Hierarchical 3D starfish-like Ni3S4–NiS on reduced graphene oxide for high-performance supercapacitors

In this research, Ni₃S₄–NiS with starfish morphology was synthesized with a simple hydrothermal method and then hybridized with reduced graphene oxide (rGO) as a material for high-performance supercapacitors. The crystal structure and morphology of the as-prepared materials were studied by X-ray diffraction spectroscopy and electron microscopy. Uniform distribution of Ni₃S₄–NiS on rGO was observed from electron microscopy images. The results showed that Ni₃S₄–NiS/rGO with a specific capacitance of 1578 Fg^-1 and discharge time of 603 s at the current density of 0.5 Ag^-1 has more capacity and stability relative to Ni₃S₄–NiS. The cyclic stability after 5000 cycles showed that the Ni₃S₄–NiS/rGO electrode is stable, and 91% of its corresponding initial capacitance retained at the end of 5000 cycles. The good results in capacitance and stability of this electrode can be regarded as an improvement for the development of highly efficient and economic supercapacitors for portable electronic devices.     

Multistage portfolio optimization with stocks and options

We develop a multistage portfolio optimization model that utilizes options for mitigating market risk in a dynamic setting. Due to the key role of scenarios in the quality of investment decisions, a new scenario generation method is proposed that characterizes the dynamic behavior of asset returns. This methodology takes the dependence structure of different asset returns into account, and also considers serial correlations of each of the asset returns. Moreover, it preserves marginal distributions of asset returns. Also, it precludes arbitrage opportunities. To investigate the role of options, we implement the scenario generation method on a set of stocks selected from the New York Stock Exchange. Results show the high performance of the proposed scenario generation method. Afterwards, the generated set of scenarios is used as the uncertainty set for the multistage portfolio optimization model. Static and dynamic assessments are used for measuring the performance of options in mitigating market risks and generating additional returns. Finally, backtesting simulations are used for assessing different trading strategies of options.     

Design and implementing wireless multimedia sensor network for movement detection using FPGA local co-processing

In recent years, many researches have been conducted on designing wireless multimedia sensor networks. But, implementing these networks faces several challenges. One of these challenges is the bulky nature of the multimedia data which needs powerful radios with high data rates for transmission and requires much more energy. So, in some applications it is more efficient to process the data locally and send the results to the base station which allows WMSNs to be implemented using simple and cheap network nodes. In this paper a wireless multimedia sensor network has been designed which processes the images locally using small FPGA processors in order to detect possible motions and the time and location of the detected movements will be sent to the base station. The network is implemented to perform two motion detection algorithms separately using Spartan 6 FPGAs and the local results of motion detection and global result of the network are presented.

     

Variable sampling plan for resubmitted lots based on process capability index and Bayesian approach

Acceptance sampling plans are applied for quality inspection of products. Among the design approaches of sampling plan, the most important one is to use process capability indices in order to improve the quality of manufacturing processes and the quality inspection of products. But, selection of estimators of process capability index and their sampling distribution is very important. Bayesian statistical technique can be used to obtain the sampling distribution. In this paper, a variable sampling plan is developed for resubmitted lots based on process capability index and Bayesian approach. In the proposed sampling plan, lots are inspected several times depending on the quality level of the process. In addition, this paper presents an optimization model for determining the decision parameters of developed sampling plan with regards to the constraints related to the risk of consumer and producer. Two comparison studied have been done including: First, the methods of double sapling plan (DSP), multiple dependent state (MDS) sampling plan, and repetitive group sampling (RGS) plan are elaborated, and also in order to comparing developed sampling plans, an expected number of products as average sample number (ASN) is used for different developed plans; second, a comparison study between Bayesian approach and exact probability distribution is carried out and their results are analyzed. It is observed that the ASN values of MDS sampling plan is less than ASN values of other methods, and also the ASN values of different variable sampling plans based on Bayesian approach is less than ASN values obtained using exact approach.     

Determination of Capacity Benefit Margin in Multiarea Power Systems Using Particle Swarm Optimization

Available transfer capability (ATC) is a key index of the remaining capability of a transmission system for future transactions. To calculate the ATC between two areas in an interconnected power system, capacity benefit margin (CBM) is one of the indexes that need to be assessed. CBM ensures security of system operation when the system faces generation deficiency in some areas. In this paper, three new methods are introduced which reflect different objectives for CBM assessment. This provides more flexibility of choices for market participants. In the proposed methods, CBM determination is formulated as an optimization problem and particle swarm optimization (PSO) method is used to solve the problem. The numerical results for modified IEEE reliability test system are presented to demonstrate the effectiveness of the proposed approaches.     

Power System Stabilizer Services Pricing in an Electricity Market

This article proposes a mathematical-based framework for power system stabilizer service pricing/valuation in an electricity market. For this purpose, the excitation system service, in response to operating point change, is modeled as load. Such modeling allows the valuation of excitation system service by means of the marginal price cost. The proposed method captures the normalized rotor angle and voltage deviations indices to value the automatic voltage regulator-power system stabilizer dynamic service. Development of such load-based model for stability service gives rise to an appropriate financial compensation mechanism for the generators, in return for their services. The proposed modeling provides an opportunity to modify the independent system operator objective function. Modification of the independent system operator objective function is done by adding two new terms regarding active and reactive powers, explaining the automatic voltage regulator–power system stabilizer service, and several new related constraints. The proposed modeling scheme could also successfully address the power system stabilizer robustness valuation in the market. Efficiency of the proposed strategy/objective function has been verified on two test systems in an electricity market. Simulation results reveal that the proposed method appropriately separates power system stabilizer service from the generation re-dispatch in response to operating point change.     

Study of critical buckling loads and modes of cross-ply laminated annular plates

Buckling of composite annular plates under uniform internal and external radial edge loads have been investigated using energy method. Trefftez rule is used in the stability equations. The symmetric buckling of symmetric cross-ply laminates is considered. In this paper, buckling behavior for the three laminates (90/0)_2s, (90/0₂/90)_s and (90₂/0₂)_s are studied. Influence of some parameters such as thickness, stacking sequence, type of supports and the ratio of hole to sheet radius on buckling loads and modes are investigated. The results of the energy method are compared with the results of numerical method. Based on the results, in the plates with clamped boundary conditions the symmetric buckling assumption is not accurate, contrary to other boundary conditions.     

On the self-scheduling of a power producer in uncertain trading environments

This work presents a scenario-based approach to the self-scheduling problem of a price taker power producer in a DA market. It concentrates on three categories of uncertainty including price, forced outage and generation reallocation and analyses their effects on the producer revenue. To tackle the uncertainties a set of price scenarios are so generated that their means and covariance matrix are the same as the base-case scenario. Forced outage and generation reallocation of generator for each price scenario are appropriately modeled through a probabilistic methodology. In this work Downside Risk (DR) is employed as the risk measure which quantifies the downside violations from a specified target. A risk-constrained self-scheduling problem is therefore formulated and solved as a mixed integer linear programming problem. Numerical results for a case study are discussed.     

Influence of Nitrogen on Hydrogenated Amorphous Carbon Thin Films Deposited by Plasma Focus Device

To carry out our research, a plasma focus device is used to deposit thin films of nitrogen doped hydrogenated amorphous carbon (a-C:H:N) onto the stainless steel-AISI-304 substrates at room temperature. Thin films are deposited with the same numbers of focus shots, at the same distance from the anode tip and with different partial pressures of nitrogen in the mixtures of acetylene/nitrogen as working gas. The nitrogen contents of deposited films are studied using nuclear reaction analysis (NRA) techniques. The results prove that nitrogen contents of the samples do not increase significantly by increasing partial pressure of nitrogen of the working gas for both sets of the samples. Moreover, NRA results exhibit the limitation of nitrogen incorporated into the samples, when this experimental setup is used. G-peak position and peak intensity ratio of the D-band to G-band (I_D/I_G) are used to investigate the diamond characters. Also, they show that sp² clustering is highly dependent on the nitrogen atomic contents and angular position of the samples. Scanning electron microscopy (SEM) shows the granular surface morphology of the films. Furthermore, it shows that angular position of the samples with respect to the anode axis plays an important role in the grain size of the surface of the samples. The thickness of the films decreases significantly by increasing angular position of the samples, while it decreases slightly by increasing partial pressure of nitrogen of the working gas. The Vickers surface hardness of the thin films exhibits significant dependency on the sp² clustering.     

An automatic phase error compensating multiphase LC oscillator: analysis and design

In this work a self phase error compensating multiphase LC oscillator is proposed. Mismatches in LC tanks are considered as the main source of phase errors. Considering this, an analytical approach is proposed to find a relationship between phase errors and their corresponding coupling factors as a necessary condition for phase error cancellation then a self compensating circuit is proposed accordingly. The compensation circuit first detects the phase errors then employs them in a current tuner to change each stage coupling factor to reduce phase errors. The building blocks of the proposed circuit are investigated and the transistor level implementation of each one is presented afterwards. The theoretical results are evaluated and confirmed through simulations using ADS software in 0.18 μm CMOS technology. Simulation results show that not only phase errors are reduced with respect to the previous methods but also this procedure does not impose any further power consumption and phase noise to the circuit.