Space as a Low-Temperature Regime of Graphs

I define a statistical model of graphs in which 2-dimensional spaces arise at low temperature. The configurations are given by graphs with a fixed number of edges and the Hamiltonian is a simple, local function of the graphs. Simulations show that there is a transition between a low-temperature regime in which the graphs form triangulations of 2-dimensional surfaces and a high-temperature regime, where the surfaces disappear. I use data for the specific heat and other observables to discuss whether this is a phase transition. The surface states are analyzed with regard to topology and defects.     

Enhancement of band-edge emission induced by defect transition in the composite of ZnO nanorods and CdSe/ZnS quantum dots

A new and general approach to enhance band-edge emission at the expense of defect emission in a semiconductor nanocomposite is proposed. The underlying mechanism is based on the resonance effect between defect transition and band-to-band excitation and transfer of excited electrons between conduction band edges. With our approach, it is possible to convert defect loss into bandgap emission. As an example, we demonstrate that the bandgap emission of ZnO nanorods can be enhanced by as much as 30 times when they are compounded with CdSe/ZnS nanoparticles.     

Evolving Networks with Nonlinear Assignment of Weight

We propose a weighted evolving network model in which the underlying topological structure is still driven by the degree according to the preferential attachment rule while the weight assigned to the newly established edges is dependent on the degree in a nonlinear form. By varying the parameter a that controls the function determining the assignment of weight, a wide variety of power-law behaviours of the total weight distributions as well as the diversity of the weight distributions of edges are displayed. Variation of correlation and heterogeneity in the network is illustrated as well.     

Water droplet impact on superhydrophobic surfaces with microstructures and hierarchical roughness

Quantitative correlation between the critical impact velocity of droplet and geometry of superhydrophobic surfaces with microstructures is systematically studied.Experimental data shows that the critical impact velocity induced wetting transition of droplet on the superhydrophobic surfaces is strongly determined by the perimeter of single micropillar,the space between the repeat pillars and the advancing contact angle of the sidewall of the micropillars.The proposed model agrees well with the experimental results,and clarifies that the underlying mechanism which is responsible for the superhydrophobic surface with hierarchical roughness could sustain a higher liquid pressure than the surfaces with microstructures.     

Frequency dependence of third harmonic generation in polyacetylene

The frequency dependence of the third harmonic generation in trans-polyacetylene is quantitatively interpreted by considering the bands of finite chain and the damping of excitation. Our theory shows that there are two distinct peaks in the spectrum of the third harmonic generation. The first one around 0.6 eV comes from the three-photon resonant transition between the edges of the valence band and conduction band; the second one around 0.9 eV is produced by the two-photon interband transition. The excitation-dependent damping is essential to determine the position of the second peak. The theoretical results agree well with the experimental data.     

A robust method for detecting nuclear materials when the underlying model is inexact

This paper is concerned with the detection and identification of nuclides from weak and poorly resolved gamma-ray energy spectra when the underlying model is not known exactly. The algorithm proposed and tested here pairs an exciting and relatively new model selection algorithm with the method of total least squares. Gamma-ray counts are modeled as Poisson processes where the average part is taken to be the model and the difference between the observed gamma-ray counts and the model is considered random noise. Physics provides a template for the model, but we add uncertainty to this template to simulate real life conditions. Unlike most model selection algorithms whose utilities are demonstrated asymptotically, our method emphasizes selection when data is fixed and finite (after all, detector data is undoubtedly finite). Simulation examples provided here demonstrate the proposed algorithm performs well.     

Ultrasound attenuation in solid CD4

We have measured the attenuation of 4 and 12 MHz longitudinal and transverse sound in solid CD₄ between 4 and 77 K. Absolute values for absorption at 77 K were determined from the variation in output amplitude as the length of the solid was reduced. As temperature is varied, the excess attenuation over a constant background undergoes maxima in the vicinity of the phase transitions at 22.1 and 27.0 K. The peak around the upper transition, which involves orientational ordering but not structural change, does not obey all the criteria of a single-relaxation model, but that model produces useful information on the hindering of molecular reorientation near the transition temperature, consistent with inferences drawn from thermal expansion measurements. Neither a relaxation model nor a critical-exponent model fits the attenuation data for the lower transition, in which both orientational and structural changes are now known to occur.     

A Simple Asymmetric Evolving Random Network

We introduce a new oriented evolving graph model inspired by biological networks. A node is added at each time step and is connected to the rest of the graph by random oriented edges emerging from older nodes. This leads to a statistical asymmetry between incoming and outgoing edges. We show that the model exhibits a percolation transition and discuss its universality. Below the threshold, the distribution of component sizes decreases algebraically with a continuously varying exponent depending on the average connectivity. We prove that the transition is of infinite order by deriving the exact asymptotic formula for the size of the giant component close to the threshold. We also present a thorough analysis of aging properties. We compute local-in-time profiles for the components of finite size and for the giant component, showing in particular that the giant component is always dense among the oldest nodes but invades only an exponentially small fraction of the young nodes close to the threshold.     

Analysis of phase transition points for a two-color agent-based model

The agent-based model treated in the present study describes dynamics of two types of population in a gravity-like potential field. In previous studies, the model was known to exhibit various spatiotemporal patterns on two-dimensioanl lattice systems. However, the patterns were classified depending purely on eye observations, and the underlying dynamics of these patterns were not fully explored. It remained a question to be answered if these eye observation-based classifications could be confirmed by any analytical means. To pursue the question, we first suggest several analytic quantities, such as convergence time steps and reaction speed, to replace the eye observations. As a result, we show that a phase diagram can be reasonably drawn on the contour diagram of the time steps. In addition, we find a power-law scaling in the reaction speed, confirming that a phase transition really is involved there. Next, as a main part of the present study, we apply analytical methods to calculate two important phase transition points from the system. The results from the analytical approach agreed well with the numerically obtained phase transition points from the agent-based model. In general, the paper serves as an example study of estimating global phenomena of complex systems in terms of local parameters of the system.     

Temperature-dependent theory of tunneling in the fractional quantum Hall effect

Recent experiments have studied the tunneling current between two edges of the same fractional quantum Hall liquid as a function of temperature and voltage. The experimental findings for low temperatures are at odds with the model where the edges are described as chiral Luttinger liquids, while the data at high temperatures are quite consistent with the same model. Here, we argue that a temperature dependence of the tunneling amplitude, not foreseen in previous works, can explain this discrepancy.     

On the model for the diffusion of hydrogen in titanium hydride

The diffusion parameters of hydrogen in the gamma phase of titanium hydride are discussed in the light of nuclear magnetic resonance measurements and inelastic neutron scattering data. A comparison with a previously proposed electrostatic model for diffusion is made. It is shown that the electrostatic model is not satisfactory in explaining hydrogen diffusion in titanium. An alternate potential well system based on inelastic neutron scattering data is shown to be consistent with nuclear magnetic resonance measurements. The model can in principle be used for estimating the tunneling contribution to diffusion. The potential well shape is consistent with the notion that for hydrogen diffusion in titanium, the activation energy is given by the difference between the ground state and the well height, in contrast to the case of hydrogen diffusion in niobium where the activation energy is less than this value.     

Islanding mechanism and band edges in InAs/GaAs nanostructures

Within the continuum elasticity theory, we investigate the substrate orientation effects on the Stranski–Krastanov (SK) growth mode and the band edges in InAs/GaAs nanostructures. Attending to the first part of the study, we estimate the transition thickness and the accumulated stress for substrate orientations (1 1 3) and (1 1 5) and we compare with the values obtained previously in InAs/GaAs (0 0 1) nanostructures. Assuming a coherent behavior at the substrate/film interface in the investigated substrate orientations, we consider a sigmoidal-type function for the dependence of the lattice parameter on the height. To evaluate the transition thickness, a minimization of the total free energy density with the slope is made. Similar to the orientation (0 0 1), in (1 1 3) and (1 1 5)-oriented substrates, two different stability regimes for the total free-energy density as well as for the accumulated stress are obtained. These regimes are directly related to the two stages of the SK growth mode. Although the relief strain mechanisms seem similar in all orientations, a delay in the 2D–3D phase transition is induced for high Miller indexes of the substrate. The non-rigid substrate approximation applied in InAs/GaAs nanostructures yields successful results for the transition thicknesses; the fraction of strained substrate being greater in InAs/GaAs (1 1 3). On the other hand, within our model, quantum dots formation is predicted for InAs/GaAs (1 1 1) heterostructures. Attending to the second, we find for all substrate orientations investigated, the strain-induced shifts lower the energies of the conduction band edges, while they raise the energies of the heavy- and light-holes band edges. In addition, the energy shifts are less significant for orientation (1 1 3), where the compressive stresses are smaller.     

Cascading failures of overload behaviors using a new coupled network model between edges

With the development of network science,the coupling between networks has become the focus of complex network research.However,previous studies mainly focused on the coupling between nodes,while ignored the coupling between edges.We propose a novel cascading failure model of two-layer networks.The model considers the different loads and capacities of edges,as well as the elastic and coupling relationship between edges.In addition,a more flexible load-capacity strategy is adopted to verify the model.The simulation results show that the model is feasible.Different networks have different behaviors for the same parameters.By changing the load parameters,capacity parameters,overload parameters,and distribution parameters reasonably,the robustness of the model can be significantly improved.     

Non-linear free vibrations of buckled plates with deformable loaded edges

In the great majority of papers dealing with non-linear dynamic buckling of plates it is assumed that the edge at which the in-plane load is applied is not deformable (rigid). In those few references in which buckling with deformable edges is examined normally a variational approach is used, based on “trial” functions for the in-plane displacements, which approach often leads to incorrect results. In this paper an exact form of the solution is found for the in-plane displacements, it being assumed that the membrane force is, at all times, exactly equal to the load applied at the corresponding loaded edge. As is well known, when the plate is buckled through a rigid beam these two forces are only on average equal to each other. It is shown here that the deformability of the loaded edges for plates undergoing large deformations should be taken into account for square-shaped plates, especially for those close to the so-called “golden-cut” shape (the aspect ratio between the edges equal to √2), while for long rectangular plates this effect may be disregarded.     

ANDERSON TRANSITION ZONE IN THE SOUKOULIS-ECONOMOU MODEL OF ONE-DIMENSIONAL INCOMMENSURATE SYSTEMS

Using numerical calculation method, we have studied the Anderson transition in the Soukoulis-Economou model of one-dimensional incommensurate systems. Our results in-dicate that the Anderson transition in this model should take place gradually, i.e., the transition from the extended state to the localized state should pass through a zone in which the intermediate state is located. We call it the Anderson transition zone of the Soukoulis-Economou model. This new conclusion differs from the traditional concept, which holds that the Anderson transition of the Soukoulis-Economou model occurs abruptly at the mobility edges of this model.     

基于小波与重调和方程的扩散去噪模型的研究

在图像处理过程中, 为了在图像去噪时更好地保留图像的角点、尖峰和窄边缘, 利用重调和方程的应力平衡性及其高阶偏导数的局部极大值, 构建新算子, 建立重调和扩散模型. 考虑到若图像中的噪声很强, 则会在处理后的图像上留下一些孤立的斑点, 且图像的纹理是在较大范围上具有的统计特性, 而新建模型只能保留局部细节, 图像大范围上的信息没有得到很好保留, 故对上述新建模型做进一步改进, 采用小波变换提取图像的高频部分, 对这部分运用应力平衡性构建新算子, 从局部上较稳定地控制图像的细节信息, 建立波域重调和扩散模型. 分析与仿真结果表明, 该模型与Perona-Mailik模型相比较保留了更多的图像信息, 有效地增强了图像的边缘, 同时很好地保持了图像的角点、尖峰、和窄边缘, 是一个理想的模型.     

Two-Dimensional Wetting Transition Modeling with the Potts Model

A droplet of a liquid deposited on a surface structured in pillars may have two states of wetting: (1) Cassie-Baxter (CB), the liquid remains on top of the pillars, also known as heterogeneous wetting, or (2) Wenzel, the liquid fills completely the cavities of the surface, also known as homogeneous wetting. Studies show that between these two states, there is an energy barrier that, when overcome, results in the transition of states. The transition can be achieved by changes in geometry parameters of the surface, by vibrations of the surface or by evaporation of the liquid. In this paper, we present a comparison of two-dimensional simulations of the Cassie-Wenzel transition on pillar-structured surfaces using the cellular Potts model (CPM) with studies performed by Shahraz et al. In our work, we determine a transition diagram by varying the surface parameters such as the interpillar distance (G) and the pillar height (H). Our results were compared to those obtained by Shahraz et al. obtaining good agreement.     

Mimicking the LCDM model with stealths

We present a new cosmological model that mimics the Lambda Cold Dark Matter by using a stealth field. This kind of field is characterized as not coupling directly to gravity; however, it is connected to the underlying matter content of the universe model. As is well known, stealth fields do not back-react on the space-time; however, their mimicry skills show how this field and its self-interaction potential determines the cosmic evolution. We show the study of the simplest model that can be developed with the stealth field.     

Instabilities and disorder-driven first-order transition of the vortex lattice

Transport studies in a Corbino disk suggest that the Bragg glass phase undergoes a first-order transition into a disordered solid. This transition shows sharp reentrant behavior at low fields. In contrast, in the conventional strip configuration, the phase transition is obscured by the injection of the disordered vortices through the sample edges, which results in the commonly observed vortex instabilities and smearing of the peak effect in NbSe2 crystals. These features are found to be absent in the Corbino geometry in which the circulating vortices do not cross the sample edges.