The Cycle Concept

The early experiments on respiration in whole animals had established that carbohydrate was completely oxidized to carbon dioxide and water. 

The first suggestion that substrates in carbohydrate oxidation might exert catalytic effects on the oxidation of other intermediates (cf.earlier demonstration of such action in the urea cycle by Krebs and Henseleit, 1932 see Chapter 6) arose from the work of Szent-Gyorgi (1936). He demonstrated that succinate and its 4C oxidation products catalytically stimulated the rate of respiration by muscle tissues. He also observed that reactions between the 4C intermediates were reversible and that if muscle was incubated with oxaloacetate, fumarate and malate made up 50-75% of the products, 2-oxoglutarate 10-25% and, significantly, 1-2% of the C was converted to citrate. These observations were 

When his studies on carbohydrate oxidation restarted in Sheffield, Krebs experiments included studies on the anaerobic dismutation of pyruvate by bacteria and various animal tissues. Assuming the role for the dicarboxylic acids postulated by Szent-Gyorgi, the main question was the route by which the carbon atoms of pyruvate were converted to succinate. In May 1936 Krebs had observed that if 2-oxoglutarate was added to pyruvate, the yield of succinate was enormously increased. In his notebook written that year (Holmes, 1993) Krebs postulated  

By the beginning of October that year results from Johnson s experiments allowed Krebs to report at a Biochemical Society meeting in Cambridge If pyruvic acid is added to tissues under anaerobic conditions, together with malic acid or oxaloacetic acid, very considerable quantities of citric acid are formed.  

Besides Szent-Gyorgi and Krebs, other groups were attacking the problem of carbohydrate oxidation. Weil-Malherbe suggested It is probable that the further oxidation of succinic acids passes through the stages of fumaric, malic, and oxaloacetic acid pyruvic acid is formed by the decarboxylation of the latter and the oxidative cycle starts again. K.A.C. Elliott, from the Cancer Research Laboratories at the University of Pennsylvania, also proposed a cycle via some 6C acid. 

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The referenced Siemens Westinghouse pnblication presented the cycle concept and overall performance valnes. Neither specific stream information nor assnmptions were presented. The stream data and assumptions presented here were developed by Parsons. The stream data were developed using an ASPEN simulation which yielded performance numbers in general agreement with the publication. 

Modification.s of the cycles of conventional plants using the semi-closed gas turbine cycle concept... 

Several of the gas turbine cycle options discussed m this section (intercooling, recuperation, and reheat) are illustrated in Figure 4. These cycle options can be applied singly or in various combinations with other cycles to improve thermal efficiency. Other possible cycle concepts that are discussed include thermochemical recuperation, partial oxidation, use of a humid air turbine, and use of fuel cells. 

The example demonstrates that the concepts in chemistry rely heavily on notions from group theory, specifically the concept, introduced in Sec. 11, of the equivalence of configurations with respect to a permutation group. The cycle index and the main theorem of Sec. 16 play a role. 

A little later (1929) the Russian physicist Andronov pointed out3 that the stationary state of self-excited oscillations discovered by van der Pol is expressible analytically in terms of the limit cycle concept of the theory of PoincarA... 

The deep philosophical significance of the new theory lies precisely at this point, and consists in replacing a somewhat metaphysical concept of the harmonic oscillator (which could never be produced experimentally) by the new concept of a physical oscillator of the limit cycle type, with which we are dealing in the form of electron tube circuits and similar self-excited systems. 

With this aim, Carnot proceeded to introduce the novel conception of a reversible cycle of operations, and arrived at the exceedingly important result that the motive power capacity for doing wrork] of heat is independent of the agents employed to develop it its quantity is determined solely by the temperatures of the bodies between which, in the final result [i.e., after the completion of the cycle], the transfer of heat occurs. Let there be given a source, and a refrigerator, at temperatures Ti, T2 respectively, where Tx > T2. In order that finite quantities of heat may be added to or taken from these without change of their temperatures, we may suppose them to consist of... 

An early concept of the cycle of thermodynamic processes as relating to steam engine heat-energy performance. 

A concept of the cycle of thermodynamic processes, introduced later than the Carnot cycle. Modifications of the Rankine cycle are of practical importance in boiler design, in relating the successive thermodynamic changes as water is converted to steam, expands and converted to mechanical energy in a turbine, then condenses and returns to the boiler. 

First we add to the previous concept of ancestry or domination the concept of back domination and combine the two in the concepts of chain domination and of cycle domination. These ideas also play an important role in graph oriented discussions of program optimization. 

The same concept of volumetric in situ heating by microwaves was also exploited by Larhed and coworkers in the context of scaling-up a biochemical process such as the polymerase chain reaction (PCR) [25], In PCR technology, strict control of temperature in the heating cycles is essential in order not to deactivate the enzymes involved. With classical heating of a milliliter-scale sample, the time required for heat transfer through the wall of the reaction tube and to obtain an even temperature in the whole sample is still substantial. In practice, the slow distribution of heat... 

The first electrodeposition of a compound superlattice appears to have been by Rajeshwar et al. [219], where layers of CdSe and ZnSe were alternately formed using codeposition in a flow system. That study was proof of concept, but resulted in a superlattice with a period significantly greater then would be expected to display quantum confinement effects. There have since been several reports of very thin superlattices formed using EC-ALE [152, 154, 163, 186], Surface enhanced Raman (SERS) was used to characterize a lattice formed from alternated layers of CdS and CdSe [163]. Photoelectrochemistry was used to characterize CdS/ZnS lattices [154, 186]. These EC-ALE formed superlattices were deposited by hand, the cycles involving manually dipping or rinsing the substrate in a sequence of solutions. 

The solid sorbent material must also be heated and cooled for regeneration and absorption cycles. Because the solid C02 sorbents operate at higher temperatures than the liquid absorption systems, they provide opportunities for simultaneous WGS reaction with C02 removal improving the CO conversion in sorbent-enhanced reaction process (SERP). A number of studies have been reported on the SERP concept and are currently underway as discussed in later sections. 

To actually understand how labeled carbons travel through the TCA cycle, you have to draw out the chemical structures of the cycle members, put a tiny little asterisk by the labeled carbon, and follow it around and around. There are two concepts, however, that you have to know in order to do this. First, the two carbons entering the cycle as acetyl-CoA are not lost as C02 during the first turn of the TCA cycle. 

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