Mutual interference considered power allocation in OFDM-based cognitive networks: the multiple SUs case

Power allocation for secondary users (SUs) in cognitive networks is an important issue to ensure the SUs’ quality of service. When the mutual interference between the primary users (PUs) and the SUs is taken into consideration, it is wanted to achieve the conflict-free power allocation while synchronously maximizing the capacity of the secondary network. In this paper, the optimal power allocation problem is considered in orthogonal frequency division multiplexing cognitive networks. The single SU case is primarily formulated as a constrained optimization problem. On this basis, the multiple SUs case is then studied and simulated in detail. During the analysis, the mutual interference among the PUs and the SUs is comprehensively formulated as the restrictions on the SU’s transmission power and the optimization problems are finally resolved by iterative water-filling algorithms. Consequently, the proposed power allocation scheme restrains the interference to the primary network, as well as maximizing the capacity of the secondary network. Specifying the multiple-SUs case, simulation results are exhibited in a simplified scenario to confirm the efficiency of the proposed water-filling algorithm, and the influence of the mutual interference on the power allocation and the system capacity is further illustrated.     

Characterization of thermally damaged concrete using a nonlinear ultrasonic method

Thermal damage in concrete usually induces contact-type defects, which result in degradation of the concrete's performance. This paper attempts to visualize the thermal damage in a multiscale, and characterizes the thermally damaged concrete using a nonlinear ultrasonic method. An impact-modulation method is used to obtain nonlinearity parameters, as a quantitative measure of contact-type defects, and shows better sensitivity than phase velocity variation as a linear ultrasonic method for thermally damaged concrete. The measured nonlinearity parameter is compared with the permeable pores, which reflect the occurrence of opening and pores in thermally damaged concrete. Degradation of concrete strength due to thermal damage is also assessed via the measurement.     

A data mining approach considering missing values for the optimization of semiconductor-manufacturing processes

Due to the rapid development of information technologies, abundant data have become readily available. Data mining techniques have been used for process optimization in many manufacturing processes in automotive, LCD, semiconductor, and steel production, among others. However, a large amount of missing values occurs in the data set due to several causes (e.g., data discarded by gross measurement errors, measurement machine breakdown, routine maintenance, sampling inspection, and sensor failure), which frequently complicate the application of data mining to the data set. This study proposes a new procedure for optimizing processes called missing values-Patient Rule Induction Method (m-PRIM), which handles the missing-values problem systematically and yields considerable process improvement, even if a significant portion of the data set has missing values. A case study in a semiconductor manufacturing process is conducted to illustrate the proposed procedure.     

ATRP with Alkyl Pseudohalides Acting as Initiators and Chain Transfer Agents: When ATRP and RAFT Polymerization Become One

All controlled radical polymerization (CRP) procedures rely on a dynamic and rapid equilibrium between dormant and active species. This equilibrium can be established through different mechanisms and all the resulting CRP processes have their own advantages and limitations. Therefore, it becomes interesting to investigate the possibility of combining CRP techniques to eliminate specific drawbacks of each individual procedure. Atom transfer radical polymerization (ATRP) with alkyl pseudohalides acting as initiators and chain transfer agents was developed for that purpose. The process relies on a dual mechanism involving both activation deactivation and reversible addition fragmentation chain transfer (RAFT). This peculiar characteristic of ATRP with alkyl pseudohalides acting as chain transfer agents made it possible to overcome some of the limitations typically associated with conventional ATRP and RAFT polymerization as well as to prepare new responsive materials.     

Direct evidence for the formation of ordered carbides in a ferrite-based low-density Fe–Mn–Al–C alloy studied by transmission electron microscopy and atom probe tomography

We study the structure and chemical composition of the κ-carbide formed as a result of isothermal transformation in an Fe–3.0Mn–5.5Al–0.3C alloy using transmission electron microscopy and atom probe tomography. Both methods reveal the evolution of κ-particle morphology as well as the partitioning of solutes. We propose that the κ-phase is formed by a eutectoid reaction associated with nucleation growth. The nucleation of κ-carbide is controlled by both the ordering of Al partitioned to austenite and the carbon diffusion at elevated temperatures.     

Synthesis of 1-phenyl-1-xylyl ethane by Friedel–Crafts alkylation of xylene with α-methylbenzyl alcohol over mordenite

In the Friedel–Crafts alkylation of xylene to prepare 1-phenyl-1-xylyl ethane (PXE), α-methylbenzyl alcohol was used as an alkylating agent over a mordenite catalyst. The catalyst was characterized by MAS-NMR, N₂ adsorption/desorption, NH₃-TPD, and various other techniques and was found to possess strong Brønsted acid sites. When temperature was low, the main product was bis-(α-methylbenzyl) ether. However, as the temperature went up, PXE and heavies, styrene trimers and heavier oligomers, became main products. The formation of PXE, occurring on strong acid sites, is favored by raising temperature, space velocity, pressure, and xylene/MBA ratio within the experimental ranges. As the catalyst deactivates, the selectivities to PXE and heavies decrease and those to linear dimer and styrene increase. A reaction mechanism is proposed.     

Finite element contact analysis on a horn-holder assembly for wire bonding

The joint structure of a transducer horn-holder assembly for a wire bonder was examined through finite element contact analysis. Three-dimensional modeling and analysis was carried out to survey the internal physics of this structure and to verify the accuracy of a proposed computation relative to measurement. After validation, a two-dimensional model was built to conduct parametric studies and improve the efficiency and speed of the computation. Several factors such as boundary conditions, modeling boundary, and mesh density, were considered to obtain consistency with the three-dimensional analysis. Arc angle and the position of each holder boss were chosen as design parameters. A designed computation approach was applied for efficiency in computation. As a result, a guideline for holder boss design was suggested, and the main factors and their influence on stress concentration in the transducer horn were surveyed.     

Development of a plate-fin type gas turbine recuperator

A plate-fin type recuperator for a gas turbine/fuel cell hybrid power generation system was designed, manufactured, and tested. Performance analysis shows that the performance of the system is directly affected by the performance of the recuperator. Therefore, the recuperator should be designed and manufactured carefully, and its performance should be tested and verified before it is integrated into the system. In this paper, the developing procedure including designing, manufacturing, and testing of a cross flow plate-fin type recuperator was presented. Performance test results showed that the design requirements of the recuperator were almost satisfied. Based on the test results, improved design to reduce the size of the recuperator was suggested.     

Effect of the fluorine-addition order on the hydrodesulfurization activity of fluorinated NiW/Al2O3 catalysts

Fluorinated NiW/Al₂O₃ catalysts with different orders of fluorine addition have been prepared, tested for hydrodesulfurization (HDS) of thiophene, and characterized using nitric oxide chemisorption and temperature-programmed sulfidation. The catalyst surface area has been affected by fluorine addition but not by the order of fluorination. The fluorine addition-order does not affect the amount of fluorine retained in the catalysts after the calcination and the reaction steps, either. On the other hand, the order of fluorine addition changes the dispersion of the nickel and the tungsten species, incorporation of nickel with the tungsten edge sites, and consequently the HDS activity of the catalysts. The catalyst fluorinated in the last step, i.e., after addition of both tungsten and nickel, shows the highest activity in thiophene HDS, which is supported by other experimental results indicating the most nitric oxide chemisorption and the largest incorporation of nickel with the tungsten species. Accordingly, enhancement of the catalyst activity by fluorination is due to the repartition of the metal species rather than to partial solubilization of alumina in the fluorine-addition step.     

On the scalability of ad hoc networks

We investigate the inherent scalability problem of ad hoc networks originated from the nature of multihop networks. First, the expected packet traffic at the center of a network is analyzed. The result shows that the expected packet traffic at the center of a network is linearly related with the network size, that is, the expected packet traffic at the center of a network is O(k), where k is the radius of a network. From the result, the upper bound of the diameter of a network D=2k, that guarantees the network is scalable, is obtained. The upper bound is given by C/r-1, where C is the channel capacity available to each node and r is the packet arrival rate at each node.