Role of machining defects and residual stress on the AISI 304 fatigue crack nucleation

Machining defects as rebuilt material and dislodgement were often induced by cutting of difficult to machining AISI 304 stainless steel. Their density increases with a decreasing of cutting speed. The effect of these defects on surface topography and residual stress was evaluated by roughness and X‐ray diffraction measurements coupled with numerical simulation. The role of the rebuilt material on the distribution of fatigue crack nucleation sites was investigated by scanning electron microscope examination of post fatigue samples loaded at different imposed strain amplitudes. The association of machining defects and fatigue crack nucleation sites was attributed to the contribution of additional tensile residual stresses induced by rebuilt material rather than local stress concentration. Moreover, the fatigue crack coalescence is promoted by increasing the rebuilt material density. When the machining defect density increases from 5 to 60 particles/mm², the fatigue life decreases from ?22% to ?65% with respect to the electropolished surface.     

Dynamic denoising studies in wideband radio channel measurement and modeling

The fixed level and dynamic denoising method was studied based on indoor-to-outdoor measured channel impulse responses ORs） at 5.25 GHz with radio frequency （RF） 100 MHz bandwidth. It is found that the dynamic ranges, peak powers and noise floors of the IRs are with close correlations. The comparisons with different denoising methods are given by deriving the power delay profiles （PDPs）, root mean square （RMS） delay spread （RMS DS）, number of paths （NOPs） and Ricean K-factors. It is concluded that the traditional fixed level noise cut is under estimate of DS and NOPs. The Ricean K-factors are of little sensitive to noise cut irrespective of what kind of methods applied. The PDPs are not very sensitive to the fixed level noise cut, however, obvious changes can be found by dynamic noise cut. The dynamic noise cut is preferred when clear noise floors is observed and decided from the measured IRs, it＇s of importance in data post processing for wideband radio channel measurements as well as the relevant modeling work.     

Analyse et modélisation de la permittivité effective statique de la ligne microruban suspendue

New numerical quasi-static model for the computer aided design (CAD) and analysis of suspended microstrip lines is reported. This model is applicable up to ε_r = 20 and over the range 0.001 ≤ u ≤ 1000, where u = w/h ₁ is the structure’s variable (w is the width of the strip and h ₁ is the air gap’s thickness). The practical cases are limited to a thickness h ₁ of the same order of h ₂ which is the dielectric’s thickness. This yields to choose 0.5 ≤ m ≤ 1.5. The parameter m is dependent on the structure’s variable u. This model is conceived to corroborate the results of the variational approach in any point of its ranges of validity, with a raised error with 1.2%. Although the variational approach allows accurate values of the effective permittivity, but the computing time is relatively high which quickly becomes prohibitory if the Finished Coupled Elementary Lines method is used. The present model is an improvement over the previous variational method as it not only takes lower computing time but it also valid up to high values of ε_r and over the range 0.001 ≤ u ≤ 1000. This work is important by the fact that it seeks to visualise the formal model of the effective permittivity, generally masked in a direct variational treatment.     

Stenting after optimal lesion debulking (sold) registry. Angiographic and clinical outcome

BACKGROUND: Coronary stenting has reduced restenosis in focal de novo lesions, but its impact has been less pronounced in complex lesion subsets. Preliminary data suggest a role for plaque burden in promoting intimal hyperplasia after stent implantation. The aim of this study was to test the hypothesis that plaque removal with directional atherectomy before stent implantation may lower the intensity of late neointimal hyperplasia, reducing the incidence of in-stent restenosis. METHODS AND RESULTS: Seventy-one patients with 90 lesions underwent directional atherectomy before coronary stenting. Intravascular ultrasound-guided stenting was performed in 73 lesions (81%). Clinical success was achieved in 96% of patients. Procedural complications were as follows: emergency bypass surgery in 1 patient (1.4%), who died 2 weeks later; Q-wave myocardial infarction in 2 patients (2.8%); and non-Q-wave myocardial infarction in 8 patients (11.3%). None of the patients had stent thrombosis at follow-up. Angiographic follow-up was performed in 89% of eligible patients at 5.7+/-1.7 months. Loss index was 0.33 (95% CI, 0.26 to 0.40), and angiographic restenosis was 11% (95% CI, 5% to 20%). Clinical follow-up was performed in all patients at 18+/-3 months. Target lesion revascularization was 7% (95% CI, 3% to 14%). CONCLUSIONS: Directional atherectomy followed by coronary stenting could be performed with good clinical success rate. Also, these data point to a possible reduction in angiographic restenosis and a significant reduction in the need for repeated coronary interventions. Therefore, a randomized clinical trial seems appropriate to test the validity of this approach.     

Perception-based microtuning over MIDI networks

MIDI has intrinsic limitations that have held back the development of flexible microtunable systems. The author evaluates previous solutions and address the problem of pervasive microtuning in MIDI networks within the context of the general weaknesses and underusage of MIDI technology. Then the author describes the prototyped and patent-pending solution called U-Tune, which involves implementing pervasive microtuning over a MIDI network.     

Induced electrodeposition of tungsten with nickel from acidic citrate electrolyte

Induced electrodeposition of Ni–W alloys was carried out onto steel substrates from acidic citrate baths (pH 4.5) under different conditions of concentration of electrolyte, current density and temperature. Bright and highly adherent Ni–W deposits were successfully obtained with a relatively high cathodic current efficiency CCE (80–85%). The CCE increases greatly with increasing pH and Ni²⁺ ion content in the bath. The W% in the alloy deposits is in the range of 4–20 wt% depending on the operating condition. The W content in the deposit was found to increase with an increase in Ni²⁺ ion content, pH and temperature. The surface morphology was examined by scanning electron microscopy while the structure of the alloy was examined by X-ray diffraction analysis.     

Damage evolution and infrared thermography in woven composite laminates under fatigue loading

An analytical model based on cumulative damage has been used for predicting the damage evolution in composite materials. The model is verified with experimental data from a carbon/epoxy composite fatigued under tension–tension load. Fatigue tests of specimens have been monitored with an infra-red thermography system. By analysing the temperature of the external surface during the application of cyclic loading, it is possible to evaluate the damage evolution. The model agrees well with the experimental data, and it can be used to predict the evolution of damage in composites.     

In Situ Neutron and X-Ray Powder Diffraction Study of Cation Ordering and Domain Growth in the Dielectric Ceramic Ba3ZnTa2O9–Sr2GaTaO6

In situ methods are ideally suited to study the development of property-critical structural features during material processing. As an example of their potential in the area of complex oxide electroceramics, here, we apply X-ray synchrotron and neutron powder diffraction to investigate the ordering processes responsible for optimizing the microwave dielectric properties of the commercial electroceramic barium zinc tantalate (BZT) doped with strontium gallate. The collection of synchrotron diffraction data with high resolution and high intensity during processing has allowed the development of cation site order and growth of ordered domains to be followed during the multi-stage thermal treatment processing used by industry. Complementary neutron diffraction data reveal changes in the cation–oxygen bonding associated with development of the cation-ordered trigonal perovskite structure. The effects of material loss with processing at temperatures of up to 1525°C are discussed following experiments using open and closed systems. The complex nature of the ordering is confirmed by the coexistence of two BZT phases and the formation of a further zinc-deficient phase. The implications of these observations and relation to the industrial processing procedures are discussed.     

The Influence of C60 Powders On Cultured Human Leukocytes

In order to check its possible acute toxicity, C₆₀ was incorporated into living human phagocytes. It was observed that C₆₀ has no influence on the survival of human leukocytes.