Curing process of powdered phenol–formaldehyde resol resins and the role of water in the curing systems

The curing behavior of two kinds of commercial powdered resol phenolic resins was studied by differential scanning calorimetry. Liquid‐state ¹³C‐NMR spectroscopy was used to aid in understanding the curing behavior by detecting the structure of powdered resins. The reaction mechanism was interpreted with the dependency of activation energy on the degree of conversion. The results indicate that there are differences in the curing mechanism between core and face phenolic resins. The curing process of core resin was faster than that of face resin at the same reaction temperature. The water added in the curing system played an important role of plasticizer or diluent according to different curing stages and water content. In the initial curing stage, water mainly diluted the system and retarded the curing reactions. However, at the higher degrees of conversion, water played the role of plasticizer to decrease the effect of diffusion on the curing reactions to make the curing reactions more complete. The excess water added in the curing system played the role of diluent at almost all stages during the curing process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1371–1378, 2003     

Thermal and kinetic properties of poly(lactic acid) and transglutaminase‐crosslinked wheat gluten blends

Wheat gluten (10 g) was crosslinked (XL) using 10 units of transglutaminase. Different blends of XL gluten and poly(lactic acid) (PLA) were mixed in a Brabender mixer at 180°C for 10 min. Neat PLA and blends were analyzed using modulated DSC (MDSC). Neat PLA displayed a glass transition (T_g) and exothermic (Cry) followed by endothermic (Mel) transitions. The profile showed a T_g of 0.46 J/g/°C, Cry with 29.9 J/g, whereas Mel exhibited 28.7 J/g. XL wheat gluten displayed one T_g with 0.45 J/g/°C. Samples were subjected to repeated heating and cooling cycles to show the level of compatibility between the two polymers. The activation energy (E_a) and pre‐exponential factor (Z) were determined according to Borchardt and Daniels (B/D) kinetics approach. The blends showed increased E_a values with an increase in the amount of XL gluten. In the presence of 5 and 20% XL gluten, the E_a of PLA increased from 150 to 200 kJ/mol, respectively. A higher number of cycles caused an increase in E_a. The T_g temperature of different PLA/XL gluten blends can be predicted by Gordon–Taylor equation and its modified forms. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Fairness-related challenges in mobile opportunistic networking

The fundamental challenge in opportunistic networking, regardless of the application, is when and how to forward a message. Rank-based forwarding techniques currently represent one of the most promising methods for addressing this message forwarding challenge. While these techniques have demonstrated great efficiency in performance, they do not address the rising concern of fairness amongst various nodes in the network. Higher ranked nodes typically carry the largest burden in delivering messages, which creates a high potential of dissatisfaction amongst them. In this paper, we adopt a real-trace driven approach to study and analyze the trade-offs between efficiency, cost, and fairness of rank-based forwarding techniques in mobile opportunistic networks.Our work comprises three major contributions. First, we quantitatively analyze the trade-off between fair and efficient environments. Second, we demonstrate how fairness coupled with efficiency can be achieved based on real mobility traces. Third, we propose FOG, a real-time distributed framework to ensure efficiency–fairness trade-off using local information. Our framework, FOG, enables state-of-the-art rank-based opportunistic forwarding algorithms to ensure a better fairness–efficiency trade-off while maintaining a low overhead. Within FOG, we implement two real-time distributed fairness algorithms; Proximity Fairness Algorithm (PFA), and Message Context Fairness Algorithm (MCFA). Our data-driven experiments and analysis show that mobile opportunistic communication between users may fail with the absence of fairness in participating high-ranked nodes, and an absolute fair treatment of all users yields inefficient communication performance. Finally our analysis shows that FOG-based algorithms ensure relative equality in the distribution of resource usage among neighbor nodes while keeping the success rate and cost performance near optimal.     

Local nonlinear unknown input observer

This paper proposes a new nonlinear unknown input observer. The observer design approach utilizes the first order Taylor expansion. The observer gains are then obtained by a systematic method. In this paper, we added some improvements to this method. The developed approach also can enable observer design for a large class of differentiable nonlinear systems. The necessary and sufficient conditions for the existence of the observer are given. A numerical example is given to illustrate the attractiveness and the simplicity of the new design procedure.     

Stability analysis of neutral systems with mixed delays

The stability of neutral systems with mixed delays is studied in this paper. A new discretized Lyapunov functional method is proposed. The method in this paper is less conservative than the existing ones and the results are very close to the analytical results. In addition, this method allows the coefficient matrix of the neutral term to have time-varying uncertainties.     

Investigating the influence of the counter Si-cell on the optoelectronic performance of high-efficiency monolithically perovskites/silicon tandem cells under various optical sources

Nowadays, tandem structures have become a valuable competitor to conventional silicon solar cells, especially for perovskite over silicon, as metal halides surpassed Si with tunable bandgaps, high absorption coefficient, low deposition, and preparation costs. This led to a remarkable enhancement in the overall efficiency of the whole cell and its characteristics. Consequently, this expands the usage of photovoltaic technology in various fields of applications not only under conventional light source spectrum in outdoor areas, i.e., AM1.5G, but also under artificial light sources found indoors with broadband intensity values, such as Internet of things (IoTs) applications to name a few. We introduce a numerical model to analyze perovskite/Si tandem cells (PSSTCs) using both crystalline silicon (c-Si) and hydrogenated amorphous silicon (a-Si:H) experimentally validated as base cells. All proposed layers have been studied with J-V characteristics and energy band diagrams under AM1.5G by using SCAPS-1D software version 3.7.7. Thereupon, the proposed architectures were tested under various artificial lighting spectra. The proposed structures of Li4Ti5O12/CsPbCl3/MAPbBr3/CH3NH3PbI3/Si recorded a maximum power conversion efficiency (PCE) of 25.25% for c-Si and 17.02% for a-Si:H, with nearly 7% enhancement concerning the Si bare cell in both cases.     

High-strength corundum ceramics with a lowered sintering temperature

Factors affecting the sintering, formation of a fine crystalline structure, and strength of aluminum oxide ceramics are considered. A ceramics with a strength of up to 600 MPa fabricated at 1450°C in an air medium has been presented. It is shown that the sintering temperature of ceramics based on Al₂O₃ (including -Al₂O₃) can be decreased to 1200°C.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 10, pp. 2 – 5, October, 1996.     

Combining temporal partitioning and temporal placement techniques for communication cost improvement

In this paper, we present a typical temporal partitioning methodology that temporally partitions a data flow graph on reconfigurable system. Our approach optimizes the communication cost of the design. This aim can be reached by minimizing the transfer of data required between design partitions and the routing cost between FPGA modules. Consequently, our algorithm is composed by two main steps. The first step aims to find a temporal partitioning of the graph. This step gives the optimal solution in term of communication cost. Next, our approach builds the best architecture, on a partially reconfigurable FPGA, that gives the lowest routing cost between modules. The proposed methodology was tested on several examples on the Xilinx Virtex-II pro. The results show significant reduction in the communication cost compared with others famous approaches used in this field.     

2-Level error (drift) compensation for low-cost MEMS-based inertial measurement unit (IMU)

In this paper, we extend the 1-level compensation method for MEMS-based IMUs, dealing mainly with stochastic drifts, described in our previous work Yudanto et al. (Proc SPIE, 9517:95,172H-95–95,172H-12, 2015) to a 2-level compensation method dealing with both stochastic and temperature drifts. While the 1-level compensation method is based on an automatic detection of systems states which triggers an online recalibration of the sensors parameters, the 2-level compensation method extends the 1-level compensation method by using a model-based approach to remove the temperature influences in the sensors outputs. The 2-level compensation schemes are then integrated together to allow an algorithmic framework that can be used in an easy way to auto-calibrate MEMS-based IMUs. Experiments using an industrial MEMS-based IMU under various operating conditions have been conducted to demonstrate the added value of the 2-level compensation method. The experimental results show that the estimations of acceleration and angular velocity based on the 2-level compensation method are in general more accurate than the ones obtained based on the 1-level compensation method.