The effect of flotation cell shape on deinking behaviour

Studies were undertaken to investigate the deinking behaviour of different shaped deinking cells of the same volume. For comparative purposes, most oprational variables were kept constant, and the same injector was used throughout the study. The position of the injector, however, was varied in some cases to go along with the particular cell shape being studied. Three types of cell shapes were studied, (1) cylindrical with tangential air injection, (2) rectanular with vertical injection, and (3) rectangular with horizontal injection. Eucalyptus/toner slurries and news/mag wastepaper slurries were deinked. Flow patterns in the cells and the corresponding deinking efficiencies were measured. It was found that strong and excessive re-circulatory flows within the cells could under certain conditions be a major factor in reducing brightness lift. Vertical injection into a rectangular cell gave stable flow patterns, non-wavy froth removal and sustained brightness lift for a wide range of feed and airflow rates. Horizontal injection into a similar rectangular shaped cell exhibited quite different characteristics. High brightness lift was possible for certain conditions and not for others. Wavy froth and excessive recirculation flow patterns varied with feed and airflow. The cylindrical cell with tangential injection gave stable circulatory flow and stable froth removal at low flow rates but was unable to deink at high flows

The G Dwarf Problem Exists in Other Galaxies

Stellar population models with abundance distributions determined from the analytic Simple model of chemical evolution fail to match observations of the nuclei of bulge-dominated galaxies in three respects. First, the spectral energy distribution in the mid-ultraviolet range 2000 < lam < 2400 exceeds observation by ~ 0.6 mag. Most of that excess is due to metal-poor main sequence stars. Second, the models do not reproduce metal-sensitive optical absorption features that arise mainly from red giant stars. Third, the strength of a Ca II index sensitive to hot stars does not jibe with the predicted number of A-type horizontal branch stars. The number of metal poor stars in galaxies is at least a factor of two less than predicted by the Simple model, exactly similar to the ``G Dwarf problem'' in the solar cylinder. Observations at larger radii in local group galaxies indicate that the paucity of metal poor stars applies globally, rather than only in the nuclei. Because of the dominance of metal rich stars, primordial galaxies will have a plentiful dust supply early in their star formation history, and thus will probably have weak Lyman-alpha emission, as is apparently observed. We confirm that early-type galaxies cannot have been formed exclusively from mergers of small all-stellar subsystems, a result already established by dynamical simulations. The constraint of peaked abundance distributions will limit future chemical evolution models. It will also make age estimates for the stellar populations in early type galaxies and bulges more secure.Comment: 14 pages, LaTeX includes 3 postscript figures. Uses AAS LaTeX v 4.0 and times.sty. Accepted for publication in the Astronomical Journal. Postscript available at http://shemesh.gsfc.nasa.gov/~dorman/Ben.htm

The coexistence of pressure waves in the operation of quartz-crystal shear-wave sensors

It is demonstrated that an AT-cut quartz crystal driven in the thickness-shear-wave mode and typically used as a sensor to monitor the viscoelastic shear-wave properties of a fluid also produce longitudinal pressure waves. Unlike the shear wave, these waves are capable of long-range propagation through the fluid and of reflection at its boundaries, notably at an outer fluid–air interface. They introduce a component into the measured electrical impedance and resonance frequency shift of the crystal, which reflects the setting up of cyclic pressure-wave resonances in the fluid. This has important implications for the practical employment of these crystal as sensors. Under appropriate conditions, as demonstrated for water and n-octane, it is possible to determine the propagating properties of sound waves in a fluid simultaneously with the viscoelastic shear-wave properties. These experiments are supported by an analysis of the appropriate hydrodynamic equations for waves in the crystal–fluid system, which predicts electrical characteristics in close agreement with those found experimentally

Sudan Grass, Soybeans, and Other Supplementary Hay and Pasture Crops

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Innervation and Muscle Cell Infiltration of Plastic Compressed Collagen Constructs

Abstract not available

Selecting Windows

Covers double-hung, horizontal sliding, casement, awning, jalousie, top-hinged, and fixed windows. Includes patio doors and skylights

Asteroid Cooling Rates Indicated by K-Feldspar Exsolution Textures in H4 Ordinary Chondrites

Undisturbed thermal metamorphism in ordinary chondrite (OC) asteroids, produced through the radioactive decay of 26Al, is expected to result in an onion-shell-like structure. In such a structure, the inner layers of the asteroid experience more extensive thermal metamorphism, as represented by higher petrologic type, than the exterior layers. Furthermore, cooling rates are expected to be slower for OCs of high petrologic type than those of low petrologic type. However, cooling rates determined using metallographic methods and pyroxene diffusion are inconsistent with onion-shell-style cooling and have resulted in new models. These models argue for the disruption of the asteroid after peak metamorphism followed by reaccretion into a rubble pile. Improved constraints on cooling rates would provide a better understanding of the timing and scale of disruptive events. Feldspar microtextures are another tool that can be used to determine asteroid cooling rates. In OC chondrules, plagioclase is present as either a primary phase, or a secondary phase forming from the crystallization of mesostasis glass through petrologic type 4, followed by chemical and textural equilibration. Potas-sium feldspar is observed in petrologic types 3.6-6, as either patches or lamellae exsolved from albite in a perthite texture, often near pores or fractures. Exsolution occurs most commonly, and most extensively, in petrologic type 4. Because the feldspar exsolution wavelength is related to the rate at which grains cooled from the solvus temperature, determined from the minerals bulk composition, the chondrite cooling rate can be measured from regions of exsolution. We have previously reported the perthite exsolution cooling rate of Avanhandava, an H4 chondrite, to be 1 C per 1-4 months over a temperature interval of 765-670 C. A peristerite exsolution texture was also present in the Na-rich lamellae for which we estimated a cooling rate of 1 C in 103-104 years from 570-540 C. Overall, the cooling rates determined from Avanhandava are consistent with pyroxene diffusion (fast cooling at high temperatures) and metallographic rates (slow cooling at low temperatures), hence with the rubble pile model of disruption and reaccretion. Here, we characterize feldspar microtextures in four additional H4 chondrites to test the consistency of feldspar cooling rates across a range of samples. We show that all H4s are similar and support rubble pile models

On the function of somatic and dendritic SK channels in cortical pyramidal neurons

Small-conductance Calcium-activated Potassium (SK) channels play an important role in regulating neuronal excitability. Recent evidence indicates SK channels regulate NMDA receptor activation in dendritic spines and play a role in regulating synaptic plasticity. Using confocal fluorescent Calcium imaging, we investigate the activation of SK channels in spines and dendrites of layer 5 (L5) cortical pyramidal neurons during action potentials (APs). The inhibition of SK channels with apamin results in a location-dependent increase in Calcium influx into dendrites and spines during backpropagating APs (average increase ~40%). This effect was occluded by block of R-type voltage-dependent calcium channels (VDCCs), but not by inhibition of N- or P/Q-type VDCCs, or block of calcium release from intracellular stores. These results indicate that dendritic SK channels regulate Calcium influx into dendrites and spines presumably by regulating the waveform of the backpropagating action potential. In addition, they show that SK channel activation is specifically controlled by Calcium influx through R-type VDCCs, complimenting previous work indicating that SK channels are located within 25-50 nm of their calcium source, in a Calcium nanodomain. SK channels have also long been known to contribute to the medium afterhyperpolarization (mAHP) at the soma for many neuronal types, including L5 pyramidal neurons, where they regulate action potential output gain and the propensity for burst firing. During the experiments using confocal Calcium imaging we noticed that the Calcium indicator used, Oregon Green BAPTA-1, which acts as a fast calcium buffer, blocked the SK mAHP. Subsequent experiments using low concentrations of the slow calcium buffer EGTA (1 mM) produced the same result, suggesting that somatic SK channels are not tightly co-localised with their calcium source. We estimate a coupling distance of greater than 150 nm, suggesting that calcium signaling between somatic SK channels and their calcium source occurs within a microdomain. Consistent with this idea, we show that all known subtypes of VDCCs except R-type were Calcium sources for the apamin-sensitive mAHP at the soma. Spike timing dependent plasticity (STDP) is a form of plasticity whereby the strength of connections between neurons in the brain are modulated following the pairing of postsynaptic APs with presynaptic activity within a narrow time window. The influx of calcium during EPSP-AP pairing is crucial to the induction of STDP. Given we show that dendritic SK channels can be activated by and influence calcium influx during bAPs, we investigated whether dendritic SK channel activation by bAPs can regulate STDP. We show that SK channels activated by bAPs significantly suppress EPSPs at negative timings for L5-L5 synaptic connections by dampening the activation of NMDA receptors. SK channels also suppressed EPSPs in layer 2/3 and hippocampal CA1 pyramidal neurons. Finally, we show that the induction of both LTP and LTD for L5-L5 synaptic connections is constrained by SK channel activation, presumably through their capacity to limit dendritic calcium influx during EPSP-AP pairing. In conclusion, these findings provide new insights into the function of SK channels and the multifaceted role calcium plays in neuronal function