Response tension

Now let s think about the surface tension responsible for the smooth surface of a liquid. The surface of a liquid is smooth because intermolec-... 

Fortune, N. S., Geeves, M. A., and Ranatunga, K. W. (1991). Tension responses to rapid pressure release in glycerinated rabbit muscle fibers. Proc. Natl. Acad. Sci. USA 88, 7323-7327. 

A ich, in principle, gives the interfacial tension response to area chcinges. Here refers to the back-transformation. Alternatively, the response may also be written as... 

Figure 2 shows the surface tension response values, y(t), in concomitance with a trapezoidal pulse of surface area, Ain A (t), for a sea water sample collected in the late winter. A constant value of y( t), as seen in the figure, indicates that no (soluble or insoluble) film is present at the bubble surface, even after a long time. 

Fig. 5. Example of phase difference between dynamic surface tension response (circles, left axis scale) and input area perturbation (small triangles, right axis scale), for a submicellar aqueous solution of a standard surfactant (DC12PO), at concentration c = 1.6 x 10-5 mol dm-3. Temperature T = 22.0 °C...

The stored Ca + can be released by either caffeine orlPg. Many studies (e.g., Endo eta/., 1977 Saida and Nonomura, 1978 Itoh et al, 1982a,b Saida, 1982) used the transient tension response elicited by the released Ca2+ as a measure of Ca + uptake into the SR. In order to observe a contractile effect, a solution with a weak Ca + buffering capacity (0.1 mM EGTA) has to be used so that Ca + released from the store, instead of being bound by the buffer system, is made available to the contractile elements. The limitations of this index of Ca + uptake have been discussed previously (Meisheri et al, 1985 Yamamoto and van Breemen,... 

Siuface rheology has to be taken into account when describing siuface movement and adsorption/desoiption kinetics. Some brief information on surface rheology is given in Section 3.2. The rate of normal and lateral surfactant transport and dynamic surface tension response on external disturbances depends on relaxation properties, into which Section 3.1. introduces. 

Fig. 6.1. Schematic of different transient area changes (solid lines) and the corresponding interfacial tension responses (dotted lines) (a) - step type, (b) - ramp type, (c) - square pulse, (d) -trapezoidal change...

The surface tension response fimction Ay(t) of relaxations at the liquid/liquid interface has exactly the same form as the one at the liquid/air interface, except the characteristic frequency is defined in a different way, taking into account the peculiarity of solubility of the surfactant in both adjacent phases (cf. Eq. (6.22)). 

By applying the inverse Fourier-Transform, according to the calculus discussed in (Miller et al., 1991), the interfacial tension response can be calculated. Under the assumption of a step-type disturbance the response function reads ... 

By changing the shape of the ring, which is immersed into the solution, small area changes of the solution surface can be applied. The surface tension response after such deformations are registered via force measurements using a Wilhelmy plate. 

The software driven apparatus allows different types of area changes step and ramp type, square pulse and trapezoidal as well as sinusoidal area deformations. The construction ensures that area changes are almost isotropic. Area changes used in transient and harmonic relaxation experiments are of the order of 1 to 5%. The surface tension response measured via the Wilhelmy balance has an accuracy of better than 0.1 mN/m. 

Transient relaxation experiments of protein adsorption layers were published by Miller et al. (1993a, c, d). The experiments were performed using a modified pendent drop technique described in Section 6.3.4. The surface tension response to three subsequent square pulse perturbations of 0.1 mg/ml HA adsorbed at the aqueous solution/air interfaces (Miller et al. 1993a) are shown in Fig. 6.21. 

Fig. 6.22 Interfacial tension relaxation of 0.02 mg/ml HA to three square pulses at 24°C at the water/decane interface a) drop area change, b) surface tension response according to Miller et al. (1993c)...

Appendix 6A Application of System Theory for the Determination of Interfacial Tension Response Functions to Small Interfacial Area Disturbances... 

The function F(ico)=F f(t) is the image function of f(t). After rearrangement of Eq. (6A.2), using the laws of the Laplace-Fourier transformation (cf. Appendix 4E), the measurable surface tension response Ay(t) of the system to the area disturbance Ain A(t) is obtained. 

Appendix 6B Interfacial Tension Response Functions Ay(T) to Harmonic and Several Types of Transient Area Disturbances... 

To calculate the interfacial tension response to any small area changes, the Fourier transform of the time function AlnA(t) has to be determined. For a periodic area change... 

The interfacial tension response of a system now results from the appropriate combination of an exchange function s(ico) with the actual area change fimction F(AlnA(t)) according to Eq. (6A.5). 

The following interfacial tension responses are obtained periodic area change -... 

Action on Skeletal Muscle Quinine increases the tension response to a single maximal stimulus delivered to muscle, but it also increases the refractory period of muscle so that the response to tetanic stimulation is diminished. The excitability of the motor end-plate region decreases so that responses to repetitive stimulation and to acetylcholine are reduced. Thus, quinine can antagonize the actions of physostigmine on skeletal muscle. Quinine also may produce respiratory distress and dysphagia in patients with myasthenia gravis. 

In the drop shape technique sinusoidal area changes can be easily generated via changes of the drop volume in a very accurate way. The Fourier analysis of the surface tension response however shows that besides the main mode with the period T of the generated oscillation there are also modes with periods of 3T/2, T/2, T/4 and T/8. The origin of these modes is not yet fully understood but certainly caused by deviation of the area changes from harmonicity and surface layer compression/expansion beyond the limits of a linear theory. 

Fig. 4,44 Surface tension response for a Triton X-100 solution at I TO mol/I a) change of surface tension with time b) same as in (a) but plotted over the area change A(t)/A during oscillation according to...

While the tilt is a measure of the dilational elasticity, the thickness is proportional to the exchange of matter rate, sometimes named dilational viscosity. The ellipse thickness corresponds to the phase shift between the generated area oscillation and the surface tension response. With increasing frequencies the thickness decreases while the tilt angle increases up to a final value of representing the dilational elasticity modulus So. 

Very recently examples of rheological studies on blood were published elsewhere [242]. As an example we want to discuss some results of these investigations here. Fig. 4.45 shows the surface tension response after a step-type area change of a pendent drop area by about 10% for 6 serum samples from one and the same patient at different stages of his acute kidney insufficiency [243]. 

Fig. 4.45 Surface tension response of serum from a 46 years old patient admission suffering from an acute kidney insufficiency admission to hospital (), thfir PY (O. Cl), after haemodialysis ( ), polyuria ( ), leaving the hospital ( )...

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