DC magnetization studies in Nb/Fe superconducting multilayers

The behavior of superconducting transition temperature T_C in superconducting/ferromagnetic (S/F) multilayers as a function of different layer thicknesses and for varying magnetic moment μ_B of the F layer atoms is studied. Multilayer structures consist of five bilayers of constant superconducting Nb layer thickness of 400 Å and Fe of 6 and 24 Å each. The analysis of the magnetization data revealed that for t_Fe=6 Å, the Fe layer is non-magnetic. The interpretation of the observed T_C behavior is attributed to the change of the interaction of the cooper pairs with this layer at the onset of ferromagnetism for t_Fe=6 Å. The hysteresis curve recorded under isothermal conditions at 4.5 K for [Nb (400 Å)/Fe (6 Å)]₅ multilayers shows the usual M–H hysteresis behavior which is typical of a hard type-II superconductor exhibiting an irreversibility field H_irr of 3.5 kOe with substantial pinning at lower field. In addition, [Nb(400 Å)/Fe(6 Å)]₅ multilayer displays anomalous behavior in the form of paramagnetic peak in the superconducting state just below the transition temperature T_C=6.25 K.     

Application of a hot-melt granulation process to enhance fenofibrate solid dose manufacturing

Evaluation of hot-melt granulation of fenofibrate and croscarmellose sodium and its cooling time for the molten mass in a ratio of 55:45 was conducted to assess the manufacturing process capability to produce an acceptable granulation which flows well on Korsch PH300 tablet compression machine. The formation of the drug-polymer eutectic mixture was investigated by differential scanning calorimetry, scanning electron microscopy and X-ray powder diffraction. The physical properties of the hot-melt was determined by examining the milled blocks after solidification and milling after cooling periods of 10, 20 and 30 d. The milled material was assessed for the effect of hold time of the blend on the solid dose compression characteristics. The impact of cooling on the processing of the blocks was assessed after 10, 20 and 30 d of cooling. The study suggests that after the hot-melt formed the fenofibrate crystallized independently and a solid solution with croscarmellose sodium was not formed. The age of the blocks determined the hardness of the crystals, changing the processing nature of the granules with respect to compression and powder flow characteristics. The blocks processed after 20 d and beyond produced granules with a characteristic suitable for holding the blend for 14 d in the bin with no impact on flow properties and compressibility of the blend. There was no chipping, capping, sticking or picking observed and a higher compression speed was achieved.     

Optimization of microstructure development: application to hot metal extrusion

A new process design method for controlling microstructure development during hot metal deformation processes is presented. This approach is based on modern control theory and involves state- space models for describing the material behavior and the mechanics of the process. The challenge of effectively controlling the values and distribution of important microstructural features can now be systematically formulated and solved in terms of an optimal control problem. This method has been applied to the optimization of grain size and certain process parameters such as die geometry profile and ram velocity during extrusion of plain carbon steel. Various case studies have been investigated, and experimental results show good agreement with those predicted in the design stage.     

State-space representation and optimal control of non-linear material deformation using the finite element method

A state-space model for representing the non-linear material deformation and an optimal control scheme for obtaining desired process conditions in the deforming material are presented in this paper. The formulation is general for various metal-forming processes including forging and extrusion operations. The state variables selected in the formulation are the die/billet contact nodal velocities and the nodal velocities of the critical finite elements of the billet. The control input is the ram velocity, which is determined by using the linear quadratic regulator (LQR) theory to maintain desired strain rates within the selected finite elements. The influence of an optimally designed ram velocity on the deforming material is studied using performance measures. This paper includes the development of the state-space model from non-linear finite element formulation, optimal control strategy and numerical example cases with discussions.     

Transport and Entrapment of Particles in Steel Continuous Casting

A particle-capture model based on local force balances has been developed, implemented into computational models of turbulent fluid flow and particle transport, and applied to simulate the entrapment of slag inclusions and bubbles during the continuous casting of steel slabs. Turbulent flow of molten steel is computed in the nozzle and mold using transient computational fluid flow models, both with and without the effects of argon gas injection. Next, the transport and capture of many particles are simulated using a Lagrangian approach. Particles touching the dendritic interface may be pushed away, dragged away by the transverse flow, or captured into the solidifying shell according to the results of a local balance of ten different forces. This criterion was validated by reproducing experimental results in two different systems. The implications of this criterion are discussed quantitatively. Finally, the fluid flow/particle transport model results and capture criterion are applied together to predict the entrapment distributions of different sized particles in a typical slab caster. More large particles are safely removed than small ones, but the entrapment rate into the solidifying shell as defects is still very high.