The synthesis of block copolyetherketones based on 4,4′‐dichlorodiphenylketone,phenolphthaleine, and bisphenol A and investigation of their properties

Block structured polyethers based on phenolphthaleine, 4,4′‐dichlorodiphenylketone, and bisphenol A with different degrees condensation (n = 1, 5, 10, and 20) were synthesized by means of acceptor‐catalytic polycondensation. Equaimolar quantities of chloranhydrides of iso‐ and terephthalic acids were used. Higher molecular masses were obtained from longer oligoketones with higher condensation degrees. Better molecular packing, increased thermal and mechanical properties were obtained with higher condensation degrees of oligoketones. © 2007 Wiley Periodicals, Inc. JAppl Polym Sci, 2008     

Optimized Machine Learning Algorithms for Investigating the Relationship Between Economic Development and Human Capital

Computational Economics - In Economic Development, human capital was previously seen as production factors but gradually evolved into endogenous growth theories. Most of the previous studies have...     

Combined forecasts in portfolio optimization: A generalized approach

In this paper a general mathematical model for portfolio selection problem is proposed. By considering a forecasting performance according to the distributional properties of residuals, we formulate an extended mean-variance-skewness model with 11 objective functions. Returns and return errors for each asset obtained using different forecasting techniques, are combined in optimal proportions so as to minimize the mean absolute forecast error. These proportions are then used in constructing six criteria related to the mean, variance and skewness of return forecasts of assets in the future and forecasting errors of returns of assets in the past. The obtained multi-objective model is scalarized by using the conic scalarization method which guarantees to find all non-dominated solutions by considering investor preferences in non-convex multi-objective problems. The obtained scalar problem is solved by utilizing F-MSG algorithm. The performance of the proposed approach is tested on a real case problem generated on the data derived from Istanbul Stock Exchange. The comparison is conducted with respect to different levels of investor preferences over return, variance, and skewness and obtained results are summarized.     

Reconstructing 3D trajectories of independently moving objects using generic constraints

The 3D reconstruction of scenes containing independently moving objects from uncalibrated monocular sequences still poses serious challenges. Even if the background and the moving objects are rigid, each reconstruction is only known up to a certain scale, which results in a one-parameter family of possible, relative trajectories per moving object with respect to the background. In order to determine a realistic solution from this family of possible trajectories, this paper proposes to exploit the increased linear coupling between camera and object translations that tends to appear at false scales. An independence criterion is formulated in the sense of true object and camera motions being minimally correlated. The increased coupling at false scales can also lead to the destruction of special properties such as planarity, periodicity, etc. of the true object motion. This provides us with a second, ‘non-accidentalness’ criterion for the selection of the correct motion among the one-parameter family.     

Performance of a Tied-Arch Reinforced Concrete Railway Bridge: Rating, Safety Assessment, and Bond Length Evaluation

This study presents investigations regarding visual inspection, dynamic testing, and finite-element modeling of an approximately 80-year old reinforced concrete tied-arch railway bridge that is still in service in Turkey. Investigations were conducted as part of a systematic periodic inspection along Ankara-Zonguldak railway line. The bridge is subject to heavy freight trains with increasing axle loads. Field tests such as material tests and dynamic tests were used to calibrate the finite-element model of the bridge. Detailed information regarding testing and model updating procedure is given. Based on test results, computer model was refined. The calibrated model of the bridge structure was then used for structural assessment and evaluation. Despite sufficient overall safety, local details were found to be problematic. Due to insufficient bond length in hanger-to-arch connection, a strengthening scheme using steel channel sections was proposed.     

Phase Relations in the System Al2O3─Ce2Si2O7 in the Temperature Range 900° to 1925°C in Inert Atmosphere

Equilibrium relationships in the system Al₂O₃-Ce₂Si₂O₇ in inert atmosphere have been investigated in the temperature range 900° to 1925°C. A simple eutectic reaction was found at 1375°C and 51 mol% Ce₂Si₂O₇. A high-low polymorphic transformation in Ce₂Si₂O₇ was observed at 1274°C. New XRD patterns are suggested for both polymorphs of cerium pyrosilicate. The melting point of Ce₂Si₂O₇ was found to be 1788°C. A value for ΔH°_m,Ce2Si2O7 of 36.81 kJ/mol was calculated from the initial slope of the experimentally determined liquidus in equilibrium with the pyrosilicate phase.     

Isothermal Oxidation Behavior of Mo-Si-B Intermetallics at 1450°C

Five Mo-Si-B multiphase intermetallic compositions were synthesized and oxidized isothermally at 1450°C in flowing air. Average mass change rates were strongly dependent on sample composition, particularly boron content. An Mo₅Si₃ matrix material containing 1.6 wt% boron exhibited parabolic mass gain with a rate of 5.3 × 10^-4 mg²(cm⁴.h), while a similar material with 0.14 wt% boron oxidized rapidly in a linear manner at a rate of -3.3 mg/(cm².h). Oxidation rates of the Mo-Si-B intermetallics were compared to that of MoSi₂ oxidized at 1450°C under identical conditions.