Using Memes

In safety management, we have memes that tell us to do or use certain procedures and methods. We continue to use memes even when they do not work in our current culture. In addition, a meme that worked well in one organization may be rejected in another location. 

To ensure that the detector electrode used in MEMED is a noninvasive probe of the concentration boundary layer that develops adjacent to the droplet, it is usually necessary to employ a small-sized UME (less than 2 /rm diameter). This is essential for amperometric detection protocols, although larger electrodes, up to 50/rm across, can be employed in potentiometric detection mode [73]. A key strength of the technique is that the electrode measures directly the concentration profile of a target species involved in the reaction at the interface, i.e., the spatial distribution of a product or reactant, on the receptor phase side. The shape of this concentration profile is sensitive to the mass transport characteristics for the growing drop, and to the interfacial reaction kinetics. A schematic of the apparatus for MEMED is shown in Fig. 14. 

A linear approximation for the velocity term, used to treat the DME problem [74], does not work for MEMED, because the concentration boundary layers tend to be much larger for MEMED due to the longer drop times employed. 

MEMED has been used to study the hydrolysis of triphenylmethyl chloride (TPMCl) in a... 

MEMED has also been used to investigate the nature of coupled ion-transfer processes involved in spontaneous electron transfer at ITIES [80]. In this application, a key strength of MEMED is that all of the reactants and products involved in the reaction can be measured, as shown in Figs. 19 and 20. The redox reaction studied involved the oxidation of either ferrocene (Fc) or decamethylferrocene (DMFc) in a DCE phase (denoted by Fcdce) by either IrCle or Fe(CN)g in the aqueous phase (denoted by Ox ) ... 

The MEMED technique has been used to study the hydrolysis of aliphatic acid chlorides in a water/l,2-dichloroethane (DCE) solvent system [3]. It was shown unambiguously that the reaction proceeds via an interfacial process and shows saturation kinetics as the concentration of acid chloride in the DCE increases the data were well fitted to a model based on a pre-equilibrium involving Langmuir adsorption at the interface. First-order rate constants for interfacial solvolysis of CH3(CH2) COCl were 300 150(n = 2), 200 100(n = 3) and 120 60 s-1( = 8). 

Liquid/liquid interfaces have been discussed in Chapter 8. A related approach involves using an expanding droplet of a nonaqueous solvent positioned above a stationary microelectrode (microelectrochemical measurements at expanding droplets, or MEMED) (18,19). More recent work has probed bilayer lipid membranes (BLMs). A BLM is produced by placing a small amount of a lipid, such as lecithin, on a small orifice ( 600 /xin... 

MEME DNA or Protein motifs using EM http //meme.nbcr.net... 

The suite of tools described in this section enables the discovery of motifs in groups of related protein or DNA sequences (MEME), the use of these motifs to search a sequence database (MAST), and the integration of these motifs into an HMM... 

MEME [91] uses statistical modeling (expectation maximization) techniques to construct conserved sequence motifs from a collection of, presumably, related protein or nucleic acid sequences. According to the Web site,... 

MEME represents motifs as position-dependent letter-probability matrices which describe the probability of each possible letter at each position in the pattern. Individual MEME motifs do not contain gaps. Patterns with variable-length gaps are split by MEME into two or more separate motifs. MEME takes as input a group of DNA or protein sequences (the training set) and outputs as many motifs as requested. MEME uses statistical modeling techniques to automatically choose the best width, number of occurrences, and description for each motif, (http //meme.sdsc.edu/meme/intro.html)... 

MAST [92] uses a motif description (e.g., one generated by MEME) to search a sequence database for sequences matching the motif. 

META-MEME [93-95] can be used to integrate motifs discovered by MEME, as well as information derived from sets of related sequences, into a single motif-based HMM. The latter can be used to search sequence databases for homologs. 

FIG. 16 Theoretical first-order reaction approach curves for MEMED. Final drop radius = 0.05 cm, drop time = 6.3 s, and D = 7.0 x 10-6 cm2 s 1 were used in the simulation. From top to bottom the curves are for first-order interfacial rate constants of 1 x 10 5, 1 x 10 4, 1 X 10 3, and 1 x 10 2cms and a transport-controlled process. 

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