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This paper presents a new rate adaptive resource allocation technique for multiuser Orthogonal Frequency Division Multiplexing (OFDM) systems. We optimize both bit and subcarrier allocation by considering Rate maximization and Total Power constraint satisfaction. We solve them effectively by combining them into a multi-objective optimization problem. We propose using a Non Dominated Sort Genetic Algorithm (NSGA-II) -a multi-objective optimization using Genetic Algorithm. Instead of combining many conflicting objectives into a single function, the NSGA-II uses multiple objective optimizations and brings out solutions which provide a better trade-off taking all conditions into consideration. The simulation results and their marked improvement over previous algorithms provide the basis to this.

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Cellulose nanocrystals (CNC) are naturally-derived nanostructures of growing importance for the production of composites having attractive mechanical properties, and offer improved sustainability over purely petroleum-based alternatives. Fabrication of CNC composites typically involves extrusion of CNC suspensions and gels in a variety of solvents, in the presence of additives such as polymers and curing agents. However, most studies so far have focused on aqueous CNC gels, yet the behavior of CNC-polymer gels in organic solvents is important to their wider processability. Here, we study the rheological behavior of composite polymer-CNC gels in dimethylformamide, which include additives for both UV and thermal crosslinking. Using rheometry coupled with in-situ infrared spectroscopy, we show that under external shear, CNC-polymer gels display progressive and irreversible failure of the hydrogen bond network that is responsible for their pronounced elastic properties. In the absence of cross-linking additives, the polymer-CNC gels show negligible recovery upon cessation of flow, while the presence of additives allows the gels to recover via van der Waals interactions. By exploring a broad range of shear history and CNC concentrations, we construct master curves for the temporal evolution of the viscoelastic properties of the polymer-CNC gels, illustrating universality of the observed dynamics with respect to gel composition and flow conditions. We therefore find that polymer-CNC composite gels display a number of the distinctive features of colloidal glasses and, strikingly, that their response to the flow conditions encountered during processing can be tuned by chemical additives. These findings have implications for processing of dense CNC-polymer composites in solvent casting, 3D printing, and other manufacturing techniques. arXiv:1901.04373v1 [cond-mat.soft]

Abstract-Different from previous works in cooperative spectrum sensing that assumed the sensing channels independent identically distributed (i.i.d.), we investigate in this paper the independent but not identically distributed (i.n.i.d.) situations. In particular, we derive the false-alarm probability and the detection probability of cooperative spectrum sensing with the scheme of energy fusion over i.n.i.d. Rayleigh, Nakagami, and Rician fading channels. From the selected numerical results, we can see that cooperative spectrum sensing still gives considerably better performance even over i.n.i.d. fading environments.

We have measured the Raman spectra of Sb doped (ZrTe 5Ϫx Sb x ; 0ϽxϽ0.25) and Hf doped (Zr y Hf 1Ϫy Te 5 ; 0ϽyϽ1) pentatellurides in the 90-300 cm Ϫ1 range, and compared them to the corresponding spectrum for the parent material ZrTe 5. X-ray diffraction data revealed that the pentatelluride structure prevails at all doping concentrations. With increasing Sb concentration, the linewidths for three of the four Raman peaks observed at 115, 120, and 147 cm Ϫ1 in the parent material broadened with insignificant change in the linewidth for the fourth peak at 180 cm Ϫ1. Interestingly, the peak intensity for the mode at 180 cm Ϫ1 gradually diminishes in ZrTe 5Ϫx Sb x up to xϭ0.15, and completely vanishes in the xϭ0.20 compound. On the other hand, the electrical and Raman properties of Zr y Hf 1Ϫy Te 5 exhibit a systematic shift from the corresponding properties of ZrTe 5 to that of HfTe 5 for increasing Hf concentration in the sample. Implications of the disappearance of the resistivity anomaly with concomitant vanishing of 180 cm Ϫ1 Raman mode in the Sb doped samples for xϭ0.20 composition are presented.

Graphene has attracted much attention as an impermeable membrane and a protective coating against oxidation. While many theoretical studies have shown that defect-free graphene is impermeable, in reality graphene inevitably has defects in the form of grain boundaries and vacancies. Here, we study the effects of N-dopants on the impermeability of few-layered graphene (FLG) grown on copper using chemical vapor deposition. The grain boundaries in FLG have minimal impact on their permeability to oxygen as they do not provide a continuous channel for gas transport due to high tortuosity. However, we experimentally show that the N-dopants in FLG display multiple configurations that create structural imperfections to selectively allow gas molecules to permeate. We used a comprehensive array of tools including Raman spectroscopy, X-ray photoelectron spectroscopy, optically stimulated electron emission measurements, and density functional theory of N-doped graphene on copper to elucidate the effects of dopant configuration on the impermeability of graphene. Our results clearly show that oxygen can permeate through graphene with non-graphitic nitrogen dopants that create pores in graphene and oxidize the underlying Cu substrate while graphitic nitrogen dopants do not show any changes compared to the pristine form. Furthermore, we observed that the work function of graphene can be tuned effectively by changing the dopant configuration.