The influence of resin characteristics on the high speed melt spinning of isotactic polypropylene. II. On-line studies of diameter,birefringence, and temperature profiles

An investigation was carried out of the high speed melt spinning of three polypropylene resins with melt flow indices of 12, 35, and 300. On-line measurements were made of diameter, birefringence, and temperature as a function of distance from the spinneret for a range of spinning conditions for each polymer. A plateau (decrease of cooling rate) in the temperature profile was associated with the occurrence of crystallization in the spinline. The position of this plateau correlated with a rapid rise in the birefringence profile and a rapid decrease in the rate of drawdown in the diameter profile. The temperature and birefringence profiles were used to determine the temperature and position on the spinline at which the onset of crystallization occurred. It was found that the position and temperature of crystallization onset varied considerably with changes in take-up velocity, extrusion temperature, and resin melt index (weight average molecular weight). The crystallization onset occurred nearer the spinneret and at higher temperatures with (1) an increase of take-up velocity, (2) a decrease of extrusion temperature, or (3) a decrease of resin melt flow index. An analysis was carried out to estimate the rate of stress development with distance along the spinline; the results were also used to estimate the stress at the onset of crystallization for each spinning condition. It was concluded that the observed behavior could be attributed to the role of spinline stress in producing molecular orientation and consequent increase of crystallization rate.     

The Role of Cations in Some Inorganic Hydrolysis Reactions

Cations which shift certain equilibria from left to right by forming a compound with one of the reaction products were investigated with respect to their kinetic role in the process. Silver ions have no influence on the rate of the hydrolysis of cyanogen iodide. Similarly, cations which form sparingly soluble carbonates do not influence the rate of hydration of carbon dioxide. On the other hand, the hydrolysis of chlorine is accelerated by Ag⁺ and, to a lesser extent, by Cd²⁺ and Fe(III). It is shown that the effect is not due simply to a bimolecular reaction between chlorine and the cation. In the case of Ag⁺, heterogeneous catalysis may play some role, in analogy with the solvolysis of organic halides. In the case of Cd²⁺, there is spectrophotometric evidence for compounds between Cl₂ and HOCl on the one hand, and the cation on the other. It is suggested that these compounds interconvert more rapidly than do the parent substances. A similar mechanism may be operative in the case of Fe(III), and, possibly, also in the case of Ag⁺.     

Stress–Strain Behavior of Nicalon-Fiber-Reinforced Calcium Aluminosilicate Composites under Tensile Fatigue Conditions

The unusual stress–strain hysteresis loop shape exhibited by ceramic-matrix composites under cyclic loading has previously been explained as a result of either strain rate dependence of the frictional shear stress or crack closure. This investigation has determined that the response is due to neither mechanism. Instead, it is proposed that a variation of interfacial shear strength occurs during each cycle. A static coefficient of friction dominates immediately after loading or unloading. A much lower dynamic coefficient of friction operates once fiber sliding begins. This dynamic coefficient appears to be very dependent on surface roughness.     

Palmqvist Crack Extension and the Center-Loaded Penny Crack Analogy

Palmqvist crack extension in WC-Co can be described using the center-loaded penny crack analogy. When Palmqvist cracks are represented by semicircles of diameter l (l=crack length measured from an impression corner), the stress intensity factor which controls crack extension differs from that of a half-penny crack of radius l+a (2a = impression size) by only a slowly varying factor m=2^1/2 (l/a)^1/2; m≅1.0 to 2.4 for WC-Co and m≅0.8 to 1.4 for ceramics.     

Inductive Model Generation for Text Classification Using a Bipartite Heterogeneous Network

Algorithms for numeric data classification have been applied for text classification. Usually the vector space model is used to represent text collections. The characteristics of this representation such as sparsity and high dimensionality sometimes impair the quality of general-purpose classifiers. Networks can be used to represent text collections, avoiding the high sparsity and allowing to model relationships among different objects that compose a text collection. Such network- based representations can improve the quality of the classification results. One of the simplest ways to represent textual collections by a network is through a bipartite heterogeneous network, which is composed of objects that represent the documents connected to objects that represent the terms. Heterogeneous bipartite networks do not require computation of similarities or relations among the objects and can be used to model any type of text collection. Due to the advantages of representing text collections through bipartite heterogeneous networks, in this article we present a text classifier which builds a classification model using the structure of a bipartite heterogeneous network. Such an algorithm, referred to as IMBHN （Inductive Model Based on Bipartite Heterogeneous Network）, induces a classification model assigning weights to objects that represent the terms for each class of the text collection. An empirical evaluation using a large amount of text collections from different domains shows that the proposed IMBHN algorithm produces significantly better results than k-NN, C4.5, SVM, and Naive Bayes algorithms.     

The Free Fatty Acid Content of Fish Oil,Part II: The Effect of Anchovy Quality on the Free Fatty Acid Content of the Resulting Anchovy Oil and Meal

The free fatty acid (FFA) content of anchovy oil and the residual lipids in anchovy meal were studied as a function of the length and temperature of the delay between catching and processing the fish. It was found that there was a marked increase in the FFA content of the press oil and the residual meal lipids as a result of increased-delay between catching and processing. It was also found that — other things being equal — lean anchovy yielded oils with higher FFA values than fatty anchovy. Calculation showed that the phospholipid level of an anchovy meal may serve as a useful quality index.     

New phospholipid fatty acids from the marine spongeCinachyrella alloclada uliczka

The fatty acid composition of phospholipids from the Senegalese spongeCinachyrella alloclada was examined. Two new fatty acids not hitherto found in nature, namely 10,13-octadecadienoic acid and 16-tricosenoic acid, were identified. 8-Hexadecenoic, 13-nonadecenoic and 5,9,13-trimethyltretradecanoic fatty acids were also found for the first time in sponges. The latter compound (1.4% of the total fatty acid mixture), an isoprenoid fatty acid, accompanies the major fatty acid 4,8,12-trimethyltridecanoic acid (19.7%). The monomethyl branched fatty acids (22%) identified include 23-methylpentacosanoic acid (anteiso-26∶0), not previously observed in sponged. The major long-chain fatty acids encountered were the known 17-tetracosenoic 19-heptacosadienoic and 5,9,23-tricontatrienoic acid. Some sixty fatty acids were identified as methyl esters andN-acyl pyrrolidides by gas chromatography and gas chromatography/mass spectrometry.     

Bonelike Hydroxyapatite Induction by a Gel-Derived Titania on a Titanium Substrate

Gel-derived titania coating on commercial pure (c.p.) titanium induces hydroxyapatite formation onto its surface from a simulated body fluid (SBF, a metastable calcium phosphate solution). The induced apatite is similar to bone apatite in that it is poorly crystallized, calcium-deficient, and carbonate-containing. Furthermore, the carbonate (CO^2–3) groups go into the apatite lattice and lie at the positions of PO^3–4 and OH^– to replace these ionic groups, resembling the (CO^2–3) groups of bone apatite. Therefore, the apatite induced by the gel-derived titania is said to be bonelike. A chemical stimulation, stemming from abundant hydroxyl groups and negative charges at the surface of the titania gel, is believed to be responsible for the bonelike apatite induction. The potential of bone-bonding is predicted for the gel-derived titania, for it is an efficient bonelike apatite inducer in the SBF.     

Degradation of Leaf Litter Phenolics by Aquatic and Terrestrial Isopods

To investigate species-specific decomposition rates of litter from native (Quercus faginea) and introduced (Eucalyptus globulus) tree species in Portugal, we monitored changes in the phenolic signature of leaf litter during decomposition as mediated by an aquatic, Proasellus coxalis (Isopoda: Asellota), and two terrestrial, Porcellio dispar and Eluma caelatum (Isopoda: Oniscidea), detritivores. Although the litter of Eucalyptus and Quercus did not differ in overall protein precipitation capacity, we detected differences in terms of contents of particular phenolic compounds and phenol oxidation products. Accordingly, we observed food-specific consumption rates in Proasellus, but not in the terrestrial isopods. Proasellus digested Eucalyptus at significantly higher rates than Quercus, whereas the opposite was the case for Eluma, and Porcellio digested both litter types equally well. Despite slight differences in detail, effects of Proasellus on changes in the signature of litter phenolics were similar for both litter types, whereas terrestrial isopods—Porcellio and Eluma, although they differed from each other—digestively degraded phenolic compounds in Eucalyptus and Quercus litter, respectively, in different ways. Overall, however, degradation of litter phenolics was similarly effective on both litter types. From these data, we conclude that decomposition of Eucalyptus litter does not proceed more slowly than of litter from native Portuguese trees.     

Simulation of the nitrogen balance in the soil and a winter wheat crop

A simulation model for winter wheat growth, crop nitrogen dynamics and soil nitrogen supply was tested against experimental data. When simulations of dry matter production agreed with measurements, nitrogen uptake was simulated accurately. The total amount of soil mineral nitrogen as well as the distribution of mineral nitrogen over the various soil layers were generally simulated well, except for experiments in which fertilizer was applied late in spring. In these experiments, applied nitrogen disappeared because it could not be accounted for by the model. Some explanations for this disappearance are briefly discussed.