Reverse Link Performance of DS-CDMA Cellular Systems through Closed-Loop Power Control, Base Station Assignment, and Antenna Arrays in 2D Urban Environment

The interference reduction capability of antenna arrays, base station assignment, and the power control algorithms have been considered separately as means to increase the capacity in wireless communication networks. In this paper, we propose smart step closed-loop power control (SSPC) algorithm and base station assignment method based on minimizing the transmitter power (BSA-MTP) technique for direct sequence-code division multiple access (DS-CDMA) receiver in a 2D urban environment. This receiver consists of conjugate gradient adaptive beamforming and matched filter in two stages using antenna arrays. In addition, we study an analytical approach for the evaluation of the impact of power control error (PCE) on the DS-CDMA cellular systems. The simulation results indicate that the SSPC algorithm and the BSA-MTP technique can significantly improve the network bit error rate in comparison with conventional methods. Our proposed methods can also significantly save total transmit power and extend battery life in mobile units. In addition, we show that the convergence speed of the SSPC algorithm is faster than that of conventional algorithms. Finally, we discuss two parameters of PCE and channel propagation conditions (path-loss parameter and variance of shadowing) and their effects on the capacity of the system via some computer simulations.     

Stochastic Differential Equations for Modeling of High Maneuvering Target Tracking

In this paper, we propose a new adaptive single model to track a maneuvering target with abrupt accelerations. We utilize the stochastic differential equation to model acceleration of a maneuvering target with stochastic volatility (SV). We assume the generalized autoregressive conditional heteroscedasticity (GARCH) process as the model for the tracking procedure of the SV. In the proposed scheme, to track a high maneuvering target, we modify the Kalman filtering by introducing a new GARCH model for estimating SV. The proposed tracking algorithm operates in both the non‐maneuvering and maneuvering modes, and, unlike the traditional decision‐based model, the maneuver detection procedure is eliminated. Furthermore, we stress that the improved performance using the GARCH acceleration model is due to properties inherent in GARCH modeling itself that comply with maneuvering target trajectory. Moreover, the computational complexity of this model is more efficient than that of traditional methods. Finally, the effectiveness and capabilities of our proposed strategy are demonstrated and validated through Monte Carlo simulation studies.     

Single-step synthesis of activated carbon/γ-Fe2O3 nano-composite at room temperature

Magnetically activated carbon (MAC) nano-composite was synthesized by a simple single-step wet chemical method at room temperature. The structure, surface area, morphology and magnetic properties of as-prepared composite were characterized by X-ray diffraction (XRD), Brunaure–Emmet–Teller analysis (BET), Fourier transform infrared spectrum, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometry. SEM and TEM analysis indicated that the spherical maghemite (γ-Fe₂O₃) nanoparticles of average particle size 22±2 nm were homogeneously dispersed onto Treated Activated Carbon (TAC). Also, using Scherrer's formula, the average crystallite maghemite nano-particles on the TAC were estimated to be about 19 nm. According to BET analysis, the MAC was of 356 m²/g surface area and 0.36 cm³/g pore volume. The MAC nano-composite exhibited a nearly superparamagnetic property with a saturation magnetization (Ms) of 3.15 A m²/kg. It is suggested that this method could be a more efficient and practical way to produce magnetically modified activated carbon for use as a magnetic adsorbent to remove contaminants.     

Impact of Secondary User Block on the TCP Throughput in Cognitive Radio Sensor Networks

The cognitive radio sensor network (CRSN) has emerged as a promising solution to overcome spectrum under-utilization and spectrum scarcity problems in a resource-constrained wireless sensor network. In CRSN, TCP has to cope with a new type of packet loss due to the primary users arrival, known as secondary user blocking loss (SBL), otherwise It leads to significant TCP throughput degradation. In this paper, two main contributions are provided on the modeling of SBL and throughput evaluation of transport layer protocol for CRSN. First, it is identified two main factors of SBL and the probability of them is modeled by a discrete-time Markov chain. Second, a new congestion control algorithm is proposed to distinguish between actual congestion from the wrong congestion due to the SBL by considering the dynamic nature of CRSN. The obtained results through proposed model are verified using the COGNS framework based on NS2, which is a simulation framework for cognitive radio sensor networks. The proposed algorithm is compared with some of the well-known transport protocol TFRC-CR, OHTP and TCP Reno. The results confirm that our proposed algorithm is the best among them.

     

Energy efficient resource allocation in two-tier OFDMA networks with QoS guarantees

Wireless Networks - In this paper, we introduce the joint power and subchannel allocations techniques for OFDMA based femtocell networks with focus on uplink direction. These techniques minimize...     

Detecting the Source of Contaminant Zones Down-Gradient of the Alborz Sharghi Coal Washing Plant Using Geo-electrical Methods,Northeastern Iran

Environmental contamination from the Alborz Sharghi coal washing plant in northeast Iran was evaluated with geo-electrical techniques. The internal structure of a coal waste pile was first studied using one dimensional geo-electrical techniques, including a Schlumberger array. The oxidised zone had low resistivity while the unoxidised shallower and middle to deeper levels had higher resistivity. Next, the geo-electrical surveys were repeated after 6 months to investigate possible changes in the oxidation zone associated with seasonal variations. Precipitation affected the shallower levels of the pile. Two dimensional geo-electrical surveys, including a dipole–dipole array, were then conducted between the pile and tailings impoundments. Low resistivity values in the area appeared to indicate contaminated zones at depth. Again, two surveys were conducted at a 6 month interval. Results indicate the transportation of contaminants to deeper layers due to atmospheric precipitation. Considering the expansion of the contamination zones, the results of prior chemical analysis of the tailings impoundment water, and the increasing trend of the resistivity values in the deeper layers of the pile, seepage from the tailings impoundment is the most likely source of pollution in the area.     

The Effect of Time and Temperature of Nitridation-Oxidation Process on Properties and Corrosion Resistance of AISI 316L Steel

In this research, AISI 316L austenitic stainless steel has been subjected to plasma nitriding and oxidation- nitridation heat treatment at several temperatures for different times. Plasma nitriding of the samples was performed in N₂/H₂ = 1/3 atmosphere at temperatures of 425, 450, and 475°C for 5 h. To study the effects of the combined nitridation-oxidation process on mechanical and physical properties, the samples have been exposed in O₂/H₂ = 1/5 oxidating atmosphere at 425, 450, and 500°C for 15, 30, and 60 min, respectively. The mechanical and physical properties of the samples were studied after nitridation-oxidation heat treatment. The microstructural properties were examined by optical microscopy and scanning electron microscopy; the phases were analyzed by X-ray diffraction. The wear behavior of the oxidized-nitrided samples was studied using pin-on-disk tribotesting. The hardness and depth of the nitrided layer were measured by a Vickers hardness tester. The corrosion resistance of both untreated and treated samples was tested by the Tafel polarization and potentiodynamic polarization in 3.5% NaCl solution at ambient temperature. The results indicate that the combined nitridation-oxidation heat treatment improves both the pitting corrosion and wear resistances of AISI 316L steel and further increases its hardness.     

新型PEO/纳米结构ZrO_2镁合金涂层的抗菌活性及腐蚀行为（英文）

为了增强镁合金的耐腐蚀性和抗菌活性,先采用等离子体电解氧化(PEO)在镁合金上制备一层结合层,再用空气等离子喷涂(APS)制备纳米结构ZrO_2表面涂层。采用电化学试验研究涂层样品的腐蚀行为,采用琼脂扩散法对其进行大肠杆菌病原菌抑菌活性评价,并与无涂层样品进行对比。与PEO涂层和无涂层镁合金相比,PEO/纳米ZrO_2涂层样品的腐蚀电流密度最低,电荷传递阻力最高,相位角和阻抗模量最高。PEO结合涂层被纳米ZrO_2表面涂层完全密封,能够显著延缓侵蚀性离子向镁合金表面迁移,显著提高镁合金在模拟体液(SBF)中的耐蚀性。此外,PEO/纳米ZrO_2涂层的抗菌活性也高于PEO涂层和无涂层镁合金,这是由于ZrO_2纳米颗粒通过作用于细胞膜而降低了大肠杆菌的生长速率。     

Corrosion and Erosion Analysis of AlCrN/CrN Multilayered Coating Applied by Cathodic Arc Physical Vapor Deposition (PVD)

Protection of Metals and Physical Chemistry of Surfaces - A multilayered AlCrN/CrN coating was applied on stainless steel C-450 precipitation hardened stainless steel by cathodic arc vapor...     

Investigation on the influence of various welding parameters on the arc thermal efficiency of the GTAW process by calorimetric method

Arc efficiency of Gas Tungsten Arc Welding (GTAW) was determined by calorimetric method. A water-cooled anode calorimeter was designed and manufactured to measure the arc thermal efficiency, which was determined as a function of current, arc length, polarity and gas flow rate for GTAW of mild steel. With Direct Current Electrode Negative (DCEN) polarity and 5 mm arc length, a thermal efficiency of 67±4% was obtained, which was independent of the welding current. With Direct Current Electrode Positive (DCEP) polarity and 5 mm arc length, arc thermal efficiency was determined as 52±4%. The experimental data show that the arc efficiency decreases from 67% to 58% and 51% as the arc length increases from 5 mm to 11 and 17.5 mm, respectively. The experimental results also show that the arc efficiency is not significantly affected by the shielding gas flow rate.