Stepwise Propagation Research Articles

Polymorph sampling with coupling to extended variables: enhanced sampling of polymorph energy landscapes and free energy perturbation of polymorph ensembles.

A novel approach to computationally enhance the sampling of molecular crystal structures is proposed and tested. This method is based on the use of extended variables coupled to a Monte Carlo based crystal polymorph generator. Inspired by the established technique of quasi-random sampling of polymorphs using the rigid molecule constraint, this approach represents molecular clusters as extended variables within a thermal reservoir. Polymorph unit-cell variables are generated using pseudo-random sampling. Within this framework, a harmonic coupling between the extended variables and polymorph configurations is established. The extended variables remain fixed during the inner loop dedicated to polymorph sampling, enforcing a stepwise propagation of the extended variables to maintain system exploration. The final processing step results in a polymorph energy landscape, where the raw structures sampled to create the extended variable trajectory are re-optimized without the thermal coupling term. The foundational principles of this approach are described and its effectiveness using both a Metropolis Monte Carlo type algorithm and modifications that incorporate replica exchange is demonstrated. A comparison is provided with pseudo-random sampling of polymorphs for the molecule coumarin. The choice to test a design of this algorithm as relevant for enhanced sampling of crystal structures was due to the obvious relation between molecular structure variables and corresponding crystal polymorphs as representative of the inherent vapor to crystal transitions that exist in nature. Additionally, it is shown that the trajectories of extended variables can be harnessed to extract fluctuation properties that can lead to valuable insights. A novel thermodynamic variable is introduced: the free energy difference between ensembles of Z' = 1 and Z' = 2 crystal polymorphs.

Uncertainty Quantification in Mineral Resource Estimation

AbstractMineral resources are estimated to establish potential orebody with acceptable quality (grade) and quantity (tonnage) to validate investment. Estimating mineral resources is associated with uncertainty from sampling, geological heterogeneity, shortage of knowledge and application of mathematical models at sampled and unsampled locations. The uncertainty causes overestimation or underestimation of mineral deposit quality and/or quantity, affecting the anticipated value of a mining project. Therefore, uncertainty is assessed to avoid any likely risks, establish areas more prone to uncertainty and allocate resources to scale down potential consequences. Kriging, probabilistic, geostatistical simulation and machine learning methods are used to estimate mineral resources and assess uncertainty, and their applicability depends on deposit characteristics, amount of data available and expertise of technical personnel. These methods are scattered in the literature making them challenging to access when needed for uncertainty quantification. Therefore, this review aims to compile information about uncertainties in mineral resource estimation scatted in the literature and develop a knowledge base of methodologies for uncertainty quantification. In addition, mineral resource estimation comprises different interdependent steps, in and through which uncertainty accumulates and propagates toward the final estimate. Hence, this review demonstrates stepwise uncertainty propagation and assessment through various phases of the estimation process. This can broaden knowledge about mineral resource estimation and uncertainty assessment in each step and increase the accuracy of mineral resource estimates and mining project viability.

Prediction and optimization of joint quality in laser transmission welding using serial artificial neural networks and their integration with Markov decision process

Laser transmission welding is a highly accurate method for joining plastics, but its diverse process parameters require effective modeling for optimal results. Traditional artificial neural networks (ANNs) typically establish predictive models between laser processing parameters and welding strength, neglecting the crucial role of welding morphology in feature extraction, thus diminishing accuracy. To address this, we developed a serial ANN model based on statistically evident correlations, which predicts joint morphology and strength sequentially, resulting in a 47% improvement in predictive accuracy and a mean error of just 7.13%. This two-layered approach effectively reduces the stepwise propagation of errors in ANNs, allowing the first layer to provide a refined data representation for the second layer to predict welding strength. Furthermore, finding the optimal laser parameter set is time-consuming and computationally demanding with traditional ANN-based optimization methods. To address this, we integrated the Markov decision process with the serial ANN for the first time and proposed a novel varying step strategy for the model, enabling a balance of swift convergence and avoidance of suboptimal solutions. Notably, the Markov-serial ANN model attained enhanced optimization results using only 15.5% of the computational resources required by a standard parameter interval optimization methodology. Welding experiments verified the reliability of the Markov-serial ANN, achieving a mean error of 4.54% for welding strength.

Boosting efficient attention assisted cyclic adversarial auto-encoder for rotating component fault diagnosis under low label rates

In practical engineering scenarios with limited labeled samples, conventional semi-supervised diagnostic methods face challenges in achieving satisfactory identification outcomes. To address the aforementioned issues, this paper introduces an incremental semi-supervised learning (ISL) approach based on boosting efficient attention (BEA) assisted cyclic adversarial auto-encoder (CAAE), referred to as BEA-CAAE. The CAAE enhances unsupervised feature representation by simultaneously constraining the distribution of encoded features and aligning elements of the reconstructed samples through a cyclic encoding strategy. The BEA improves classical attention weights' activation strength to better capture vital information, thereby boosting the feature extraction capabilities of both CAAE and the classifier. The ISL employs a stepwise pseudo-label propagation strategy to incrementally filter high-confidence samples, enhancing sample and label utilization, and improving diagnostic accuracy under low label rate conditions. Experiments conducted on multiple test rigs with simple structures as well as large-scale rotating components test rigs that mimic real-world engineering conditions have demonstrated that the proposed method exhibits a significant advantage over existing semi-supervised fault diagnosis approaches in terms of fault diagnosis accuracy and generalization capability, especially under low label rate conditions.

Early uplift and exhumation of the Tanggula granitoid pluton since the Late Cretaceous: Implications for the stepwise topographic growth model in the eastern Qiangtang terrane

Abstract Reconstructing the uplift process of the eastern Qiangtang terrane is crucial for understanding the growth model of the central Tibetan Plateau. However, due to the limited amount of data available, it is not well constrained. The Tanggula granitoid pluton is an outstanding geological feature in the eastern Qiangtang terrane, and thus could provide crucial constraints on its uplift history. We applied multiple thermochronologic systems over a broad temperature range, including apatite U-Pb, biotite and K-feldspar 40Ar/39Ar, apatite and zircon fission-track, and zircon (U-Th)/He, to study samples from the Tanggula granitoid pluton. The results exhibit the expected relative age order of these thermochronologic systems, with 242–238 Ma apatite U-Pb ages, 218–204 Ma biotite 40Ar/39Ar ages, 197–191 Ma K-feldspar 40Ar/39Ar ages, 94–81 Ma zircon fission-track ages, 70–58 Ma zircon (U-Th)/He ages, and 61–39 Ma apatite fission-track ages. Using these thermochronologic ages and thermal history modeling results, we reconstructed a comprehensive thermal history for the pluton, from which three rapid cooling phases were revealed. The earliest rapid cooling phase (220–180 Ma; ~5.25 °C/m.y.) closely followed the emplacement of the Tanggula granitoid pluton, and thus is primarily an expression of natural cooling triggered by conduction with the surrounding rocks. In contrast, the rapid cooling during 100–60 Ma and since 20 Ma can be interpreted to represent intense exhumation, with corresponding exhumation of 5.0–6.0 km and 2.3–2.8 km, as well as an average exhumation rate of 0.125–0.150 mm/yr and 0.115–0.140 mm/yr, respectively. According to the thermal history, the earliest uplift in the Tanggula region could have been initiated as early as the Late Cretaceous. Using the published data, we determined that the onset of rapid uplift and exhumation in the entire eastern Qiangtang terrane had a northeastward, stepwise propagation process. The region within or around Anduo first experienced rapid uplift and exhumation that initiated during the late Early Cretaceous (ca. 130 Ma), the Tanggula region to the northeast experienced rapid uplift and exhumation that initiated during the Late Cretaceous (ca. 100 Ma), and the region farther to the northeast in Tuotuohe and Yushu–Nangqian experienced rapid uplift and exhumation that initiated in the late Paleocene (ca. 60 Ma). The northeastward stepwise uplift and exhumation in the eastern Qiangtang terrane was likely caused by the combined Lhasa–Qiangtang and India–Asia continental collisions.

Low Frequency Magnetic Field Observations of Natural Positive Leaders Featuring Stepwise Propagation

AbstractWe examine the low‐frequency (LF) magnetic pulses recorded for the positive leader in two natural lightning flashes as recorded on the high‐speed video camera. The captured positive leader in both cases propagated in a stepwise manner at least over several milliseconds according to the concurrent sequence of LF magnetic pulses. By comparing with previous studies on positive leaders under different situations, the average inter‐pulse intervals (11.7 and 20.3 μs, respectively) obtained for our natural cases are shorter than that of upward positive leaders in rocket‐triggered (typically >25 μs) and tower‐initiated lightning (62 μs in one case). Hence, the stepwise propagation of positive leaders in natural lightning is likely more frequent than that in object‐induced lightning, reflecting a possible influence of ambient electric field and other meteorological factors on the stepwise feature of positive leader. The stepwise extension might be common for positive leaders developing in various scenarios.

Features of electric field distribution along helium atmospheric plasma jet in stepwise propagation mode of guided streamer

Features of electric field distribution along helium atmospheric plasma jet in stepwise propagation mode of guided streamer

Middle–Late Cenozoic Stepwise Deformation Propagation in Eastern Tibet

AbstractThe uplift and deformation styles of the Tibetan Plateau have been long debated on stepwise growth and crustal channel flow. Here, we offer new insight into this issue by constraining the pulsed exhumation history of the Yalong thrust belt in eastern Tibet, using apatite and zircon (U–Th)/He data from three ∼1 km vertical transects. The results revealed two rapid cooling pulses in the Late Oligocene (∼24 Ma, 50°C/m.y.) and the Middle Miocene (17–14 Ma, 35 °C/m.y.), respectively, which we ascribe to the staged‐thrusting faulting of this belt. These thrust faulting events indicated upward and eastward growth of the Tibetan Plateau, further suggested that the high topographic relief across the Yalong thrust belt mainly formed (at least) since the Late Oligocene. The available documents from paleoaltimetry, basin sediment accumulation, and thermochronometers and our new results reveal a regional‐scale stepwise propagation pattern of tectonic deformation during the Middle–Late Cenozoic in eastern Tibet.

Stepwise development of atmospheric pressure plasma jet driven by bursts of high-voltage nanosecond pulses at multi-tens MHz

This study employs the bursts of high-voltage nanosecond pulses at multi-tens MHz to drive the helium atmospheric pressure plasma jet. Such bursts are obtained by modulating a high-voltage nanosecond pulse based on the wave reflections in a coaxial cable. The development processes and mechanisms of the plasma jet are analyzed in detail based on the discharge waveforms, discharge images, gas temperature, electron density, and axial electric field. Because the time interval between adjacent pulses is much shorter than the characteristic plasma decay time, the discharge channel driven by the first pulse still has high residual electron density and conductivity when the second pulse arrives. The first discharge channel serves as an extension of the high-voltage electrode. In this case, the second discharge starts at the end of the first discharge channel and continues to propagate forward. Driven by the bursts of high-voltage nanosecond pulses, the stepwise propagation of a guided streamer along the plasma jet is observed. The characteristic of the stepwise development of the guided streamer is stable and repeatable under the same condition and does not change at different helium flow rates if the flow is laminar. Reducing the cable length results in a higher equivalent pulse frequency in the bursts and significantly increases the plasma jet length. However, an excessively high frequency will cause a rise in gas temperature and pressure fluctuation in helium flow, resulting in a reduction in the length of the laminar region and an unstable discharge.

Oxygen Propagation Fronts in Porous Media Under Evaporative Conditions at the Soil/Atmosphere Interface: Lab‐Scale Experiments and Model‐Based Interpretation

AbstractThe interchange of gas components and volatile compounds between terrestrial and atmospheric compartments is critical for biogeochemical cycles and has important environmental and climate implications. In this study, we focus on oxygen and we explore the coupling between oxygen mass transfer and evaporation at the soil/atmosphere interface. We performed well‐controlled single‐phase and two‐phase laboratory experiments to determine the spatial and temporal evolution of oxygen fronts and to elucidate the coupling between mass and heat transfer in porous media with different grain sizes and under different evaporative conditions (i.e., no evaporation, natural, and enhanced evaporation). We also developed a non‐isothermal multiphase and multicomponent model to quantitatively interpret the experimental outcomes. The experiments and modeling allowed us to characterize the effects of external forcing (i.e., temperature gradients, humidity conditions) and internal factors (e.g., grain size) on the transport and distribution of oxygen in the different setups. Depth‐resolved spatial profiles and breakthrough curves of oxygen in the two‐phase experiments with evaporation are notably different from the single‐phase experiments due to the progressive gas invasion. The two‐phase experiments reveal a stepwise propagation pattern of oxygen that migrates considerably faster and penetrates deeper in the porous media in contrast to the relatively slow diffusion‐dominated transport regime in the absence of evaporation. The outcomes also show deeper and faster oxygen propagation in finer‐textured porous media under similar evaporative conditions, indicating the importance of internal factors for the distribution of the fluid phases and for the migration behavior of gas components in two‐phase systems.

Atmospheric Propagation Modelling for Terrestrial Radio Frequency Communication Links in a Tropical Wet and Dry Savanna Climate

Atmospheric impairment-induced attenuation is the prominent source of signal degradation in radio wave communication channels. The computation-based modeling of radio wave attenuation over the atmosphere is the stepwise application of relevant radio propagation models, data, and procedures to effectively and prognostically estimate the losses of the propagated radio signals that have been induced by atmospheric constituents. This contribution aims to perform a detailed prognostic evaluation of radio wave propagation attenuation due to rain, free space, gases, and cloud over the atmosphere at the ultra-high frequency band. This aim has been achieved by employing relevant empirical atmospheric data and suitable propagation models for robust prognostic modeling using experimental measurements. Additionally, the extrapolative attenuation estimation results and the performance analysis were accomplished by engaging different stepwise propagation models and computation parameters often utilized in Earth–satellite and terrestrial communications. Results indicate that steady attenuation loss levels rise with increasing signal carrier frequency where free space is more dominant. The attenuation levels attained due to rain, cloud, atmospheric gases, and free space are also dependent on droplet depths, sizes, composition, and statistical distribution. While moderate and heavy rain depths achieved 3 dB and 4 dB attenuations, the attenuation due to light rainfall attained a 2.5 dB level. The results also revealed that attenuation intensity levels induced by atmospheric gases and cloud effects are less than that of rain. The prognostic-based empirical attenuation modeling results can provide first-hand information to radio transmission engineers on link budgets concerning various atmospheric impairment effects during radio frequency network design, deployment, and management, essentially at the ultra-high frequency band.

A time‐based arc‐length like method to remove step size effects during fracture propagation

AbstractAn arc‐length like method is presented which alters the size of the time increment when simulating crack propagation problems. By allowing the time increment to change during the time step a constraint can be imposed, which is used to enforce the fracture to propagate a single element length per time step. This removes the effect of the (interface) element size on propagating fractures, and therefore allows smooth fracture propagation during the simulation. The benefits of the scheme are demonstrated for three cases: mode‐I crack propagation in a double cantilever beam, a shear fracture including inertial and viscoplastic effects in the surrounding material, and a pressurized fracture inside a poroelastic material. These cases highlight the ability of this scheme to obtain more accurate and nonoscillatory results for the force–displacement relation, to remove numerically induced stepwise fracture propagation, and to allow for arbitrary propagation velocities. An added benefit is that plastic strains surrounding a fracture are no longer affected by the (interface) element size.

IFN-γ Drives TNF-α Hyperproduction and Lethal Lung Inflammation during Antibiotic Treatment of Postinfluenza Staphylococcus aureus Pneumonia.

Inflammatory cytokine storm is a known cause for acute respiratory distress syndrome. In this study, we have investigated the role of IFN-γ in lethal lung inflammation using a mouse model of postinfluenza methicillin-resistant Staphylococcus aureus (MRSA) pneumonia. To mimic the clinical scenario, animals were treated with antibiotics for effective bacterial control following MRSA superinfection. However, antibiotic therapy alone is not sufficient to improve survival of wild-type animals in this lethal acute respiratory distress syndrome model. In contrast, antibiotics induce effective protection in mice deficient in IFN-γ response. Mechanistically, we show that rather than inhibiting bacterial clearance, IFN-γ promotes proinflammatory cytokine response to cause lethal lung damage. Neutralization of IFN-γ after influenza prevents hyperproduction of TNF-α, and thereby protects against inflammatory lung damage and animal mortality. Taken together, the current study demonstrates that influenza-induced IFN-γ drives a stepwise propagation of inflammatory cytokine response, which ultimately results in fatal lung damage during secondary MRSA pneumonia, despite of antibiotic therapy.

Role of charge accumulation in guided streamer evolution in helium DBD plasma jets

Experimental data are presented on the evolution of a helium atmospheric pressure plasma jet driven by a tailored voltage waveform generated as bunches of voltage pulses consisting of a superposition of approx 43 kHz bipolar square pulses and approx 300 kHz oscillations. The characteristics of directed ionization waves (guided streamers) are compared for bunches with different first pulse polarities and different bunch duty cycles. The longest and brightest streamers are achieved at the voltage bunch with the first negative pulse and a minimum duty cycle. The dynamics of streamers at the voltage bunch with the first positive pulse are characterized by the shortest length and a lower brightness. The plasma jet length can be smoothly changed by varying the number of pulses in the bunch and the polarity of the first pulse. It is thus possible to precisely localize the region of a strong field in space by combining the parameters of the applied voltage (the duty cycle and polarity of the first pulse of a bunch) with a stepwise propagation mode of a guided streamer.

Transition from one-pass mode to stepwise propagation of a guided streamer along a helium plasma jet

The transition from the one-pass mode to the stepwise mode of guided streamer propagation along a helium atmospheric pressure plasma jet is presented. The propagation of the guided streamer was recorded for a special waveform of the applied voltage, which was the superposition of ≈45 kHz bipolar square pulses and ≈350 kHz damped oscillations. Stepwise propagation of the streamer occurred at a certain voltage amplitude and gas flow rate. The transition from one-pass propagation to stepwise propagation was observed for a preturbulent gas flow with an increasing voltage amplitude. The reverse transition from stepwise propagation to one-pass propagation at a lower gas flow rate in a laminar gas flow was recorded. The transition from one mode to another is associated with an increase in the air admixed content in the helium flow.

Bridging microstructure and crystallography with the micromechanics of cleavage fracture in a lamellar pearlitic steel

The present paper focuses on the microstructure-based cleavage crack propagation in a Charpy impact tested fully pearlitic steel by correlating microstructure and crystallography with the overall fracture behavior. The importance of pearlite lamellae orientation in providing preferred fracture paths is discussed, encompassing the mechanism of interface decohesion and stepwise crack propagation through a mathematical model simulation. While the {100} cleavage cracking is well familiar in pearlitic steels, crack propagation along the {110} crystallographic planes can also prevail in some pearlite colonies or nodules. This is related to suppressing the crack tip dislocation emissions due to restricted slip transferability across the lamellae interfaces. Besides, the strain incompatibility due to large elastic modulus or Schmid factor mismatch across the pearlite nodule boundaries is responsible for triggering internodular cracking in the steel. Connecting the framework of fracture mechanics with the experimental observations, the mechanisms pertaining to different types of tear ridges formed within a pearlite colony are proposed. This certainly illuminates the role of lamellae orientation in the process of crystal bending and shearing at the tear ridges formed within the colonies or at the twist nodule boundaries.

Anisotropic, Wrinkled, and Crack-Bridging Structure for Ultrasensitive, Highly Selective Multidirectional Strain Sensors

HighlightsTwo functionally different anisotropic layers are rationally assembled for highly selective and stretchable multidirectional strain sensors.Concurrently excellent selectivity, sensitivity, stretchability, and linearity up to 100% strain is demonstrated for the first time in a multidirectional strain sensor.A novel stepwise crack propagation mechanism is proposed to enable high stretchability and linearity.

Characteristics of Electric Currents in Upward Lightning Flashes From a Windmill and its Lightning Protection Tower in Japan, 2005–2016

AbstractWe examine the lightning current of 81 upward lightning (UL) initiated from a windmill and its lightning protection tower in Japan under winter thunderstorms from 2005 to 2016. Among 81 UL, the negative, positive, and bipolar lightning account for 64%, 12%, and 24%, respectively. After checking the current waveforms during the initial stage (IS) of negative UL, we found that self‐initiated negative UL have larger peak value and shorter rise time compared to other‐triggered ones, although two types of negative UL show no significant difference in charge transfer and duration. Among 18 self‐initiated negative UL, half of them are initiated from the windmill. On the other hand, only two of 27 other‐triggered negative UL are from the windmill and both of them have smaller current peak value, shorter duration, and smaller charge transfer. According to whether or not the IS current waveforms exhibit pulsation, we have classified UL into type S (smooth), SP (transition from smooth to pulsation), and P (pulsation). We found that the rate of slow current rise for most type P UL is larger than 0.1 kA/ms, whereas for all type S UL the rate is smaller than 0.01 kA/ms. The type SP UL shows a slow current rise rate ranging from 0.01 to 0.1 kA/ms. We found that the current pulsation of type P UL corresponds to the stepwise propagation of a positive leader. Based on these results, we have discussed the effect of the lightning protection tower and the stepwise propagation of positive leaders.

Stick‐slip like behavior in shear fracture propagation including the effect of fluid flow

AbstractShear‐based fracture propagation in fluid‐saturated porous materials is investigated using a displacement–pressure formulation that includes acceleration and inertial effects of the fluid. Pressure‐dependent plasticity with a nonassociated flow rule is adopted to realistically represent the stresses in the porous bulk material. The domain is discretized using unequal order T‐splines and cast into a finite element method using Bézier extraction. An implicit scheme is used for the temporal integration. The solid acceleration‐driven fluid flow reacts to stress waves, but it results in pressure oscillations. Adding fluid acceleration terms dampens these oscillations and increases the fluid pressure near the fracture tips. By simulating a typical shear fracture case, it is shown that stick‐slip like, or stepwise, fracture propagation occurs for a high permeability, also upon mesh refinement. The acceleration driven fluid flow results in a build‐up of pressure near the fracture tip. Once this pressure region encompasses the fracture tip, propagation arrests until the pressure has diffused away from the crack tip, after which propagation is resumed and the build‐up of pressure begins anew. This results in a stick‐slip like behavior, with large arrests in the fracture propagation. Stepwise propagation related to the initial conditions has also been observed, but disappears once the fracture length exceeds the size of the region influenced by the initial conditions.

Effects of Time‐Dependent Contact Angle on Wettability of Subcritically Water‐Repellent Soils

AbstractRecent studies have indicated that under certain conditions, most soils are water repellent to some degree, which impacts agricultural fields, pastures, forests, grasslands, and turf areas. Soil water repellency originates from amphiphilic molecules that reorient during contact with water. However, models to describe the flow in soils affected by time‐dependent contact angle (CA(t)) are still lacking. The current study aims to close this gap. The measured CA(t) for an oleic acid‐coated glass surface and a uniform capillary tube indicated that the initial CA was substantially higher for the latter. However, the rate of CA decrease was similar for both cases in spite of the fact that the contact area between the water and the tube wall continuously increases by the capillary rise. This indicates that the amphiphilic molecules reorientation at the vicinity of the contact line rather than at the wetted tube area controls the CA dynamics. A mathematical model for flow in a uniform and sinusoidal capillary tube with CA(t) < 90° that includes model for the reorientation of the amphiphilic molecules was introduced. The model for uniform case was successfully verified by comparison with measured capillary rise in a coated uniform tube. The simulations indicated that nonuniform pore geometry amplifies the effect of CA(t) on the capillary rise dynamics. The stepwise meniscus propagation in the sinusoidal capillary tubes is driven by the time for the meniscus to reach the converging section of the tube. The retardation in capillary rise increases with tube waviness.