Direct readers

Besides the literature mentioned in the references, we would like to direct readers to a series of websites, whose purpose is to diffuse information on the current research on food and nutrition, endocrine disrupters, hormonal-dependent diseases, and biotechnologies, to a wider community of scientists and physicians as well as to a non-scientific audience. 

We will limit ourselves to reviewing recent SAXS and SANS studies of putatively fully unfolded states formed at equilibrium. We direct readers interested in partially folded states (kinetic and equilibrium molten globules and their brethren) to a number of excellent recent articles and reviews (Kataoka and Goto, 1996 Kataoka et al., 1997 Uversky etal., 1998 Pollack et al., 1999 Doniach, 2001). Similarly, we will not discuss in detail the technical aspects of scattering studies or the precise interpretation of scattering profiles, but instead direct the reader to the appropriate resources (Glatter and Kratky, 1982 Doniach et al., 1995 Kataoka and Goto, 1996 Doniach, 2001). 

The advantage of ICP is that the emissions are of such intensity that it is usually more sensitive than flame AA (but less sensitive than graphite furnace AA). In addition, the concentration range over which the emission intensity is linear is broader. These two advantages, coupled with the possibility of simultaneous multielement analysis offered by the direct reader polychromator design, make ICP a very powerful technique. The only real disadvantage is that the instruments are more expensive. See Workplace Scene 9.3. 

ICP is used for the determination of ppm levels of metals in liquid samples. It is not suitable for the noble gases, halogens, or light elements such as H, C, N, and 0. Sulfur requires a vacuum monochromator. A direct reader ICP excels at the rapid analysis of multi-element samples. 

Spectral interferences, such as line overlaps, are prevalent and must be corrected for accurate quantitative analysis. With a scanning instrument it may be possible to move to an interference free line. With a direct reader, sophisticated computer programs apply mathematical corrections based on factors previously determined on multi-element standards. 

Throughout this book, the Further Reading references at the end of each chapter, while not exhaustive, are intended to point the way into the specific literature related to the chapter in question. At the end of the book, General References will direct readers to globally useful literature. Titles in bold at the end of each chapter are texts that are fully cited in the General References at the end. 

Switch-Board Optics. The preceding discussion has summarized the various approaches which have been taken to achieve a practical spectrometer for SMA. The direct reader, the vidicon detector, and the development of image device/echelle systems... 

In compiling the information in this chapter, I have relied heavily on several very comprehensive reviews that have appeared over the past few years [1-7]. In particular, the 1978 review by T irro et al. [1] is extremely thorough in describing the intra- and intermolecular photophysics and chemistry of upper singlet and triplet states. In fact, rather than reproduce the same details here, I direct the reader to this review for a summary of upper state behavior reported prior to 1978. (A description of azulene and thione anomalous fluorescence is included since these systems are the best-known systems that display upper state behavior.) I also direct readers to the reviews by Johnston and Scaiano [2] and Wilson and Schnapp [3] which focus on the chemistry of both upper triplet states and excited reaction intermediates as studied by laser flash photolysis (one- and two-color methods) and laser jet techniques. Also, Johnston s thorough treatment of excited radicals and biradicals [4] and the review of thioketone photophysics and chemistry by Maciejewski and Steer [5] are excellent sources of detailed information. 

Cross references placed throughout the encyclopedia direct readers to where information on subjects without their own entries can be found. 

We would like to stress that this chapter is a review of coupled cluster theory. It is not primarily intended to provide an analysis of the numerical performance of the coupled cluster model, and we direct readers in search of such information to several recent publications. " Instead, we offer a detailed explanation of the most important aspects of coupled cluster theory at a level appropriate for the general computational chemistry community. Although many of the topics described here have been discussed by other au-thors, ° this chapter is unique in that it attempts to provide a concise, practical introduction to the mathematical techniques of coupled cluster theory (both algebraic and diagrammatic), as well as a discussion of the efficient... 

Here we wish to exemplify how metal corrosion can be interpreted from both a thermodynamic and electrochemical kinetic point of view. This simple introduction may serve to direct readers to some of the more detailed literature on the chemistry of corrosion. 

Dow developed their direct reader for their own in-house use. In 1947 Dow licensed BA to produce and market BA—Dow direct readers. The principal market for these instruments was the steel industry. Virtually simultaneously ARL had developed a technically somewhat different, direct reader (called the quantometer), which was principally sold to the aluminum industry. 

On urging from Ford Motor Company, BA undertook a further refinement of the direct reader in the early 1950s. The original BA—Dow direct reader was a moderately large instrument that needed to be housed in a laboratory with a controlled environment. In particular, changes in heat and humidity caused the instrument to malfunc-... 

The principle advantage to the direct reader was speed, and this was gained by buiid-ing data interpretation into the instrument, making it an example of "Muller Instrumentation." Photomultiplier tubes collected light at preselected spectral lines electronics did the rithmetic to determine how much light was collected at the various spectral lines and the writing involved in displaying this information on dials. Human interpretation was avoided, and the routine operation of the instrument was deskilled. 

The nicest possible summary of the transformation in instrumentation and objectivity can be read off a 1959 advertisement. In 1959 BA advertised their spectrometers by comparing analytical methods, wet chemistry, spectrographic methods, and direct reading (figure 6.1). An iconic summary was presented for each approach. As with any effective ad, the visual point is made quickly and clearly wet chemical analysis takes more steps than spectrographic analysis, which itself takes more steps than spectrometric analysis (using a direct reader). Furthermore, the steps involved are easier with spectrographic methods than with wet chemical analysis, and easier still with spectrometric methods. 

The increased reproducibility of spark emission is more conducive to quantitative analysis than is arc emission. Spark emission spectrometers often employ a more sophisticated detection system. Rather than impinging on a photographic plate, the dispersed radiation passes onto an array of photomultiplier tubes positioned at preset wavelengths. The photomultiplier is more accurate and faster to use in quantitative measurements than film (12). Such an instrument is called a direct reader and will be discussed further in relation to inductively coupled plasma emission spectroscopy. 

There is qualitative or quantitative determination of about 70 elements all or most of which can be simultaneously determined. Analysis time can be very shorty as is the case with direct readers. 

In a typical instrument, schematically shown in Figure 4.10, the photographic film is replaced with an opaque barrier that has several slits located at wavelengths appropriate to the elements to be analyzed. Behind each slit is mounted a photomultiplier tube, which directly converts radiant energy into electrical energy, permitting a rapid readout. Direct readers are very useful in high speed routine quantitative work. From few to many elements can be determined simultaneously. 

Finally, the binding constants may be computed. Readers may consult Yermiyahu et al. (1997b) for details, or we can direct readers to appropriate... 

Almost all companies producing spectrometers offer direct readers. They vary from quite small instruments, capable of determining 6-12 elements simultaneously, to large dispersion instruments that can determine as many as 50 elements simultaneously. Many instruments also can interchange photographic recording and direct reading. 

Many spectrometers are available as packaged units. For example, small emission spectrographs are available as complete units including power source, arc-spark stand, etc. Those units used as direct readers include... 

Direct reading spectrometers can provide analytical data on routine samples in 2-3 min with an average error of 1-2 %. In the metallurgical industries the direct reader easily provides valuable data while a metal is in the molten state so composition can be adjusted as desired. 

Since direct readers are not versatile or easily readjusted for different samples, most laboratories using them also have available another instrument using photographic recording. The photographic units usually are used for qualitative scanning, nonroutine quantitative analysis, and method development. 

Metals and alloys as well as the raw materials from which they are made are analyzed primarily by spectroscopic methods. The iron and steel as well as the aluminum industries rely on spectroscopic analysis in all steps of their processes. Many of the analyses are needed in a very short time thus these industries make wide use of multielement direct reading spectrometers to provide needed analytical data. It is important to control the composition of the molten metals before further processing and the direct reading spectrometers can supply routine analytical information in less than 2 min, something impossible with photographic recording or with chemical wet methods. Some control laboratories have direct readers capable of simultaneously determining 30 elements. 

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