Initiation sites for discontinuous precipitation in some Cu-base alloys

A systematic effort has been made to investigate the suitability of various interfaces, natural as well as artificial, to initiate discontinuous precipitation. The interfaces studied in the present investigation include sample surface (external), and grain and interphase boundaries. It has been demonstrated that in addition to grain boundaries, non-conventional initiation sites like coherent faces of a twin or eutectic/eutectoid boundaries under favourable conditions may also nucleate discontinuous precipitation. In general, the ability of an interface to undergo thermally activated migration appears to be the most important criterion for the initiation of discontinuous precipitation

Material Strength Effect in the Shock Compression of Alumina

The Hugoniot elastic limits (HEL) of a high-density aluminum oxide ceramic (Lucalox) and a slightly lower-density ceramic (porosity approximately 4%) were determined to be 112±13 and 83±5 kbar, respectively. Above the HEL, the shock-stress-volume Hugoniot curves for both materials are offset by 40 kbar or more above their hydrostatic-pressure-volume curves. These results indicate that shear stresses with magnitudes of about 30–40 kbar persist in aluminum oxide to shock-pressure levels of at least 300 kbar

Riparian Shading and Groundwater Enhance Growth Potential for Smallmouth Bass in Ozark Streams

Moderation of stream temperatures by riparian shading and groundwater are known to promote growth and survival of salmonid fishes, but effects of riparian shade and groundwater on to be growth of warmwater stream fishes are poorly understood or assumed to be negligible. We used stream temperature models to relate shading from riparian vegetation and groundwater inflow to summer water temperatures in Missouri Ozark streams and evaluated effects of summer water temperatures on smallmouth bass, Micropterus dolomieu, growth using a bioenergetics model. Bioenergetics model simulations revealed that adult smallmouth bass in non-spring-fed streams have lower growth potential during summer than fish in spring-fed streams, are subject to mass loss when stream temperatures exceed 27°C, and will likely exhibit greater interannual variation in growth during summer if all growth-influencing factors, other than temperature, are identical between the two stream types. Temperature models indicated that increased riparian shading will expand the longitudinal extent of thermal habitat capable of supporting adult smallmouth bass growth in spring-fed stream reaches when mean daily air temperatures exceed 27°C. Optimum growth temperature (22°C) will be present only in spring-fed streams under these conditions. Potential for increasing shade through riparian restoration is greatest for streams \u3c5 m wide and along north–south reaches of larger streams. However, temperature models also indicated that restoring riparian shading to maximum levels throughout a watershed would increase the total stream mileage capable of supporting positive growth of adult smallmouth bass by only 1–6% when air temperatures are at or near average summer maxima; increases in suitable thermal habitat would be greatest in watersheds with higher spring densities. Riparian management for maintenance or restoration of the thermal habitat of adult smallmouth bass during summer should be focused in areas strongly influenced by groundwater. Restoring riparian shading along spring-fed warmwater streams will likely benefit adult smallmouth bass growth and may ultimately influence population sizes

Coherent Propagation of Polaritons in Semiconductor Heterostructures: Nonlinear Pulse Transmission in Theory and Experiment

The influence of coherent optical nonlinearities on polariton propagation effects is studied within a theory-experiment comparison. A novel approach that combines a microscopic treatment of the boundary problem in a sample of finite thickness with excitonic and biexcitonic nonlinearities is introduced. Light-polarization dependent spectral changes are analyzed for single-pulse transmission and pump-probe excitation

1028-63 Cardiac Troponin T as a Marker for Perioperative Myocardial Ischemia in Noncardiac Surgical Patients

Episodes of perioperative myocardial ischemia (PMI) occur in 18 to 74% of noncardiac surgical patients with or at risk for coronary artery disease (CAD). PMls correlate with adverse postoperative cardiac outcome. To determine the diagnostic value of cardiac troponin T(TnT) in PMI, we studied 28 patients (63.9±8.9 years) undergoing peripheral vascular surgery (n=16) or carotid endarterectomy (n=12). Patients included had either documented CAD (n=16) or two (n=7) or more (n=5) risk factors (age >65 years, smoking. diabetes mellitus. hypertension, or hypercholesterolemia >240 mg/dL). Patients with uninterpretable ECG for PMI were excluded. 12-lead ECG recordings and blood sampling for measurement of CK-MB activity and TnT levels (ELISA troponin 1. Boehringer Mannheim, Germany) were carried out preoperatively, and immediately, 20 h, 48 h, 72 h, and 84 h postoperatively. ECG recordings were analysed by an independent blinded cardiologist for signs of PMI (new ST segment depression >0.1 mV 60 ms after the J point, new T inversion). We found an overall incidence of ECG documented PMI of 54% (n=15), 93% occuring immediately postoperatively. Patients undergoing peripheral vascular surgery developed significantly less PMI than carotid surgical patients (38% vs. 75%; p<0.05, Fisher's Exact test). TnT levels >0.1 μg/L were found in 80% (n=12) of patients with PMI (ECG). Only one patient without ECG-documented PMI had TnT levels >0.1 μg/L. Thus, comparing a TnT cut off level of 0.1 μg/L with intermittent 12-lead ECG recording, we found a sensitivity of 80% and a specifity of 92%. We were unable to detect elevated levels of CK-MB in any patient (tab.).overall (n=28)per. vase. surg. (n=16)carotid surg. (n=12)CK-MB >6 U/L000ECG(PMI)15(54%)6 (38%)9(75%)TnT >0.1 μg/L13(46%)5(31%)8(67%)ConclusionIn contrast to CK-MB, TnT is a specific and sensitive marker of PMI in patients with or at risk for CAD undergoing noncardiac surgery

Kinetics of the eutectoid transformation in the Cu-In system

The present study concerns a detailed investigation of the kinetics of the eutectoid transformation in the Cu-In system based on both the isothermal growth rate of the eutectoid colony (monitored by microstructural change) and enthalpy changes during non-isothermal heating (determined by differential scanning calorimetry) of solution-treated and quenched samples. The maximum growth distance of the eutectoid cells and the equilibrium interlamellar spacing have been determined by optical and scanning electron microscopy in the temperature range 600-825 K. The reaction front velocity was observed to increase with the isothermal ageing temperature in the temperature range studied. A detailed analysis of the isothermal growth kinetics through the models available in the literature has yielded an activation energy of 125-127 kJ mol for the operating diffusion process, which is comparable with that for discontinuous precipitation in Cu-In or for grain boundary tracer diffusion of 115 In in Cu, but significantly lower than that for volume diffusion of In in the β Cu-In alloy. A subsequent differential scanning calorimetric study has indicated a similar activation energy of 133 kJ mol −1 for the concerned eutectoid transformation. It is thus concluded that the eutectoid transformation in the Cu-In system is a boundary-diffusion-controlled process. C 1999 Kluwer Academic Publisher

Thermodynamic aspects of the grain boundary segregation in Cu (Bi) alloys

AbstractÐThe grain boundary segregation of Bi in dilute polycrystalline Cu±Bi alloys was systematically studied as a function of temperature and composition. The temperature dependencies of the Gibbsian excess of Bi at the grain boundaries exhibited discontinuous changes at the temperatures close to, but dierent from the bulk solidus temperatures. The observed segregational phase transition was interpreted in terms of prewetting model.