Disk storage

The system should support all the inspection types available in the PSP-3 P-scan, T-scan and Through Transmission, TOFD and A-scan. It should be possible to record data for all the inspection types simultaneously. The developments in computer hardware, in particular disk storage, during the last years have made it feasable to increase the emphasis on the A-scan recording modes. It has also been feasible to extend the P-scan format to include P-scan image storage in a full 3D format, that allows cross-section views to be generated off-line. 

This tool, which they call pseudospectralmethods, promises to reduce the CPU, memory and disk storage requirements for many electronic structure calculations, thus pemiitting their application to much larger molecular systems. In addition to ongoing developments in the underlying theory and computer... 

With the current impressive CPU and main memory capacity of relatively in expen sive desktop PC s, non-direct SCFaft tnilto calculations involving 300-400 basis function scan be practical. However, to run til esc kin ds of calcti latiori, 20 GBytes of li ard disk space rn ight be needed. Such big disk space is unlikely to be available on desktop PCs.. A direct SCb calculation can elim inate th e n eed for large disk storage. 

The present approach is one of the second-generation multireference perturbation treatments first opened by the CIPSI algorithm 20 years ago. Even if the spirit of these new treatments is different, mainly because the reference space is chosen on its completeness rather than on energetical criteria, it remains that the unavoidable problems of disk storage, bottleneck of variational approaches, can now be conveniently transferred to the problem of CPU time which is less restrictive. 

With 2D spectra, depending on the kind of experiment, problems with resolution and/or sensitivity may arise. Resolution is an inherent problem with 2D experiments and is mainly caused by the limited amount of spectrometer time and disk storage capacity. Sensitivity may be a problem when measuring small sample amounts or weak effects (NOESY, ROESY,. ..). In heteronuclear 2D experiment.s the sensitivity problem is more pronounced with X- rather than with H detection. 

Whether digital information is stored on-line, near-line, or off-line will usually depend upon the expected retrieval requirements. Little used off-line material may be stored on magnetic tape, while the enhanced accessibility of disk storage may be chosen for high-demand on-line material. 

Considerable savings in storage can be made. Using RI as described here, the conventional implementation can be used, but with much less demand for disk storage. Furthermore, the transformation from atomic to MO bases can be realized for the three-index matrices with a formal gain of one order in the scaling of this task [28],... 

The data reduction hardware is based on a Hewlett-Packard 9825A desk top computer. It is supported by one megabyte of flexible disk storage, a printer/plotter and the necessary interface equipment for on-line LSC data collection. Reliability was a prime factor when the hardware was chosen. The LSC(s) and data system run virtually unattended, 24 hours a day, 365 days a year. Samples are typically counted for two minutes each plus one minute for the external standard. Therefore, data from the four counters are received by the HP9825A at an average interval of 45 seconds. With such a demand on the system, computers require good service support, more so than other instruments. Since installation in May, 1977, there have been less than two work days of cumulative downtime. 

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