Modeling of the dynamic delamination of L-shaped unidirectional laminated composites

One of the widely used geometrically complex parts in advanced commercial aircraft is the L-shaped composite. Due to the sharp curved geometry, interlaminar opening stresses are induced and delamination occurs under considerable mode-mixities in L-shaped beams. Dynamic phenomena during delamination initiation and propagation of L-shaped beams are investigated using dynamic (explicit) finite element analysis in conjunction with cohesive zone methods. The 2-D model consists of 24 plies of unidirectional CFRP laminate with an initial 1 mm crack at the center of the laminate at the bend. Loading is applied parallel to one of the arms quasi-statically. The loading type yields different traction fields and mode-mixities in the two sides of the crack in which delamination occurs under shear stress dominated loading on one crack tip and opening stress dominated loading on the other. The speed of the delamination under shear dominated loading at one side is 800 m/s and under normal stress dominated loading is 50 m/s. In addition radial compressive waves at the interface are observed. Finally, as the thickness is changed, a different failure mode is observed in which a secondary crack nucleates at the arm and propagates towards the center crack.     

An approximate method for static and dynamic analyses of multi‐bay coupled shear walls

In this study an approximate method based on the continuum approach and transfer matrix method for static and dynamic analyses of multi‐bay coupled shear walls is presented. The whole structure is idealized as a sandwich beam in this method. Initially the differential equation of this equivalent sandwich beam is written, then shape functions for each storey can be obtained by the solution of differential equations. By using boundary conditions and storey transfer matrices which are obtained by these shape functions, system modes and periods can be calculated. Reliability of the study is shown with a few examples. A computer program has been developed in MATLAB and numerical samples have been solved for demonstration of the reliability of this method. The results of the samples display the agreement between the present method and the other methods given in the literature. Copyright © 2007 John Wiley & Sons, Ltd.     

Extended kalman filtering for the modeling and analysis of ICG pharmacokinetics in cancerous tumors using NIR optical methods

Compartmental modeling of indocyanine green (ICG) pharmacokinetics, as measured by near infrared (NIR) techniques, has the potential to provide diagnostic information for tumor differentiation. In this paper, we present three different compartmental models to model the pharmacokinetics of ICG in cancerous tumors. We introduce a systematic and robust approach to model and analyze ICG pharmacokinetics based on the extended Kalman filtering (EKF) framework. The proposed EKF framework effectively models multiple-compartment and multiple-measurement systems in the presence of measurement noise and uncertainties in model dynamics. It provides simultaneous estimation of pharmacokinetic parameters and ICG concentrations in each compartment. Moreover, the recursive nature of the Kalman filter estimator potentially allows real-time monitoring of time varying pharmacokinetic rates and concentration changes in different compartments. Additionally, we introduce an information theoretic criteria for the best compartmental model order selection, and residual analysis for the statistical validation of the estimates. We tested our approach using the ICG concentration data acquired from four Fischer rats carrying adenocarcinoma tumor cells. Our study indicates that, in addition to the pharmacokinetic rates, the EKF model may provide parameters that may be useful for tumor differentiation.     

Optimization of fineness to maximize the strength activity of high-calcium ground fly ash – Portland cement composites

Depending on their physical and chemical properties and the amount of replacements with cement, fly ashes may provide an economical production possibility in concrete industry and improve the mechanical and durability performance of concrete. In recent years, ultrafine fly ash has become one of the necessary ingredients of high-performance concrete. However, many of the fly ashes are coarse in nature, hence grinding is necessary to obtain sufficient performance in concrete production. In this study, the effect of grinding on strength activity of ground high-calcium fly ashes was investigated. Physical characteristics such as sieve fineness, grain particle size characteristics and Blaine specific surface area were also determined and compared with raw fly ash. Some case studies and possible interactions between fineness of fly ash, strength and water demand of mortars were discussed. The optimization of fineness coupled with the adjustment of water content were found as the key parameters of effective utilization of high-calcium fly ashes from the view point of strength maximization of cement mortars.     

On the dataset shift problem in software engineering prediction models

A core assumption of any prediction model is that test data distribution does not differ from training data distribution. Prediction models used in software engineering are no exception. In reality, this assumption can be violated in many ways resulting in inconsistent and non-transferrable observations across different cases. The goal of this paper is to explain the phenomena of conclusion instability through the dataset shift concept from software effort and fault prediction perspective. Different types of dataset shift are explained with examples from software engineering, and techniques for addressing associated problems are discussed. While dataset shifts in the form of sample selection bias and imbalanced data are well-known in software engineering research, understanding other types is relevant for possible interpretations of the non-transferable results across different sites and studies. Software engineering community should be aware of and account for the dataset shift related issues when evaluating the validity of research outcomes.     

An overview of Turkish lignite qualities by logistic analysis

As an indispensable energy source, lignite is almost exclusively used in power generation in Turkey. To assess the quality level of Turkish lignite, a multivariate statistical analysis was conducted. The relationship among the lignite quality parameters has been investigated using a response method that is the logistic regression method. The analysis determines the effect of multiple predictor variables such as moisture, ash and sulphur presented simultaneously to predict membership of the two calorific value categories. By this way, a reliable binary response regression structure was constructed considering all the lignite fields in Turkey. Both the experiments on identifying the influential measurements and the measure of goodness of fit indicated that the overall model has a big capability to exhibit the relationship among the parameters of the Turkish lignite.     

Drilling thick fabric woven CFRP laminates with double point angle drills

Carbon fiber reinforced plastics (CFRPs) have many desirable properties, including high strength-to-weight ratio, high stiffness-to-weight ratio, high corrosion resistance, and low thermal expansion. These properties make CFRP suitable for use in structural components for aerospace applications. Drilling is the most common machining process applied to CFRP laminates, and it is difficult due to the extremely abrasive nature of the carbon fibers and low thermal conductivity of CFRP. It is a challenge for manufacturers to drill CFRP materials without causing any delamination on the work part while also considering the economics of the process. The subject of this study is the drilling of fabric woven type CFRP laminates which are known to be more resistant to delamination than unidirectional type CFRP laminates. The objective of this study is to investigate the influence of double point angle drill geometry on drilling performance through an experimental approach. An uncoated carbide and two diamond coated carbide drills with different drill tip angles are employed in drilling experiments of aerospace quality thick fabric woven CFRP laminates. Force and torque measurements are used to investigate appropriate drilling conditions based on drill geometry and ideal drilling parameters are determined. Tool life tests of the drills were conducted and the condition of the diamond coating is examined as a function of drilling operational parameters. High feed rate drilling experiments are observed to be favorable in terms of drill wear. Feed is observed to be more important than speed, and the upper limit of feed is dictated by the drill design and the rigidity of the machine drill. Hole diameter variation due to drill wear is monitored to determine drill life. At high feeds, hole diameter tolerance is observed to be more critical than hole exit delamination during drilling of fabric woven CFRP laminates.     

Effect of platinum doping on the structural and electrical properties of SnO2 thin films

The investigation of Pt doping effect on the structural and electrical properties of SnO₂ thin films was aimed in this study. For this purpose, the polycrystalline pure and Pt-doped SnO₂ thin films were deposited onto n-type silicon substrate and the Pt sputter power was varied as 0 (un-doped), 2, 5 and 7 W by using radio frequency confocal sputtering system. The structural properties of the samples were analysed by X-ray diffraction measurements. The structural results show that the 5 W Pt-doped SnO₂ sample has better crystallinity than the other samples. The results of the electrical measurements as current–voltage, capacitance–voltage and conductance–voltage were also obtained and discussed in detail for fabricated diodes. The analysis of electrical characteristics shows that the use of different Pt doping has significant effect on electrical properties of such devices. The study also provides an improved supplemental understanding to the related technologies which use Pt-doped SnO₂ materials.     

Rutile TiO<Subscript>2</Subscript> films as electron transport layer in inverted organic solar cell

Titanium dioxide (TiO₂) thin films were prepared by sol–gel spin coating method and deposited on ITO-coated glass substrates. The effects of different heat treatment annealing temperatures on the phase composition of TiO₂ films and its effect on the optical band gap, morphological, structural as well as using these layers in P3HT:PCBM-based organic solar cell were examined. The results show the presence of rutile phases in the TiO₂ films which were heat-treated for 2 h at different temperatures (200, 300, 400, 500 and 600 °C). The optical properties of the TiO₂ films have altered by temperature with a slight decrease in the transmittance intensity in the visible region with increasing the temperature. The optical band gap values were found to be in the range of 3.28–3.59 eV for the forbidden direct electronic transition and 3.40–3.79 eV for the allowed direct transition. TiO₂ layers were used as electron transport layer in inverted organic solar cells and resulted in a power conversion efficiency of 1.59% with short circuit current density of 6.64 mA cm^?2 for TiO₂ layer heat-treated at 600 °C.     

Mesoporous nanocrystalline ZnO microspheres by ethylene glycol mediated thermal decomposition

Zinc oxide (ZnO) nanostructures with various morphologies have been fabricated in literature owing to their potential applications in various emerging fields. In this study, we report a facile, one-step gram-scale synthesis of nanocrystalline mesoporous ZnO microspheres by thermal decomposition of zinc acetate dihydrate in ethylene glycol at 250?°C for 12?h. The average size of the hollow microspheres is found to be 3.01?±?0.52?µm, which are formed by loosely bonded nanocrystallites with average sizes of 17?±?4?nm. We propose a formation mechanism for the mesoporous microspheres, Ostwald ripening of spherical-like nanocrystallites, on the basis of the results obtained by different synthesis durations. We also report the possibility of tuning the morphologies of the obtained ZnO by simply modifying the thermal decomposition solution, where porous ZnO nanoplates are obtained when a mixture of ethylene glycol and water is used and ZnO nanorods with aspect ratios of ～3 are synthesized by using diethylene glycol. ZnO nanowires with lengths up to several microns are fabricated when no solvent is used, i.e. thermal decomposition in air atmosphere. Microstructural and phase characterizations of the samples are conducted by using a field-emission gun scanning electron microscope and X-ray diffractometer. Performances of the obtained nanocrystalline mesoporous ZnO microspheres in photocatalytic degradation of Rhodamine B and as active anode materials in lithium-ion batteries are also presented.