Effect of nitrogen addition on the microstructure and mechanical behavior of 317L and 904L austenitic stainless steel welds

A systematic study of the effect of nitrogen addition on the microstructure and mechanical behavior of two different austenitic stainless steel welds, namely, 317L and 904L was carried out. For this, nitrogen content of the welds was altered by introducing different proportions of nitrogen gas into the argon shielding gas during welding. Nitrogen addition to 317L weld changed solidification mode from primary ferrite to primary austenite. As 904L weld solidify by primary austenitic mode, no change in the solidification mode was found with N addition. The results showed that, with rise in nitrogen content of the welds, various mechanical properties like ultimate tensile strength and ductility had improved significantly and that the welds prepared with 1 vol% N₂ in the shielding gas indeed failed in the base alloy making the weld stronger than the parent metal. It was noticed that the effect of N towards improving the mechanical properties 904L weld was higher than that found in the case of 317L weld.     

Analysis of Acquired Indoor LTE-A Data from an Actual HetNet Cellular Deployment

Wireless Personal Communications - Increasing the user downlink throughput is always a task of utmost importance for any cellular network service provider. However, most of the research is only...     

Corrosion inhibition of mild steel by benzotriazole derivatives in acidic medium

Benzotriazole derivatives, namely, N-[1-(benzotriazolo-1-yl)alkyl] aryl amine (BTMA), N-[1-(benzotriazolo-1-yl)aryl] aryl amine (BTBA), and 1-hydroxy methyl benzotriazole (HBTA), were synthesized and their inhibition behaviour on mild steel in 0.5 M H₂SO₄ at room temperature was investigated by various techniques. Preliminary screening of the inhibition efficiency (IE) was carried out using weight-loss measurements. Potentiodynamic polarization and AC impedance studies were used to investigate the inhibitor mechanism. Benzotriazole derivatives were found to act as mixed type inhibitors. Among the compounds studied, HBTA exhibited the best performance giving more than 95% IE in H₂SO₄ solutions. The passive film characterization was done using FTIR spectrum.     

Susceptibility to atrial fibrillation: a study in an ovine model of pacing-induced early heart failure

INTRODUCTION: The development of susceptibility to atrial fibrillation (AF) is a common consequence of many forms of cardiovascular disease, especially heart failure. In this study we used a sheep model of pacing-induced stable early heart failure to describe, quantify, and relate the level of susceptibility to AF to changes in structural and electrophysiologic parameters. METHODS AND RESULTS: Epicardial electrodes were implanted on the atria and right ventricles of nine sheep. The AF threshold, atrial vulnerability period, atrial effective refractory period (ERP), and interatrial conduction time were examined during control and over a 6-week period of ventricular pacing at 190 beats/min. Left atrial (LA) area and left ventricular (LV) fractional shortening were monitored using echocardiography. There were significant increases in LA susceptibility to AF (P < 0.0003), LA area (P < 0.0002), and LA ERP400 (P < 0.0002). Rate of increase in LA area was related positively to AF susceptibility (P = 0.02) and inversely to LA ERP400 (P = 0.002). LV fractional shortening decreased to approximately 50% of control value (P < 0.00001). No changes were observed in right atrial electrophysiology. CONCLUSION: In this study, susceptibility (the ability of an extrastimulus to induce AF) was rigorously measured within a predetermined format. Significant relationships were found to exist between susceptibility, certain of the observed changes in atrial electrophysiology and structure.     

A mathematical model for gravity-induced distortion during liquid-phase sintering

The online version of the original article can be found at     

Vitamin A requirements assessed by plasma response to supplementation during pregnancy

The intestinal parasitic helminth infections of man in Bonny and Isiokpo communities were studied between May 1992 and March 1994. Of the 2008 stool samples examined from Bonny community, 503 (25.0%) were infected. 305 (26.7%) of these infections were males while 198 (22.9%) were females. Ascaris lumbricoides (24.1%) occurred most frequently, followed by Hookworms (18.0%), Trichuris trichiura (17.3%,) Strongyloides stercoralis (10.1%) and Enterobius vermicularis (0.1%). Peak infection (41.7%) was recorded for the males in (10-14) years age bracket. The use of bush as a toilet facility had the highest parasitic infection (38.3%), followed by that of shoreline (35.3%), pit (33.3%), Bucket (27.8%) and of water closet (7.5%). Degree of infection relative to source of drinking water showed that well water was associated with highest infection (43.3%) while the pipe borne water was the lowest (18.0%). From Isiokpo community 2,462 stool samples were examined for intestinal parasites 1,633 (66.3%) people were infected consisting of 862 (64.8%) males and 771 (68.2%) females. Higher parasitic infection of females in this community was attributed to the cultural and occupational factors. Frequency of occurrence of individual helminth was as follows: A-lumbricoides (64.5%), T. trichiura (59.4%), Hookworms (58.8%), S. stercoralis (25.1%), Hymenolepsis nana (2.9%) and E. vermicularis (0.3%). Prevalence of infection was significantly higher in Isiokpo than in Bonny because the climatic and edaphic factors were conducive to larval development and infectivity. On the contrary, the saline soil and surface water of Bonny community constituted harsh environmental conditions inimical to larval development and infectivity. Observations on parasitic infections in relation to toilet facilities and source of drinking water were similar to those made in Bonny. The study therefore demonstrated that the provision of pipe borne water and water closet facilities in rural Niger Delta communities could reduce helminth infections of man.     

Thermogravimetric studies of Y1Ba2Cu3O7−x superconductors

The synthesis conditions and oxygen stoichiometry were determined using a thermogravimetric analyser. The kinetics of oxygenation at different temperatures and at different atmospheres were studied. The oxygenation kinetics were found to be sensitive to porosity of the material. The appropriate oxygenation temperature was found to be 400 °C. For oxygenation temperatures below 400 °C, the oxygenation occurs by a nucleation and growth process, whereas for higher temperatures it is diffusion limited.     

Parameterized algorithms for feedback set problems and their duals in tournaments

The parameterized feedback vertex (arc) set problem is to find whether there are k vertices (arcs) in a given graph whose removal makes the graph acyclic. The parameterized complexity of this problem in general directed graphs is a long standing open problem. We investigate the problems on tournaments, a well studied class of directed graphs. We consider both weighted and unweighted versions.     

Variations in sintering kinetics and microstructure of alumina with chromium and molybdenum additions

Chromium and molybdenum were introduced into alumina through gel synthesis. Both elements are soluble in aluminium hydroxide and low-temperature (<1400°C) aluminium oxide. In the course of transformation from hydroxide to oxide, the evaporation-condensation of vapour phase (below 1000° C) causes shrinkage of the porous compact due to particle rearrangement and growth through capillary drag and adsorption. Subsequently, differences in agglomerate structure, grain growth, solute atmosphere and densification arise because of variations in the crystal lochemical behaviour of chromium and molybdenum. The solute atmospheres of chromia-vacancy and molybdenum metal reveal sub-grain boundaries and dislocations. In chromia-alumina solid solution these defects annihilate and contribute to densification (98%th) with increase in temperature to 1600° C. However, with further rise in temperature to 1700° C, the solid solution desinters to 85%th and creep cavities show transition from grain boundary to lattice creep. In Mo-Al₂O₃ composite the defects are locked by molybdenum solute, and as a result there is an insignificant increase in densification (30%th at 1600°C).