Activation Enthalpies of Deformation-Induced Lattice Defects in Severe Plastic Deformation Nanometals Measured by Differential Scanning Calorimetry

Samples of 99.99 pct pure copper and nickel of 99.998 pct purity were deformed by high-pressure torsion (HPT) at different hydrostatic pressures, to different shear strains. Activation enthalpies (Q) were determined by differential scanning calorimetry (DSC) using Kissinger’s method. For the one annealing peak found in HPT Cu, Q amounts to Q = 0.78 to 0.48 eV depending on the shear strain applied. In the case of Ni, the activation enthalpies of the two annealing peaks were determined as Q = 0.65 eV and Q = 0.95 eV, respectively, with no obvious dependence on shear strain, although this has been indicated by the annealing peak temperatures. Applying defect specific analyses of the annealing peaks, it turned out that the larger Q value represents the annihilation of dislocations and agglomerates, while the smaller one reflects the annihilation of single or double vacancies. Concerning the strain dependence of the larger Q, two possible explanations have been discussed: (1) the annihilation of dislocations assisted by the strain-dependent density of vacancy agglomerates and (2) the annihilation of dislocations enhanced by a strain-dependent level of long-range internal stresses. Because of closer correlations of Q with external and internal stresses at very high shear strains, explanation (2) has been favored.     

Comparison of four methods for monitoring the kinetics of curing of a phenolic resin

The kinetics of curing of several phenolic resin compounds were studied with the use of four techniques: viscometry, infrared spectroscopy (IR), differential scanning calorimetry (DSC), and thermomechanical analysis. The objective was to compare the effectiveness of these methods. It was found that the viscosity increase during oligomer curing can be described by an exponential function, and that the rate of viscosity increase can be described in terms of a “viscometric” kinetic constant, k_η. The gel‐time, t*, was found by extrapolation of the time dependence of the reciprocal viscosity. The product (t*k_η) appears to be constant for all temperatures. It was concluded that each experimental technique reflects a different kinetic process, and it is not possible to correlate the results of one technique with those of another. The degree of conversion at the gel point, β*, depends on temperature, and it is thought that this is due to the heterogeneous nature of curing. The glass temperature (as determined from the maximum in the loss tangent) is related to the degree of curing by the DiBenedetto equation, which can be used to determine the degree of conversion during the final stages of the reaction. POLYM. ENG. SCI. 45:95–102, 2005. © 2004 Society of Plastics Engineers     

Fracture properties of marble–mortar compounds

Marble panels for outdoor cladding of buildings are generally fastened with mortar and/or anchors. Due to environmental influences (e.g. solar heat, rain and snow), such panels can start to bow and crack, such that eventually they may detach from the wall, possibly causing damage to humans and the environment. Different marble–mortar compounds have been tested for their mechanical and fracture-mechanical characteristics (adhesive strength, notch tensile strength, specific fracture energy, crack growth resistance and characteristic length) by means of the pull-out test and the wedge-splitting method. The propagation of a crack in the marble–mortar compound is characterized on the basis of fracture-mechanics and by use of the load displacement curve. The advantages of using a mortar bed rather than anchors are considered.      

Reliability screening of high-k dielectrics based on voltage ramp stress

High-k development moves towards integration into CMOS processes rising attention for the reliability assessment. In this paper, the methodology for reliability screening is discussed based on constant voltage stress and voltage ramp stress. It will be shown that both procedures yield equivalent results and the determined reliability parameters are compatible. Better control of the overall measurement time favours the voltage ramp stress as preferred fast screening method for integration of high-k dielectrics.     

Metabolite channeling and compartmentation in the human cell line AGE1.HN determined by 13C labeling experiments and 13C metabolic flux analysis

This study focused on analyzing active pathways and the metabolic flux distribution in human neuronal AGE1.HN cells that is a desirable basis for a rational design and optimization of producing cell lines and production processes for biopharmaceuticals. ¹³C-labeling experiments and ¹³C metabolic flux analysis were conducted using glucose, glutamine, alanine and lactate tracers in parallel experiments. Connections between cytosolic and mitochondrial metabolite pools were verified, e.g., flux from TCA cycle metabolite ¹³C to glycolytic metabolites. It was also found that lactate and alanine are produced from the same pyruvate pool and that consumed alanine is mainly directly metabolized and secreted as lactate. Activity of the pentose phosphate pathway was low being around 2.3% of the glucose uptake flux. This might be compensated in AGE1.HN by high mitochondrial malic enzyme flux producing NADPH. Mitochondrial pyruvate transport was almost zero. Instead pyruvate carbons were channeled via oxaloacetate into the TCA cycle which was mainly fed via α-ketoglutarate and oxaloacetate during the investigated phase. The data indicate that further optimization of this cell line should focus on the improved substrate usage which can be accomplished by an improved connectivity between glycolytic and mitochondrial pyruvate pools or by better control of the substrate uptake.     

Towards a conceptualisation of quality in information technology projects

Quality has been extensively studied in repetitive operations, but it remains under-researched in projects. The uncertainty and dynamics of projects challenge the principles of quality developed for repetitive operations, and call for project-tailored solutions. This article explores the attributes of quality in projects, based on interviews conducted within a large IT-services company. An adapted repertory grid was used to investigate the understanding of quality by comparing concrete examples of projects considered as high or low quality. Eight attributes of quality were identified, which indicate a tension between a mechanistic standpoint of quality, and the need to incorporate less tangible aspects.