A unified model for metal/organic interfaces: IDIS, ‘pillow’ effect and molecular permanent dipoles

A unified model, embodying the induced density of interface states (IDIS) model, the reduction of the metal work function due to the adsorbed molecules (‘pillow’ effect) and molecular permanent dipoles, is presented for describing the barrier formation at metal/organic interfaces. While the IDIS model and ‘pillow’ effect have been described in previous approaches, in this paper we show how to introduce molecular permanent dipoles in the interface barrier formation. Examples for Au or Al/organic interfaces are discussed, which show the validity of our results and the generality of our formalism.     

‘Superluminal paradox’ in wave packet propagation and its quantum mechanical resolution

We analyse in detail the reshaping mechanism leading to apparently ‘superluminal’ advancement of a wave packet traversing a classically forbidden region. In the coordinate representation, a barrier is shown to act as an effective beamsplitter, recombining envelopes of the freely propagating pulse with various spacial shifts. Causality ensures that none of the constituent envelopes are advanced with respect to free propagation, yet the resulting pulse is advanced due to a peculiar interference effect, similar to the one responsible for ‘anomalous’ values which occur in Aharonov’s ‘weak measurements’. In the momentum space, the effect is understood as a bandwidth phenomenon, where the incident pulse probes local, rather than global, analytical properties of the transmission amplitude T(p)$T\left(p\right)$. The advancement is achieved when T(p)$T\left(p\right)$ mimics locally an exponential behaviour, similar to the one occurring in Berry’s ‘superoscillations’. Seen in a broader quantum mechanical context, the ‘paradox’ is but a consequence of an attempt to obtain ‘which way?’ information without destroying the interference between the pathways of interest. This explains, to a large extent, the failure to adequately describe tunnelling in terms of a single ‘tunnelling time’.     

‘Electron collapse’ and the resistivity of liquid cesium

The electron collapse in cesium is pictured as the formation of a ‘virtual bound state’, the tunneling process accounting for the 6s-5d dynamic conversion. The anomalous variation of the resistivity of liquid cesium with pressure has been explained satisfactorily.     

Two-dimensional ‘hat-scratch’ periodic structures induced by a single femtosecond laser pulse on silica glass

Two-dimensional ‘hat-scratch’ structures are fabricated on silica glass by the interference of three non-coplanar beams originating from a single femtosecond laser pulse. The scanning electron microscope (SEM) characterizations show that the as-formed structures are composed of hat holes and scratch marks. The experimental results indicate that the structures are dependent on the intensity of laser beam. The formation of the two-dimensional ‘hat-scratch’ structures is mainly due to the combined laser ablation effects including ionization, shock wave, plasma expansion, and phase explosion.     

Geometry of ‘standoffs’ in lattice models of the spatial Prisoner’s Dilemma and Snowdrift games

The Prisoner’s Dilemma and Snowdrift games are the main theoretical constructs used to study the evolutionary dynamics of cooperation. In large, well-mixed populations, mean-field models predict a stable equilibrium abundance of all defectors in the Prisoner’s Dilemma and a stable mixed-equilibrium of cooperators and defectors in the Snowdrift game. In the spatial extensions of these games, which can greatly modify the fates of populations (including allowing cooperators to persist in the Prisoner’s Dilemma, for example), lattice models are typically used to represent space, individuals play only with their nearest neighbours, and strategy replacement is a function of the differences in payoffs between neighbours. Interestingly, certain values of the cost–benefit ratio of cooperation, coupled with particular spatial configurations of cooperators and defectors, can lead to ‘global standoffs’, a situation in which all cooperator–defector neighbours have identical payoffs, leading to the development of static spatial patterns. We start by investigating the conditions that can lead to ‘local standoffs’ (i.e., in which isolated pairs of neighbouring cooperators and defectors cannot overtake one another), and then use exhaustive searches of small square lattices (4×4$4\times 4$ and 6×6$6\times 6$) of degree k=3,k=4$k=3,k=4$, and k=6$k=6$, to show that two main types of global standoff patterns–‘periodic’ and ‘aperiodic’–are possible by tiling local standoffs across entire spatially structured populations. Of these two types, we argue that only aperiodic global standoffs are likely to be potentially attracting, i.e., capable of emerging spontaneously from non-standoff conditions. Finally, we use stochastic simulation models with comparatively large lattices (100×100$100\times 100$) to show that global standoffs in the Prisoner’s Dilemma and Snowdrift games do indeed only (but not always) emerge under the conditions predicted by the small-lattice analysis.     

Electron spectroscopy and density-functional study of ‘ferric wheel’ molecules

The Li-centered ‘ferric wheel’ molecules with six oxo-bridged iron atoms form molecular crystals. We probed their electronic structure by X-ray photoelectron and soft X-ray emission spectroscopy, having calculated in parallel the electronic structure of a single ‘ferric wheel’ molecule from first-principles by tools of the density-functional theory, using, specifically, the Siesta method. The Fe local moments were found to be 4μ_B, irrespective of their mutual orientation. Neighbouring atoms, primarily oxygen, exhibit a noticeable magnetic polarization, yielding effective spin S=5/2 per iron atom, that can get inverted as a ‘rigid’ one in magnetic transitions. Corresponding energy preferences can be mapped onto the Heisenberg model with effective exchange parameter J of about −80 K.     

Elimination mechanism promotes cooperation in coevolutionary prisoner’s dilemma games

We propose an elimination mechanism in the study of the evolutionary prisoner’s dilemma games on evolving networks. It assumes that after each round of playing, players whose payoffs are below a certain threshold will be eliminated from the game and the same number of new nodes will be added to the network to maintain the size of the network constant. Numerical results show that moderate values of elimination threshold can result in a maximum cooperation level in the evolutionary prisoner’s dilemma game. Moreover, the elimination mechanism can make the network structure evolve into a high heterogeneity in degree distribution, which is considered to be helpful in promoting cooperation in evolutionary games. The present study may provide new insight for understanding the evolution of cooperation in light of the law ‘survival of the fittest’ in nature.     

Quantum chemical modelling of ‘green’ luminescence in self activated perovskite-type oxides

We discuss the origin of the intrinsic visible band emission of ABO₃ perovskite oxides (so-called ‘green luminescence’) which remains a topic of high interest during the last quarter of the century. We present a theoretical calculation modelling of this emission in the framework of a concept of charge transfer vibronic excitons [Phys. Solid State, 40 (1998) 834], i.e. as a result of radiative recombination of correlated (bound) self-trapped electron and hole polarons in the highly polarizable ABO₃-type matrix. The Intermediate Neglect of Differential Overlap method combined with the Large Unit Cell periodic defect model was used for quantum chemical calculations and theoretical simulation of the green emission for a series of model ABO₃ perovskites. The ‘green’ luminescence energies for PbTiO₃, SrTiO₃, BaTiO₃, KNbO₃ and KTaO₃ perovskite-type crystals agree well with those experimentally observed earlier.     

Single-step laser deposition of functionally graded coating by dual ‘wire-powder’ or ‘powder-powder’ feeding—A comparative study

The creation of iron-copper (Fe-Cu) alloys has practical application in improving the surface heat conduction and corrosion resistance of, for example, conformal cooling channels in steel moulds, but is difficult to achieve because the elements have got low inter-solubility and are prone to solidification cracking. Previous work by these authors has reported a method to produce a graded iron-nickel-copper coating in a single-step by direct diode laser deposition (DLD) of nickel wire and copper powder as a combined feedstock. This work investigates whether dual powder feeds can be used in that process to afford greater geometric flexibility and compares attributes of the ‘nickel wire and copper powder’ and ‘nickel powder and copper powder’ processes for deposition on a H13 tool steel substrate.In wire-powder deposition, a higher temperature developed in the melt pool causing a clad with a smooth gradient structure. The nickel powder in powder-powder deposition did not impart much heat into the melt pool so the melt pool solidified with sharp composition boundaries due to single metal melting in some parts. In wire-powder experiments, a graded structure was obtained by varying the flow rates of wire and powder. However, a graded structure was not realised in powder-powder experiments by varying either the feed or the directions. Reasons for the differences and flow patterns in the melt pools and their effect on final part properties of parts produced are discussed.     

Multiple scale analysis of complex networks using the empirical mode decomposition method

Empirical mode decomposition (EMD) method can decompose any complicated data into finite ‘intrinsic mode functions’ (IMFs). In this paper, we use EMD method to analyze and discuss the structural properties of complex networks. A random-walk method is used to collect the data series of network systems. Utilizing the EMD method, we decompose the obtained data into finite IMFs under different spatial scales. The analysis results show that EMD method is an effective tool for capturing the topological properties of network systems under different spatial scales, such as the modular structures of network systems and their energy densities.     

The multi-agent Parrondo’s model based on the network evolution

A multi-agent Parrondo’s model is proposed in the paper. The model includes link A based on the rewiring mechanism (the network evolution) + game B (dependent on the spatial neighbors). Moreover, to produce the paradoxical effect and analyze the “agitating” effect of the network evolution, the dynamic processes of the network evolution + game B are studied. The simulation results and the theoretical analysis both show that the network evolution can make game B which is losing produce the winning paradoxical effect. Furthermore, we obtain the parameter space where the strong or weak Parrondo’s paradox occurs. Each size of the region of the parameter space is larger than the one in the available multi-agent Parrondo’s model of game A + game B. This result shows that the “agitating” effect of rewiring based on the network evolution is better than that of the zero-sum game between individuals.     

‘Exact’ Hartree-Fock calculations for atomic-hydrogen crystal

Preliminary ‘exact’ Hartree-Fock calculations are presented for a simple-cubic atomic-hydrogen crystal. Two types of basis orbitals have been considered. Orbital parameters and lattice spacing have been roughly optimized. The Fermi surface is found to be nearly spherical. It is made plausible that the Hartree-Fock limit has been nearly reached.     

Cellular automata simulation of traffic including cars and bicycles

As ‘greening’ of all aspects of human activity becomes mainstream, transportation science is also increasingly focused around sustainability. Modal co-existence between motorised and non-motorised traffic on urban networks is, in this context, of particular interest for traffic flow modelling. The main modelling problems here are posed by the heterogeneity of vehicles, including size and dynamics, and by the complex interactions at intersections. Herein we address these with a novel technique, based on one-dimensional cellular automata components, for modelling network infrastructure and its occupancy by vehicles. We use this modelling approach, together with a corresponding vehicle behaviour model, to simulate combined car and bicycle traffic for two elemental scenarios—examples of components that would be used in the building of an arbitrary network. Results of simulations performed on these scenarios, (i) a stretch of road and (ii) an intersection causing conflict between cars and bicycles sharing a lane, are presented and analysed.     

Hierarchical structure of Turkey’s foreign trade

We examine the hierarchical structures of Turkey’s foreign trade by using real prices of their commodity export and import move together over time. We obtain the topological properties among the countries based on Turkey’s foreign trade during the 1996-2010 period by using the concept of hierarchical structure methods (minimal spanning tree, (MST) and hierarchical tree, (HT)). These periods are divided into two subperiods, such as 1996-2002 and 2003-2010, in order to test various time-window and observe the temporal evolution. We perform the bootstrap techniques to investigate a value of the statistical reliability to the links of the MSTs and HTs. We also use a clustering linkage procedure in order to observe the cluster structure much better. From the structural topologies of these trees, we identify different clusters of countries according to their geographical location and economic ties. Our results show that the DE (Germany), UK (United Kingdom), FR (France), IT (Italy) and RU (Russia) are more important within the network, due to a tighter connection with other countries. We have also found that these countries play a significant role for Turkey’s foreign trade and have important implications for the design of portfolio and investment strategies.     

‘Symmetrical face’ based improved LPP method for face recognition

As one of the most important branches of pattern recognition and computer vision, face recognition has more and more become the focus of researches. In real word applications, the face image might have various changes owing to varying illumination, facial expression and poses, so we need sufficient training samples to convey these possible changes. However, most face recognition systems cannot capture many face images of every user for training, non-sufficient training samples have become one bottleneck of face recognition. In this paper, we propose to exploit the symmetry of the face to generate ‘symmetrical face’ samples and use an improved LPP method to perform classification. Experimental results show that our method can get a high accuracy.     

Correlations,hierarchies and networks of the world’s automotive companies

We investigate, within the scope of econophysics, the correlations, hierarchies and networks of the world’s automotive companies over the 2003–2010 period by using the concept of a minimal spanning tree (MST) and hierarchical tree (HT). We derive a hierarchical organization and construct the MSTs and HTs for the 2003–2010 period and illustrate how the MSTs and their associated HTs developed over time. These periods are divided into two subperiods, such as 2003–2006 and 2007–2010, in order to test various time-windows and understand the temporal evolution of the correlation structure over time. We perform the bootstrap techniques to investigate a value of the statistical reliability to the links of the MSTs. We also use average linkage cluster analysis (ALCA) to observe the cluster structure more clearly in HTs. From the structural topologies of these trees, we identify different clusters of companies according to their geographical proximity and economic ties. Our results show that some companies are more important within the network, due to a tighter connection with other companies. We also find that these important companies play a predominant role in the world’s automotive industry.     

The cosmological ‘constant’ and quantization in five dimensions

Campbell?s theorem ensures that all vacuum space-times in general relativity can be embedded in five dimensions, with the 4D scalar curvature expressed as an effective cosmological ‘constant’ Λ which depends on the extra coordinate. This Λ-landscape can be used to give insight to certain physical phenomena, such as the big bang and quantized particles.     

Hierarchical structures of correlations networks among Turkey’s exports and imports by currencies

We have examined the hierarchical structures of correlations networks among Turkey’s exports and imports by currencies for the 1996–2010 periods, using the concept of a minimal spanning tree (MST) and hierarchical tree (HT) which depend on the concept of ultrametricity. These trees are useful tools for understanding and detecting the global structure, taxonomy and hierarchy in financial markets. We derived a hierarchical organization and build the MSTs and HTs during the 1996–2001 and 2002–2010 periods. The reason for studying two different sub-periods, namely 1996–2001 and 2002–2010, is that the Euro (EUR) came into use in 2001, and some countries have made their exports and imports with Turkey via the EUR since 2002, and in order to test various time-windows and observe temporal evolution. We have carried out bootstrap analysis to associate a value of the statistical reliability to the links of the MSTs and HTs. We have also used the average linkage cluster analysis (ALCA) to observe the cluster structure more clearly. Moreover, we have obtained the bidimensional minimal spanning tree (BMST) due to economic trade being a bidimensional problem. From the structural topologies of these trees, we have identified different clusters of currencies according to their proximity and economic ties. Our results show that some currencies are more important within the network, due to a tighter connection with other currencies. We have also found that the obtained currencies play a key role for Turkey’s exports and imports and have important implications for the design of portfolio and investment strategies.