First cycle effect

The relaxation phenomenon described herein is also called first-cycle effect, secondary break-in, waittime effect, memory effect, and hysteresis phenomenon which is in connection with the characteristic changes of the cyclic voltammograms obtained for -> polymer-modified electrodes [iii-vi]. 

All the ion and solvation changes discussed so far in this section relate to chemically reversible processes. Anecdotally, it is widely accepted in the redox polymer modified electrode literature that the first redox cycle of a newly deposited film is atypical. Although the reasons and processes are chemically rather different, this is reminiscent of the first cycle effect discussed in Sect. 2.7.3.6 for Prussian Blue films. PVF provides a typical example of this first cycle, or break-in , effect. The initial EQCM response to PVF oxidation in water (after its deposition from an organic solvent, typically dichloromethane) is quite different from that of a previously cycled film [132]. The result is most clearly demonstrated by considering the mass flux - or, better stiU, the difference between the total mass flux and the elec-tron/ion flux-as a function of apphed potential or film charge. Such plots show a once-only pulse of solvent into a new film this solvent (typically ca. five solvent molecules per ferrocene redox site) is retained ( trapped ) within the film thereafter and provides the baseline upon which subsequent redox-driven solvation... 

Since the system is processed as thermoplastics are processed, its reprocessability was studied under repeated cycles of extrusion in the MPT. Results of reprocessability studies are shown in Table 5. It is evident that after the first cycle viscosity increased slightly, which may be due to the orientation effect. In the subsequent cycles viscosity remained almost constant. Therefore, it is concluded that the zinc stearate plasticized zinc salt of m-EPDM is melt processable just as thermoplastics. 

Table 3 indicates that 5%Pt,l%Bi/C is active for three reaction cycles in the selective oxidation of the chosen alcohols. For primary alcohols the use of water as solvent can promote the aldehyde to carboxylic acid reaction (3). This effect is observed in the selective oxidation of 1-octanol where octanoic acid is formed with 97% selectivity in the first cycle dropping to 81% in the third. In the selective oxidation of geraniol only citral is observed as the oxidation product. The presence of the double bond stabilises the aldehyde even in the presence of... 

If j Rf is exactly the magic angle and infinite spinning speed is assumed, the first-order anisotropic terms are zero for both single and DQ coherence (33). This does not hold true for finite spinning speed, but a complete averaging of the first-order effect occurs at the exact rotor cycles. Therefore, the x evolution time has to match exactly a multiple of the rotor period. The second-order anisotropy refocusing occurs for... 

Following the reactions in Scheme 4, the olefin 13 would have to be generated before the formation of the 7r-crotyl species 2. Because the amount of the catalyst present is usually small as compared to the amount of product formed (1000 moles of product/mole catalyst), the quantity of 13 produced will not be significant and should be readily separable from the desired product. In the special case when crotyl chloride is used as the activator, hexadiene can be produced during the very first cycle of reaction, i.e., 13 = 1,4-hexadiene. Among the organic halides, the chloride derivatives are the most effective activators. Bromides are somewhat effective, while fluorides and iodide are rather ineffective (77). 

As for the mechanism of asymmetric aminohydroxylation, it has been proposed that there are at least two catalytic cycles in the reaction system (Scheme 4-38).77b It is also suggested that both electronic and steric factors play important roles in the reaction. In the first cycle, in which the turnover occurs, effects of the ligand on selectivity are possible. For the ligand-independent... 

In the first cycle, methanol oxidation peaks are seen in both the anodic and cathodic sweeps around 0.7 V. As mentioned earlier, P -OH formation on Ptdll) does not occur to any substantial extent until 1.2 V. Therefore this current decrease over 0.7 V is not due to deactivation of platinum by the svuface Pt-OH formation. The cxirrent increase on the reversed sweep indicated that this current is not limited by methanol diffusion or active accumulated intermediates, either. It simply seems that platinum loses its catalytic activity over 0.7 V regardless whether platinvim is oxidized or not. Anion effects is not likely the reason because the same phenomena are found in percloric add also. Trace amount of impurities, such as chloride ions, may play some roles. 

A strong argument for this assumption has been that this effect always appears in voltammetric experiments with freshly polished electrodes and only in the reverse sweep of the first cycle [6, 51,... 

During continuous redox cycling, the first cycle usually differs from the following ones. This effect is referred as break-in. In poly(vinylferrocene), PVF, films this has been related to the incorporation of solvent and ions into the film, decreasing its resistivity [132]. This effect has been observed for several polyelectrolyte and polymer-modified electrodes, for example, polyaniline [155]. 

Some of the early descriptions of the effect of MOX on red wine included an interesting cycling effect where certain organoleptic aspects of wine quality appear to get worse before the continued application of MOX leads to the desired improvements (Dykes and Kilmartin, 2007 Parish et al., 2000 Vinovation, 2009). In the first "structuring" phase (for several days to weeks), the wine tannins are said to become more aggressive and the varietal aromas decrease, after which the tannins soften and... 

Fig. 7 a and b. Scheme of the thermomechanical behaviour of a well phase-separated thermoelasto-plastic. Stress-strain (or time) curves. Plots of heat effects versus time. First loading (ABC) and unloading (CD) cycle. Second loading (AC) and unloading (CD) cycle. The yielding point occurs at B. AD indicates the residual deformation after the first cycle. AB on the dQ/dT-time curve is the endo-effect resulting from the initial small-strain deformation AB U9)... 

In Figure 2 we show the equivalent results with a reasonably effective stabilizing agent, ferrocyanide, present. In this figure we show results with HF present (no oxide) for comparison as curve (d). The first cycle of a freshly etched electrode in the 0,1 M potassium ferrocyanide/water solution is indicated in the current/voltage characteristics as curve (a). Now in curve... 

More recently a flowsheet has been developed which employs 30% TBP/OK as the solvent.349-446 447 This involves the use of an acid feed to the first cycle to assist in zirconium decontamination and suppress hydrolysis. An acid-deficient partition cycle then follows in which the U-Th separation is effected. A pilot plant (JUPITER) has been constructed at Julich in Germany to process Th02/U02 fuel using this flowsheet. Although a complete separation of thorium, uranium and FPs is possible using TBP in the Thorex process,448 alternative approaches... 

Dukes persuaded Elsevier that the published literature was too large to be comfortably encompassed in a four-yearly cycle, and he suggested that the volumes should be produced annually instead. The four-yearly volume could then concentrate on providing a complementary critical encyclopaedic survey of the entire field. The first Side Effects of Drugs Annual was published in 1977. The first encyclopaedic edition of Meyler s Side... 

Second year male example cycles This reported example was several interviewed athletes first cycle containing an injectable testosterone. Testosterone propionate was chosen due to a distinctly lower degree of water retention (due to active-life) and because it was only briefly active in the system. This allow myself and others to end administration of the testosterone quickly if unacceptable negative side effects resulted and circulatory levels reduced after 2-3 days. Kind of like avoiding a serious car wreck at the expense of a scratch. 

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