A Reinforcement Learning Based Routing in Cognitive Radio Networks for Primary Users with Multi-stage Periodicity

Wireless Personal Communications - Designing an efficient routing protocol for cognitive radio networks is critical due to the dynamic behavior of the primary users. Based on empirical studies, the...     

Numerical analysis of rock fracturing by gas pressure using the extended finite element method

High energy gas fracturing is a simple approach of applying high pressure gas to stimulate wells by generating several radial cracks without creating any other damages to the wells.In this paper,a numerical algorithm is proposed to quantitatively simulate propagation of these fractures around a pressurized hole as a quasi-static phenomenon.The gas flow through the cracks is assumed as a one-dimensional transient flow,governed by equations of conservation of mass and momentum.The fractured medium is modeled with the extended finite element method,and the stress intensity factor is calculated by the simple,though sufficiently accurate,displacement extrapolation method.To evaluate the proposed algorithm,two field tests are simulated and the unknown parameters are determined through calibration.Sensitivity analyses are performed on the main effective parameters.Considering that the level of uncertainty is very high in these types of engineering problems,the results show a good agreement with the experimental data.They are also consistent with the theory that the final crack length is mainly determined by the gas pressure rather than the initial crack length produced by the stress waves.     

Theoretical Drawbacks in Fuzzy Ranking Methods and Some Suggestions for a Meaningful Comparison: An Application to Fuzzy Risk Analysis

Comparing fuzzy numbers has become one of the key challenging issues in fuzzy sets. Many researchers have proposed different procedures to rank fuzzy numbers, but the results frequently contradict each other. This work addresses the key weakness of several fuzzy ranking methods which have been introduced in recent articles. In this paper, we reveal that in nearly all ranking methods that the ranking procedure depends on the height of fuzzy numbers the result is unreliable. However, the final aim of this study is to propose some suggestions for a meaningful comparison in new methods. We demonstrate our reasoning with several numerical cases taken from literature.     

Three‐dimensional FDTD modeling of neurons to solve EEG and MEG forward problem

Neuronal activities including calcium sodium current, ligands current, and synaptic transmembrane current create electromagnetic fields. Here, an analytic method is suggested to obtain the electromagnetic fields and potential signals resulting from the function of nerve cells inside the brain. Modeling simulates the behavior of cells three‐dimensionally. The proposed method employs the electric scalar potential and magnetic vector potential to solve the time‐domain three‐dimensional equations using the partial differential method. All ion flows are considered as electrical current densities. In this method, the brain and desired cells are meshed to solve the problem using the numerical method. As an example, the electric fields, magnetic fields, and signals generated by cingulum nerve fibers are illustrated and compared in C_z, F_z, and T3 electrode positions. A direct analysis method based on the same mechanism and biophysics of the nervous system is proposed. Employing this direct method leads not only to a better understanding of neuronal activity but also to a more accurate vision regarding the accuracy/inaccuracy of experimental and inverse methods. The analysis of these data provides insights into the brain function processes.     

Novel mesoporous Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript>/CTAB–SiO<Subscript>2</Subscript> as an effective adsorbent for the removal of amoxicillin and tetracycline from water

The current study was carried out to investigate the efficiency of using magnetic mesoporous of cetyltrimethylammonium bromide-functionalized silica-coated magnetite for removing amoxicillin (AMX) and tetracycline (TC) from tap water, river water, and medical wastewater as real samples. The properties of the synthesized adsorbent were characterized through transmission electron microscopy (TEM), scanning electron microscopy, X-ray diffraction spectrometry, Fourier transform infrared spectroscopy, vibrating sample magnetometry, pH_pzc, and also Brunauer, Emmett, and Teller (BET) methods. The BET surface area and the average diameter of mesoporous Fe₃O₄/SiO₂/CTAB–SiO₂ in accordance with TEM were 157.8 m² g^?1 and around 55 nm, respectively. In batch tests, the adsorption parameters, including the initial concentration, contact time, pH of solution, ionic strength, and adsorbent dose, were analysed. The experimental adsorption data were modelled using different classical and recently developed models. According to the results, the maximum adsorption capacities of AMX and TC on mesoporous Fe₃O₄/SiO₂/CTAB–SiO₂ were found to be 362.66 and 220.70 mg g^?1, respectively. Also, the results indicated that AMX and TC loaded on the adsorbent could be easily desorbed with 0.1 mol L^?1 HNO₃⁺ acetonitrile (1:1, v/v) and the adsorbent showed good reusability for the adsorption of the drugs studied.     

An overview of dynamic anomaly detection in social networks via control charts

Detection of anomalies in social networks has always been a topic of interest in the realm of social network analysis. However, in recent years, researchers from industrial process monitoring area have applied their methods for monitoring social networks. In this review paper, we discuss social network monitoring approaches that apply control charts to detect anomalies in social networks. We mention the characteristics of the approaches and will shed some light on different topics that can be considered for further investigation by interested researchers.     

Quarter car active suspension system: Minimum time controller design using singular perturbation method

Suspension systems have been widely applied to vehicles. Every vehicle moving on the randomly profiled road is exposed to vibration and shocks which is harmful both for the passengers in terms of comfort and for the durability of the vehicle itself. From this point of view, it is important to reset to zero displacement, velocity and acceleration of car in minimum time. So, this paper proposes a new minimum time controller based on bang-bang control for the quarter car active suspension systems. First by using singular perturbation method the original suspension system is decomposed into two fast and slow singular subsystems in theory, and then by Pontryagain’s Minimum Principle (PMP) and switching functions, the controller is designed for each subsystem and finally the optimal final time is obtained as maximum optimal time concluded of two subsystems. By using a degree of stability technique with two parameters (instead of four parameters), the optimal time is more reduced and leads to great simplifications in practical implementation. The performance of the controller is compared with the Sub optimal Linear Quadratic Regulator (SLQR) controller using two types of road profiles (step and bump) implemented in MATLAB/Simulink. Test results demonstrate the proposed controller is very more effective and simpler in eliminating fluctuations in suspension systems that finally provide the passengers comfort.     

Multi-robot, dynamic task allocation: a case study

This article presents a subgrouping approach to the multi-robot, dynamic multi-task allocation problem. It utilizes the percentile values of the distributional information of the tasks to reduce the task space into a number of subgroups that are equal to the number of robotic agents. The subgrouping procedure takes place at run-time and at every designated decision-cycle to update the elements of these subgroups using the relocation information of the elements of the task space. Furthermore, it reduces the complexity of the decision-making process proportional to the number of agents via introduction of the virtual representatives for these subgroups. The coordination strategy then uses the votes of the robotic agents for these virtual representatives to allocate the available subgroups. We use the elapsed time, the distance traveled, and the frequency of the decision-cycle as metrics to analyze the performance of this strategy in contrast to the prioritization, the instantaneous, and the time-extended coordination strategies.     

MHD natural convection in a nanofluid filled inclined enclosure with sinusoidal wall using CVFEM

Magnetohydrodynamic flow in a nanofluid filled inclined enclosure is investigated numerically using the Control Volume based Finite Element Method. The cold wall of cavity is assumed to mimic a sinusoidal profile with different dimensionless amplitude, and the fluid in the enclosure is a water-based nanofluid containing Cu nanoparticles. The effective thermal conductivity and viscosity of nanofluid are calculated using the Maxwell–Garnetts and Brinkman models, respectively. Numerical simulations were performed for different governing parameters namely the Hartmann number, Rayleigh number, nanoparticle volume fraction and inclination angle of enclosure. The results show that in presence of magnetic field, velocity field retarded, and hence, convection and Nusselt number decreases. At Ra = 10³, maximum value of enhancement for low Hartmann number is obtained at γ = 0°, but for higher values of Hartmann number, maximum values of E occurs at γ = 90°. Also, it can be found that for all values of Hartmann number, at Ra = 10⁴ and 10⁵, maximum value of E is obtained at γ = 60° and γ = 0°, respectively.     

Eicosapentaenoic acid promotes apoptosis in Ramos cells <Emphasis Type="Italic">via</Emphasis> activation of caspase-3 and -9

Eicosapentaenoic acid (EPA; 20∶5n−3) may reduce the cell number in cultured leukemia/lymphoma cells owing to reduced cell proliferation, induction of cell death, or a combination of these processes. EPA has been shown to promote apoptosis in Ramos cells, and our present study was focused on a possible cell cycle arrest and the pathways by which the apoptotic process is induced. Apoptosis may proceed along the intrinsic (mitochondrial) or the extrinsic (death receptor) pathway, which are mediated via different caspases. Caspases are a class of homologous cysteine proteases recognized as pivotal mediators of apoptosis. We investigated whether EPA affects progression of the cell cycle or promotes apoptosis directly. By incorporation of [³H]thymidine and [³H]valine, we showed that DNA, as well as protein synthesis, was reduced after incubation of Ramos cells with EPA for 6h. We monitored cell cycle distribution by 5-bromo-2′-deoxyuridine staining and observed no cell cycle arrest in the EPA-incubated cells. Incubation of cells with EPA caused PS-flipping, as demonstrated by annexin V-binding (flow cytometry), and cleavage of poly(ADP-ribose) polymerase measured by Western blot analysis. Furthermore, we observed increased activity of caspase-3 and-9, but not of caspase-8. Whereas inhibitors of caspase-3 and-9 reduced EPA-induced apoptosis, inhibition of caspase-8 did not. This suggests that EPA may promote apoptosis via the intrinsic pathway in Ramos cells. Thus, the reduction in cell number can be explained by a direct apoptotic effect of EPA rather than via cell cycle arrest.