Evolution of acicular ferritic microstructure in a titanium bearing HSLA steel

An attempt has been made to design and develop acicular ferritic steels by adopting three-stage controlled rolling, with titanium alone as microadditive. Process parameters such as finish rolling temperature (FRT), amount of deformation during the last pass and also the cooling rate after finishing have been altered to obtain different microstructural effects. Optical as well as transmission electron microscopy studies indicated that acicular ferritic microstructure can be engendered by applying a minimum deformation of 25 % at the finishing pass followed by water quenching. Decreasing the FRT from 850 °C, for water quenched steels deformed 33 %, resulted in the refinement of polygonal ferrite, whereas the reverse is the case with the aspect ratio of acicular ferrite. The volume fraction of acicular ferrite progressively increases as the FRT is lowered. Evaluation of tensile properties suggested that yield strength as high as ~ 600 MPa with an elongation of ~ 25 %, could be obtained by finishing at a lower temperature of 750 °C. An impact transition temperature (ITT) of -53 °C indicated that the steel possesses adequate toughness properties. As weldability is one of the criteria for structural applications, this aspect too has been investigated.     

Implicit objective integration for sensitivity analysis in non-linear solid mechanics

Incrementally objective integration schemes are proposed for the accurate and efficient determination of design sensitivity coefficients (DSCs) for solid mechanics problems with both material and geometrical non-linearities. The derivation of these schemes are based on the direct differentiation of objective schemes that are used in stress analysis for problems of this class. Two widely used objective stress rates, the Jaumann rate and the Green–Naghdi rate, are considered here within the same setting with only minor changes of the integration scheme. Numerical results are presented for a simple shear problem with different material constitutive laws, including a hypoelastic model and a unified isotropic viscoplastic model, for these two objective rates. The numerical results are compared with analytical solutions or direct integration solutions. The close agreement among these solutions demonstrates the accuracy and efficiency of the proposed scheme.     

A novel and simple approach to enhance ultraviolet photosensitivity: activated-carbon-assisted growth of ZnO nanoparticles

An activated-carbon (AC) assisted route is developed to synthesize a ZnO nanoparticle network. The route involves simple addition of AC to the solution containing the zinc salt and finally removing them by burning at higher temperature to form a sponge-like porous ZnO nanoparticles. The surface area measurements show that AC-assisted ZnO nanoparticles (AC-ZnO) have a higher surface area than those synthesized without AC (B-ZnO), which is further confirmed by the field emission scanning electron microscope (FESEM) and high resolution transmission electron microscope (HRTEM) images. Ultraviolet (UV) absorbance results show that the optical quality remains almost unchanged for both types of nanoparticles. Enhanced and faster UV photosensitivity has been observed for the AC-ZnO. The change in the UV photosensing properties demonstrated here provides a new approach to synthesizing other high surface area materials for novel physical and chemical properties.     

Correlation of Burning Rate with Spread Rate for Downward Flame Spread Over PMMA

Burning rate of solid fuel and laminar flame spread rate are both well studied topics for flame spread in downward configuration. Yet, despite well-developed theories, not much experimental data is available to correlate the two. In this work, experiments are performed under ambient conditions in downward spread configuration for a wide range of thicknesses (2 mm to 24 mm) for flat samples of Poly-Methyl Methacrylate (PMMA). The samples are held by two ceramic plates in order to obtain a two-dimensional propagation that is independent on the sample width. By analyzing videos of the experiments, the instantaneous spread rate is obtained using a recently developed MATLAB based tool. The shape of the pyrolyzing fuel is carefully measured after extinguishing the flame during a steady propagation. The spread rate and the burn angle, which is defined as the angle subtended by the pyrolyzing surface with respect of the fuel surface, are correlated, producing an expression for the burning rate in terms of the burn angle and flame spread rate. As the fuel thickness is increased, the burn angle and burning rate decrease and reach asymptotic limits for thermally thick fuels, in analogy with the spread rate limit. The comparison with data from literature suggests that in the thick limit the value of mass flux for PMMA (about 10 g/m² s) tends to the one of non-spreading flames. The presented geometrical approach to study the downward spread problem avoids the use of the B number and local gradients in order to calculate the mass burning rate of the fuel.     

Regioselective Friedel–Crafts Reaction of Electron‐Rich Benzenoid Arenes and Spiroepoxyoxindole at the Spiro‐Centre: Efficient Synthesis of Benzofuroindolines and 2H‐ Spiro[benzofuran]‐3,3′‐oxindoles

Metal triflate‐catalysed intermolecular Friedel–Crafts reactions involving electron‐rich benzenoid arenes and spiroepoxyoxindoles at the spiro‐centre have been developed for the exclusive regioselective synthesis of 3‐aryl‐(3‐hydroxymethyl)oxindoles with an all‐carbon quaternary centre. Selective ring opening of spiroepoxyoxindoles with phenols provided a direct access to 3‐(hydroxymethyl)‐3‐(2‐hydroxyaryl)oxindoles. We have utilized this methodology successfully as the key step for the synthesis of benzofuroindolines and 2H‐spiro[benzofuran]‐3,3′‐oxindoles.

     

Synthesis of aryl-substituted naphthalene-linked pyrrolobenzodiazepine conjugates as potential anticancer agents with apoptosis-inducing ability

A library of new aryl‐substituted naphthalene C8‐linked pyrrolo[2,1‐c][1,4]benzodiazepine (PBD) conjugates with various linker architectures were designed, synthesized, and evaluated for their anticancer activity against a panel of 11 human cancer cell lines. All 32 conjugates show anticancer potential, with some of them exhibiting particularly high activity (0.01–0.19 μM ). Thermal denaturation studies showed effective DNA binding capacity relative to DC‐81. In assays for biological activity relating to cell‐cycle distribution, these PBD conjugates induce G₀/G₁‐phase arrest and also cause an increase in the levels of p53 and caspase‐9 proteins, followed by apoptotic cell death. One conjugate in particular is the most promising candidate of the series, with the potential to be selected for further studies, either alone or in combination with existing anticancer therapies.     

Stochastic earthquake response control of structures by liquid column vibration absorber with uncertain bounded system parameters

The present work deals with optimum design of liquid column vibration absorber (LCVA) for seismic vibration control of structures characterized by uncertain system parameters. This involves optimization of the frequency and damping properties of LCVA considering uncertain properties of the structure and ground motion parameters. The study on optimum design of tuned mass damper system considering random system parameters is noteworthy. But, the same is not the case for liquid dampers. Moreover, though the probabilistic methods are powerful, the approach cannot be applied in many real situations when the required detailed information about uncertain parameters is limited. In such cases, the interval method is a viable alternative. With the aid of matrix perturbation theory using first order Taylor series expansion of dynamic response function and its interval extension, the vibration control problem under bounded uncertainty is transformed to appropriate deterministic optimization problems. This requires optimizing two separate objective functions correspond to a lower bound and an upper bound optimum solutions. A numerical study is performed to study the effect of system parameter uncertainty on the optimization of LCVA parameters and its response reduction efficiency. Though the efficiency is not completely eliminated, the advantage of the LCVA tends to reduce as the level of uncertainty increases. It is also seen that neglecting the effect of system parameter uncertainty may overestimate the damper performance.     

The Application of a Recyclable Organocatalytic System to the Asymmetric Domino Michael/Henry Reaction in Aqueous Media

A new type of pyrrolidine‐based organocatalyst has been developed and found to be very effective for the domino Michael/Henry reaction in aqueous solvents. For the reaction involving pentane‐1,5‐dial and various nitroolefins, good yields (65–85%) and excellent enantioselectivities (99%) were obtained using this catalyst. In addition, the catalyst could be recycled up to four times resulting in good yields and up to seven times with good enantioselectivity.     

Vacuum system of SST-1 Tokamak

Vacuum chambers of Steady State Superconducting (SST-1) Tokamak comprises of the vacuum vessel and the cryostat. The plasma will be confined inside the vacuum vessel while the cryostat houses the superconducting magnet systems (TF and PF coils), LN₂ cooled thermal shields and hydraulics for these circuits. The vacuum vessel is an ultra-high (UHV) vacuum chamber while the cryostat is a high-vacuum (HV) chamber. In order to achieve UHV inside the vacuum vessel, it would be baked at 150 °C for longer duration. For this purpose, U-shaped baking channels are welded inside the vacuum vessel. The baking will be carried out by flowing hot nitrogen gas through these channels at 250 °C at 4.5 bar gauge pressure. During plasma operation, the pressure inside the vacuum vessel will be raised between 1.0 × 10^?4 mbar and 1.0 × 10^?5 mbar using piezoelectric valves and control system. An ultimate pressure of 4.78 × 10^?6 mbar is achieved inside the vacuum vessel after 100 h of pumping. The limitation is due to the development of few leaks of the order of 10^?5 mbar l/s at the critical locations of the vacuum vessel during baking which was confirmed with the presence of nitrogen gas and oxygen gas with the ratio of ～3.81:1 indicating air leak. Similarly an ultimate vacuum of 2.24 × 10^?5 mbar is achieved inside the cryostat. Baking of the vacuum vessel up to 110 °C with ±10 °C deviation was achieved with a net mass flow rate of 0.8 kg/s at 1.5 bar gauge inlet pressure and supply temperature of 230 °C at the heater end. Also during gas feed system installation, the pressure inside the VV was raised from 3.01 × 10^?5 mbar to 1.72 × 10^?4 mbar by triggering a pulse of lower amplitude of 25 voltage direct current (VDC) for 100 s to piezoelectric valve. This paper describes in detail the design and implementation of the various vacuum subsystems including relevant experimental results.