Effect of the cocatalyst on the copolymerization of ethylene and propylene with high activity Ziegler-Natta catalyst

Summary Ethylene and propylene were copolymerized in n-heptane in the presence of high activity heterogeneous Ziegler-Natta catalyst to study the effect of the cocatalyst on the microstructure and molecular weight of the copolymer. Seven aluminium alkyls of structure Al((CH₂)_nCH₃)₃, where n = 0—3, 5, 7 or 11, and one of structure Al(C(CH₃)₃)₃, were used as cocatalysts. The effect of the Al/Ti mole ratio was also studied. Modern molecular modelling techniques were used to calculate the volume of the cocatalyst and the electron density around aluminium. The size of the cocatalyst molecule was found to have a marked effect on the activity of the catalyst: the smaller the cocatalyst the higher the activity. Higher electron density around aluminium increased the randomness of the copolymer.     

Effect of viscosity ratio and processing conditions on the morphology of blends of liquid crystalline polymer and polypropylene

The effect of viscosity ratio and processing conditions on LCP/PP blend morphology was studied. The viscosity ratio (η_LCP/η_PP) was varied from 0.1 to 3.6 by using five different polypropylene grades as the matrix and two LCPs as the dispersed phase (20 wt %). The most spontaneous fiber formation was achieved when the viscosity ratio was between 0.5 and 1. In addition to shear forces, elongational forces are important in achieving a highly fibrillar structure and significant mechanical reinforcement. The lubricating effect induced by the low viscosity of LCP was most pronounced for the blends exhibiting a fibrillar morphology. The morphologies of blends produced by different mixing equipment differed only slightly. The greatest variation in the mixing efficiency was found for blends whose components had totally dissimilar melt viscosities. The slight differences in morphology due to melt blending in dissimilar equipment were decreased after injection molding, whereas the differences in morphology due to dissimilar viscosity ratios were still evident in the injection molded blends. Thus, the viscosity ratio at processing in the actual processing conditions is of great importance. © 1994 John Wiley & Sons, Inc.     

Long-term tests of reinforced concrete beams loaded by temperature gradient or settlement of a support

The creep of concrete has a considerable influence on the relaxation of the restraint effects and restraint stresses; particularly if the temperature of the concrete is higher than normal. The risk of cracking, for example, caused by the settlement of supports, is also diminished owing to creep; particularly if the rate of restrained displacement (settlement of a support) is slower than the rate of creep. It is difficult to consider the effect of relaxation from a calculational point of view, because the time dependences of several factors cannot be reliably modelled.In this research the relaxation of the restraint effects, due to both sudden and slow settlement of a support, was examined as a function of time; the relaxation of the restraint effect due to a thermal gradient was also investigated. In particular, was observed that the relaxation was fairly rapid in a heated beam. The relaxation of restraint effects caused by the settlement of supports was also considerable.     

Open systems interconnection — the teletex-based session protocol: Part 1

Two draft proposals for an international standard for the teletex-based session protocol have now been considered by the ISO. The ECMA 75 protocol has been found to be relatively complex as a result of ECMA having to sort out some weak points within the protocol. S.62, proposed by the CCITT, is quite suitable for the kernel of the session service, but not for the entire service. The paper suggests possible developments towards an international standard, and discusses the specification of the BAS subset. It then examines the services available, and how they operate. A proposal for a standard for service conventions is presented, along with a summary of the parameters of the service elements.     

Boreal freshwater fish diet modifies the plasma lipids and prostanoids and membrane fatty acids in man

The effect of fish diet on 43 healthy male students was studied. They ate a fish-containing meal for 15 weeks on an average of 3.7 times per week. Twenty-one of them voluntarily restricted their lipid intake while the rest ate normally. Controls continued their usual eating habits (19 students). The meals consisted of Finnish freshwater fish (87%) (vendace, pike, perch and rainbow trout) and brackish water fish (13%) (Baltic herring) that provided about 1 g of ω-3 polyunsaturated fatty acids per day (0.25 g eicosapentaenoic acid and 0.55 g docosahexaenoic acid). During the diet, ω-3 fatty acids increased in erythrocyte ghosts and platelets at the expense of ω-6 fatty acids. The concentration of serum cholesterol diminished in those fish consumers who lowered their lipid intake. Apolipo-protein A₁ and B were lowered in both fish-consuming groups. Triglyceride levels also showed a tendency to decrease. The formation of thromboxane B₂ during incubation of whole blood decreased in both fish-consuming groups. The decrease of plasma 6-keto-PGF_1α was not statistically significant, if compared with the controls. The results obtained indicate that a moderate intake of fish-containing meals has some beneficial effects on the plasma lipid and prostanoid metabolism, when coronary heart disease risk factors are considered.     

Lossless handover for wireless ATM

Handover is one of the key research topics for the emerging wireless ATM networks. This paper describes a handover mechanism for intra-switch handovers for wireless ATM. The handover procedure is simple enough to be implementable as a limited enhancement to ATM switch platforms for fixed network, yet provides low delay and lossless handover when used together with a suitable radio interface. The paper also reports on initial simulation result.     

Genetic changes in inherited and sporadic ovarian carcinomas by comparative genomic hybridization: extensive similarity except for a difference at chromosome 2q24-q32

Germ-line mutations in the BRCA1 and BRCA2 genes confer a predisposition to breast as well as ovarian carcinoma. Except for loss of the respective wild-type allele, somatic genetic changes needed for the progression of inherited ovarian tumors are unknown. A genome-wide search for such alterations was performed by comparative genomic hybridization analysis on BRCA1 and BRCA2 mutation-positive (n = 20) ovarian carcinoma specimens. Comparison with sporadic ovarian carcinomas (n = 20) revealed extensive genetic similarity between the inherited and sporadic carcinomas with the sole exception of a frequent gain of 2q24-q32 in the inherited group, suggesting the presence of an oncogene at 2q24-q32 operating in the absence of BRCA1 function. The overall similarity of gains and losses by comparative genomic hybridization suggests a common main pathway in tumor progression of both inherited and sporadic ovarian carcinomas.     

Diagnosis of meningococcal meningitis by broad-range bacterial PCR with cerebrospinal fluid

We used broad-range bacterial PCR combined with DNA sequencing to examine prospectively cerebrospinal fluid (CSF) samples from patients with suspected meningitis. Fifty-six CSF samples from 46 patients were studied during the year 1995. Genes coding for bacterial 16S and/or 23S rRNA genes could be amplified from the CSF samples from five patients with a clinical picture consistent with acute bacterial meningitis. For these patients, the sequenced PCR product shared 98.3 to 100% homology with the Neisseria meningitidis sequence. For one patient, the diagnosis was initially made by PCR alone. Of the remaining 51 CSF samples, for 50 (98.0%) samples the negative PCR findings were in accordance with the negative findings by bacterial culture and Gram staining, as well as with the eventual clinical diagnosis for the patient. However, the PCR test failed to detect the bacterial rRNA gene in one CSF sample, the culture of which yielded Listeria monocytogenes. These results invite new research efforts to be focused on the application of PCR with broad-range bacterial primers to improve the etiologic diagnosis of bacterial meningitis. In a clinical setting, Gram staining and bacterial culture still remain the cornerstones of diagnosis.     

Reading long words embedded in sentences: Informativeness of word halves affects eye movements.

The possibility was explored that the informativeness of a specific region within a word can influence eye movements during reading. In Experiment 1, words containing identifying information either toward the beginning or toward the end were displayed asymmetrically around the point of fixation so that the reader was initially presented with either the informative or noninformative zone. Words were read with shorter summed initial fixation time when the reading was started from the informative zone. In Experiments 2 and 3, the target words were presented in sentences that were to be comprehended. More attention was given to the informative endings of words than to redundant endings. The latter were also skipped more often. The duration of the first fixation was not affected by information distribution within the word, whereas the second fixation duration was. The results of these experiments lend good support to the hypothesis of immediate lexical control over fixation behavior and to the notion of a convenient viewing position. (PsycINFO Database Record (c) 2010 APA, all rights reserved)