two experiments it was inferred that the impulse which was transmitted could not have been of a true excitatory nature. It was held, on the contrary, that the strong stimulus had given rise to a variation, whether of increase or diminution, of hydrostatic pressure. This variation of pressure, it was assumed, had been hydromechanically transmitted, and, on reaching the distant pulvinus, had inflicted on it a blow which had proved as effective as if a mechanical stimulus had been applied locally. It is thus held that in Mimosa there is a mere transmission of stimulus but no transmission of excitation.

Butterfly Swarms

EVEN your varied correspondence from all parts of the world has rarely furnished us with such a wonderfully complete and interesting personal observation as that of Mr. Sydney B. J. Skertchly (NATURE, vol. xx. p. 266) on the West African breeding grounds of Vanessa cardui, and the almost mechanical impulse and simultaneity with which such a swarm as that which he describes free themselves from the pupa-case and set forth on their migration. Can any one throw a similar light on the periodicity of Colias edusa? V. cardui is a more constant insect in this neighbourhood than any other with which I am acquainted; but the numbers in June of this year were quite unusual. Also we remarked that they were very high-coloured and vigorous, unlike the ordinary washed-out hybernated specimens of early summer. As one of your correspondents has remarked of his neighbourhood, so here C. edusa swarmed in 1877. It was the prevailing insect. In 1878 we had hardly a solitary example. The so-called C. helice—the pale variety of C. edusa—was frequent in 1877. I saw none of C. hyale; indeed, have never seen that insect here.