Cold model study of local liquid holdup in the dropping zone using x-ray

It is important to know and to quantify the liquid holdups both dynamic and static at local levels as it will lead to understand various blast furnace phenomena properly such as slag/metal.gas.solid reactions, gas flow behaviour and interfacial area between the gas/solid/liquid. In the present study, considering the importance of local liquid holdup and non-availability of holdup data in these systems, an attempt has been made to quantify the local holdups in the dropping and around raceway zones in a cold model study using a non-wetting packing for liquid. In order to quantify the liquid holdups at microscopic level, a previously developed technique, X-ray radiography, has been used. It is observed that the liquid flows in preferred paths or channels which carry droplets/rivulets. It has been found that local holdup in some regions of the packed bed is much higher than average at a particular flow rate and this can have important consequences for the correct modelling of such systems.

Relation between Local Structure and Glass Forming Ability of Liquid Alloys

An attempt has been made to describe the glass forming ability (GFA) of liquid alloys, using the concepts of the short range order (SRO) and middle range order (MRO) characterizing the liquid structure.A new approach to obtain good GFA of liquid alloys is based on the following four main factors: (1) formation of new SRO and competitive correlation with two or more kinds of SROs for crystallization, (2) stabilization of dense random packing by interaction between different types of SRO, (3) formation of stable cluster (SC) or middle range order (MRO) by harmonious coupling of SROs, and (4) difference between SRO characterizing the liquid structure and the near-neighbor environment in the corresponding equilibrium crystalline phases. The atomic volume mismatch estimated from the cube of the atomic radius was found to be a close relation with the minimum solute concentration for glass formation. This empirical guideline enables us to provide the optimum solute concentration for good GFA in some ternary alloys. Model structures, denoted by Bernal type and the Chemical Order type, were again tested in the novel description for the glass structure as a function of solute concentration. We illustrated the related energetics of the completion between crystal embryo and different types of SRO. Recent systematic measurements also provide that thermal diffusivity of alloys in the liquid state may be a good indicator of their GFA.

Modified McMurray Inverter with Pulse Forming Network Commutation Circuits

The modified McMurray Inverter with Pulse Forming Network (PFN) has been explained. The current and voltage waveshapes of the PFN commutation ci rcuit have been compared with conventional L-commutation circuit. The design method of PFN has been explained. Advantages of this type of commutation have been discussed. Experimental results are given.

Influence of Tempered Microstructures on the Transformation Behaviour of Cold Deformed and Intercritically Annealed Medium Carbon Low Alloy Steel

This research is focused on understanding the role of microstructural variables and processing parameters in obtaining optimised dual phase structures in medium carbon low alloy steels. Tempered Martensite structures produced at 300, 500, and 650 degrees C, were cold rolled to varied degrees ranging from 20 to 80% deformation. Intercritical annealing was then performed at 740, 760, and 780 degrees C for various time duration ranging from 60 seconds to 60 minutes before quenching in water. The transformation behaviour was studied with the aid of optical microscopy and hardness curves. From the results, it is observed that microstructural condition, deformation, and intercritical temperatures influenced the chronological order of the competing stress relaxation and decomposition phase reactions which interfered with the rate of the expected alpha -> gamma transformation. The three unique transformation trends observed are systematically analyzed. It was also observed that the 300 and 500 degrees C tempered initial microstructures were unsuitable for the production of dual structures with optimized strength characteristics.

Efficacies of multivalent vs monovalent poly(ether imine) dendritic catalysts within a generation in multiple C-C bond forming reactions

Dendrimers are ideal platforms to study multivalent effects due to the presence of uniform end groups at their peripheries. This report concerns with a study of multivalent dendritic catalysts, both within and across dendrimer generations, and their effects to mediate C-C bond forming reactions on multivalent substrates that have two and three acrylate reactive sites. As many as fourteen multivalent dendritic catalysts were prepared using 0-3 generations of poly(propyl ether imine) dendrimers, incorporated with Pd(II) catalytic sites, both within and across the dendrimer generations. C-C Bond forming reactions of these substrates with iodobenzene, mediated by uniform concentration of the metal across all catalysts, showed formation of partially and fully functionalized cinnamates in varying ratios, depending on the extent of clustering of catalytic moieties at the peripheries of dendrimers within a dendrimer generation. In a given generation, higher clustering of catalytic moieties greatly assisted multiple C-C bond formations than presenting the same in lesser number. The studies demonstrate true benefits of clustering catalytic moieties within a dendrimer generation and the beneficial effects applicable to catalysis of substrates presenting more than one reactive center. (C) 2011 Elsevier B.V. All rights reserved.

The omega phase formation during laser cladding and remelting of quasicrystal forming AlCuFe on pure aluminum

We report the formation omega phase in the remelted layers during laser cladding and remelting of quasicrystal forming Al65Cu23.3Fe11.7 alloy on pure aluminum. The omega phase is absent in the clad layers. In the remelted layer, the phase nucleates at the periphery of the primary icosahedral phase particles. A large number of omega phase particles forms enveloping the icosahedral phase growing into aluminum rich melt, which solidify as alpha-Al solid solution. On the other side it develops an interface with aluminum. A detailed transmission electron microscopic analysis shows that omega phase exhibits orientation relationship with icosahedral phase. The composition analysis performed using energy dispersive x-ray analyzer suggests that this phase has composition higher aluminum than the icosahedral phase. The analysis of the available phase diagram information indicates that the present results represent large departure from equilibrium conditions. A possible scenario of the evolution of the omega phase has been suggested.

Characterization of the dynamics of glass-forming liquids from the properties of the potential energy landscape

We develop a framework for understanding the difference between strong and fragile behavior in the dynamics of glass-forming liquids from the properties of the potential energy landscape. Our approach is based on a master equation description of the activated jump dynamics among the local minima of the potential energy (the so-called inherent structures) that characterize the potential energy landscape of the system. We study the dynamics of a small atomic cluster using this description as well as molecular dynamics simulations and demonstrate the usefulness of our approach for this system. Many of the remarkable features of the complex dynamics of glassy systems emerge from the activated dynamics in the potential energy landscape of the atomic cluster. The dynamics of the system exhibits typical characteristics of a strong supercooled liquid when the system is allowed to explore the full configuration space. This behavior arises because the dynamics is dominated by a few lowest-lying minima of the potential energy and the potential energy barriers between these minima. When the system is constrained to explore only a limited region of the potential energy landscape that excludes the basins of attraction of a few lowest-lying minima, the dynamics is found to exhibit the characteristics of a fragile liquid.

Cause and Effect of Feedback: Multiphase Gas in Cluster Cores Heated by AGN Jets

Multiwavelength data indicate that the X-ray-emitting plasma in the cores of galaxy clusters is not cooling catastrophically. To a large extent, cooling is offset by heating due to active galactic nuclei (AGNs) via jets. The cool-core clusters, with cooler/denser plasmas, show multiphase gas and signs of some cooling in their cores. These observations suggest that the cool core is locally thermally unstable while maintaining global thermal equilibrium. Using high-resolution, three-dimensional simulations we study the formation of multiphase gas in cluster cores heated by collimated bipolar AGN jets. Our key conclusion is that spatially extended multiphase filaments form only when the instantaneous ratio of the thermal instability and free-fall timescales (t(TI)/t(ff)) falls below a critical threshold of approximate to 10. When this happens, dense cold gas decouples from the hot intracluster medium (ICM) phase and generates inhomogeneous and spatially extended Ha filaments. These cold gas clumps and filaments ``rain'' down onto the central regions of the core, forming a cold rotating torus and in part feeding the supermassive black hole. Consequently, the self-regulated feedback enhances AGN heating and the core returns to a higher entropy level with t(TI)/t(ff) > 10. Eventually, the core reaches quasi-stable global thermal equilibrium, and cold filaments condense out of the hot ICM whenever t(TI)/t(ff) less than or similar to 10. This occurs despite the fact that the energy from AGN jets is supplied to the core in a highly anisotropic fashion. The effective spatial redistribution of heat is enabled in part by the turbulent motions in the wake of freely falling cold filaments. Increased AGN activity can locally reverse the cold gas flow, launching cold filamentary gas away from the cluster center. Our criterion for the condensation of spatially extended cold gas is in agreement with observations and previous idealized simulations.

Strongly magnetized cold degenerate electron gas: Mass-radius relation of the magnetized white dwarf

We consider a relativistic, degenerate electron gas at zero temperature under the influence of a strong, uniform, static magnetic field, neglecting any form of interactions. Since the density of states for the electrons changes due to the presence of the magnetic field (which gives rise to Landau quantization), the corresponding equation of state also gets modified. In order to investigate the effect of very strong magnetic field, we focus only on systems in which a maximum of either one, two, or three Landau level(s) is/are occupied. This is important since, if a very large number of Landau levels are filled, it implies a very low magnetic field strength which yields back Chandrasekhar's celebrated nonmagnetic results. The maximum number of occupied Landau levels is fixed by the correct choice of two parameters, namely, the magnetic field strength and the maximum Fermi energy of the system. We study the equations of state of these one-level, two-level, and three-level systems and compare them by taking three different maximum Fermi energies. We also find the effect of the strong magnetic field on the mass-radius relation of the underlying star composed of the gas stated above. We obtain an exciting result that it is possible to have an electron-degenerate static star, namely, magnetized white dwarfs, with a mass significantly greater than the Chandrasekhar limit in the range 2.3-2.6M(circle dot), provided it has an appropriate magnetic field strength and central density. In fact, recent observations of peculiar type Ia supernovae-SN 2006gz, SN 2007if, SN 2009dc, SN 2003fg-seem to suggest super-Chandrasekhar-mass white dwarfs with masses up to 2.4-2.8M(circle dot) as their most likely progenitors. Interestingly, our results seem to lie within these observational limits.