Cycles reverse

The Carnot cycle is a reversible cycle. Reversing the cycle will also reverse the directions of heat and work interactions. The reversed Carnot heat engine cycles are Carnot refrigeration and heat pump cycles. Therefore, a reversed Carnot vapor heat engine is either a Carnot vapor refrigerator or a Carnot vapor heat pump, depending on the function of the cycle. 

Suppose a thermally driven heat pump operates at temperatures Th, Tm, and T1. At the high temperature Th, heat Qh is supplied to the heat pump at temperature Tm, heat is generated by the heat pump and at the temperature T1, heat Qi is extracted from a low temperature source. For a Carnot cycle (reversible process) the following relations hold ... 

Giacomelli CE, Norde W (2001) The adsorption-desorption cycle. Reversibility of the BSA-silica system. J Colloids Interf Sci 233(2) 234-240... 

So far, it seems that the cycle life obtained for these Mg insertion cathodes is rather low. For instance, Novak et al. [433,434] showed that cathodes such as MgxV308 could be cycled reversibly more than 50 times, but the capacity decreases to about 50% of its initial capacity (=150 mAh/gr) after 20 cycles. However, it is clear that this work presents an important breakthrough, as it shows the feasibility of R D of insertion cathodes for secondary Mg batteries. Further promising work in this field was demonstrated recently by Sanchez and Pereira-Ramos [435], who showed that Mg can be inserted reversibly, by electrochemical means, into the cation-deficient oxide mix Mn2.15Coo.37(up to 0.23 Mg per mole oxide) from PC/Mg(C104)2 solutions at potentials around 2.9 V versus Li/Li+. 

Miki K, Sudo A (1996) Adaptation of circadian corticosterone and catecholamine rhythms to light-dark cycle reversal in the rat. Ind-Health 34 133-138... 

We shall give to the quantity Sj), which reduces to zero for every closed cycle, reversible or not, the imme of compensaJted transformation relative to tiie modification which causes the stem to pass from the state 0 to the state 1. 

In a simplified catalytic cycle, reversible coordination of the dienophile to the Lewis acid (LA) activates the substrate toward diene cycloaddition. In the catalyst turnover event, the Lewis acid-product complex dissociate to reveal the de-complexed cycloadduct and regenerated catalyst (Scheme 2). While this catalytic cycle neglects issues of product inhibition and nonproductive catalyst binding for dienophiles having more than one Lewis basic site, the gross features of this process are less convoluted than many other enantioselective reactions e.g., olefin dihydroxylation, aldol reactions), a fact which may provide insight as to why this process is frequently used as a test reaction for new Lewis acid catalysts. 

Cyclical Processes or Cycles Reversible and Irreversible Cycles... 

The corollary is that in a repetitive switching scenario (steady state), an inductor must be able to reset every cycle. Reversing the argument — any circuit configuration that makes inductor reset an impossibility, is not a viable switching topology. 

Unfortunately, when hydride alloys traditionally used for compressors are cycled at temperatures over 100 C, their performance can deteriorate through a process termed "disproportionation." In relatively few cycles, reversible hydrogen absorption capacity is lost, which would cause a hydride compressor to stop working. 

Argininosuccinate lyase (the third enzyme of the cycle) reversibly catalyzes the cleavage of argininosuccinate to arginine and fumarate ... 

In cytochrome c, on the other hand, the heme is closer to the surface of the protein. Also, the other ligands are bound so strongly that oxygen cannot coordinate. This microenvironment favours electron transfer, so that the iron cycles reversibly through its II and III oxidation states. 

CYCLE, REVERSIBLE - Theoretical thermodynamic cycle, composed of a series of reversible processes, which can be completely reversed. 

Two-cycle reversible changes in the absorbance of a CdSe-NA QDs-PMMA film on a glass substrate under exposures switched between Nj and 9400 ppm xylenes mixed with Nj. Reprinted from Sensors and Actuators B, 141, 26 (2009). Copyright (2009), with permission from Elsevier. 

PL peak intensity responses to exposures of xylenes balanced in a dry air from an AAO/CdSe QD (core dot) sample placed on Si.The inset (a) shows two-cycle reversible PL enhancement of the sample upon exposure to a high level of xylenes vapor and the inset (b) is a zoomed-in sensing trace at low levels of xylenes. Reprinted with permission from Appl. Phys. Lett., 97,113105 (2010). Copyright (2010), American Institute of Physics. 

These remarkable electrochemical properties have many potential applications, in batteries, electrochromic display devices, supercapacitors and, more recently, for the conception and production of various sensors for molecular electronics. The main problem, however, is cycling reversibility, which will determine the suitability of PPP for these applications. The electroactivity of a given PPP depends on several factors, particularly on the nature of solvent and electrolyte, and on the potential range at which it is cycled. 

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