Propagation Regime Research Articles

A Crack‐Length Control Technique for Phase‐Field Fracture in FFT Homogenization

ABSTRACTModeling the propagation of cracks at the microscopic level is fundamental to understand the effect of the microstructure on the fracture process. Nevertheless, microscopic propagation is often unstable and when using phase‐field fracture poor convergence is found or, in the case of using staggered algorithms, leads to the presence of jumps in the evolution of the cracks. In this work, a novel method is proposed to perform micromechanical simulations with phase‐field fracture imposing monotonic increases of crack length and allowing the use of monolithic implementations, being able to resolve all the snap‐backs during the unstable propagation phases. The method is derived for FFT‐based solvers in order to exploit its very high numerical performance in micromechanical problems, but an equivalent method is also developed for Finite Elements (FE) showing the equivalence of both implementations. It is shown that the stress‐strain curves and the crack paths obtained using the crack control method are superposed in stable propagation regimes to those obtained using strain control with a staggered scheme. J‐integral calculations confirm that during the propagation process in the crack control method, the energy release rate remains constant and equal to an effective fracture energy that has been determined as a function of the concretization for FFT simulations. Finally, to show the potential of the method, the technique is applied to simulate crack propagation through the microstructure of composites and porous materials providing an estimation of the effective fracture toughness.

A New Thermodynamic Approach to Multimode Fiber Self‐cleaning and Soliton Condensation

AbstractA new thermodynamic theory for optical multimode systems is proposed. Theory is based on a weighted Bose–Einstein law, and includes the state equation, the fundamental equation for the entropy and a metric to measure the accuracy of the thermodynamic approach. The theory is used to compare the experimental results of two propagation regimes in multimode fibers, specifically the self‐cleaning in the normal chromatic dispersion region and the soliton condensation in the anomalous dispersion region. Surprising similarities are found in terms of thermodynamic parameters, suggesting a common basis for the thermalization processes observed in the two propagation regimes.

Demodulation of Pulsed Acoustic Signals in Strongly Non-Linear Propagation Regimes

Demodulation of Pulsed Acoustic Signals in Strongly Non-Linear Propagation Regimes

Chapter 9. Albertine Rift Stratigraphy 1: Sedimentary Architecture

A persistent problem that has hampered a general understanding of Albertine Rift early continental rift basins has been the lack of a high-resolution stratigraphic framework within which to correlate sediments across their onshore outcrop. Crucial to resolving this problem is resolving how the three-dimensional stacking architecture of sediments is controlled by a combination of evolving rift basin structure and the glacial climatic cyclicity experienced at the Equatorial Tropics of East Africa during deposition. Rift basin structural styles and subsidence rates are modelled and their merits discussed in light of the field evidence gathered from around the Albertine Rift. After establishing the mechanism of structural development in the basins, the impact of glacially-driven climatic oscillations on sedimentary lithofacies is also incorporated to produce a combined glacial climatic cyclicity model (GCCM) for Albertine Rift basin evolution. This superimposes lake level transgressive – regressive cyclicity upon a tectonic regime of fault propagation and depocentre retreat away from rift margins. The model predicts the resulting stratigraphic architecture that should develop in outcrop areas and is supported by field evidence of not only lithofacies characteristic of arid (glacial) and wet (interglacial) climatic conditions but also cycles of 3-D terrace development, channel incision and sediment backfilling.

Enhancing high-order harmonic mode-locking in Er/Yb-Doped fiber lasers with sub-MHz fundamental frequency via optoacoustic resonance

We present an experimental study of a long Er/Yb-doped fiber ring laser with a low fundamental frequency of 0.678 MHz. By solely adjusting the quarter-wave plate in the polarization controller, we uncovered a series of reproducible laser generation regimes. Among these, multiple soliton bunches were harmonically mode-locked to low-order cavity harmonics (from the 3rd to the 8th). Notably, we also identified a regime featuring a stable soliton train harmonically mode-locked to the 472nd cavity harmonic at 320 MHz. This regime demonstrated exceptional harmonic mode-locking stability, with a supermode suppression level of 49 dB corresponding to the timing jitter on the order of a few picoseconds. We attribute this remarkable stability to an exact optoacoustic resonance between the laser repetition rate and the fiber eigen acoustic mode frequencies, specifically identified as R06 and TR2,15. These findings represent a significant advancement in high-performance fiber laser operation, particularly in enhancing the stability of lasers with sub-MHz fundamental frequencies capable to generate regular pulses with much higher repetition rates.

Damping of Strong GHz Waves near Magnetars and the Origin of Fast Radio Bursts

We investigate how a fast radio burst (FRB) emitted near a magnetar would propagate through its surrounding dipole magnetosphere at radii r = 107–109 cm. First, we show that a GHz burst emitted in the O-mode with luminosity L ≫ 1040 erg s−1 is immediately damped for all propagation directions except a narrow cone along the magnetic axis. Then, we examine bursts in the X-mode. GHz waves propagating near the magnetic equator behave as magnetohydrodynamic (MHD) waves if they have L ≫ 1040 erg s−1. The waves develop plasma shocks in each oscillation and dissipate at r∼3×108L42−1/4 cm. Waves with lower L or propagation directions closer to the magnetic axis do not obey MHD. Instead, they interact with individual particles and require a kinetic description. The kinetic interaction quickly accelerates particles to Lorentz factors 104–105 at the expense of the wave energy, which again results in strong damping of the wave. In either propagation regime, MHD or kinetic, the dipole magnetosphere surrounding the FRB source acts as a pillow absorbing the radio burst and reradiating the absorbed energy in X-rays. These results constrain the origin of observed FRBs. We argue that the observed FRBs avoid damping because they are emitted by relativistic outflows from magnetospheric explosions, so that the GHz waves do not need to propagate through the outer equilibrium magnetosphere surrounding the magnetar.

Generation and Absorption of Photons by a Two-Level Atom Ultrastrongly Coupled to an Electromagnetic Field

Within the Rabi quantum model, it has been shown theoretically that a two-level atom ultrastrongly coupled to an electromagnetic field generates or absorbs photons. Photons can be generated if the field is initially in the vacuum state. Under certain initial states of the atom + field system, the absorption of photons is possible in the field mode in the ultrastrong atom–field coupling regime. If the atom is initially in the ground (unexcited) state and the field is in the vacuum state, photons can be generated under resonance condition ωa ≈ ωf or ξ ≡ ωa/ωf ≈ 1, where ωa and ωf are the atomic transition and field frequencies, respectively, in the ultrastrong coupling regime. At the negative detuning when ξ 1 or ωa ωf, Rabi oscillations of the average number of photons with are observed in the case of the ultrastrong coupling with the atom–field coupling constant ; in this case, the population of the excited atomic state is Pe(t) ≈ 0.5. At a large positive detuning when ξ 1, photons are not generated, i.e., , and the atom remains in the initial state, i.e., Pe(t) ≈ 0. The statistics of photons in the generation regime is nearly chaotic: the variance of photons is much larger than the level of the coherent field state (i.e., is super-Poisson). Field photons are absorbed without the excitation of the atom in the ultrastrong coupling regime in the case of the coherent initial state of the field 0)$$\\end{document}]]> for certain positive detuning values. In this case, the field becomes sub-Poisson.

Evidence of 1+1D Photorefractive Stripe Solitons Deep in the Kerr Limit.

The Kerr nonlinearity allows for exact analytic soliton solutions in 1+1D. While nothing excludes that these solitons form in naturally occurring real-world 3D settings as solitary walls or stripes, their observation had previously been considered unfeasible because of the strong transverse instability intrinsic to the extended nonlinear perturbation. We report the observation of solitons that are fully compatible with the 1+1D Kerr paradigm limit hosted in a 2+1D system. The waves are stripe spatial solitons in bulk copper doped potassium-lithium-tantalate-niobate (KLTN) supported by unsaturated photorefractive screening nonlinearity. The parameters of the stripe solitons fit well, in the whole existence domain, with the 1+1D existence curve that we derive for the first time in closed form starting from the saturable model of propagation. Transverse instability, that accompanies the solitons embedded in the 3D system, is found to have a gain length much longer than the crystal. Findings establish our system as a versatile platform for investigating exact soliton solutions in bulk settings and in exploring the role of dimensionality at the transition from integrable to nonintegrable regimes of propagation.

Harnessing biomass waste-to-energy for sustainable electricity generation: prospects, viability, and policy implications for low-carbon urban development

AbstractBiomass waste-to-energy (WtE) generation is a potential pathway for green urban transition in developing countries which can contribute significantly to sustainable development goal 7: affordable and clean energy. However, unlike fossil fuel energy systems, the economic returns from WtE systems are low because WtE generation is capital-intensive and requires subsidies. This study examines the prospects of a sustainable biomass electricity generation from rice husk (RH) using a large dataset of rice milling activities in a fast paced urban transition economy. The study analyzes the viability of several RH biomass electricity generation scenarios using indicators such as net electricity output, economic returns (benefits), and levelized cost of electricity (LCOE). The results show that several mills/mill clusters generate sufficient daily RH that can power between 0.8 and 2.2 MW plant with a combined electricity output of about 500,000 MWh per annum. The economic analyses show that all RH biomass electricity generation scenarios return positive economic benefits under reduced social discount rates of 2–6%. Moreover, the LCOE of all scenarios are less than those of electricity generated from other sources. These results demonstrate that biomass waste-to-energy generation is viable for green urban development through low-carbon decentralized energy systems. Several policy implications of the findings are highlighted, including the need for policymakers and energy stakeholders to adopt sustainable biomass energy generation models such as “design, build, and operate” (DBO) to achieve sustainable WtE generation regimes that ensure green urban transition. Such a model will contribute to a circular economy and facilitates sustainable urban development that satisfies climate-related SDGs. Graphic abstract

Multimode light generation in an injection semiconductor laser based on a chiral AlAs/(Al, Ga)As/GaAs microcavity

Experimental investigations of chiral injection AlAs/(Al, Ga)As/GaAs vertical-cavity surface-emitting lasers in the multimode generation regime are performed. A high circular polarization degree 70% of different generation modes measured with a high spectral resolution, is demonstrated. Detailed maps of spatial and angular distribution of laser radiation intensity were constructed.

Role of the inverse Čerenkov effect in the formation of ultrashort Raman solitons in silica microspheres.

We theoretically demonstrate a new regime, to the best of our knowledge, of the formation of ultrashort optical solitons in spherical silica microresonators with whispering gallery modes. The solitons are driven by a coherent CW pump at the frequency in the range of normal dispersion, and the energy is transferred from this pump to the solitons via two channels: the Raman amplification and inverse Čerenkov effect. We discuss three different regimes of soliton propagation and we also show that these Raman solitons can be controlled by weak coherent CW signals.

Interplay mechanisms between hydraulic fractures and natural fractures in various propagation regimes

It is crucial for the successful development of fractured reservoirs to understand the interaction behavior between hydraulic fractures and natural fractures. This work employed a true-triaxial fracturing experiment using prefabricated samples with natural fractures, along with a three-dimensional (3 D) numerical model, to investigate the interaction mechanisms between hydraulic fractures and preexisting natural fractures. Various influencing factors, including the horizontal stress difference, injection rate, fluid viscosity, and approach angle, are considered. The results reveal three distinct modes of interaction between hydraulic fractures and natural fractures: crossing, deflection, and arrest. As the horizontal stress difference, injection rate, and viscosity increase, the interaction between hydraulic and natural fractures undergoes a gradual shift, evolving from arrest to deflection and ultimately crossing. A smaller approach angle enhances the likelihood of hydraulic fractures being captured by natural fractures. Furthermore, the evaluation criterion of propagating ability is proposed based on the dimensionless value to facilitate the evaluation of the interplay between hydraulic and natural fractures. The interaction behavior diagrams between hydraulic fracture and natural fracture in different regimes is established. It shows that the fracture penetration capacity gradually increases from toughness-dominated regime to viscous-dominated regime, as evidenced by the phased arrangement of arrest, deflection, and crossing in their interaction with natural fractures. When the tensile strength and cohesion of natural fractures is high, hydraulic fractures tend to pass through directly, while conversely, they are easily arrested by natural fractures. The research findings can offer valuable insights for optimizing the fracturing in unconventional reservoirs with developed natural fractures.

Table-top source for x-ray absorption spectroscopy with photon energies up to 350 eV.

We present a table-top setup for x-ray absorption spectroscopy (XAS) based on high harmonic generation (HHG) in noble gases. Using sub-millijoule pump pulses at a central wavelength of 1550nm, broadband HHG in the range of 70-350eV was demonstrated. The HHG coherence lengths of several millimeters were achieved by reaching the nonadiabatic regime of harmonic generation. Near edge x-ray absorption fine structure spectroscopy experiments on the boron K edge of a boron foil and a hexagonal boron nitride (hBN) 2D material demonstrate the capabilities of the setup. Femtosecond pulse duration makes pump-probe XAS experiments with corresponding time resolution possible.

Demodulation of Pulsed Acoustic Signals in Strongly Nonlinear Propagation Regimes

Demodulation of Pulsed Acoustic Signals in Strongly Nonlinear Propagation Regimes

The energy balance of a hydraulic fracture at depth

We detail the energy balance of a propagating hydraulic fracture. Using the linear hydraulic fracture model which combines lubrication flow and linear elastic fracture mechanics, we demonstrate how different propagation regimes are related to the dominance of a given term of the power balance of a growing hydraulic fracture. Taking an energy point of view allows us to offer a physical explanation of hydraulic fracture growth behaviours, such as, for example, the transition from viscosity to toughness dominated growth for a radial geometry, fracture propagation after the end of the injection or transition to self-buoyant elongated growth. We quantify the evolution of the different power terms for a series of numerical examples. We also discuss the order of magnitudes of the different terms for a industrial-like hydraulic fracturing treatment accounting for the additional dissipation in the injection line.

Optical beam spread in seawater

We study the spatial and angular distribution of light in a narrow stationary beam propagating in a medium like seawater. For a power-law parametrization of the seawater phase function, using radiative transfer analysis, we derive analytical expressions that determine the radiance distribution in the medium. Both the case of intermediate source–receiver distances, where absorption only begins to affect spreading of the beam, and the asymptotic regime of beam propagation are examined. For the main characteristics of the radiance distribution (the total power, the variance of the angular and radial distributions), scaling relations involving the inherent optical parameters of seawater are found. To validate the expressions obtained we carry out Monte Carlo simulation for commonly adopted seawater scattering models (of Petzold and Morel et al) and their analytical parameterizations. For optical parameters typical to seawater, the predicted analytical laws are in excellent agreement with the results of the Monte Carlo computations.

Evaluation of a Rapid Diagnostic Tool to Estimate Geometry Evolution of Multiple Simultaneously Propagating Fractures from Crosswell Fiber-Optic Strain Measurements

Summary Crosswell low-frequency distributed acoustic sensing (LF-DAS) strain rate measurements generate data useful for hydraulic fracture (HF) diagnostics. These data contain information about HF geometry; however, interpreting the data has relied on time-consuming and computationally expensive numerical interpretation methods. This study aims to evaluate the applicability of a rapid diagnostic tool, known as the “zero strain rate location method” (ZSRLM), for characterizing the geometry of multiple fractures propagating simultaneously. Simulations of multiple fracture propagation are conducted using a planar 3D multifracture simulator that incorporates 3D rock deformation, fluid flow in the wellbore, fluid leakoff, and multiscale fracture propagation regimes. A supertimestepping algorithm is used to solve the nonlinear parabolic equations governing fluid-driven fractures. The far-field strain profile induced by multiple propagating fractures along a crosswell fiber-optic cable is computed using the displacement discontinuity method (DMM). Various scenarios are simulated by adjusting key completion parameters, including the number of clusters, cluster spacing, in-situ stress states, and geomechanical properties. The ZSRLM is then applied to the computed strain field to estimate fracture extents and propagation rates. The accuracy of the ZSRLM is assessed by comparing the estimated fracture geometry parameters with the known simulated values. Our observations indicate that the ZSRLM is not effective when two or more fractures approach the observation well at similar times, as it becomes challenging to discern unique strain-rate converging patterns on waterfall plots for each fracture. However, when fracture arrivals at the monitor well are offset, distinct strain rate patterns emerge, enabling the application of the ZSRLM. Errors between simulated and estimated fracture extent propagation rates are quantified. Finally, the ZSRLM is applied to a field case involving multicluster fracture propagation, and the interpretation of the results is discussed in light of these findings. This research demonstrates the applicability of the ZSRLM for diagnosing the velocities and final extents of multiple fractures propagating simultaneously. The method offers a rapid means of characterizing stimulations using crosswell LF-DAS measurements, which can inform decisions regarding completion design, well spacing, and landing zone. The study contributes to the advancement of efficient fracture diagnostics in the industry, reducing the reliance on numerical interpretation methods.

Flat-topped optical spectrum as a specific marker of multi-pulse grouping in a soliton fiber laser.

We report the experimental observation of a stable generation regime in a soliton fiber laser, characterized by a distinct flat-topped optical spectrum. Notably, in multi-pulse generation, this specific spectrum shape prevents the harmonic mode-locking state, instead connecting the solitons into bound complexes or tight chaotic bunches. Physically, this suggests that in the observed regime, long-range attractive forces dominate over the inter-pulse repulsion across the entire laser cavity. Our experimental findings align with numerical simulations, which demonstrate that the predominance of a long-range inter-pulse attraction is due to a complex interaction mechanism. This mechanism combines the generation of dispersive waves with dissipative forces arising from gain depletion and recovery.

Non-self-similar light transport in scattering media

Transport processes underpin a wide variety of phenomena, ranging from chemistry, to physics and ecology. Despite their pervasiveness, however, several distinctive features of these processes are still elusive, making it difficult to recognize and classify the associated transport regimes. Using light scattering as a probe to explore different propagation regimes, we report on the experimental observation of non-self-similar light transport through turbid membranes. Our results show that a breakdown of self-similarity can arise for light waves even in the presence of isotropic and homogeneous disorder, and can be tuned by varying the turbidity of the system. By introducing the concept of self-similarity for light propagation, we provide a unified framework for the classification of light transport regimes—overcoming the dichotomy between normal and anomalous diffusion—and show that non-self-similar propagation is a common and experimentally accessible phenomenon. This insight can help to understand and model other scenarios where light transport is dominated by rare propagation events, such as in nonlinear and active media, but also in other fields of research beyond optics. Published by the American Physical Society 2024

Modeling the Dispersion of Waves in a Multilayered Inhomogeneous Membrane with Fractional-Order Infusion

The dispersion of elastic shear waves in multilayered bodies is a topic of extensive research due to its significance in contemporary science and engineering. Anti-plane shear motion, a two-dimensional mathematical model in solid mechanics, effectively captures shear wave propagation in elastic bodies with relative mathematical simplicity. This study models the vibration of elastic waves in a multilayered inhomogeneous circular membrane using the Helmholtz equation with fractional-order infusion, effectively leveraging the anti-plane shear motion equation to avoid the computational complexity of universal plane motion equations. The method of the separation of variables and the conformable Bessel equation are utilized for the analytical examination of the model’s resulting vibrational displacements, as well as the dispersion relation. Additionally, the influence of various wave phenomena, including the dependencies of the wavenumber on the frequency and the phase speed on the wavenumber, respectively, with the variational effect of the fractional order on wave dispersion is considered. Numerical simulations of prototypical cases validate the formulated model, illustrating its applicability and effectiveness. The study reveals that fractional-order infusion significantly impacts the dispersion of elastic waves in both single- and multilayer membranes. The effects vary depending on the membrane’s structure and the wave propagation regime (long-wave vs. short-wave). These findings underscore the potential of fractional-order parameters in tailoring wave behavior for diverse scientific and engineering applications.