22,577 research outputs found
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
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 . We
obtain as well an exact expression for for all kinds of diffusion.
Moreover, we show that 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
Thermal inactivation of Byssochlamys nivea in pineapple nectar combined with preliminary high pressure treatments
Byssochlamys nivea is a thermal resistant filamentous fungi and potential micotoxin producer. Recent studies have verified the presence of ascospores of such microorganism in samples of pineapple nectars. Although the majority of filamentous fungi have limited heat resistance and are easily destroyed by heat, Byssochlamys nivea ascospores have shown high thermal resistance. The aim of this work was to evaluate the application of linear and Weibull models on thermal inactivation (70, 80 and 90ºC) of Byssochlamys nivea ascospores in pineapple nectar after pretreatment with high pressure (550MPa or 650MPa during 15min). Following the treatments, survival curves were built up for each processing temperature and adjusted for both models. It was observed that survival curves at 90°C after high pressure pretreatment at 550 MPa/15 min did not fit well to linear and Weibull models. For all the other treatments, the Weibull model presented a better fit. At 90ºC without pressure treatment, the Weibull model also showed a better adjustment, having a larger R2 and a smaller RMSE. Regarding the process effectiveness, a 5-log reduction (t5), as recommended for pasteurization, was only achieved for Byssochlamys nivea ascospores presented in pineapple nectar at 90ºC/10.7 min with previous high pressure treatment of 650 MPa for 15 min. Considering the high intensity and energy demanding process with possibly product damage, other preventive and alternative treatments are being investigated
Avaliação da intensidade da queima-das-folhas em cultivares de coqueiro.
Anais do 1º Simpósio da Rede de Recursos Genéticos Vegetais do Nordeste (I RGVNE), Cruz das Almas, nov. 2013
Is it really possible to grow isotropic on-lattice diffusion-limited aggregates?
In a recent paper (Bogoyavlenskiy V A 2002 \JPA \textbf{35} 2533), an
algorithm aiming to generate isotropic clusters of the on-lattice
diffusion-limited aggregation (DLA) model was proposed. The procedure consists
of aggregation probabilities proportional to the squared number of occupied
sites (). In the present work, we analyzed this algorithm using the noise
reduced version of the DLA model and large scale simulations. In the noiseless
limit, instead of isotropic patterns, a () rotation in the
anisotropy directions of the clusters grown on square (triangular) lattices was
observed. A generalized algorithm, in which the aggregation probability is
proportional to , was proposed. The exponent has a nonuniversal
critical value , for which the patterns generated in the noiseless limit
exhibit the original (axial) anisotropy for and the rotated one
(diagonal) for . The values and were found for square and triangular lattices, respectively.
Moreover, large scale simulations show that there are a nontrivial relation
between noise reduction and anisotropy direction. The case (\bogo's
rule) is an example where the patterns exhibit the axial anisotropy for small
and the diagonal one for large noise reduction.Comment: 12 pages, 8 figure
Light scattering by a medium with a spatially modulated optical conductivity: the case of graphene
We describe light scattering from a graphene sheet having a modulated optical
conductivity. We show that such modulation enables the excitation of surface
plasmon-polaritons by an electromagnetic wave impinging at normal incidence.
The resulting surface plasmon-polaritons are responsible for a substantial
increase of electromagnetic radiation absorption by the graphene sheet. The
origin of the modulation can be due either to a periodic strain field or to
adatoms (or absorbed molecules) with a modulated adsorption profile.Comment: http://iopscience.iop.org/0953-8984/24/24/24530
AN ATTEMPT TO LINK THE BRAZILIAN HEIGHT SYSTEM TO A WORLD HEIGHT SYSTEM
This paper deals with the geopotential approach to investigate the present BrazilianHeight System (BHS). Geopotential numbers are derived from Global PositioningSystem (GPS) satellite surveying and disturbing potential on selected benchmarks.A model for the disturbing potential can be obtained by an existing set of sphericalharmonic coefficients such as the Earth Gravity Model 2008 (EGM08). Theapproach provides absolute evaluation of local normal geopotential numbers (akaspheropotential numbers) related to a so-called World Height System (WHS). Totest the validity of the proposed methodology, a numerical experiment was carriedout related to a test region in Southern Brazil. The accuracy of the derivedgeopotential numbers was tested versus local normal geopotential numbers based on262 GPS/leveling points. The root mean square error (RMSE) value for metricoffset of BHS derived from geopotential numbers and the disturbing potentialmodeling in the test area was estimated to be near 0.224 meters in the absolute view.Therefore, since these spheropotential numbers are referred to a local datum, theseresults of comparisons may be an indicator of the mean bias of local network due tothe effect of local Sea Surface Topography (SSTop) and possible offset between theunknown reference for the BHS and the quasigeoid model in the region
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 , as opposed to the usual 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.
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