The reinitiation mechanism of HCl catalysis in PVC degradation

Summary The effect of HCl on the thermal degradation of PVC has been studied. Changes in UV and visible spectra and kinetics of HCl loss indicate that HCl is able to reinitiate the allyl-activated zip elimination by proton exchange with polyenes. Also polyene-consuming secondary reactions are accelerated by HCl.     

Image database

The notion of the image database is still unstructured. We examine recent work under this heading as well as related work in computer vision and conventional database technology. It appears that the principal difficulties in fusing the two disciplines are: the arbitrary nature of discrete representations of continuous scenes; and the lack of linear ordering in two dimensions. A possible solution to these problems is suggested.     

Flicker photometric sensitivity and chromatic adaptation in color-deficient and normal observers

Congenital red-green color deficients and observers with normal color vision were asked to make flicker photometric matches on a red background, on a green background, and with no background present. Adaptation had no effect on the matches made by color deficients, but clearly affected the matches of normal observers. There were small differences between the matches of different observers. We attempted to characterize these differences by fitting the R and G curves of Smith and Pokorny to the data. Two parameters, Λ_max and optical density, were varied to obtain the best fit. Extremely good fits were obtained, suggesting that individual differences can be characterized with these two parameters.     

Terrain visibility

Visibility indices, matrices, graphs, and maps are defined for digital elevation terrain models and their properties are established. Several potential applications of geometric terrain visibility in geographic information systems are presented. Direct applications include the location of observation points and hiding places, the determination of line-of-sight relay networks for microwave communications, scenic and hidden surface paths, and aids to navigation. Indirect applications allow inferences about physiographic terrain features: the mutual visibility among surface points yields considerable information about the landscape. The preservation of the visibility model also provides a check on data reduction (compression) in digital elevation models. Algorithms for computing terrain visibility on both triangulated irregular networks and rectangular grids are reviewed and experimental results from several sources are reported. It is shown that terrain visibility is invariant under certain projective transformations, and therefore relative elevations can be reconstructed from visibility maps.     

Long chain hydrocarbon profiles of Duncan grapefruit,Dancy mandarin and their hybrids

Saturated and monounsaturated long chain hydrocarbons were determined in Duncan grapefruit, Dancy mandarin and their three hybrids: Seminole, Orlando and Minneola. The four most prominent hydrocarbons in the saturated group weren-C₂₃ and C₂₅, and iso C₂₃ and C₂₅. In the monounsaturated group Duncan, Dancy and Seminole showed C₂₉ as dominant, while C₂₅ predominated in Orlando and Minneola. Seminole, Orlando and Minneola accumulated a noticeably higher percentage of branched chain monoenes than either of their parents. The saturated and monounsaturated hydrocarbon profiles of Orlando and Minneola were completely different from their parents. S.E. Market. Nutr. Res. Div., ARS, USDA.     

Style context with second-order statistics

Patterns often occur as homogeneous groups or fields generated by the same source. In multisource recognition problems, such isogeny induces statistical dependencies between patterns (termed style context). We model these dependencies by second-order statistics and formulate the optimal classifier for normally distributed styles. We show that model parameters estimated only from pairs of classes suffice to train classifiers for any test field length. Although computationally expensive, the style-conscious classifier reduces the field error rate by up to 20 percent on quadruples of handwritten digits from standard NIST data sets.     

New telechelic polymers and sequential copolymers by polyfunctional initiator transfer agents (inifers)

Summary Three-arm star polyisobutylenes carrying tert.-chlorine end groups and a phenyl ring at the center of the star (see formula II in the Introduction) have been prepared by a continuous polymerization process. Thus into a stirred glass reactor were fed continuously a mixed feed of monomer plus trinifer (TCC) and a separate feed of BCl₃ coinitiator in methyl chloride solvent at –40°C, and the product plus unreacted ingredients were removed continuously. Stationary conditions were maintained by keeping the rates of input and output (i.e., volumes) equal and constant. After a short induction phase (2–3 residence times) telechelic polymers of essentially theoretical number average end functionalities (¯F_n=3.0+0.1), close to theoretical molecular weights (¯M_n) and molecular weight distributions were obtained. The polymerization kinetics are discussed and compared to that of an earlier semicontinuous process used for the routine synthesis of telechelic polyisobutylenes.