Dynamic Virtual Resource Allocation in Virtualized multi-RAT Cellular Networks

The legacy wireless systems are designed to exploit static configuration and deployment, and cannot handle the discrepancies of the spatio-temporal traffic demand. Cloud RAN (C-RAN) is a novel flexible radio technology that utilizes the virtualization concepts and can efficiently address the static deployment of conventional wireless systems. The C-RAN also leverages high radio network flexibility by introducing the network function virtualization approach to wireless networks. This paper presents a novel C-RAN platform that virtualizes and operates with full GSM and LTE systems. The presented platform is solely based on open-source and off the shelf solutions, providing easy implementation, low cost and high scalability. The paper also introduces a novel dynamic resource allocation algorithm that facilitates the C-RAN’s optimal performance in dynamic scenarios. The proposed algorithm is analyzed and validated on the presented C-RAN platform. The results of the performance analysis clearly show the advantages of the proposed dynamic resource allocation algorithm. Moreover, they prove the applicability of the C-RAN platform for variety of different scenarios.     

A correlation to describe interfacial heat transfer coefficient during solidification of Al–Si alloy casting

A thin wall Al–9 wt.% Si alloy casting was made in a sand mold prepared by CO₂ process. The thermal history obtained from the experiment was used to solve an inverse heat conduction problem (IHCP). The IHTC was estimated by an iterative algorithm based on the function specification method. Acquired IHTC values are given as a function of time and as a function of the casting surface temperature at the interface. It has been found that pattern of IHTC variation with casting surface temperature can be described by an equation which has been proposed as a new correlation model. In order to verify broader applicability of the proposed correlation, its use is demonstrated on the IHTC results taken from the literature.     

Impurity removal and overall rate constant during low pressure treatment of liquid silicon

The research presented analyzes the effect of low pressure on the amount and reduction of impurity elements in upgraded metallurgical grade silicon. The achieved pressure was 5 kPa in the commercial electro-resistance furnace in the magnesia and mullite refractory material. The chemical composition was determined by ICP-MS method. Elements such as Al, Fe, Mn, Cu or Zn had the highest evaporation rates where higher evaporation was achieved at higher melt temperatures. The overall rate constant was deduced for four melt temperatures indicating high values even for low melt temperatures. The interfacial boundary between Si and mullite refractory showed no dissolution of Al into the liquid Si.     

Spark plasma sintering of ZrC–SiC ceramics with LiYO2 additive

Spark plasma sintering (SPS) of ZrC–SiC composite powders in the presence of LiYO₂ sintering additive was studied. The starting powders were obtained by a carbothermal reduction (CTR) of natural mineral zircon (ZrSiO₄), which provided an intimate mixing of in-situ created ZrC and SiC powders. This composite powder and LiYO₂ as additive were densified by spark plasma sintering. Microstructural features of the composite were investigated by XRD, SEM/EDS and AFM analysis. The sintered composite material possesses promising mechanical properties and excellent cavitation resistance which was observed with a cavitation erosion test. The values of Vickers microhardness and fracture toughness of the composite material are 20.7 GPa and 5.07 MPam^1/2, respectively.     

Design Optimization of a Portable Thermophoretic Precipitator Nanoparticle Sampler

Researchers at the National Institute for Occupational Safety and Health (NIOSH) are developing methods for characterizing diesel particulate matter in mines. Introduction of novel engine and exhaust aftertreatment technologies in underground mines is changing the nature of diesel emissions, and metrics alternative to the traditional mass-based measurements are being investigated with respect to their ability to capture changes in the properties of diesel aerosols. The emphasis is given to metrics based on measurement of number and surface area concentrations, but analysis of collected particles using electron microscopy (EM) is also employed for detailed particle characterization. To collect samples for EM analysis at remote workplaces, including mining and manufacturing facilities, NIOSH is developing portable particle samplers capable of collecting airborne nano-scale particles. This paper describes the design, construction, and testing of a prototype thermophoretic precipitator (TP) particle sampler optimized for collection of particles in the size range of 1–300 nm. The device comprises heated and cooled metal plates separated by a 0.8 mm channel through which aerosol is drawn by a pump. It weighs about 2 kg, has a total footprint of 27 × 22 cm, and the collection plate size is approximately 4 × 8 cm. Low power consumption and enhanced portability were achieved by using moderate flow rates (50–150 cm³/min) and temperature gradients (10–50 K/mm with ΔT between 8 K and 40 K). The collection efficiency of the prototype, measured with a condensation particle counter using laboratory-generated polydisperse submicrometer NaCl aerosols, ranged from 14–99%, depending on temperature gradient and flow rate. Analysis of transmission electron microscopy images of samples collected with the TP confirmed that the size distributions of collected particles determined using EM are in good agreement with those determined using a Fast Mobility Particle Sizer.

Copyright 2012 American Association for Aerosol Research     

Application of Design of Experiments and Multilayer Perceptron Neural Network in Optimization of the Spray-Drying Process

The aim of this study was to investigate the effect of changing spray-drying parameters on the production of a naratriptan/maltodextrin/lactose composite, as well as to evaluate the application of design of experiments and multilayer perceptron (MLP) neural network in studying the spray-drying process. The system was spray dried as an aqueous solution using a Büchi 290-Mini Spray Dryer (Büchi Laboratoriums-Technik AG, Switzerland). A 2^4?1 factorial design study was undertaken to select the spray-drying processing variables that significantly affect the production yield, outlet air temperature, and residual moisture content. The process parameters studied were inlet air temperature, pump speed, aspirator setting (drying air flow rate), and feed concentration. After performing this screening study, three process parameters, pump speed, inlet air temperature, and feed concentration, were selected for further analysis, applying a central composite design and artificial neural network. Overall, the parameter that had the greatest influence on each investigated response was pump speed. It significantly influenced yield, moisture content, and particle size. Interaction between inlet air temperature and feed concentration was the only statistically significant interaction that influenced the moisture content. Particle size was mostly influenced by feed concentration as well as by a pump speed. A multilayer perceptron was the type of artificial neural network applied. The selected MLP structure had three layers: the first layer had three input units, the second layer had three hidden units, and the third layer had four output units. The selected MLP was trained through 10,000 epochs. Design of experiments using response surface methodology allows insight into interactions between variables, and an artificial neural network provides better prediction potential, enabling simultaneously determination of several outputs. Design of experiments and artificial neural network proved to be useful tool for optimization of the spray-drying process, where a design space for achieving the best process yields and optimum particle characteristics was established. There is a possibility that this conclusion can be drawn for other maltodextrin/lactose systems with other drug substances or for other similar spray-dried systems (the feedstock type is a carbohydrate-based aqueous solution). In future work, this will be tested with other materials.