Compression-decompression cycles

The peripheral substitution with hydrophobic chains on one hemisphere and hydrophilic groups on the other provides the perfect hydrophobic/hydrophilic balance allowing the formation of stable Langmuir films. In addition, a perfect reversibility has been observed in successive compression/decompression cycles (Fig. 18). 

The variation of refractive index n(D) of the medium separating the mica surfaces is shown in figure 6b (for PE02), both before and after adsorption of polymer, as well as following replacement of the polymer solution by pure electrolyte after adsorption. The results show that adsorption of the PEO is essentially irreversible, and that little polymer appears to desorb either following compression/decompression cycles, or in pure solvent. The value of the adsorbance T estimated from the n(D) profiles is 4 1.5 mg m-2 for both polymers. 

Figure 19 Volume V of phosphates as a function of pressure p. An initial compression cycle and a subsequent compression/decompression cycle is shown. A hysteresis occurs in the pressure range 18 GPa < p < 26 GPa, indicated by points A and B. Reproduced with permission from Ref. 19.

Figure 14. Raman spectra of porous Si in a compression-decompression cycle [263]. In the compression process, the characteristic spectrum of nanocrystalline Si disappears above M3 GPa and a broad amorphous feature emerges. In the decompression process, the characteristic spectrum of the LDA form grows below 9 GPa, which indicates an HDA-to-LDA transition.

Raman spectra for the sample were conducted in a compression-decompression cycle. In this experiment, the crystalline diffraction began to disappear above 7-8 GPa during compression, and pressure-induced amorphization was indicated by the Raman spectra above 13 GPa (Fig. 14). The resultant HDA Si exhibits the Raman spectrum that differs from the spectrum of normal -Si (LDA Si). Rather, the characteristics of the spectrum for HDA Si resemble those of the (3-tin crystal, which indicates that HDA Si has a (locally) analogous structure to the (3-tin structure. The synthesis of the HDA form of Si by Deb et al. [263] has a strong resemblance to that of water (ice) by Mishima et al. [149, 196]. Whereas compression induced amorphization that was almost completed at 13-15 GPa, decompression induced an HDA-LDA transition below 10 GPa, which is clearly shown in the Raman spectra (Fig. 14). This is the first direct observation of an amorphous-amorphous transition in Si. The spectrum at 0 GPa after the pressure release exhibits the characteristic bands of tetrahedrally coordinated -Si (LDA Si). Based on their experimental findings Deb et al. [263] discussed the possible existence of liquid-liquid transition in Si by invoking a bond-excitation model [258, 259]. They have predicted a first-order transition between high-density liquid (HDL) and low-density liquid... 

Figure 15. Electrical resistance measurements of a-Si in a compression-decompression cycle [264],...

Figure 21. X-ray absorption spectroscopy data of a-Ge in a compression-decompression cycle [272]. 

Kaletunc, G., Normand, M.D., Nussinovitch, A., and Peleg, M. (1991). Determination of elasticity of gels by successive compression-decompression cycles. Food Hydrocolloids., 5, 237-247. 

Figs. 2a-c show various blind experiments d (p) obtained in a compression/decompression cycle. Fig.2a compares a blind experiment conducted on compressing up to 0.7 GPa (solid line) and up to 1.5 GPa (dashed line), all other parameters being equal. It is evident that there is a hysteresis of up to 0.1 mm at intermediate pressures and also a slight hysteresis after full decompression. The hysteresis is much more pronounced for the experiment conducted up to 1.5 GPa. It is, therefore, necessary to use two separate correction functions d (p) for the compression part and the decompression part, especially for experiments conducted in the range 0-1.5 GPa, or even higher. It is not valid to extrapolate correction functions d°(p) to higher pressures. 

By evaluating the compression cycle with the Heckel equation for both compression and decompression phases, it is possible to obtain a fairly comprehensive characterization of the mechanisms of volume reduction. For example, the compression cycle was applied to characterize consolidated lactose, sodium chloride, and sodium bicarbonate with 45% moisture. Sodium chloride and sodium bicarbonate were shown to be homogeneous and practically nonelastic, nonporous materials with consolidation behavior similar to metal powders. However, lactose suffered some elastic deformation with some degree of fragmentation and elasticity during the compression-decompression cycle (Duberg and Nystrom, 1986). 

Fig. 3.18. The force F, scaled by the local curvature radius iE, as a function of the mica/mica separation D. A complete compression/decompression cycle is shown (filled/open circles). The void regions are caused by the mechanical instability dF/dD > k). Inset the array of dislocation loops.

Figure 6. LDA-to-HDA transformation from water experiments at (a) T = 77K and (b) T = 130-140K. A sharp change in volume occurs at P 0.6 (a) and 0.35 GPa (b). In both cases, results upon decompressing HDA are included. Only at 7 = 130 — 140K, the LDA-to-HDA transition is reversible. In (b), curves labeled as a, b, and c are the volume upon compression of LDA, following decompression of HDA, and subsequent compression of the recovered LDA. The hysteresis in the compression-decompression cycle in (b) and the sharpness oftheLDA-to- HDA transitions supports the view that LDA and HDA are separated by a first-order transition. Adapted from Refs [13,23].

Abstract The interfacial properties of tracheal aspirate from infants with untreated neonatal respiratory distress syndrome (NRDS), and NRDS infants after therapy with the exogenous surfactant Curosurf were assessed. The interfacial characteristics of the aspirate (equilibrium surface tension, maximal and minimal surface tension during lateral compression-decompression cycles) were determined with the pendant drop method. Our results show that the tracheal aspirate of infants with untreated NRDS had high equilibrium, maximal and minimal surface tension values. In contrast, the samples from infants, treated with Curosurf , showed lower surface tension values, suggesting that the application of Curosurf improves the composition and the properties of the pulmonary surfactant in the infant lung. 

TABLE 6 Thickness of Double Electric Layers and n f.l2n)(p l for Particles of Polystyrene Latex Covered by Hydrolyzed Poly(acrylamide) as Function of the Number of Compression-Decompression Cycles, N... 

The positive aspect of the SerDes approach is the large amount of bandwidth available, ranging from 1 to 3 GB/s. Even when using a sensor with HD resolution, compression is unnecessary. With no compression/decompression cycle, the latency of the system is naturally very low. Serial point-to-point solutions with an embedded control channel and the implementation of power over signal allow for the use of a two-wire cable. 

We have also investigated the effect of slow and rapid compression-decompression cycles on the force-distance profiles, which shows a characteristic hysteretic behaviour for adsorbed chains in good solvents (dashed curve, Fig. 2). Figure 5 shows the results of a series of slow and rapid compression-decompression cycles with the end-grafted PS-X. Within the scatter, the profiles are the same, the effect of slow relaxation of the compressed layers being markedly absent. 

Fig, 5. Interaction between mica sheets bearing end-adsorbed PS-X for different rates of compression and decompression. The rates vary from compression following overnight incubation to a rapid (-5 in each direction) compression-decompression cycle. Different symbols correspond to different compression or decompression runs. 

Alternatively, native proteins such as cytochromes can be enclosed in reverse micelles of glycerides, glycolipids, phospholipids, or other surfactants capable of organizing biomolecules at the air-water interface [36-38,43-45]. Collapse of the micelles and LB formation with multiple compression-decompression cycles furnishes orientated lipid-supported protein monolayers displaying high packing densities [55],... 

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