Separation performance investigation of packed distillation columns using simple NEQ approach based on packing multicomponent efficiencies and effective mass transfer coefficients

A simple non-equilibrium modeling approach is proposed to simulate multicomponent distillation process in packed columns. The real behavior of the column is simply considered by the evaluation of interphase mass transfer rate based on the overall mass transfer coefficient. Two distinct methods are used to calculate this overall coefficient including the effective mass transfer coefficient method and the packing efficiency method. The modelling procedure consists of an iterative segment-wise algorithm implemented in a MATLAB home-code. For verification, the obtained composition profiles from a structured and a random packed column are compared with reported experimental data. Comparisons show that the packing efficiency-based model could acceptably predict the experimental profiles with an average relative deviation of 18% and 25% for structured and random packed columns, respectively. This confirms that our simple non-equilibrium approach is a reliable and robust model for the performance evaluation of packed columns.     

Impact of TH‐UWB interference on MB‐OFDM UWB systems: interference modeling and performance analysis

In this paper, the coexistence issue between multiband‐orthogonal frequency‐division multiplexing (MB‐OFDM) and time‐hopping ultra‐wideband (TH‐UWB) networks is widely analyzed. For this purpose, to study and model the TH‐UWB interference, an analytical framework which describes key features of the interference distribution is provided. The interference distribution is studied in the context of TH‐UWB's signaling parameters. Our results reveal that the interference distribution highly depends on its time‐hopping parameters. Therefore, choosing proper time‐hopping parameters leads to less destructive interferences. The Generalized Gaussian and the Symmetric‐α‐Stable (SαS) distributions are used to model the interference‐plus‐noise signal. The maximum likelihood and a characteristic function‐based regression‐type methods are adopted to estimate parameters of Generalized Gaussian and SαS distributions, respectively. Moreover, the interference channel effects on the impulsive behavior of the TH‐UWB signal is studied. It is shown that impulsive behavior of the faded interference signals highly depends on the channel time‐dispersiveness. Furthermore, an exact performance of a multiband‐orthogonal frequency‐division multiplexing system impaired by a TH‐UWB system is derived. The comparison of the analytical performance, the empirical simulation, and the approximation results show that both approximation methods are valid for low interference‐to‐noise‐ratio, while SαS provides a more accurate approximation for high interference‐to‐noise‐ratio. Copyright © 2015 John Wiley & Sons, Ltd.     

Multi-level wordline driver for robust SRAM design in nano-scale CMOS technology

In this paper, a multi-level wordline driver scheme is presented to improve 6T-SRAM read and write stability. The proposed wordline driver generates a shaped pulse during the read mode and a boosted wordline during the write mode. During read, the shaped pulse is tuned at nominal voltage for a short period of time, whereas for the remaining access time, the wordline voltage is reduced to save the power consumption of the cell. This shaped wordline pulse results in improved read noise margin without any degradation in access time for small wordline load. The improvement is explained by examining the dynamic and nonlinear behavior of the SRAM cell. Furthermore, during the hold mode, for a short time (depending on the size of boosting capacitance), wordline voltage becomes negative and charges up to zero after a specific time that results in a lower leakage current compared to conventional SRAM. The proposed technique results in at least 2× improvement in read noise margin while it improves write margin by 3× for lower supply voltages than 0.7 V. The leakage power for the proposed SRAM is reduced by 2% while the total power is improved by 3% in the worst case scenario for an SRAM array. The main advantage of the proposed wordline driver is the improvement of dynamic noise margin with less than 2.5% penalty in area. TSMC 65 nm technology models are used for simulations.     

Development of Bio-Inspired- and Wavelet-Based Hybrid Models for Reconnaissance Drought Index Modeling

The present study aimed to model reconnaissance drought index (RDI) time series at three various time scales (i.e., RDI-6, RDI-9, RDI-12). Two weather stations located at Iran, namely Tehran and Dezful, were selected as the case study. First, support vector regression (SVR) was utilized as the standalone modeling technique. Then, hybrid models were implemented via coupling the standalone SVR with two bio-inspired-based techniques including firefly algorithm (FA) and whale optimization algorithm (WOA) as well as wavelet analysis (W). Accordingly, the hybrid SVR-FA, SVR-WOA, and W-SVR models were proposed. It is worth mentioning that six mother wavelets (i.e., Haar, Daubechies (db2, db4), Coifflet, Symlet, and Fejer-Korovkin) were employed in development of the hybrid W-SVR models. The performance of models was assessed through root mean square error (RMSE), mean absolute error (MAE), Willmott index (WI), and Nash-Sutcliffe efficiency (NSE). Generally, the implemented coupled models illustrated better results than the standalone SVR in modeling the RDI time series of studied locations. Besides, the Coifflet mother wavelet was found to be the best-performing wavelet. The most accurate results were achieved for RDI-12 modeling via the W-SVR utilizing db4(2) at Tehran station (RMSE = 0.253, MAE = 0.174, WI= 0.888, NSE = 0.934) and Coifflet(2) at Dezful station (RMSE = 0.301, MAE = 0.166, WI= 0.910, NSE = 0.936). As a result, the hybrid models developed in the current study, specifically W-SVR ones, can be proposed as suitable alternatives to the single SVR.

     

Effect of methane content and the oscillating electric field between electrodes on atmospheric Ar/methane plasma jet and DLC coating deposition

In this work, the effects of the methane gas flow and the internal oscillating electric field between electrodes on radio-frequency(RF) atmospheric pressure argon/methane plasma jet and process of diamond-like carbon(DLC) film deposition have been investigated. Properties of RF atmospheric Ar/methane plasma jet such as active species density, length, electron temperature,appearance and ionization process of argon/methane plasma jet are changed due to the changing of methane flow content and electric field vector and its gradient. With increasing methane flow,the formation of C2 hydrocarbon and CH band content is decreased because injected electrical energy to a mixture of Ar/methane gases is insufficient to stabilize the ionization process of methane gas and the electrical-chemical reaction rate is decreased. With shortening the gas gap between two electrodes, electric field strength and its gradient are increased leading to more energy injection to the electron. Electrical-chemical reactions are strengthened leading to increasing the CH band content. These phenomena introduce the Ar/methane plasma jet in different modes causing to deposit the DLC film with different structures and properties. With using quartz glass and alumina ceramic as dielectric barriers tubes, RF atmospheric pressure Ar/methane plasma jet has been used to deposit DLC coating in different modes. Increasing methane content and shortening the gas gap leads to decreasing sp3 bonded content and the quality of the deposited film.     

Efficient schema-based XML-to-Relational data mapping

Storing and querying XML documents using a RDBMS is a challenging problem since one needs to resolve the conflict between the hierarchical, ordered nature of the XML data model and the flat, unordered nature of the relational data model. This conflict can be resolved by the following XML-to-Relational mappings: schema mapping, data mapping and query mapping. In this paper, we propose: (i) a lossless schema mapping algorithm to generate a database schema from a DTD, which makes several improvements over existing algorithms, (ii) two linear data mapping algorithms based on DOM and SAX, respectively, to map ordered XML data to relational data. To our best knowledge, there is no published linear schema-based data mapping algorithm for mapping ordered XML data to relational data. Experimental results are presented to show that our algorithms are efficient and scalable.     

A fast and reliable routing technique for wireless mesh networks

In wireless mesh networks (WMNs), real time communications (e.g., Voice over IP (VoIP) and interactive video communications) may often be interrupted as packets are frequently lost or delayed excessively. This usually happens due to the unreliability of wireless links or buffer overflows along the routing paths. The mesh connectivity within the WMN enables the capability to enhance reliability and reduce delay for such applications by using multiple paths for routing their packets. The vital components in multi‐path routing for achieving this are the pre‐determined formation of paths and the technique that the paths are deployed for packet traversal. Therefore, we propose a novel multi‐path routing protocol by introducing a new multi‐path organization and a traffic assignment technique. The designed technique dubbed as FLASH (Fast and reLiAble meSH routing protocol) discovers one primary path between a pair of source and destination based on a new proposed metric, and thereafter selects mini‐paths, which connect pairs of intermediate nodes along the primary path. The primary path and mini‐paths are concurrently deployed, as multiple copies of packets are routed through. This technique compensates for possible outage at intermediate wireless nodes or their corresponding wireless links along the primary path. Routing along mini‐paths is performed in such a way that redundant copies do not cause an excessive congestion on the network. The effectiveness of the proposed scheme is evaluated analytically and through extensive simulations under various load conditions. The results demonstrate the superiority of the proposed multi‐path organization in terms of reliability and satisfactory achievements of the protocol in enhancing delay and throughput compared to the existing routing protocols, especially for long distances and in congested conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

Shut-down margin study for the next generation VVER-1000 reactor including 13 × 13 hexagonal annular assemblies

Shut-Down Margin (SDM) for the next generation annular fuel core of typical VVER-1000, 13 × 13 assemblies are calculated as the main aim of the present research. We have applied the MCNP-5 code for many cases with different values of core burn up at various core temperatures, and therefore their corresponding coolant densities and boric acid concentrations. There is a substantial drop in SDM in the case of annular fuel for the same power level. Specifically, SDM for our proposed VVER-1000 annular pins is calculated when the average fuel burn up values at the BOC, MOC, and EOC are 0.531, 11.5, and 43 MW-days/kg-U, respectively.     

Distributed semi‐adaptive compressive sensing data collection in wireless sensor networks

Recently, many researches have been conducted to exploit the compressive sensing (CS) theory in wireless sensor networks (WSNs). One of the most important goals in CS is to prolong the lifetime of WSNs. But CS may suffer from some errors during the reconstruction phase. In addition, an adaptive version of CS named Bayesian compressive sensing has been studied to improve the reconstruction accuracy in WSNs. This paper investigates these adaptive methods and identifies their associated problems. Finally, a distributed and semi‐adaptive CS‐based data collection method is proposed. The proposed method tackles the aforementioned problems. Simulation results show that considering both lifetime and accuracy factors as a compound metric, the proposed method yields a 200% improvement compared with the Bayesian compressive sensing‐based method and outperforms other compared methods in the literature.