Evolution of internal stress and microstructure in Ti50Cu50 alloy films: influence of substrate temperature and composition

The growth stress of Ti₅₀Cu₅₀ alloy films on alumina substrates was measured in situ under ultrahigh vacuum conditions with a cantilever beam technique as a function of substrate temperature and variation of copper concentration. The growth stress of films deposited at low temperature is interpreted to indicate the growth of amorphous respectively nanocrystalline films. At substrate temperatures above 300 °C, a novel tensile stress contribution is interpreted to be due to the formation of a preferentially oriented film of metastable copper vacancy superstructured γ-TiCu. Finally, at substrate temperatures above 365 °C, a polycrystalline γ-TiCu film is formed.Annealing of low-temperature alloy films gives rise to irreversible tensile stress changes indicating restructuring of the films. The stress change measured when annealing a superstructured γ-TiCu film is compressive and is assigned to the transformation of the metastable superstructure to polycrystalline γ-TiCu. The magnitude of this compressive stress contribution is strongly dependent on the copper concentration, i.e., copper vacancy concentration.     

Melting behavior of polypropylene fibers studied by differential scanning calorimetry

Polypropylene fibers produced in a compact-spinning process were studied by differential scanning calorimetry (DSC). With unrestrained fibers, the onset of melting increases with decreasing draw ratio, increasing M_w/M_n, decreasing extrusion temperature, increasing annealing ratio, and increasing draw-down ratio. These trends are discussed in terms of restraints and reorganization. The onset of melting is shifted to lower temperatures as the heating rate increases for all combinations of material and processing parameters, indicating suppressed reorganization. At low draw ratios, the height and width of the endotherm are affected by the spinline stress, and a secondary peak or shoulder is observed on the high temperature side of the main peak. The magnitude of the secondary peak increases with decreasing M_w/M_n, increasing draw ratio, decreasing draw-down ratio, and decreasing heating rate, but its position mainly depends on the heating rate. This indicates that the secondary peak may be due to the melting of structures that have been reorganized during the heating scan. As the draw ratio increases, the melting regime broadens, especially towards lower temperatures, and several maxima emerge on the DSC curve. Reorganization and shrinkage during heating may explain these observations. © 1995 John Wiley & Sons, Inc.     

Symmetric and asymmetric left ventricular hypertrophy in patients with end-stage renal failure on long-term hemodialysis

BACKGROUND: Patients with end-stage renal disease on regular hemodialysis have an increased prevalence of left ventricular (LV) hypertrophy that is associated with morbidity and mortality. Asymmetric septal hypertrophy and impairment of LV outflow can occur in these patients and may contribute to adverse outcomes. More insight into the prevalence, extent, geometry, and promoting factors of LV hypertrophy is important. METHODS: An unselected group of 62 patients (31 women), aged 55 +/- 14 years, on maintenance hemodialysis was investigated by Doppler echocardiography. Eight patients with valvular heart disease were excluded from further analysis. We assessed prevalence of LV hypertrophy and asymmetric septal hypertrophy, as well as parameters of LV geometry and LV filling and outflow dynamics. RESULTS: Prevalence of LV hypertrophy was 65%. Patients were analyzed according to LV mass and geometry. Mean LV mass index was normal (105 +/- 17 g/m2) in Group 1 without LV hypertrophy (n = 19); it was markedly elevated in Group 2 (symmetric hypertrophy, n = 22) and Group 3 (asymmetric hypertrophy with systolic anterior movement of mitral valve, n = 7), and highest (191 +/- 54 g/m2) in Group 4 (asymmetric hypertrophy without systolic anterior movement of mitral valve, n = 6, p < 0.001). Age, body mass index, and duration of hypertension were associated with LV hypertrophy and asymmetric septal hypertrophy (p = 0.01). Group 3 with systolic anterior motion of mitral valve had the smallest end-diastolic LV diameters (p = 0.02); increased heart rates, and increased ejection velocities in the LV outflow tract (p = 0.03, and p = 0.005, respectively, vs. Groups 1, 2, and 4) which pointed to an impairment of LV outflow. CONCLUSIONS: Symmetric LV hypertrophy and asymmetric septal hypertrophy are frequent in patients on maintenance hemodialysis. Predictors for LV hypertrophy were age and body mass index, and, particularly for asymmetric septal hypertrophy, age and hypertension duration. Volume withdrawal during hemodialysis may lead to symptomatic hypotension due to dynamic obstruction in some patients with severe asymmetric septal hypertrophy.     

Properties of electrolytes in the micropores of activated carbon

The dependence of the composition of aqueous electrolytes in the pore system of activated carbon on the potential has been determined by monitoring the amount of ions exchanged with the external electrolyte upon immersion and upon changing the electrode potential. From the investigation with KF solutions, a quantity δ/√? = 4 × 10⁻¹⁰ m is evaluated where δ is half the width of the micropores, and ? the (relative) permittivity. This is in accordance with δ ≈ 1 nm and ? ≈ 7 applying to essentially immobilized water and fits into the results with the other electrolytes. Anions are adsorbed in the cases of sodium perchlorate and potassium hydroxide, while protons are adsorbed in the case of acids (HCl, H₂SO₄). The adsorption of ClO₄⁻ seems to result from electrostatic interaction with the solid, while H⁺ and OH⁻ are strongly chemisorbed, probably at surface groups like >CO. Ionic mobilities of ions in the micropores have been determined from conductance measurements concerning the pore electrolyte of a single spherical particle of activated carbon. Mobilities are more than one order of magnitude lower than those in bulk electrolyte, probably due to an increased viscosity of the liquid in the narrow pores and/or to the coulombic interaction with charged domains of the solid. The rate of charging of the capacitor (solid/micropore electrolyte) is assisted by macropores distributing ions throughout the carbon material.     

The Influence of Phototrophic Biomass on Fe and S Redox Cycling in an Acid Mine Drainage-Impacted System

We examined the effects of organic carbon from oxygenic photosynthetic algal biomass on the redox cycling of Fe and S in an acid mine drainage (AMD)-impacted system. Fe(III)-rich sediments from the field site with abundant algae contained fewer Fe(II) oxidizing bacteria and lower rates of Fe(II) oxidation compared to sediments that did not contain abundant algae. The addition of algal biomass to sediments that did not previously contain abundant algae inhibited microbiological Fe(II) oxidation and enhanced microbiological Fe(III) and sulfate reduction. As Fe(III) reduction proceeded, sulfate was released into solution due to the reductive solubilization of Fe(III) (hydr)oxy-sulfate phases. Our results indicate that in systems where oxidative precipitation of Fe is exploited as an AMD treatment strategy, the abundant organic carbon provided by photosynthetic organisms may inhibit or reverse Fe(II) oxidation.