Fall detection using single-tree complex wavelet transform

The goal of Ambient Assisted Living (AAL) research is to improve the quality of life of the elderly and handicapped people and help them maintain an independent lifestyle with the use of sensors, signal processing and telecommunications infrastructure. Unusual human activity detection such as fall detection has important applications. In this paper, a fall detection algorithm for a low cost AAL system using vibration and passive infrared (PIR) sensors is proposed. The single-tree complex wavelet transform (ST-C$\mathbb{C}$WT) is used for feature extraction from vibration sensor signal. The proposed feature extraction scheme is compared to discrete Fourier transform and mel-frequency cepstrum coefficients based feature extraction methods. Vibration signal features are classified into “fall” and “ordinary activity” classes using Euclidean distance, Mahalanobis distance, and support vector machine (SVM) classifiers, and they are compared to each other. The PIR sensor is used for the detection of a moving person in a region of interest. The proposed system works in real-time on a standard personal computer.     

Monolithic Perovskite/Silicon Tandems with >28% Efficiency: Role of Silicon-Surface Texture on Perovskite Properties

Textured silicon wafers used in silicon solar cell manufacturing offer superior light trapping, which is a critical enabler for high-performance photovoltaics. A similar optical benefit can be obtained in monolithic perovskite/silicon tandem solar cells, enhancing the current output of the silicon bottom cell. Yet, such complex silicon surfaces may affect the structural and optoelectronic properties of the overlying perovskite films. Here, through extensive characterization based on optical and microstructural spectroscopy, it is found that the main effect of such substrate morphology lies in an altering of the photoluminescence response of the perovskite, which is associated with thickness variations of the perovskite, rather than lattice strain or compositional changes. With this understanding, the design of high-performance perovskite/silicon tandems is rationalized, yielding certified power conversion efficiencies of >28%.     

Electrosynthesis of benzoquinone from phenol on α and β surfaces of PbO2

Electrosynthesis of benzoquinone from phenol was investigated in acetonitrile-water mixtures on α-PbO₂ and β-PbO₂ electrodes. The influence of water concentration, electrolysis potential, initial phenol concentration and temperature on benzoquinone production was also studied. Different electrocatalytic activities of α and β structures of PbO₂ were determined.     

Solubility / retention relationships in supercritical-fluid chromatography

The effects of temperature, pressure and supercritical fluid density on solubility-retention relationship of solutes in supercritical fluid partition chromatography are investigated. New retention data for naphthalene and phenanthrene are obtained as a function of pressure at different temperatures. The mobile-phase partial molar volumes of the solutes are determined from infinite-dilution fugacity coefficients and used to model the pressure dependence of solute retention that reveals the nature of interactions between the stationary phase and the solute. Relationships between pressure and temperature dependence of solubility and retention of solutes are also illustrated.     

Novel first-order differential class-AB log-domain allpass filters

The first-order differential class-AB log-domain filters are proposed. They are systematically derived using the state–space synthesis procedure. It is also demonstrated that the present second filter cannot be realized without using differential class-AB type. To the best knowledge of the authors, the filters are the first log-domain first-order allpass filters in the literature. PSPICE simulations are performed using both, bipolar junction transistors (BJT) and ideal devices to confirm the theoretical analysis. Tolerable differences are observed due to BJT non-idealities such as finite-beta, non-zero ohmic junction resistances and early voltages.     

A fluorescence study on dissolution of polymeric glasses prepared in various molecular weights

Poly(methyl methacrylate) (PMMA) discs in various molecular weights, M_w, were prepared by free-radical polymerization of methyl methacrylate (MMA). Pyrene (P) was introduced during polymerization as a fluorescence probe to monitor the gelation and dissolution processes in chloroform vapor and solvent, respectively. In-situ steady state fluorescence (SSF) experiments were performed to monitor vapor uptake and chain desorption processes. Direct illumination of PMMA discs were performed to excite the P molecules embedded inside the PMMA glass. Variation in P intensity, I, was monitored during the swelling of the PMMA material exposed to chloroform vapor. It was observed that PMMA film swells like a crosslinked polymeric gel at early times by obeying the Li-Tanaka equation. Swelling time constants, τ_c, of PMMA discs were measured and found to have a strong correlation with the molecular weight, of PMMA. In a separate experiment, when the PMMA discs were in chloroform, desorption of PMMA chains from glass discs was monitored by observing the change of pyrene fluorescence intensity. A diffusion model with a moving boundary was employed to quantify the fluorescence data observed from dissolving PMMA discs made at various molecular weights. It was observed that desorption coefficient, D, decreased by increasing M_w by obeying the D≈M_w ⁻¹ law. Presented at the 80th Annual Meeting of the Federation of Societies for Coatings Technology, October 30–November 1, 2002, New Orleans, LA. Department of Physics, 80626 Maslak, Istanbul. Turkey.     

Simulation-Based Decision Support System for Economical Supply Chain Management of Rebar

The economics of a materials management system is defined by the size of the shipments, the scheduling strategy that allows contractors to handle uncertainty and variability in the supply chain, and the timing of the shipments, which in turn depend on the environment in which the project is taking place. This study presents a simulation-based decision support system to assist contractors in selecting the most economical rebar management system prior to the start of construction by recommending lot sizes (large, small), a scheduling strategy (optimistic, neutral, pessimistic), and buffer sizes (large, medium, small) given the conditions of the project. This model is of benefit to contractors and researchers because it generates the probable cost of inventory of 18 alternative rebar management systems ranging from just in case (JIC) to just in time (JIT) and including different variations in between. It allows contractors to select the alternative with least cost of inventory at the planning stages of a project. The simulation model was tested by using actual data obtained from a trade center project in Istanbul, Turkey. As expected, the test indicated that JIC was the most economical rebar management system in a case study conducted in a developing country, as it generated a savings of 4.8% over JIT.     

Realization of Fully Controllable Negative Inductance with Single Operational Transresistance Amplifier

A grounded negative inductance emulator is proposed with full independent control on both the inductance value and the condition. It uses a single operational transresistance amplifier (OTRA), a capacitor, and five resistors, two of which are for independent control. Experimental results, which confirm the theoretical analysis, are presented.     

Optimization of properties of fly ash aggregates for high-strength lightweight concrete production

The optimization of properties of lightweight fly ash aggregates for suitability in high-strength lightweight fly ash concrete production was investigated using response surface methodology (RSM). Design-Expert software was used to establish the design matrix and to analyze the experimental data. The relationships between the sintering parameters (temperature, binder content and binder type) and experimentally obtained three responses (specific gravity, water absorption and crushing strength) were established. Also, the optimization capabilities in Design-Expert software were used to optimize the sintering process. Historical data design technique under RSM was performed to optimize the input parameter interactions which showed the best conditions for preparation of fly ash pellets. According to the obtained results, the developed models are statistically accurate and can be used for further analysis. The experimental values agreed with the predicted ones, thus indicating suitability of the model employed and the success of RSM in optimizing the sintering conditions.