Secrecy Outage of a Cognitive Radio Network with Selection of Energy Harvesting Relay and Imperfect CSI

Wireless Personal Communications - This paper investigates the physical layer security of an underlay cognitive radio network with relay selection scheme under threats of an eavesdropper. We...     

Two-Way Secure Communication with Multiple Untrusted Half-Duplex AF Relays

Wireless Personal Communications - In this paper, we analyze the secrecy outage probability (SOP) of a cognitive cooperative radio network in a two-way communication in which two secondary source...     

Secure communication in cognitive radio networks with untrusted AF relays

In this paper, two underlay based cognitive cooperative radio networks, each with one secondary source (SS), one secondary destination (SD), N untrusted secondary amplify and forward relays (USAFRs), one primary transmitter, and one primary receiver (PU‐RX), are considered for evaluating the secrecy performance. The SS sends the information to the SD in two time slots via multiple USAFRs in the absence of direct link between SS and SD. In the first time slot, SS and SD transmit the message and jamming signal to multiple USAFRs, respectively. In the second slot, a selected USAFR amplifies and forwards the combined received signals to the SD. The transmit powers of the secondary nodes are chosen so as to maintain the overall interference at PU‐RX below a specified limit. The transmit power of a selected USAFR is derived using the harvested energy from the RF signals of SS and SD. Two network scenarios of eavesdropping by USAFRs are studied: in one case, all USAFRs eavesdrop; while in the second case, only the selected USAFR eavesdrops the message during forwarding of the signal and power is allocated to secondary nodes on the basis of outage threshold of primary network. We investigate the secrecy outage probability (SOP) in both of the networks under several physical parameters. Analytical framework for evaluating SOP for both the cases are given while SOP in single integration form is given for the second case. MATLAB simulation results are presented for both the cases.     

Kinetics and mechanism of the thermal decomposition of potassium persulphate ions in aqueous solutions at 50°C in the presence of nitrogen gas and methacrylonitrile monomer

The initial rate of persulphate (I) decomposition at 50°C in the presence of nitrogen and methacrylonitrile (MAN) in an unbuffered aqueous solution (pH 4–7) may be written as: in the concentration ranges of persulphate (I) (0.25–2.50) × 10^?2 (m/dm³) and of (MAN) 0.18–0.36 (m/dm³). During the reaction, a white substance (polymethacrylonitrile) separates out in the colloidal state or in the precipitate form from the medium depending on the ionic strength of the medium. The pH of the medium was found to decrease rapidly and continuously with time in the absence of methacrylonitrile, but it decreased slowly and continuously with time in the presence of the monomer, MAN. If an additional quantity of MAN is injected late in a run, the rate of persulphate decomposition is further accelerated in a given run. However, the rate of persulphate decomposition is found to decrease continuously in the presence of MAN with time, i.e., as the monomer is converted to polymer. It is suggested that MAN accelerates the decomposition of persulphate ions, due to the following reactions in the aqueous phase: and where (M_j^˙)w is a-water soluble oligomeric or polymeric (j = 1–10) free radical. The estimated values of k₅ and k₁₀ are 1.05 × 10^?5 and 1.14 × 10³ (in dm³/m/s), respectively.     

Improved infrared photoluminescence characteristics from circularly ordered self-assembled Ge islands

The formation of circularly ordered Ge-islands on Si(001) has been achieved because of nonuniform strain field around the periphery of the holes patterned by focused ion beam in combination with a self-assembled growth using molecular beam epitaxy. The photoluminescence (PL) spectra obtained from patterned areas (i.e., ordered islands) show a significant signal enhancement, which sustained till 200 K, without any vertical stacking of islands. The origin of two activation energies in temperature-dependent PL spectra of the ordered islands has been explained in detail.     

Adsorptive removal of congo red dye (CR) from aqueous solution by Cornulaca monacantha stem and biomass-based activated carbon: isotherm,kinetics and thermodynamics

Cornulaca monacantha stem (CS) and biomass stem-based activated carbon (CS^AC) were explored for the removal of congo red (CR) dye from water system. The biomaterial was characterized using Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) and field emission scanning electron microscope (FESEM). The BET surface area of biomass stem-based activated carbon (CS^AC) was recorded to be 304.27 m²/g. The influence of different parameters such as initial CR concentration, adsorbent dosage, contact time, adsorbate pH and temperature onto CR adsorption were studied.The maximum adsorption of CR dye 97.19% and 86.43% were achieved at 55°C using CS^AC and CS adsorbents, respectively. The isotherm, kinetics and thermodynamic study were also investigated to explore the adsorption mechanism. The adsorption isotherm closely follow the Langmuir model (R² = 0.99) suggesting the monolayer adsorption of CR dye. Kinetic results indicated that pseudo second-order and Elovich model provide the better regression coefficient. Thermodynamic study revealed the feasible, spontaneous and endothermic nature of adsorption process. The regeneration study implies that adsorbent was efficiently recovered from CR dye with 0.01 mol/L NaOH solution. The CS^AC adsorbent possesses 75.75% uptake for CR dyes after 6th cycles of desorption-adsorption, respectively. .     

Characterization of porous structure of coal char from a single devolatilized coal particle: Coal combustion in a fluidized bed

The combustion characteristics of coal char are highly dependent on initial pore structure of devolatilized char as well as on the structural evolution during the combustion of char. The development of pore structure also throws light on the mechanism of the combustion process. In the present work evolution of pore structure of partially burnt coal char of Indian origin has been investigated experimentally in a batch-fluidized bed and analyzed. The BET surface area, micropore surface area and porosity of char at various levels of carbon burn-off have been determined. Experimental specific surface area has been found to agree well with theoretical prediction using random pore model. Modified random pore model is used to determine the active surface area. Char combustion mechanism based on shrinking unreacted core and shrinking reacted core models are delineated during the course of reaction at various bed temperatures. This is substantiated with the proportional representation of ash and carbon matrix in scanning electron microscope images. It is also concluded that in the present investigation the mean pore size is much smaller and hence the Knudsen diffusion predominates. Analysis based on similar experimental observations and models for pore structure evolution to investigate char combustion reaction regime has not been reported in literature.     

Effect of thermal pretreatment on recovery of nickel and cobalt from Sukinda lateritic nickel ore using microorganisms

Experimental investigation made previously on microbiological leaching of nickel and cobalt from the laterite nickel ore of Sukinda Valley reveals that the recovery was not very much promising under any favorable conditions. Therefore, in order to improve the efficiency for bioleaching, the homogenized lateritic ore in palletized form is thermally pretreated by roasting at different temperatures. The parameters studied for the bioleaching experiments were the four types of pretreated ore which were roasted at different temperatures, i.e., 300 °C, 400 °C, 600 °C and 800 °C, in shake flask by using a mixed mesophilic acidophilic bacterial consortium consisting predominantly of the Acidithiobacillus ferrooxidans strain. It was observed that the pretreated ore at 600 °C with 10% (w/v) pulp density showed maximum recovery of nickel and cobalt, i.e., 59.18% (4.556 ppm) and 65.09% (0.546 ppm), using 10% (v/v) (2.5 × 10⁸ cells/ml) consortium concentration at 1.5 pH, 30 °C, and 150 rpm after an incubation period of 31 days.     

Modelling of combustion characteristics of high ash coal char particles at high pressure: Shrinking reactive core model

Combustion of a single-particle high ash coal char at elevated pressure has been analyzed. A fully transient shrinking reactive core model incorporating a simple mechanistic kinetic scheme is used to study the combustion characteristics of high ash coal char. The model includes heat and mass transfer phenomena, reaction kinetics and intra-particle details. Finite volume method (FVM) has been used to solve partial differential equations representing fully transient conservation equations. The char combustion model predicts the mass-loss profile and burnout time of the char particle at different temperature and oxygen concentration. The computed results are found to agree well with the published experimental findings of pressurized combustion of high ash coal char. The effects of bulk temperature, total pressure and initial particle size on combustion characteristic and burnout time have been examined through model simulation.