On the effect of stress on nucleation and growth of precipitates in an Al-Cu-Mg-Ag alloy

A study has been made of the effect of an externally applied tensile stress on Ω and Θ′ precipitate nucleation and growth in an Al-Cu-Mg-Ag alloy and a binary Al-Cu alloy which was used as a model system. Both solutionized and solutionized and aged conditions were studied. The mechanical properties have been measured and the microstructures have been characterized by transmission electron microscopy (TEM). The volume fraction and number density, as well as the precipitate size, have been experimentally determined. It was found that for as-solutionized samples aged under stress, precipitation occurs preferentially parallel to the stress axis. A threshold stress has to be exceeded before this effect can be observed. The critical stress for influencing the precipitate habit plane is between 120 and 140 MPa for Ω and between 16 and 19 MPa for Θ′ for the aging temperature of 160 °C. The major effect of the applied stress is on the nucleation process. The results are discussed in terms of the role of the lattice misfit between the matrix and the precipitate nucleus.     

A three-dimensional finite analysis of adaptive remodelling in the proximal femur

A finite element analysis of adaptive bone remodelling in the proximal femur is presented. The use of a three-dimensional model permits a realistic representation of femur geometry, and also allows the possibility of examining the effects of fully three-dimensional loading situations. The long-term pattern of remodelling shows a realistic evolution of density distribution, with a tendency towards a steady state, though the simplified load cases used to model gait are not sufficient to predict the formation of the cortical shell.     

Reduction of vibration level in rotordynamics by design optimization

We focus on the reduction of the vibration level of rotors by optimizing the shape of the body. The target is to reduce rotor weight and rotor vibrations leading to higher efficiency and less noise. We consider a finite element discretization of the rotor using a Rayleigh beam model which includes rotary inertia and gyroscopic moments leading to nonself-adjoint systems. We present a general algebraic framework for this case. The mass function is the objective function of the optimization problem and constraints are set on the nonlinear and nonconvex functions of critical speed and unbalanced response. For the numerical solution, algorithms belonging to the class of sequential convex programming are applied for the example of a turbocharger. A remarkable reduction of mass of an initially given prototype could be achieved while significantly reducing the unbalanced response and raising the critical speeds.     

Assessment of the aluminum-rich corner of the Al–Cu–Mg–(Ag) phase diagram

The thermodynamic expressions for the phases found in the aluminum-rich corner of the Al–Cu–Mg–(Ag) system were evaluated and refined to develop a self-consistent database. Microstructural characterization and thermal analysis aided in revising published thermodynamic data for the Al–Cu–Mg and Al–Cu–Mg–Ag systems. To represent the presence of silver an additional interaction energy term was formulated for the S phase, which was completed with the help of ab initio calculations that predicted silver substitution for aluminum within the phase.     

Noninvasive detection of hepatic lipidosis in dairy cows with calibrated ultrasonographic image analysis

The aim was to test the accuracy of calibrated digital analysis of ultrasonographic hepatic images for diagnosing fatty liver in dairy cows. Digital analysis was performed by means of a novel method, computer-aided ultrasound diagnosis (CAUS), previously published by the authors. This method implies a set of pre- and postprocessing steps to normalize and correct the transcutaneous ultrasonographic images. Transcutaneous hepatic ultrasonography was performed before surgical correction on 151 German Holstein dairy cows (mean ± standard error of the means; body weight: 571 ± 7 kg; age: 4.9 ± 0.2 yr; DIM: 35 ± 5) with left-sided abomasal displacement. Concentration of triacylglycerol (TAG) was biochemically determined in liver samples collected via biopsy and values were considered the gold standard to which ultrasound estimates were compared. According to histopathologic examination of biopsies, none of the cows suffered from hepatic disorders other than hepatic lipidosis. Hepatic TAG concentrations ranged from 4.6 to 292.4 mg/g of liver fresh weight (FW). High correlations were found between the hepatic TAG and mean echo level (r = 0.59) and residual attenuation (ResAtt; r = 0.80) obtained in ultrasonographic imaging. High correlation existed between ResAtt and mean echo level (r = 0.76). The 151 studied cows were split randomly into a training set of 76 cows and a test set of 75 cows. Based on the data from the training set, ResAtt was statistically selected by means of stepwise multiple regression analysis for hepatic TAG prediction (R² = 0.69). Then, using the predicted TAG data of the test set, receiver operating characteristic analysis was performed to summarize the accuracy and predictive potential of the differentiation between various measured hepatic TAG values, based on TAG predicted from the regression formula. The area under the curve values of the receiver operating characteristic based on the regression equation were 0.94 (<50 vs. ≥50 mg of TAG/g of FW), 0.83 (<100 vs. ≥100 mg of TAG/g of FW), and 0.97 (<50 vs. ≥100 mg of TAG/g of FW). The CAUS methodology and software for digitally analyzing liver ultrasonographic images is considered feasible for noninvasive screening of fatty liver in dairy herd health programs. Using the single parameter linear regression equation might be ideal for practical applications.     

Reoperative surgery for organic hyperinsulinism: indications and operative strategy

Organic hyperinsulinism has a good chance of cure by operation, although patients with diffuse or multiple disease run a high risk of recurrence or persistence of disease. Surgical management and outcome in these patients are presented and discussed. Between 1986 and April 1997 a total of 62 patients were operated on for organic hyperinsulinism [solitary 48, multiple 3, multiple endocrine neoplasia type I (MEN-I) 2, diffuse 4, malignant 5]. Persistence or recurrence occurred in 10 patients (16%). Among the six that persisted, four were malignant and two benign. All four of those that recurred were benign. Patients with benign disease presented with multiple tumors (n = 3), MEN-I syndrome (n = 1), and diffuse/nodular hyperplasia (n = 2). The duration between diagnosis and reintervention ranged from 1 to 10 years. Preoperative diagnosis was able to localize tumors in three patients (computed tomography 1, angiography 2, calcium stimulation 1). Operative procedures were multiple enucleations in two patients with sporadic disease, subtotal resection plus enucleation in the case of MEN-I syndrome, subtotal resection for diffuse hyperplasia, left resection for adenomatosis, and tumor extirpation after multiple previous operations. Long-term clinical and biochemical cure was achieved in five of six patients (mean follow-up 5 years). Octreotide therapy shows good symptomatic control in the patient with operative failure. Reintervention for organic hyperinsulinism is successful (80% cure) and requires preoperative imaging and individual surgical management.     

Vibration measurements in PWR obrigheim by use of in-core accelerometers

Two accelerometers were inserted into the reactor of the NPP Obrigheim (Germany), one into the core and the other above the core. The amplitude of different components vibrations (fuel element (FE), reactor pressure vessel-core barrel (RPV/CB) and the instrument string-instrument tube (IS/IT) system) were measured. Neutron-mechanical scale factors (SFs) were calculated for the in-core detectors.     

The influence of grain structure on the ductility of the al- cu- li- mn- cd alloy 2020

The effect of various grain structures, produced by thermomechanical treatments, on the monotonie tensile properties of the Al-Cu-Li-Mn-Cd alloy 2020 was investigated. Materials having a completely or partially recrystallized structure exhibit elongations between 4 and 8 pct when aged to peak strength. For both cases the low ductility is associated with (a) planar deformation, (b) random texture, (c) the presence of large intermetallic compounds along the recrystallized grain boundaries, and (d) precipitate free zones. The first three enhance crack nucleation at high angle grain boundaries, and subsequent crack propagation occurs along the precipitate free zones. The completely unrecrystallized materials have elongations between 10 and 13 pct in both longitudinal and transverse directions. The high ductility is associated with a sharp texture and a transgranular fracture mode. The maximum ductility is obtained by reducing the unrecrystallized grain size. The results of this study suggest that improved properties of a 2020-type alloy may be obtained by lowering the Fe and Si contents to remove coarse constituent phases, eliminating Cd, and replacing Mn with Zr in order to obtain a highly textured, unrecrystallized structure.