Directed movement

From 760 to 960°C, circulating fans, normally without baffles, are used to improve temperature uniformity and overall heat transfer by adding some convection heat transfer. They create a directional movement of the air or atmosphere but not the positive flow past the heating elements to the work as in a convection furnace. Heating elements ate commonly chrome—nickel alloys in the forms described previously. Sheathed elements are limited to the very low end of the temperature range, whereas at the upper end silicon carbide resistors may be used. In this temperature range the selection of heating element materials, based on the combination of temperature and atmosphere, becomes critical (1). 

The presence of ions in solution is what gives a sodium chloride solution the ability to conduct electricity. If positively and negatively charged wires are dipped into the solution, the ions in the solution respond to the charges on the wires. Chloride anions move toward the positive wire, and sodium cations move toward the negative wire. This directed movement of ions in solution is a flow of electrical current. Pure water, which has virtually no dissolved ions, does not conduct electricity. Any solution formed by dissolving an ionic solid in water conducts electricity. Ordinary tap water, for example, contains Ionic Impurities that make It an electrical conductor. 

The streaming potential (Dorn effect) relates to a movement of liquid that generates electric potential, and electroosmosis occurs when a direct electric potential causes movement of the liquid. The sedimentation potential relates to sedimentation (directed movement) of charged particles that generates electric potential, and electrophoresis occurs when a direct electric potential causes a movement of charged particles. 

Directed movement energy Interaction between phases (partition, adsorption) ... 

Neutrophils may move at speeds of up to 20 /tm min-1 in response to chemoattractants such as denatured proteins, lipids, peptides or C5a. Movement may be defined either as chemokinesis, which is generalised (non-directional) locomotive activity, or as chemotaxis, which is orientation and directional migration up a concentration gradient. A concentration difference at opposite ends of the cell of only 1% is sufficient to activate such directional movement. However, neutrophils do not respond chemotactical-ly to static gradients of chemoattractants, and both temporal and directional changes in chemoattractant concentrations are required. 

Figure 4.11. Polarisation of a neutrophil during phagocytosis. During directional movement (chemotaxis) the neutrophil becomes polarised, assuming an anterior head , which is flattened and free of cytoplasmic granules, and a posterior tail .

Table VIII lists a variety of substances that are known chemotaxins. Chemotaxins attract white blood cells, primarily neutrophils, eosinophils and macrophages, to a specific site by causing directed movement. Once these cells arrive they phagocytize and degrade invading microorganisms, and/or release hydrolytic enzymes which can cause subsequent tissue injury. These cells also release bronchoconstrictors, which provides another mechanism worthy of consideration.

It acts as the motor for movement of animal cells. Not only muscle cells (see p. 332), but also cells of noncontractile tissues contain many different motor proteins, which they use to achieve coordinated and directed movement Cell movement shape changes during growth, cytoplasmic streaming, and cell division are all made possible by components of the cytoskeleton. 

The directed movement or locomotion of an organism placed within an electric field. 

The nervous system consists of the brain, spinal cord, and peripheral nerves. Whereas the hormones generated by the endocrine system discussed in the preceding section direct longer-term activities of the body, the nervous system sends impulses very rapidly to direct movement and response of the body. At intervals that are generally of slightly less than 1 sec, a sequence of nerve impulses directs the heart to beat from before birth to death, 24 h each day, 7 days of the week. If just a few of these impulses fail, life ends. 

Apicella P, Legallet E, Nieoulloan A, Trouche E (1986) Differential time-course of reaction time recovery depending on variations in the amplitude of a goal-directed movement after nigrostriatal lesion in monkeys. Neurosci Lett 55 79-84. 

Current Density Associated with the Directed Movement of Ions in Solution, in Terms of Ionic Drift Velocities... 

Dawes AT, Edelstein-Keshet L. Phosphoinositides and Rho proteins spatially regulate actin polymerization to initiate and maintain directed movement in a one-dimensional model of a motile ceU. Biophys. J. 2646 92 744-768. 

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