Word, in computers

OCR (optical character recognition) off site (always hyphenated) offline (one word in computer context)... 

It was reahzed quite some decades ago that the amount of information accumulated by chemists can, in the long run, be made accessible to the scientific community only in electronic form in other words, it has to be stored in databases. This new field, which deals with the storage, the manipulation, and the processing of chemical information, was emerging without a proper name. In most cases, the scientists active in the field said they were working in "Chemical Information . However, as this term did not make a distinction between librarianship and the development of computer methods, some scientists said they were working in "Computer Chemistry to stress the importance they attributed to the use of the computer for processing chemical information. However, the latter term could easily be confused with Computational Chemistry, which is perceived by others to be more limited to theoretical quantum mechanical calculations. 

It is important to realize that whenever qualitative or frontier molecular orbital theory is invoked, the description is within the orbital (Hartree-Fock or Density Functional) model for the electronic wave function. In other words, rationalizing a trend in computational results by qualitative MO theory is only valid if the effect is present at the HF or DFT level. If the majority of the variation is due to electron correlation, an explanation in terms of interacting orbitals is not appropriate. 

It is important to realise that the fitting of a polynomial to a series of (x,y)-data pairs is really independent of the actual values in the x-vector. In other words, in the above example, it does not matter whether the x-values are between 140 and 150 or between 1 and 11 or between -5 and +5. What matters is the relationship between the x-values and their revalues. As the data are equidistant, any equidistant vector with the right number of values can be used to generate F. In the improved SavGol function we chose the values from -n to +n. The second important observation is that consequently we do not have to recalculate F each time and more importantly, we do not have to recalculate its pseudo-inverse F+, which is computed outside the loop for all points. The result is a routine which is much faster and numerically much sounder ... 

Spelling errors are the easiest and quickest errors to detect. No one is a perfect speller, but there are many ways to insure that the words you have used throughout your paper are spelled correctly. The first and quickest way to check for spelling errors is to run a spell check on your computer. This program instantly enables the computer to scan through the entire paper and point out obvious spelling errors. But be careful, however, when you use a computer. Computers do not check the meaning of words in context. In other words, you may write a sentence that states ... 

The various methods used in quantum chemistry make it possible to compute equilibrium intermolecular distances, to describe intermolecular forces and chemical reactions too. The usual way to calculate these properties is based on the independent particle model this is the Hartree-Fock method. The expansion of one-electron wave-functions (molecular orbitals) in practice requires technical work on computers. It was believed for years and years that ab initio computations will become a routine task even for large molecules. In spite of the enormous increase and development in computer technique, however, this expectation has not been fulfilled. The treatment of large, extended molecular systems still needs special theoretical background. In other words, some approximations should be used in the methods which describe the properties of molecules of large size and/or interacting systems. The further approximations are to be chosen carefully this caution is especially important when going beyond the HF level. The inclusion of the electron correlation in the calculations in a convenient way is still one of the most significant tasks of quantum chemistry. 

FigureB.B Frequencies of passive voice (expressed as the number of passive verbs per 500 words) in sections of chemistry journal articles, determined through a computer-based analysis of 60 journal articles (approximately 300,000 words).

The number of additional Fourier spectral components to recover is the option of the researcher. The number of iterations to execute with the most general computer program written is also the option of the researcher. A tolerance is presently used to determine the number of iterations performed. However, it is found in practice that only 5 or 10 iterations yield sufficiently accurate results for nearly all experimental data of interest. With the presently used computer program, restoration is to the spatial function, and the improved spatial function and the improved values of the coefficients are both generated with each iteration. If the improved Fourier spectrum is not desired, then additional computational time could be saved by neither reading nor writing the Fourier coefficients. When M data points are treated, the computer memory requirements are seldom more than 1M words. If it is not necessary to determine the extended Fourier spectrum, then more than 5M words are seldom needed in computer memory. 

Throughout this course, your instructor will very likely have specialized software available on computers and will offer help in their application. It is important for your education and career that you become widely knowledgeable and skilled in the use of the computer and software. It will be a tool that you will continue to use at the home and office. Many new terms will be introduced in this experiment. All words in bold print are defined in a glossary at the end of the experiment. 

I will discuss the iterative improvement of phases and electron-density maps in Chapter 7. For now just take note that obtaining the final structure entails both calculating p(x,y,z) from structure factors and calculating structure factors from some preliminary form of p(x,y,z). Note further that when we compute structure factors from a known or assumed model, the results include the phases. In other words, the computed results give all the information needed for a "full-color" diffraction pattern, like that shown in Plate 3d, whereas experimentally obtained diffraction patterns lack the phases and are merely black and white, like Plate 3e. 

Some authors also take the approach to compute images that look as if they were taken under some canonical illuminant (e.g. Forsyth (1992)). In general, it is important that the output computed by a color constancy algorithm is not affected by changes of the illuminant. In other words, the computed descriptor should be constant irrespective of the illuminant. Otherwise, we would not have a color constancy algorithm. But at the same time, the output has to be nontrivial. If we would not make this assumption, a trivial color constancy algorithm could be found, which returns the same constant value for all input images. This was also pointed out by Forsyth (1992). 

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