Edge State Magnetism of Single Layer Graphene Nanostructures

We study edge state magnetism in graphene nanostructures using a mean field theory of the Hubbard model. We investigate how the magnetism of the zigzag edges of graphene is affected by the presence of other types of terminating edges and defects. By a detailed study of both regular shapes, such as polygonal nanodots and nanoribbons, and irregular shapes, we conclude that the magnetism in zigzag edges is very robust. Our calculations show that the zigzag edges that are longer than three to four repeat units are always magnetic, irrespective of other edges, regular or irregular. We, therefore, clearly demonstrate that the edge irregularities and defects of the bounding edges of graphene nanostructures does not destroy the edge state magnetism

Sensory organ like response determines the magnetism of zigzag-edged honeycomb nanoribbons

We present an analytical theory for the magnetic phase diagram for zigzag edge terminated honeycomb nanoribbons described by a Hubbard model with an interaction parameter U . We show that the edge magnetic moment varies as ln U and uncover its dependence on the width W of the ribbon. The physics of this owes its origin to the sensory organ like response of the nanoribbons, demonstrating that considerations beyond the usual Stoner-Landau theory are necessary to understand the magnetism of these systems. A first order magnetic transition from an anti-parallel orientation of the moments on opposite edges to a parallel orientation occurs upon doping with holes or electrons. The critical doping for this transition is shown to depend inversely on the width of the ribbon. Using variational Monte-Carlo calculations, we show that magnetism is robust to fluctuations. Additionally, we show that the magnetic phase diagram is generic to zigzag edge terminated nanostructures such as nanodots. Furthermore, we perform first principles modeling to show how such magnetic transitions can be realized in substituted graphene nanoribbons.Comment: 5 pages, 5 figure

Thinning-free Polygonal Approximation of Thick Digital Curves Using Cellular Envelope

Since the inception of successful rasterization of curves and objects in the digital space, several algorithms have been proposed for approximating a given digital curve. All these algorithms, however, resort to thinning as preprocessing before approximating a digital curve with changing thickness. Described in this paper is a novel thinning-free algorithm for polygonal approximation of an arbitrarily thick digital curve, using the concept of "cellular envelope", which is newly introduced in this paper. The cellular envelope, defined as the smallest set of cells containing the given curve, and hence bounded by two tightest (inner and outer) isothetic polygons, is constructed using a combinatorial technique. This envelope, in turn, is analyzed to determine a polygonal approximation of the curve as a sequence of cells using certain attributes of digital straightness. Since a real-world curve=curve-shaped object with varying thickness, unexpected disconnectedness, noisy information, etc., is unsuitable for the existing algorithms on polygonal approximation, the curve is encapsulated by the cellular envelope to enable the polygonal approximation. Owing to the implicit Euclidean-free metrics and combinatorial properties prevailing in the cellular plane, implementation of the proposed algorithm involves primitive integer operations only, leading to fast execution of the algorithm. Experimental results that include output polygons for different values of the approximation parameter corresponding to several real-world digital curves, a couple of measures on the quality of approximation, comparative results related with two other well-referred algorithms, and CPU times, have been presented to demonstrate the elegance and efficacy of the proposed algorithm

Investigating the role of ICT intervention in grassroots innovation using structural equation modelling approach

Research on information communication technologies (ICT) for entrepreneurship development is burgeoning, yet our understanding of the use of ICT in support of grassroots innovation remains unclear. This paper examines the moderating role of the use of ICT on the relationship between grassroots innovation (GRI) and entrepreneurial success (ES). The study involved 400 grassroots entrepreneurs selected from three states in India, and the moderating effect of the use of ICT was analysed using moderated structural equation modelling. The results revealed that the use of ICT partially moderates the relationship between the new learning practices and economic benefits. It also partially moderates the relationship between local solution and economic benefits, but it fully moderates the relationship between networking capabilities and economic benefits, where the relationship is stronger when the use of ICT is high. Furthermore, the study found that the use of ICT does not moderate the relationship between new learning practice and non-economic benefits, relationship between local solution and non-economic benefits and relationship between networking capabilities and non-economic benefits

Migraine: treatments, comorbidities, and quality of life, in the USA

This study sought to characterize the experience of stress, treatment patterns, and medical and disability profile in the migraineur population to better understand how the experience of migraines impacts the social and psychological functioning of this group. A 30-minute self-report survey was presented via a migraine-specific website with data collection occurring between May 15 and June 15, 2012. Recruitment for the study was done through online advertisements. In total, 2,907 individuals began the survey and 2,735 met the inclusion criteria for the study. The sample was predominantly female (92.8%). Migraine-associated stress was correlated with length of time since first onset of symptoms (P \u3c 0.01) and number of symptoms per month (P \u3c 0.01). Disorders related to stress, such as depression (P \u3c 0.01) and anxiety (P \u3c 0.01), were also positively correlated with the measured stress resulting from migraines. Migraine-associated stress must be understood as a multidimensional experience with broader impacts of stress on an individual correlating much more highly with negative mental and physical health profiles. Stress resulting from frequent migraine headaches may contribute to the development of medical and psychological comorbidities and may be a part of a cyclical relationship wherein stress is both a cause and effect of the social and medical impairments brought about by migraine

Estimation of carrier life time from intrinsic photoluminescence of ZnO

Comprehensive knowledge of the optical properties, particularly of the room temperature (RT) photoluminescence (PL), of ZnO is essential for the future employment of this wideband gap (~3.3 eV at 300 K) II-VI compound semiconductor in photonic and optoelectronic device structures [1]. Hence, vigorous research activities on ZnO thin films, epilayers, and crystals took place during the last two decades, encompassing a vast variety of effects and phenomena such as birefringence, photocurrent, PL including sub-band gap emission, reflectance, transmittance, excitonic properties, Raman modes, and absorption edge steepness [1-4]. However, despite that large body of knowledge and its essential importance for light emitting processes, a discussion of the ZnO PL lineshape is not found in the literature [5]

Rate of Excitation Energy Transfer between Fluorescent Dyes and Nanoparticles

Long range resonance energy transfer (RET) between a donor and an acceptor molecule is increasingly being used in many areas of biological and material science. The phenomenon is used to monitor the in vivo separation between different (bio) polymers/units of (bio) polymers and hence the dynamics of various biomolecular processes. Because of the sensitivity of the rate on to the distance between the donor (D) and the acceptor (A), the technique is popularly termed as "spectroscopic ruler". In this work we examine the distance and orientation dependence of RET in three different systems: (i) between a conjugated polymer and a fluorescent dye, (ii) between a nanometal particle (NMP) and a fluorescent dye and (iii) between two NMP. We show that in all the three cases, the rate of RET follows a distance dependence of d^(- sigma) where exponent sigma approaches 6 at large d (F"orster type dependence) but has a value varying from 3-4 at short to intermediate distance. At short separation, the amplitude of rate is considerably smaller than predicted by the F"orster theory.Comment: 23 pages, 9 figure