SU(4) Theory for Spin Systems with Orbital Degeneracy

The isotropic limit of spin systems with orbital degeneracy is shown to have global SU(4) symmetry. On many 2D lattices, the ground state does not posses long range order, which may explain the observed spin liquid properties of $LiNiO_2$. In the SU(4) Neel ordered state, spin-spin correlations can be antiferromagneitc between two neighboring sites with parallel magnetic moments.Comment: 11 pages, 2 figures. submitted to PR

Evaluation of the Noah\u27s Ark: Wood Mechanical Properties Affected by Water Immersion

This study focuses on the mechanical properties of different wood types related to Noah’s Ark and their degradation over time as the ark experienced over a year in water. The objective of this research was to evaluate the wood mechanical properties affected by water immersion as a function of time to see if the strength and stiffness would be diminished. Wood specimens from white oak, teak, and pitch-coated and non-coated southern yellow pine were chosen, because they represent upper and lower bounds of the elastic moduli and strengths of different wood types found around the world. Teak is thought to best represent gopher (term used in the bible) wood, since it was prevalently used as a structural material in the Middle East. The different wood types were soaked in fresh water and salt water for one year (the total time of the flood event). The tensile, compressive and flexural properties of the wood specimens were tested every two months, and the results were statistically analyzed. Since all of the wood types gave similar degradation trends in their mechanical properties over time, one would expect that the mechanical behaviors of gopher wood would exhibit the same trends. Even pitch was used to coat some wood specimens for comparison to provide understanding of the corrosion protection by water-proofing. The bottom line is that the mechanical properties and consequential dimensional stability of gopher wood would not have changed significantly by water immersion (30% maximum), even if it was in salt water and even if there were no pitch to cover the wood. This 30% reduction is not enough to diminish the structural integrity of the ark

Device performance simulations of multilayer black phosphorus tunneling transistors

© 2015 AIP Publishing LLC.We report a theoretical investigation of ballistic transport in multilayer black phosphorus (BP) tunneling transistors (TFETs) with HfO2 as the gate oxide. First-principles calculations show that monolayer BP can be preserved well on HfO2 (111) surface. For a better device performance, the optimum layer and transport direction at different channel lengths are investigated. It is shown that BP TFETs have larger drain current in the armchair direction (AD) than in the zigzag direction, and the current difference can be several orders of magnitude. On-state current can be enhanced in the BP TFETs using thicker BP film, while the minimal leakage current is increased at the same time. To reduce the leakage current and subthreshold swing in the multilayer BP TFETs, lower source/drain doping concentration and smaller drain voltage should be applied. Compared to monolayer MoS2, MoSe2, and MoTe2 TFETs monolayer BP TFETs in AD can reach larger on-state current at the same Ion/Ioff ratio.published_or_final_versio

Synthesis, Structure and Magnetic Properties of New Layered Iron-Oxychalcogenide Na2Fe2OSe2

A new layered iron-oxychalcogenide Na2Fe2OSe2 has been synthesized and structurally characterized by powder X-ray diffraction. The structure is formed by alternate stacking of the newly discovered [Fe2OSe2] blocks and double layers of Na. Conductivity study shows that Na2Fe2OSe2 is a semiconductor with activation energy of 0.26 eV. Magnetic susceptibility and heat capacity measurements reveal an antiferromagnetic phase transition occurs at TN=73 K. A broad maximum of magnetic susceptibility and a slow decay of the specific heat above TN, arises as a result of two-dimensional short-range spin correlation.Comment: 4 pages, 4 figure

Quantum Dot in Z-shaped Graphene Nanoribbon

Stimulated by recent advances in isolating graphene, we discovered that quantum dot can be trapped in Z-shaped graphene nanoribbon junciton. The topological structure of the junction can confine electronic states completely. By varying junction length, we can alter the spatial confinement and the number of discrete levels within the junction. In addition, quantum dot can be realized regardless of substrate induced static disorder or irregular edges of the junction. This device can be used to easily design quantum dot devices. This platform can also be used to design zero-dimensional functional nanoscale electronic devices using graphene ribbons.Comment: 4 pages, 3 figure

Quality of Service Oriented Access Point Selection Framework for Large Wi-Fi Networks

This paper addresses the problem of Access Point (AP) selection in large Wi-Fi networks. Unlike current solutions that rely on Received Signal Strength (RSS) to determine the best AP that could serve a wireless user’s request, we propose a novel framework that considers the Quality of Service (QoS) requirements of the user’s data flow. The proposed framework relies on a function reflecting the suitability of a Wi-Fi AP to satisfy the QoS requirements of the data flow. The framework takes advantage of the flexibility and centralised nature of Software Defined Networking (SDN). A performance comparison of this algorithm developed through an SDN-based simulator shows significant achievements against other state of the art solutions in terms of provided QoS and improved wireless network capacity