Ladder-Like Versus Hexagonal Organic–Inorganic Hybrid Materials in the Extraction of Lead Ions

Meso-structured and ladder organic–inorganic hybrid materials functionalized with ammonium carboxylate groups were prepared. These materials were obtained by the sol–gel process starting from the cyanopropyltriethoxysilane precursor as a building block. Hydrolysis of CN to COOH groups followed by treatment with triethylamine gives rise to cationic exchange materials. These materials exhibit a high chelating capability towards cations and can be used for water treatment. Lead ion (Pb²⁺) was tested as example; and, some tests were made on the meso-structured and ladder material for further comparison in efficacy of extractions.     

Response Surface Analysis and Modeling of Flaxseed Oil Yield in Supercritical Carbon Dioxide

Supercritical fluid extraction of flaxseed oil with carbon dioxide was performed. Effects of particle size, pressure, temperature and the flow rate of supercritical carbon dioxide (SC-CO₂) were investigated. Response surface methodology was used to determine the effects of pressure (30–50 MPa), temperature (50–70 °C) and SC-CO₂ flow rate (2–4 g/min) on flaxseed oil yield in SC-CO₂. The oil yield was represented by a second order response surface equation (R ² = 0.993) using the Box-Behnken design of experiments. The oil yield increased significantly with increasing pressure (p < 0.01), temperature (p < 0.05) and SC-CO₂ flow rate (p < 0.01). The maximum oil yield from the response surface equation was predicted as 0.267 g/g flaxseed for 15 min extraction of 5 g flaxseed particles (particle diameter <0.850 mm) at 50 MPa pressure and 70 °C temperature, with 4 g/min solvent flow rate. Total extraction time at these conditions was predicted as 22 min.     

New coalition formation game for spectrum sharing in cognitive radio networks

In cognitive radio networks, Secondary Users (SUs) can access the spectrum simultaneously with the Primary Users (PUs) in underlay mode. In this case, interference caused to the licensed users has to be effectively controlled. The SUs have to make spectrum access decisions in order to enhance their quality of service, but without causing harmful interference to the coexisting PUs. In this paper, we propose a cooperative spectrum decision, which enables the SUs to share the spectrum with the PUs more efficiently. Our approach is based on a new coalitional game in which the coalition value is a function of the SUs' spectral efficiencies, the inter‐SUs interference, and the interference caused to the PUs. By applying new Enter and Leave rules, we obtain a stable coalition structure. Simulation results show that the SUs' spectral efficiencies are considerably increased and that the interference caused to the coexisting PU is reduced by about 7.5% as compared to an opportunistic spectrum access scheme. Moreover, the proposed coalitional game results in a more balanced spectrum sharing in the network. Copyright © 2014 John Wiley & Sons, Ltd.     

基于自能量回收的全双工用户协作NOMA系统性能分析

自干扰的存在是全双工(Full Duplex,FD)用户协作中继系统中的不利因素,本文研究了基于自能量回收(Self-Energy Recycling,SER)的FD用户协作非正交多址(Non-Orthogonal Multiple Access,NOMA)中继系统,在FD用户中继处考虑了不同的转发协议以及同时的信息和...     

基于STBC的无线认知NOMA系统物理层安全性能研究

基于非正交多址接入（NOMA,Non-Orthogonal Multiple Access）的认知无线电（CR,Cognitive Radio）网络物理层传输面临主用户干扰和第三方窃听双重干扰威胁.本文提出利用空时编码（STBC,Space Time Block Coding）技术提高认知用户物理层安全性能,推导了任意认知用户的安全中断概率闭合表达式.通过蒙特卡洛仿真进行验证,结果表明,所提STBC-CR-NOMA相比未采用STBC编码方案的CR-NOMA可以明显提高用户的安全中断概率,且随着认知发射功率的增大,近端用户安全中断性能提高越大,而远端用户安全中断性能提升受认知基站发射功率的影响较小.仿真结果还表明,通过调整功率分配系数对远端用户和近端用户的安全中断性能影响不同.     

Comparative behavior of a nonlinear system subjected to impulsive load

Analytical and experimental studies of the dynamic response of a system with geometric and material nonlinearity are described. The dynamic excitation consists of an impulsive base acceleration. The dynamic system consists of a cantilever beam with a lumped mass and a gapped support beam at the free end. The material nonlinearity considers both the effect of yielding and the effect of strain rate on the inital yield level.Two analytical models are considered. The first is a generalized single degree-of-freedom system with a bilinear hysteresis. The second is a multiple degree-of-freedom system which uses beam elements with concentrated plastic hinges to represent the system. Numerical methods are used to solve the resulting equations of dynamic equilibrium.Experimental studies are performed and accelerations and residual plastic deformations are measured. Critical comparisons are made between the calculated and measured responses. The results show that the single degree of freedom model may overestimate the displacement response.     

Laser heating mechanism including evaporation process initiating laser drilling

A laser heating mechanism initiating the drilling process is examined. The study includes conduction and convection effects and assumes a steady-state evaporation process. This enables estimation of the limits of the Fourier theory in laser drilling applications. Using the model described in the analysis, maximum temperature attained inside the material, nucleation, explosion process and drilling efficiency are predicted. The results obtained from the present work for the vapor front velocity are compared to those obtained from previous experiments. In addition, a laser drilling experiment is carried out while monitoring the surface evaporation process. This enables correlation of the theoretical results with the experiments.     

Preadolescent girls with attention-deficit/hyperactivity disorder: II. Neuropsychological performance in relation to subtypes and individual classification.

This study examined executive functions, motor speed, and language processing in a diverse, preadolescent sample of 93 girls with attention-deficit-hyperactivity disorder (ADHD) combined type, 47 ADHD inattentive type, and 88 age- and ethnicity-matched comparison girls. Testing was performed without stimulant medication. All 10 neuropsychological variables showed significant omnibus subgroup differences, with 8 of 10 combined versus comparison contrasts significant (average effect size medium) and 6 of 10 inattentive versus comparison contrasts significant (average effect size small to medium), but only 2 of 10 combined versus inattentive contrasts significant (average effect size small). Results were robust to statistical control of demographic variables, comorbidities, and IQ. Discriminant function analysis revealed relatively high sensitivity but only modest specificity in predicting ADHD from comparison status from test performance; classification of the inattentive type was extremely poor. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Heat transfer in forced convection boiling of oil–non-azeotropic binary refrigerant mixtures

In this paper, the results of the heat transfer, forced convection, boiling characteristics of non-azeotropic refrigerant mixtures and oil are presented. This includes heat transfer coefficients for pure and binary mixtures under boiling conditions outside enhanced surface tubing. Local convective heat transfer coefficients have been determined using a modified Wilson-plot technique. Heat transfer correlations were established as a function of the binary mixture mass flow rate, and oil concentration, as well as key flow parameters.     

Adaptive control of a stewart platform-based manipulator

This article presents the implementation of a joint-space adaptive control scheme used to control noncompliant motion of a Stewart platform-based manipulator (SPBM) that is used in a facility called the Hardware Real-Time Emulator (HRTE) developed at Goddard Space Flight Center to emulate space operations. The SPBM is comprised of two platforms and six linear actuators driven by dc motors, and possesses six degrees of freedom. The article briefly reviews the development of the adaptive control scheme, which is composed of proportional-derivative (PD) controllers whose gains are adjusted by an adaptation law driven by the errors between the desired and actual trajectories of the SPBM actuator lengths. The derivation of the adaptation law is based on the concept of model reference adaptive control (MRAC) and Lyapunov direct method under the assumption that SPBM motion is slow as compared to the controller adaptation rate. An experimental study is conducted to evaluate the performance of the adaptive control scheme implemented to control the SPBM to track a vertical and circular paths under step changes in payload. Experimental results show that the adaptive control scheme provides superior tracking capability as compared to fixed-gain controllers.