Analysis of Heuristic Graph Partitioning Methods for the Assignment of Packet Control Units in GERAN

Over the last few years, graph partitioning has been recognized as a suitable technique for optimizing cellular network structure. For example, in a recent paper, the authors proposed a classical graph partitioning algorithm to optimize the assignment of cells to Packet Control Units (PCUs) in GSM-EDGE Radio Access Network. Based on this approach, the quality of packet data services in a live environment was increased by reducing the number of cell re-selections between different PCUs. To learn more about the potential of graph partitioning in cellular networks, in this paper, a more sophisticated, yet computationally efficient, partitioning algorithm is proposed for the same problem. The new method combines multi-level refinement and adaptive multi-start techniques with algorithms to ensure the connectivity between cells under the same PCU. Performance assessment is based on an extensive set of graphs constructed with data taken from a live network. During the tests, the new method is compared with classical graph partitioning approaches. Results show that the proposed method outperforms classical approaches in terms of solution quality at the expense of a slight increase in computing time, while providing solutions that are easier to check by the network operator.     

Comparison of textural information from argon(87 K) and nitrogen(77 K) physisorption

Argon(87 K) and nitrogen(77 K) adsorption of three types of porous samples (microporous, microporous-mesoporous and mesoporous) was evaluated. The shapes of isotherms, specific surface areas, mesopore-, micropore- and net pore volumes, pore-size distributions (PSD) and positions of micropore and mesopore PSD’s maxima were compared to ascertain the credibility of individual adsorbates for the texture information estimation. The shapes of adsorption isotherms for Ar and N₂ of all samples are similar and the adsorbed amounts at relative pressure x = 0.975 differ slightly. For mesoporous samples some differences are observed between specific mesopore surface areas derived from nitrogen and argon isotherms. Radii of pore size maxima from Ar(87 K) PSD’s are on average systematically lower than from N₂(77 K) for all samples. The Saito-Foley approach for ZSM-5 samples gives consistently lower mean pore radius from N₂(77 K) adsorbate than from Ar(87 K). This difference probably arises from the multiplication factor, Ω, in the Saito-Foley equation which includes physical properties (magnetic susceptibility, polarizability etc. at 77 and 87 K) and is not easy to obtain with sufficient precision. The use of both adsorbates Ar(87 K) and N₂(77 K) possesses some advantages as well some disadvantages and the comparison of textural properties of individual samples must be evaluated with respect to adsorbate.     

Three dimensional stress analysis of solid oxide fuel cell anode micro structure

One of the most common problems in solid oxide fuel cells (SOFCs) is the delamination and thus the degradation of electrode/electrolyte interface which occurs in the consequences of the stresses generated within the different layers of the cell. Nowadays, the modeling of this problem under certain conditions is one of the main issues for the researchers. The structural and thermo-physical properties of the cell materials (i.e. porosity, density, Young's modulus etc.) are usually assumed to be homogenous in the mathematical modeling of solid oxide fuel cells at macro-scale. However, during the real operation, the stresses created in the multiphase porous layers might be very different than those at macro-scale. Therefore, micro-level modeling is required for an accurate estimation of the real stresses and the performance of SOFCs. This study presents a microstructural characterization and a finite element analysis of the delamination and the degradation of porous solid oxide fuel cell anode and electrode/electrolyte interface under various operating temperatures, compressing forces and material compositions by using the synthetically generated microstructures. A multi physics computational package (COMSOL) is employed to calculate the Von Misses stresses in the anode microstructures. The maximum thermal stress in the electrode/electrolyte interface and three phase boundaries is found to exceed the yield strength at 900 °C while 800 °C is estimated as a critical temperature for the delamination and micro cracks due to thermal stress generated. The thermal stress decreases in the grain boundaries with increasing content of one of the phases (either Ni or YSZ) and the porosity of the electrode. A clamping load higher than 5 kg cm⁻² is also found to exceed the shear stress limit.     

Preparation,characterization, and mechanical properties of poly(ε‐caprolactone)/polylactic acid blend composites

Mechanical properties of poly(ε‐caprolactone) (PCL) and polylactic acid (PLA) blend reinforced with Dura and Tenera palm press fibers were studied. Dicumyl peroxide (DCP) was used as compatibilizer in the blend composites. Fourier transforms infrared spectrophotometer (FTIR) and field emission scanning electron microscope (FESEM) was used to study the effect of treatment on the fibers and fiber/matrix adhesion respectively. The uncompatibilized blend composites exhibited higher Young's modulus than the compatibilized blend composites. Impact strength of compatibilized blend composites of Tenera fibers (FM) increased by 161% at 10 wt% fiber load more than the uncompatibilized blend composites at same fiber load. The Dura fibers (FN) enhanced impact strength by 133% at 10 wt% fiber load. Tensile strength increased by 40% for compatibilized FM blend composites. In conclusion, it was observed that DCP incorporation resulted in good interfacial adhesion as revealed by the FESEM micrographs and evidenced in the improved mechanical properties. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Development of a Coconut- and Palm-Based Fat Blend for a Cookie Filler

Thirteen fat blends intended for cookie filler (CF) production that consist of 20–70 % palm mid-fraction (PMF), 20–70 % virgin coconut oil (VCO), and 0–10 % palm stearin (POs) were developed based on the solid fat contents (SFC) of the fat portions extracted from five commercial CF samples: A, B, C, D, and E. A mixture design was applied for fat blend optimization, and the combination that best approached the target SFC values was composed of 70 % PMF, 20 % VCO, and 10 % POs. The optimized coconut- and palm-based fat blend (O-CP) exhibited a steeper SFC profile, with 8.2 % (±0.2) SFC at 25 °C (room temperature) and 0.2 % (±0.2) SFC at 37 °C (body temperature); lower slip melting point of 34.0 °C (±0.0); and a lower iodine value (IV) of 40.25 g/100 g (±1.04). In addition, O-CP contained higher proportions of medium-chain fatty acids (MCFA) and lauric acid (C12:0) of 3.2 % (±0.18) and 9.7 % (±0.43), respectively. In terms of its thermal profile, O-CP showed no significant difference in terms of its crystallization range, 49.7 °C (±2.66) with the exception of sample C, but it exhibited a smaller melting range, 65.8 °C (±1.47), compared to the fat portions of the commercial samples. The ranges represented the span between the onset and offset temperatures of both crystallization and melting profiles as determined by differential scanning calorimetry.     

Creep crack growth in P22 and P91 welds — overview from SOTA and HIDA projects

Creep crack growth (CCG) tests on two pressure vessel steels, P22 (2.25Cr1Mo) and P91 (9CrMoVNb) were carried out in two European Commission supported projects: SMT 2070 ‘SOTA’ and BE1702 ‘HIDA’.Tests in the SOTA project were conducted on the all-weld and cross-weld compact tension (CT) specimens; in the case of cross-weld specimens the electrical discharge machined (edm) notches were placed at various positions inside the HAZ to study the effect of notch position on CCG characteristics. These tests were conducted at 550°C (P22) and 600°C (P91).Tests in the HIDA project were carried out on the base metal and cross-weld CT specimens; in the case of cross-weld specimens the edm notches were placed in the centre of the HAZ. These tests were carried out at higher temperatures than those in the SOTA project i.e. at 565°C (P22) and 625°C (P91). In this project CCG tests were also carried out on large seam-welded pipes (feature specimens) with edm notches positioned in the base metal and in the centre of HAZ.The base and weld metals used in both projects were from the same cast/pedigree. This paper discusses the findings of the two projects and implications for crack growth in the weldments of these two steels.     

Study of rotational temperature of oxygen DC glow discharge in Silica and Pyrex discharge tubes

Active DC glow discharges in oxygen have been studied in Silica and Pyrex discharge tubes for medium pressures up to 550 Pa and for discharge currents up to 40 mA. Electric field strength measured by a double-probe technique was found to increase with the pressure and to decrease with the discharge current, which is typical for DC glow discharges. We have focused on the emitted radiation. The rotational temperature (T_rot) of molecular oxygen was determined from the ^PP and ^PQ branches of the well-resolved atmospheric A-band of molecular oxygen at 760 nm. Good agreement between values of T_rot obtained from particular branches was found. The increase of the rotational temperature with increasing pressure and discharge current has been observed in both discharge tubes, however, the values of rotational temperature were systematically higher in the tube made of Pyrex glass. This difference was explained by the particular thermal conductivity of the tube material.     

Elastomeric Protein Bioactive Eutectogels for Topical Drug Delivery

Therapeutic deep eutectic solvents (THEDES) are an emerging family of eutectic mixtures gaining increasing interest in the biomedical space. The immobilization of THEDES into polymer networks allows bioactive eutectogels to expand their application scope to topical drug delivery. Herein, this work presents the first set of elastomeric eutectogels constructed by supporting a therapeutic eutectic system with skin permeation ability in a protein scaffold dynamically crosslinked by a natural polyphenol. In this ionic eutectic, gelatin undergoes gelation through an unexpected mechanism in striking contrast with classical hydrogels, which is herein thoroughly studied. Interestingly, the polyphenol controls the conformation of the protein structure, enabling tuning up the mechanical and viscoelastic behavior of the dynamic eutectogel networks from elastic to hyperelastic. The resultant protein eutectogels exhibit strain-hardening behavior, thermoreversible gel-to-sol transition, and excellent adhesive performance. Furthermore, these versatile materials retain the bioactivity of the liquid THEDES and favor skin occlusion, assisting the delivery of both hydrophilic and hydrophobic substances in ex vivo porcine skin in a time-dependent penetration process. These ultrastretchable eutectogels show new interplays between protein scaffolds and eutectic mixtures, paving the way for innovative therapeutic soft materials.