Real-time Propagation Research Articles

High-performance bamboo-wood composite materials based on the natural structure and original form of bamboo: Fracture behavior and mechanical characterization

Reducing the destruction of bamboo's original structure to produce high-utilization and high-performance engineered bamboo products has long been a goal in the industry. This study developed a new natural arc-shaped laminated bamboo-wood lumber (NALBWL) based on the natural structure and original form of bamboo, using equal arc-shaped bamboo split (EASB) and poplar veneer. A multi-scale analysis of the bending performance and crack propagation dynamics of EASB and NALBWL was conducted. EASB's modulus of elasticity (MOE) and rupture (MOR) were 1.06 and 1.17 times higher than those of air-dried bamboo, respectively, exhibiting excellent mechanical properties. Additionally, its toughness in the full and elastic-plastic stages were 1.24 and 1.38 times higher than those of air-dried bamboo. NALBWL's MOE and MOR were 12.73 GPa and 174.41 MPa, fully meeting structural material requirements and even surpassing most engineered bamboo products. Moreover, NALBWL's radial bending load values were 2.29 and 2.24 times higher than that of EASB and air-dried bamboo, respectively, and it also demonstrated excellent water heat and drying resistance in impregnation and peeling performance. Real-time crack propagation analysis indicated that NALBWL's superior mechanical properties benefited from the respective advantages of bamboo and poplar veneer. This work showcased the application of "natural form-inspired design" in developing bamboo-wood composite materials, and the conclusion provided a reference for the sustainable development of engineered bamboo products and the study of biomass material fracture mechanisms.

The social force model: a behavioral modeling approach for information propagation during significant events

Information diffusion otherwise known as the propagation, spread or dissemination of information occurs when a piece of information flows from a particular individual/community to another in a social network. Studies related to information propagation involve problems regarding the factors that affect the information propagation, how the information is disseminated, the speed of propagation, etc. Researchers have proposed information propagation models to understand the phenomenon and to answer these questions. These models have been effectively used in applications such as behavior analysis, public health care, etc. Although several studies are carried out in this field, the literature demands identifying the most influential factors of propagation in real time in cases of sudden unexpected significant disasters/epidemics/pandemics, since the existing propagation models seem unfit during such circumstances. In this paper, a novel information propagation model which predicts the top propagators of information related to a particular context is proposed. This model utilizes the past few weeks' data during a sudden outbreak of a disaster and identifies the most influential attributes of a user profile to predict the top propagators of the future. The proposed Social Force Model is inspired by a model used in studying the fear propagation pattern in pedestrian dynamics in real-life situation [Cornes FE, Frank GA, Dorso CO. Fear propagation and the evacuation dynamics. Simul Model Pract Theory. 2019;95:112–133.]. We have effectively mapped the various forces which constitute the Social Force Model such as the Desired Force, the Social Force and the Granular Force with respect to the online social network context in order to discover the key spreaders of information during a specific context. Apart from identifying the propagators, the proposed model discovers the key attributes by analyzing the behavior of users based on their past activities in the online social network.

Many-body enhancement of high-harmonic generation in monolayer MoS2

Many-body effects play an important role in enhancing and modifying optical absorption and other excited-state properties of solids in the perturbative regime, but their role in high harmonic generation (HHG) and other nonlinear response beyond the perturbative regime is not well-understood. We develop here an ab initio many-body method to study nonperturbative HHG based on the real-time propagation of the non-equilibrium Green’s function with the GW self energy. We calculate the HHG of monolayer MoS2 and obtain good agreement with experiment, including the reproduction of characteristic patterns of monotonic and nonmonotonic harmonic yield in the parallel and perpendicular responses, respectively. Here, we show that many-body effects are especially important to accurately reproduce the spectral features in the perpendicular response, which reflect a complex interplay of electron-hole interactions (or exciton effects) in tandem with the many-body renormalization and Berry curvature of the independent quasiparticle bandstructure.

Quasi-one- and quasi-two-dimensional symbiotic solitons bound by dipolar interaction.

We study the formation of quasi-one- (quasi-1D) and quasi-two-dimensional (quasi-2D) symbiotic solitons bound by an interspecies dipolar interaction in a binary dipolar Bose-Einstein condensate. These binary solitons have a repulsive intraspecies contact interaction stronger than the intraspecies dipolar interaction, so that they can not be bound in isolation in the absence of an interspecies dipolar interaction. These symbiotic solitons are bound in the presence of an interspecies dipolar interaction and zero interspecies contact interaction. The quasi-1D solitons are free to move along the polarization z direction of the dipolar atoms, whereas the quasi-2D solitons move in the x-z plane. To illustrate these, we consider a ^{164}Er-^{166}Er mixture with scattering lengths a(^{164}Er)=81a_{0} and a(^{166}Er)=68a_{0} and with dipolar lengths a_{dd}(^{164}Er)≈a_{dd}(^{166}Er)≈65a_{0}, where a_{0} is the Bohr radius. In each of the two components a>a_{dd}, which stops the binding of solitons in each component in isolation, whereas a binary quasi-1D or a quasi-2D ^{164}Er-^{166}Er soliton is bound in the presence of an interspecies dipolar interaction. The stationary states were obtained by imaginary-time propagation of the underlying mean-field model; dynamical stability of the solitons was established by real-time propagation over a long period of time.

Fracture propagation and evaluation of dual wells, multi-fracturing, and split-time in Fuyu oil shale

Reservoir stimulation is crucial for in-situ exploitation, it can promote a fracture network and increase the heat transfer area. Therefore, it directly affects heat injection and products transportation efficiencies. Conventional reservoir stimulation techniques, such as hydraulic fracturing are widely used. However, hydraulic fracturing in a vertical well tends to generate simple fractures that are unfavorable for heat transfer, and real-time fracture propagation is difficult to monitor, thus failing to precisely control the hydraulic fracturing scale. In addition, there are few qualitative and quantitative criteria in reservoir-scale fracture evaluations for interpreting the overall hydraulic fracturing effect. Consequently, in this study, dual wells, multi-fracturing, and split-time technology (DMS) were designed and conducted based on microseismic monitoring in field experiment to find real-time fracture propagation. Furthermore, based on Hugot's research on connecting microseismic events by spatiotemporal sequences, we proposed a step index and path intensity considering microseismic event intensities to evaluate the effect on hydraulic fracturing. The results showed that a three-dimensional fracturing zone with a 60 × 30 × 8 m length, width, and height was generated at a 476–484 m depth, which corresponded to the designed hydraulic fracturing and facilitated heat transfer and product migration. Higher pump pressure and rate harmed hydraulic fracturing, blocking proppant migration during which the FK1-4 coefficient of viscosity reached 70 N⋅s/m2, 1.4 times greater than that of FK1-2 and FK1-5 according to Poiseuille's law. The hydraulic fracturing effect in FK1-4 was superior than that in FK1-2 and FK1-5. This study serves as a reference for monitoring oil shale exploitation via in-situ pyrolysis.

Finite-Temperature Correlation Functions Obtained from Combined Real- and Imaginary-Time Propagation of Variational Thawed Gaussian Wavepackets.

We apply the so-called variational Gaussian wavepacket approximation (VGA) for conducting both real- and imaginary-time dynamics to calculate thermal correlation functions. By considering strongly anharmonic systems, such as a quartic potential and a double-well potential at high and low temperatures, it is shown that this method is partially able to account for tunneling. This is contrary to other popular many-body methods, such as ring polymer molecular dynamics and the classical Wigner method, which fail in this respect. It is a historical peculiarity that no one has considered the VGA method for representing both the Boltzmann operator and the real-time propagation. This method should be well suited for molecular systems containing many atoms.

Sparse-Stochastic Fragmented Exchange for Large-Scale Hybrid Time-Dependent Density Functional Theory Calculations.

We extend our recently developed sparse-stochastic fragmented exchange formalism for ground-state near-gap hybrid DFT to calculate absorption spectra within linear-response time-dependent generalized Kohn-Sham DFT (LR-GKS-TDDFT) for systems consisting of thousands of valence electrons within a grid-based/plane-wave representation. A mixed deterministic/fragmented-stochastic compression of the exchange kernel, here using long-range explicit exchange functionals, provides an efficient method for accurate optical spectra. Both real-time propagation as well as frequency-resolved Casida-equation-type approaches for spectra are presented, and the method is applied to large molecular dyes.

Chiral Spectroscopy of Bulk Systems with Propagated Localized Orbitals.

We present approaches for the simulation of electronic circular dichroism, Raman, and Raman optical activity (ROA) spectra for isolated and periodic systems as well as subsystem analysis thereof. The method is based on the use of time-dependent maximally localized Wannier functions in the CP2K package and accounts for origin dependencies inherent to the Gaussian and plane wave with pseudopotentials approach as well as the origin dependence of the magnetic dipole and electric quadrupole operators. Tests on the H-bonded enantiomers of alanine by harmonic normal-mode analysis and on an aqueous solution of l-alanine by ab initio molecular dynamics obeying periodic boundary conditions (PBCs) are presented as total and subsystem-resolved spectra. To our knowledge, this is the first instance of an ROA spectrum derived from real-time propagation obeying PBCs and the first ROA simulation considering off-, pre-, and on-resonance effects within PBCs.

Efficient solution of the non-unitary time-dependent Schrodinger equation on a quantum computer with complex absorbing potential

We explore the possibility of adding complex absorbing potential at the boundaries when solving the one-dimensional real-time Schrödinger evolution on a grid using a quantum computer with a fully quantum algorithm described on a n qubit register. Due to the complex potential, the evolution mixes real- and imaginary-time propagation and the wave function can potentially be continuously absorbed during the time propagation. We use the dilation quantum algorithm to treat the imaginary-time evolution in parallel to the real-time propagation. This method has the advantage of using only one reservoir qubit at a time, that is measured with a certain success probability to implement the desired imaginary-time evolution. We propose a specific prescription for the dilation method where the success probability is directly linked to the physical norm of the continuously absorbed state evolving on the mesh. We expect that the proposed prescription will have the advantage of keeping a high probability of success in most physical situations. Applications of the method are made on one-dimensional wave functions evolving on a mesh. Results obtained on a quantum computer identify with those obtained on a classical computer. We finally give a detailed discussion on the complexity of implementing the dilation matrix. Due to the local nature of the potential, for n qubits, the dilation matrix only requires 2n CNOT and 2n unitary rotation for each time step, whereas it would require of the order of 4n+1 C-NOT gates to implement it using the best-known algorithm for general unitary matrices.

Simple and General Unitarity Conserving Numerical Real-Time Propagators of the Time-Dependent Schrödinger Equation Based on Magnus Expansion.

Magnus expansion (ME) provides a general way to expand the real-time propagator of a time-dependent Hamiltonian within the exponential such that the unitarity is satisfied at any order. We use this property and explicit integration of Lagrange interpolation formulas for the time-dependent Hamiltonian within each time interval and derive approximations that preserve unitarity for the differential time evolution operators of general time-dependent Hamiltonians. The resulting second-order approximation is the same as using the average of Hamiltonians for two end points of time. We identify three fourth-order approximations involving commutators of Hamiltonians at different times and also derive a sixth-order expression. A test of these approximations along with other available expressions for a two-state time-dependent Hamiltonian with sinusoidal time dependences provides information on the relative performance of these approximations and suggests that the derived expressions can serve as useful numerical tools for time evolution in time-resolved spectroscopy, quantum control, quantum sensing, real-time ab initio quantum dynamics, and open system quantum dynamics.

GPAW: An open Python package for electronic structure calculations.

We review the GPAW open-source Python package for electronic structure calculations. GPAW is based on the projector-augmented wave method and can solve the self-consistent density functional theory (DFT) equations using three different wave-function representations, namely real-space grids, plane waves, and numerical atomic orbitals. The three representations are complementary and mutually independent and can be connected by transformations via the real-space grid. This multi-basis feature renders GPAW highly versatile and unique among similar codes. By virtue of its modular structure, the GPAW code constitutes an ideal platform for the implementation of new features and methodologies. Moreover, it is well integrated with the Atomic Simulation Environment (ASE), providing a flexible and dynamic user interface. In addition to ground-state DFT calculations, GPAW supports many-body GW band structures, optical excitations from the Bethe-Salpeter Equation, variational calculations of excited states in molecules and solids via direct optimization, and real-time propagation of the Kohn-Sham equations within time-dependent DFT. A range of more advanced methods to describe magnetic excitations and non-collinear magnetism in solids are also now available. In addition, GPAW can calculate non-linear optical tensors of solids, charged crystal point defects, and much more. Recently, support for graphics processing unit (GPU) acceleration has been achieved with minor modifications to the GPAW code thanks to the CuPy library. We end the review with an outlook, describing some future plans for GPAW.

Real-Time Time-Dependent Density Functional Theory for Simulating Nonequilibrium Electron Dynamics.

The explicit real-time propagation approach for time-dependent density functional theory (RT-TDDFT) has increasingly become a popular first-principles computational method for modeling various time-dependent electronic properties of complex chemical systems. In this Perspective, we provide a nontechnical discussion of how this first-principles simulation approach has been used to gain novel physical insights into nonequilibrium electron dynamics phenomena in recent years. Following a concise overview of the RT-TDDFT methodology from a practical standpoint, we discuss our recent studies on the electronic stopping of DNA in water and the Floquet topological phase as examples. Our discussion focuses on how RT-TDDFT simulations played a unique role in deriving new scientific understandings. We then discuss existing challenges and some new advances at the frontier of RT-TDDFT method development for studying increasingly complex dynamic phenomena and systems.

X-ray induced ultrafast charge transfer in thiophene-based conjugated polymers controlled by core-hole clock spectroscopy.

We explore ultrafast charge transfer (CT) resonantly induced by hard X-ray radiation in organic thiophene-based polymers at the sulfur K-edge. A combination of core-hole clock spectroscopy with real-time propagation time-dependent density functional theory simulations gives an insight into the electron dynamics underlying the CT process. Our method provides control over CT by a selective excitation of a specific resonance in the sulfur atom with monochromatic X-ray radiation. Our combined experimental and theoretical investigation establishes that the dominant mechanism of CT in polymer powders and films consists of electron delocalisation along the polymer chain occurring on the low-femtosecond time scale.

Three-Wave Mixing of Dipole Solitons in One-Dimensional Quasi-Phase-Matched Nonlinear Crystals

A quasi-phase-matched technique is introduced for soliton transmission in a quadratic [χ (2)] nonlinear crystal to realize the stable transmission of dipole solitons in a one-dimensional space under three-wave mixing. We report four types of solitons as dipole solitons with distances between their bimodal peaks that can be laid out in different stripes. We study three cases of these solitons: spaced three stripes apart, one stripe apart, and confined to the same stripe. For the case of three stripes apart, all four types have stable results, but for the case of one stripe apart, stable solutions can only be found at ω 1 = ω 2, and for the condition of dipole solitons confined to one stripe, stable solutions exist only for Type1 and Type3 at ω 1=ω 2. The stability of the soliton solution is solved and verified using the imaginary time propagation method and real-time transfer propagation, and soliton solutions are shown to exist in the multistability case. In addition, the relations of the transportation characteristics of the dipole soliton and the modulation parameters are numerically investigated. Finally, possible approaches for the experimental realization of the solitons are outlined.

Symmetry-informed surrogates with data-free constraint for real-time acoustic wave propagation

A deep neural network is developed as a symmetry-informed surrogate model to estimate the stress of acoustic waves at any arbitrary location, time, and wave excitation width, as a kind of implicit representation of acoustic wave propagation. To improve the model performance, we suggest a physic-informed training residual by employing the symmetry constraint of acoustics. Compared to the FEM simulation using COMSOL Multiphysics, the R2 score of the surrogate model was greater than 98%, and its inference performance was about 215 times faster. The proposed residual can be characterized by three benefits: no architectural changes to the surrogate model are required, no labeled data or reference solutions are necessary, and the generalization ability of the surrogate model is enhanced in all input directions. Numerical investigation validates the superior generalization of the model trained with the symmetry constraint, along with the examination of the regularization rate and sampling approach, the additional hyperparameters induced by the proposed residual. Furthermore, we demonstrate the potential viability of real-time simulations from surrogate models through a practical application of the trained model for flaw detection. The results indicate that the capability of the data-driven surrogate model for generalized implicit representation can be enhanced by adopting the physic-informed training residual.

Meta-generalized gradient approximations in time dependent generalized Kohn-Sham theory: Importance of the current density correction.

We revisit the use of Meta-Generalized Gradient Approximations (mGGAs) in time-dependent density functional theory, reviewing conceptual questions and solving the generalized Kohn-Sham equations by real-time propagation. After discussing the technical aspects of using mGGAs in combination with pseudopotentials and comparing real-space and basis set results, we focus on investigating the importance of the current-density based gauge invariance correction. For the two modern mGGAs that we investigate in this work, TASK and r2SCAN, we observe that for some systems, the current density correction leads to negligible changes, but for others, it changes excitation energies by up to 40% and more than 0.8eV. In the cases that we study, the agreement with the reference data is improved by the current density correction.

Fracture parameters analysis of compact tension specimens with deflected fatigue cracks: ZK60 magnesium alloy

Precise monitoring of crack growth and a comprehensive understanding of crack propagation rate are crucial for the evaluation of the structural integrity of magnesium alloys with defects. Different crack deflections caused by the coupling of specimen orientations and crack sizes significantly increase the challenge to magnesium alloy evaluation. In this paper, the systematic finite element analysis was conducted for compact tension (CT) specimens with deflection cracks. A wide range of geometric variations including initial crack length, crack deflection angle and crack propagation length were analyzed. Complete solutions of the stress intensity factor (KI and KII), T-stress and the compliance at the load line were determined. The results showed that the geometric sizes have a significant coupling effect on the fracture mechanics parameters, and the non-deflected cracked formula recommended by the ASTM standard is not applicable to the deflection crack specimens. Then, a prediction method of kinked fatigue crack length of CT specimen based on the compliance multiplier method was proposed. To further verify the importance of the fracture parameters obtained, CT fatigue crack growth (FCG) tests of ZK60 magnesium (Mg) alloy under different orientations and initial crack sizes were carried out. The FCG rate curves of ZK60 Mg alloy under different crack growth driving forces were compared and illustrated. The developed compliance multiplication method can accurately predict the real-time crack propagation length.

Visualization of electrographic flow fields of increasing complexity and detection of simulated sources during spontaneously persistent AF in an animal model.

Mapping algorithms have thus far been unable to localize triggers that serve as drivers of AF, but electrographic flow (EGF) mapping provides an innovative method of estimating and visualizing in vivo, near real-time cardiac wavefront propagation. One-minute unipolar EGMs were recorded in the right atrium (RA) from a 64-electrode basket catheter to generate EGF maps during atrial rhythms of increasing complexity. They were obtained from 3 normal, animals in sinus rhythm (SR) and from 6 animals in which persistent AF which was induced by rapid atrial pacing. Concurrent EGF maps and high-resolution bipolar EGMs at the location of all EGF-identified sources were acquired. Pacing was subsequently conducted to create focal drivers of AF, and the accuracy of source detection at the pacing site was assessed during subthreshold, threshold and high-output pacing in the ipsilateral or contralateral atria (n = 78). EGF recordings showed strong coherent flow emanating from the sinus node in SR that changed direction during pacing and were blocked by ablation lesions. Additional passive rotational phenomena and lower activity sources were visualized in atrial flutter (AFL) and AF. During the AF recordings, source activity was not found to be correlated to dominant frequency or f wave amplitude observed in concurrently recorded EGMs. While pacing in AF, subthreshold pacing did not affect map properties but pacing at or above threshold created active sources that could be accurately localized without any spurious detection in 95% of cases of ipsilateral mapping when the basket covered the pacing source. EGF mapping can be used to visualize flow patterns and accurately identify sources of AF in an animal model. Source activity was not correlated to spectral properties of f-waves in concurrently obtained EGMs. The locations of sources could be pinpointed with high precision, suggesting that they may serve as prime targets for focal ablations.

Experimental study on fracture and acoustic emission properties of internally cured concrete with super absorbent polymer subjected to high temperature

The three-point bending experiment was conducted on notched beams containing five different SAP contents to investigate the influence of high temperature on the fracture performance of Superabsorbent Polymer (SAP) concrete. Acoustic Emission (AE) technology was employed to monitor real-time crack propagation, and scanning electron microscopy (SEM) was utilized to analyze the micro-pore structure. The experimental results reveal the following findings. After exposure to high temperatures, the peak strength of SAP concrete continuously decreases. Compared to specimens at 20 °C, the strength loss after exposure to temperatures of 200 °C, 400 °C, and 600 °C is approximately 11%, 55%, and 87%, respectively. However, the introduction of SAP can reduce the proportion of strength loss in the concrete. Additionally, SAP improves the toughness of the concrete, with an increase in ductility coefficient ranging from 4.0 to 6.8 times as the loading temperature increases. Similar to the strength variation pattern, the initial fracture toughness of SAP concrete exhibits a significant decrease with increasing heating temperature. The loss in initiation toughness after exposure to temperatures of 200 °C, 400 °C, and 600 °C is approximately 11%, 42%, and 85%, respectively, while the loss in unstable fracture toughness is 11%, 46%, and 74%. Based on the experimental results, this study proposes two temperature-dependent fitting models for the peak strength and fracture toughness of SAP concrete, which are compared and validated with the experimental results. SEM analysis reveals a loose and porous internal structure in SAP concrete. Through the analysis of AE signals at different temperatures, the fracture process is elucidated based on the b-value method. Moreover, RA-AF analysis indicates that an increase in temperature reduces the proportion of tensile-type cracks in specimens with the same SAP content. From the temperature loaded results spanning 20 °C–600 °C, the proportion of tensile cracks decreases from 80% to 50%, indicating a transition in the failure mode from tension to shear. However, this trend is not significantly affected by the temperature increase, suggesting that the failure mode of the specimens is primarily determined by the internal pore structure of the concrete rather than the temperature load. The research findings provide experimental evidence for the application of SAP concrete in engineering projects.

Differentially Private Distributed Optimization With an Event-Triggered Mechanism

This study concentrates on the differential private distributed optimization problem with an event-triggered mechanism, whose goals include preserving the privacy of agents’ initial states and local cost functions and improving communication efficiency. A distributed event-triggered mechanism is integrated into the differentially private subgradient-push distributed optimization algorithm and then a new algorithm named as DP-ETSP is designed, where the real-time information propagation among agents is avoided. Additionally, under the proposed event-triggered mechanism, an analysis of mean-square consensus and optimality over time-varying directed networks is made when the added Laplace noises meet some specific decaying conditions. Convergence rate results are further established under a specific stepsize, which are equal to the rate of stochastic gradient-push algorithm without event-triggered communication. Moreover, the differential privacy preservation performance is analyzed and the rule for selecting privacy level is discussed. Finally, the feasibility and effectiveness of DP-ETSP are verified in two simulation cases.