Relaxation tension

Drug-free parents freely resort to other activities for relaxing tension, reducing emotional discomfort, or increasing well-being besides relying on substance use. 

Nervines—These substances are said to calm, soothe, and relax tensions caused by nervous excitement, strain, or fatigue. 

It was determined, for example, that the surface tension of water relaxes to its equilibrium value with a relaxation time of 0.6 msec [104]. The oscillating jet method has been useful in studying the surface tension of surfactant solutions. Figure 11-21 illustrates the usual observation that at small times the jet appears to have the surface tension of pure water. The slowness in attaining the equilibrium value may partly be due to the times required for surfactant to diffuse to the surface and partly due to chemical rate processes at the interface. See Ref. 105 for similar studies with heptanoic acid and Ref. 106 for some anomalous effects. 

The Imass Dynastat (283) is a mechanical spectrometer noted for its rapid response, stable electronics, and exact control over long periods of time. It is capable of making both transient experiments (creep and stress relaxation) and dynamic frequency sweeps with specimen geometries that include tension-compression, three-point flexure, and sandwich shear. The frequency range is 0.01—100 H2 (0.1—200 H2 optional), the temperature range is —150 to 250°C (extendable to 380°C), and the modulus range is 10" —10 Pa. 

The standard conventional finishing process has been modified to suit the purposes for different fabrics and garments. Eor example, tubular knits are frequently handled using specialized equipment to control tension and to get adequate padding. Some tubular knits are subjected to wet-on-wet padding, dried and cured in large dmm dryers, and steam-treated to achieve a relaxed and nondistorted knit. 

Stress relaxation performance is usually determined in bending, where the initially imposed stress is 50 to 100% of the yield strength at the tension side of the stressed samples. Test details are presented in Reference 23. Data is presented as the percentage of the initial stress that remains as a function of time at exposure temperature. 

Elastomeric Fibers. Elastomeric fibers are polyurethanes combiaed with other nonelastic fibers to produce fabrics with controlled elasticity (see Fibers, elastomeric). Processing chemicals must be carefully selected to protect all fibers present ia the blend. Prior to scouriag, the fabrics are normally steamed to relax uneven tensions placed on the fibers duriag weaving. Scouriag, which is used to remove lubricants and siting, is normally conducted with aqueous solutions of synthetic detergents and tetrasodium pyrophosphate, with aqueous emulsions of perchloroethylene or with mineral spidts and sodium pyrophosphate. 

These small-molecule thiols serve to transfer NO from erythrocytes to endothelial receptors, where it acts to relax vascular tension. NO itself is a reactive free-radical compound whose biological half-life is very short (1-5 sec). S-nitrosoglutathione has a half-life of several hours. 

Muscle relaxant. A compound that, by either central or peripheral actions, decreases muscle tension. 

Abspaltung,/. splitting off, cleavage, separation, abspaonen, v.t. relieve from tension, release (a spring, etc.) relax (allow to) expand cut off (steam). — abgespaont, p.a. released, etc. unstrung, unnerved. 

Abspaonung, /. release (from tension) relaxation expansion lassitude, abspateln, v.t. scrape off (with a spatula), absperrbar, a. capable of being shut off, etc. (see absperren). 

FIGURE 2.18 Inotropic and lusitropic responses of guinea pig left atria to (3-adrenoceptor stimulation. Panels A to C isometric tension waveforms of cardiac contraction (ordinates are mg tension abscissae are msec), (a) Effect of 0.3 nM isoproterenol on the waveform. The wave is shortened due to an increase in the rate of diastolic relaxation, whereas no inotropic response (change in peak tension) is observed at this concentration, (b) A further shortening of waveform duration (lusitropic response) is observed with 3 nM isoproterenol. This is concomitant with positive inotropic response (increase maximal tension), (c) This trend continues with 100 nM isoproterenol, (d) Dose-response curves for ino tropy (filled circles) and lusitropy (open circles) in guinea pig atria for isoproterenol, (e) Dose-response curves for inotropy (filled circles) and lusitropy (open circles) in guinea pig atria for the P-adrenoceptor partial agonist prenalterol. Data redrawn from [6]. 

The second major assumption is that the material is elastic, meaning that the strains are directly proportional to the stresses applied and when the load is removed the deformation will disappear. In engineering terms the material is assumed to obey Hooke s Law. This assumption is probably a close approximation of the material s actual behavior in direct stress below its proportional limit, particularly in tension, if the fibers are stiff and elastic in the Hookean sense and carry essentially all the stress. This assumption is probably less valid in shear, where the plastic carries a substantial portion of the stress. The plastic may then undergo plastic flow, leading to creep or relaxation of the stresses, especially when the stresses are high. 

Although blood pressure control follows Ohm s law and seems to be simple, it underlies a complex circuit of interrelated systems. Hence, numerous physiologic systems that have pleiotropic effects and interact in complex fashion have been found to modulate blood pressure. Because of their number and complexity it is beyond the scope of the current account to cover all mechanisms and feedback circuits involved in blood pressure control. Rather, an overview of the clinically most relevant ones is presented. These systems include the heart, the blood vessels, the extracellular volume, the kidneys, the nervous system, a variety of humoral factors, and molecular events at the cellular level. They are intertwined to maintain adequate tissue perfusion and nutrition. Normal blood pressure control can be related to cardiac output and the total peripheral resistance. The stroke volume and the heart rate determine cardiac output. Each cycle of cardiac contraction propels a bolus of about 70 ml blood into the systemic arterial system. As one example of the interaction of these multiple systems, the stroke volume is dependent in part on intravascular volume regulated by the kidneys as well as on myocardial contractility. The latter is, in turn, a complex function involving sympathetic and parasympathetic control of heart rate intrinsic activity of the cardiac conduction system complex membrane transport and cellular events requiring influx of calcium, which lead to myocardial fibre shortening and relaxation and affects the humoral substances (e.g., catecholamines) in stimulation heart rate and myocardial fibre tension. 

Very frequent are the cases of stress-induced crystallizations. A typical case is that of slightly vulcanized natural rubber (1,4-m-polyisoprene) which, under tension producing a sufficient chain orientation, is able to crystallize, while it reverts to its original amorphous phase by relaxation [75],... 

For example, for alkyl (8-16) glycoside (Plantacare 818 UP) non-ionic surfactant solution of molecular weight 390 g/mol, an increase in surfactant concentration up to 300 ppm (CMC concentration) leads to a significant decrease in surface tension. In the range 300 < C < 1,200 ppm the surface tension was almost independent of concentration. In all cases an increase in liquid temperature leads to a decrease in surface tension. This surface tension relaxation is a diffusion rate-dependent process, which typically depends on the type of surfactant, its diffusion/absorption kinetics, micellar dynamics, and bulk concentration levels. As the CMC is approached the absorption becomes independent of the bulk concentration, and the surfactant... 

Sahlin, K., Edstrom, L., Sjoholm, H., Hultman, E. (1981). Effects of lactic acid accumulation and ATP decrease on muscle tension and relaxation. Am. J. Physiol. 240, C121-C126. 

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