Computationally efficient method for analyzing guard channel schemes

Call admission control (CAC) is important for cellular wireless networks in order to provide quality of service (QoS) requirements to users. Guard channel scheme is one of the CAC schemes. There are different computational models for analyzing the guard channel scheme which make unrealistic assumption of exponential distribution for both call holding duration and cell residence time for computational tractability. On the other hand, there are some more realistic models for guard channel schemes which capture general distributions of call holding duration and cell residence time by phase type distributions but are computationally cumbersome to implement. The state-spaces of the Markov chains for those models make the computation intractable. In this paper, we develop a tractable computational model to analyze guard channel scheme with general cell residence time and call holding duration captured by phase type distributions. We make our mathematical model computationally tractable by keeping track of the number of calls in different phases of the channel holding time instead of the phase of the channel holding time of individual calls.     

Modifications to COBRA-TF to model dispersed flow film boiling with two flow,four field Eulerian–Eulerian approach – Part 2

In the first part of the paper, the modifications performed to improve the dispersed flow film boiling model in COBRA-TF have been described. The improvements were achieved by adding a small droplet field to the code’s solution scheme. The conservation equations, the source terms for the equations and the models developed were summarized. In this paper, the effects of spacer grids on the dispersed flow heat transfer and COBRA-TF modifications for the spacer grid models are presented. The results of the code predictions are presented by comparing the experimental data from Rod Bundle Heat Transfer experiments with the results of code simulations performed with original and modified code. Measurements and calculations for the spacer grid temperature have been compared. The results of the analysis performed with the modified code indicate the improvement in code predictions for the spacer grid temperature.     

Determination of Coordinated Maintenance Scheduling Frequencies for a Group of Machines

An economic model of maintenance planning for a machine shop is developed. Maintenance can be performed on an individual machine or the entire group of machines simultaneously. The coordinated maintenance on the group would save on the fixed costs associated with separate overhauls. The frequencies of maintenance on each machine within two consecutive coordinated overhauls and the time between these coordinated overhauls is determined. The resulting model selects a solution that is close to the minimum of the total cost of production and maintenance.     

Simulation in decision making—a case study

An example of how simulation is used in analyzing a material handling system is presented. The Monte Carlo simulation of the Olinkraft plant not only provides the information on the effect of expansion on existing conveyer facilities, but also suggests the ways to improve the existing mode of operation. Validity of simulation is obtained by following the visual displays of the workings of different parts of the system within the simulation.     

The effect of petrochemical and oil-refining enterprises on the sanitary state of the soil cover]

Pollution of soil and agricultural plants was studied in the areas of petrochemical and oil-processing enterprises. Massive soil pollution was found in the adjacent 1-3-km areas. Hydrocarbons and metals from wastes accumulate in onions, radish, potatoes, and apples.     

Design of a just-in-time periodic material supply system for the assembly lines and an application in electronics industry

The purpose of the paper is the development of a mathematical model and a heuristic approach where the routes are constructed and the service period is determined for the design of an internal milk-run material supply system. The material supply by this system occurs on a just-in-time basis from a central warehouse to several stations of an assembly line. The objective of the proposed mathematical model is the minimization of the total material handling and inventory holding cost. Besides, the proposed heuristic approach intends to construct routes based on an initial service period value and attempts to improve the solution by considering different period values. The most suitable solution is decided on the basis of the least total material handling and WIP/inventory holding cost. The application of the proposed heuristic in a TV assembly plant demonstrates the utility of it to the real practice.     

Highly conductive polymer materials based multi-walled carbon nanotubes as counter electrodes for dye-sensitized solar cells

Poly(3,4-ethylenedioxxythiophene) (PEDOT), polyaniline (PANI) and polythiophene (PTh) based multi-walled carbon nanotube (MWCNT) composites were successfully prepared using RF-rotating plasma grafting method. Morphological characterizations of composites were determined using scanning electron microscopy (SEM), which showed that conducting polymers (CPs) of PEDOT, PANI and PTh were coated on the surface of CNTs. The surface properties of the Carbon Nanotube (CNT) composites were also determined by using Infrared Spectra (FT-IR), X-ray Photon Spectra (XPS), and Scanning Electron Microscopy-Energy Dispersive X-ray Spectra (SEM-EDX) analysis. X-ray photon spectra results confirmed the formation of the composites. Composites of MWCNT were used in dye-sensitized solar cells (DSSCs) as counter electrodes and exhibited short-circuit photocurrent densities of 11.19, 10.70 and 8.54 mA/cm² for PANI/MWCNT, PTh/MWCNT and PEDOT/CNT, respectively.