An alternative method for the measurement of the mechanical impulse of a vertically directed blast.
An alternative method for the measurement of the total mechanical impulse of a vertically directed blast due to an explosive charge is presented. The method differs from apparatus that employ a vertically displaced mass (similar in principle to the ballistic pendulum) in that a relatively compact spring-damper system is employed to constrain the movement of the mass. The mechanical impulse is determined by integrating, with respect to time, the net force applied to the spring-damper system. The details of an explosive impulse measuring instrument rated to 12 kN s are presented.
Effects of Pelvic Skeletal Asymmetry on Trunk Movement: Three-Dimensional Analysis in Healthy Individuals Versus Patients With Mechanical Low Back Pain
Study Design. Comparative analysis and correlational research design were used to investigate the association between anthropometry and biomechanical performance among asymptomatic subjects and patients with low back pain (LBP). Objectives. To examine the association between pelvic asymmetry and patterns of trunk motion in asymptomatic and LBP subjects. Secondary objective was to investigate the association between restricted trunk motion, laterality of referred pain, and pelvic asymmetry. Summary of Background Data. Subtle pelvic asymmetry (exhibited as either lateral pelvic tilt or iliac rotational asymmetry), which is common among normal individuals, has not been convincingly linked to abnormalities in back movements. Given the difficulty in diagnosing most LBP, a classification using pelvic asymmetry and patterns of movement could be helpful in establishing a rational treatment plan. Methods. Fifty-nine subjects with no history of LBP and 54 patients with mechanical unilateral LBP were tested. An anthropometric frame was used to measure pelvic asymmetry in standing. Dynamic motion data, comprised of the principal and coupled movements, were collected using the Qualysis Motion Capture System. Results. While the groups did not differ in the total range of lumbar movement, the LBP group exhibited significantly higher asymmetry in the principal motion. The groups differed significantly in the pattern of coupled rotation during lateral flexion. Asymmetry in lumbar lateral flexion was highly related to two types of pelvic asymmetry: lateral pelvic tilt (LPT) and iliac rotation asymmetry (IRA). Asymmetry in lumbar axial rotation was highly related to IRA but weakly related to LPT. Conclusions. This study demonstrates objective differences in patterns of lumbar movement between asymptomatic subjects and patients with LBP. The study also demonstrates that subtle anatomic abnormality in the pelvis is associated with altered mechanics in the lumbar spine. We suggest that asymmetry of lumbar movement may be a better indicator of functional deficit than the absolute range of movement in LBP.
Laminar heat or mass transfer in rectangular channels and in cylindrical tubes for fully developed flow: comparison of solutions obtained for various boundary conditions
Abstract A comparison is made of results obtained with various boundary conditions at the wall of the channels. By comparing blood Sherwood numbers for finite wall resistance with those for constant concentration boundary condition only a small variation is found for various points along the blood channel.