The geology and ore deposits of the Quiruvilca district, Peru

The Quiruvilca copper-lead-zinc district is in the Department of La Libertad in north-central Peru. The only large mine in this area is the Quiruvilca mine, owned and operated by the Northern Peru Mining and Smelting Co. The mine lies in bedded andesitic and basaltic volcanics, which have been intruded by a small plug of andesite. Numerous dikes and breccia pipes cut rocks surrounding the small plug. To the west of the Quiruvilca mine are four dacite plugs enclosed by sandstone, and 7 kilometers to the east slightly metamorphosed Cretaceous sediments crop out. The ore deposits of the district are mesothermal and epithermal and were formed by fissure filling. Mineralization followed a pre-existing set of tension and shear fractures and the veins form a well-defined oblique grid pattern. Only a few of the many veins in the area are productive. The wider ones, which average a meter in width, are being exploited. On the basis of mineralogy, the mineralized area can be divided into four distinct zones. From the center outward these zones are: 1) the Enargite zone, 2) the Transition zone, 3) the Lead-Zinc zone, and 4) the Stibnite zone

High temperature measurement of water vapor absorption

An investigation was undertaken to measure the absorption coefficient, at a wavelength of 10.6 microns, for mixtures of water vapor and a diluent gas at high temperature and pressure. The experimental concept was to create the desired conditions of temperature and pressure in a laser absorption wave, similar to that which would be created in a laser propulsion system. A simplified numerical model was developed to predict the characteristics of the absorption wave and to estimate the laser intensity threshold for initiation. A non-intrusive method for temperature measurement utilizing optical laser-beam deflection (OLD) and optical spark breakdown produced by an excimer laser, was thoroughly investigated and found suitable for the non-equilibrium conditions expected in the wave. Experiments were performed to verify the temperature measurement technique, to screen possible materials for surface initiation of the laser absorption wave and to attempt to initiate an absorption wave using the 1.5 kW carbon dioxide laser. The OLD technique was proven for air and for argon, but spark breakdown could not be produced in helium. It was not possible to initiate a laser absorption wave in mixtures of water and helium or water and argon using the 1.5 kW laser, a result which was consistent with the model prediction

Catalogue of the Living Collection of the Iowa State University Botany Department Greenhouses

The Botany Department greenhouses at Iowa State University are a rooftop facility including 17 separate houses, divided into three temperature zones. Some illuminated houses are provided to encourage good plant growth during the winter. One greenhouse is operated as a short-day facility and provided with curtained chambers for short days. Summer cooling of the greenhouses is effected by evaporative coolers. The living teaching and research collections include over 800 plane taxa, ranging from bryophytes to orchids and composites. Propagation materials, as available, may be provided to other educational institutions for teaching or research

Micromagnetic modeling of the heat-assisted switching process in high anisotropy FePt granular thin films

The dynamic process of assisted magnetic switchings has been simulated to investigate the associated physics. The model uses a Voronoi construction to determine the physical structure of the nanogranular thin film recording media, the Landau-Lifshitz-Bloch equation is solved to evolve the magnetic system in time. The reduction of the magnetization is determined over a range of peak system temperatures and for a number of anisotropy values. The results show that the heat-assisted magnetic recording process is not simply magnetization reversal over a thermally reduced energy barrier. To achieve full magnetization reversal (for all anisotropies investigated), an applied field strength of at least 6 kOe is required and the peak system temperature must reach at least the Curie point (T c). When heated to T c, the magnetization associated with each grain is destroyed, which invokes the non-precessional linear reversal mode. Reversing the magnetization through this linear reversal mode is favorable, as the reversal time is two orders of magnitude smaller than that associated with precession. Under these conditions, as the temperature decreases to ambient, the magnetization recovers in the direction of the applied field, completing the reversal process. Also, the model produces results that are consistent with the concept of thermal writability; when heating the media to T c, the smaller grains require a larger field strength to reverse the magnetization

Human Visual Search as a Deep Reinforcement Learning Solution to a POMDP

When people search for a target in a novel image they oftenmake use of eye movements to bring the relatively high acuityfovea to bear on areas of interest. The strategies that controlthese eye movements for visual search have been of substantialscientific interest. In the current article we report a new com-putational model that shows how strategies for visual searchare an emergent consequence of perceptual/motor constraintsand approximately optimal strategies. The model solves a Par-tially Observable Markov Decision Process (POMDP) usingdeep Q-learning to acquire strategies that optimise the trade-off between speed and accuracy. Results are reported for theDistractor-ratio task

Ultra-fast aqueous polymerisation of acrylamides by high power visible light direct photoactivation RAFT polymerisation

The effect of visible LED power (λmax = 402 nm, 451 nm) on kinetics and control of direct photoactivation RAFT polymerisations of acrylamide and dimethylacrylamide are investigated. By increasing power supplied to the LEDs from 6 to 208 W, the polymerisation time required to reach >85% conversion is reduced from 12 hours to 11 minutes for acrylamide. Similar conversions are shown to be obtainable in 5 minutes for dimethylacrylamide, all without any exogenous photoinitiator or catalyst. This increase in polymerisation rate is attributed to an increase in both photon flux and a coincident increase in polymerisation temperature at higher light intensities. With both 402 nm and 451 nm LEDs exciting the same n → π* electronic transition, little difference in rate of polymerisation is seen between the two light sources. Minimal reduction in polymerisation control is observed at high irradiation intensity for acrylamide, while an increased production of low molecular weight dead chains is observed for dimethylacrylamide. This is shown to be mitigated by controlling the polymerisation temperature to 17 °C which caused both a reduction in low molecular weight tailing and an increased polymerisation time. Visible light direct photoactivation RAFT is also shown to have application in the synthesis of ultra-high molecular weight acrylamide polymers (Mn > 1 000 000 g mol−1)

Cleavage of macromolecular RAFT chain transfer agents by sodium azide during characterization by aqueous GPC

Accurate and reliable analysis of polymers by GPC is vital in the field of controlled radical polymerisation. Often, water-soluble polymers are analysed by aqueous gel permeation chromatography (GPC) in a solvent containing dilute sodium azide as an anti-microbial agent. Previous reports have shown that sodium azide at high concentration is able to remove terminal CTA groups from polymer chains, producing thiol-terminated polymers. This study demonstrates that GPC sample preparation of RAFT polymers in aqueous solvents containing dilute (200 ppm) sodium azide can cause significant changes in the measured molecular weight distribution. These changes occur within hours of dissolving the polymer sample and are shown to be due to cleavage of the CTA in the polymer chain together with disulfide coupling of the resulting polymeric thiols. The extent to which this occurs is strongly dependent on the CTA attached to the polymer; an almost 10-fold difference in the rate of CTA removal is observed between different RAFT agents. The by-product of the reaction between sodium azide and RAFT polymers is also investigated and shown to be an unstable thiatriazole-functionalised Z group. The thiatriazole then degrades further to form a nitrile-functionalised Z group, N2 and elemental sulfur

Simulations of stressosome activation emphasize allosteric interactions between RsbR and RsbT

<p>Abstract</p> <p>Background</p> <p>The stressosome is a bacterial signalling complex that responds to environmental changes by initiating a protein partner switching cascade, which leads to the release of the alternative sigma factor, σ^B. Stress perception increases the phosphorylation of the stressosome sensor protein, RsbR, and the scaffold protein, RsbS, by the protein kinase, RsbT. Subsequent dissociation of RsbT from the stressosome activates the σ^B cascade. However, the sequence of physical events that occur in the stressosome during signal transduction is insufficiently understood.</p> <p>Results</p> <p>Here, we use computational modelling to correlate the structure of the stressosome with the efficiency of the phosphorylation reactions that occur upon activation by stress. In our model, the phosphorylation of any stressosome protein is dependent upon its nearest neighbours and their phosphorylation status. We compare different hypotheses about stressosome activation and find that only the model representing the allosteric activation of the kinase RsbT, by phosphorylated RsbR, qualitatively reproduces the experimental data.</p> <p>Conclusions</p> <p>Our simulations and the associated analysis of published data support the following hypotheses: (i) a simple Boolean model is capable of reproducing stressosome dynamics, (ii) different stressors induce identical stressosome activation patterns, and we also confirm that (i) phosphorylated RsbR activates RsbT, and (ii) the main purpose of RsbX is to dephosphorylate RsbS-P.</p