Conditional Gradient Method for Double-Convex Fractional Programming Matrix Problems

We consider the problem of optimizing the ratio of two convex functions over a closed and convex set in the space of matrices. This problem appears in several applications and can be classified as a double-convex fractional programming problem. In general, the objective function is nonconvex but, nevertheless, the problem has some special features. Taking advantage of these features, a conditional gradient method is proposed and analyzed, which is suitable for matrix problems. The proposed scheme is applied to two different specific problems, including the well-known trace ratio optimization problem which arises in many engineering and data processing applications. Preliminary numerical experiments are presented to illustrate the properties of the proposed scheme.     

Effect of Clay Addition on the Properties of Carbon Nanotubes-Filled Immiscible Polyethylene/Polypropylene Blends

The effects of organically modified clay (OMC) incorporation on the microstructure and the electrical and mechanical properties of polypropylene (PP)/polyethylene (PE) blends filled with carbon nanotubes (CNT) were investigated. All blends were prepared by melt mixing in a batch mixer. The microstructures were characterized by scanning electron microscopy. In the OMC:CNT filled blends, the CNT were found to selectively localize within the PE phase, while the clay particles were observed in the PP phase. The electrical resistivity of OMC:CNT filled blends did not show any significant change as a result of the clay addition since it was localized in the CNT-free phase. On the other hand, the addition of clay degraded the blends' mechanical properties due to the poor adhesion between the OMC and the PP matrix.     

Optimization of an ammonia-cooled rectangular microchannel heat sink using multi-objective non-dominated sorting genetic algorithm (NSGA2)

The ever decreasing size of modern electronic packaging has induced researchers to search for an effective and efficient heat removal system to handle the continuously increasing power density. Investigations have involved different geometry, material and coolant to address the thermal management issues. This paper reports the potential improvement in the overall performance of a rectangular microchannel heat sink using a new gaseous coolant namely ammonia gas. Using a multi-objective general optimization scheme with the thermal resistance model as an analysis method in combination with a non-dominated sorting genetic algorithm as an optimization technique, it was found that significant reduction in the total thermal resistance up to 34?% for ammonia-cooled compared to air-cooled microchannel heat sink under the same operating conditions is achievable. In addition, a considerable decrease in the microchannel heat sink’s mass up to 30?% was achieved due to the different heat sink’s material used.     

Diacetylenes with Ionic‐Liquid‐Like Substituents: Associating a Polymerizing Cation with a Polymerizing Anion in a Single Precursor for the Synthesis of N‐Doped Carbon Materials

Imidazolium‐ and benzimidazolium‐substituted diacetylenes with bromide or nitrogen‐rich dicyanamide and tricyanomethanide anions were synthesized and used as precursors for the preparation of N‐doped carbon materials. On pyrolysis under argon at 800 °C both halide precursors afforded graphite‐like structures with nitrogen contents of about 8.5 %. When the dicyanamide and tricyanomethanide precursors were thermolyzed at the same temperature, graphite‐like structures were obtained that exhibit nitrogen contents in the range 17–20 wt %; thereby, the benefit of associating a polymerizing cation with a polymerizing anion in a single precursor was demonstrated. On pyrolysis at 1100 °C the nitrogen contents of the latter pyrolysates remain high (ca. 6 wt %). Adsorption measurements with krypton at 77 K indicated that the materials are nonporous. The highest electrical conductivity was observed for a pyrolysate with one of the lowest nitrogen contents, which also has the highest degree of graphitization. Thus, the quest for N‐rich carbons with high electrical conductivities should include both maximization of the nitrogen content and optimization of the degree of graphitization. Crystallographic investigation of the precursors and spectroscopic characterization of the pyrolysates prepared by heating at 220 °C indicate that construction of the final carbon framework does not involve the intermediate formation of a polydiacetylene.     

Novel Pyrimidine‐based Ferrocenyl substituted Organometallic Compounds: Synthesis,Characterization and Biological Evaluation

Some novel pyrimidine‐based ferrocenyl substituted organometallic compounds were synthesized via multistep reactions, well characterized by different spectroscopic techniques and elemental analyses and evaluated for in vitro antiprotozoal susceptibility against HM1: IMSS strain of Entamoeba histolytica. The results of antiprotozoal susceptibility unveiled these compounds, as new leads in protozoal chemotherapy as most of the organometallics displayed an exceptionally higher antiamoebic activity (IC₅₀ = 0.055 μM ‐ 0.815 μM) than the reference drug metronidazole which gave IC₅₀ (50% inhibitory concentration) value 1.781 μM in our experiments, concluding that newly synthesized organometallic compounds have potential to be employed as effective antiamoebic agents and these organometallics can be very useful for further optimization work on amoebic chemotherapy.     

Photoconductivity derived from an exact modelling of the uncompensated one-donor model. I—simplified models revisited; and description of the method of solving the exact model equations

Abstract

Photoconductivity associated with a simple photoconductor model, containing one localised (donor) level, is taken up carefully through different approaches. Two simplified approaches are analysed, that are based on the assumption that some transitions between this level and the allowed bands can be neglected. The respective roles played by these hypotheses are specified through a hierarchical classification, and the limits of validity of the combined approximations are carefully stated. In a parallel direction, the related complete model is presented, which excludes no transitions and is based on Fermi—Dirac statistics. The resolution procedure of the resulting non-linear system of equations is then described, with the purpose of comparing the respective behaviours of all those models.