Development Of Instability Research Articles

Analysis of the Features of Water Circulation in the Northern Part of the Black Sea for Different Seasons on the Basis of the Results of Numerical Modeling with the Assimilation of the Data of Hydrological Surveys in 2016

The analysis of the dynamic and energy characteristics of water circulation in the northern part of the Black Sea was performed on the basis of the assimilation in the numerical model of the data of three hydrological surveys in 2016, carried out on expeditions of 87, 89 and 91 cruises of the R/V Professor Vodyanitsky (summer, autumn and autumn-winter seasons). Numerical experiments were implemented on a horizontal grid (~1.6 km × ~1.6 km) with 27 vertical horizons and an atmospheric effect close to the real one was used. A procedure of assimilation of the observational data was based on the Kalman filter, taking into account the heterogeneity and nonisotropy of the errors of the estimates of the temperature and salinity fields. The integral energy terms in the kinetic and potential energy budget equations for three seasons were estimated. In the summer season, there was a slight weakening of the RC and the main mechanism for the formation of anticyclonic eddies near Sevastopol and near the southeastern shores of Crimea was baroclinic instability of the current (as evidenced by the increase in the slope of isopycnical surfaces and negative values of the work of the buoyancy force). An anticyclonic eddy near Yalta with a radius of about 25 km was generated due to the development of shear instability of the current. In the autumn season, the RC jet was pressed to the shore and there was a decrease in the number of eddies in comparison to the summer season. The formation of anticyclonic eddies with a radius of about 35–40 km in the western part of the region was caused by barotropic instability of the current, the formation of eddies along the Crimean coast – by baroclinic instability. In the autumn-winter season, the RC had a pronounced jet character and there was an increase in the processes of baroclinic instability with the generation of eddies of different scales between the coast and the RC, as well as in the area, located between 31.5 and 33° E, with the weakening of the wind effect. During all seasons, small-scale anticyclonic and cyclonic eddies could be generated along the western and eastern coast of Crimea in the upper layer when current flowed around the coastline and inhomogeneities of the bottom topography under the action of weak winds.

Evolution and hot electron generation of laser–plasma instabilities in direct-drive inertial confinement fusion

A series of 2D in-plane plane wave particle-in-cell simulations find distinctive paths of laser-plasma instability evolution in OMEGA-scale implosions, depending on the initial electron temperature. At low temperatures, two-plasmon decay (TPD) dominates in both initial growth and the steady state. At high temperatures, the initial dominant modes switch to stimulated Raman scattering, but TPD still dominates a steady state characterized by cavitation and Langmuir turbulence. A hot electron scaling is also obtained from the simulations that, when combined with laser/plasma conditions from hydro simulations, can predict hot electron generation in implosions that do not employ smoothing-by-spectral-dispersion (SSD). It also shows that under the same laser/plasma conditions, SSD can reduce hot electron generation.

Effect of notch depth ratio and specimen width on mode II fracture properties of ECC

Engineered Cementitious Composites (ECCs) can be used as repair and reinforcement materials, which can improve the shear performance of the structure. Hence, doubled-notched and unnotched half-symmetric loading tests are used to study the mode II fracture properties of ECC and concrete, and the fracture failure morphology and fracture parameters of ECC and concrete are compared. The effects of the notch depth ratios of 0, 0.1, 0.3, and 0.5 and the specimen widths of 200 mm, 250 mm, and 300 mm on the mode II fracture properties of ECC and concrete are investigated. The mode II crack development of ECC can be divided into four stages: microcrack development stage, multiple cracking stage, main crack formation stage, and crack instability development stage. It can be found that ECC not only has high ultimate tensile strain and energy dissipation capacities, but also has obviously better ability to resist the unstable propagation of shear cracks than concrete. ECC can meet the high shear resistance requirements of some parts of the structure.

Observations and Modeling of Unstable Proton and α Particle Velocity Distributions in Sub-Alfvénic Solar Wind at Parker Solar Probe Perihelia

Past observations show that solar wind (SW) acceleration occurs inside the sub-Alfvénic region, reaching the local Alfvén speed at typical distances ∼10–20 solar radii (R s ). Recently, Parker Solar Probe (PSP) traversed regions of sub-Alfvénic SW near perihelia in encounters E8–E12 for the first time, providing data in these regions. It became evident that the properties of the magnetically dominated SW are considerably different from the super-Alfvénic wind. For example, there are changes in the relative abundances and drift of α particles with respect to protons, as well as in the magnitude of magnetic fluctuations. We use data of the magnetic field from the FIELDS instrument, and construct ion velocity distribution functions (VDFs) from the sub-Alfvénic regions using Solar Probe ANalyzer for Ions data, and run 2.5D and 3D hybrid models of proton-α sub-Alfvénic SW plasma. We investigate the nonlinear evolution of the ion kinetic instabilities in several case studies, and quantify the transfer of energy between the protons, α particles, and the kinetic waves. The models provide the 3D ion VDFs at the various stages of the instability evolution in the SW frame. By combining observational analysis with the modeling results, we gain insights on the evolution of the ion instabilities, the heating and the acceleration processes of the sub-Alfvénic SW plasma, and quantify the exchange of energy between the magnetic and kinetic components. The modeling results suggest that the ion kinetic instabilities are produced locally in the SW, resulting in anisotropic heating of the ions, as observed by PSP.

Enhanced Cycling Performance by Transition Metal Substitution on Li2CuO2 Cathode Additive for Advanced Lithium-Ion Battery

Lithium-Ion batteries (LIBs) have made remarkable progress in the last decade and have been employed so far as the most popular power source for electric vehicles (EVs). However, the energy density issue still remains a drawback for LIBs on long-range driving of EVs for the reason of significant irreversible Li+ loss in the initial charging process of LIBs, induced by a spontaneous formation of solid electrolyte interphase (SEI) on the anode surface. Therefore, strategic studies are required to maximize the energy density of LIBs as compensation of the initial loss of Li+ during cell operation. The utilization of a Li-excess cathode additive in commercial cathodes is an ideal approach to minimize the loss of energy density of LIBs. Recently, Li2CuO2 has been proposed as a potential cathode additive with many advantages over other candidates, including the following: (i) high charge capacity (~ 490 mAh g-1), (ii) comparable operating voltage window (2.5 ~ 4.3 V vs. Li/Li+) to commercial cathode materials, and (iii) abundance of copper (Cu) on the earth. But, its practical use is still restricted by the structural instability and spontaneous oxygen (O2) evolution (> 3.8 V vs. Li/Li+), which results in loss of reversibility during subsequent cycling. It is thus crucial to reinforce the structure of Li2CuO2 to make it more reliable as a cathode additive for charge compensation. In a pursuit of improving the structural stability of Li2CuO2, herein, we demonstrate structural modification via co-substitution by heteroatoms, such as nickel (Ni) and manganese (Mn), for improving the structural stability and electrochemical performance of Li2CuO2. Such an approach effectively enhances the reversibility of Li2CuO2 by suppressing continuous structural degradation and O2 gas evolution during cycling. Our findings provide new conceptual pathways for developing advanced cathode additives for high-energy LIBs.

Mutational landscape of intestinal crypt cells after long-term in vivo exposure to high fat diet

Obesity is a modifiable risk factor in cancer development, especially for gastrointestinal cancer. While the etiology of colorectal cancer is well characterized by the adenoma-carcinoma sequence, it remains unclear how obesity influences colorectal cancer development. Dietary components of a high fat diet along with obesity have been shown to modulate the cancer risk by perturbing the homeostasis of intestinal stem cells, yet how adiposity impacts the development of genomic instability has not been studied. Mutational signatures are a powerful way to understand how a complex biological response impacts genomic stability. We utilized a mouse model of diet-induced obesity to study the mutational landscape of intestinal crypt cells after a 48-week exposure to an experimental high fat diet in vivo. By clonally enriching single crypt derived cells in organoid culture and obtaining whole genome sequences, we analyzed and compared the mutational landscape of intestinal epithelial cells from normal diet and high fat diet mice. Single nucleotide substitution signatures and indel signatures present in our cohort are found equally active in both diet groups and reflect biological processes of normal aging, cellular replication, and oxidative stress induced during organoid culturing. Thus, we demonstrate that in the absence of activating mutations or chemical exposure, high fat diet alone is not sufficient to increase genomic instability.

Субъекты развития системных экономических кризисов: уроки XX века

The paper attempts to identify the main subjects that contribute to the development of systemic economic crises that occur with the periodicity of N. Kondratiev’s cycles. Catastrophe theory approaches were used to assess the sustainability of economic growth. Econometric models of stable and unstable relationships between economic growth rates and growth rates of personal consumption of the population, government spending and investment were tested. Unstable connections were modeled in the form of equations of the elementary theory of catastrophes. At the same time, models of stable links and models of catastrophes of various types were built. Judgments about instability were made in the case when the catastrophe models turned out to be more deterministic. The obtained estimates of the stability of economic growth suggest that the early development of instability and the creation of prerequisites for an economic crisis were facilitated by the policies of states and the strategies of financial capital. Signs of instability due to these factors are found 25–30 years before the onset of the crisis. Summarizing the results of the study suggests that the strategies of financial capital and the policy of the state as subjects of the economy can contribute to the development of systemic economic crises.

Long-term slope instability induced by the reactivation of mass transport complexes: An underestimated geohazard on the Norwegian continental margin

Submarine landslides are significant geohazards, capable of displacing large volumes of sediment from continental margins to deposit mass transport complexes (MTCs) and generate offshore tsunamis. However, the reactivation of MTCs after their initial failure has long been overlooked. By analyzing high-quality three-dimensional seismic reflection data and seismic attribute maps, as well as comparing the geometry of different MTCs, we investigate the development of long-term slope instability and its hazardous consequences on the northwest flank of the Storegga Slide on the Norwegian margin. Our results demonstrate that the reactivation of MTCs can deform both their inner structure and overlying strata, promoting the formation of sinuous channels and local slope failures on the seafloor. These findings further reveal the MTCs that are underconsolidated or comprise slide blocks may remain unstable for a long time after their initial failure, particularly when affected by slope undercutting and a corresponding reduction in lateral support. This study shows that MTC-prone sequences are more likely to comprise regions of continental slopes with long-term instability and recurring marine geohazards.

Characterization of an active landslide structure with integrated electrical resistivity tomography and multi‐channel analysis of surface waves methods in Değirmendere district, Sakarya (Türkiye)

AbstractLandslides following the development of slope instability can have serious consequences. Geophysical surveys have potential to aid in the understanding of landslides and their instability. This study described a landslide that occurred under particular geomorphological and meteorological conditions in Erenler (Sakarya, NW Türkiye) using electrical resistivity tomography (ERT) and multi‐channel analysis of surface waves (MASW) surveys and mechanical drillings. Data showed that the landslide is characterized by downslope movement of an altered clay unit over a claystone unit. The traditional landslide model used to interpret geoelectric data involves sliding of a relatively low‐resistivity material over higher resistivity bedrock. Here, the ERT survey showed a relatively high‐resistivity sliding material moving over relatively low‐resistivity bedrock units corresponding to the claystone unit. The relatively lower resistivity of the whole study area was related to the clay‐rich materials detected in the boreholes. This low‐resistivity unit was detected at high velocity in the MASW section, and it was understood that this layer was a compact structure acting like bedrock. The detected slip surfaces, landslide scars and slip surface toe indicate that the movement character of the landslide is retrogressive. The study results showed that the integrated and comparative use of different geophysical methods effectively reduces interpretation uncertainties and potential errors and leads to much better landslide characterization.

Nonlinear evolution of magnetorotational instability in a magnetized Taylor-Couette flow: Scaling properties and relation to upcoming DRESDYN-MRI experiment

Nonlinear evolution of magnetorotational instability in a magnetized Taylor-Couette flow: Scaling properties and relation to upcoming DRESDYN-MRI experiment

Numerical study of instability development in supersonic jets with a rectangular cross section

Numerical study of instability development in supersonic jets with a rectangular cross section

Instability evolution of a shock-accelerated thin heavy fluid layer in cylindrical geometry

Instability evolutions of shock-accelerated thin cylindrical SF $_6$ layers surrounded by air with initial perturbations imposed only at the outer interface (i.e. the ‘Outer’ case) or at the inner interface (i.e. the ‘Inner’ case) are numerically and theoretically investigated. It is found that the instability evolution of a thin cylindrical heavy fluid layer not only involves the effects of Richtmyer–Meshkov instability, Rayleigh–Taylor stability/instability and compressibility coupled with the Bell–Plesset effect, which determine the instability evolution of the single cylindrical interface, but also strongly depends on the waves reverberated inside the layer, thin-shell correction and interface coupling effect. Specifically, the rarefaction wave inside the thin fluid layer accelerates the outer interface inward and induces the decompression effect for both the Outer and Inner cases, and the compression wave inside the fluid layer accelerates the inner interface inward and causes the decompression effect for the Outer case and compression effect for the Inner case. It is noted that the compressible Bell model excluding the compression/decompression effect of waves, thin-shell correction and interface coupling effect deviates significantly from the perturbation growth. To this end, an improved compressible Bell model is proposed, including three new terms to quantify the compression/decompression effect of waves, thin-shell correction and interface coupling effect, respectively. This improved model is verified by numerical results and successfully characterizes various effects that contribute to the perturbation growth of a shock-accelerated thin heavy fluid layer.

Development of the self-modulation instability of a relativistic proton bunch in plasma

Self-modulation is a beam–plasma instability that is useful to drive large-amplitude wakefields with bunches much longer than the plasma skin depth. We present experimental results showing that, when increasing the ratio between the initial transverse size of the bunch and the plasma skin depth, the instability occurs later along the bunch, or not at all, over a fixed plasma length because the amplitude of the initial wakefields decreases. We show cases for which self-modulation does not develop, and we introduce a simple model discussing the conditions for which it would not occur after any plasma length. Changing bunch size and plasma electron density also changes the growth rate of the instability. We discuss the impact of these results on the design of a particle accelerator based on the self-modulation instability seeded by a relativistic ionization front, such as the future upgrade of the Advanced WAKefield Experiment.

FEATURES OF THE FLOW STRUCTURE IN A RECTANGULAR TRENCH

The study of features of the flow structure in rectangular trenches in a wide range of Reynolds numbers was carried out by means of direct numerical simulation of the flow in the channel and on а plate. Both isothermal and non-isothermal formulations of the problem were considered. Water and air were used as the investigated fluids. The flow structure inside and around the trench in the rectangular channel in the range of Reynolds numbers based on the trench length Re<=9000 was studied in a three-dimensional setting. In the Reynolds numbers range Re>=10000, unsteady flow around a plate with a trench was considered in two-dimensional formulation of the problem. Depending on the Reynolds number, the flow structure in the trench, the influence of geometric parameters on the vortices scales in the trench, their localization and intensity were analyzed. The scale of inhomogeneity of the trench flow in the transverse direction was obtained. The features of non-stationary behavior and interaction of vortex formations with each other and with the external flow at higher Reynolds numbers are considered, development of instability of the vortex structure in the trench and its influence on characteristics of the external flow are shown: from regular oscillations at certain frequency to gradual chaosization of the flow around the trench as the Reynolds number increases, when fractional and multiple frequencies appear. A comparison was made with the vortex structure obtained by other researchers for similar geometric parameters of the trench. The contributions of frictional drag and shape drag to the overall hydraulic drag of the trench, as well as the streamlined surface downstream the trench, are considered. Intensity of heat exchange processes inside the trench, localization of the maximum values of heat fluxes, dependence of heat transfer on the oncoming flow speed were evaluated.

Numerical Investigation of Rotating Instability Development in a Wide Tip Gap Centrifugal Compressor

In the current study, full-stage unsteady simulations were performed to investigate rotating instability inception mechanisms in a particularly large tip clearance centrifugal compressor with a vaneless diffuser and a volute. Four operating points along a speed line were analysed to understand the influence of the mass flow reduction on flow structures. Close to the peak efficiency, an unsteady interaction between the tip clearance vortices and splitter blades was observed. Considering other studies, the influence of the tip gap size was analysed. Then, a large-scale vortex shedding from the leading edges of the main blades was detected when the stage operated near the maximum pressure ratio. It was demonstrated that shed vortices were caused by the combination of the radial gradient of the tangential velocity under the tip vortex and the reverse backflow near the casing. Previous studies on axial compressors refer to these vortical structures as backflow vortices. These vortices cause a significant increase in the incidence angle in the tip region.

Exploiting satellite SAR for archaeological prospection and heritage site protection

ABSTRACT Optical and Synthetic Aperture Radar (SAR) remote sensing has a long history of use and reached a good level of maturity in archaeological and cultural heritage applications, yet further advances are viable through the exploitation of novel sensor data and imaging modes, big data and high-performance computing, advanced and automated analysis methods. This paper showcases the main research avenues in this field, with a focus on archaeological prospection and heritage site protection. Six demonstration use-cases with a wealth of heritage asset types (e.g. excavated and still buried archaeological features, standing monuments, natural reserves, burial mounds, paleo-channels) and respective scientific research objectives are presented: the Ostia-Portus area and the wider Province of Rome (Italy), the city of Wuhan and the Jiuzhaigou National Park (China), and the Siberian “Valley of the Kings” (Russia). Input data encompass both archive and newly tasked medium to very high-resolution imagery acquired over the last decade from satellite (e.g. Copernicus Sentinels and ESA Third Party Missions) and aerial (e.g. Unmanned Aerial Vehicles, UAV) platforms, as well as field-based evidence and ground truth, auxiliary topographic data, Digital Elevation Models (DEM), and monitoring data from geodetic campaigns and networks. The novel results achieved for the use-cases contribute to the discussion on the advantages and limitations of optical and SAR-based archaeological and heritage applications aimed to detect buried and sub-surface archaeological assets across rural and semi-vegetated landscapes, identify threats to cultural heritage assets due to ground instability and urban development in large metropolises, and monitor post-disaster impacts in natural reserves.

Non-contact actuated snap-through buckling of a pre-buckled bistable hard-magnetic elastica

Snap-through buckling of bistable structures is a classic topic in mechanics which has been widely studied and applied in various fields such as mechanical meta-materials and soft robotics. Obstacles that hinder broader applications of conventional bistable structures include the requirement of contact actuation to trigger instability and difficulty to control post-buckling configurations. In contrast, hard magnetic elastica (HME), a composite made of hard ferromagnetic particles and soft elastomer that deforms in response to an externally applied magnetic field, exhibits great potential to bring major advances in this field by allowing non-contact actuation and programmable control of snap-through buckling via magnetization distribution (M−distribution). Here, we develop a theoretical framework to trace the instability and post-buckling evolution process of snap-through buckling of a bistable HME. In contrast to the conventional snapping through end-end shortening, the design space for bistable HME includes two key parameters: the remanent magnetization density after pre-magnetization and the external magnetic field. We focus on two simple yet practical cases: a fixed amplitude of magnetization density along the HME with direction reversed at the magnetization interface (M−interface), and a uniform magnetic field with varied direction. We identify an optimal position for the single M−interface and direction for the uniform actuation field for pre-buckled beams with two-ends fixed, which can reduce the required actuation field for snapping to nearly half in comparison with the symmetric cases. Experiments and finite element analysis are performed to validate the model predictions. Our work may stimulate further studies on utilizing snap-through buckling in applications where fast and large shape transitions from one stable state to another can be actuated in a low-energy, non-contact mode through a remotely applied stimulus field.

Modal dynamics of self-excited thermoacoustic instabilities in even and odd numbered networks of lean-premixed combustors

Can-to-can acoustic interactions in a circumferential network of lean-premixed combustors have a prominent role in the development of complicated modal dynamics and large-scale pattern formations in can-annular gas turbine combustion systems. Despite recent progress in understanding these instabilities, however, previous relevant studies have been limited to an even number of constituent combustors; a fundamental characteristic of the modal dynamics in a can-annular arrangement consisting of an odd number of combustors remains unknown. To address this question, we compare key features of thermoacoustic instabilities in four-coupled (N = 4) and five-coupled (N = 5) can-annular combustor configurations obtained over a broad range of operating conditions. In conjunction with FEM-based Helmholtz simulations, our experimental data show that the dynamic behavior of the even-N case is characterized by the well-known interaction pattern, out-of-phase alternating modulations among the networked combustors. For the odd-N case, however, the can-annular system features complex phase dynamics originating from simultaneous excitation of the degenerate mode pair. We highlight that the development of self-excited azimuthal instabilities in the annular cross-talk section is associated with the modal interaction of the degenerate pair in the odd-N configuration. The initially degenerate pair can be split into two closely-spaced non-degenerate modes, and in consequence their modal interaction gives rise to a periodic transition between spinning and standing azimuthal modes in the annulus. Despite the formation of remarkably different inter-combustor interactions in the two can-annular configurations, however, the entire set of instability data collapses into very similar frequency regimes, suggesting the importance of flame-acoustic interactions occurring within each combustor, namely intra-combustor interactions.

Mid-term results of the treatment of acute postero-lateral rotational instability of the elbow joint

Background: Dislocations of the forearm are rare injuries with the annual incidence of 6.1 cases per 100 000 population. Postero-lateral rotational instability is the most common complication after the conservative treatment of forearm dislocations. To restore the congruency and provide early movements in the elbow joint, the primary repair or reconstruction of the damaged ligaments of the elbow are required. Aim: to evaluate the clinical and functional results after the surgical repair of the elbow joint ligaments in acute postero-lateral rotational instability. Methods: The study was based on a retrospective analysis of a series of clinical cases, including 17 patients with acute postero-lateral rotational instability, among them 5 simple forearm dislocations, 9 fracture-dislocations of the forearm and 3 fractures of the radial head. Refixation of the lateral ulnar ligament was performed with anchor fixation or bone tunnels. The evaluation was performed using the clinical aspects (the lateral pivot shift test, the range of motion), according to the scale for the evaluation of the elbow joint functional condition (MEPS), Oxford scale of the elbow joint evaluation (OEC), the X-ray results were also estimated. Results: In all the cases the elbow joint stability had been achieved, according to the X-ray and clinical aspects. In 4 cases, additional plasty of the medial collateral ligament was needed and performed after the restoration of the lateral ligament complex. According to the MEPS scale, 58% of the achieved results were excellent, 35% were good and 5.8% were satisfactory. Conclusion: The restoration of the lateral ulnar collateral ligament complex is a safe and effective procedure, which restores the elbow joint stability and allows the patients to return to full physical activity and avoid the development of postero-lateral rotational joint instability.

Filamentary-like structures of plasma in a small 3-kJ dense plasma-focus discharge in pure deuterium

Filament-like structures were observed during discharges in a small 3-kJ plasma focus device operated with pure deuterium. These structures were recorded by means of two different laser diagnostic techniques: a schlieren system and a differential laser interferometry. They present the novel fine-scale (submillimeter) plasma structures recorded during the radial implosion, at the pinch stagnation, at the development of instabilities, and during a decay of the dense plasma column, when hard x-rays and fusion-produced neutrons were generated. The temporal uncertainty of these observations was about 2 ns, and the spatial one amounted to 40 μm. The filamentation seems be a natural and spontaneous process which occurs in high-current, hot, and dense plasmas produced in plasma focus devices. The observed filaments have usually longitudinal and/or azimuthal orientations. Their higher plasma density and appearance in regions of the measured and assumed current flows can be interpreted as the formation of plasma-current filaments with concentrated magnetic energy. These filamentary effects should be studied due to their possible role during the evolution of instabilities and the formation of small sources emitting fast electrons and ions.