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...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.展开更多
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 a...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.展开更多
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,...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.展开更多
文摘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.
文摘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.
基金supported by the National Key Research and Development Program of China(Grant No.2018YFC1508401)the National Natural Science Foundation of China(Grant No.51879065)the Project of Electric Power Construction Corporation of China(Grant No.DJ-ZDZX-2016-02).
文摘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.
