The brittle and ductile behavior of clay samples containing a crack under mixed mode loading

The mechanics of propagation of a single crack in brittle and ductile samples of clay as well as their mode of failure were investigated. The crack in the brittle and in the ductile samples was subjected to a mixed-mode (Mode I and Mode II) type of loading. In the brittle and ductile samples, secondary cracks developed from the tips of the original crack. The secondary cracks did not follow the plane of the original crack but formed an angle α with this plane. The angle of crack propagation α was greater in the brittle than in the ductile samples. The brittle samples failed when the secondary cracks reached the edges of the samples. Their mode of failure was a typical tensile failure. In the ductile samples, the secondary cracks extended for a limited distance from the tips of the original crack and did not influence the failure of the samples that was recorded to be in shear. The Maximum Tangential Stress criterion predicted well the direction of crack propagation in the brittle clay samples. The direction of crack propagation in the ductile samples of clay was found to be a function of their water content. From the laboratory results, a relationship from which to obtain the angle of crack propagation α in the ductile samples is presented.     

Structure and stability of halogenated polymers: Part 1—Ring-chlorinated polystyrene

Ring-chlorinated polystyrene has been prepared by reaction between polymer and chlorine at −20°C in the presence of iodine, using a 1·2:1 molar ratio of chlorine to styrene units. Although the product has a composition corresponding precisely to 1 Cl atom per styrene unit and the predominant site of chlorination is the para position in the aromatic ring, some ortho chlorination, backbone chlorination and unchlorinated structures have been shown to be present by characterisation spectroscopically and from degradation experiments.The chlorinated polymer loses the backbone chlorine readily as HCl at temperatures from 200°C. The resulting unsaturation in the backbone appears to destabilise the polymer towards chain scission and the main breakdown process, which resembles that of polystyrene in consisting of depolymerisation and transfer reactions, occurs over a wider temperature range and at lower temperatures than the decomposition of polystyrene. Products have been identified and estimated quantitatively.     

The reaction of carbon and water as catalyzed by a nickel surface

Many of the individual steps which make up the reaction of carbon and water to produce CO and H₂ were studied on a nickel foil surface using temperature-programmed reaction spectroscopy (TPRS), Auger electron spectroscopy (AES), and ultraviolet photoelectron spectroscopy (UPS). Surface graphite and carbide, two metastable surface carbon forms, were prepared by dehydrogeneration of C₂H₂ and served as reactant carbon. UPS of the graphite monolayer in contact with the metal yielded a valence electronic structure that could be interpreted in terms of the bulk band structure of graphite. The fully carbided Ni surface was active for H₂O dissociation with an estimated activation energy ≤ 5 kcal/mol. The reaction of graphitic carbon in contact with the nickel surface and adsorbed oxygen occurs directly without isolated prior breaking of carbon-carbon bonds. The estimated activation energy for the direct reaction was 44 kcal/mol. A different catalytic reaction cycle involving carbon-carbon bond breaking followed by oxidation of the carbide is energetically more demanding. The activation energy for direct carbon-carbon bond breaking was estimated to be between 65 and 70 kcal/mol. Following this demanding step, the reaction between carbidic carbon and oxygen proceeded with estimated activation energy of 31 kcal/mol.     

The flocculation of kaolin suspensions with cationic polyacrylamides of varying molar mass but the same cationic character

Cationic polyacrylamides of varying molar masses but of similar charge density were tested as flocculants for kaolin suspensions. Flocculant performance was assessed by determining the extent of polymer adsorption, the subsidence rates of the flocculated suspensions and the residual turbidities of the resulting supernatants. The sol concentration was kept constant at 20 g kaolin dm⁻³ in 10⁻³ mol dm⁻³ NaCl solution; pH was varied from 3 to 10. It was found that the subsidence rates did not reflect the trends of polymer adsorption. Polymer adsorption decreased while subsidence rates increased as the molar mass of the polymers increased. Increased adsorption of polymer with pH did not result in higher rates of subsidence. The principal effect of the quaternary cationic charge is to produce a partially extended polymer molecule at all values of the pH. The positive polymeric charge is of secondary importance to the length of the molecule in determining the efficacy of flocculation by polymer bridging and does not counteract the increasing self-repulsion of the clay particles with increasing pH which produced poor floc formation.     

The role of the dilation and tachyon in constructing the string functional integral

We show how to incorporate dilaton and tachyon backgrpunds into Polyakov's functional integral without breaking the Weyl invariance of the classical action.     

The 1377 keV level in 57Co

The lifetime of the 1377 keV level has been measured using Doppler shift and direct timing techniques. The Doppler shift measurement provided a limit τ > 3 ps and the direct timing measurment gave τ = 27 ± 14ps. The lifetime is compared with the predictions of various models for the structure of ⁵⁷Co.     

Light charged particle emission in 485 MeV 56Fe + 197Au reactions: Correlations with heavy fragments and relationships to spin and lifetime

Emission of ⁴He and ¹H has been studied in reactions of 485 MeV ⁵⁶Fe + ¹⁹⁷Au, using low-threshold detector arrays for light charged particles, and two heavy-fragment trigger detectors placed at symmetrically opposite angles with respect to the beam direction. The light charged particles were measured both in singles and in coincidence with heavy products of deeply inelastic and fission reactions detected near the grazing angle. Statistical model analyses of the data show that most of the ⁴He/¹H intensity is due to evaporation from energy equilibrated emitters both in deeply inelastic and fission reactions. In deeply inelastic reactions, the observed ⁴He/¹H emission can be attributed to evaporation from the post-scission reactant-like products, while in fusion-like fission reactions evaporation from pre- and post-scission sources are observed in comparable amounts. Angle-integrated multiplicities for ₄He and ¹H are deduced for each source of emission, and are compared with results from similar systems. The experimental ⁴He/¹H multiplicity ratios indicate roughly equal probability for ⁴He and ¹H evaporation from a given excited source. The observation of pre-scission ⁴He/¹H in fusion-like fission reactions supports the notion that thermal equilibration and subsequent particle evaporation proceed more rapidly than the collective motions that drive the system toward fission. Conversely, the lack of appreciable ⁴He/¹H emission from pre-scission sources in deeply inelastic reactions implies that the interaction times are short compared to the time required for particle evaporation.