Instability Processes Research Articles

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.

Vibration sensor as the basis of an equipment monitoring system

Currently, the high complexity and instability of engineering production processes leads to the need to make management decisions under conditions of uncertainty, which significantly affects the efficiency of production as a whole. Reducing uncertainty in operational production planning of machine-building industries is possible by analyzing data on the flow of technological processes collected using equipment monitoring systems, i.e. measuring and information systems. It is proposed to use vibration sensors as the main source of information to obtain reliable data on the operation of equipment. General issues regarding vibration sensors are considered and a variant of their classification according to various features is presented, such as sensitivity, operating principle, method of obtaining information, signal conversion mechanism, signal measurement method. Several versions of vibration sensors have been developed, designed to collect information about the level of vibration during processing and included in the diagnostic module for monitoring equipment operation. The first version of the printed circuit board is based on a microcontroller based on ATMega328P, designed to read MEMS accelerometer data and transmit the collected information using a wireless communication module to the operator panel for display in real time and transmission for storage and processing to the server. To charge the battery, a charge controller based on the TP4056 chip and a low-dropout linear stabilizer TPS730 are used. In the second option, the MPU9250 inertial measurement module is used, and information processing and data transmission is carried out using a specialized module NINA-B306. A printed circuit board of any of the presented options is installed in a vibration control sensor mounted on the back side of a three-jaw chuck inside the machine body. This placement of the diagnostic module eliminates the possibility of its unintentional damage while ensuring the required quality and reliability of signal transmission. The vibration sensor, fixed to the cartridge using quick-release strips, consists of a board located in the housing. Above the board there is an insert that protects the board from the battery. The housing is closed from above with a lid using screw washers through a gasket to ensure the housing is sealed. The clamping screw is used to secure the board in the case. The vibration sensor is turned on using a button. The proposed vibration sensor can be used as the basis of an measuring and information systems, because information about the level of vibration of a technological system, recorded by sensors, like a human cardiogram, provides comprehensive information about its condition. A diagnostic module built on the basis of a vibration sensor will increase the efficiency and “transparency” of machining processes and collect statistical data that allows assessing the efficiency of equipment operation.

Влияние систематической холодовой нагрузки на спектральные характеристики тета- и альфа-ритмов ЭЭГ курсантов военного вуза

The study was focused on the features of spectral characteristics of the EEG alpha and theta ranges in the military academy cadets undergoing specific training to improve cold resistance (cold exposure training). The study was aimed to assess the impact of the military academy cadets’ incremental exposure to the graduated cold stress (cold exposure training) on spectral characteristics of the EEG alpha and theta rhythms. Students of the civil higher educational institution and military academy cadets were assessed (58 individuals in total). Cadets underwent a specific program focused on improving cold resistance (cold exposure training). Background EEG in the alpha and theta frequency ranges was recorded. Statistical data processing involved nonparametric comparison using the Mann–Whitney U test. The results were obtained suggesting that there were significant differences in spectral characteristics of alpha and theta rhythms between the group of foreign cadets and the controls. The cold exposure training program was effective in the group of Russian cadets, which had an effect on the cerebral homeostasis stability with some degree of instability of neurodynamic processes in the CNS. In foreign cadets, regular cold exposure training resulted in the pronounced disintegration of cortical-subcortical and intracortical interactions, as well as in the formation of binary alpha-theta structure of background EEG.

Study of Time–Frequency Domain of Acoustic Emission Precursors in Rock Failure during Uniaxial Compression

Predicting rock bursts is essential for maintaining worker safety and the long-term growth of subsurface infrastructure. The purpose of this study is to investigate the precursor reactions and processes of rock instability. To determine the degree of rock damage, the research examines the time-varying acoustic emission (AE) features that occur when rocks are compressed uniaxially and introduces AE parameters such as the b-value, γ-value, and βt-value. The findings suggest that the evolution of rock damage during loading is adequately reflected by the b-value, γ-value, and βt-value. The relationships between b-value, γ-value, and βt-value are studied, as well as the possibility of using these three metrics as early-warning systems for rock failure.

Impact of non-diffusive interactions on Turing instability

Observational studies of the chemical reactions have shown that the uniform state, driven by the diffusion differences of activator and inhibitor species, can seed the spontaneous emergence of spatially organized patterns—also known as Turing instability. The presence of diffusive interaction between the species in discrete media can naturally form the structure of the network Laplacian, thereby resulting in that the Turing instability can be better understood via the eigenvectors and eigenvalues of the graph Laplacian. However, it is still unclear whether and under which conditions the Turing instability can be induced in the absence of diffusive transport. In this work, to overcome the limitation of network Laplacian matrix that only has non-positive eigenvalues, we investigate the effects of non-diffusive (or no-local) coupling between the species on the Turing instability for the directed and undirected networks, respectively, where the interaction matrix may produce the positive and negative eigenvalues. In particular, we first derive the critical conditions that the Turing instability occurs by employing the linear stability analysis. Then we apply them to the networked systems governed by the FitzHugh–Nagumo dynamics and obtain the critical range of eigenvalues of the interaction matrix. Finally, we use the Girko’s circular law to predict the eigenvalues’ distribution, and show, via extensive numerical simulations, the transition process of the Turing instability depending on network size, network connectivity and connection weights (intraspecific interaction strength). Our results reveal that in the absence of diffusive transport, the Turing instability still can arise, offering a new perspective on the generation mechanism of the Turing instability.

Stability analysis of roadbed under flood scouring

Soil roadbed along the river suffers from water erosion at the bottom and collapse at the top under flood scouring, which leads to the suspension of upper pavement slab. In order to ensure the safety of soil roadbed along the river, this study explored the development mechanism of soil roadbed damage by flood in actual cases, and proposed the evolution process of instability under roadbed scouring. The stability law of roadbed along the river under flood scouring was analyzed, and the stability safety factor was corrected to analyze the sensitivity of water depth, flow rate, river bending angle and stability safety factor K in working conditions. The sensitivity of width and height of soil roadbed after flood scouring to water depth, flow velocity, river bending angle was investigated. Moreover, numerical simulation was carried out to determine the displacement nephogram and maximum shear stress nephogram of soil roadbed along the river under the conditions of road surface and roadbed load, vehicle loading or constant change of water depth. By comparing the above theories and engineering cases, the water damage mechanism of soil roadbed along the river was further verified.

Smoothed Particle Hydrodynamics (SPH) Analysis of Slope Soil–Retaining Wall Interaction and Retaining Wall Motion Response

The occurrence of slope instability disasters seriously endangers the safety of people’s lives and property in China. Therefore, it is essential to study the slope instability process and the interaction between soil and retaining walls. In this paper, the smoothed-particle hydrodynamics (SPH) method, based on the elastoplastic constitutive model of rock and soil, was used to simulate the entire process of slope instability and the interaction between soil and retaining walls. The model, based on the classical elastic–plastic theory, includes linear elastic deformation and plastic deformation following the non-associated flow rule under the Drucker–Prager (DP) yield criterion. By considering the plastic characteristics of geotechnical materials, this method can accurately simulate the slope movement process. The model was established, calculated, and compared with a slope example, thus verifying its feasibility. Furthermore, the motion response of the retaining wall under different conditions was studied, which provides a new numerical simulation platform for the stability checking of the retaining wall and motion analysis after the interaction between the retaining wall and slope soil.

THE RELATIONSHIP OF HOPE WITH QUARTER LIFE CRISIS IN FINAL YEAR STUDENTS IN WEST SUMATRA

This research aims to determine the relationship between hope and quarter life crisis in final year students in West Sumatra. Hope is the ability possessed by an individual to create a strategy in achieving a goal with the overall motivation he has to recognize the strategy chosen in achieving a goal. Meanwhile, the quarter life crisis is a process of high instability, drastic changes, too many choices and feelings of panic and helplessness. This phase appears in individuals aged 18 to 29 years. This research uses quantitative methods with a quantitative correlational research design. The population in this study were final year students in West Sumatra with a total of 195 students as subjects. The sampling technique used was purposive sampling. The data collection tool uses the quarter life hope and crisis scale. Data analysis uses the product moment correlation coefficient. The results of the research show that there is a negative relationship between hope and the quarter life crisis in final year students in West Sumatra (r=-0.514: p=0.00). A significant negative relationship means that if an individual has high hopes then the level of quarter life crisis for the individual will be low, and if the level of quarter life crisis is high then the level of hope experienced by the individual will tend to be low.

THE RELATIONSHIP OF HOPE WITH QUARTER LIFE CRISIS IN FINAL YEAR STUDENTS IN WEST SUMATRA

This research aims to determine the relationship between hope and quarter life crisis in final year students in West Sumatra. Hope is the ability possessed by an individual to create a strategy in achieving a goal with the overall motivation he has to recognize the strategy chosen in achieving a goal. Meanwhile, the quarter life crisis is a process of high instability, drastic changes, too many choices and feelings of panic and helplessness. This phase appears in individuals aged 18 to 29 years. This research uses quantitative methods with a quantitative correlational research design. The population in this study were final year students in West Sumatra with a total of 195 students as subjects. The sampling technique used was purposive sampling. The data collection tool uses the quarter life hope and crisis scale. Data analysis uses the product moment correlation coefficient. The results of the research show that there is a negative relationship between hope and the quarter life crisis in final year students in West Sumatra (r=-0.514: p=0.00). A significant negative relationship means that if an individual has high hopes then the level of quarter life crisis for the individual will be low, and if the level of quarter life crisis is high then the level of hope experienced by the individual will tend to be low.

The Need for Multi‐Century Projections of Sea Level Rise

AbstractThe latest assessment report of the Intergovernmental Panel on Climate Change (IPCC) provided scenario‐based local sea level projections to 2150 and characterized the long‐term committed global mean sea level rise on 2,000‐ and 10,000‐year time horizons associated with peak surface warming levels. Turner et al. build on the scientific assessment of the IPCC to provide time‐continuous projections of future sea level rise to 2500. These projections fill an important knowledge gap to help inform coastal decision‐making processes and more fully quantify the benefits of mitigation actions in terms of limiting future sea level rise. However, limited understanding of ice instability processes remains a key scientific challenge and improved observational and modeling capability are critical to reducing uncertainties and monitoring the trajectory of observed change.

A coupled hydro-thermo-mechanical model based on TLF-SPH for simulating crack propagation in fractured rock mass

In this paper, a hydro-thermo-mechanical coupling model based on the smoothed particle hydrodynamics with total Lagrangian formula (HTM-TLF-SPH) is proposed to simulate the crack propagation and instability process of fractured rock mass. TLF-SPH uses the Lagrangian kernel approximation, that is, the kernel function and its gradient need only be calculated once in the initial configuration, which is much more efficient than the smoothed particle hydrodynamics (SPH) based on the Euler kernel approximation. In TLF-SPH, particles interact with each other through virtual link, and the crack propagation path of rock mass is tracked dynamically by capturing the fracture of virtual link. Firstly, the accuracy and robustness of the HTM-TLF-SPH coupling model are verified by a reference example of drilling cold shock, and the simulation results agree well with the analytical solutions. Then, the crack propagation law of surrounding rock and the evolution characteristics of physical fields (displacement, seepage and temperature fields) after excavation and unloading of deep roadway under the coupling condition of hydro-thermo-mechanical are investigated. In addition, the seepage and heat transfer processes of the surrounding rock of Daqiang coal mine under different coupling conditions are successfully simulated. Meanwhile, the effect of the boundary water pressure difference on the temperature and seepage fields under the hydro-thermal coupling condition is quantitatively analyzed.

Fabrication of Self-Wrinkling Polymer Films with Tunable Patterns through an Interfacial-Fuming-Induced Surface Instability Process.

Inspired by the superglue fuming method for fingerprint collection, this study developed a novel interfacial-fuming-induced surface instability process to generate wrinkled patterns on polymeric substrates. High-electronegativity groups are introduced on the substrate surface to initiate the polymerization of monomer vapors, such as ethyl cyanoacrylate, which results in the formation of a stiff poly(ethyl cyanoacrylate) capping layer. Moreover, interfacial polymerization resulted in the covalent bonding of the substrate, which led to the volumetric shrinkage of the composite and the accumulation of compressive strain. This process ultimately resulted in the development and stabilization of wrinkled surface morphologies. The authors systematically examined parameters such as the modulus of the epoxy substrate, prestrain, the flow rate of fuming, and operating temperature. The aforementioned technique can be easily applied to architectures with complex outer morphologies and inner surfaces, thereby enabling the construction of surface patterns under ambient conditions without vacuum limitations or precise process control. This study is the first to combine fuming-induced interfacial polymerization with surface instability to create robust wrinkles. The proposed method enables the fabrication of intricate microwrinkled patterns and has considerable potential for use in various practical applications, including microfluidics, optical components, bioinspired adhesive devices, and interfacial engineering.

Numerical study on the characteristics of roadway failure and instability in coal seam with rock parting

In order to explore the mechanism of rockburst in coal seam with rock parting, a combination of on-site and numerical experiment is used to study the failure and instability process, crack propagation mechanism, and influencing factors. The following four points were addressed: (1) the instability is a process that roadway in coal seam with rock parting go through from stable locking in the initial stress unloading stage to slipping unlocking, and then to spatter ejection in slipping dynamic load disturbance stage. (2) The fracture development caused by unloading excavation of coal seam with rock parting will change from shear crack to tensile crack. In this process, coal-rock contact surface slip and coal-rock fracture are coupled with each other. (3) The greater the mining depth is, the greater the lateral pressure coefficient is, and the higher the rockburst risk is. On the contrary, the lower the risk of rockburst. (4) When choosing the support form of roadway in coal seam with rock parting, the two supporting forms of bolting (cable) and supplementary masonry support should be preferred. The results enrich the theory of the dynamics of surrounding rock fracture in coal mine, further clarify the potential dangers to mining-area roadways and working faces, and provide technical information to ensure the safe and efficient mining of bifurcated coal seam.

Impact of Western Ghats orography on the simulation of extreme precipitation over Kerala, India during 14–17 August 2018

The state of Kerala, located in southwest peninsular India, has experienced a series of extremely heavy rainfall events in the past few years, resulting in severe flooding and landslides. Among these events, an extremely heavy rainfall episode (50 to 480 mm/day) occurred during 14–17 August 2018 had led to devastating floods along the southwest coast of India. In this study, we have chosen this event as a case study to analyze the role of orography, using a high-resolution (1-km) cloud-resolving WRF model configuration. We conducted four numerical sensitivity experiments to examine the impact of different topographic configurations, ranging from no-mountain to plateau, moderate, and steep mountain terrains, on the simulation of the extreme rainfall event. The results of the mountain sensitivity experiments indicate that as mountain height increases, simulated low-level wind decelerates quickly. This flow blocking is also manifested in parameters such as reduced upper-air wind intensity, increased dynamical convergence, and increase of vertical velocities at the Western Ghat (WG) mountain barriers, which lead to the variations in moist instability and cloud microphysical processes influencing the horizontal and vertical distribution of solid-phase hydrometeors. Furthermore, the results also show that a reduction in the orography of the WGs decreases the vertical extension of low-level jet winds to upper levels, weakens the tropical easterly flow, and decreases the wind shears between the lower and upper troposphere. In addition, the results suggest that large-scale variations in mountain orography in numerical simulations can affect the simulated magnitude and direction of moisture transport, which may have played a role in determining the magnitude and distribution of simulated rainfall over Kerala.

Dynamics of acoustically-induced droplet instability

The advancement of the theory of droplet stability in the acoustic field is of significant value in improving ultrasonic atomization and ultrasonic levitation technology. In this work, in order to reveal the detailed mechanism of acoustic droplet instability and give the instability criterion for easy application, the dynamics of droplet instability in standing wave acoustic field (19.8 kHz) is studied by combining practical experiment, theoretical derivation and numerical calculation. The acoustic instability of the droplet occurring near the wave nodes is mainly manifested in two typical modes: disk instability and edge-sharpening instability. The appearance of these two instability modes depends on the relative magnitude of the standing wave field strength. Specifically, with the gradual enhancement of the intensity of the standing wave field, the instability mode of the droplet will gradually change from disc instability to edge-sharpened instability.The droplets show obvious self-accelerating expansion in the equatorial plane in the instability process. The positive feedback between the droplet aspect ratio and the negative pressure of acoustic radiation at the equator of the droplet is the reason for the above self-accelerating behavior. The theoretical results obtained through deduction indicate that the amplitude of the negative acoustic radiation pressure at the droplet equator is proportional to the square of the droplet aspect ratio. The surface tension of the droplet is the main factor hindering its deformation, while the acoustic radiation suction at the equator is the main factor driving the deformation of the droplet. Based on this, the force equilibrium equation of the droplet interface is established, and the dimensionless criterion of acoustic droplet instability, i.e. the acoustic Weber number <i>We</i><sub>a</sub>, is derived. When <i>We</i><sub>a</sub>≤1, the droplet interface stays in equilibrium, and when <i>We</i><sub>a</sub> >1, the equatorial acoustic suction is larger than the surface tension, and the droplet instability occurs, and the average error between the experimental results and the theoretical results is only 9%.

Study on the precursory characteristics and influencing factors of rockburst in the bifurcation area of coal seam.

To explore the precursory characteristics and influencing factors of rockburst in the bifurcation area of coal seam, the evolution and expansion of fracture and the energy accumulation and dissipation characteristics of coal-rock parting-coal structure (CRCS) during failure and instability process are explored from a micro-scopic perspective, and the influence of coal and rock parting parameters on the instability is studied. The following four points are addressed: (1) Compared with the single coal structure or the coal- rock combined structure, the CRCS can more directly reflect the geological structure characteristics of the coal seam in the bifurcated area; (2) The failure and instability process of CRCS includes two types of instability: slip and fracture. The slip instability is characterized by low strength and high energy release, which is very difficult to predict. (3) Before the failure of CRCS, there are several precursor signal characteristics, such as the shortened development time of the "stable-fracture-stable" cycle, abnormal slip dislocation of the contact surface, and rapid accumulation of rock fracture energy. (4) The inclination angle of the contact surface affects the instability form, the strength of the rock parting affects the instability state, and the thickness of the rock parting affects the impact tendency. The research results have important theoretical significance for preventing rockburst caused by failure and instability in bifurcated area of coal seam.

A Brain Ischemia-Reperfusion Model for the Study of Tau Phosphorylation and O-GlcNAcylation.

Cerebral ischemia produces a decrease, loss, or instability of the assembly processes in the neuronal cytoskeleton, related to the alteration in the normal processes of phosphorylation of the Tau protein, triggering its hyperphosphorylation and altering the normal processes of formation of neuronal microtubules. Here we describe the methods used to study the impact of middle cerebral artery occlusion (MCAo) on neurological functions and Tau phosphorylation in Wistar rat brain.