Simplified Design Model for an Ion Exclusion Column

A simplified design model for a chromatographic ion exclusion column is developed in which the flxed bed of resin is dividl~d into a number of perfectly mixed equilibrium stages and the liquid Aow rate is constant. The model is represented by the following dimensionless differential equation which results from the combination of a material balance about the rth stage and a second-degree phase equilibrium relationship: ( 1 /h}(f, - 1/;,-1l + K (clf,/dT) + M\u3e/;, (df,/dT) = 0, where K and Mare dimensionless groups while 1 /his the number of equilibrium stages. 1/; and T are dimensionless concentration and time, respectively. The numerical solutions of this E~quation for single, square wave inputs are presented for different values of the dimension· less groups, feed volumes, and number of stages. The resulting calculated elution curves and experimentally determined curves are compared. Design applications are discussed

Exploring agroecological practices in Canada

Non-Peer Reviewe

mut-7 of C. elegans, Required for Transposon Silencing and RNA Interference, Is a Homolog of Werner Syndrome Helicase and RNaseD

AbstractWhile all known natural isolates of C. elegans contain multiple copies of the Tc1 transposon, which are active in the soma, Tc1 transposition is fully silenced in the germline of many strains. We mutagenized one such silenced strain and isolated mutants in which Tc1 had been activated in the germline (“mutators”). Interestingly, many other transposons of unrelated sequence had also become active. Most of these mutants are resistant to RNA interference (RNAi). We found one of the mutated genes, mut-7, to encode a protein with homology to RNaseD. This provides support for the notion that RNAi works by dsRNA-directed, enzymatic RNA degradation. We propose a model in which MUT-7, guided by transposon-derived dsRNA, represses transposition by degrading transposon-specific messengers, thus preventing transposase production and transposition

Assessment of performance of turbo-alternators at the Jebba Hydroelectric Power Station in Nigeria from 2005 – 2014

The Nigerian power system consists of several sets of aged turbo-alternators (TAs) associated with frequent failures and limited installed capacity. This paper presents the results of a study of the performance of the turbo-alternators at one of the most important power stations in the country. The energy conversion characteristic of each of the turbo-alternators is studied by comparing the electrical power output with the total hydro-energy available on a daily basis. Similarly the availability was examined by generating the stochastic sequence of up-times for each TA. The results indicate that energy conversion remained essentially linear throughout the third decade of operations. Availability was however found to vary considerably from year to year with the worst performances occurring in the first five years - an indication of poor state of repair of the machines during that quinquennium. In conclusion, the results indicate that despite their age the TAs have many more years of service left provided maintenance is carried out diligently. Enhanced maintainability will however require both retro-fitting and a forward looking maintainability strategy.Keywords: Hydro–Power, Turbo-Alternators, Energy conversion, Availability, Maintainability, Nigerian Power Syste

Weed survey and management practices used in alfalfa (Medicago sativa) seed fields in 1997

Non-Peer ReviewedA weed survey in alfalfa seed fields, located primarily in northeast Saskatchewan, was conducted in 1997. Following the weed survey, a farm management questionnaire was used to determine the influence of farm management practices on the surveyed weed community. Results from the weed survey and farm management questionnaire were compared to a similar survey and questionnaire conducted in 1989-90. Wild oats and green foxtail were the most abundant annual grass weeds and their relative abundance did not change significantly. Narrow-leaved hawk’s beard generally decreased in relative abundance while perennial weed species usually increased. Herbicides were the most common weed management practice used in Saskatchewan alfalfa seed fields and their use increased compared to the previous questionnaire. Group 1 herbicide use exceeded the recommended frequency to delay the onset of resistance in wild oats and green foxtail in over half of the fields surveyed. The increase in herbicide use may account for the reduction in relative abundance of some annual broad-leaved weed species between 1989-90 and 1997. The decrease in annual weed competition may have allowed some perennial weeds, which are harder to control with herbicides, to increase in relative abundance

Bounds on the diameter of Cayley graphs of the symmetric group

In this paper we are concerned with the conjecture that, for any set of generators S of the symmetric group of degree n, the word length in terms of S of every permutation is bounded above by a polynomial of n. We prove this conjecture for sets of generators containing a permutation fixing at least 37% of the points.Comment: 17 pages, 6 table

direct laser interference patterning of stainless steel by ultrashort pulses for antibacterial surfaces

Abstract Direct Laser Interference Patterning (DLIP) with ultrashort pulses was exploited to produce tailored periodic sub-micrometer structures on stainless steel surfaces to reduce bacterial attachment and retention. Laser pulses with wavelength 1030 nm and duration 8 ps were employed to form a two-beam line interference pattern that was applied in a two-pass strategy to produce fine cross-wise surface structures with a period of ~ 850 nm and a depth of ~ 500 nm. The laser setup and process parameters were selected based on a simple theoretical model of the resulting interference pattern and ablation depth to limit the number of contact points available for bacterial cells with dimensions 500–2000 nm. Periodic 'cones' and 'holes' were produced covering areas of 250 mm2 with the same interference pattern by exploiting the dependence of laser-induced periodic surface structures on polarization. Cones and holes yielded reductions in E. coli retention of 99.8% and 99.4%, respectively, and S. aureus retention of 70.6% and 79.1%, respectively, after two hours immersion in bacterial solution compared to reference samples. Such reductions achieved over large surface areas suggests that this approach is appropriate for upscaling and high throughput production of antibacterial metallic surfaces in the food and healthcare industries

Numerical Analysis of Ca2+ Depletion in the Transverse Tubular System of Mammalian Muscle

AbstractCalcium currents were recorded in contracting and actively shortening mammalian muscle fibers. In order to characterize the influence of extracellular calcium concentration changes in the small unstirred lumina of the transverse tubular system (TTS) on the time course of the slow L-type calcium current (ICa), we have combined experimental measurements of ICa with quantitative numerical simulations of Ca2+ depletion. ICa was recorded both in calcium-buffered and unbuffered external solutions using the two-microelectrode voltage clamp technique (2-MVC) on short murine toe muscle fibers. A simulation program based on a distributed TTS model was used to calculate the effect of ion depletion in the TTS. The experimental data obtained in a solution where ion depletion is suppressed by a high amount of a calcium buffering agent were used as input data for the simulation. The simulation output was then compared with experimental data from the same fiber obtained in unbuffered solution. Taking this approach, we could quantitatively show that the calculated Ca2+ depletion in the transverse tubular system of contracting mammalian muscle fibers significantly affects the time-dependent decline of Ca2+ currents. From our findings, we conclude that ion depletion in the tubular system may be one of the major effects for the ICa decline measured in isotonic physiological solution under voltage clamp conditions

Geometry of Frictionless and Frictional Sphere Packings

We study static packings of frictionless and frictional spheres in three dimensions, obtained via molecular dynamics simulations, in which we vary particle hardness, friction coefficient, and coefficient of restitution. Although frictionless packings of hard-spheres are always isostatic (with six contacts) regardless of construction history and restitution coefficient, frictional packings achieve a multitude of hyperstatic packings that depend on system parameters and construction history. Instead of immediately dropping to four, the coordination number reduces smoothly from $z=6$ as the friction coefficient $\mu$ between two particles is increased.Comment: 6 pages, 9 figures, submitted to Phys. Rev.