Ultrasonic Transmission Method Research Articles

Dislocation-interstitial interactions in an iron-0.05% C alloy

A 5 MHz ultrasonic transducer transmission method was used to study recovery processes subsequent to plastic deformation in a polycrystalline, high purity iron-0.05% carbon alloy. Simultaneous and continuous measurements were made of stress relaxation and attenuation recovery in the temperature range 77° K < T < 300° K. Below about 180°K, the effect of interstitial pinning of dislocations was Found to be negligible. Above this temperature, interstitial pinning was found to be a two-stage thermally activated process with a time exponent of 2 3 in the first stage, changing to 1 2 in the second. The activation energy of the first stage was determined as 12.5 kcal/mole by a Granato-Hikata-Lücke analysis and as 11 kcal/mole by an Arrhenius analysis of the time to transition from the first to the second stage. It is argued that for the first stage these values are consistent with Schoeck and Seeger re-organization of carbon interstitials about strain induced screw dislocations. The second stage is believed to be Cottrell-Bilby bulk diffusion toward the dislocations.

The use of echoencephalography to differentiate intracerebral hemorrhage and brain softening.

U 'LTRASOUND wave was first used in the diagnosis of intracranial disease by Dussik 2 in 1942 when he applied an ultrasonic transmission method. In recent years a reflection method has been used with excellent results. Ultrasonic diagnosis of intracranial disease is based on the observation of the shift of the midline echo, which corresponds with the reflected echo of the midline structure, as well as on the observation of the reflected echo derived from the intracranial lesion itself. We have found in our surgical treatment of hypertensive intracerebral hemorrhage that it has often been difficult to differentiate intracerebral hemorrhage from cerebral softening. In intracerebral hemorrhage the echogram shows a midline echo shift whereas in cerebral softening there is none. We have found, however, that when the hematoma is small enough not to produce a midline echo shift, the hematoma echo with its multiple spike-like pattern derived from hematoma itself is a better diagnostic guide. 6-8 We are now reporting our experiences with echoencephalography in the differential diagnosis of intracerebral hemorrhage, cerebral softening, and subarachnoid hemorrhage.

On the Detection of Brain Tumors by Ultrasonics

The investigation reported here verifies Dussik's finding that an ultrasonic transmission method can yield ventriculograms without air injection. The outline of the liquid filled ventricle within the brain is usually deformed in the presence of a tumor. The ventricular geometry is depicted by graphical (automatic scanning) representation of intensity transmitted through the head. Experimental evidence indicates a safe working margin below pain and damage thresholds. The method utilizes the large available range of differential attenuation (order of .01 db/cm in the liquid and 1 to 3 db/cm in brain tissue, at frequencies of 1 to 3 megacycles). Results of basic studies on attenuation, scattering and resolution capabilities are reported.