Prediction techniques comparative modeling methods

Recent developments in spectroscopic techniques allow for accurate measurement of orientations of structural units in deformed polymeric systems Infrared dichroismCI-R-D) H - N-M.R. spectroscopy, fluorescence polarization (F.P.) are three methods which find increasing use in experimental investigations- The experiments reported in the present paper concern effectively simultaneous measurements of orientation by fluorescence polarization and of stress-strain relationship. It is worth noting that the transition moments of the label involved in fluorescence polarization are not sensitive to their immediate environment. Previous models are briefly reviewed and a new model of orientation of real networks is proposed- Then the fluorescence polarization technique is described and theoretical predictions are compared with measurements on polyisoprene vulcaniza-tes. 

The simplest method for generating a statistical QSAR model is to use multiple linear regression (MLR), employing a number of calculated data to explain the measured activity data. Metrics, such as the F value and can be used to describe the statistical validity of the result, and cross-validated (q ) is used to measure the predictivity of the model. For small numbers of descriptors compared to the number of molecules, this method can provide adequate results. However, the number of properties that can be generated far exceeds the number of molecules in most analyses. In these cases, the MLR approach will rarely provide a QSAR model that is statistically predictive outside of the molecules used to build the model. A number of other techniques are provided in Tsar to handle these large datasets. 

The pore size distributions of several types of porous solid have been determined from their nitrogen adsorption isotherms using a new analysis method (ref. 1). In contrast to earlier thermodynamic methods (which break down at small pore sizes), the new approach is based on a molecular model of nitrogen adsorption in a pore. The development of this technique means that, for the first time, the distribution of pore sizes may be calculated over both the mesopore and micropore size ranges using a single analysis method. The use of the new method is illustrated with a series of results obtained from carbon, silica and alumina samples. Its predictions are compared with those obtained using established analysis methods. 

---