Chemical channels

The kinetic study of the decarboxylation of aliphatic acids in co-oxidation with cumene showed the following two chemical channels of C02 production [104],... 

The possible dissociation channels for the fragmentation of a triatomic molecule were discussed in Section 1.4. The linear ABC molecule can fragment into three chemical channels, A+B+C, A+BC(n), and AB(n )+C with the diatoms being produced in particular vibrational states denoted by quantum numbers n and n, respectively. Furthermore, each of the fragment atoms and molecules can be created in different electronic states. The total energy Ef = Ei + hu is the same in all cases and therefore the different channels are simultaneously excited by the monochromatic light pulse. The dissociation channels differ merely in the products and in the way the total energy partitions between translation and vibration. 

D. Bradley. Chemical channels win 2003 Nobel prize. Education in Chemistry, January 2004,41(1), 6. 

Since ancient times, an abundance of data showing the rather complicated, and at times mysterious, pattern of relationships between different species of a given biocenosis has been accumulated. In many cases it was suspected that these interactions were monitored and controlled with the help of chemicals excreted into the surroundings. Later experimental studies provided convincing data attesting to the universal occurrence of this chemical channel and the efficiency of its operation for informational exchange in biological communities. Here are some examples. 

There is another interesting contrast between the TR scheme and these other two-photon/two-frequency schemes. In order to direct amplitude out of competing chemical channels, one requires significant control over the momentum of the prepared state, which is what one is controlling via the pulse delay in the TR scheme. In contrast, the initially prepared states of HH and BS have little or no momentum. This may account for the emphasis in the TR scheme on chemically distinct arrangement channels, while the emphasis in the HH and BS schemes is on chemically identical but electronically distinct arrangement channels. With that introduction we proceed to review the recent work of Holme and Hutchinson, and Brumer and Shapiro. 

For reactive scattering, however, the Buttle correction cannot be applied easily since there exists no reasonable zero order Hamiltonian with two or more chemical channels for which analytic solutions are known. Although a Buttle type correction may be determined in a basis, it adds substantially to the computational effort required. 

The main differences between mobile and fixed types of carriers (see refs. 33, 37, 53, 60-63) have been well summarised in the context of electron and hydrogen transport through the respiratory chain by Chance et They compared the current flow and fluid flow models of Holton and Lunde-gardh with the normal kinetic oxido-reduction model, and pointed out that the latter consists of a series of bimolecular reactions, while the former is equivalent to a unimolecular process. Hence, in the fixed carrier model there is effectively a single chemical channel, whereas in the bimolecular or circulating mobile carrier model there are two chemical channels. 

The Lindemann mechanism as well as reactions occurring via formation of long-lived complexes involve participation of highly internally excited intermediate species that may ultimately dissoeiate by one or more chemical channels. For example, the intermediate complex AB in reaction (42) may form new products Pi -b P2, or decay back to reactants, A-bB. The total rate constant for decay of AB is the sum of the two rate constants, +k2, and the relative importance of these competing processes is defined as the product branching ratio k2/k Of key im-... 

A few approximate experimental data are available on the redistribution of energy after N2F4 has been excited by CO2 lasers operating in the 10.6 im region. Data on the chemical channel leading to N2F4 dissociation are given in the previous section. 

Nanoscale wetting phenomena become particularly important for the miniaturization of open microfluidic systems in which liquid is not transported in closed channels but on lyophilic lanes on otherwise lyophobic surfaces. Flow on these so-called chemical channels is less prone to clogging, the samples can be accessed more easily, and cleaning the device is easy. However, evaporation has to be controlled. 

On a completely wetting chemical channel ( eq = 0), one can observe axially homogeneous rivulets only if the contact angle 6 of the rivulet (which is pinned at the channel edge by the chemical step if 9 is smaller than the equilibrium contact angle on the surrounding substrate) is smaller than a certain critical angle. Macroscopically... 

Figure 3.7 Stable bulge-like (a) and metastable ridge-like (b) drop morphology on a chemical channel with sharp chemical steps. The equilibrium contact angle on the channel and the reduced fluid volume are 6 eq = 38° and V= 4.0, respectively. The channel edges, at which the contact line is pinned, are indicated by red lines, and the free three-phase contact line on the channel is indicated by the black line. The figure is provided from Ref. [116] (Fig. 4.3) by courtesy of the author.

Koplik, T. S. Lo, M. Rauscher, and S. Dietrich, Pearling instability of nanoscale fluid flow confined to a chemical channel, Phys. Fluids, 18, 032104(2006). 

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