Magnetization profile for impurities in graphene nanoribbons

The magnetic properties of graphene-related materials and in particular the spin-polarised edge states predicted for pristine graphene nanoribbons (GNRs) with certain edge geometries have received much attention recently due to a range of possible technological applications. However, the magnetic properties of pristine GNRs are not predicted to be particularly robust in the presence of edge disorder. In this work, we examine the magnetic properties of GNRs doped with transition-metal atoms using a combination of mean-field Hubbard and Density Functional Theory techniques. The effect of impurity location on the magnetic moment of such dopants in GNRs is investigated for the two principal GNR edge geometries - armchair and zigzag. Moment profiles are calculated across the width of the ribbon for both substitutional and adsorbed impurities and regular features are observed for zigzag-edged GNRs in particular. Unlike the case of edge-state induced magnetisation, the moments of magnetic impurities embedded in GNRs are found to be particularly stable in the presence of edge disorder. Our results suggest that the magnetic properties of transition-metal doped GNRs are far more robust than those with moments arising intrinsically due to edge geometry.Comment: submitte

Impurity segregation in graphene nanoribbons

The electronic properties of low-dimensional materials can be engineered by doping, but in the case of graphene nanoribbons (GNR) the proximity of two symmetry-breaking edges introduces an additional dependence on the location of an impurity across the width of the ribbon. This introduces energetically favorable locations for impurities, leading to a degree of spatial segregation in the impurity concentration. We develop a simple model to calculate the change in energy of a GNR system with an arbitrary impurity as that impurity is moved across the ribbon and validate its findings by comparison with ab initio calculations. Although our results agree with previous works predicting the dominance of edge disorder in GNR, we argue that the distribution of adsorbed impurities across a ribbon may be controllable by external factors, namely an applied electric field. We propose that this control over impurity segregation may allow manipulation and fine-tuning of the magnetic and transport properties of GNRs.Comment: 5 pages, 4 figures, submitte

Large Eddy Simulation Combined With Equivalent Diameter For Turbulent Jet Modelling And Gas Dispersion

CFD modelling combines transport phenomena and numerical approaches to solve physical problems. Although numerical modelling of flow scenarios is the cutting edge of flow modelling, there seems to be room for improvement. This paper proposes an approach for jet modelling in a low Mach number computational code. The methodology is based on the equivalent diameter and velocity profile calculated downstream from the jet leak orifice. The novel model DESQr (Diameter of Equivalent Simulation for Quicker Run) is combined with LES (Large Eddy Simulation) to calculate the gas jet profile due to accidental releases. The model is implemented in the framework of FDS (Fire Dynamics Simulator) and the open source code is modified to handle gas dispersion scenarios. Numerical findings for jet modelling and gas dispersion are compared with experimental data. The results are also compared with a commercial CFD tool. Good agreement is observed. Significant computational time reduction is achieved. A free open source CFD tool emerges and the results presented in this work are promising.33352554020th Brazilian Congress of Chemical Engineering (COBEQ)OCT 19-22, 2014Florianopolis, BRAZI

Exponential behavior of the interlayer exchange coupling across non-magnetic metallic superlattices

It is shown that the coupling between magnetic layers separated by non-magnetic metallic superlattices can decay exponentially as a function of the spacer thickness $N$, as opposed to the usual $N^{-2}$ decay. This effect is due to the lack of constructive contributions to the coupling from extended states across the spacer. The exponential behavior is obtained by properly choosing the distinct metals and the superlattice unit cell composition.Comment: To appear in Phys. Rev.

Retraction methods and fixed point free maps with null minimal displacements on unit ball

In this paper we consider the class of H\"older-Lipschitz maps on unit ball $B_X$ of a Banach space $X$, and the question we deal with is whether for any $\alpha\in (0,1)$ and $\lambda>0$ there exists a fixed-point free map $T\colon B_X\to B_X$ such that $\|Tx - Ty\|\leq \lambda\|x - y\|^\alpha$ for all $x, y\in B_X$ and $\mathrm{d}(T,B_X)=0$. We show that if $X$ has a spreading Schauder basis then such a map can always be built, answering a question posed by the first author in \cite{Bar}. In the general case, using a recent approach of R. Medina \cite{M} concerning H\"older retractions of $(r_n)$-flat closed convex sets, we show that for any decreasing null sequence $(r_n)\subset \mathbb{R}$, there exists a fixed-point free mapping $T$ on $B_X$ so that $\|T^nx - T^n y\|\leq r_n(\| x - y\|^\alpha +1)$ for all $x, y\in B_X$ and $n\in\mathbb{N}$. New results related to Lipschitz maps are also obtained.Comment: Comments welcom

A Review of 'Human Insecurities in Southeast Asia'

Debates on human insecurities are crucial in a changing world that witnesses high social inequality, degradation of environment, social tensions and a growing violation of human rights. Unfortunately, all these issues permeate the social structures of Southeast Asian countries in different ways. In that region civil society faces problems that are diverse, as seen in the political tensions in Thailand, the deterritorialization of indigenous peoples in Philippines and Malaysia, human rights violations in Myanmar, and numerous other challenges. Such setting demands different approaches from institutions and communities to overcome pending risks threatening their populations

A Review of 'Law's Impunity: Responsibility and the Modern Private Military Company'

The mercenaries and mercenarism are two points of concern for scholars studying the rules of war throughout history. Both in jus ad bellum (JAB) and jus in bellum (JIB) we can find a framework of international law crafted to impede the participation of individuals motivated to take part in hostilities to get private gain. Nevertheless, paradoxically, the problem is when corporations are supported by domestic law to perform serviced in ground combats abroad. In the latter case, Human Rights Law (HRL), International Humanitarian Law (IHL) and International Criminal Law (ICL) present numerous gaps that make it difficult to incriminate corporations, which perpetuate the impunity among private organizations involved in human rights violations in conflict zones

Analytical results for long time behavior in anomalous diffusion

We investigate through a Generalized Langevin formalism the phenomenon of anomalous diffusion for asymptotic times, and we generalized the concept of the diffusion exponent. A method is proposed to obtain the diffusion coefficient analytically through the introduction of a time scaling factor $\lambda$. We obtain as well an exact expression for $\lambda$ for all kinds of diffusion. Moreover, we show that $\lambda$ is a universal parameter determined by the diffusion exponent. The results are then compared with numerical calculations and very good agreement is observed. The method is general and may be applied to many types of stochastic problem

A Review of ‘Human Insecurities in Southeast Asia’

Debates on human insecurities are crucial in a changing world that witnesses high social inequality, degradation of environment, social tensions and a growing violation of human rights. Unfortunately, all these issues permeate the social structures of Southeast Asian countries in different ways. In that region civil society faces problems that are diverse, as seen in the political tensions in Thailand, the deterritorialization of indigenous peoples in Philippines and Malaysia, human rights violations in Myanmar, and numerous other challenges. Such setting demands different approaches from institutions and communities to overcome pending risks threatening their populations