Tensile properties, fracture toughness and crack growth study of alloy C-276

The results of tensile testing involving austenitic Alloy C-276 indicated that this material is capable of maintaining adequate structural strength at temperatures relevant to the H2SO4 decomposition process related to the nuclear hydrogen generation. This alloy exhibited a unique phenomenon known as dynamic strain aging, which has been studied as a function of both temperature and strain rate. An average value of 55 KJ/mole has been determined to be the activation energy for plastic deformation under tensile loading at different temperatures. Increased crack extension was observed in wedge-loaded double-cantilever-beam specimens exposed to an acidic solution and subjected to higher initial stress intensity factor values. The self-loaded specimens did not exhibit cracking in the same environment. Ductile failures were observed at temperatures up to 600°C. However, intergranular brittle failures were observed at higher temperatures

Photoselective excited state dynamics in ZnO–Au nanocomposites and their implications in photocatalysis and dye-sensitized solar cells

Improving the performance of photoactive solid-state devices begins with systematic studies of the metal–semiconductor nanocomposites (NCs) upon which such devices are based. Here, we report the photo-dependent excitonic mechanism and the charge migration kinetics in a colloidal ZnO–Au NC system. By using a picosecond-resolved Förster resonance energy transfer (FRET) technique, we have demonstrated that excited ZnO nanoparticles (NPs) resonantly transfer visible optical radiation to the Au NPs, and the quenching of defect-mediated visible emission depends solely on the excitation level of the semiconductor. The role of the gold layer in promoting photolytic charge transfer, the activity of which is dependent upon the degree of excitation, was probed using methylene blue (MB) reduction at the semiconductor interface. Incident photon-to-current efficiency measurements show improved charge injection from a sensitizing dye to a semiconductor electrode in the presence of gold in the visible region. Furthermore, the short-circuit current density and the energy conversion efficiency of the ZnO–Au NP based dye-sensitized solar cell (DSSC) are much higher than those of a DSSC comprised of only ZnO NP. Our results represent a new paradigm for understanding the mechanism of defect-state passivation and photolytic activity of the metal component in metal–semiconductor nanocomposite systems

Exploring the role of phytochemicals as biopharmaceuticals targeting Acute Respiratory Distress Syndrome (ARDS) virus: an Overview

ALI (Acute lung injury) and its more fatal form ARDS (acute respiratory distress syndrome) together represent a broad spectrum of lung diseases, which are characterized by the abrupt onset of pulmonary inflammation with fluid filled alveoli resulting in hypoxia. With the advancement of several diagnostic tools, especially discovery of multiplex RT-PCR, increased the chance to investigate the involvement of different respiratory viruses in causing ARDS. There are several different viruses responsible for ARDS and among them few are capable of causing pandemic. Influenza viruses such as H5N1 and H1N1 causing pandemic in 2009. Also among different corona viruses, severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV) and most recently a novel betacoronavirus strain, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been identified. Till date, the therapy against virus induced ARDS has not been optimized. Naturally existing phytochemicals and plant biotechnology could offer prospective solutions for the treatment against virus induced ARDS by developing inhibitors, low-cost vaccines and antibodies, which could not only be useful for treatment but could also be used for diagnosis. In this present COVID-19 pandemic, use of plant based therapeutic approach has already been adopted by several pharma companies to treat ARDS and there are several molecules currently under clinical trials with encouraging results. This review provides detailed outlook on ARDS pandemic causing viruses, pathophysiology of viruses and role of phytochemicals and plantibodies as anti-viral agent. Further, it summarizes list of phytochemicals and their mode of action in these pathogenic viruses

Dynamics of light harvesting in ZnO nanoparticles

We have explored light harvesting of the complex of ZnO nanoparticles with the biological probe Oxazine 1 in the near-infrared region using picosecond-time-resolved fluorescence decay studies. We have used ZnO nanoparticles and Oxazine 1 as a model donor and acceptor, respectively, to explore the efficacy of the Förster resonance energy transfer (FRET) in the nanoparticle-dye system. It has been shown that FRET from the states localized near the surface and those in the bulk of the ZnO nanoparticles can be resolved by measuring the resonance efficiency for various wavelengths of the emission spectrum. It has been observed that the states located near the surface for the nanoparticles (contributing to visible emission at λ≈550 nm) can contribute to very high efficiency (>90%) FRET. The efficiency of light harvesting dynamics of the ZnO nanorods has also been explored in this study and they were found to have much less efficiency (∼40%) for energy transfer compared to the nanoparticles. The possibility of an electron transfer reaction has been ruled out from the picosecond-resolved fluorescence decay of the acceptor dye at the ZnO surface

Pterocarpus angolensis: Botanical, Chemical and Pharmacological Review of an Endangered Medicinal Plant of India

Herbal products for primary health care are gaining huge interests of the people and the various healthcare professionals. This is mainly because of the local availability and cost-effectiveness of plant remedies over expensive modern treatments. Pterocarpus angolensis, a deciduous plant belonging to the family of Fabaceae is mainly found in the tropical regions of Africa. This tree is rich in medicinal properties which are immensely used by the locals in Africa for the treatment of ringworm infections, ulcers, urinary schistosomiasis, skin injury, etc. The extracts of   P. angolensis are treasured in Africa for their effectiveness against many diseases like gonorrhea, mouth diseases, diarrhea, etc. It is reported to have inhibitory activity against various pathogens like Escherichia coli, Staphylococcus aureus, and Salmonella typhimurium because of the high concentration of bioactive compounds like flavonoids, tannins, and other phenolic compounds in the bark and leaves of the tree. Various research papers demonstrated the polar and nonpolar constituents of this plant showing antimicrobial, anti-plasmodial activities against Streptococcus agalactiae, Candida krusei, etc. In India, very few of these plants have been reported to be alive in the Darjeeling district, West Bengal. But, lack of proper documentation or research paper led to negligence related to the importance of this species and it has already been listed in the IUCN Red List of threatened species. The main objective of this review is to spread awareness about the conservation of the plant possessing such remarkable properties. Secondly, to provide an overview of the phytochemical screening of various important medicinal constituents that this plant possesses and this might lead to change in the field of modern medicine

Time-Dependent Fatigue Crack Propagation Behavior of Two Solid-Solution-Strengthened Ni-Based Superalloys—INCONEL 617 and HAYNES 230

The fatigue crack propagation (FCP) as well as the sustained loading crack growth (SLCG) behavior of two solid-solution-strengthened Ni-based superalloys, INCONEL 617 (Special Metals Corporation Family of Companies) and HAYNES 230 (Haynes International, Inc., Kokomo, IN), were studied at increased temperatures in laboratory air under a constant stress-intensity- factor (K) condition. The crack propagation tests were conducted using a baseline cyclic triangular waveform with a frequency of 1 3 Hz. Various hold times were imposed at the maximum load of a fatigue cycle to study the hold time effect. The results show that a linear elastic fracture mechanics (LEFM) parameter, stress intensity factor (K), is sufficient to describe the FCP and SLCG behavior at the testing temperatures ranging from 873 K to 1073 K (600 C to 800 C). As observed in the precipitation-strengthened superalloys, both INCONEL 617 and HAYNES 230 exhibited the time-dependent FCP, steady SLCG behavior, and existence of a damage zone ahead of crack tip. A thermodynamic equation was adapted to correlate the SLCG rates to determine thermal activation energy. The fracture modes associated with crack propagation behavior were discussed, and the mechanism of time-dependent FCP as well as SLCG was identified. Compared with INCONEL 617, the lower crack propagation rates of HAYNES 230 under the time-dependent condition were ascribed to the different fracture mode and the presence of numerous W-rich M6C-type and Cr-rich M23C6-type carbides. Toward the end, a phenomenological model was employed to correlate the FCP rates at cycle/time-dependent FCP domain. All the results suggest that an environmental factor, the stress assisted grain boundary oxygen embrittlement (SAGBOE) mechanism, is mainly responsible for the accelerated time dependent FCP rates of INCONEL 617 and HAYNES 230

Creep Deformation of Alloys 617 and 276 at 750-950 °C

Alloys 617 and 276 were subjected to time-dependent deformation at elevated temperatures under sustained loading of different magnitudes. The results indicate that Alloy 617 did not exhibit strains exceeding 1 percent (%) in 1000 h at 750, 850 and 950 °C when loaded to 10% of its yield strength (YS) values at these temperatures. However, this alloy was not capable of sustaining higher stresses (0.25YS and 0.35YS) for 1000 h at 850 and 950 °C without excessive deformation. Interestingly, Alloy 617 showed insignificant steady-state creep rate at 750 °C irrespective of the applied stress levels. Alloy 276 almost met the maximum creep deformation criterion when tested at 51 MPa–750 °C. Severe creep deformation of both alloys at 950 °C could be attributed to the dissolution of carbides and intermetallic phases remaining after solution annealing or precipitated during quenching