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.     

Methyltransferase Contingencies in the Pathway of Everninomicin D Antibiotics and Analogues

Everninomicins are orthoester oligosaccharide antibiotics with potent activity against multidrug-resistant bacterial pathogens. Everninomicins act by disrupting ribosomal assembly in a distinct region in comparison to clinically prescribed drugs. We employed microporous intergeneric conjugation with Escherichia coli to manipulate Micromonospora for targeted gene-replacement studies of multiple putative methyltransferases across the octasaccharide scaffold of everninomicin effecting the A₁, C, F, and H rings. Analyses of gene-replacement and genetic complementation mutants established the mutability of the everninomicin scaffold through the generation of 12 previously unreported analogues and, together with previous results, permitted assignment of the ten methyltransferases required for everninomicin biosynthesis. The in vitro activity of A₁- and H-ring-modifying methyltransferases demonstrated the ability to catalyze late-stage modification of the scaffold on an A₁-ring phenol and H-ring C-4’ hydroxy moiety. Together these results establish the potential of the everninomicin scaffold for modification through mutagenesis and in vitro modification of advanced biosynthetic intermediates.     

Scattering and absorption by thin metal wires in rectangularwaveguide-FDTD simulation and physical experiments

The high-frequency internal impedance model of a round ohmic conductor is incorporated into the subcell thin-wire formulation of the finite-difference time-domain method to model the microwave properties of metal wires. For magnetic metals, such as steel, an effective conductivity is introduced to account for the increase in ohmic loss due to the high-frequency permeability. Physical experiments with half-wave resonant copper- and steel-wire inclusions, supported by a dielectric slab in a standard S-band rectangular waveguide, support the formulation     

Predicting postlaryngectomy voice outcome in an era of primary tracheoesophageal fistulization: a retrospective evaluation

The aim of this study was to investigate the effect of the absence of elongate spermatids (ES) from the rat seminiferous epithelium on the quantitative secretion and synthesis of the three major Sertoli cell secretory proteins--SGP-1, SGP-2 and CP-2. Seminiferous tubules (ST) were isolated (a) from normal 28-day-old rats, in which the most mature germ cell type is the round spermatid, (b) from normal adult rats at stages IX-XIV of the spermatogenic cycle, i.e. after spermiation, or at stages I-V and VI-VIII, when ES are still attached to the Sertoli cell, and (c) at stages VI-VIII from normal adult rats and from rats treated with methoxyacetic acid (MAA) in order to specifically deplete ES at these stages. Two-dimensional SDS PAGE combined with computerized image analysis was used to analyse 35S-methionine-labelled intracellular and secreted proteins. In the case of SGP-1 and SGP-2, almost all of the protein synthesized by ST was secreted. The total amount of both SGP-1 and CP-2 secreted by unstaged ST from immature rats was significantly lower than that secreted by unstaged ST from adult rats. The total amount of SGP-1 and CP-2 secreted by adult ST at stages IX-XIV of the spermatogenic cycle also declined dramatically compared to ST at earlier stages. The proportion of the total CP-2 synthesized by ST which was secreted also declined in all situations in which ES were absent from the seminiferous epithelium. The synthesis of only SGP-2 was changed by ES depletion from ST at stages VI-VIII, which was almost doubled compared to synthesis of this protein by ST from control rats. Our results suggest strongly that the secretion of SGP-1 and SGP-2 is via the constitutive pathway, and that regulation of these two proteins by ES is at the level of protein synthesis. In contrast, the regulation of CP-2 by ES is predominantly at the level of secretion, suggesting that this protein is secreted via a regulated pathway. Our findings add to the evidence showing that ES play a major role in the regulation of Sertoli cell function.     

ATMOSPHERIC DEPOSITION OF CHEMICAL SPECIES TO POLAR SNOW

Particles and gases can deposit from the atmosphere to polar snow by several mechanisms. Dry deposition can be considered to consist of three steps: aerodynamic transport from the free atmosphere to the viscous sublayer near the surface, boundary layer transport across the sublayer, and interactions with the surface. The particle dry deposition mass flux is dominated by the largest particles present in a size distribution. Wet deposition includes in-cloud and below-cloud scavenging, where the former refers to uptake of particles during nucleation of cloudwater as well as scavenging of particles and gases by existing droplets and ice crystals. Of all the wet deposition mechanisms, nucleation scavenging is often the most important mechanism for particles in the polar regions. Finally, incorporation of particles and gases into fog droplets and subsequent settling of the fog to the snow surface can be an important removal process in regions of frequent fog. For Summit, Greenland, the total deposition of MSA, SO₄^2-, Na⁺, K⁺, and Ca²⁺ during May 24-July 13, 1993 was dominated by wet deposition: this mechanism accounted for an average of 62% of the total deposition for these species. Fog and dry deposition accounted for 21% and 17% of the total, respectively. These results suggest that all three mechanisms may need to be considered when estimating total deposition of certain chemical species to polar snow.     

Integrated carbon nanotube field emission differential amplifier: Modeling and measurement of the common-mode rejection ratio

A novel integrated vacuum field emission (VFE) differential amplifier (diff-amp) utilizing carbon nanotube (CNT) emitters has been developed. A dual-mask microfabrication process was employed to achieve a VFE diff-amp by integrating identical CNT VFE transistors with built-in split gates and integrated anodes. The identical pair of triode amplifiers was well-matched in their device characteristics. The measured ac small-signal characteristics of the diff-amp showed a common-mode-rejection ratio (CMRR) of ~ 320 (~ 50 dB). The proposed analytical model of the CMRR was verified to be in good agreement with the experimental data. The successful implementation of the CNT diff-amp demonstrates a new way to achieve temperature and radiation tolerant VFE integrated microelectronics.     

Relationships between urbanization and the oak resource of the Minneapolis/St. Paul Metropolitan area from 1991 to 1998

Urbanization was associated with loss and transformation of the oak forest in the Twin Cities (Minneapolis and St. Paul) metropolitan area (TCMA) over a recent 7-year interval. Between 1991 and 1998, urbanization increased based on several indicators: population density, area of developed land, and area of impervious surface—total impervious area and area within three classes of increasing degree of imperviousness (protected, affected, and degraded). We quantified relationships between changes in urbanization and changes in several parameters describing the oak forest at the scale of ecological subsection. Increased total and affected impervious area were strongly correlated with decreased area of oak forest when changes of the urbanization indicators and oak were expressed as percentages of the subsection area. Relationships were reversed when changes were expressed as percentages of the 1991 values. Increased population density was strongly correlated with increased loss in numbers and increased isolation of oak patches, but weakly correlated with loss of oak forest area. This is the first study to quantify relationships between changes in urbanization and changes in a specific forest cover type. Our results demonstrate complexities of urbanization impacts on a metropolitan forest resource, and highlight the importance of selected variables, spatial and temporal scales, and expressions of change when quantifying these relationships.