Nanoscratch-induced deformation behaviour in B4C particle reinforced ultrafine grained Al alloy composites: a novel diagnostic approach

We report on the novel application of nanoscratch characterization to provide insight into the plasticity mechanisms responsible for the behaviour of composites. Accordingly, we conduct deformation characterization with nanoscratch testing (DCNT) to study the deformation behaviour of two B₄C reinforced ultrafine grained Al alloy tri-modal composites with average B₄C particle sizes of ~1–6?μm and ~500?nm, respectively. To highlight the type of mechanistic information revealed in a DCNT study of composites, we concentrate on the influence of B₄C particle size on deformation mechanisms.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

Comparative thermodynamic studies of aqueous glutaric acid, ammonium sulfate and sodium chloride aerosol at high humidity

Aerosol optical tweezers are used to simultaneously characterize and compare the hygroscopic properties of two aerosol droplets, one containing inorganic and organic solutes and the second, referred to as the control droplet, containing a single inorganic salt. The inorganic solute is either sodium chloride or ammonium sulfate and the organic component is glutaric acid. The time variation in the size of each droplet (3-7 microm in radius) is recorded with 1 s time resolution and with nanometre accuracy. The size of the control droplet is used to estimate the relative humidity with an accuracy of better than +/-0.09%. Thus, the Kohler curve of the multicomponent inorganic/organic droplet, which characterizes the variation in equilibrium droplet size with relative humidity, can be determined directly. The measurements presented here focus on high relative humidities, above 97%, in the limit of dilute solutes. The experimental data are compared with theoretical treatments that, while ignoring the interactions between the inorganic and organic components, are based upon accurate representations of the activity-concentration relationships of aqueous solutions of the individual salts. The organic component is treated by a parametrized fit to experimental data or by the UNIFAC model and the water activity of the equilibrium solution droplet is calculated using the approach suggested by Clegg, Seinfeld and Brimblecombe or the Zdanovskii-Stokes-Robinson approximation. It is shown that such an experimental strategy, comparing directly droplets of different composition, enables highly accurate measurements of the hygroscopic properties, allowing the theoretical treatments to be rigorously tested. Typical deviations of the experimental measurements from theoretical predictions are shown to be around 1% in equilibrium size, comparable to the variation between the theoretical frameworks considered.     

Ricci flow of negatively curved incomplete surfaces

We show uniqueness of Ricci flows starting at a surface of uniformly negative curvature, with the assumption that the flows become complete instantaneously. Together with the more general existence result proved in [10], this settles the issue of well-posedness in this class.     

Elastic electron deuteron scattering

Measurements of the ratio of the deuteron to proton electric form factors were made for low q. The rms radius of the deuteron structure factor was found to be 1.9635 ± 0.0045 fm, yielding an rms charge radius of 2.095 ± 0.006 fm.     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

Quasi-static deformation and final fracture behaviour of aluminium alloy 5083: influence of cryomilling

The commercial aluminium alloy 5083 was processed via cryomilling to produce nanocrystalline (NC) powders with an average grain size of ～25–50?nm. The powders were subsequently degassed at 723 K (450°C), pre-heated and immediately quasi-isostatic (QI)-forged to produce a thermally stable bulk ultrafine grain (UFG) material having average grain size values ranging from 190 to 350?nm, depending on the processing conditions used. In this paper, the tensile properties and fracture behaviour of the bulk UFG material are presented and compared with the tensile properties of its conventionally processed counterpart. The specific influence of preheat temperature on strength and ductility of the alloy is briefly discussed. Three different pre-heat temperatures of 523, 623 and 723?K (250, 350 and 450°C) were chosen and used with the primary objective of controlling grain growth during forging. The influence of preheat temperature on tensile deformation and final fracture behaviour is highlighted. The macroscopic fracture modes of the bulk nanostructured material (BNM) prepared following three pre-heat temperatures are investigated. The microscopic mechanisms controlling tensile deformation and final fracture behaviour are discussed with regards to the intrinsic microstructural effects in the UFG alloy, nature of loading, and the kinetics and mechanisms of deformation.