Spiral graphone and one sided fluorographene nano-ribbons

The instability of a free-standing one sided hydrogenated/fluorinated graphene nano-ribbon, i.e. graphone/fluorographene, is studied using ab-initio, semiempirical and large scale molecular dynamics simulations. Free standing semi-infinite arm-chair like hydrogenated/fluorinated graphene (AC-GO/AC-GF) and boat like hydrogenated/fluorinated graphene (B-GO/B-GF) (nano-ribbons which are periodic along the zig-zag direction) are unstable and spontaneously transform into spiral structures. We find that rolled, spiral B-GO and B-GF are energetically more favorable than spiral AC-GO and AC-GF which is opposite to the double sided flat hydrogenated/fluorinated graphene, i.e. graphane/fluorographene. We found that the packed, spiral structures exhibit unexpected localized HOMO-LUMO at the edges with increasing energy gap during rolling. These rolled hydrocarbon structures are stable beyond room temperature up to at least $T$=1000\,K.Comment: Phys. Rev. B 87, 075448 (2013

Fast water flow through graphene nanocapillaries: a continuum model approach involving the microscopic structure of confined water

Water inside a nanocapillary becomes ordered, resulting in unconventional behavior. A profound enhancement of water flow inside nanometer thin capillaries made of graphene has been observed [B. Radha et.al., Nature (London) 538, 222 (2016)]. Here we explain this enhancement as due to the large density and the extraordinary viscosity of water inside the graphene nanocapillaries. Using the Hagen-Poiseuille theory with slippage-boundary condition and incorporating disjoining pressure term in combination with results from molecular dynamics (MD) simulations, we present an analytical theory that elucidates the origin of the enhancement of water flow inside hydrophobic nanocapillaries. Our work reveals a distinctive dependence of water flow in a nanocapillary on the structural properties of nanoconfined water in agreement with experiment, which opens a new avenue in nanofluidics.Comment: 5 pages, 4 Figure

Markov Properties of Electrical Discharge Current Fluctuations in Plasma

Using the Markovian method, we study the stochastic nature of electrical discharge current fluctuations in the Helium plasma. Sinusoidal trends are extracted from the data set by the Fourier-Detrended Fluctuation analysis and consequently cleaned data is retrieved. We determine the Markov time scale of the detrended data set by using likelihood analysis. We also estimate the Kramers-Moyal's coefficients of the discharge current fluctuations and derive the corresponding Fokker-Planck equation. In addition, the obtained Langevin equation enables us to reconstruct discharge time series with similar statistical properties compared with the observed in the experiment. We also provide an exact decomposition of temporal correlation function by using Kramers-Moyal's coefficients. We show that for the stationary time series, the two point temporal correlation function has an exponential decaying behavior with a characteristic correlation time scale. Our results confirm that, there is no definite relation between correlation and Markov time scales. However both of them behave as monotonic increasing function of discharge current intensity. Finally to complete our analysis, the multifractal behavior of reconstructed time series using its Keramers-Moyal's coefficients and original data set are investigated. Extended self similarity analysis demonstrates that fluctuations in our experimental setup deviates from Kolmogorov (K41) theory for fully developed turbulence regime.Comment: 25 pages, 9 figures and 4 tables. V3: Added comments, references, figures and major correction

A state-of-the-art review on the integration of Building Information Modeling (BIM) and Geographic Information System (GIS)

The integration of Building Information Modeling (BIM) and Geographic Information System (GIS) has been identified as a promising but challenging topic to transform information towards the generation of knowledge and intelligence. Achievement of integrating these two concepts and enabling technologies will have a significant impact on solving problems in the civil, building and infrastructure sectors. However, since GIS and BIM were originally developed for different purposes, numerous challenges are being encountered for the integration. To better understand these two different domains, this paper reviews the development and dissimilarities of GIS and BIM, the existing integration methods, and investigates their potential in various applications. This study shows that the integration methods are developed for various reasons and aim to solve different problems. The parameters influencing the choice can be summarized and named as "EEEF" criteria: effectiveness, extensibility, effort, and flexibility. Compared with other methods, semantic web technologies provide a promising and generalized integration solution. However, the biggest challenges of this method are the large efforts required at early stage and the isolated development of ontologies within one particular domain. The isolation problem also applies to other methods. Therefore, openness is the key of the success of BIM and GIS integration

Oxygen-rich microporous carbons with exceptional hydrogen storage capacity

Porous carbons have been extensively investigated for hydrogen storage but, to date, appear to have an upper limit to their storage capacity. Here, in an effort to circumvent this upper limit, we explore the potential of oxygen-rich activated carbons. We describe cellulose acetatederived carbons that combine high surface area (3800 m2 g-1) and pore volume (1.8 cm3 g-1) that arise almost entirely (> 90%) from micropores, with an oxygen-rich nature. The carbons exhibit enhanced gravimetric hydrogen uptake (8.1 wt% total, and 7.0 wt% excess) at -196 ºC and 20 bar, rising to a total uptake of 8.9 wt% at 30 bar, and exceptional volumetric uptake of 44 g l-1 at 20 bar, and 48 g l-1 at 30 bar. At room temperature they store up to 0.8 wt% (excess) and 1.2 wt% (total) hydrogen at only 30 bar, and their isosteric heat of hydrogen adsorption is above 10 kJ mol-1

Stability, local structure and electronic properties of borane radicals on the Si(1 0 0)

Deposition of a thin B layer via decomposition of B2H6 on Si (PureB process) produces B-Si junctions which exhibit unique electronic and optical properties. Here we present the results of our systematic first-principles study of BHn (n = 0–3) radicals on Si(1 0 0)2 × 1:H surfaces, the initial stage of the PureB process. The calculations reveal an unexpectedly high stability of BH2 and BH3 radicals on the surface and a plausible atomic exchange mechanism of surface Si atoms with B atoms from absorbed BHn radicals. The calculations show strong local structural relaxation and reconstructions, as well as strong chemical bonding between the surface Si and the BHn radicals. Electronic structure calculations show various defect states in the energy gap of Si due to the BHn absorption. These results shed light on the initial stages of the complicated PureB process and also rationalize the unusual electronic, optical and electrical properties of the deposited Si surfaces

Cigarette butt-derived carbons have ultra-high surface area and unprecedented hydrogen storage capacity

Discarded cigarette filters, in the form of cigarette butts, are a major waste disposal and environmental pollution hazard due to mainly containing cellulose acetate which is nonbiodegradable; 5.8 trillion cigarettes are smoked worldwide per annum generating > 800 000 metric tons of cigarette butts. Apart from causing litter, cigarette butts contain contaminants such as toxic heavy metals, which can leach into waterways, potentially causing harm to both humans and wildlife. In an effort to turn dangerous waste into value products, this study explores the valorisation of discarded smoked cigarette filters/butts. We show that porous carbons derived from cigarette butts, via sequential benign hydrothermal carbonisation and activation, are super porous and have ultra-high surface area (4300 m2 g-1) and pore volume (2.09 cm3 g-1) arising almost entirely (> 90%) from micropores. The carbons also have uncharacteristically high oxygen content associated with O-containing functional groups (COOH, C-OH and C=O), and show anomalous behaviour with respect to the effect of activation temperature on porosity, the latter being ascribable to the chemical mix present in cigarette butts and their hydrochar products. Due to the combined effects of high surface area, high microporosity and an oxygen-rich nature, the carbons exhibit unprecedentedly high hydrogen storage capacity of 8.1 wt% excess uptake, and 9.4 wt% total uptake at -196 ºC and 20 bar, rising to total uptake of 10.4 wt% and 11.2 wt% at 30 and 40 bar, respectively. The hydrogen storage capacity is the highest reported to date for any porous carbons and attains new levels for porous materials in general. This work also raises the question on whether valorisation can solve the intractable cigarette butt problem