Instability Processes Research Articles

Study on key parameters of buckling deformation instability and fracture of rock beams and asymmetric distribution law of stope stress.

The moving deformation of the strata and the redistribution of stope stress after mining show asymmetrical characteristics, which do not conform to the symmetrical structural characteristics of the original rock beam fracture. To further analyze the deformation of rock beams and the asymmetry law of stope pressure distribution after strata caving, the detailed process of instability and deformation of composite rock beams before failure was revealed through similar material simulation, theoretical analysis, and numerical simulation. Through similar simulation experiments, the structural characteristics of strata caving were observed. After excavation, the caving angle near the open-off cut side of the model is greater than that on the stop-mining line side. The maximum bending moment of the rock beam is located at the open-off cut side. The rock beam fracture is located on the partial open-off cut side in the middle of the rock beam. The rock beam on the open-off cut side is easy to shear slip and not easy to hinge. The rock beam in front of the advancing direction of the working face is easily hinged. Based on the structural characteristics of strata caving, considering the thickness of the composite rock beam, the two-hinged arch mechanical model for rock beam fracture is established. On this basis, the key parameters of rock beam instability and fracture such as limit load, additional horizontal stress, limit break distance, and break position are analyzed. Based on the deformation characteristics of two hinged arches, the caving structure and the asymmetric distribution mechanism of stress redistribution during the deformation of overburden in stope are explained. Finally, the deformation of rock beam and the asymmetry of stress distribution in stope are verified by numerical calculation. The results show that the concentrated stress value of the coal pillar at the open-off cut side is greater than that in front of the working face. There is a pressure relief area behind the working face, and the pressure relief area has a certain range. The range of stress concentration area, pressure relief area, and stress value tend to be stable, and only the range of the original rock stress zone expands when the working face is advanced to a certain distance. The asymmetric distribution of compaction stress in goaf is related to the buckling deformation of strata.

The place of the climate agenda in modern global communications

The subject of our research is the climate agenda as part of the environmental policies of states. The author's attention to this issue is due to the instability of the international system, which is influenced by current crises and conflict relations between countries. It was important for us to consider how strongly the processes of instability affect the fulfillment of their obligations by global players. We also identified key factors influencing the adoption of current strategic documents. We analyzed the main documents approved at the UN on climate change, adopted in 2021-2023. Scientific novelty manifests itself in several key aspects. First of all, decisions are considered from the point of view of making political decisions and building communication processes. The second aspect is related to the identification of factors influencing the implementation of environmental policy. And finally, we looked at how global crises affected the climate agenda and whether it was transformed on a global scale. The result of the study is the conclusion that the problem of climate change remains key. Moreover, attempts are being made to strengthen the “natural resources – climate change – responsibility” link, which is reflected in plans to introduce a complete phase-out of fossil fuels. Serious steps are being taken to involve developing countries in this process through the provision of financial and other support. Young people have been identified as the main driver of the fight against climate change, which indicates the long-term nature of key decisions. Moreover, international agreements involve further transformation of the existing system through adjustments to national goals, diversification of the energy sector, economic reforms and changes to existing financial systems aimed at achieving climate goals.

Detection of Close Kuiper Belt Binaries with HST WFC3

Binaries in the Kuiper Belt are common. Here we present our analysis of the Solar System Origins Legacy Survey (SSOLS) to show that using a point-spread function (PSF)-fitting method can roughly double the number of binaries identified in that data set. Out of 198 Kuiper Belt objects (KBOs) observed by SSOLS, we find 23 to be visually separated binaries, while a further 19 are blended PSF binaries detectable with the method we present here. This is an overall binary fraction of 21% for the SSOLS data set of cold classical KBOs. In addition, we tested our fitting methods on synthetic data, and while we were able to show them to be very effective at detecting certain blended-PSF binary KBOs, fainter or closer binary KBOs may easily be missed, suggesting that the close binary KBO fraction could be even higher. These results strongly support the idea that most (if not all) KBOs were formed through the streaming instability process, and as a consequence, most KBOs were formed as near-equal mass binaries.

Estimation of landslide during heavy rainfall based on FEM-MPM model

In 2016, Typhoon No. 10 landed on Hokkaido, Japan and resulted in slope failures near Nissho Pass. The massive precipitation generated serious runoff within the catchment area, which accounted for the slope instability. Besides, the rainfall induced slope instability developed as landslide. However, the traditional slope instability analyses were often finished ignoring the transportation of instable soil. This study conducted soil runout analysis as well as slope instability analysis with a finite element method-material point method (FEM-MPM) model to catch the disaster area. In the slope instability analysis using three-dimensional (3D) FEM model, runoff and infiltration were considered at the same time to evaluate the slope instability during heavy rainfall. Here, the surface flow and subsurface flow were governed by shallow water equation, Richards’s equation and Green-Ampt infiltration capacity model. Then, based on the hydraulic field result, local factor of safety (LFS) distribution and dangerous spots were given by FEM model. Subsequently in the soil runout analysis using two-dimensional (2D) and 3D MPM model, large deformation part after failure and the soil transportation were examined to reveal the amount of soil that is risky to be washed away during heavy rainfall. The simulation results proved the appropriateness of this simulation method to reproduce the slope instability and landslide process during heavy rainfall.

Simulation and validation of instability transient process in multistage high-speed axial compressor based on the body-force model

In this paper, a method for simulating the instability transient process of the axial compression system based on the body-force model is developed, and a corresponding simulation program is developed. Simulations of the transient process of instability were carried out on a high-speed four-stage compressor and compared with experimental data. At 50% of the design rotational speed, the type of instability was rotating stall, and the simulated and experimental stall cell propagation speed were very close to each other. At 70% of the design rotational speed, the type of instability was surge. A “surge loop” was simulated, and the surge period and the percentage of time spent in each phase were consistent with the experiments. The simulation successfully predicted the blockage in the surge re-pressurization phase, proving the reliability of the simulation results. In addition, the computation yields more information about the flow field. By summing the blade forces of all grids on a blade row by volume, the surge loadings are obtained. The analysis of the axial momentum equation shows that the obtained blade force variations are reasonable. The simulation time of the multistage axial compressor is greatly reduced compared to the full annulus three-dimensional unsteady Reynolds-averaged Navier–Stokes method, demonstrating its great advantage in the design phase of the compressor.

Fabrication of Self‐Wrinkling Polymer Films with Tunable Patterns through an Interfacial‐Fuming‐Induced Surface Instability Process (Small 19/2024)

Fabrication of Self‐Wrinkling Polymer Films with Tunable Patterns through an Interfacial‐Fuming‐Induced Surface Instability Process (Small 19/2024)

Model test study on the dynamic response of surrounding rock in deep buried tunnel under explosive plane wave

In order to clarify the dynamic failure mechanism in deep buried tunnels, a modeling test of the dynamic response of the surrounding rock in deep buried tunnels under the action of explosion plane wave was carried out by using the geotechnical multi-functional test device. Based on Froude’s similarity theory, a model with dimensions of 1600 × 1300 × 400 mm was constructed using low-strength cement mortar. Using the detonating fuse as the explosive source, the explosion tests were conducted with an equivalent TNT amount of 52.8 g and 105.6 g, respectively. According to the measured data, the stress and deformation characteristics of the surrounding rock, the motion and deformation characteristics of the tunnel and the dynamic instability process of the tunnel were analyzed. The results show that explosive stress waves exhibit exponential attenuation above the arch crown of the tunnel, with the rate of attenuation depending on the amount of explosive used. The deformation process of the surrounding rock of the crown in the tunnel arch under the action of the explosion stress wave was compression followed by tension, which fully proves the existence of the reflected tensile wave. Movement and deformation parameters within the tunnel escalate as the explosive charge increases, especially at the crown of the arch. According to the monitoring results of the motion camera, the dynamic instability process of the tunnel was divided into several stages, such as initial calm, tunnel vibration, particle ejection, atomization, local block ejection, and return to calm. The results of the study have important reference value for the safe excavation and effective support of deep underground engineering.

Energy evolution and strain localization in fractured sandstone under freeze-thaw cycling and uniaxial loading-unloading

In cold regions, combined cyclic freeze-thaw (F-T) and loading-unloading can cause rock slope instability and sliding. The macro-failure of rock masses originates from the expansion of strain localization areas driven by energy. Therefore, a deep understanding of the energy evolution and strain distribution can reveal the instability process. Along these lines, in this work, intact and intermittently jointed sandstones were subjected to a cyclic F-T environment and subsequently carried out uniaxial graded loading-unloading to obtain their mechanical parameters and X-ray computed tomography images. By investigating the energy density, it was found that the input, elastic, dissipated, and damage energies all increased with loading according to a quadratic polynomial function, with the energies obeying a linear allocation law. Meanwhile, F-T changed the energy storage capacity and energy dissipation coefficient of the rock by causing meso-damage. To measure the meso-scale strain localization characteristics, the advanced digital volume correlation technique was also used to obtain three-dimensional strain fields. In terms of local strain, the failure behavior of intact specimens under the application of low and high numbers of F-T cycles was controlled by potential fracture bands and frost-heave cracks, respectively, while fractured specimens were mainly dependent on the macro-fracture arrangement. However, both frost heaving and thawing transformed sandstone from brittle to ductile. In terms of statistical strain, the equivalent strain (εeq) showed a log-normal distribution and continued to deviate to the right due to loading-unloading. Meanwhile, the normal strain (εxx, εyy, εzz) exhibited a normal distribution, where fractured sandstone mainly developed along with the slip direction. Finally, the intrinsic correlations among the energy parameters, meso-damage, and macro-failure were discussed. From our analysis, three stages of energy allocation and transformation were revealed, namely the uniform allocation of damage energy, banded accumulation of damage energy, and fracture caused by the elastic energy release.

TRANSFORMATIONAL CHANGES IN THE UKRAINIAN SOCIO-CULTURAL SPACE AT THE END OF THE XX - FIRST HALF OF THE XXI CENTURY

In the article, the author examines the transformational changes in the Ukrainian socio-cultural space of the end of the ХХ-th – the first half of the ХХІ-st century. The ХХІ-st century is characterized by great transformations not only in the economic and social context, but also in the sphere of cultural life, which is intensively developing in various directions. The author notes that Ukraine is currently experiencing a nation-state revival and the introduction of democratic values in conditions that are difficult and contradictory due to the instability and revolutionary nature of many sociopolitical and socio-economic processes that began in the 1990s and as a result of this , even to this day, the worldview and value orientations that regulate human behavior and relationships, which has a significant impact on the sociocultural situation in Ukraine, remain undefined. Global social changes, if they are systemic and related to the establishment of a new social order, are always accompanied by cultural transformations and characterized as a «reevaluation of all values». The situation became much more complicated due to the annexation of Crimea by Russia, the hybrid war in Donbas, and later the full-scale invasion of Russia on the territory of Ukraine on February 24, 2022, which became new difficult challenges for our country. According to the author, in connection with the new historical context, new conditions for the development of the sphere of culture arose, which caused the formation of a new socio-cultural situation, which is characterized by a change in socio-cultural orientation and ideals, rethinking and creation of a new hierarchy of values. The author believes that the foundations of socio-cultural development of Ukrainian society today are based on all manifestations of unique cultural and social values; development of common cultural, spiritual and educational spaces; active use of the Ukrainian language in all spheres; preservation and dissemination of cultural heritage; popularization and development of the cultural environment; ensuring maximum access to cultural properties, their preservation; stimulating investments for the development of cultural and social spheres, etc. Keywords: transformational processes, socio-cultural activity, socio-cultural development, socio-cultural policy, man, society, culture

Geohazard features of the north-western Sicily and Pantelleria

ABSTRACT We present maps of geohazard features identified across north-western Sicily and Pantelleria in the framework of the Magic project (MArine Geohazard along Italian Coasts), which involved Italian marine geological researchers in 2007-2013. These seafloor features were recognized using high-resolution bathymetry data and rely on the morphological expression of the seafloor and shallow sub-surface processes. The north-western Sicily is a complex continental margin, affected by morphodynamic, depositional, and tectonic processes. The Egadi offshore is controlled by fault escarpments and alternating retreating and progradational processes. Ustica and Pantelleria submerged edifices show the effect of volcanic activity. The Ustica seafloor is interested in volcanic, tectonic, and gravitational instability processes, while the Pantelleria offshore underwent erosive-depositional processes and the effect of bottom currents. Two levels of interpretation are represented: the physiographic domain at a scale of 1:250.000 and the morphological units and morpho-bathymetric elements at a 1:100.000 scale.

Physical insight into the abnormal VTH instability of Schottky p-GaN HEMTs under high-frequency operation

In this Letter, we investigate the threshold voltage (VTH) instability of Schottky p-GaN gate high electron mobility transistors (SP-HEMTs) under high-frequency operation by a resistive-load hard switching method. The abnormal VTH instability is observed, which is different between fully and partially depleted SP-HEMTs (FD- and PD-HEMTs). Notably, for FD-HEMT, VTH shifts positively with effective stress time. However, the VTH instability in PD-HEMT is more complex. At low VGS (e.g., 3 V) and high VGS (e.g., 6 V), VTH shifts positively with stress time consistently. Nevertheless, at intermediate VGS levels (e.g., 4 and 5 V), VTH initially shifts positively and then negatively, displaying a non-monotonous variation. Furthermore, the frequency dependence of VTH is contingent upon VGS. At low VGS, VTH exhibits a negative shift with the increase in frequency. This trend inverses when VGS exceeds 4 V. And it should be noted that the extracted VTH under high-frequency operation is lower than their quasi-static values for both transistor types. This work depicts the physical process and mechanism of the abnormal VTH instability; different from the quasi-static case, hole accumulation effects will be enhanced due to the high dV/dt, which results in a lower VTH. The distinct VTH behaviors of FD- and PD-HEMTs are closely related to the trapping effects, as well as hole accumulation and insufficiency, within the two different p-GaN gate layers.

Efficient multimode vectorial nonlinear propagation solver beyond the weak guidance approximation

In this paper, we present an efficient numerical model able to solve the vectorial nonlinear pulse propagation equation in circularly symmetric multimode waveguides. The algorithm takes advantage of the conservation of total angular momentum of light upon propagation and takes into account the vectorial nature of the propagating modes, making it particularly relevant for studies in ring-core fibers. While conventional propagation solvers exhibit a computational complexity scaling as Nmode4, where Nmode is the number of considered modes, the present solver scales as Nmode3/2. As a first example, it is shown that orbital angular momentum modulation instability processes take place in ring-core fibers in realistic conditions. Finally, it is predicted that the modulation instability process is followed by the appearance of breather-like angular structures.

Thermomagnetic instability in superconducting lead-porous glass nanocomposites

In this paper we examine the mechanisms leading to thermomagnetic instability in nanostructured materials and study their regularities. The appearance of thermomagnetic instabilities in the superconducting state of various materials remains one of the problems of applications of superconductors. We studied the temperature and the magnetic field dependences of the magnetization m(T, H) and heat capacity C(T, H) of a nanocomposite consisting of interconnected lead filaments embedded in nanoporous glass (Pb-PG) with filament diameter d = 7 nm. Porous glass contains an arbitrarily orientated multiply connected system of pores of approximately the same size; lead in the nanocomposite forms a replica of the pore system. Thermomagnetic instability was previously observed in this material in superconducting state at T ≤ 5 K on m(H) dependencies in magnetization studies. We established that high enough external heater power P used during the heat capacity measurements in external magnetic field C(H) at T ≤ 5 K can initiate thermomagnetic instability and penetration of magnetic flux into the nanocomposite. The thermomagnetic instability is generally preceded by a sequence of small heat release events with the same magnitude as P. Another sequence of small heat release events is observed in the region close to Hc2. These events are presumably linked to the thermomagnetic instability process and are caused by small redistribution of magnetic flux in the nanocomposite.

Cavitation and crack nucleation in thin hyperelastic adhesives

The present study investigates in the failure of adhesive bondings with structural silicone sealants. Point connectors of two circular metal adherends bonded with DOWSIL™ TSSA are subjected to tensile loading. We formulate and use a constitutive law that captures volumetric softening owing to the formation of cavities. Therein, cavitation is considered a process of elastic instability which is homogenized with a pseudo-elastic approach. Ultimate failure initiating from the free edges is predicted employing the framework of finite fracture mechanics. The concept requires both a strength-of-materials condition and a fracture mechanics condition to be satisfied simultaneously for crack nucleation. For the former, we use a novel multiaxial equivalent strain criterion. For the latter, we employ literature values of the fracture toughness of DOWSIL™ TSSA . The predicted onset of cavitation and ultimate failure loads are in good agreement with our experiments. The proposed model provides initial crack lengths that allow for the derivation of simple engineering models for both initial designs and proof of structural integrity while simultaneously extending the range of usability of the structural silicone compared to standardized approaches.

Modes of Nanodroplet Formation and Growth on an Ultrathin Water Film.

Using nanobubbles as geometrical confinements, we create a thin water film (∼10 nm) in a graphene liquid cell and investigate the evolution of its instability at the nanoscale under transmission electron microscopy. The breakdown of the water films, resulting in the subsequent formation and growth of nanodroplets, is visualized and generalized into different modes. We identified distinct droplet formation and growth modes by analyzing the dynamic processes involving 61 droplets and 110 liquid bridges within 31 Graphene Liquid Cells (GLCs). Droplet formation is influenced by their positions in GLCs, taking on a semicircular shape at the edge and a circular shape in the middle. Growth modes include liquid mass transfer driven by Plateau-Rayleigh instability and merging processes in and out-of-plane of the graphene interface. Droplet growth can lead to the formation of liquid bridges for which we obtain multiview projections. Data analysis reveals the general dynamics of liquid bridges, including drawing liquids from neighboring residual water films, merging with surrounding droplets, and merging with other liquid bridges. Our experimental observations provide insights into fluid transport at the nanoscale.

Investigation and Monitoring for Ever-Updating Engineering Geological Models: The Example of the Passo della Morte Landslide System

In mountainous regions, where large valleys are essential corridors for settlements and infrastructures, landslide hazard management is a pressing challenge. Large, slow-moving landslides are sometimes difficult to detect. On the one hand, the identification of geomorphological evidence supported by a detailed analysis of possible geological predisposing factor is crucial. On the other hand, to confirm the state of activity of the landslide, displacements should also be detected through monitoring. However, monitoring is challenging when large areas and volumes are involved and when cost effectiveness is an issue. This study presents a comprehensive analysis of the Passo della Morte landslide system, located in the Carnian Alps, which has historically posed a significant threat to critical road infrastructures, including a 2200 m long tunnel. The area is exploited as an example of how an iterative 3M approach (Monitoring, Modeling, and Mitigation), can inform and update engineering geological models of unstable slopes by enabling a detailed comprehension of landslide dynamics, facilitating in turn the development of more effective strategies for risk management and mitigation. Through detailed investigation and continuous monitoring over nearly two decades, the engineering geological model has been refined, integrated with new field data, and has progressively improved understanding of slope instability processes. This work underscores the importance of a dynamic and adaptive approach to geological hazard management, providing a valuable framework for similar challenges in other regions.

Combined effect of warming, nutrients, and species pool size on the seasonal variability of phytoplankton composition: A modeling perspective

AbstractThe anticipated long‐term rise in temperature can have numerous effects on freshwater phytoplankton, however, there is a great deal of uncertainty about how biogeochemical processes modify community functioning under a warming climate. Previous works regarding a large shallow lake and a mesocosm study showed a positive relationship between the temporal variability of phytoplankton composition and mean temperature, which might be a sign of warming‐stimulated instability in ecosystem processes. To elucidate whether these observations are part of a more general phenomenon, we combined a numerical model describing the dependence of algal growth on temperature and nutrient concentration with a multispecies, multi‐nutrient model. We ran simulations representative of changes in phytoplankton communities with randomized initial species composition under different temperature scenarios (current annual temperature pattern increased with 1°C, 2°C, or 3°C), various levels of nitrogen and phosphorus supply and different degrees of temporal variability in those supplies. The model outputs showed that seasonal variability in composition can be enhanced by warming through the mechanistic links between nutrient availability, temperature, and species‐specific growth rates, but the rate of increase is also dependent on nutrient ratios and the size of the species pool. Moreover, temporal variability in nutrient loads also enhanced compositional variability, but the rate of increase also depended on the level of nutrient supply. The results of our study hint that the impact of climate change and eutrophication on phytoplankton dynamics can be more intricate than spatiotemporally limited field or experimental observations would suggest.

Planetesimal and planet formation in transient dust traps

The ring-like structures in protoplanetary discs that are observed in the cold dust emission by ALMA might be explained by dust aggregates trapped aerodynamically in pressure maxima. We investigate the effect of a transient pressure maximum that develops between two regimes with different turbulent levels. We study how such a pressure maximum collects dust aggregates and transforms them into large planetesimals and Moon-mass cores that can further grow into a few Earth-mass planets by pebble accretion, and eventually into giant planets by accreting a gaseous envelope. We developed a numerical model, incorporating the evolution of a gaseous disc, the growth and transport of pebbles, N-body interactions of growing planetary cores, and their backreaction to a gas disc by opening a partial gap. Planetesimal formation by streaming instability is parametrised in our model. A transient pressure maximum efficiently accumulates dust particles that can grow larger than millimetre-sized. If this happens, dust aggregates can be transformed by the streaming instability process into large planetesimals, which can grow further by pebble accretion according to our assumptions. As the gas evolves towards a steady state, the pressure maximum vanishes, and the concentrated pebbles not transformed into planetesimals and accreted by the growing planet drift inward. During this inward drift, if the conditions of the streaming instability are met, planetesimals are formed in the disc within a wide radial range. A transient pressure maximum is a favourable place for planetesimal and planet formation during its lifetime and the concentration of pebbles induces continuous formation of planetesimals even after its disappearance. In addition, the formation of a planet can trigger the formation of planetesimals over a wide area of the protoplanetary disc.

Flow physics during durge of an axial-centrifugal compressor

Aerodynamic instability design is one of the crucial elements when designing a compressor. Unstable phenomenon such as surge harms the compressor in both performance and structure integrity. The complex unsteady flow process during instability strongly relates to the compressor design. This paper investigates the transient instability process using URANS on a three-stage-axial and one-stage-centrifugal combined compressor under its off-design conditions. Results show that the compressor suffers two surge patterns. The mild surge happens first, with a higher frequency than the traditional mild surge. Then, with the decrease of valve opening, the deep surge is initiated, and the axial stages work at the peak pressure ratio because the mass flow rate is limited by the choked radial diffuser. Moreover, analysis of aerodynamic loads reveals that IGV and the first rotor have the largest unsteady force among all blade rows. According to the flow field, the rotor root and stator tip suffer the most serious impulse caused by reversed flow during surge conditions.

Experimental Investigation on the Aerodynamic Instability Process of a High-Speed Axial-Centrifugal Compressor

Abstract Aerodynamic instability plays an important role in compressor design and may cause performance degradation and fatigue damage. In this paper, an experimental study on the evolution of aerodynamic instability is carried out on a compressor that combines the performance benefits of an axial stage and centrifugal stage. The spatiotemporal characteristics of unsteady wall pressure were obtained using fast-responding pressure transducers over a range of operating conditions. The results show that the axial stage works on the positive slope of the performance characteristic curve from choke to stall at low-speed operating conditions, and mainly features rotating instability. Rotating stall is also observed in the impeller (IMP) and diffuser passages. At medium-speed operating conditions, the centrifugal stage suffers a high-frequency mild surge, alternating with rotating stall. With the increase in back pressure, the mild surge diminishes, and rotating stall persists. This behavior is similar to a two-regime-surge, which has been reported for centrifugal compressors. At high-speed operating conditions, the compressor directly reaches surge without other instabilities. Further analysis of the spatial pattern of the rotating stall revealed the existence of a high-pressure region near the volute tongue, resulting in obvious pressure distortion along the circumferential direction at the volute inlet. This induced the amplitude difference of stall cells in corresponding diffuser passages. The disturbance caused by stall cells propagates upstream through the blade passage, and the largest pressure disturbance induced by the stall cell propagation appears in a circumferential position 45 deg downstream of the volute tongue at the impeller inlet and the axial stage inlet.