On contribution of pores into the effective elastic properties of carbon/carbon composites

In this paper, we discuss the effect of porosity on the effective elastic properties of unidirectional carbon/carbon composites (carbon fibers in pyrolytic carbon matrix) densified by chemical vapor infiltration (CVI). It is shown that CVI treatment results in formation of irregularly shaped pores randomly oriented in the plane perpendicular to the direction of fiber (transverse plane). These pores are analyzed using numerical conformal mapping procedure, and their contribution to the effective elastic properties is expressed in terms of the cavity compliance contribution tensor. Components of this tensor are found for a variety of typical pores shapes.     

Carbon mesophase-substrate interactions

The formation, growth and coalescence of mesophase materials have been followed by hot stage microscopy and by room temperature examination of polished surfaces for various mesophase-forming materials and in the presence of various substrates. The appearance of mesophase particles should be preceded by polymerization of isotropic material into sheet-like molecules, followed by orientation of the sheet-like molecules into ordered regions. Precipitation, growth and coalescence should require ordering of small molecules in a viscous medium. Our results indicate that dynamic motion in the fluid, rather than the presence of nucleating particles, is the controlling factor, very likely reflecting a small mesophase-isotropic liquid interfacial energy. Where dynamic motion is restricted, as in the interstices of a yarn, mesophase formation and growth are also restricted. Alignment of mesophase material with a substrate is primarily controlled by the motion of the mesophase droplets as they flow across the substrate. In general, substrates are not wetted by mesophase in the presence of isotropic material. Certain surfaces are wetted by the mesophase droplets but alignment appears to be controlled more by flow orientation than by surface energy interaction.     

Stereological characterization of the interaction between interfaces and its application to the sintering process

The degree or extent to which two different types of interfaces,e.g. grain boundaries and the void-solid interface in a sinter structure or grain boundaries and the particle-matrix interface in a dispersion hardened alloy, intersect, is an important factor in many materials. A method is presented here which allows the degree of this interaction to be quantitatively established from simple metallographic measurements made on a planar section through the structure. The results of the application of this technique to a number of copper sinter structures are presented. From these results some insight into the degree of interaction between the grain boundaries and the void-solid interface and its variation during the sintering process is obtained. EDWARD H. AIGELTINGER, formerly with the Metallurgical Department, University of Melbourne, Parkville, Australia     

Cohesion between sister chromatids must be established during DNA replication

BACKGROUND: Cohesion between sister chromatids, which opposes the splitting force exerted by the mitotic spindle during metaphase, is essential for their segregation to opposite poles of the cell during anaphase. In Saccharomyces cerevisiae, cohesion depends on a set of chromosomal proteins called cohesins, which include structural maintenance of chromosomes 1p (Smc1p), Smc3p and sister chromatid cohesion 1p (Scc1p). Strains with mutations in the genes encoding these proteins separate sister chromatids prematurely and fail to align them in metaphase. This leads to missegregation of chromosomes in the following anaphase. RESULTS: In a normal cell cycle, Scc1p was synthesized and recruited to chromosomes at the onset of S phase. Using cells that expressed Scc1p exclusively from a galactose-inducible promoter, we showed that if Scc1p was synthesised only after completion of S phase, it still bound to chromosomes but failed to promote sister chromatid cohesion. CONCLUSIONS: Cohesion between sister chromatids must be established during DNA replication, possibly following the passage of a replication fork. Furthermore, Scc1p (and other cohesins) are needed both for maintaining cohesion during mitosis and for establishing it during S phase. Establishment of sister chromatid cohesion is therefore an essential but hitherto neglected aspect of S phase.     

Die Bedeutung von Gas-Metall-Reaktionen für die Reinigung und den Einsatz hochschmelzender Metalle

Zusammenfassung Die hochschmelzenden Metalle der VA-Gruppe und der VIA-Gruppe k?nnen bei h?heren Temperaturen Gase interstitiell in L?sung aufnehmen. Dadurch ergeben sich entscheidende Ver?nderungen vieler mechanischer und physikalischer Eigenschaften der Metalle. Es werden die Vorg?nge bei der Gasaufnahme und der Gasabgabe besprochen sowie insbesondere Daten über Eigenschafts?nderungen der Metalle durch gel?ste Gase, Daten über die Kinetik der Gasaufnahme und der Gasabgabe sowie Beziehungen zum Berechnen thermodynamischer Gleichgewichte und station?rer Zust?nde angegeben. Dabei finden die Metalle V, Nb, Ta, Mo, W und die Gase N₂, O₂, H₂, H₂O, CO sowie CH₄ Berücksichtigung. An Hand einiger Anwendungs-beispiele wird auf die Bedeutung von Gas-Metall-Reaktionen in der Praxis hingewiesen.     

Communication.

Occam's Razor, Morgan's Canon, and the principle of parsimony suggest that the simpler of two hypotheses is to be preferred. With due respect to Jones' informative comment (American Psychologist, 1968, 23(3), p. 202; see record 1990-55844-001), psychological terminology often defies communication. Syntality, syncretism, synergy, and now synidetics (or syneidetics)--Good grief, Charlie Brown! (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ion etching of amorphous and semicrystalline fibres

Ion etching of amorphous and semicrystalline fibres produces structures which can be observed in either the transmission electron microscope or the scanning electron microscope. The structures so produced have previously been identified as resulting from the etching process (artifacts), or as representing characteristics of the material, or both. The artifacts can be eliminated or minimized by rotating the sample during irradiation, using a low angle of incidence, and ensuring that the temperature of the sample surface remains low. When such precautions are used, amorphous fibres and semicrystalline fibres which arenot oriented remain featureless after ion etching. Oriented semicrystalline fibres, however, develop a striated structure which is oriented perpendicular to the stretch direction. The spacing between the striations is in the range of 500 to 5000 å, an order of magnitude larger than the characteristic lamellar spacing in the materials. These transverse structural features reflect characteristic features of drawn fibres; but the relation between these features and the lamellar spacing is unclear.