USE OF COMPUTERS

In most fields of physical chemistry, the use of digital computers is considered indispensable. Many things are done today that would be impossible without modem computers. These include Hartree-Fock ab initio quantum mechanical calculations, least-squares refinement of x-ray crystal stmctures with hundreds of adjustable parameters and mar r thousands of observational equations, and Monte Carlo calculations of statistical mechanics, to mention only a few. Moreover computers are now commonly used to control commercial instalments such as Fourier transform infrared (FTIR) and nuclear magnetic resonance (FT-NMR) spectrometers, mass spectrometers, and x-ray single-crystal diffractometers, as well as to control specialized devices that are part of an independently designed experimental apparatus. In this role a computer may give all necessary instaic-tions to the apparatus and record and process the experimental data produced, with relatively little human intervention. 

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Labor costs tend to be higher (although this can be overcome to some extent by use of computer control). 

The generalized use of computers makes seemingly complex calculations quite easy to perform however, curves and tables are still invaluable when one needs to obtain approximate values or to take into account the sensitivity of a property to operating conditions or to a mixture s characteristics. 

Computer assisted operations (CAO) involves the use of computer technology to support operations, with functions ranging from collection of data using simple calculators and PCs to integrated computer networks for automatic operation of a field. In the extreme case CAO can be used for totally unmanned offshore production operations with remote... 

The solution adopted by us is the use of computer simulations of mathematical models of the process and the mock-up situations. Eventually, simulation techniques will become so accurate, that the mock-up step can be discarded. For the time being it is reasonable to use such models to generate corrections for smaller differences between mock-up and process. 

Hoover W G and Ree F H 1967 Use of computer experiments to locate the melting transition and calculate the entropy in the solid phase J. Chem. Phys. 47 4873-8... 

Although, the notion of molecular dynamics was known in the early turn of the century, the first conscious effort in the use of computer for molecular dynamics simulation was made by Alder and Wainright, who in their paper [1] reported the application of molecular dynamics to realistic particle systems. Using hard spheres potential and fastest computers at the time, they were able to simulate systems of 32 to 108 atoms in 10 to 30 hours. Since the work of Alder and Wainright, interests in MD have increased tremendously, see... 

The use of computers for the design of chemical syntheses was first demonstrated by Corey and Wipke in 1969 with their program OCCS [30]. The successor to OCCS, LHASA [31], is generally considered to be the first synthon-based system. Its development is still going on. Currently, three groups are working on LHASA, one at Harvard University, USA [32], one at the University of Leeds, UK [33], and... 

However, better use of spectral information for more rapid elucidation of the structure of a reaction product, or of a natural product that has just been isolated, requires the use of computer-assisted structure elucidation (CASE) systems. The CASE systems that exist now are far away from being routinely used by the bench chemist. More work has to go into their development. 

The first step in designing a new compound is to find compounds that have even a slight amount of usefulness for the intended purpose. These are called lead compounds. Once such compounds are identified, the problem becomes one of refinement. Computational techniques are a fairly minor part of finding lead compounds. The use of computer-based techniques for lead compound identification is usually limited to searching databases for compounds similar to known lead compounds or known to treat diseases with similar causes or symptoms. 

This book was designed to aid in research, rather than as a primary text on the subject. However, students may find some sections helpful. Advanced undergraduate students and graduate students will find the basic topics and applications useful. Beginners are advised to first become familiar with the use of computational chemistry software before delving into the advanced topics section. It may even be best to come back to this book when problems arise during computations. Some of the information in the advanced topics section is not expected to be needed until postgraduate work. 

Many of the topics covered in analytical chemistry benefit from the availability of appropriate computer software. In preparing this text, however, I made a conscious decision to avoid a presentation tied to a single computer platform or software package. Students and faculty are increasingly experienced in the use of computers, spreadsheets, and data analysis software their use is, I think, best left to the personal choice of each student and instructor. 

Once the peaks have been collected and stored, the computer can be asked to work on the data to produce a mass spectrum and print it out, or it can be asked to carry out other operations such as library searching, producing a mass chromatogram, and making an accurate mass measurement on each peak. Many other examples of the use of computers to process mass data are presented in other chapters of this book. 

C. D. Cowfer, ed.. Use of Computers in NDE Engineering and Data Acquisition Systems, NDE Vol. 2, The American Society of Mechanical Engineers, New York, 1986. 

Computer Control. The use of computer systems to control the operation of submerged arc furnaces, including calcium carbide, has been successfully demonstrated in the United States (see Expert systems Process control). Operations direcdy under control are mix batching, electrode position and sHp control, carbide gas yield, power control, and cooling water systems. Improvements in energy usage, operating time, and product quaHty are obtained. 

The second area, the implementation of a modem process monitoring and control system, is the most dramatic current appHcation of CAD/CAM technology to the chemical process industry. The state of the art is the use of computer graphics to display the process flow diagram for sections of the process, current operating conditions, and controUer-set points. The process operator can interact directly with the control algorithms through the... 

Many database producers provide online access to thek databases or distribute thek databases on compact disc read-only-memory (CD-ROM) and so are also considered vendors or producer/vendors. Whereas numerical growth in vendors is indicated (Fig. 1), the success of the database industry is largely a result of the transition of the information industry from paper-based to computer-based services (see Computer technology Informiation RETRIEVAL, Inforitation STORAGE MATERIALS). Thus industry growth can also be measured in terms of the increase in use of computer-readable databases as exemplified by the number of searches. 

The use of computers is essential in probabilistic design (Siddal, 1983). However, research has shown that even the most complete computer supported analytical methods do not enable the designer to predict reliability with sufficiently low statistical risk (Fajdiga et al., 1996). Far more than try to decrease the statistical risk, which is probably impossible, it is hoped that the approach will make it possible to model a particular situation more completely, and from this provide the necessary redesign information which will generate a reliable design solution. 

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