Behaviour descriptors

There is a wealth of information about pupils now available in schools - the challenge is to distinguish what is relevant and what is not what does it mean and how can we use it to best effect Often pupils will present an uneven picture when professionals start looking at their behaviour, learning attainment, attitude and so on. Causes of difficulties can be in the home, peers, teacher, curriculum or a mixture of ever57thing. Behaviour descriptors or inclusion indicators are extremely useful in helping to piece together an overall picture of the problem, and of areas of success. 

Based on the experience with tertiary phosphines, the importance of the steric properties of NHC hgands in determining chemical behaviour has been immediately recognised. The main practical problem, however, is that NHC hgands substantiaUy present a local symmetry axis, whereas phosphines present a local symmetry axis. This imphes that the well-accepted molecular descriptor used to quantify steric properties in phosphines, the Tohnan cone angle [78], cannot be applied to NHC ligands. 

In Section 42.2 we have discussed that queuing theory may provide a good qualitative picture of the behaviour of queues in an analytical laboratory. However the analytical process is too complex to obtain good quantitative predictions. As this was also true for queuing problems in other fields, another branch of Operations Research, called Discrete Event Simulation emerged. The basic principle of discrete event simulation is to generate sample arrivals. Each sample is characterized by a number of descriptors, e.g. one of those descriptors is the analysis time. In the jargon of simulation software, a sample is an object, with a number of attributes (e.g. analysis time) and associated values (e.g. 30 min). Other objects are e.g. instruments and analysts. A possible attribute is a list of the analytical... 

Patterson, D.E., Cramer, R.D., Ferguson, A.M., Clark, R.D., and Weinberger, L.E. Neighborhood behaviour a useful concept for validation of Molecular Diversity descriptors. 

Martin YC, Kofron JL, Traphagen LM. (2002) Do Structurally Similar Molecules Have Similar Biological Activities /. Med. Chem. 45 4350-4358. Patterson DE, Cramer RD, Ferguson AM, Clark RD, Weinberger LE. (1996) Neighbourhood Behaviour A Useful Concept for Validation of Molecular Diversity Descriptors. /. Med. Chem. 39 3049-3059. 

Before analysing the mechanical behaviour of amorphous polymers, it is useful to briefly give information on their molecular characteristics, the main descriptors used for plastic deformation and fracture, the micromechanisms of deformation, and some of the experimental procedures. 

Though SSA was used in our previous papers on this topic, hereafter the strain softening behaviour will be discussed in considering preferentially nSSA as descriptor. 

An attempt has been made to analyse whether the electrophilicity index is a reliable descriptor of the kinetic behaviour. Relative experimental rates of Friedel-Crafts benzylation, acetylation, and benzoylation reactions were found to correlate well with the corresponding calculated electrophilicity values. In the case of chlorination of various substituted ethylenes and nitration of toluene and chlorobenzene, the correlation was generally poor but somewhat better in the case of the experimental and the calculated activation energies for selected Markovnikov and anti-Markovnikov addition reactions. Reaction electrophilicity, local electrophilicity, and activation hardness were used together to provide a transparent picture of reaction rates and also the orientation of aromatic electrophilic substitution reactions. Ambiguity in the definition of the electrophilicity was highlighted.15... 

A set of studies reporting the travel behaviour of professional and work groups is implicitly connected to two other frequently measured demographic descriptors previous travel experience and membership of special associations, interest groups or clubs. In particular measures of club membership as well as personal investment in products help define involvement and specialisation in many market segments (Woods, 2003). This specialisation topic will also be explored in the following section on tourist markets pertaining to particular tourist products. 

Distance travelled to the destination is often used as a demographic descriptor. It addresses the effort of the tourist, is often allied to the expense involved and serves also to indicate familiarity with the product for firsttime visitors versus repeat visitors. Local, regional, intrastate and interstate visitors are frequently contrasted in tourist behaviour studies. The differences in visitors use of facilities such as visitor centres and their participation in activities is often markedly different for travellers arriving from near... 

Three types of descriptors of human risk are especially useful and important in risk characterization (Kimmel et al., 2006). The first of these is related to interindividual variability — i.e. the range of variability in population response to an agent and the potential for highly susceptible subpopulations. The second is related to highly exposed individuals — i.e. individuals who are more highly exposed because of occupation, residential location, behaviour, or other factors. The third descriptor that is sometimes used to characterize risk is the margin of exposure (MOE) — i.e. the ratio of the NOAEL (or BMDL/BMCL) from the most appropriate or sensitive species to... 

Enantiotropism and monotropism were referred to in Chapter 1. We now provide a thermodynamic basis for these two important descriptors of polymorphic behaviour. 

The parameter normally measured in capillary electrophoresis is migration (retention) time, /. In a given CE system this parameter is inversely proportional to the electrophoretic mobility, pi. The pt (cm /V) is a normalized parameter allowing for comparison of data obtained in different CE systems. If a series of analytes are analyzed under the same conditions then the 1/r and pt are equivalent. There are only a few reports on QSRR analysis of CE data. This may suggest the unsuitability of routinely determined mobility parameters as the LEER descriptors of analyte behaviour. Probably the reproducibility of analyte migration times in CE is poor due mainly to the non-reproducible electroosmotic flow velocity 26. ... 

Such indices represent bond descriptors and describe the bond character, the importance of bond character to the physical and chemical behaviour of compounds being well known. Bond character is closely related to the capacity of bonded atoms to exchange electrons, and such capacity is commonly well represented by the - electronegativity X of the bonded atoms. 

Theoretical chemistry and, especially, quantum chemistry constitute the basic core of computational chemistry, and their success covers the field of molecular geometries and energies, reactivity, spectroscopic properties, behaviour of electrons in atoms and molecules, and various other fundamental chemical topics [Lipkowitz and Boyd, 1990]. Therefore, the term computational chemistry is also used in a more restricted sense to denote the mathematical approaches (and their software implementations) to the calculation of molecular properties from theoretical chemistry. -> Quantum-chemical descriptors are derived from computational chemistry in this restricted sense. 

GAl was found to be a useful index for the discrimination of cis/trans isomerism (- cis/trans descriptors) and to model the chromatographic behaviour of phosphorus derivatives. 

The choice of suitable QSAR/QSPR approaches as well as effective molecular descriptors also depends on the characteristic behaviour of the studied property. 

Different physical properties and molecular models have been used to define the molecular surface the most common are reported below together with the descriptors proposed as measures of surface areas and molecular volume (- volume descriptors). Molecular surface area and volume are parameters of molecules that are very important in understanding their structure and chemical behaviour such as their ability to bind ligands and other molecules. An analysis of molecular surface shape is also an important tool in QSAR and - drug design-, in particular, both - molecular shape analysis and - Mezey 3D shape analysis were developed to search for similarities among molecules, based on their molecular shape. 

A fundamental task is how to predict and understand experimental facts, i.e. physico-chemical properties, biological activities, and environmental behaviour, from symbolic representations of real objects such as molecules by molecular descriptors. 

The density per particle of shape function cr(r) is seen to be a simpler alternative for the density as the fundamental carrier of information in the study of the electronic structure of atoms and molecules, up to the limit that the shape function holographic theorems can be formulated. Just as in DFT, a variational theorem can be written down and an alternative set of reactivity descriptors can be conceived. The long-range behaviour of the function yields information which reconciles density and shape function theory. 

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