Analytical Solution for facilitated transport across a membrane

An analytical expression for the facilitation factor of component A across a liquid membrane is derived in case of an instantaneous reaction A(g)+B(l)AB(l) inside the liquid membrane. The present expression has been derived based on the analytical results of Olander (A.I.Ch.E. J. 6(2) (1960) 233) obtained for the enhancement factor for G–L systems with bulk. The analytical expression for the facilitation factor allows for arbitrary diffusivities of all species involved and does not contain any simplification or approximations. The facilitation factor starts from the value of unity, goes through a maximum and then reduces back to unity as the equilibrium constant is increased. The maximum facilitation factor occurs at higher values of the equilibrium constant as the ratio of the permeate-complex over carrier diffusivity is reduced whereas the maximum facilitation factor occurs at the same value of the equilibrium constant for all values of DA/DB (ratio of the permeate over carrier diffusivity). A similar behavior is seen for the flux of A as a function of the equilibrium constant. The facilitation factor remains constant with changes in the film thickness whereas the flux of A reduces with an increase in the thickness of the film. A linear increase of the facilitation factor and flux of A are seen with increasing initial carrier concentration

Multiplicity of Solutions for a Reactive Variable Viscous Couette Flow under Arrhenius Kinetics

This paper investigates the properties of solution for a reactive temperature dependent viscous Couette flow through parallel plates with non-uniform temperature. We showed that the problem has two distinct solutions and the solution breaks down for some values of the Frank-kameneskii parameter. Effect of various parameters in the model are presented and discussed. Keywords: Arrhenius kinetics, Couette flow, variable viscosity, Bratu-type equatio

Numerical Simulation of Pavement Life Deterioration: Tree-Roots’ Effects

Conference ProceedingsFlexible pavement is usually designed to last for at least 20 years, however sometimes the first failure is formed after the first year of use. This failure has been associated with; overloading of the structure, use of poor materials, drainage problem and inadequate pavement thickness, and poor compaction; without considering presence of tree-root in pavement layers. However, with the numerous advantages of finite element model (FEM) in designing pavement structure and coupled with the fact that it’s a non-destructive tool, it makes its use sustainable. Therefore, this study focuses on investigating the impact of tree-roots on design life of flexible pavement using FEM. Results of the study show that tree-roots within any layer, and most especially within the subgrade layer, have a great effect on its bearing capacity. Moreover, it was found that this effect decreases subgrade life by approximately 13 - 67 %, with respect to the root thickness and this consequently decreases the entire pavement life

Ants as predators of the egg parasitoid Trichogramma cacoeciae (Hymenoptera: Trichogrammatidae) applied for biological control of the olive moth, Prays oleae (Lepidoptera: Plutellidae) in Portugal

The detrimental effect of predators on Trichogramma cacoeciae March. releases to control the olive moth, Prays oleae Bern., in the Trás-os-Montes region (Northeast of Portugal), was evaluated during three releases against the flower generation of the pest in 2002. At 1 and 3 h and at 1, 3, 7 and 14 days after each release, 30 Trichogramma releasing cards were examined in the field and predators were collected and identified. Furthermore, at 1, 3, 7 and 14 days after each release, the percentage of egg predation on the cards was also determined. Formicidae were the most abundant group of predators at 99.1% of the total individuals collected. Ten species were identified, Camponotus aethiops, C. lateralis, C. piceus, C. truncatus, Crematogaster auberti, C. scutellaris, Lasius niger, Leptotorax angustulus, Plagiolephis pygmaea and Tapinoma nigerrimum. T. nigerrimum was the most abundant species, both in total numbers as well as in the number of occupied cards. One day after release, the percentage of predation was 24.0% in the first release, 59.4% in the second and 38.0% in the third. Three days after release, the percentage of predation varied from 60.2 to 83.4% during the three release events. Seven days after release, the percentage of predation increased to 97.8% of the total eggs on cards

T-duality for the sigma model with boundaries

We derive the most general local boundary conditions necessary for T-duality to be compatible with superconformal invariance of the two-dimensional N=1 supersymmetric nonlinear sigma model with boundaries. To this end, we construct a consistent gauge invariant parent action by gauging a U(1) isometry, with and without boundary interactions. We investigate the behaviour of the boundary conditions under T-duality, and interpret the results in terms of D-branes.Comment: 48 pages, LaTeX, v2: typos corrected, references adde

Feasibility Study of Switching Function Approaches in Sliding Mode control for a spacecraft’s attitude control system

Sliding Mode Control (SMC) is well known as a robust control approach and is proven to be able to deal with nonlinear systems. To achieve this capability, the SMC controller input design is divided into two parts: a sliding surface design (continuous control) and a switching function design (discontinuous control). A spacecraft's attitude model is a multi-input and multi-output (MIMO) system and thus control design is difficult for some methodologies, however, in this case a SMC, is straightforward to construct. In this paper, for the continuous part, a reduction of order method (ROOM) is used to construct the sliding surface. For the discontinuous control, three different switching functions are designed and evaluated such as relays with constant gains, relays with state dependent gains and linear feedback with switched gains. The main contribution of this paper is to both analyse and investigate the limitations of these three switching functions at two different points (critical gains and proper gains) on a spacecraft's attitude model. The gains are selected using trial and error techniques as long as these gains meet the sufficiency conditions for the existence of a sliding mode. The discontinuous control is a high-speed switching function that produces chattering in the control input; however, solutions for chattering drawbacks are not discussed here. The best switching function is chosen based on the spacecraft's attitude transient performance requirements

Intelligent transportation system as an effective remedy to improve the public transportation in South Africa

South African transportation is generally observed as uncoordinated with hitches and pitfalls. The ease of public transportation movement is highly dangerous with unguaranteed safety and comfort. Despite the funds budgeted for public transport restructuring and management in South Africa running into billions, the situation is still left exasperated. However, the solution to the transport system is rather a long-term infrastructure plan in which improvement can be achieved in a piece meal manner. This study provides a solution to the challenges faced in public transportation by improving the public transport system via application of Intelligent Transportation System (ITS) to improve safety and reduce congestion resulting to a sustainable and efficient transportation system. Quantitative analysis was carried out on public transportation vehicle owners, drivers, public transportation users and non-users within Free State to assess the current state of public transportation that could potentially be solved by ITS and the challenges likely to be faced. The use of questionnaires was used to assist in identifying elements needed for successful integration of ITS into South African Public TransportationPapers Presented at the 2018 37th Southern African Transport Conference 9-12 July 2018 Pretoria, South Africa. Theme "Towards a desired transport future: safe, sufficient and affordable"

Effect of ethrel and nitrogen on nitrate reductase activity, photosynthesis, biomass and yield of mustard (Brassica juncea L. Czern and Coss)

      The plants of mustard (Brassica juncea L. Czern and Coss; cultivar Alankar) were treated with 200 µL/L ethrel (2-chloro ethyl phosphonic acid) at flowering stage (60 d after sowing) along with basal application of nitrogen 40, 60, and 80 kg N ha-1. Effect of ethrel and nitrogen on leaf area index (LAI), net photosynthetic rate (PN), nitrate reductase (NR) activity and plant dry mass were recorded at 80 and 100 d after sowing. At harvest pods plant-1, 1000 seed mass and seed yield were recorded. Ethrel 200 µL/L x 80 kg N ha-1 treatment enhanced all the characteristics studied during the experiment