Dual-level

Thus, a computer attached to a mass spectrometer must operate on two levels. When mass spectral information is arriving, this must be acquired in real time. When the computer has spare time, it controls the operation of the instrument. Both operations are carried out at such a high speed that the dual level of computer tasks is not obvious. 

The characteristics of a polished surface are that it should be level on a macroscopic scale related, for example, to machine and grinding marks of 1-5 /im depth, and be smooth and bright on a microscopic scale typically 1-100 nm size for fine grained metal. To achieve dual levelling and smoothing a solution must satisfy three requirements by including three types of constituent ... 

Fundamental Transitions Using a Dual Level Approach... 

In the following we present results on fundamental vibrational transitions of isolated AT base pairs microsolvated with 1-4 water molecules. The aim of this study is twofold First to find out about overall changes of IR transitions of base pair modes due to the interaction with water molecules. And, second, to test the performance of a dual level approach combining density functional (DFT) and semiempirical PM3 data to expand the PES. Throughout we will assume that the deviations from equilibrium structures are small enough such... 

Since multimode calculations are rather expensive we have chosen to scrutinize the effect of the PM3 approximation by comparing different 2D models of AT-(H20)2 at the full DFT, PM3, and dual level. The results are compiled in Table 3. The correlation between the nh2 and <5nh2 modes is rather well-desribed by the dual level scheme, the error being just a few cm-1. The... 

Instead of ignoring the atoms less directly connected to the reacting center, it is also possible to treat them at a lower level of theory than the key central part. This leads to the general class of hybrid methods. Most of these are dual-level techniques, but as mentioned below, it is also possible to use multilevel approaches. In many cases, the lower level method is simply molecular mechanics that together with a QM method for the central region gives QM/MM methods. QM/QM techniques are also possible. In all hybrid methods, as well as choosing the different levels to apply to the different... 

Marti S, V Moliner (2005) Improving the QM/MM description of chemical processes A dual level strategy to explore the potential energy surface in very large systems. J. Chem. Theory Comput. 1 (5) 1008-1016... 

The first problem in Section II. A was the appearance of parasitic molecules to destroy the hypercycle—that is, the mutually catalytic reaction cycle. If only the replication process of molecules is concerned, it is not so easy to resolve the problem. Here we consider the dual level of replication—that is, molecular and cellular replication. 

Dual-level direct dynamics of the hydroxyl radical reaction with ethane and haloethanes Toward a general reaction parameter method ... 

The IVTST method has been applied successfully to the reactions Cl + CH4 [55], OH + CH4 [18], OH + CD4 [57], and OH + C2H6 [7d]. Because these applications were very successful, and because IVTST can be incorporated into electronic structure codes in a very systematic and general way, IVTST may often be the method of choice for future applications. Hence further development of the method would probably be very useful. Nevertheless we are currently even more enthusiastic about dual-level schemes, which are discussed next. 

Our third generation direct dynamics scheme is called VTST with interpolated corrections (VTST-IC) or dual-level direct dynamics (DLDD) or triple-slash (///) dynamics. This approach involves three steps [49c] ... 

HL[HessL]///LL denotes a higher level of HL, except for the hessians which are calculated at level HessL, and a lower level of LL in a dual-level direct dynamics calculation. 

For high risk processes, dual-level alarm-level instrumentation (i.e., high/high-high, low/low-low, etc.) and automatic process control (PLC, DCS, etc.) and shutdown, which are backed up by human intervention, should always be considered. Where alarm indications are used, they should be provided such that an acknowledgment by an operator is required, typically undertaken by touch screens today. 

A. Femandez-Ramos, J. Rodriguez-Otero and M.A. Rfos, High level and dual level direct dynamics in the intramolecular proton transfer of hydrogenoxalate anion. Influence of tunneling and isotopic effect, J. Phys. Chem. A, 102 (1998) 2954. 

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