Review on Fischer–Tropsch synthesis in supercritical media

A detailed review of the recent works regarding applications of supercritical media in Fischer–Tropsch synthesis (FTS) is presented. Differences in activity, CH₄ and CO₂ selectivity, hydrocarbon and olefin distributions, catalyst stability and heat transfer between supercritical Fischer–Tropsch syntheses (SC-FTS) and conventional gas phase Fischer–Tropsch synthesis (GP-FTS) are compared. The effects of temperature, pressure, solvent type, supercritical media/syngas molar ratio on SC-FTS are discussed. Finally selective production of wax via SC-FTS is briefly presented. Experimental analyses reveal that unique properties of supercritical media can improve FTS catalyst activity and selectivity in SC-FTS due to higher heat and mass transfer rates in comparison to GP-FTS.     

Interference Alignment and Degrees of Freedom of the $K$-User Interference Channel

For the fully connected K user wireless interference channel where the channel coefficients are time-varying and are drawn from a continuous distribution, the sum capacity is characterized as C(SNR)=K/2log(SNR)+o(log(SNR)) . Thus, the K user time-varying interference channel almost surely has K/2 degrees of freedom. Achievability is based on the idea of interference alignment. Examples are also provided of fully connected K user interference channels with constant (not time-varying) coefficients where the capacity is exactly achieved by interference alignment at all SNR values.     

A parallel genetic local search algorithm for intrusion detection in computer networks

The security of networked computers plays a strategic role in modern computer systems. This task is so complicated because the determination of normal and abnormal behaviors in computer networks is hard, as the boundaries cannot be well defined. One of the difficulties in such a prediction process is the generation of false alarms in many anomaly based intrusion detection systems. However, fuzzy logic is an important solution to reduce the false alarm rate in determining intrusive activities. This paper proposes a parallel genetic local search algorithm (PAGELS) to generate fuzzy rules capable of detecting intrusive behaviors in computer networks. The system uses the Michigan's approach, where each individual represents a fuzzy rule which has the form “if condition then prediction.” In the presented algorithm the global population is divided into some subpopulations, each assigned to a distinct processor. Each subpopulation consists of the same class fuzzy rules. These rules evolve independently in the proposed parallel manner. Experimental results show that the presented algorithm produces fuzzy rules, which can be used to construct a reliable intrusion detection system.     

Effect of treating atmosphere in plasma post-oxidation of nitrocarburized AISI 5115 steel

In this study quenched and tempered AISI 5115 steel was plasma-nitrided and nitrocarburized at 550 °C for 5 h in atmospheres of 80% N₂ balanced with various amounts of CO₂ and H₂ gases. The amount of CO₂ varied from 0 to 10 vol%. The highest amount of ε phases was formed in the compound layer after treating in atmosphere containing 7 vol% CO₂. Optimized compound layer was post-oxidized for 1 h at 450 °C under O₂/H₂ volume ratios of 1/1 and 3/1 as well as 100% oxygen. The treated samples were characterized using metallographic techniques, XRD, SEM, roughness measurement and potentiodynamic methods. The results showed that the growth rate of the oxide layer increased with increasing O₂ in the oxidizing gas mixture. X-ray diffraction analysis of oxidized layers confirmed the formation of highest amount of magnetite at post-oxidation in an atmosphere with the O₂/H₂ volume ratio of 1/1. Electrochemical polarization tests proved the enhancement of corrosion resistance by plasma post-oxidation and the highest corrosion resistance obtained after oxidizing under an O₂/H₂ volume ratio of 1/1.     

A direct sequence spread spectrum code acquisition circuit for wireless sensor networks

Narrow band (NB), spread spectrum (SS), and ultra wide band (UWB) are three physical layer bandwidth types used in wireless sensor networks (WSN). SS and UWB technologies have many advantages over NB, which make them preferable for WSN. Synchronisation of different nodes in a WSN is an important task that is necessary to improve cooperation and lifetime of nodes. Code acquisition is the main step of a node’s time synchronisation. In this article, a pseudo noise code generator and a code acquisition circuit are proposed, designed and tested using direct sequence SS technique. To investigate the properties of the designed circuits, simulations are carried out via Xilinx Foundation Series software in the real mode. The results demonstrate excellent performance of the proposed algorithms and circuits in all realistic conditions. The code acquisition circuit proposed an adaptive testing window for single dwell serial search method. The code acquisition circuit is a clock phase free approach, thus the clock coherency step is cancelled. Moreover, clock phase difference between transmitter and receiver nodes does not mostly affect the acquisition and thus synchronisation time.     

Molecular dynamics study for CH4/H2S separation through functionalized nanoporous graphyne membrane

Molecular dynamics simulations were employed to investigate the effect of chemical functionalization and applied pressure on the CH₄/H₂S separation performance using graphyne as a membrane. A pore was created on the graphyne surface and then functionalized with hydroxyl group and fluorine. The number of methane and hydrogen sulfide molecules in the simulated systems was 100 molecules from each of them, which were placed between graphyne and graphene nanosheet as a barrier. The results indicated that nanoporous graphyne can be suitable membrane for gas separation, especially in the absence of applied pressure, which is an acceptable condition for gas separation systems.     

Proposed soil classification based on the experiences of soft-ground tunneling in Iran

Bulletin of Engineering Geology and the Environment - An essential step in successful mechanized and conventional tunneling operations is a thorough characterization of ground conditions and...     

Application of modified complementary reservoir approach in analysis of water distribution networks under pressure-deficient conditions

Hydraulic simulation models which simulate water distribution systems in different operating conditions are essential tools to evaluate network reliability. Simulation models found in most commercial software are not effectively capable of analyzing demand nodes under critical conditions such as fire-fighting demand or network pipe breakage. In the current study, a combination of hydraulic model and complementary reservoir solution (CRS) method is used for solving network's problems in critical conditions for both series-looped networks and a part of water network in Ilam city (Iran). Obtained results show that CRS provide more than actual need on the demand node for some reservoir total pressure heads. Thus, two modified versions of CRS method are proposed to deal with failures of CRS in such cases. Obtained results demonstrate improved efficiency in the combined model for analyzing networks in abnormal conditions.