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EDITORIAL

J Biomech Eng. 1977;99(3):125. doi:10.1115/1.3426280.
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Abstract
Commentary by Dr. Valentin Fuster

RESEARCH PAPERS

J Biomech Eng. 1977;99(3):126-147. doi:10.1115/1.3426281.

The one-dimensional theory of steady flow in a thin-walled tube, partially collapsed by a negative transmural pressure difference, is developed in a general way. The mechanics of the flow is closely coupled to the mechanics of the tube. The latter is characterized by a “tube law”: the relationship between cross-sectional area and transmural pressure difference. Features analogous to those in gas dynamics and free-surface flow may manifest themselves: a characteristic wave propagation speed; opposite phenomena at flow speeds, respectively, less than and greater than the wave speed; choking; and shocklike transitions. There are many practical examples of such flows, mainly in physiology and medicine. The one-dimensional, steady analysis includes the effects of friction, lengthwise variations in external pressure, variations in elevation, resting area, wall stiffness, and mechanical properties. The speed index S (ratio of flow speed to wave speed), analogous to the Mach and Froude numbers, appears naturally in the results as a controlling parameter of behavior. Various practical ways of passing continuously from subcritical (S < 1) to supercritical (S > 1)speed are suggested. A preliminary theory of shocklike, dissipative transitions is developed, the results of which depend sensitively on the tube law. Explicit working formulas are developed for several simple types of flow (friction alone; changes in rest area alone; changes in external pressure or elevation alone) for a simple, approximate tube law. Various modes of flow behavior for a flow affected by both friction and gravity are explored.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1977;99(3):148-154. doi:10.1115/1.3426282.

A technique is presented for the simultaneous determination of thermal conductivity and thermal diffusivity of biomaterials. Measurements are derived from the transient power supplied to a thermistor probe operated in a self-heated mode. The thermal properties are extracted through the use of an appropriate thermal model. Thermal conductivity is determined through a simple algebraic equation. Thermal diffusivity is determined from a convenient set of nondimensionalized curves. The technique can be used in vivo and in vitro. Measurements can be made in sample volumes of less than 1 cc in less than 30 s.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1977;99(3):155-159. doi:10.1115/1.3426283.

HeLa cells, suspended in solution, were subjected to well-defined temperature protocols on a microscope stage specifically designed for this purpose. Simultaneously, the appearance of the first irreversible morphological change in the cells was monitored and used as an indicator of damage. For constant temperature protocols, an Arrhenius relationship was found between the measured damage time and the cell temperature, yielding an activation energy of 249 kJ/mole (59.5 kcal/mole) and a frequency factor of 9.09 × 1036 s−1 . On the basis of this result and of Henriques’ damage integral concept [1], working relationships have been derived to express the damage time for two additional temperature protocols; viz., 1 a linearly increasing temperature, and 2 a linearly increasing temperature followed by a constant temperature. These relationships show the dependence of the damage time on the heating rate, the maximum attained temperature, the damage kinetics and the initial cell temperature.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1977;99(3):160-165. doi:10.1115/1.3426284.

An electromechanical transducer was developed to enable measurement of the general six degree-of-freedom relative motion between lumbar vertebrae of the in-vitro human spine. The transducer system is to be used in the evaluation of various spinal fixation devices in studies of fracture dislocated spines. Preliminary testing of the system has shown it to be an accurate and general means of measuring relative spatial motion between two bodies over a limited range.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1977;99(3):166-170. doi:10.1115/1.3426285.

The dynamic response of the human ankle joint to a band-limited (0 to 50 Hz) gaussian torque disturbance superimposed on a constant bias torque is observed at different levels of voluntary contraction of the leg muscles acting about the ankle. The compliance of the ankle joint, defined as the ratio of the joint rotation and applied torque is modeled by a second-order, linear dynamic model. The visco-elastic properties of the joint are shown to be linear functions of the muscle activation.

Commentary by Dr. Valentin Fuster

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