Graphene for spintronics: giant Rashba splitting due to hybridization with Au

Graphene in spintronics has so far primarily meant spin current leads of high performance because the intrinsic spin-orbit coupling of its pi-electrons is very weak. If a large spin-orbit coupling could be created by a proximity effect, the material could also form active elements of a spintronic device such as the Das-Datta spin field-effect transistor, however, metal interfaces often compromise the band dispersion of massless Dirac fermions. Our measurements show that Au intercalation at the graphene-Ni interface creates a giant spin-orbit splitting (~100 meV) in the graphene Dirac cone up to the Fermi energy. Photoelectron spectroscopy reveals hybridization with Au-5d states as the source for the giant spin-orbit splitting. An ab initio model of the system shows a Rashba-split dispersion with the analytically predicted gapless band topology around the Dirac point of graphene and indicates that a sharp graphene-Au interface at equilibrium distance will account for only ~10 meV spin-orbit splitting. The ab initio calculations suggest an enhancement due to Au atoms that get closer to the graphene and do not violate the sublattice symmetry.Comment: 16 pages (3 figures) + supplementary information 16 pages (14 figures

New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens

Fossil evidence points to an African origin of Homo sapiens from a group called either H. heidelbergensis or H. rhodesiensis. However, the exact place and time of emergence of H. sapiens remain obscure because the fossil record is scarce and the chronological age of many key specimens remains uncertain. In particular, it is unclear whether the present day ‘modern’ morphology rapidly emerged approximately 200 thousand years ago (ka) among earlier representatives of H. sapiens1 or evolved gradually over the last 400 thousand years2. Here we report newly discovered human fossils from Jebel Irhoud, Morocco, and interpret the affinities of the hominins from this site with other archaic and recent human groups. We identified a mosaic of features including facial, mandibular and dental morphology that aligns the Jebel Irhoud material with early or recent anatomically modern humans and more primitive neurocranial and endocranial morphology. In combination with an age of 315?±?34 thousand years (as determined by thermoluminescence dating)3, this evidence makes Jebel Irhoud the oldest and richest African Middle Stone Age hominin site that documents early stages of the H. sapiens clade in which key features of modern morphology were established. Furthermore, it shows that the evolutionary processes behind the emergence of H. sapiens involved the whole African continent

On the mechanics of FG nanobeams: A review with numerical analysis

Since the classical continuum theories are insufficient to account the small size effects of nanobeams, the nonlocal continuum theories such as Eringen's nonlocal elasticity theory, couple stress theory, strain gradient theory and surface elasticity theory have been proposed by researchers to predict the accurate structural response of isotropic and functionally graded composite nanobeams. This review focuses on research work concerned with analysis of size dependent nanoscale isotropic and functionally graded beams using classical and refined beam theories based on Eringen's nonlocal elasticity theory. The present review article also highlight the possible scope for the future research on nanobeams. In the present study, the authors have developed a new hyperbolic shear deformation theory for the analysis of isotropic and functionally graded nanobeams. The theory satisfy the traction free boundary conditions at the top and the bottom surfaces of the nanobeams. Analytical solutions for the bending, buckling and free vibration analysis of simply-supported nanobeams are obtained using the Navier method. To ensure that the present theory is accurate and valid, the results are compared to previous research

New hybrid decentralized evolutionary approach for DIMACS challenge graph coloring & wireless network instances

The Graph Coloring Problem is an NP-hard combinatorial optimization problem, and it is being used in different real-world environments. The chromatic integer is determined using different probabilistic methods. This paper explores a new hybrid decentralized evolutionary approach that applies the fixed colors and reduces the edge conflicts iteratively using greedy, split and conquer strategies. This article explores a new hybrid decentralized stochastic methodology for solving graph coloring. The method is constructed by combining the following strategies: Greedy heuristics, split & conquer, and decentralized strategy with an advanced & enhanced global search evolutionary operator. These hybrid design strategies are exhibited on complex DIMACS challenge benchmark graphs and wireless network instances. The proposed approach minimizes the complexity and converges to the optimal solution within a minimal time. The minimum percentage of successful runs obtained for the DIMACS benchmarks lies in (82%, 85%) except for the difficult instance latin_square_10.col, the vertices count n = 900 and edges count m = 307350. For the latin_square_10.col graph, the minimum color is reduced to 97 compared to other methods with less successful runs percentage. For the difficult instance flat1000_76_0.col graph, the minimum color is reduced to 76 compared to other methods, resulting in a better successful run. The method obtains the minimum color as χ(G) for the difficult instances le.col and flat.col graphs compared to other methods. The time taken to execute the developed technique is compared with the competing methods, and the proposed method outperforms very competitively in finding the minimum color for large graphs and also in finding the better solution with the high frequency of convergence (> 98%) in the channel allocation of wireless networks compared to the current methods

Editorial Mathematical Modeling and Optimization of Functionally Graded Structures

Functionally graded structures such as beams, plates, and shells are those in which the volume fractions of two or more materials are varied continuously as a function of position along certain direction(s) of the structure to achieve a required function. Due to the dramatic increase in the use of functionally graded materials (FGMs) in a variety of engineering structures (e.g., mechanics, aerospace, automotive, nuclear, civil engineering, and medical prosthetics), as typical and principal mathematical issues, modeling and optimization of functionally graded structures have attracted the attention of many scientists in recent years for predicting the mechanical behavior of such structures This special issue collects selected papers on modeling aspects and the analysis of structures embedding functionally graded materials (FGMs). S. Topal and S. Dag presented in their paper two different -integral-based computational techniques, which can be used to conduct fracture mechanics analysis of orthotropic functionally graded materials subjected to hygrothermal stresses. The methods presented in this paper are shown to be effective ways of taking into account hygrothermal effects and evaluating fracture mechanics parameters and thus can be used to solve fracture and fatigue problems involving complex geometric configurations and loading conditions. In the paper by S. R. Mahmoud et al., the effect of nonhomogeneity and rotation on the free vibrations for elastodynamic problem of orthotropic hollow sphere is dis- Nonlocal elasticity model for bending analysis of sigmoid functionally graded materials (S-FGMs) nanoscale plates is presented in the paper by W. Y. Jung and S. C. Han using a first-order shear deformation theory and Hamilton's principle. The material properties of S-FGM nanoscale plate are assumed to vary according to sigmoid function (two power law distributions) of the volume fraction of the constituents. The effects of nonlocal parameters, power law index, aspect ratio, elastic modulus ratio, side-to-thickness ratio, and loading type on bending and vibration response are investigated in detail. The work presented in the paper 2 Mathematical Problems in Engineering by W. Y. Jung and S. C. Han can be helpful while designing nanoelectromechanical system and microelectromechanical system devices using the S-FGM nanoscale plates. In the paper of F. Tornabene and A. Ceruti, the generalized differential quadrature method has been presented as a means, to investigate the static and dynamic analysis of functionally graded and laminated composite doubly curved shells and panels. The mechanical models presented by F. Tornabene and A. Ceruti, is based on the so-called first-order shear deformation theory (FSDT). Three different optimization schemes and methodologies are implemented. The particle swarm optimization, Monte Carlo, and genetic algorithm approaches have been applied to define the optimum volume fraction profile for optimizing the first natural frequency and the maximum static deflection of the considered shell structure. In the paper presented by A. E. Alshorbagy et al., the boundary value problem of the uncoupled thermoelastic behavior of functionally graded plate is formulated and solved. First, the temperature distribution is predicted to be used in the thermoelastic analysis of functionally graded plate. Then, a finite element model based on the firstorder shear deformation plate (FSDT) theory is proposed, accounting for the exact neutral plane position, for modeling the functionally graded plates. A comparative study is performed to illustrate the effect of considering the neutral plane position. The paper presented by S. Kim et al. deals with the thermoelastic characteristics of circular disk TBC specimens with and without a functionally graded layer between the top and bond coats. Two partial differential equations are derived based on thermoelastic theory, and the thermoelastic characteristics, such as temperature distribution profiles, displacement, and stresses, are determined through mathematical approaches. Because of the complexity of the governing equations, a finite volume approach is adopted to analyze the thermoelastic characteristics. The papers published in this special issue only discuss some of the most significant topics about the mathematical modeling and optimization of functionally graded structures. However, the included papers present significant contributions and promising methods