Optimal pricing, lot-sizing and marketing planning in a capacitated and imperfect production system

In the classical economic production quantity (EPQ) problem demand is considered to be known in advance. However, in the real-world, demand of a product is a function of factors such as product’s price, its quality, and marketing expenditures for promoting the product. Quality level of the product and specifications of the adopted manufacturing process also affect the unit product’s cost. Therefore, in this paper we consider a profit maximizing firm who wants to jointly determine the optimal lot-sizing, pricing, and marketing decisions along with manufacturing requirements in terms of flexibility and reliability of the process. Geometric programming (GP) technique is proposed to address the resulting nonlinear optimization problem. Using recent advances in optimization techniques we are able to optimally solve the developed, highly nonlinear, mathematical model. Finally, using numerical examples, we illustrate the solution approach and analyze the solution under different conditions.     

Cluster Size Optimization in Sensor Networks with Decentralized Cluster-Based Protocols

Network lifetime and energy-efficiency are viewed as the dominating considerations in designing cluster-based communication protocols for wireless sensor networks. This paper analytically provides the optimal cluster size that minimizes the total energy expenditure in such networks, where all sensors communicate data through their elected cluster heads to the base station in a decentralized fashion. LEACH, LEACH-Coverage, and DBS comprise three cluster-based protocols investigated in this paper that do not require any centralized support from a certain node. The analytical outcomes are given in the form of closed-form expressions for various widely-used network configurations. Extensive simulations on different networks are used to confirm the expectations based on the analytical results. To obtain a thorough understanding of the results, cluster number variability problem is identified and inspected from the energy consumption point of view.     

Quantitative analysis of the ankle strategy under translational platform disturbance.

The ankle strategy is one of the postural adjustment maneuvers humans utilize when the support platform is disturbed. This paper presents a quantitative analysis of the ankle strategy. A three-link sagittal biped model is considered. The first link represents the two legs locked together. The second link represents the two thighs locked together. The third link represents the hip, the torso, the upper limbs, the neck, and the head. The dynamics, control, and stability of the three-link biped, under platform translation, are considered. The disturbance of the platform is represented as an input and the effect of the muscular system is reduced to a set of torques applied to the joints and across the joints. Two digital computer simulations are presented to demonstrate the behavior of the biped under backward or forward platform disturbance. The simulations are compared with experimental measurements of humans subjected to postural disturbances. It is shown that the effect of a horizontal disturbance at the ankle appears to be about 40 times that of the effect of the disturbance at the knees and at least a few hundred times larger than the effect of a disturbance at the hip. This means that, under translational platform disturbance, the ankle angle is subjected to the largest excursion. The knee and the hip angle excursions are relatively minor. Consequently, the biped, as a whole, appears to move as a single inverted pendulum. Major postural corrections are initiated by the ankle excursion. Further, when the available ankle torque is limited or nonexistent, the stability requires resorting to the knee or hip strategies.     

Thermophysical Properties of Porous Sandstones: Measurements and Comparative Study of Some Representative Thermal Conductivity Models

The thermal conductivity and thermal diffusivity of porous consolidated sandstones have been measured simultaneously by the transient-plane source (TPS) technique in the temperature range from 280 to 330 K at ambient pressure using air as the saturant. The porosity and density parameters are measured using standard American Society for Testing and Materials (ASTM) methods at 307 ± 1 K. Data are presented for five types of samples ranging in porosity from 8 to 17 vol. %, taken from various positions above the baseline. The thermal conductivity and constituents of the minerals vary with porosity as well as with the position of the sample from the baseline. The thermal conductivity data are discussed in the framework of simple mixing laws and empirical models. Simple correlations between the effective density and porosity, and between the effective thermal conductivity and porosity, are also established     

An assessment of the ability of computational fluid dynamic models to predict reactive gas–solid flows in a fluidized bed

Fine grid, two dimensional simulations of reactive gas–solid flows occurring in a fluidized bed reactor were carried out using the Eulerian multi-fluid kinetic theory of granular flow (KTGF) approach in the commercial flow solver, ANSYS FLUENT 12.1. The fuel reactor of a pilot scale Chemical Looping Combustion rig, operated in the bubbling fluidization regime at the Vienna University of Technology, was simulated. Grid dependence studies were carried out as well as sensitivity studies to the fuel inlet condition and the inclusion of gas phase turbulence. Simulations could not accurately reproduce the experimental trend for the case when highly reactive nickel oxide was used as the oxygen carrier material, but in general satisfactory quantitative agreement was observed. The failure to correctly capture the experimental trend was primarily attributed to the fine length-scales at the feed gas inlets not being adequately resolved even at the finest grid investigated. The trend quickly worsened when coarser grids were used, indicating that the generality of the model is lost when grid dependence effects are present. A number of possible dimensional effects were also discussed. Subsequently, the model was used to successfully capture another experimental trend obtained with a much less reactive ilmenite oxygen carrier material. The model captured this trend correctly because the reaction was now limited by the reaction rate and not by species transfer to the large scale gas-emulsion interfaces. Results were therefore not as sensitive to the correct hydrodynamic modelling of the interface, especially near the gas inlets, and the model retained its generality over a wide range of operating conditions.     

3D numerical investigation of ZnO/Zn hydrolysis for hydrogen production

The current research is focused on the hydrogen production through a two‐step ZnO/Zn thermochemical water splitting cycle. In the present paper, numerical modeling of the second step is conducted using Computational Fluid Dynamics (CFD)2, where steam reacts with zinc to produce hydrogen. The parametric study shows that the hydrogen yield is relatively insensitive to the steam/zinc molar ratio and inversely proportional to the argon/steam molar ratio. For large argon to steam molar ratios, hydrogen yield is relatively insensitive to the inlet temperature of zinc and steam, and increases marginally with an increase in the argon inlet temperature. Five different reactor configurations were evaluated comprehensively. Among all configurations, a cylindrical reactor with a tangential inlet for argon and zinc, and a radial inlet for steam (both in the bottom plane of the reactor) and a tangential outlet in the top plane of the reactor produced the highest hydrogen yield of 88%. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis,Corrosion and Bioactivity Evaluation of Gelatin/Silicon and Magnesium Co-Doped Fluorapatite Nanocomposite Coating Applied on AZ31 Mg Alloy

In this study, a nano-composite composed of gelatin as the matrix and Si-Mg-FA nano-particles as an additive was deposited on the AZ31 Mg alloy via dip coating method. In addition, a coating composed of MgO, MgSiO₃ and Mg₂SiO₄ phases was applied on the AZ31 Mg alloy by anodizing process. It was found that the Nano-composite coating with a uniform distribution of nano-particles within the gelatin matrix with the thickness of about 9 µm was dense, crack-free and uniform whereas the surface of anodized layer was relatively coarse due to the presence of flaws and micro-cracks. The surface morphology, EDS analysis and FTIR results revealed the ability of nano-composite coated specimen to form the bone-like apatite. Due to the presence of aforementioned phases and special surface features, the anodized specimen possessed higher and lower corrosion resistance than uncoated and nano-composite coated specimens, respectively. The passive coating resistances (R_CT) of nano-composite, anodized specimen and uncoated samples were 2164, 1449 and 1024 Ω cm², respectively.     

Current and Temperature Dependent Matching Fields in Nb Film of Rectangular Array of Holes

Nanoengineered periodic array of holes on superconducting thin films have a great interest due to their excellence for the studies of the vortex pinning mechanisms in the type-II superconductors. Rectangular array of holes has been fabricated over a microbridge of Nb superconducting thin film by e-beam lithography. Rectangular array of holes have two type of scenario, at low magnetic fields matching effects are sharp and narrow while at high fields wide and shallower. In this work, we study the matching pinning effect by the artificial hole array in superconducting Nb thin films. We observed that as the inter distance between holes is decreased; the sharp matching effects become dominant and vice versa.