AMD method

The parallel-replica method [5] is perhaps the least glamorous of the AMD methods, but is, in many cases, the most powerful. It is also the most accurate AMD method, assuming only first-order kinetics (exponential decay) i.e., for any trajectory that has been in a state long enough to have lost its memory of how it entered the state (longer than the correlation time icorr, the time after which the system is effectively sampling a stationary distribution restricted to the current state), the probability distribution function for the time of the next escape from that state is given by... 

The parallel-replica method also correctly accounts for correlated dynamical events (there is no requirement that the system obeys TST), unlike the other AMD methods. This is accomplished by allowing the trajectory that made the transition to continue for a further amount of time Afcorr > Tcorr, during which recrossings or follow-on events may occur. The simulation clock is then advanced by Afcorr, the new state is replicated on all processors, and the whole process is repeated. 

As a consequence of this unfavorable scaling with N, applications of the AMD methods to date have involved at most a few thousand atoms, and have typically been much smaller than that. Since many processes of interest require larger system sizes to capture the essential physics, we are seeking ways to make larger AMD simulations feasible. One important step in this direction is our recent development of a spatially parallel TAD approach [34], which we describe very briefly here. 

Ultrastable faujasitic catalysts are a cornerstone of the petroleum industry, and it is not surprising that much effort has been devoted to the study of their properties amd methods of preparation. The following summarizes the most important observations ... 

The AMD method of Burger is also based on vertical TLC. This system for automated multiple development of thin-layer chromatograms is discussed in Chapter 11 Special Methods in TLC . This equipment falls into the top price bracket and is included here only for completeness. 

Multiple development was traditionally performed manually. It consists of repeated developments of a plate in the same direction with the same solvent over the same distance. The result is narrower bands and improved resolution and detection sensitivity. The Rf values become very precise and are adequate enough for identification. A variation of this method is automated multiple development (AMD) and shows promising future. The HPTLC/AMD method was used to monitor phenylureas, carbamates and triazines in drinking water. HPTLC can also be performed using polar modified stationary phases to separate pesticides in various foodstuffs such as triazines in corn, asparagus, tomatoes, grapes and potatoes [14]. 

Kralecik, P. (1996). A new TLC/AMD method for testing of textiles for carcinogenic amines arising from azo dyes. GIT Spez. Chromatogr. 16 125-129. 

The direct coupling of HPLC and HPTLC seems to be a very powerful method in the multiresidue analysis of pesticides. An instrument was developed for the direct connection of these chromatographic methods. The effluent obtained from a HPLC column was transferred directly to a TLC plate widi this device. According to the Camag AMD method, the plates were developed by a 20-step universal elution gradient from methanol-dichloromethane to n-hexane. The compounds investigated in this system were benomyl, 2,4-D, etrimfos, atrazine, phenylmercury acetate, and linuron. Densi-tometric evaluation was carried out with a computer-controlled Camag TLC scanner n, with HP 9816 S and TLC evaluation software 86. This method opens a new way in the automated multiresidue analysis of pesticides (134). 

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