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In order to fully explore the merits of the multi-tier heterogeneous network (HetNet) and ultra-dense small cell deployments, the evolution of the cellular network architecture is on the way. Based on the frameless network architecture, this paper proposes the control plane (CP) and user plane (UP) adaptation strategy to improve the system energy efficiency (EE). In this paper, we give a three-step system EE optimization with constraints on the CP/UP adaptation. We optimize the system EE via CP and UP construction and adaptation while guaranteeing the user quality of service (QoS). In the first step, the CP construction and adaptation scheme is proposed through the Voronoi Diagram with EE improvements. In the second step, by jointly allocating the AE and subchannel resources, we construct the on-demand user-centric UP. In the last step, based on the UP construction from the second step, we adjust each UP to optimize the EE performance. This is achieved by employing game theory. Furthermore, we verify the existence and uniqueness of the Nash Equilibrium for the non-cooperative game model with pricing. Finally, the system-level simulation results show that, with constraints on the QoS of the users, the system EE performances are improved. [ABSTRACT FROM AUTHOR]

Fe1+yTe1−xSex is characterized by its complex magnetic phase diagram and highly orbital-dependent band renormalization. Despite this, the behavior of nematicity and nematic fluctuations, especially for high tellurium concentrations, remains largely unknown. Here we present a study of both B1g and B2g nematic fluctuations in Fe1+yTe1−xSex (0 ≤ x ≤ 0.53) using the technique of elastoresistivity measurement. We discovered that the nematic fluctuations in two symmetry channels are closely linked to the corresponding spin fluctuations, confirming the intertwined nature of these two degrees of freedom. We also revealed an unusual temperature dependence of the nematic susceptibility, which we attributed to a loss of coherence of the dxy orbital. Our results highlight the importance of orbital differentiation on the nematic properties of iron-based materials. Despite a significant amount of research, there are still many unknowns about the underlying mechanisms of the superconductivity in Fe-based superconductors, in particular the roles of magnetism and nematicity. Here, the authors investigate the compositional dependence of the nematic susceptibility in Fe1+yTe1−xSex and the interplay between nematic and spin fluctuations, as well as the effect of orbital differentiation on nematic instability. [ABSTRACT FROM AUTHOR]

In this paper, multiple device-to-device (D2D) communication underlaying cellular multiuser multiple inputs multiple outputs (MU-MIMO) systems is investigated. This type of communication can improve spectral efficiency to address future demand, but interference management, user clustering, and resource allocation are three key problems related to resource sharing. Interference alignment (IA) is proposed to better mitigate in-cluster interference compared with a multiplex scheme, and user clustering and resource allocation are jointly investigated using binary-integer programming. In addition to an exhaustive search for a maximum throughput, we propose a two-step suboptimal algorithm by reducing the search space and applying branch-and-bound searching (BBS). To further obtain a good trade-off between performance and complexity, we propose a novel algorithm based on distance-constrained criteria for user clustering. The simulation results show that the IA and multiplex schemes acquiring user clustering gains outperform the orthogonal scheme without user clustering. Besides, the proposed two-step and location-based algorithms achieve little losses compared with the optimal algorithm under low complexities. [ABSTRACT FROM AUTHOR]

Engineering the electromagnetic environment of a nanometre-scale light emitter by use of a photonic cavity can significantly enhance its spontaneous emission rate, through cavity quantum electrodynamics in the Purcell regime. This effect can greatly reduce the lasing threshold of the emitter, providing a low-threshold laser system with small footprint, low power consumption and ultrafast modulation. An ultralow-threshold nanoscale laser has been successfully developed by embedding quantum dots into a photonic crystal cavity (PCC). However, several challenges impede the practical application of this architecture, including the random positions and compositional fluctuations of the dots, extreme difficulty in current injection, and lack of compatibility with electronic circuits. Here we report a new lasing strategy: an atomically thin crystalline semiconductor-that is, a tungsten diselenide monolayer-is non-destructively and deterministically introduced as a gain medium at the surface of a pre-fabricated PCC. A continuous-wave nanolaser operating in the visible regime is thereby achieved with an optical pumping threshold as low as 27 nanowatts at 130 kelvin, similar to the value achieved in quantum-dot PCC lasers. The key to the lasing action lies in the monolayer nature of the gain medium, which confines direct-gap excitons to within one nanometre of the PCC surface. The surface-gain geometry gives unprecedented accessibility and hence the ability to tailor gain properties via external controls such as electrostatic gating and current injection, enabling electrically pumped operation. Our scheme is scalable and compatible with integrated photonics for on-chip optical communication technologies. [ABSTRACT FROM AUTHOR]

By first-principles calculations, we investigate the geometric stability, electronic and optical properties of the type-II PN-WSe2 and type-I PAs-WSe2 van der Waals heterostructures(vdWH). They are p-type semiconductors with indirect band gaps of 1.09 eV and 1.08 eV based on PBE functional respectively. By applying the external gate field, the PAs-WSe2 heterostructure would transform to the type-II band alignment from the type-I. With the increasing of magnitude of the electric field, two heterostructures turn into the n-type semiconductors and eventually into metal. Especially, PN/PAs-WSe2 vdWH are both high refractive index materials at low frequencies and show negative refractive index at high frequencies. Because of the steady absorption in ultraviolet region, the PAs-WSe2 heterostructure is a highly sensitive UV detector material with wide spectrum. The type-II PN-WSe2 heterostructure possesses giant and broadband absorption in the near-infrared and visible regions, and its solar power conversion efficiency of 13.8% is higher than the reported GaTe–InSe (9.1%), MoS2/p-Si (5.23%) and organic solar cells (11.7%). It does project PN-WSe2 heterostructure a potential for application in excitons-based solar cells. [ABSTRACT FROM AUTHOR]

Pyrrolidines and piperidines are important building blocks in organic synthesis. Numerous methods exist for constructing substituted pyrrolidines and piperidines. However, efficient syntheses of pyrrolidines and piperidines bearing chiral tertiary alcohols are limited. Here we report an efficient enantioselective nickel-catalyzed intramolecular reductive cyclization of N-alkynones. A P-chiral bisphosphorus ligand DI-BIDIME is designed and applied in the synthesis of tertiary allylic siloxanes bearing pyrrolidine and piperidine rings in high yields and excellent enantioselectivities, with triethylsilane as reducing reagent. The highest turn over number achieved is 1000 (0.1 mol% catalyst loading) with > 99:1 er. This reaction provides a practical way to synthesize pyrrolidine and piperidine derivatives with chiral tertiary alcohols from easily accessible starting materials under mild conditions. The products can be scaled up and transformed to various useful chiral intermediates. The P-chiral bisphosphorus ligand developed in this study represents one of the few ligands for highly enantioselective cyclization of alkynones. Transition metal-catalyzed cyclization of alkynes and carbonyls offers a useful route to cyclic allylic alcohols, but typically uses precious metal catalysts. Here, enantioselective nickel-catalyzed reductive cyclization of N-alkynones gives tertiary allylic alcohols in up to 99:1 er with catalyst loadings of 0.1 mol% [ABSTRACT FROM AUTHOR]