Asymptotically optimum detection of primary user in cognitive radio networks

Traditionally, the frequency spectrum is licensed to users by government agencies in a fixed manner where the licensee has exclusive right to access the allocated band. However, with increasing demand for the spectrum and scarcity of vacant bands, a spectrum policy reform seems inevitable. Meanwhile, recent measurements suggest the possibility of sharing spectrum among different parties subject to interference-protection constraints. In order to enable access to an unused licensed spectrum, a secondary user has to monitor licensed bands and opportunistically transmit whenever no primary signal is detected. Spectrum-sharing between a primary licensee and a group of secondary users has been studied. The structure of an asymptotically optimum detector based on the measurements of all secondary users is derived and the effect of the quantisation error in such a system is evaluated. Also, it is shown that by using the proposed detector in a sequential detection structure, it is possible to shorten the decision time needed by the detector. The results show the superiority of the proposed detector to other schemes.     

Optimizing the Runoff Estimation with HEC-HMS Model Using Spatial Evapotranspiration by the SEBS Model

Most of the commonly used hydrological models do not account for the actual evapotranspiration (ETa) as a key contributor to water loss in semi-arid/arid regions. In this study, the HEC-HMS (Hydrologic Engineering Center Hydrologic Modeling System) model was calibrated, modified, and its performance in simulating runoff resulting from short-duration rainfall events was evaluated. The model modifications included integrating spatially distributed ETa, calculated using the surface energy balance system (SEBS), into the model. Evaluating the model’s performance in simulating runoff showed that the default HEC-HMS model underestimated the runoff with root mean squared error (RMSE) of 0.14 m³/s (R²?=?0.92) while incorporating SEBS ETa into the model reduced RMSE to 0.01 m³/s (R²?=?0.99). The integration of HECHMS and SEBS resulted in smaller and more realistic latent heat flux estimates translated into a lower water loss rate and a higher magnitude of runoff simulated by the HECHMS model. The difference between runoff simulations using the default and modified model translated into an average of 95,000 m³ runoff per rainfall event (equal to seasonal water requirement of ten-hectare winter wheat) that could be planned and triggered for agricultural purposes, flood harvesting, and groundwater recharge in the region. The effect of ETa on the simulated runoff volume is expected to be more pronounced during high evaporative demand periods, longer rainfall events, and larger catchments. The outcome of this study signifies the importance of implementing accurate estimates of evapotranspiration into a hydrological model.

     

Reserve estimation of an open pit mine under price uncertainty by real option approach

Reserve estimation is a key to find the correct NPV in a mining project. The most important factor in reserve estimation is the metal price. Metal price fluctuations in recent years were exaggerated, and imposed a high degree of uncertainty to the re-serve estimation, and in consequence to the whole mine planning procedure. Real option approach is an efficient method of deci-sion making in the uncertain conditions. This approach has been used for evaluation of defined natural resources projects until now. This study considering the metal price uncertainty used real option approach to prepare a methodology for reserve estimation in open pit mines. This study was done on a copper cylindrical deposit, but the achieved methodology can be adjusted for all kinds of deposits. This methodology was comprehensively described through the examples in such a manner that can be used by the mine planners.     

Dehydration of water/1-1-dimethylhydrazine mixtures by zeolite membranes

In this research, dehydration of water/1-1-dimethylhydrazine (UDMH) mixtures by zeolite NaA and hydroxy sodalite membranes has been investigated. Support of these membranes has been tubular mullites that have been made by extruding a mixture of about 67–75% kaolin clay and 33–25% distilled water using an extruder. Zeolite NaA and hydroxy sodalite membranes have been coated on the external surface of the porous supports by the hydrothermal synthesis.

UDMH/water mixtures have been separated at ambient temperature and pressure by pervaporation (PV) using these zeolite membranes. These membranes showed very high selectivity of water for all UDMH mixtures. For the UDMH/water mixtures, separation factor as high as 10 000 has been obtained for UDMH feed concentration of 2%. Total mass fluxes of 1.05–0.2 kg/(m² h) have been also obtained.     

Modeling of Hydrogen Permeation through Pd Membrane on Ceramic Supports Activated via Pd Nanoparticles–TiO2–Bohemite Suspension

Theoretical Foundations of Chemical Engineering - Thin dense Pd composite membrane was prepared via electroless plating method. Pd nanoparticles embedded polyethylene glycol (PEG) was used in...     

Investigation of Creep Feed Grinding Parameters and Heat treatment Effects on the Nickel-base Superalloys

The Nickel base Superalloys are the most famous complicated and useable of Superalloys to make hot zone components of the gas turbines. The complicated dimensional tolerances, specially at the root of the blade show importance of grinding processes at the production of blades root. The prediction of the effect of machining parameters on the soundness of component surface strengthening for reaching to a suitable surface finishing and avoiding from crack formation at the work part during machining operation often is not easy and feasible so needs to more industrial investigation.This research is about frame 5 blade designed by GE and made from Superalloy IN738LC has been investigated. The formation of a plastically deformed and heat affected zone during grinding of Superalloy IN738LC with a high depth of cut but slow work speed (creep feed grinding) was investigated. Parameters such as work speed, depth of cut and radial dressing speed have been considered as variables and their effects have been studied. During experimental performed, the voltage and current of motor measured and power and special energy calculated.Some samples heat-treated (of the 1176℃ for 1 hr under neutral argon gas and cooling rate of 15℃/min up to 537℃ and then air cooling) to study grains recrystallization. Other samples have been created from the roots of blades and then coated by Nickel to measure boundary layer micro-hardness. The results show that increasing work speed leads to increasing the use power. Increasing the depth of cut, by increasing material removal rate, and the radial dressing speed, by decreasing power, lead to decreasing special energy. The temperature created by grinding lead to decreasing plastic deformation and boundary layer formation. When the radial dressing speed changes from 1 to 0.6μm/rev and other parameters are kept unchanged the roughness of surface increases and the special energy decreases. Sufficient dressing is very essential in limiting the width of the molten zone to few micrometers. As a result, it was found that local melting at contact spots to be a rather common mechanism during grinding of superalloys, lead to so-called white layers which can easily be observed on metallographic cross sections.     

MC-MLAS: Multi-channel Minimum Latency Aggregation Scheduling in Wireless Sensor Networks

Data aggregation is a key, yet time-consuming functionality in wireless sensor networks (WSNs). Multi-channel design is a promising technique to alleviate interference as a primary reason for long latency of TDMA aggregation scheduling. Indeed, it provides more potential of parallel transmissions over different frequency channels, thus minimizing time latency. In this paper, we focus on designing a multi-channel minimum latency aggregation scheduling protocol, named MC-MLAS, using a new joint approach for tree construction, channel assignment, and transmission scheduling. To our best knowledge, this is the first work in the literature which combines orthogonal channels and partially overlapping channels to consider the total latency involved in data aggregation. Extensive simulations verify the superiority of MC-MLAS in WSNs.     

A mechanistic approach to evaluate the potential of the debonding distress in asphalt pavements

The debonding distress in asphalt pavement structures is a critical problem that affects the performance of asphalt concrete pavements. It occurs at the layer interface due to the poor bond quality between adjacent asphalt concrete layers and/or when stresses at the layer interface exceed the strengths of the material at the interface. The debonding of the adjacent layers, especially the top surface layer of an asphalt pavement, is a contributing factor to the premature cracking of pavements. Hence, the debonding distress can lead to a reduction in the life of the pavement. This paper presents an analytical and experimental framework to evaluate the potential for debonding at the layer interface of asphalt concrete pavements. Computational analysis was performed to determine the critical stress and strain states in layered asphalt pavements under moving vehicle loads using the Layered ViscoElastic pavement analysis for Critical Distresses (LVECD) computer program developed at North Carolina State University. This computational analysis enables a greater understanding of the critical stress that is involved in debonding and the ways that such stress is affected by pavement design parameters and environmental conditions. In addition, a prediction model was developed that can determine the shear bond strength at the interface of asphalt concrete layers with different tack coat materials at various temperatures, loading rates and normal confining stresses. The systematic and mechanistic framework developed in this study employs the maximum shear ratio concept as a shear failure criterion and provides a tool to evaluate the effects of various loading, environmental and pavement factors on the debonding potential of asphalt pavements. The overall advantages of the mechanistic framework and approach using the LVECD analysis tool will help lead to better understanding of the debonding mechanism, proper selection of the tack coats, and economic benefit in highway pavement maintenance and rehabilitation costs.     

Numerical investigation of the configuration of the pools on the flow pattern passing over pooled stepped spillway in skimming flow regime

Spillways are hydraulic structures which transfer water to the downstream. Stepped spillways areseriously attended to, since they are highly efficient regarding energy dissipation. In this study, the flow pattern over stepped spillways was simulated with five different pool configurations. The VOF method was used to simulate the flow free surface, and K??(RNG) was employed to model turbulence. The results obtained fromthe numerical model were fairly consistent with the experimental results. The results demonstrated that theflow velocity and the residual head showed significant differences in the spillway width with regard to different pool configurations. The pool configuration in which the pools were installed as staggered configuration of flat and pooled steps showed the least residual head at the downstream and as a result the greatest energy dissipation.     

Analysis and suppression of spurious modes of the ring shape anchored RF MEMS contour mode disk resonator

One of the most encumbering issues in RF MEMS resonators is spurious modes. The problem of spurious modes becomes more critical, when the ring type resonators are used. In the ring shape anchored contour mode disk resonator, for achieving a low serial resistance, the inner radius of the disk must be increased. This causes the spurious modes to become too close to the desired mode and degrade the operation of the resonator. In this work, spurious modes of before-mentioned device are introduced and their characteristics are evaluated by exact analytical approach. Based on those analytical approaches, we introduce two techniques for spurious mode suppression. The first technique is based on exciting the desired mode by proper electrode engineering and hence is an electrical approach. The second technique is reconfiguring of the anchor from a continuous ring to crossed ring segments and locating the segments on the phase discriminating lines to increase the insertion loss for spurious modes and decrease the losses for the fundamental mode. The final harmonic analysis verifies that the proposed techniques result a resonator with a pure frequency spectrum and spurious modes excluded over a very wide frequency range.