Aspects of discontinuous precipitation reactions in Ag-7.5Cu

Since the crystallographic orientation of a cellular colony derives from the grain it grows away from, experimental interest in discontinuous precipitation (DP) has centred on how nucleation and growth rates are affected by the misorientation of the initiating grain boundary. There has been little attention paid to the nature of the interface at the reaction front. Ageing experiments on Ag-7.5Cu at 2500C showed there to be two DP colony populations with distinctly different growth behaviours. EBSD studies have shown that as the colonies grow there is a build-up of misorientation behind the reaction front and eventually the fast growing colonies are surrounded by interfaces close to particular low Σ coincident site lattice (CSL) misorientations with respect to the grain into which they are growing. On the other hand, slow growing colonies are characterised by misorientations close to a different set of low ΣCSLs. The growth mechanisms behind this behaviour will be discussed

Applications of Electron Backscatter Diffraction (EBSD) in Archaeology

Electron backscattered diffraction (EBSD) has been used to study samples of archaeological gold, silver, copper and bronze prepared using simple metallographic etches. EBSD maps of orientation and local misorientation revealed the metals’ microstructures and deformation substructures, and from this, combined in some cases with information on the crystallographic texture (also determined by EBSD), the methods of manufacture and working of the artefacts were determined. EBSD was also used to examine discontinuous precipitation at grain boundaries in a silver alloy at a high resolution

Using size distributions for determining growth mechanisms of grain boundary precipitates

In the past various single parameters such as the mean, mode or maximum of the precipitate size distribution have been used in experiments to determine growth mechanisms. In the present study the development with aging time of the size and shape distributions of bcc precipitates at grain boundaries in an fcc material (Co-20Fe at 1003oK) have been compared with possible theoretical models to determine the rate controlling process. The growth of these precipitates is initially well described by the grain boundary dependent collector plate mechanism of Brailsford and Aaron. As the precipitates grow low energy facets are formed which can move only by the propagation of ledges and growth becomes interface controlled. The precipitates’ diffusion fields soon overlap and coarsening occurs with interface control. The results demonstrate that this would not have been revealed using simpler measures of precipitate size

The control of seed-borne fungi by fumigation

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A K_ATP channel opener inhibited myocardial reperfusion action potential shortening and arrhythmias

Low concentrations of certain K<sub>ATP</sub> channel openers have been reported to exert a moderate inhibitory effect on arrhythmias during post-ischaemic early myocardial reperfusion, but the accompanying effects on the time course of changes in action potentials in intact hearts have not yet been studied. We report that in rat isolated hearts, reperfusion following 10 min of regional no-flow ischaemia was associated with both an acute, marked, but transient, shortening of ventricular repolarisation (by 63%) during reperfusion, and a high incidence (90%) of ventricular tachyarrhythmias. The K<sub>ATP</sub> channel opener Ro 31-6930 [2-(6-cyano-2,2-dimethyl-2H-1-benzopyran-4-yl)-pyridine 1-oxide], delivered prior to ischaemia at a relatively low concentration (0.5 μM), significantly reduced the incidence and duration of reperfusion arrhythmias, and prevented the associated acute action potential shortening during reperfusion, each in a glibenclamide (1 μM)-sensitive manner (P<0.05, <i>n</i>=10–15 hearts). This was associated with a moderate and non-arrhythmogenic action potential shortening during ischaemia (a potentially “cardioprotective” effect). However, these data highlight the potential harm these drugs may cause, since a higher concentration of Ro 31-6930 caused marked shortening of action potentials and significant pro-arrhythmia during ischaemia

Do K_ATP channels open as a prominent and early feature during ischaemia in the Langendorff-perfused rat heart?

The objective was to investigate whether myocardial adenosine triphosphate-sensitive K<sup>+</sup> (K<sub>ATP</sub>) channels open during the first 10 min of regional ischaemia in Langendorff-perfused rat hearts. Changes in monophasic action potentials and arrhythmias were studied during myocardial ischaemia in both the presence and absence of pharmacological K<sub>ATP</sub> modulation. Ligation of the left main coronary artery for 10 min did not shorten the action potential duration (APD). The APD<sub>50</sub> and APD<sub>80</sub> (15.5 +/- 1.0 and 38.1 +/- 2.3 ms, respectively [mean +/- S.E., n = 15 hearts], immediately prior to ligation) increased transiently during the first 4 min of ligation (by 160 and 79% respectively, P < 0.05), before returning to pre-ligation values, but without a significant below-baseline-shortening. The cardiac electrogram showed no accompanying ventricular tachyarrhythmia (VT). These results raised the possibility that the myocardial K<sub>ATP</sub> channels had not opened during the ligation. The K<sub>ATP</sub> opener Ro 31-6930 (0.5 and 5 microM) shortened the APD50 and APD80 during coronary ligation, to significantly below both their control and pre-occlusion values (P < 0.05), and caused a concentration-dependent increase in both the incidence and duration of VT during the ligation. Ro 31-6930 at 5 microM also shortened APD50 and APD80 even before ligation (by 50 and 62% respectively, P < 0.05), and abolished the normal APD-lengthening seen during ischaemia. The K<sub>ATP</sub> blocker glibenclamide (1 μM) abolished both the APD-shortening and pro-arrhythmic effects of the K<sub>ATP</sub> opener, both before and during coronary ligation, yet when delivered on its own, at the same concentration which abolished the effects of K<sub>ATP</sub> activation, it had no significant effect on the APD changes seen during the coronary ligation alone. These results suggest that, in Langendorff-perfused rat hearts in the absence of drugs, K<sub>ATP</sub> channels do not open during early myocardial ischaemia

Inhibition of NO-synthase and degranulation of rat omental mast cells in vitro

Mast cell amines, platelet-activating factor (PAF), thromboxanes and leukotrienes have been shown to be released during nitric oxide-synthase inhibition in the rat intestine. Mast cells in rat isolated omentum (OMCs) or isolated from the rat peritoneal cavity (PMCs) have been used here to investigate the relationship(s) between these agents. N-nitro-L-arginine methyl ester (L-NAME, 100 μM) caused some degranulation of OMCs, but no enhancement of histamine release from PMCs. PAF (5 μM) and U46619 (1 μM) degranulated OMCs and enhanced histamine release from PMCs. Pre-treatment of the omentum with BN52021 (10 μM) inhibited degranulation of OMCs in response to L-NAME, PAF or U46619. Pretreatment with 1-benzylimidazole (5 or 50 μM) inhibited the effect of L-NAME but not that of PAF. Indomethacin (1 μM) or sodium nitroprusside (10 μM) also inhibited the effects of L-NAME, but nordihydroguaiaretic acid (30 μM) did not. In PMCs BN52021 inhibited PAF-induced, but not U46619-induced, release of histamine. These results suggest that inhibition of nitric oxidesynthase in the omentum by L-NAME allows thromboxanes to release PAF, which in turn degranulates and releases histamine from OMCs

Microstructures of ancient and historic silver

The microstructures of silver-copper alloys from archaeological and historical contexts have been of particular interest since age-related changes at grain boundaries were first mooted as an indicator of antiquity and authenticity. Subsequent discussion has focused on how such structures might be reproduced by appropriate heat treatments but there was only limited experimental investigation of these precipitation phenomena. A second strand of interest has been the embrittlement of archaeological silver by segregation of impurities to grain boundaries. More recently industrial interest has developed in silver-copper alloys because of their use as solders and in electrical contact, and a growing number of papers on sterling and other silver alloy microstructures is being published. To interpret the microstructures of ancient and historic silver the key question is how to distinguish between the respective contributions of manufacture, age and the environment. This paper will describe and discuss a series of heat treatment experiments on wrought Britannia and Sterling silver and also on cast Sterling, the microstructure of cast silver being hitherto a rather neglected topic. The simple eutectic silver-copper system can exhibit a variety of precipitate morphologies and these have been characterised using optical microscopy, scanning and transmission electron microscopy, electron backscatter diffraction, and microhardness and nanoindenter testing. As a test case for discriminating between the effects of manufacture and age a series of medieval Islamic silver coins with a range of mint technologies has been examined in detail and the results presented here. The data will also be used to highlight the limits within which age-related modifications of the microstructure can be expected to be observed

Boundary selectivity of crack paths in corrosion fatigue of stainless steel

Stress corrosion and corrosion fatigue cracks are frequently very branched and there have been extensive attempts to define the characteristics of crack-stopping features. EBSD has been used to examine the full length (~8mm) of a corrosion fatigue crack in stainless steel. The grain boundary character distribution of the cracked boundaries is compared to that of the rest of the material and observations presented on the effect of grain boundary character on the choice of crack path at grain boundary junctions of different configurations and orientations with restect to the principle stres

Possible bi-directional link between ETA receptors and protein kinase C in rat blood vessels

Possible links have been investigated between activation of protein kinase C (PKC) and endothelin (ET) production by small blood vessels. Perfusion pressures were recorded from rat isolated mesenteric artery, with or without the small intestine attached, before and after addition to the perfusate of either ET-1, ET-3 or the PKC activator 12-deoxyphorbol 13-phenylacetate (DOPPA). Rises in perfusion pressure in response to ET-1 (10−8 M)or DOPPA (10−6 M) were reduced significantly by pre-treatment with either the ETA receptor antagonist PD151242 (10−6 M) or the PKC inhibitor Ro 31-8220 (10−6 M). ET-3 (10−8 M) had a significant, albeit small, effect only when the gut was still attached to the mesentery. Inthis latter preparation ET-1 and DOPPA increased the permeability of villi microvessels to colloidal carbon in the perfusate. This effect of DOPPA was reduced by pre-treatment with either PD151242 or Ro 31-8220, but the effects of ET-1 were reduced significantly only by Ro 31-8220. ET-3 (10−8 M) was without effect. The results suggest a possible bi-directional link between ETA receptors and PKC in the intestinal vasculature