In situ repair welding of steam turbine shroud for replacing a cracked blade

A root-cracked blade in a high-pressure steam turbine of a nuclear power plant had to be replaced with a new blade by cutting the shroud to remove the cracked blade. This necessitated in situ welding of a new shroud piece with the existing shroud after the blade replacement. The in situ welding of the shroud, a 12% Cr martensitic stainless steel with tempered martensite microstructure, was carried out using gastungsten arc welding and 316L austenitic stainless steel filler metal followed by localized postweld heat treatment at 873 K for 1 h using a specially designed electrical resistance-heating furnace. Mock-up trials were carried out to ensure that sound welds could be made under the constraints present during the in situ repair welding operation. In situ metallography of the repair weld after postweld heat treatment confirmed the adequate tempering of the martensitic structure in the heat-affected zone. Metallurgical investigations carried out in the laboratory on a shroud test-piece that had been welded using the same procedure as employed in the field confirmed the success of the in situ repair operation. The alternate option available was replacing the cracked blade and the shroud piece to which it is riveted with a new one, reducing the height of all the blades attached to the shroud by machining, riveting the blades with reduced height to the new shroud, and, finally, dynamic balancing of the entire turbine after completion of the repair. This option is both time-consuming and expensive. Hence, the successful completion of this repair welding resulted in enormous savings both in terms of reducing the downtime of the plant and the cost of the repair. The turbine has been put back into service and has been operating satisfactorily since December 2000.     

The role of support on the performance of platinum-based catalysts for the total oxidation of polycyclic aromatic hydrocarbons

A range of Pt supported catalysts have been evaluated for the total oxidation of naphthalene. Catalysts contained 0.5 wt% Pt on a range of supports (γ-Al₂O₃, TiO₂, SiO₂, SnO₂, and CeO₂₎. SiO₂ was the best support, the 0.5%Pt/SiO₂ catalyst showing a conversion to carbon dioxide of over 90% at 200 °C (100 vppm naphthalene, GHSV = 45,000 h⁻¹). The catalyst also showed a considerably higher activity (in the temperature range 100–175 °C) than a CeO₂ catalyst recently reported to be one of the most effective catalysts for the total oxidation of naphthalene. The high activity of the 0.5%Pt/SiO₂ catalyst has been attributed to the relatively low dispersion and relatively large size of Pt particles. Furthermore, due to the acidic and non-reducible nature of the SiO₂, platinum is expected to have a weak interaction with the support. XPS data identified the presence of Pt⁰ on the surface and this contributes to the high activity.     

Immune Checkpoint Inhibitors: A Promising Treatment Option for Metastatic Castration-Resistant Prostate Cancer?

Since 2010, several treatment options have been available for men with metastatic castration-resistant prostate cancer (mCRPC), including immunotherapeutic agents, although the clinical benefit of these agents remains inconclusive in unselected mCRPC patients. In recent years, however, immunotherapy has re-emerged as a promising therapeutic option to stimulate antitumor immunity, particularly with the use of immune checkpoint inhibitors (ICIs), such as PD-1/PD-L1 and CTLA-4 inhibitors. There is increasing evidence that ICIs may be especially beneficial in specific subgroups of patients with high PD-L1 tumor expression, high tumor mutational burden, or tumors with high microsatellite instability/mismatch repair deficiency. If we are to improve the efficacy of ICIs, it is crucial to have a better understanding of the mechanisms of resistance to ICIs and to identify predictive biomarkers to determine which patients are most likely to benefit. This review focuses on the current status of ICIs for the treatment of mCRPC (either as monotherapy or in combination with other drugs), mechanisms of resistance, potential predictive biomarkers, and future challenges in the management of mCRPC.     

Active Transport of Hepatotoxic Pyrrolizidine Alkaloids in HepaRG Cells

1,2-unsaturated pyrrolizidine alkaloids (PAs) are secondary plant metabolites occurring as food contaminants that can cause severe liver damage upon metabolic activation in hepatocytes. However, it is yet unknown how these contaminants enter the cells. The role of hepatic transporters is only at the beginning of being recognized as a key determinant of PA toxicity. Therefore, this study concentrated on assessing the general mode of action of PA transport in the human hepatoma cell line HepaRG using seven structurally different PAs. Furthermore, several hepatic uptake and efflux transporters were targeted with pharmacological inhibitors to identify their role in the uptake of the PAs retrorsine and senecionine and in the disposition of their N-oxides (PANO). For this purpose, PA and PANO content was measured in the supernatant using LC-MS/MS. Also, PA-mediated cytotoxicity was analyzed after transport inhibition. It was found that PAs are taken up into HepaRG cells in a predominantly active and structure-dependent manner. This pattern correlates with other experimental endpoints such as cytotoxicity. Pharmacological inhibition of the influx transporters Na⁺/taurocholate co-transporting polypeptide (SLC10A1) and organic cation transporter 1 (SLC22A1) led to a reduced uptake of retrorsine and senecionine into HepaRG cells, emphasizing the relevance of these transporters for PA toxicokinetics.     

Effect of cutting process on the stress corrosion susceptibility of AISI 304L stainless steel

During manufacturing of a component, cutting, turning, grinding, and milling operations are inevitable and these operations induce surface residual stresses. In this study, it is shown that, depending on the process employed for cutting, residual stresses generated at the cut surfaces can vary widely and they can, in turn, make the cut surfaces of austenitic stainless steel (SS) prone to stress corrosion cracking (SCC). An austenitic SS 304L plate was cut using three different procesess: bandsaw cutting, cutting using the cut-off wheel, and shearing. Surface residual stress measurement using the X-ray diffraction (XRD) technique is carried out close to the cutting edges and on the cross-section. SCC susceptibility studies were carried out as per ASTM G36 in 45% boiling magnesium chloride solution. Optical microscopic examination showed the presence of cracks, and confocal microscopy was used to measure the depth of cracks. The study confirmed that high tensile residual stresses present in the cut surfaces produced by cut-off wheel and shear cutting make the surfaces susceptible to SCC while the surfaces produced by bandsaw cutting are resistant to SCC. Hence, it is shown that there is a definite risk of SCC for product forms of austenitic SS with cut surfaces produced using cutting processes that generate high tensile residual stresses stored for a long period of time in a susceptible environment.     

Degradation of Lake Ziway,Ethiopia: A study of the environmental perceptions of school students

Lake Ziway in Ethiopia is a freshwater lake supporting multitude uses, including irrigation, fishing, water supply and recreation. However, the lake is being degraded primarily because of various land‐ and water‐use activities in its watershed. Recognizing these human impacts on the lake's water quality and quantity, the perceptions of school students were surveyed under the belief that the future of the lake is largely dependent on this younger generation. The goal of this study was to better understand how students actually recognize the extent to which various human activities impact the water quantity and quality of Lake Ziway. As major stakeholders in their communities, the perceptions of school students from four high schools regarding the changes to the lake over time were investigated. Students were contacted by purposive sampling, based on criteria of student academic performances, and their proximity to the lake. Their perceptions were studied on the basis of an interview survey. The majority of students indicated that high levels of human activities, especially water abstractions and water pollution, were the main lake impacts. Students believe there is a lack of sustainable utilization and protection of the lake. They suggested coordinated activities among all lake stakeholders in the participation and decision‐making process to properly manage the lake. Provision of awareness to both local administrations and local communities, concern for establishing an appropriate regulatory body and allocating a sufficient budget, and strict controls on flower farm practices in the lakeshore, also was considered to be of high priority as a means of conserving the sustainability of the lake. The result derived from this survey has important implications for facilitating improved school curricula, and for federal, regional and district level water resource management authorities, in setting priorities and developing policies for the sustainability of Lake Ziway.     

GdBaCo2O5+x layered perovskite as an intermediate temperature solid oxide fuel cell cathode

GdBaCo₂O_5+x (GBCO) was evaluated as a cathode for intermediate-temperature solid oxide fuel cells. A porous layer of GBCO was deposited on an anode-supported fuel cell consisting of a 15 μm thick electrolyte of yttria-stabilized zirconia (YSZ) prepared by dense screen-printing and a Ni–YSZ cermet as an anode (Ni–YSZ/YSZ/GBCO). Values of power density of 150 mW cm⁻² at 700 °C and ca. 250 mW cm⁻² at 800 °C are reported for this standard configuration using 5% of H₂ in nitrogen as fuel. An intermediate porous layer of YSZ was introduced between the electrolyte and the cathode improving the performance of the cell. Values for power density of 300 mW cm⁻² at 700 °C and ca. 500 mW cm⁻² at 800 °C in this configuration were achieved.     

SOLID HYDROCARBONS IN PROTEROZOIC DOLOMITES,TAOUDENI BASIN,MAURITANIA

The Taoudeni Basin (Mauritania / Mali, West Africa) was formed as a result of pre‐ Pan‐African subsidence associated with rifting at the margins of the West African craton. Hydrocarbons in the Taoudeni Basin are derived from source rocks in the Meso‐Neoproterozoic Atar Group, which is composed of facies varying from stromatolite‐dominated carbonates to organic‐rich basinal shales. The stromatolitic carbonates are dolomitized and contain solid hydrocarbons (pyrobitumen). The pyrobitumen was formed in response to a Mesozoic hydrothermal event, with peak temperatures locally reaching 380°C, which resulted in hydraulic fracturing of the carbonates. Gas shows were recorded from these carbonates in the Abolag‐1 well and suggest that they may have potential as a reservoir rock. For this study, samples of Atar Group dolostones and black shales were collected from two localities in the Mauritanian part of the Taoudeni Basin and were analyzed by means of various geochemical and microscope‐based techniques including fluid inclusion analyses. The study suggests that Meso‐Neoproterozoic source rocks generated oil and gas during the Late Neoproterozoic – Early Palaeozoic. Later, in the Jurassic, a hydrothermal event caused in‐reservoir thermal cracking of the hydrocarbons to pyrobitumen and a second phase of gas generation and migration.     

Scratch-resistant zeolite anti-reflective coating on glass for solar applications

Sol-gel SiO₂ anti-reflection (AR) coating on solar glass is known to increase the current output by a few percent, but its mechanical durability is of concern. To improve its strength, the amorphous SiO₂ may be replaced by zeolite, which is a microporous aluminosilicate crystalline material. Scratch-resistant AR coating has been prepared by the dip coating of a composition which contains aggregated zeolite nanoparticles as the structure provider and zeolite precursors as the reactive binder. AR coating with better than 5H pencil hardness can be made with a composition containing BEA zeolite. Nanoindenter measurements show that this BEA zeolite films have 1.5 GPa indent hardness and 35 GPa elastic modulus. Furthermore, the freshly prepared AR coating shows a self-cleaning effect with a water contact angle (WCA) close to zero. It can be made super-hydrophobic with larger than 130° WCA after modifying with hexamethyl-disilazane (HMDS), upon which the pencil hardness further increases to 6H.