Probability estimation based on grey system theory for simulation evaluation

In the evaluation of some simulation systems, only small samples data are gotten due to the limited conditions. In allusion to the evaluation problem of small sample data, an interval estimation approach with the improved grey confidence degree is proposed.On the basis of the definition of grey distance, three kinds of definition of the grey weight for every sample element in grey estimated value are put forward, and then the improved grey confidence degree is designed. In accordance with the new concept, the grey interval estimation for small sample data is deduced. Furthermore,the bootstrap method is applied for more accurate grey confidence interval. Through resampling of the bootstrap, numerous small samples with the corresponding confidence intervals can be obtained. Then the final confidence interval is calculated from the union of these grey confidence intervals. In the end, the simulation system evaluation using the proposed method is conducted. The simulation results show that the reasonable confidence interval is acquired, which demonstrates the feasibility and effectiveness of the proposed method.

UV–visible spectral characterization and density functional theory simulation analysis on laser-induced crystallization of amorphous silicon thin films

The effect of laser energy density on the crystallization of hydrogenated intrinsic amorphous silicon （a-Si：H） thin films was studied both theoretically and experimentally. The thin films were irritated by a frequency-doubled （λ= 532 nm） Nd：YAG pulsed nanosecond laser. An effective density functional theory model was built to reveal the variation of bandgap energy influenced by thermal stress after laser irradiation. Experimental results establish correlation between the thermal stress and the shift of transverse optical peak in Raman spectroscopy and suggest that the relatively greater shift of the transverse optical （TO） peak can produce higher stress. The highest crystalline fraction （84.5%） is obtained in the optimized laser energy density （1000 mJ/cm2） with a considerable stress release. The absorption edge energy measured by the UV- visible spectra is in fairly good agreement with the bandgap energy in the density functional theory （DFT） simulation.

High-efficiency sodium storage of Co_(0.85)Se/WSe_(2) encapsulated in N-doped carbon polyhedron via vacancy and heterojunction engineering

With the advantage of fast charge transfer,heterojunction engineering is identified as a viable method to reinforce the anodes'sodium storage performance.Also,vacancies can effectively strengthen the Na+adsorption ability and provide extra active sites for Na+adsorption.However,their synchronous engineering is rarely reported.Herein,a hybrid of Co_(0.85)Se/WSe_(2) heterostructure with Se vacancies and N-doped carbon polyhedron(CoWSe/NCP)has been fabricated for the first time via a hydrothermal and subsequent selenization strategy.Spherical aberration-corrected transmission electron microscopy confirms the phase interface of the Co_(0.85)Se/WSe_(2) heterostructure and the existence of Se vacancies.Density functional theory simulations reveal the accelerated charge transfer and enhanced Na+adsorption ability,which are contributed by the Co_(0.85)Se/WSe_(2) heterostructure and Se vacancies,respectively.As expected,the CoWSe/NCP anode in sodium-ion battery achieves outstanding rate capability(339.6 mAh g^(−1) at 20 A g^(−1)),outperforming almost all Co/W-based selenides.

IMPROVED QUANTITATIVE FEEDBACK THEORY TECHNIQUE AND APPLICATION TO THREE-AXIS HYDRAULIC SIMULATOR

In order to meet tracking performance index of three-axis hydraulic simulator, based on classical quantitative feedback theory （QFT）, an improved QFT technique is used to synthesize controller of low gain and bandwidth. By choosing a special nominal plant, the improved method assigns relative magnitude and phase tracking error between system uncertainty and nominal control plant. Relative tracking error induced by system uncertainty is transformed into sensitivity problem and relative tracking error induced by nominal plant forms into a region on Nichols chart. The two constraints further form into a combined bound which is fit for magnitude and phase loop shaping. Because of leaving out pre-filter of classical QFT controller structure, tracking performance is enhanced greatly. Furthermore, a cascaded two-loop control strategy is proposed to heighten control effect. The improved technique＇s efficacy is validated by simulation and experiment results.

A Guide to Population Modelling for Simulation

This paper outlines the fundamentals of a consistent theory of numerical modelling of a population system under study. The focus is on the systematic work to construct an executable simulation model. There are six fundamental choices of model category and model constituents to make. These choices have a profound impact on how the model is structured, what can be studied, possible introduction of bias, lucidity and comprehensibility, size, expandability, performance of the model, required information about the system studied and its range of validity. The first choice concerns a discrete versus a continuous description of the population system under study—a choice that leads to different model categories. The second choice is the model representation (based on agents, entities, compartments or situations) used to describe the properties and behaviours of the objects in the studied population. Third, incomplete information about structure, transitions, signals, initial conditions or parameter values in the system under study must be addressed by alternative structures and statistical means. Fourth, the purpose of the study must be explicitly formulated in terms of the quantities used in the model. Fifth, irrespective of the choice of representation, there are three possible types of time handling: Event Scheduling, Time Slicing or Micro Time Slicing. Sixth, start and termination criteria for the simulation must be stated. The termination can be at a fixed end time or determined by a logical condition. Population models can thereby be classified within a unified framework, and population models of one type can be translated into another type in a consistent way. Understanding the pros and cons for different choices of model category, representation, time handling etc. will help the modeller to select the most appropriate type of model for a given purpose and population system under study. By understanding the rules for consistent population modelling, an appropriate model can be created in a systematic way and a number of pitfalls can be avoided.

Charge-transfer-regulated bimetal ferrocene-based organic frameworks for promoting electrocatalytic oxygen evolution

The ferrocene(Fc)-based metal-organic frameworks(MOFs)are regarded as compelling platforms for the construction of efficient and robust oxygen evolution reaction(OER)electrocatalysts due to their superior conductivity and flexible electronic structure.Herein,density functional theory simulations were addressed to predict the electronic structure regulations of CoFc-MOF by nickel doping,which demonstrated that the well-proposed CoNiFc-MOFs delivered a small energy barrier,promoted conductivity,and well-regulated d-band center.Inspired by these,a series of sea-urchin-like CoNiFc-MOFs were successfully synthesized via a facile solvothermal method.Moreover,the synchrotron X-ray and X-ray photoelectron spectroscopy measurements manifested that the introduction of nickel could tailor the electronic structure of the catalyst and induce the directional transfer of electrons,thus optimizing the rate-determining step of^(*)O→^(*)OOH during the OER process and yielding decent overpotentials of 209 and 252 mV at 10 and 200 mA cm^(−2),respectively,with a small Tafel slope of 39 mV dec^(−1).This work presents a new paradigm for developing highly efficient and durable MOF-based electrocatalysts for OER.

Ultrathin NiO/Ni_(3)S_(2)Heterostructure as Electrocatalyst for Accelerated Polysulfide Conversion in Lithium-Sulfur Batteries

The practical application of Lithium-Sulfur batteries largely depends on highly efficient utilization and conversion of sulfur under the realistic condition of high-sulfur content and low electrolyte/sulfur ratio.Rational design of heterostructure electrocatalysts with abundant active sites and strong interfacial electronic interactions is a promising but still challenging strategy for preventing shuttling of polysulfides in lithium-sulfur batteries.Herein,ultrathin nonlayered NiO/Ni_(3)S_(2)heterostructure nanosheets are developed through topochemical transformation of layered Ni(OH)_(2)templates to improve the utilization of sulfur and facilitate stable cycling of batteries.As a multifunction catalyst,NiO/Ni_(3)S_(2)not only enhances the adsorption of polysulfides and shorten the transport path of Li ions and electrons but also promotes the Li_(2)S formation and transformation,which are verified by both in-situ Raman spectroscopy and electrochemical investigations.Thus,the cell with NiO/Ni_(3)S_(2)as electrocatalyst delivers an area capacity of 4.8 mAh cm^(-2)under the high sulfur loading(6 mg cm^(-2))and low electrolyte/sulfur ratio(4.3 pL mg^(-1)).The strategy can be extended to 2D Ni foil,demonstrating its prospects in the construction of electrodes with high gravimetric/volumetric energy densities.The designed electrocatalyst of ultrathin nonlayered heterostructure will shed light on achieving high energy density lithium-sulfur batteries.

Physics of electron emission and injection in two-dimensional materials: Theory and simulation

Electrically contacting two-dimensional(2D)materials is an inevitable process in the fabrication of devices for both the study of fundamental nanoscale charge transport physics and the design of high-performance novel electronic and optoelectronic devices.The physics of electrical contact formation and interfacial charge injection critically underlies the performance,energyefficiency and the functionality of 2D-material-based devices,thus representing one of the key factors in determining whether 2D materials can be successfully implemented as a new material basis for the development of nextgeneration beyond-silicon solid-state device technology.In this review,the recent developments in the theory and the computational simulation of electron emission,interfacial charge injection and electrical contact formation in 2D material interfaces,heterostructures,and devices are reviewed.Focusing on thermionic charge injection phenomena which are omnipresent in 2Dmaterials-based metal/semiconductor Schottky contacts,we summarize various transport models and scaling laws recently developed for 2D materials.Recent progress on the first-principle density functional theory simulation of 2D-material-based electrical contacts are also reviewed.This review aims to provide a crystalized summary on the physics of charge injection in the 2D Flatlands for bridging the theoretical and the experimental research communities of 2D material device physics and technology.

The application of nonlocal theory method in the coarse-grained molecular dynamics simulations of long-chain polylactic acid

The micro-capsules used for drug delivery are fabricated using polylactic acid（PLA）,which is a biomedical material approved by the FDA.A coarse-grained model of long-chain PLA was built,and molecular dynamics（MD）simulations of the model were performed using a MARTINI force field.Based on the nonlocal theory,the formula for the initial elastic modulus of polymers considering the nonlocal effect was derived,and the scaling law of internal characteristic length of polymers was proposed,which was used to adjust the cut-off radius in the MD simulations of PLA.The results show that the elastic modulus should be computed using nonlinear regression.The nonlocal effect has a certain influence on the simulation results of PLA.According to the scaling law,the cut-off radius was determined and applied to the MD simulations,the results of which reflect the influence of the molecular weight change on the elastic moduli of PLA,and are in agreement with the experimental outcome.

A computed tomography reconstruction algorithm based on multipurpose optimal criterion and simulated annealing theory

Although emission spectral tomography （EST） combines emission spectral measurement with optical computed tomography （OCT）, it is difficult to gain transient emission data from a large number of views, therefore, high precision OCT algorithms with few views ought to be studied for EST application. To improve the reconstruction precision in the case of few views, a new computed tomography reconstruction algorithm based on multipurpose optimal criterion and simulated annealing theory （multi-criterion simulated annealing reconstruction technique, MCSART） is proposed. This algorithm can suffice criterion of least squares, criterion of most uniformity, and criterion of most smoothness synchronously. We can get global optimal solution by MCSART algorithm with simulated annealing theory. The simulating experiment result shows that this algorithm is superior to the traditional algorithms under various noises.

Distinguishing Oil and Water Layers in a Porous Cracked Medium by Interpreting Acoustic Logging Data on the Basis of Hudson Theory

During surveys, water layers may interfere with the detection of oil layers. In order to distinguish between oil and water layers in a porous cracked medium, research on the properties of cracks and oil and water layers and their relation to acoustic logging rules is essential. On the basis of Hudson＇s crack theory, we simulated oil and water layers in crack-porous medium with different crack parameters corresponding to the well-field response. We found that in a cracked medium with high crack angle or low number density of cracks, compressional and shear wave velocities are sensitive to crack characteristics; further, these velocities are more sensitive to crack characteristics when the waves propagate through the water layer than when they propagate through the oil layer. Compressional and shear wave velocities increase with an increase in crack angle： in the water layer, the increase is approximately linear. On comparing the full waveforms observed in the oil and water layers, we find that the amplitudes of most waves are higher in the water layer. Among the considered waves, the Stoneley wave suffers maximum amplitude attenuation in the oil layer. The maximum excitation intensity for oil layer is greater than that for the water layer. These results can guide further cracked media logging field exploration work.

Cobalt disulfide/carbon nanofibers with mesoporous heterostructure and excellent hydrophilicity for high energy density asymmetric supercapacitor

Herein,a unique mesoporous heterostructure(average pore size:15 nm)cobalt disulfide/carbon nanofibers(CoS_(2)/PCNFs)composite with excellent hydrophilicity(contact angle:23.5°)is prepared using polyethylene glycol(PEG)as a pore-forming agent.The CoS_(2)/PCNF electrode exhibits excellent cycle stability(95.2%of initial specific capacitance at 10 A·g^(-1)after 8000 cycles),good rate performance(46.5%at 10 A·g^(-1)),and high specific capacity(86.1 mAh·g^(-1)at 1 A·g^(-1),about 688.8 F·g^(-1)at 1 A·g^(-1)).Density functional theory(DFT)simulation elucidates that CoS_(2)tends to transfer substantial charges to CNF.As the center of positive charge,CoS_(2)is more likely to capture negative ions in the electrolyte,thus accelerating the ion diffusion process.The excellent properties of the electrode material can not only accelerate the electrochemical reaction kinetics,but also provide abundant redox-active sites and a high Faradaic capacity for the entire electrode due to the synergistic contributions of CoS_(2)nanoparticles,mesoporous heterostructure of PCNF,and admirable hydrophilicity of the composite material.A CoS_(2)/PCNF-0.25//AC(AC:activated carbon)asymmetric supercapacitor is assembled using CoS_(2)/PCNF-0.25 as the positive electrode and AC as the negative electrode,which possesses a high energy density(35.5 Wh·kg^(-1)at a power density of 824 W·kg^(-1))and superior cycling stability(maintaining over 98%of initial capacitance after 2000 cycles).In addition,the unique CoS_(2)/PCNF electrode is expected to be widely used in other electrochemical energy storage devices,such as lithium-ion batteries,sodium-ion batteries,lithium-sulfur batteries,etc.

Structure-design and theoretical-calculation for ultrasmall Co_(3)O_(4) anchored into ionic liquid modified graphene as anode of flexible lithium-ion batteries

Cobalt oxide(Co_(3)O_(4))is currently suitable in energy storage applications because of its high capacity based on the conversion reaction mechanism.However,unmodified Co_(3)O_(4)suffers from distinctly inferior rate capability and poor cycling stability.On the basis of the aforementioned considerations and density functional theory(DFT)simulations,the three-dimensional hierarchical porous structure(HPS)ultrasmall Co_(3)O_(4)anchored into ionic liquid(IL)modified graphene oxide(GO)has been successfully prepared(ultrasmall/Co_(3)O_(4)-GA-IL).The ultrasmall/Co_(3)O_(4)-GA-IL consists of Co_(3)O_(4)co-assembled with IL modified GO to generate the HPS which can facilitate ion transfer channels through reduction of the electron and ion transportation path and transmission impedance.In addition,N-doping graphene can enhance the inherent electrical conductivity of Co_(3)O_(4),which is proved by the DFT calculations.By virtue of the novel superstructure,the ultrasmall/Co_(3)O_(4)-GA-IL electrode demonstrates a high reversible capacity of 1,304 mAh·g^(−1),an enhanced high-rate capability(715 mAh·g^(−1)at 5 C),and a capacity retention of 98.4%even after 500 cycles at 5 C rate,which corresponds to 0.0003%capacity loss per cycle.Pouch cells based on the cathode are further fabricated and demonstrate excellent mechanical and electrochemical properties under bent and folded state,highlighting the practical application of our deliberately designed electrode in wearable electronics.

Topological to trivial insulating phase transition in stanene

Electronic properties of stanene, the Sn counterpart of graphene are theoretically studied using first-principles simulations. The topological to trivial insulating phase transition induced by an out-of-plane electric field or by quantum confinement effects is predicted. The results highlight the potential to use stanene nanoribbons in gate-voltage controlled dissipationless spin-based devices and are used to set the minimal nanoribbon width for such devices, which is typically approximately 5 nm.

Mechanocatalysis of CO to CO_(2)on TiO_(2)surface controlled at atomic scale

The common ways to activate a chemical reaction are by heat,electric current,or light.However,mechanochemistry,where the chemical reaction is activated by applied mechanical force,is less common and only poorly understood at the atomic scale.Here we report a tip-induced activation of chemical reaction of carbon monoxide to dioxide on oxidized rutile TiO_(2)(110)surface.The activation is studied by atomic force microscopy,Kelvin probe force microscopy under ultrahigh-vacuum and liquid nitrogen temperature conditions,and density functional theory(DFT)modeling.The reaction is inferred from hysteretic behavior of frequency shift signal further supported by vector force mapping of vertical and lateral forces needed to trigger the chemical reaction with torque motion of carbon monoxide towards an oxygen adatom.The reaction is found to proceed stochastically at very small tip-sample distances.Furthermore,the local contact potential difference reveals the atomic-scale charge redistribution in the reactants required to unlock the reaction.Our results open up new insights into the mechanochemistry on metal oxide surfaces at the atomic scale.