Voltage-Dependent Electronic Transport Properties of Reduced Graphene Oxide with Various Coverage Ratios

Graphene is mainly implemented by these methods: exfoliating, unzipping of carbon nanotubes, chemical vapour deposition, epitaxial growth and the reduction of graphene oxide. The latter option has the advantage of low cost and precision. However, reduced graphene oxide(rGO) contains hydrogen and/or oxygen atoms hence the structure and properties of the rGO and intrinsic graphene are different. Considering the advantages of the implementation and utilization of rGO, voltage-dependent electronic transport properties of several rGO samples with various coverage ratios are investigated in this work. Ab initio simulations based on density functional theory combined with non-equilibrium Green's function formalism are used to obtain the current–voltage characteristics and the voltage-dependent transmission spectra of rGO samples. It is shown that the transport properties of rGO are strongly dependent on the coverage ratio. Obtained results indicate that some of the rGO samples have negative differential resistance characteristics while normally insulating rGO can behave as conducting beyond a certain threshold voltage. The reasons of the peculiar electronic transport behaviour of rGO samples are further investigated, taking the transmission eigenstates and their localization degree into consideration.The findings of this study are expected to be helpful for engineering the characteristics of rGO structures.

Optimal Deployment Density for Maximum Coverage of Drone Small Cells

With the proliferation of small and mini drones, Drone Small Cells(DSCs) can cooperative multiple drones to provide communication service for ground users as emergency means or supplementary ones of traditional terrestrial cellular networks. In this paper, we study the fundamental problem of optimizing the deployment density of DSCs to achieve the maximum coverage performance. Most related works do not consider cumulative inter-cell interference when studying the coverage performance of DSCs. First, we derive an approximate and closed-form expression of the cumulative inter-cell interference which comes from both probabilistic Line-of-Sight(Lo S) and Non-Line-of-Sight(NLo S) links. Then, we analyze the coverage performance of DSCs and derive the transcendental function of optimal deployment density to obtain the maximum coverage. Last, we propose an algorithm to get the optimal deployment density with low complexity. We conduct both field experiments and Matlab simulations to verify the correctness of theoretical analysis. In addition, we show the impact of some factors on the relation between the deployment density and coverage performance through extensive numerical simulations.

Rethinking Iranian Urban Housing -- A Review on the Housing Attributes under the Current Development of Tehran

Housing in the private sector in the metropolitan of Tehran in the past decades has been very much tied to the economical considerations, The current urban and building standards and regulations are believed to have very much contributed to the undermining the many social, environmental and visual potentials of the neighborhoods and to what we face today as congested apartment atmosphere where and the monotonous character of most of the neighborhoods as a result of the very same plans and regulations applied to their development namely the setbacks, land coverage ratios and floor to land area ratios with no regard to the very different characters many of these neighborhoods once had, either traditional and long-established or scenic and natural. The purpose of this paper is to briefly review the current state and trend of urban housing in Tehran and search for practical measures to improve the environment and character of urban housing in the city.

Fear the Walking Dead?Incidence and Effects of Zombie Firms in Europe

One explanation for the observed lack of economic dynamism in Europe is that so-called zombie firms are spreading and that they crowd out the growth of other,potentially more"lively",companies.Zombie firms are firms that apparently are unable to repay their debt and yet,they continue operating.The report describes estimates for 2010 and 2013 of the incidence of zombie firms across 19 European countries using firm-level data for more than one million companies.Importantly,it uses three alternative definitions of what constitutes a zombie firm to ensure robustness of estimates.The report finds that zombie firms are spreading in Europe,with the estimated incidence for 2013 being higher than for 2010.It also identifies considerable differences across countries.Zombie firm shares as of overall corporate capital are particularly high in Greece and Spain,but low in the Czech Republic and Slovakia.Distinguish among firms in terms of size and age,the report finds that larger and older firms,as compared to relatively smaller and younger firms,are more likely to be zombie firms.The report also finds that the growth of zombie firms in terms of employment crowds out the growth of other,non-zombie firms,especially young ones.Thus,one policy implication is that,greater economic activity is achieved by allowing zombie firms to exit the market.

海外可再生能源项目融资分析

随着我国能源投资国际化发展日益蓬勃,对境外有限追索权项目融资模式的探索以丰富传统海外投资模式在近年越发引起关注。卢志强先生在本文分享了他二十多年来在银行和新能源行业国内外融资的丰富经验,为我国海外投资方介绍项目融资与企业贷款的优势和方案对比、从贷方的角度分析银行对项目融资是怎么来评估以及转嫁风险、并为复杂的条款进行解读。借力外部融资除了可减少企业因负债率,更是为海外项目风险把关,确保项目更加可行和完善的。

Simulation of ice accumulation around bridge piers during river breakup periods using a discrete element model

During river breakup periods in winter or early spring, a large amount of ice floes of various sizes will be transported by flowing water. The presence of bridge piers in water alters velocity field. As a consequence, the transport process of ice floes around bridge piers will be influenced. It often causes the ice floe congestion around bridge piers. In the present study, the influences of the ice floe size and coverage ratio of ice floating on water surface on ice floe congestion have been examined. The influence of bridge pier layout on ice jam development has been assessed. Results showed that during river breakup period, the ice floe transport capacity around bridge pier decreased. With the presence of bridge piers, the critical coverage ratio of ice floating on water surface for the ice floe congestion depends on the ratio of the side length of ice floe to the pier spacing distance (a / Ln) and ice floe-length Froude number associated with the ice floe length (Fra). A discrete element model (DEM) has been developed to simulate the ice floe accumulating process around bridge piers. Simulation results agree well with those of experiments.