Attention mechanisms selective

Schwartz BD, Tomlin HR, Evans WJ, Ross KV. 2001. Neurophysiologic mechanisms of attention A selective review of early information processing in schizophrenics. Front Biosci 6 D120-D134. 

These selective attention mechanisms are extremely efficient and invaluable in many tasks. But any mechanism which is selective carries with it the penalty that information which does not conform to the characteristics selected by the filter will not get through to the brain, however important that information is. People can be concentrating so hard on one task that they are unaware of other information. Hence someone can fall down a hole because they were staring at some activity going on in the opposite direction. Presetting the filter can also lead to false alarms searching a list for the name Jones we can sometimes be fooled by James. The cost of a rapid response is an increase in errors. 

The direction of our visual gaze is a most important tool for understanding attention. This is because we gather most of our visual information during the fixations, and because to resolve details we need foveal vision. This is even imbedded in our language in the figure of speech "look here" when we want to direct a person s attention to a specific object. Thus, our visual system becomes a critical mechanism in selecting objects for attention. The selection process is reflected in the eye movements and the objects on which we fixate. 

At this point, attention can be given to specific electrophilic substitution reactions. The kinds of data that have been especially useful for determining mechanistic details include linear ffee-energy relationships, kinetic studies, isotope effects, and selectivity patterns. In general, the basic questions that need to be asked about each mechanism are (1) What is the active electrophile (2) Which step in the general mechanism for electrophilic aromatic substitution is rate-determining (3) What are the orientation and selectivity patterns ... 

The shell may be of metal (steel, alloy, or non-ferrous), plastic, wood or some combination which may require the addition of liners or inner layers of rubber, plastic or brick. The mechanical problems of attaching inner nozzles, supports and brick require considerable attention that is not an integral part of sizing the equipment. Figures 9-2A-C show a typical large steel brick-lined-membrane lined tower with corbeled brick support locations. In these towers, temperature and/or corrosive conditions usually dictate the internal lining, and the selection of the proper acid- (or alkali-) proof cements. 

Rearrangements have been included in which sulfones participate not only as reactants but also as products. Reactions have been classified according to mechanism, but although the main emphasis has been on mechanism and stereochemistry, special attention to synthetic applications has also been given, wherever appropriate. Obviously, due to space limitations as well as the vast amount of work available, only selected and representative results of general importance, as judged by the concern of the reviewer, are presented below. Thus, the exclusion of a particular piece of work in no way passes judgement on its scientific value. 

A concept named molecular manufacturing, which was originally proposed by K. Eric Drexler [99] in 1992, has attracted the attention of some investigators [100, 118-121]. Molecular manufacturing is defined as the production of complex structures via non-biological mechanosynthesis (and subsequent assembly operations) [99]. A chemical synthesis controlled by mechanical systems operating on the atomic scale and performing direct positional selection of reaction sites by atomic-precision manipulation systems is known as mechanosynthesis. 

There is evidence that protease inhibitors selectively regulate the activity of specific digestive enzymes at the level of gene expression (Rosewicz et al., 1989). Specifically, soybean trypsin inhibitor increases secretion of proteases, including a form of trypsin that is resistant to inhibition but does not cause an increase in amylase secretion. Although the relationships between protease inhibitors and exocrine pancreatic secretion have received the most attention, pancreatic secretion is increased when potato fiber is added to the diet (Jacob et al., 2000), although the mechanism and signaling pathway have not been elucidated. 

V-Sb-oxide based catalysts show interesting catal)dic properties in the direct synthesis of acrylonitrile from propane [1,2], a new alternative option to the commercial process starting from propylene. However, further improvement of the selectivity to acrylonitrile would strengthen interest in the process. Optimization of the behavior of Sb-V-oxide catalysts requires a thorough analysis of the relationship between structural/surface characteristics and catalytic properties. Various studies have been reported on the analysis of this relationship [3-8] and on the reaction kinetics [9,10], but little attention has been given to the study of the surface reactivity of V-Sb-oxide in the transformation of possible intermediates and on the identification of the sxirface mechanism of reaction. 

In recent years, much attention has been focused on rhodium-mediated carbenoid reactions. One goal has been to understand how the rhodium ligands control reactivity and selectivity, especially in cases in which both addition and insertion reactions are possible. These catalysts contain Rh—Rh bonds but function by mechanisms similar to other transition metal catalysts. 

A particular attention on the mechanisms for the formation of N20 over noble metals has been paid in our laboratory [37-40]. It was previously found that an enhancement in the initial selectivity towards the production of N2 (Table 10.1) during the CO + NO reaction can be related to an increase in the relative rate of step (13) over supported Pt-based catalysts [33], Unexpectedly, Rh exhibits a poor selectivity towards the formation of N2 at low conversion and low temperature, which has been mainly related to a stronger NO adsorption on Rh than on Pt and Pd. 

Early workers viewed carriers or catalyst supports as inert substances that provided a means of spreading out an expensive material like platinum or else improved the mechanical strength of an inherently weak material. The primary factors in the early selection of catalyst supports were their physical properties and their cheapness hence pumice, ground brick, charcoal, coke, and similar substances were used. No attention was paid to the possible influence of the support on catalyst behavior differences in behavior were attributed to variations in the distribution of the catalyst itself. 

The calculations described here have been called strain calculations, molecular mechanics, or force field calculations. We prefer the latter term. For a discussion of historical developments and a literature survey of earlier work, which are not given here, the reader is referred to a number of other reviews (1-3). The present paper deals with the description of force field types, techniques of energy minimisation, and procedures for the determination of force field parameters, and with some applications, preferentially taken from our own field of interest. In accordance with the experiences of the author, the work of Lifson and coworkers is given special attention other authors are nevertheless well represented in the context of critical comparisons. We hope that this selection, although inevitably biased, will help to improve the consistency of the presentation of the subject. 

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