Flowsheet Options for Cobalt Recovery in African Copper–cobalt Hydrometallurgy Circuits

The price of cobalt has increased by some 450% in the past two years, mainly due to increasing demand for lithium–ion batteries. With an official 2017 production of 64 kt, the Democratic Republic of Congo produces more than half of the world’s cobalt. African Copperbelt operations have traditionally focused on copper production; however, it has now become imperative to also consider cobalt recovery from these ores. A plethora of processing routes is possible. Most hydrometallurgical flowsheets recover cobalt from the raffinate of the low-grade copper solvent-extraction circuit. Downstream purification processes include sequential precipitation with a variety of reagents, solvent extraction, and ion exchange. Product choices include hydroxide, carbonate, sulfate, and metal cathode. This study assesses technical and economic advantages and limitations of various approaches to the hydrometallurgical processing of cobalt in an African context.     

The extended quadratic residue code is the only (48,24,12) self-dual doubly-even code

An extremal self-dual doubly-even binary (n,k,d) code has a minimum weight d=4/spl lfloor/n/24/spl rfloor/+4. Of such codes with length divisible by 24, the Golay code is the only (24,12,8) code, the extended quadratic residue code is the only known (48,24,12) code, and there is no known (72,36,16) code. One may partition the search for a (48,24,12) self-dual doubly-even code into three cases. A previous search assuming one of the cases found only the extended quadratic residue code. We examine the remaining two cases. Separate searches assuming each of the remaining cases found no codes and thus the extended quadratic residue code is the only doubly-even self-dual (48,24,12) code.     

Non-equilibrium particle motion in the vicinity of a single blade

The motion of sand particles close to a single moving blade was investigated using Positron Emission Particle Tracking (PEPT) during the period in which the free bed surface profile was evolving to an equilibrium shape. The area affected by the blade was divided into active and inactive regions and these were analysed separately. The characteristic heart-shape of the active region in the plan view was determined. An approximately 10-particle-diameter wide velocity transition zone is found between the two regions. While the tracer particle is in the inactive region moving away from the blade, the time dependence of the axial displacement is well described by a logarithmic relationship. The probability of particle movement towards the centre of the blade was quantified using a “central tendency” index. The calculated central tendency shows maxima at each side of the blade. The separation of the two maxima, which indicates the width of the active region, increases with fill level but is independent of rotational speed.     

Diffusion bonding of ferritic oxide dispersion strengthened alloys to austenitic superalloys

The superior high temperature mechanical strength and oxidation resistance of ferritic oxide dispersion strengthened (ODS) tubular alloys are compromised by the difficulties encountered in joining. Conventional fusion welding techniques generate a weld fusion zone which is devoid of the mechanical strength exhibited by the base material. Therefore, more sophisticated solid state joining techniques, such as diffusion bonding, must be employed when joining ODS materials. This paper describes a series of solid state diffusion bonding experiments carried out between two tubular ferritic ODS alloys and two high temperature austenitic alloys. Careful control of bonding conditions produced pressure retaining joints between one of the tubular ODS alloys and both austenitic alloys. The successful joint design was incorporated into the manufacture of a tubular creep component, which enabled a series of internally pressurized creep tests to be carried out. The microstructure developed at the bond interface of each of the four separate material couples is described and the high temperature performance of the pressure retaining joints is discussed.     

Role of Ponded Turbidity Currents in Reservoir Trap Efficiency

The capacity to store water in a reservoir declines as it traps sediment. A river entering a reservoir forms a prograding delta. Coarse sediment (e.g., sand) deposits in the fluvial topset and avalanching foreset of the delta, and is typically trapped with an efficiency near 100%. The trap efficiency of fine sediment (e.g., mud), on the other hand, may be below 100%, because some of this sediment may pass out of the reservoir without settling out. Here, a model of trap efficiency of mud is developed in terms of the mechanics of a turbidity current that plunges on the foreset. The dam causes a sustained turbidity current to reflect and form a muddy pond bounded upstream by a hydraulic jump. If the interface of this muddy pond rises above any vent or overflow point at the dam, the trap efficiency of mud drops below 100%. A model of the coevolution of topset, foreset, and bottomset in a reservoir that captures the dynamics of the internal muddy pond is presented. Numerical implementation, comparison against an experiment, and application to a field-scale case provide the basis for a physical understanding of the processes that determine reservoir trap efficiency.     

Transconductance and mobility of Si:B delta MOSFETs

Delta-doped MOSFETs have been fabricated in MBE-grown silicon using for the first time boron as the dopant within the delta layer. Current-voltage characteristics have been measured, and secondary ion mass spectrometry (SIMS) is used to confirm the location of the delta layer and the extent of layer broadening by diffusion during processing. Precise threshold voltages of the devices are difficult to determine since the devices (which all operate in depletion mode) take several volts to switch off. Transconductances of the devices have been measured, and it is shown how analysis of these results can yield estimates of the carrier mobility for transport along the delta layers despite the uncertainty in the threshold voltage. A clear transition is observed in the results which is attributed to the formation of a parasitic surface-channel field-effect transistor, providing conclusive evidence that the devices are conducting along a delta channel for part of the measured range of applied gate biases     

The Silicon Backplane Design for an LCOS Polarization-Insensitive Phase Hologram SLM

Polarization-insensitivity is achieved in a reflective spatial light modulator by laying a quarter-wave plate (QWP) at the incident wavelength directly over the mirror pixels of a silicon backplane, and forming a nematic Freedrickcz cell over the QWP to modulate the reflected phase. To achieve the highest drive voltage from the available silicon process, a switched voltage common front electrode design is described, with variable amplitude square wave drive to the pixels to maintain constant root-mean-square drive and minimize phase fluctuations during the dc balance refresh cycle. The silicon has been fabricated and liquid-crystal-on-silicon cells both with and without the QWP assembled; applications include optically transparent switches for optical networks, beam steering for add-drop multiplexers for wavelength-division-multiplexing telecommunications, television multicast, and holographic projection.     

Glyconanoparticle-DNA interactions: an atomic force microscopy study.

Glyconanoparticles which present carbohydrate and amino groups motifs at their surface were produced. These particles were highly stable and soluble in aqueous solutions. The presence of the carbohydrate groups also allowed the inclusion of more strongly binding groups, without affecting solubility. The binding of a model DNA, plasmid by these nanoparticles was studied by atomic force microscopy, transmission electron microscopy, and gel electrophoresis. Significant differences between the nanoparticles based on their affinities for the DNA were found, with implications for their potential use as nonviral gene delivery agents.     

Periodic dynamics of coupled cell networks I: rigid patterns of synchrony and phase relations

It has recently been proved by Golubitsky and coworkers that in any network of coupled dynamical systems, the possible 'rigid' patterns of synchrony of hyperbolic equilibria are determined by purely combinatorial properties of the network, known as 'balanced equivalence relations'. A pattern is 'rigid' if it persists under small 'admissible' perturbations of the differential equation — ones that respect the network structure. We discuss a natural generalisation of these ideas to time-periodic states, and motivate two basic conjectures, the Rigid Synchrony Conjecture and the Rigid Phase Conjecture. These conjectures state that for rigid hyperbolic time-periodic patterns, cells with synchronous dynamics must have synchronous input cells, and cells with phase-related dynamics must have input cells that have the same phase relations. We provide evidence supporting the two conjectures, by proving them for a special class of periodic orbits, which we call 'tame', under strong assumptions on the network architecture and the symmetries of the periodic state. The discussion takes place in the formal setting of coupled cell networks. We prove that rigid patterns of synchrony are balanced, together with the analogous result for rigid patterns of phase relations. The assumption on the network architecture simplifies the geometry of admissible vector fields, while tameness rules out patterns with non-trivial local or multilocal symmetry. The main idea is to perturb an admissible vector field in a way that retains sufficient control over the associated perturbed periodic orbit. We present two techniques for constructing these perturbations, both using a general theorem on groupoid-symmetrisation of vector fields, which has independent interest. In particular we introduce a method of 'patching' that makes local changes to an admissible vector field. Having established these results for all-to-all coupled networks and tame periodic orbits we prove more general versions that require these assumptions only on a suitable quotient network. These conditions are weaker and encompass a larger class of networks and periodic orbits. We give an example to show that rigidity cannot be relaxed to hyperbolicity. We also prove, without any technical assumptions, that rigidly synchronous or phase-related cells must be input-isomorphic, a necessary precondition for the two conjectures to hold.