22,969 research outputs found
On Energy Efficient Inter-Frequency Small Cell Discovery in Heterogeneous Networks
In this paper, we investigate the optimal inter-frequency small cell discovery (ISCD) periodicity for small cells deployed on carrier frequency other than that of the serving macro cell. We consider that the small cells and user terminals (UTs) positions are modelled according to a homogeneous Poisson Point Process (PPP). We utilize polynomial curve fitting to approximate the percentage of time the typical UT missed small cell offloading opportunity, for a fixed small cell density and fixed UT speed. We then derive analytically, the optimal ISCD periodicity that minimizes the average UT energy consumption (EC). Furthermore, we also derive the optimal ISCD periodicity that maximizes the average energy efficiency (EE), i.e. bit-per-joule capacity. Results show that the EC optimal ISCD periodicity always exceeds the EE optimal ISCD periodicity, with the exception of when the average ergodic rates in both tiers are equal, in which the optimal ISCD periodicity in both cases also becomes equal
Two-dimensional band structure in honeycomb metal-organic frameworks
Metal-organic frameworks (MOFs) are an important class of materials that
present intriguing opportunities in the fields of sensing, gas storage,
catalysis, and optoelectronics. Very recently, two-dimensional (2D) MOFs have
been proposed as a flexible material platform for realizing exotic quantum
phases including topological and anomalous quantum Hall insulators.
Experimentally, direct synthesis of 2D MOFs has been essentially confined to
metal substrates, where the interaction with the substrate masks the intrinsic
electronic properties of the MOF. Here, we demonstrate synthesis of 2D
honeycomb metal-organic frameworks on a weakly interacting epitaxial graphene
substrate. Using low-temperature scanning tunneling microscopy (STM) and atomic
force microscopy (AFM) complemented by density-functional theory (DFT)
calculations, we show the formation of 2D band structure in the MOF decoupled
from the substrate. These results open the experimental path towards MOF-based
designer quantum materials with complex, engineered electronic structures
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