Axial mixing in a 15 cm diameter reciprocating plate bubble column

Axial dispersion coefficients (E) in the liquid phase have been measured by unsteady tracer response methods in a 15 cm internal diameter reciprocating plate bubble column, using air and water in countercurrent and cocurrent flow. The operating variables studied were amplitude (0.6–1.27 cm) and frequency (0–5 Hz) of reciprocation, and the superficial velocities of the liquid and gas phases and the spacing between plates. Three types of plate were studied; conventional Karr-type plates with perforation diameters 1.43 cm, plates with smaller (0.635 cm) perforations, and single-perforation (doughnut) plates with internal diameter 7 cm. Measured values of E ranged from about 1 cm²/s to a maximum of 116 cm²/s. In general, the plates with 0.635 cm perforations gave the smallest values of E while the largest values of E were obtained with the doughnut plates, due to vortex ring shedding. The single liquid phase data for the three types of plate were approximately consistent with the correlation of Stevens and Baird (1990). The gas-liquid flow results were interpreted in terms of several different hydrodynamic effects.     

Highly conductive buried n+ layers in lnp:fe created by MeV energy Si,S, and Si/S implantation for application to microwave devices

To obtain highly conductive buried layers in InP:Fe, MeV energy Si, S, and Si/ Simplantations are performed at 200°C. The silicon and sulfer implants gave 85 and 100 percent activation, respectively, for a fluence of 8 × 10¹⁴ cm⁻². The Si/S co-implantation also gave almost 100 percent donor activation for a fluence of 8 × 10¹⁴ cm⁻² of each species. An improved silicon donor activation is observed in the Si/S co-implanted material compared to the material implanted with silicon alone. The peak carrier concentration achieved for the Si/S co-implant is 2 × 10¹⁹ cm³. The lattice damage on the surface side of the profile is effectively removed after rapid thermal annealing. Multiple-energy silicon and sulfur implantations are performed to obtain thick and buried n⁺ layers needed for microwave devices and also hyper-abrupt profiles needed for varactor diodes.     

Message filters for hardening the Linux kernel

Various mechanisms for hardening the Linux kernel (for example, enforcing system call policies, device driver failure recovery, protection against exploitation of bugs in code) are proposed in the literature. The main problem with these mechanisms is that, they require changes in the kernel code leading to the possibility of introducing new bugs and hence increasing the testing time. We propose a message filter model as an extension to object‐oriented wrappers for the Linux kernel, to dynamically provide various filtering capabilities to the kernel. This model works as a comprehensive framework for specifying system call policies, handling device driver faults, protecting the kernel against exploits of bugs in code etc, without modifying the existing kernel code. This considerably reduces the possibility of creating new bugs in the kernel code. We have integrated policies for system call interception and device driver failure handling, into the Linux kernel (2.6.9), using message filter model. Our experiments show that the overhead due to our filter objects is very low, making it a useful mechanism for providing filtering capabilities to the Linux kernel. Copyright © 2010 John Wiley & Sons, Ltd.     

Structural,electrical and magnetic properties of cobalt ferrite with Nd3+ doping

A systematic study on the influence of Nd³⁺ substitution on structural,magnetic and electrical properties of cobalt ferrite nanopowders obtained by sol–gel auto-combustion routewas reported.The formation of spinel phasewas confirmed by X-ray diffraction(XRD)data,and percolation limit ofNd3?into the spinel lattice was also observed.Fourier transform infrared spectroscopy(FTIR)bands observed ≈580 and ≈390 cm^(-1 ) support the presence of Fe³⁺ at A andBsites in the spinel lattice.The variation in microstructure was investigated by scanning electronmicroscopy(SEM),and the average grain size varies from 5.3 to 3.3 lm.The substitution of Nd³⁺ significantly affects the formation of pores and grain size of cobalt ferrite.Room-temperature saturation magnetization and coercivity decrease from 60 to 30 mA·m²·g^-1 and 19.9–17.8 mT,respectively,with Nd³⁺ substitution increasing.These decreases in magnetic properties are explained based on the presence of non-magnetic nature of Nd³⁺ concentration and the dilution of super-exchange interaction in the spinel lattice.The room-temperature direct-current electrical resistivity increases with Nd³⁺ concentration increasing,which is due to the unavailability of Fe²⁺ at octahedral B sites.     

Size Segregation of Nickel Pellets Flowing into a Packed Bed

The size segregation of nickel pellets fed to a packed bed has been measured with mixtures of sizes ranging from less than 1 mm to about 10 mm. The pellet mixture is fed to one side of a rectangular cell and then samples are removed from different lateral positions in the cell for screen analysis. During the feeding process the finer pellets tend to percolate vertically downwards while the larger pellets tend to roll down the sloping surface of the bed. The resulting segregation has been correlated with the size distribution of the feed pellets and the lateral position in the cell, using polynomial equations with three or four adjustable coefficients.     

Rutherford backscattering studies on high-energy Si-implanted InP

High-energy Si-implantations into InP:Fe were examined using Rutherford backscattering (RBS) via channeling measurements. Variable-fluence implantations at 3 MeV and variable-energy implantations for a fluence of 3 x 10¹⁴ cm⁻² were done. A damagestudy on the 3 MeV Si-implanted samples by RBS indicated formation of a continuous, buried amorphous layer for a fluence of ≈5 x 10¹⁴ cm⁻². The quality of the crystal in the region of the amorphous layer was poor after annealing at any temperature (≤900° C), indicating that the crystallization during annealing resulted in either a highly defective material or a polycrystal. For samples with damage below the continuous amorphous level, damage recovery is essentially independent of damage concentration. In the variable-energy-implanted samples, the region of damage moved deeper below the sample surface with increasing energy.     

Fe and Ti implants in In0.52Al0.48As

Single (200 keV) and multiple energy Fe implants in n-type and Ti implants in p-type material were performed in In_0.52Al_0.48As at both room temperature and 200°C. For the Fe implants, the secondary ion mass spectrometry profiles showed a severe out-diffusion for all rapid thermal annealing schemes used, independent of the implantation temperature. The Fe implant peaks observed after annealing, at 0.8Rp, Rp+ΔRp and 2Rp (where Rp and ΔRp are range and straggle, respectively) depth locations in other In-based compounds like InP and InGaAs were not observed here. On the contrary, Ti implants showed only a slight in- and out-diffusion for both room temperature and 200°C implants as in the case of InP and InGaAs. The Rutherford backscattering measurements on the annealed samples implanted at 200°C showed a crystal quality similar to that of the virgin material. The resistivity of all the samples after annealing was higher than 10⁶ Ω-cm.     

Macrosegregation in direct-chill casting of aluminium alloys

Semi-continuous direct-chill (DC) casting holds a prominent position in commercial aluminium alloy processing, especially in production of large sized ingots. Macrosegregation, which is the non-uniform chemical composition over the length scale of a casting, is one of the major defects that occur during this process. The fact that macrosegregation is essentially unaffected by subsequent heat treatment (hence constitutes an irreversible defect) leaves us with little choice but to control it during the casting stage. Despite over a century of research in the phenomenon of macrosegregation in castings and good understanding of underlying mechanisms, the contributions of these mechanisms in the overall macrosegregation picture; and interplay between these mechanisms and the structure formation during solidification are still unclear. This review attempts to fill this gap based on the published data and own results. The following features make this review unique: results of computer simulations are used in order to separate the effects of different macrosegregation mechanisms. The issue of grain refining is specifically discussed in relation to macrosegregation. This report is structured as follows. Macrosegregation as a phenomenon is defined in the Introduction. In “Direct-chill casting – process parameters, solidification and structure patterns” section, direct-chill casting, the role of process parameters and the evolution of structural features in the as-cast billets are described. In “Macrosegregation in direct-chill casting of aluminium alloys” section, macrosegregation mechanisms are elucidated in a historical perspective and the correlation with DC casting process parameters and structural features are made. The issue of how to control macrosegregation in direct-chill casting is also dealt with in the same section. In “Role of grain refining” section, the effect of grain refining on macrosegregation is introduced, the current understanding is described and the contentious issues are outlined. The review is finished with conclusion remarks and outline for the future research.     

Axial mixing and gas holdup with reciprocating doughnut plates

A 15 cm diameter reciprocating plate column has been operated under gas—liquid flow conditions with a stack of doughnut‐type plates having inner and outer diameters of 7.5 cm and 13.0 cm, respectively. Axial dispersion coefficients and gas holdup have been measured. It is found that this type of plate gives lower axial dispersion coefficients than a previously tested doughnut plate having an outer diameter almost the same as the column internal diameter, but the gas retention times are slightly lower.     

Heat transfer in a reciprocating plate column

A pilot‐scale (5.08 cm internal diameter) reciprocating plate column has been modified by the insertion of a brass test section for heat transfer measurements. Heat is supplied to liquid (water or a glucose solution) in the column from an electrical heating tape wound round the brass section, the walls of which contain thermocouples. Reciprocation of the plates in the column results in up to a seven‐fold improvement In heat transfer coefficient, to single phase liquids. Conditions are turbulent with oscillatory Reynolds numbers up to 20000. The effect of plate reciprocation is much less pronounced when the liquids are agitated by a stream of gas bubbles. The single‐phase heat transfer coefficients have been correlated for 5 different types of plates using approaches already available in the literature for turbulent systems in steady flow. The best‐fit oscillatory flow correlation differs slightly from the existing correlations for steady flow.