Mechanical impulses

Mechanical Impulse The principle of mechanical impulse when applied to fluids is usually combined with one of the other means of imparting motion. As mentioned earher, this is the case in axial-flow compressors and pumps. The turbine or regenerative-type pump is another device which functions partially oy mechanical impulse. 

In addition, it should exhibit a fairly high hysteresis level that would have the effect of dissipating the sharp mechanical impulse loads as heat. The material will develop heat due to the stress under cyclical load. Materials used are the elastomeric plastics used in the products or as a coating on products. 

The primary means of transfer of energy to the fluid that causes flow are gravity, displacement, centrifugal force, electromagnetic force, transfer of momentum, mechanical impulse, and a combination of these energy-transfer mechanisms. Displacement and centrifugal force are the most common energy-transfer mechanisms in use. 

Due to the presence of nitroglycerine, this material was found to be too sensitive to mechanical impulses (it exploded when struck by a 2 kg weight falling 30 cm). 

In spite of their advantages, mixtures with potassium perchlorate as the chief constituent are not very often used since the latter is too expensive. Other disadvantages of such mixtures lie in their rather high sensitiveness to mechanical impulses, the relatively great difficulty of detonating them, and their fairly high ability for deflagration. Potassium perchlorate is therefore often employed simply as an additive to ammonium nitrate explosives (p. 264). 

In fact, the material is pressed at such a high temperature that explosive ingredients particularly sensitive to friction and impact such as nitroglycerine and nitrocellulose may be exploded by a minute initiating thermal or mechanical impulse. 

Sensitivity to mechanical impulses becomes important, for instance, if the oven fan motor has worn bearings, causing the chromatograph to vibrate. 

Mechanical impulse 10 yV (for 3 g weight dropped 2.5 cm onto detector enclosure)... 

In comparison to ordinary dielectrics, the permittivities of the so-called ferroelectric materials are about 103 times larger. The ferroelectric material can be transformed into a new type of material called piezoelectric material by heating the ferroelectric above its Curie temperature and then cooling it in a powerful electric field. A piezoelectric crystal changes its polarization once subjected to a mechanical strain. As a result, it can deform mechanically under an electric field or produce electric impulses as a result of mechanical impulses. Currently, piezoelectric materials are widely used as force or pressure transducers with fast response times and very sensitive output. Permittivities of common dielectric and ferroelectric materials are given in Table 1.9. 

The search for ion channels that respond to mechanical impulses has been pursued in a variety of organisms. Drosophila have sensory bristles used for detecting small air currents. These bristles respond to mechanical displacement in ways similar to those of hair cells displacement of a bristle in one direction leads to substantial transmembrane current. Strains of mutant fruit flies that show uncoordinated motion and clumsiness have been examined for their electrophysiological responses to displacement of the sensory bristles. In one set of strains, transmembrane currents were dramatically reduced. The mutated gene in these strains was found to encode a protein of 1619 amino acids, called NompC forno mechano receptor potential. 

Atom cluster collisions have been investigated by means of a self-consistent and simultaneous treatment of the atomic and electronic dof involved. Fbr the collision system Na9++ Na we have examined the excitation mechanisms as well as the relaxation scenarios which strongly depend on the impact energy. Three basically different fragmentation mechanisms— impulsive fragmentation, electronic fragmentation, and statistical decay—have been discussed. 

---