Toward secure distributed spectrum sensing in cognitive radio networks [cognitive radio communications and networks]

Cognitive radio is a revolutionary technology that promises to alleviate the spectrum shortage problem and to bring about remarkable improvement in spectrum utilization. Spectrum sensing is one of the essential mechanisms of CR and is an active area of research. Although the operational aspects of spectrum sensing are being studied actively, its security aspects have attracted very little attention. In this paper, we discuss security issues that may pose a serious threat to spectrum sensing. Specifically, we focus on two security threats - incumbent emulation and spectrum sensing data falsification - that may wreak havoc in distributed spectrum sensing. We also discuss methods for countering these threats and the technical hurdles that must be overcome to implement such countermeasures.     

Allocation of QoS connections in MF-TDMA satellite systems: a two-phase approach

We address the problem of providing guaranteed quality-of-service (QoS) connections over a multifrequency time-division multiple-access (MF-TDMA) system that employs differential phase-shift keying (DPSK) with various modulation modes. The problem can be divided into two parts-resource calculation and resource allocation. We present algorithms for performing these two tasks and evaluate their performance in the case of a Milstar extremely high frequency satellite communication (EHF-SATCOM) system. In the resource-calculation phase, we calculate the minimum number of timeslots required to provide the desired level of bit-error rate (BER) and data rate. The BER is directly affected by the disturbance in the link parameters. We use a Markov modeling technique to predict the worst case disturbance over the connection duration. The Markov model is trained offline to generate a transition-probability matrix, which is then used for predicting the worst case disturbance level. We provide simulation results to demonstrate that our scheme outperforms the scheme currently implemented in the EHF-SATCOM system. The resource-allocation phase addresses the problem of allocating actual timeslots in the MF-TDMA channel structure (MTCS). If we view the MTCS as a collection of bins, then the allocation of the timeslots can be considered as a variant of the dynamic bin-packing problem. Because the this problem is known to be NP-complete, obtaining an optimal packing scheme requires a prohibitive amount of computation. We propose a novel packing heuristic called reserve channel with priority (RCP) fit and show that it outperforms two common bin-packing heuristics.     

Effect of barrier layers on the properties of indium tin oxide thin films on soda lime glass substrates

In this paper, the electrical, structural and optical properties of indium tin oxide (ITO) films deposited on soda lime glass (SLG) haven been investigated, along with high strain point glass (HSPG) substrate, through radio frequency magnetron sputtering using a ceramic target (In₂O₃:SnO₂, 90:10 wt.%). The ITO films deposited on the SLG show a high electrical resistivity and structural defects compared with those deposited on HSPG due to the Na ions from the SLG diffusing to the ITO film by annealing. However, these properties can be improved by intercalating a barrier layer of SiO₂ or Al₂O₃ between the ITO film and the SLG substrate. SIMS analysis has confirmed that the barrier layer inhibits the Na ion's diffusion from the SLG. In particular, the ITO films deposited on the Al₂O₃ barrier layer, show better properties than those deposited on the SiO₂ barrier layer.     

Influence of cationic surfactant on adsorption of Cr(VI) onto activated carbon

The effect of a cationic surfactant on the adsorption of Cr(VI) on activated carbon was investigated using cetylpyridinium chloride (CPC). At a concentration below the critical micelle concentration (CMC) of CPC, the adsorption of CPC and Cr(VI) reached equilibrium within 60 min, while it took 180 min at the concentration above CMC. CPC decreased the adsorption rate of Cr(VI) and increased the adsorption amount of Cr(VI) onto activated carbon. To analyze adsorption phenomena of Cr(VI), adsorption kinetic and isotherm were used and fitted well with the pseudo-second order kinetic model and Langmuir adsorption model, respectively. CPC introduced a cationic functional group on the surface of activated carbon and provided an adsorption site for Cr(VI).     

Bridgeless Boost Rectifier With Low Conduction Losses and Reduced Diode Reverse-Recovery Problems

A bridgeless boost rectifier with low conduction losses and reduced diode reverse-recovery problems is proposed for power-factor correction. The proposed boost rectifier can reduce the conduction losses and alleviate the diode reverse-recovery problems by using a coupled inductor and two additional diodes. Zero-current turn-off of the output diodes is achieved, and the reverse-recovery currents of the additional diodes are slowed down to reduce the diode reverse-recovery losses. All inductive components are realized on a single magnetic core by utilizing the leakage inductance of the coupled inductor. Furthermore, for the use of this topology in the practical design, the linear peak current mode control is employed for the proposed boost rectifier. A detailed analysis and a control strategy are presented. Experimental results for a 300-W prototype are also discussed to show the performance of the proposed boost rectifier     

Effect of α-lath size on the mechanical properties of Ti–6Al–4V using core time hydrogen heat treatment

ABSTRACT

When hydrogen is dissolved, brittleness occurs in the material. However, in the case of titanium and titanium alloy, hydrogen can be temporarily dissolved and removed, thereby improving the mechanical properties of titanium and titanium alloy. In this study, Core time Hydrogen Heat treatment (CHH) applies to Ti–6Al–4V alloy to improve mechanical properties. CHH was performed at 800°C and 1000°C for 2?h. Thereafter, dehydrogenation was performed for 2 h at 700°C in vacuum atmosphere to remove residual hydrogen. After the CHH at 800°C, it was found that the α-lath size in the Ti–6Al–4V was narrowed; thereby increasing the Vickers hardness and tensile strength without decreasing in elongation.     

Lumican,an Exerkine,Protects against Skeletal Muscle Loss

Exerkines are soluble factors secreted by exercised muscles, mimicking the effects of exercise in various organs, including the muscle itself. Lumican is reportedly secreted from muscles; however, its roles in skeletal muscle remain unknown. Herein, we found that lumican mRNA expression in the extensor digitorum longus was significantly higher in exercised mice than in unloading mice, and lumican stimulated myogenesis in vitro. Additionally, lumican knockdown significantly decreased muscle mass and cross-sectional area (CSA) of the muscle fiber in the gastrocnemius muscle of exercised mice. Lumican upregulated phosphorylation of p38 mitogen-activated protein kinase (MAPK) and a p38 inhibitor near completely blocked lumican-stimulated myogenesis. Inhibitors for integrin α2β1 and integrin ανβ3 also prevented lumican-stimulated myogenesis. Systemic lumican treatment, administered via the tail vein for 4 weeks, significantly increased relative muscle masses by 36.1% in ovariectomized mice. In addition, intramuscular lumican injection into unloaded muscles for 2 weeks significantly increased muscle mass by 8.5%. Both intravenous and intramuscular lumican treatment significantly increased muscle CSA. Our in vitro and in vivo experiments indicate that lumican is a muscle-secreted exerkine that affords protection against muscle loss by activating p38 MAPK via integrin receptors.