Fracture toughness behavior of ex-service 2-1/4Cr-1Mo steels from a 22-year-old fossil power plant

Elevated-temperature fracture toughness properties were developed on ex-service 2-l/4Cr-1Mo steel weldments. Fracture toughness was measured on both base and heat-affected zone (HAZ) metals. A composite specimen consisting of base, HAZ, and weld metals was used to develop fracture toughness properties in the HAZ area. It was observed that the J-R curve of the HAZ was significantly lower than that of the base metal. Increasing crack extension increased the difference between theJ-R curves of the base metal and the HAZ. Dimpled fracture was the prime fracture mode in the base metal specimen, and a mixed-mode (ductile and “granular”) fracture was found in the HAZ specimens. Scanning transmission electron microscopy (STEM) examination revealed significant intergranular carbide precipitation and agglomeration within the HAZ. The lower fracture toughness of the HAZ, as compared to the base metal, was attributed to the large accumulation of carbides in the grain boundaries of the HAZ, which weakened the grain boundaries and caused “granular” fracture.     

HEAT-TRANSFER AND GAS-HOLDUP STUDIES IN A BUBBLE COLUMN: AIR-WATER-GLASS BEAD SYSTEM

Air-holdup and heat-transfer coefficient values are measured in a 0.305 m diameter bubble column equipped with a seven-tube bundle for the air-water and air-water-glass bead system. The dependence of these two properties on air velocity (up to 0.28 m/s), temperature (297-343 K), glass bead powder average size (50-143.3 μm), solids concentration in the slurry (up to 20 weight percent) and bubble column diameter (0.108 and 0.305 m), is experimentally investigated. The effect of internals, as simulated by a single probe and a seven-tube bundle, in the two bubble columns is also examined. The models and correlations commonly employed to estimate these properties are assessed on the basis of generated data.     

Detection of micron size phantom of biological cell using concentric square ring metamaterial at microwave frequency

ABSTRACT

This paper presents simulation studies and theoretical analysis of sensing property of concentric square ring metamaterial biological materials. Phantom of dielectric cell having dimension 100 µm long and 25 µm in radius is considered. Sensor is designed using periodic arrays of split ring resonators and wires having negative permittivity and permeability at 16.694 GHz. Transmission parameters are extracted using CST MWS software. Change in resonance is observed on placing phantom close to the sensor due to the change in capacitance and inductance. Designed sensor can sense single phantom cell with 133 MHz of shift in resonance. Study shows that sensor has good sensitivity for detecting micron size dielectric objects.     

Qualitative Evolution of Asymmetric Raman Line-Shape for NanoStructures

A qualitative evolution of an asymmetric Raman line-shape function from a Lorentzian line-shape is discussed here for application in low dimensional semiconductors. The step-by-step evolution reported here is based on the phonon confinement model which is successfully used in literature to explain the asymmetric Raman line-shape from semiconductor nanostructures. Physical significance of different terms in the theoretical asymmetric Raman line-shape has been explained here. Better understanding of theoretical reasoning behind each term allows one to use the theoretical Raman line-shape without going into the details of theory from first principle. This will enable one to empirically derive a theoretical Raman line-shape function for any material if information about its phonon dispersion relation, size dependence, etc., is known.     

Structure‐Guided Design of Thiazolidine Derivatives as Mycobacterium tuberculosis Pantothenate Synthetase Inhibitors

The pantothenate biosynthetic pathway is essential for the persistent growth and virulence of Mycobacterium tuberculosis (Mtb) and one of the enzymes in the pathway, pantothenate synthetase (PS, EC: 6.3.2.1), encoded by the panC gene, has become an appropriate target for new therapeutics to treat tuberculosis. Herein, we report nanomolar thiazolidine inhibitors of Mtb PS developed by a rational inhibitor design approach. The thiazolidine compounds were discovered by using energy‐based pharmacophore modelling and subsequent in vitro screening, which resulted in compounds with a half maximal inhibitory concentration (IC₅₀) value of (1.12±0.12) μM . These compounds were subsequently optimised by a combination of modelling and synthetic chemistry. Hit expansion of the lead by chemical synthesis led to an improved inhibitor with an IC₅₀ value of 350 nM and an Mtb minimum inhibitory concentration (MIC) of 1.55 μM . Some of these compounds also showed good activity against dormant Mtb cells.     

Rheological Behavior of Polycarbosilane Part II: Effect of Heterometal (Al) Content and Nature of Bonding with Si of Polycarbosilane

A few aluminum containing polycarbosilanes named AlOR-PCS and Alac-PCS have been synthesized by the reaction of aluminum isopropoxide (AlOR) and aluminum acetylacetonate (Alac) with polycarbosilane (PCS), respectively. These materials were characterized by Fourier Transform Spectroscopy (FTIR), Thermo gravimetric Analysis (TGA) and Gel Permeation Chromatography (GPC). The rheological properties of these compounds were studied with respect to time, temperature and atmosphere (inert & air). It has been observed that the increase in metal content enhances the crosslinking of the PCS chains. Under similar conditions, the crosslinking of AlOR-PCS derivatives was found slower than Alac-PCS. GPC analysis of the samples showed the increase in molecular weight of these compounds compared to virgin PCS. TGA showed improved ceramic yield with increasing metal content. Alac-PCS gave higher ceramic yield than AlOR-PCS for similar molar ratios of metal complexes.     

H2S sensors based on SnO2 films: RGTO verses RF sputtering

Gas sensing characteristics of SnO₂ thin films prepared by RF sputtering have been investigated and compared to that of RGTO (Rheotaxially Grown and Thermally Oxidized) films. Both the sensor films exhibited a highly selective response towards H₂S with RF sputtered film showing better response characteristics. RF sputtered and RGTO films exhibited a maximum response of 54 and 15 towards 10 ppm of H₂S at an optimum operating temperature of 150 and 250 °C, respectively. Sputtered films exhibited a linear response in the wide concentration range from 500 ppb to 500 ppm while RGTO films were found to saturate for concentrations above 100 ppm. XPS investigations revealed that the RGTO films are more sub–stoichiometric or oxygen deficient than the sputtered films. Raman studies further indicates that the surface of sputtered and RGTO films are characterized by the presence of oxygen deficiency attributed to the “bridging-type” and deeper “in-plane/sub-bridging” oxygen vacancies, respectively. The improved response kinetics of the RF sputtered films is attributed to the presence of bridging type oxygen vacancies that facilitates the charge transfer between the sensor surface and H₂S molecules.     

Multiwall carbon-nanotube-doped ion conducting polymer electrolyte for electrochemical application

Electrical, structural and optical properties of a composite containing a polymer electrolyte (namely polyethylene oxide complexed with sodium iodide) and multiwall carbon nanotube (MWCNT) are reported. The films of these composites were ‘solution casted’ using the viscous solution of polyethylene oxide (PEO) complexed with sodium iodide (NaI) in desired ratios and characterised using various techniques. The conductivity versus composition plot in PEO:NaI shows conductivity maxima at 12?wt% NaI concentration while in MWCNTs doped polymer electrolyte it occurs at 40?wt% MWCNTs concentration. The surface morphology by scanning electron microscopy (SEM) shows the enhancement in amorphous reason by MWCNTs doping which is a well-known favourable condition for conductivity enhancement. The differential scanning calorimetry shows that dispersal of MWCNTs reduces the crystallinity of polymer electrolyte that is well-supported by our polarised optical micrographs and SEM measurements.     

Dynamic cellular manufacturing systems design��a comprehensive model

This paper addresses the dynamic cell formation problem (DCF). In dynamic environment, the product demand and mix changes in each period of a multiperiod planning horizon. It causes need of reconfiguration of cells to respond to the product demand and mix change in each period. This paper proposes a mixed-integer nonlinear programming model to design the dynamic cellular manufacturing systems (DCMSs) under dynamic environment. The proposed model, to the best of the author??s knowledge, is the most comprehensive model to date with more integrated approach to the DCMSs. The proposed DCMS model integrates concurrently the important manufacturing attributes in existing models in a single model such as machine breakdown effect in terms of machine repair cost effect and production time loss cost effect to incorporate reliability modeling; production planning in terms of part inventory holding, part internal production cost, and part outsourcing; process batch size; transfer batch size for intracell travel; transfer batch size for intercell travel; lot splitting; alternative process plan, and routing and sequence of operation; multiple copies of identical copies; machine capacity, cutting tooling requirements, work load balancing, and machine in different cells constraint; machine in same cell constraint; and machine procurements and multiple period dynamic cell reconfiguration. Further, the objective of the proposed model is to minimize the sum of various costs such as intracell movement costs; intercell movement costs and machine procurement costs; setup cost; cutting tool consumption costs; machine operation costs; production planning-related costs such as internal part production cost, part holding costs, and subcontracting costs; system reconfiguration costs; and machine breakdown repair cost, production time loss cost due to machine breakdown, machine maintenance overheads, etc. ,in an integrated manner. Nonlinear terms of objective functions are transformed into linear terms to make mixed-integer linear programming model. The proposed model has been demonstrated with several problems, and results have been presented accordingly.