Hole Propagation Research Articles

A prediction of crack propagation on aircraft wing via AK-TCN

The crack propagation of wing rivet holes has a significant impact on flight safety. However, accurate crack prediction is difficult. On the one hand, the calculated values based on traditional mechanics theory are conservative and have a large safety margin. On the other hand, the predicted values of deep learning do not match the mechanical theory, and the significant role of peak load in crack propagation has not been fully reflected. Therefore, this paper proposes a novel AK-TCN model for the crack prediction, considering the theoretical information constraints. Firstly, the “theoretical information assistance” technology is adopted. The calculated values (strength, life) based on mechanical theory and the measured values (stress) based on sensors are jointly used as inputs, enabling the AK-TCN model to fully extract valuable information. Secondly, the “multi-dimension feature fusion” technology is adopted. The theoretical information and measured information are mixed, and the importance of different information is adaptively adjusted, enabling the AK-TCN model to balance the foundational nature of theoretical information and the time-varying nature of measured information. Then, the “adaptive multi-scale convolution” technique is adopted. The temporal features in different periods are perceived by multi-scale convolution, and weights of them are assigned by attention mechanisms, so that the AK-TCN model can focus on certain key features that have a significant impact on crack propagation. Finally, the accuracy, effectiveness, and robustness of the proposed AK-TCN are verified by comparative experiments, ablation experiments, and noise experiments.

Computer Simulation of Charge Transfer In a DNA Molecule within a Simple Model of an Open Quantum System

The quantum-statistical model proposed earlier by Skourtis and Nitzan to describe a charge (hole) propagation in a fragment of artificial DNA molecule has been generalized and further investigated. A numerical simulation of a charge transport was carried out taking into account two different dissipative processes, including the capture of the charged carrier by the environment and the decoherence of its quantum wave properties due to the influence of stochastic fields of the environment. The interaction of the carrier with the environment is regulated by a small set of phenomenological parameters whose values vary in the process of simulation. Within this model, the propagation of a hole carrier in DNA is described by solving the quantum Franke-Kossakovski–Lindblad–Glauber–Sudarshan equation (hereinafter referred to as the Lindblad equation) for the carrier density matrix using the Lindblad MPO Solver program. Results of numerical analysis of the model are in a good agreement with experimental observations and demonstrate two different types of the charged carrier motion, presumably tunneling and incoherent hopping. The model is put in more general context and non-unitary dynamics of the hole carrier is treated within the framework of a theory of continuous quantum measurements by the environment in an open quantum system. The main concepts of the theory of decoherence and superselection for open quantum systems and the prospects for their application for further study of various mechanisms of motion of a charged carrier in DNA are briefly discussed.

Dynamic behavior description and three-dimensional cutting simulation of SiCp/Al composites with high volume fraction

According to the dynamic behavior characteristics of SiCp/Al composites, the constitutive equation of high volume fraction composites is established by SHPB dynamic compression test, shear lag model and effective medium approximation method, and the calculation results are in good agreement with the experiments. The established constitutive equation is then imported into Abaqus to establish a three-dimensional cutting simulation model, which is combined with cutting experiments to analyze the dynamic removal mechanism of material during the cutting process and the cutting surface formation process. The results show that the formation and propagation of holes and cracks play an important role in the formation of chips. The failure removal mode of SiC particles is an important factor affecting the cutting surface morphology. The research results provide an important theoretical basis and research means for the study of cutting mechanism of SiCp/Al composites with high volume fraction.

Development of Three-Dimensional Scour below Pipelines in Regular Waves

The three-dimensional scour beneath a partially-buried pipeline in regular waves was visualized using a miniature camera installed in a transparent pipeline. The scour mechanism was analyzed based on the results. Scour development was observed to start at the upstream edge of the span shoulder when the flow in the span headed downstream. The nearby sediment scoured quickly, and a new scour front formed, which can be attributed to the deflected flow entering the scour hole. The new scour front retreated gradually. The end of the original scour front deformed and moved downstream, probably due to the enhanced seepage flow near the edge of the span shoulder. After that, the new scour front extended to the downstream interface of the sediment and the pipeline, and continued to retreat until the first half of the scour process ended. In the second half of the scour process, the sediment transportation occurred in a similar but mirror-imaged manner. The scour hole propagation rate was also determined based on visualization. The results show that the scour hole propagation rate under a pipeline decreases with an increasing pipeline embedment ratio and rises with the KC (Keulegan–Carpenter) number, which is similar to the result of a previous study.

Constitutive Model of N15 Propellant considering the Confining Pressure Effect

To describe the effect of confining pressure on the mechanical responses of N15 propellant, a constitutive model considering the confining pressure effect was first established for N15 propellant based on the elastic-viscoelastic correspondence principle. Then, the mechanical properties of N15 solid propellant under different confining pressures were obtained using confining pressure test system, and the obtained results indicate that the initial modulus of propellant did not change with confining pressure, but the maximum tensile strength, rupture strength, the maximum elongation, and elongation at break increased with increasing confining pressure. In conjunction with propellants’ mesoscopic structure and cross-section analysis, the mechanical mechanism of confining pressure effect on propellant was initially disclosed. Due to confining pressure, the particle dewetting inside the propellant was reduced, the hole propagation was delayed, and crack extension inhibited germination, proving that confining pressure has a strengthening impact on the propellant. Finally, assuming that the model parameters were dependent on pressure, the model parameters acquisition and validation were conducted. The results demonstrated that constitutive model can describe confining pressure influence on the mechanical properties of N15 propellant accurately.

Dynamical formation of a magnetic polaron in a two-dimensional quantum antiferromagnet

Tremendous recent progress in the quantum simulation of the Hubbard model paves the way to controllably study doped antiferromagnetic Mott insulators. Motivated by these experimental advancements, we numerically study the real-time dynamics of a single hole created in an antiferromagnet on a square lattice, as described by the t–J model. Initially, the hole spreads ballistically with a velocity proportional to the hopping matrix element. At intermediate to long times, the dimensionality as well as the spin background determine the hole dynamics. A hole created in the ground state of a two dimensional (2D) quantum antiferromagnet propagates again ballistically at long times but with a velocity proportional to the spin exchange coupling, showing the formation of a magnetic polaron. We provide an intuitive explanation of this dynamics in terms of a parton construction, which leads to a good quantitative agreement with the numerical tensor network state simulations. In the limit of infinite temperature and no spin exchange couplings, the dynamics can be approximated by a quantum random walk on a Bethe lattice with coordination number . Adding Ising interactions corresponds to an effective disordered potential, which can dramatically slow down the hole propagation, consistent with subdiffusive dynamics. The study of the hole dynamics paves the way for understanding the microscopic constituents of this strongly correlated quantum state.

Nonlinear simulations of energetic particle-driven instabilities interacting with Alfvén continuum during frequency chirping

Toroidal Alfvén eigenmodes excited by energetic particles (EPs) and their transition to energetic particle modes are investigated using a three-dimensional nonlinear kinetic-magnetohydrodynamic hybrid simulation code. Both the symmetric chirping inside the Alfvén continuum gap for upward and downward directions and the asymmetric chirping affected by the Alfvén continuum are found in the simulations depending on the EP drive and the mode damping. For weak drive and damping, symmetric frequency chirping is observed with a chirping rate consistent with the Berk–Breizman theory (Berk et al 1997 Phys. Lett. A 234 213). For moderate drive and damping, upward chirping is dominant because downward chirping is interrupted by interaction with the Alfvén continuum. For strong drive and damping, two branches of frequency chirping are found for different poloidal harmonics. The dominant chirping is downward into the Alfvén continuum and the other is an upward chirping inside the Alfvén continuum gap. The creation and the propagation of holes and clumps are found in EP phase space, which is qualitatively consistent with the Berk–Breizman theory.

Ultrafast Aqueous Dynamics in Concentrated Electrolytic Solutions of Lithium Salt and Ionic Liquid.

In the last few decades, aqueous electrolytes based on ionic liquids (ILs) have been attractive because of their various uses in chemical sciences and potential applications in Li-ion batteries. The presence of water molecules influences the molecular structure and complex transformations occurring at ultrafast timescales because of the interaction between the water and the ionic entities of ILs. In this study, we investigate water-IL interactions that correlate the vibrational dynamics of the associated infrared probe using a fast and accurate computational approach. The obtained results from our approach are directly compared with those of the ultrafast two-dimensional infrared spectroscopy experiments. We investigated the dynamics of ion-water interactions of aqueous lithium bis(trifluoromethylsulfonyl)imide, (LiNTf2), and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, ([EMIm] [NTf2]), with the help of vibrational dynamics of the deuteroxyl probe of water molecules using wavelet analysis of trajectories of classical molecular dynamics simulations. The normalized OD stretch frequency distribution of aqueous [EMIm][NTf2] shows a heterogeneous bimodal line shape associated with both water and ion hydrogen-bonded OD populations. However, H2O/LiNTf2 solution depicts a broad spectral band without a distinct spectral feature. We observe faster timescales of frequency fluctuations, time-dependent hole propagation, and reorientation dynamics in aqueous [EMIm][NTf2] solution. At a time-lapse of 0.1 ps, the 2D IR correlation spectrum in aqueous LiNTf2 appears elongated along with the frequency diagonal. The spectral signature in the water-[EMIm][NTf2] mixture is relatively symmetric in shape, indicating faster dynamics. Our results show the characteristic behavior of water molecules present in the aqueous ionic mixtures that distinguish two mixtures dynamically. While examining water interactions in aqueous ionic solutions, we predict that the additional water in the aqueous LiNTf2 solution might be engaged in the structural arrangement of the restricted IL environment. In contrast, water in aqueous [EMIm][NTf2] enhances the dynamics. Hence, we observe that a change in the cationic constituent of the IL solution results in a substantial change in the overall system dynamics.

Evolution features of riverbeds near underwater crossing line pipes: An experimental study

It is of important significance to study the evolution law of the riverbed near underwater crossing line pipes for ensuring the safe operation of oil and gas pipelines and reducing the risk of damage by water flood disasters. In order to clarify the evolution law of the riverbed near underwater crossing line pipes and its negative effects, this paper conducted flume model experiments on underwater crossing line pipes. The physical process of riverbed evolution near pipes was observed and the effect of hydrodynamic conditions on the local pipe scour was studied. What's more, the formation mechanism of local scour at underwater crossing line pipes was revealed. And the following research results were obtained. First, when the water flow is slow, the riverbed evolution process near underwater crossing line pipes is mainly divided into six stages, including riverbed undercutting, pipe exposure, micro-pore formation, scour hole propagation, pipe suspension and scour equilibrium. Second, vortex and seepage flow are the reasons for the local scour of underwater crossing line pipes. Before pipes are exposed, the silt around the pipes is reduced by vortex. After pipes are exposed, micro-pores occur at the pipe bottom under the joint action of vortex and seepage flow. And thus, local scour is formed. Third, flow velocity and water depth jointly influence the riverbed scour duration of each stage and the maximum scour depth at the pipe bottom. When the Froude number (Fr) is in the range of 0.306–0.808, with the increase of Fr, water flow gets fast, the maximum scour depth at the pipe bottom increases, the duration for scour equilibrium decreases, the riverbed undercutting depth increases and the riverbed topographically gets flatter. The maximum scour depth at the pipe bottom is 0.9–1.6 times the pipe diameter, and the duration for scour equilibrium is between 1650 min and 2620 min. In conclusion, the experimental results provide important reference for predicting the burial depth of underwater crossing line pipes and ensuring their safe operation.

Propagation of Holes and Electrons in Metal-Organic Frameworks.

Charge transport in two zinc metal-organic frameworks (MOFs) has been investigated using periodic semiempirical molecular orbital calculations with the AM1* Hamiltonian. Restricted Hartree-Fock calculations underestimate the band gap using Koopmans theorem (ca. 2 eV compared to the experimental value of 2.8 eV). However, it almost doubles when the constraint on the wave function to remain spin-restricted is removed and the energies of the UHF Natural Orbitals are used. Charge-transport simulations using propagation of the electron- or hole-density in imaginary time allow charge-transport paths and mechanisms to be determined. The calculated relative mobilities in the directions of the three crystal axes agree with experimental expectations, but the absolute values are not reliable using the current technique. Hole-mobility along the crystal c-axis (along the metal stacks) is found to be 13 times higher in the zinc MOF with anthracene linker (Zn-ANMOF-74) than in the other directions, whereas the factor is far smaller (1.7) for electron mobility. Directional preferences are far less distinct in the equivalent structure with phenyl linkers (Zn-MOF-74). The imaginary-time simulation technique does not give quantitative mobilities. The simulations reveal a change in mechanism between the different directions: Coherent polaron migration is observed along the stacks but tunneling hops between them.

Visualization Tests on Variation of Scour Front under a Pipeline in Steady Currents

The intersection of the span shoulder and the scour hole under a pipeline, also called the scour front, can affect the scour hole extension rate and the bearing capacity of the span shoulder, which is associated with pipeline spanning and failure. Studies on scour front evolution are limited due to technical restrictions. In this study, visualization experiments on three-dimensional scour under a pipeline in steady currents were performed to reveal the evolution of the scour front at the beginning of scour process, and the parametric effects on the scour front pattern. The angle of scour front witnessed a steady drop at the start of the scour development process and fluctuated gently thereafter. This can be attributed to the decrease in the blockage effect over time. A gravitational movement was observed on the downstream end of the scour front, which is associated with the variation of fluid pressure along the scour front. The scour front pattern was described by the angle between the scour front and the streamwise direction. Parametric analysis showed that the averaged scour front angle climbs as the Froude number increases and the pipeline embedment drops. This phenomenon can be expounded by the intensified flow deflection near the span shoulder due to the enhancement of the pipeline blockage effect, caused by the ascending Froude number and descending pipeline embedment. The results of this study can be adopted in future mechanism investigations on the scour hole propagation rate and the failure analysis on the span shoulder.

Transition Metal Free Cycloamination of Prenyl Carbamates and Ureas Promoted by Aryldiazonium Salts

AbstractUpon treatment with aryldiazonium salts, prenyl carbamates and ureas undergo redox‐neutral azocycloamination. In general, N‐aryl O‐prenyl carbamates cyclize in a photocatalytic reaction with visible light and an organic dye. With electron‐deficient diazonium salts, electronic matching with an electron‐rich N‐aryl substituent results in a reaction proceeding in the ground state, without either light or photocatalyst. Cyclic voltammetry suggests that this radical reaction is initiated by hydrogen‐atom abstraction mediated by an aryl radical, followed by a radical addition cascade and proton‐coupled hole propagation. The reaction proceeds at room temperature in short reaction times, and a range of functional groups is tolerated.

Transition Metal Free Cycloamination of Prenyl Carbamates and Ureas Promoted by Aryldiazonium Salts.

Upon treatment with aryldiazonium salts, prenyl carbamates and ureas undergo redox-neutral azocycloamination. In general, N-aryl O-prenyl carbamates cyclize in a photocatalytic reaction with visible light and an organic dye. With electron-deficient diazonium salts, electronic matching with an electron-rich N-aryl substituent results in a reaction proceeding in the ground state, without either light or photocatalyst. Cyclic voltammetry suggests that this radical reaction is initiated by hydrogen-atom abstraction mediated by an aryl radical, followed by a radical addition cascade and proton-coupled hole propagation. The reaction proceeds at room temperature in short reaction times, and a range of functional groups is tolerated.

On the solid-state dewetting of polycrystalline thin films: Capillary versus grain growth approach

Solid-state dewetting of polycrystalline silver thin films was investigated with in situ and real time Environmental Scanning Electron Microscopy at High Temperature (HT-ESEM) in different annealing atmospheres: secondary vacuum or oxygen-rich (partial pressure ≥100 Pa) environment. A model where oxygen plays a key role is proposed to explain the very different observed morphologies; oxygen favours hole creation and isotropic hole propagation as well as grain selection. But, whatever the atmosphere, dewetting does not proceed through the propagation of a rim but instead involves the growth of specific grains and shrinkage of others. Models based on macroscopic curvature to account for the propagation speed of the dewetting front fail to fit the present observations. This points to a paramount role of the grain size and stability in the dewetting morphology.

Anomalous Charge‐Extraction Behavior for Graphene‐Oxide (GO) and Reduced Graphene‐Oxide (rGO) Films as Efficient p‐Contact Layers for High‐Performance Perovskite Solar Cells

AbstractReduced graphene oxides (rGO) are synthesized via reduction of GO with reducing agents as a hole‐extraction layer for high‐performance inverted planar heterojunction perovskite solar cells. The best efficiencies of power conversion (PCE) of these rGO cells exceed 16%, much greater than those made of GO and poly(3,4‐ethenedioxythiophene):poly(styrenesulfonate) films. A flexible rGO device shows PCE 13.8% and maintains 70% of its initial performance over 150 bending cycles. It is found that the hole‐extraction period is much smaller for the GO/methylammonium lead‐iodide perovskite (PSK) film than for the other rGO/PSK films, which contradicts their device performances. Photoluminescence and transient photoelectric decays are measured and control experiments are performed to prove that the reduction of the oxygen‐containing groups in GO significantly decreases the ability of hole extraction from PSK to rGO and also retards the charge recombination at the rGO/PSK interface. When the hole injection from PSK to GO occurs rapidly, hole propagation from GO to the indium‐doped tin oxide (ITO) substrate becomes a bottleneck to overcome, which leads to a rapid charge recombination that decreases the performance of the GO device relative to the rGO device.

Orbiton-magnon interplay in the spin-orbital polarons of KCuF3 and LaMnO3

We present a quasi-analytical solution of a spin-orbital model of KCuF$_{3}$, using the variational method for Green's functions. By analyzing the spectra for different partial bosonic compositions as well as the full solution, we show that hole propagation needs both orbiton and magnon excitations to develop, but the orbitons dominate the picture. We further elucidate the role of the different bosons by analyzing the self-energies for simplified models, establishing that because of the nature of the spin-orbital ground state, magnons alone do not produce a full quasiparticle band, in contrast to orbitons. Finally, using the electron-hole transformation between the $e_g$ states of KCuF$_3$ and LaMnO$_3$ we suggest the qualitative scenario for photoemission experiments in LaMnO$_3$.

Hole Transport in A-form DNA/RNA Hybrid Duplexes

DNA/RNA hybrid duplexes are prevalent in many cellular functions and are an attractive target form for electrochemical biosensing and electric nanodevice. However the electronic conductivities of DNA/RNA hybrid duplex remain relatively unexplored and limited further technological applications. Here cyclopropyl-modified deoxyribose- and ribose-adenosines were developed to explore hole transport (HT) in both DNA duplex and DNA/RNA hybrids by probing the transient hole occupancies on adenine tracts. HT yields through both B-form and A-form double helixes displayed similar shallow distance dependence, although the HT yields of DNA/RNA hybrid duplexes were lower than those of DNA duplexes. The lack of oscillatory periods and direction dependence in HT through both helixes implied efficient hole propagation can be achieved via the hole delocalization and coherent HT over adenine tracts, regardless of the structural variations.

Development and Verification of the Three-Dimensional Electrostatic Particle Simulation Code for the Study of Blob and Hole Propagation Dynamics

Development and Verification of the Three-Dimensional Electrostatic Particle Simulation Code for the Study of Blob and Hole Propagation Dynamics

Coherent hole propagation in an exactly solvable gapless spin liquid

We examine the dynamics of a single hole in the gapless phase of the Kitaev honeycomb model, focusing on the slow-hole regime where the bare hopping amplitude $t$ is much less than the Kitaev exchange energy $J$. In this regime, the hole does not generate gapped flux excitations and is dressed only by the gapless fermion excitations. Investigating the single-hole spectral function, we find that the hole propagates coherently with a quasiparticle weight that is finite but approaches zero as $t/J \to 0$. This conclusion follows from two approximate treatments, which capture the same physics in complementary ways. Both treatments use the stationary limit as an exactly solvable starting point to study the spectral function approximately (i) by employing a variational approach in terms of a trial state that interpolates between the limits of a stationary hole and an infinitely fast hole and (ii) by considering a special point in the gapless phase that corresponds to a simplified one-dimensional problem.

Charge separation in organic solar cells: Effects of Coulomb interaction, recombination and hole propagation

Bulk heterojunction (BHJ) organic photovoltaic cells are analysed within a simple efficient model that includes the important physical properties of such photovoltaic systems. In this model, in contrast with most of the previous studies, we take into account the motion of both the electron and the hole in the separation process at the donor-acceptor interface. We theoretically examine the exciton dissociation yield under the influences of charge Coulomb interaction and non-radiative recombination. We find that the electron-hole local Coulomb attraction and charge carriers' coupling parameters play an important role in the system performance and in the optimal energy conversion efficiency of the BHJ photocell. We show that the fixed-hole models tend to underestimate the yield.