Development Of Instability Research Articles

Nonlinear saturation of the ion flow driven ion sound instability in a finite length plasma

The saturation mechanism and nonlinear evolution of the ion sound instability driven by the subsonic ion flow in a finite length plasma are studied by a one-dimensional hybrid model considering kinetic ions and Boltzmann electrons. Three regimes of the instability nonlinear behavior are identified as a function of the frequency of the ion-neutral charge exchange (CX) collision fcoll. In the first (collisionless-alike) regime when the CX frequency is low, the instability is saturated by ions trapping in wave potentials leading to the formation of phase space vortexes (PSVs). One of the PSVs subsequently expands and becomes system long in the steady state. The transition to the second (medium) regime occurs when fcoll≳vp/d, where vp is the PSV expansion velocity and d is the system length. In the second regime, CX collisions convert fraction of beam ions into slow ions that can be trapped in potentials of small scale ion sound eigenmodes fluctuations. The trapping of slow ions results in the formation of a chain of small scale PSVs and the disruption of the establishment of the single system long PSV. In the third (collision-dominated) regime when fcoll≳γ (γ is the instability growth rate), CX collisions transform all beam ions into slow ions and the instability is thereby eliminated.

Carcinogenic Mechanisms of Hexavalent Chromium: From DNA Breaks to Chromosome Instability and Neoplastic Transformation.

Hexavalent chromium [Cr(VI)] is a well-established human carcinogen, yet the mechanisms by which it leads to carcinogenic outcomes is still unclear. As a driving factor in its carcinogenic mechanism, Cr(VI) causes DNA double strand breaks and break-repair deficiency, leading to the development of chromosome instability. Therefore, the aim of this review is to discuss studies assessing Cr(VI)-induced DNA double strand breaks, chromosome damage and instability, and neoplastic transformation including cell culture, experimental animal, human pathology and epidemiology studies. Recent findings confirm Cr(VI) induces DNA double strand breaks, chromosome instability and neoplastic transformation in exposed cells, animals and humans, emphasizing these outcomes as key steps in the mechanism of Cr(VI) carcinogenesis. Moreover, recent findings suggest chromosome instability is a key phenotype in Cr(VI)-neoplastically transformed clones and is an inheritable and persistent phenotype in exposed cells, once more suggesting chromosome instability as central in the carcinogenic mechanism. Although limited, some studies have demonstrated DNA damage and epigenetic modulation are also key outcomes in biopsies from chromate workers that developed lung cancer. Additionally, we also summarized new studies showing Cr(VI) causes genotoxic and clastogenic effects in cells from wildlife, such as sea turtles, whales, and alligators. Overall, across the literature, it is clear that Cr(VI) causes neoplastic transformation and lung cancer. Many studies measured Cr(VI)-induced increases in DNA double strand breaks, the most lethal type of breaks clearly showing that Cr(VI) is genotoxic. Unrepaired or inaccurately repaired breaks lead to the development of chromosome instability, which is a common phenotype in Cr(VI) exposed cells, animals, and humans. Indeed, many studies show Cr(VI) induces both structural and numerical chromosome instability. Overall, the large body of literature strongly supports the conclusion that Cr(VI) causes DNA double strand breaks, inhibits DNA repair and chromosome instability, which are key to the development of Cr(VI)-induced cell transformation.

Transient Analysis of Flow Unsteadiness And Machine Instabilities In a Centrifugal Compressor at Surge and Second Quadrant Operation

Abstract Instabilities in turbomachinery operation originate from intrinsic flow unsteadiness, sudden variations of operating conditions, and interactions with the surrounding system, affecting both system stability and machine reliability. The flow unsteadiness, presenting a characteristic behaviour, requires a deep understanding of the underlying flow fundamentals, a careful analysis using advanced experimental methods and a clear distinction on how the system might lead to instabilities. The identified approach addresses deep surge and second quadrant characterization. The analysis presented here benefits from the responsiveness and flexibility of the experimental test rig, fine tuning of the system layout, the instrumentation installation, and the transient tests procedure. The main focus area is the time-frequency analysis of flow and pressure signals at transients, thus providing a proper reconstruction of flow mechanisms and instability evolution. Valuable techniques include: short-time fast Fourier transform, wavelet analysis, and Wigner-Ville distribution; coherence between flow and pressure, to trace waves propagation, is considered too. These, presented outlining their strengths and weaknesses, are evaluated considering real time field applicability with regards to computational resources too. The experimental campaigns and data processing are presented, with a test matrix covering a wide range of parameters, including system layout and surge volume size, rotational speeds, flow rates ranging from nominal point to full second quadrant operation. These data are vital for system modeling validation for a full compressor-system digital twin. Results indicate the importance of ensuring reliable data acquisition and analysis, with adequate instrumentation range, accuracy, synchronization, responsiveness and positioning.

Rock Slope Instability Mechanism Induced by Repeated Mining in Mountain Mining Areas

When mineral resources are extracted using underground mining methods in hilly regions, landslides or slope failures can be induced frequently. In this study, slope collapse disasters in mountain mining areas were analyzed. The model test and numerical simulation of the slope impacted by repeated mining were carried out. The crack evolution and failure process were analyzed to reveal the instability mechanism. The results show that the rock mass would topple to the inside of the slope first, when the subsidence of overlying rock was induced by the mining of the upper coal seam. When repeated mining was performed in the lower coal seam, the mining induced macro-cracks that could connect with natural fissures, inducing the outward displacement of the slope. Then, the rock mass at the foot of the slope has to bear the upper load, which is also squeezed out by the collapsed rock mass, forming the potential slip zone. Finally, the instability is caused by the shear slip of the slope toe rock mass. Therefore, the instability evolution of the slope under underground repeated mining disturbance can be divided into four stages as follows: roof caving and overlaying rock subsidence, joint rock toppling, fracture penetration, and slope toe shearing and slope slipping.

Crack evolution and fractal characteristics of fractured red sandstone based on acoustic emission parameters

Rock is a widely used engineering material, and accurate understanding of its internal microcrack evolution process during loading can provide a theoretical basis for preventing instability and failure in rock engineering. The rock pressure test system and acoustic emission equipment were used to carry out uniaxial loading and acoustic emission monitoring tests on fractured red sandstone. Based on the RA and AF values of acoustic emission and the fractal theory, the internal crack patterns and evolution rules of red sandstone with different crack angles were explored. The results show that the compressive strength of red sandstone varies with the crack Angle in the shape of “U”, and there is an obvious stress drop after the elastic stage of 30° and 45° crack red sandstone, which has a good correspondence with the acoustic emission ringing count rate. During the loading process, the damage mainly caused by tension cracks first appears inside the rock, and then the tension cracks increase steadily and the shear cracks gradually increase, indicating that the rock enters the stage of fracture instability development. With the development of shear cracks, the peak strength is finally reached and the instability failure occurs. During the loading process of 30° fracture red sandstone, the corresponding stress drop phenomenon of “shear crack group” appears. According to the D/S statistical analysis of different crack samples based on acoustic emission ringing count, the fractal dimension presents a decreasing-rising-decreasing trend with the increase of crack inclination, which corresponds to the change of the complexity of crack development in rock.

Evolution and detection of vector superradiant instabilities

Evolution and detection of vector superradiant instabilities

Signatures of substorm onset in thermodynamic model of geomagnetic tail

Earlier, an entropy switch model (ESM) for substorm onset as a result of the development of localized inner magnetospheric interchange-ballooning instability, was suggested. Shown observations testify that the substorm onset is accompanied by the reversal and strong fluctuations in key magnetospheric parameters such as total magnetic field strength, plasma pressure, entropy, and some others. Independently, similar behavior was attributed to a thermodynamic theory, where the onset of a substorm is regarded as a consequence of global energy development in the geomagnetic tail. In the latter, the geomagnetic tail is taken as an open thermodynamic system with an infinite number of conserved energy links (CEL) to the external space environment, and the shaping of the substorm profile is ultimately controlled by the system properties of the tail. A comparison between the signatures of substorm onset in the ESM and CEL models is conducted, and correspondence between experimental data and theoretical results is discussed.

Computational Study of Shocked V-Shaped N2/SF6 Interface across Varying Mach Numbers

The Mach number effect on the Richtmyer–Meshkov instability (RMI) evolution of the shocked V-shaped N2/SF6 interface is numerically studied in this research. Four distinct Mach numbers are taken into consideration for this purpose: Ms=1.12,1.22,1.42, and 1.62. A two-dimensional space of compressible two-component Euler equations is simulated using a high-order modal discontinuous Galerkin approach to computational simulations. The numerical results show good consistency when compared to the available experimental data. The computational results show that the RMI evolution in the shocked V-shaped N2/SF6 interface is critically dependent on the Mach number. The flow field, interface deformation, intricate wave patterns, inward jet development, and vorticity generation are all strongly impacted by the shock Mach number. As the Mach number increases, the V-shaped interface deforms differently, and the distance between the Mach stem and the triple points varies depending on the Mach number. Compared to lower Mach numbers, higher ones produce larger rolled-up vortex chains. A thorough analysis of the Mach number effect identifies the factors that propel the creation of vorticity during the interaction phase. Moreover, kinetic energy and enstrophy both dramatically rise with increasing Mach number. Lastly, a detailed analysis is carried out to determine how the Mach number affects the temporal variations in the V-shaped interface’s features.

Collisional Mechanism of Expanding Wavenumbers Range of Weibel-Type Instability in Magnetoactive Plasma

For plasma with anisotropic velocity distribution of particles in the form of two counter-propagating bi-Maxwellian beams, including bi-Maxwellian plasma, in the presence of external magnetic field parallel to the beams, it is shown that in a wide range of parameters, particle collisions lead to the expansion of the wavenumbers range, generally towards the long-wavelength region, and weaken the conditions for the occurrence of the Weibel-type instability. In the specified expanded range, its growth rate, found by means of solving the dispersion equation for the wave vectors orthogonal to the external magnetic field, turns out to be less than or on the order of the frequency of particle collisions. Thus, in this range of parameters, the instability development and formation of large-scale magnetic turbulence in a plasma with weak particle collisions require the long-term injection of particles with anisotropic velocity distribution.

Model of astrophysical jets in magnetic fields of laser relativistic plasmas

A brief review of the results of experimental modeling of cosmic jets in superstrong magnetic fields of laser relativistic plasma is given. It is noted that the development of cyclotron instability with the generation of cyclotron radiation plays a key role in a number of processes in a plasma with a magnetic field — self-localization of plasma in the form of solitons, conversion of rotational motion of plasma into translational motion, cyclotron acceleration of charged particles, separation (stratification) of a plasma jet into separate plasma formations.

Deformation Heat in Tension of Steel Elements

The purpose of the work is an approximate computational and experimental assessment of the specific energy intensity and heat generation at various stages of the material’s operation when the sample is stretched. The paper discusses an approximate method for estimating the specific energy intensity and heat generation at four stages of tensile deformation of a steel sample. Finite element modeling of the work of the manufactured sample under elastic-plastic tension was performed in the ANSYS multifunctional software package. The load in the digital model of the sample was applied according to the full-scale test program. The experiment used flat samples in accordance with GOST 1497, a WAW-1000 testing machine with a 100T microcomputer, and a testo 875i thermal imager with a temperature sensitivity of 0.05 °C at 30 °C. We compared the obtained values on graphs of full-scale tests and a digital model of the samples, identifying critical points and deviation values. Phased loading revealed that the development of destruction occurs on the descending branches and is accompanied by the gradual development of local instability of plastic deformation in the form of a “neck”. It is shown that the heating temperature of the tensile metal can be calculated using the formulas proposed in the paper or by calculation using the ANSYS software package. The test results showed that the surface temperatures of the samples at each stage differ significantly. Four main areas were identified on the graph of changes in the sample surface temperature at a point. An analysis of the existing database of measuring instruments and the ability to obtain and process data was carried out. Experimental values of surface temperatures during continuous quasi-static deformation exceed their calculated values (up to 5 times). The kinetics of changes in the temperature field of the sample surface was carried out using thermographic instruments.

Breakdown of laminar regime in flat plate boundary layer seen in numerical solutions of the Navier–Stokes equations obtained with 16th-order scheme

Numerical solutions of the Navier–Stokes equations describing the onset and the development of the boundary layer instability of a subsonic flow about a finite width flat plate are described. They were obtained via exciters-free calculations with the 16th-order multioperators-based scheme optimized to resolve very small solutions scales. Some relevant details of the scheme are briefly outlined. The occurrence of the Tollmien–Schlichting waves near the leading edge, their downstream propagation and breakdowns some distance away are displayed. The role of the oblique waves seen in the solutions is emphasized. The nonlinear stage in the form of structured vortices followed by the solutions randomization are described.

Bifurcation of rotating surface switching at different spin-up accelerations

It has been found, for the first time, that rotating polygons (m = 1, 2) can exist in a system of two immiscible fluids, which can be in three different steady states: stable funnel, cycling switching, and rotating twin funnel. These states are achieved due to different disk acceleration values at fixed aspect ratio (h/R) = 1 and Reynolds numbers. The acceleration time of rotating disk is found to have a significant effect on instability development.

On the evolution of magnetohydrodynamic flow instability in shock-accelerated light bubble

The study investigates the evolution of flow instabilities in a magnetohydrodynamic (MHD) environment involving a shock-accelerated light cylindrical bubble. Numerical simulations were conducted using a cylindrical helium (He) bubble accelerated by a shock wave in nitrogen (N2) gas at various magnetic field strengths. The results highlight the impact of magnetic fields on flow morphology, vorticity generation, and enstrophy. The interaction between incident shock waves and the gas bubble revealed significant differences in flow patterns and interface features when magnetic fields were applied. Key findings include the quantification of shock trajectories and detailed visualizations of the evolving flow structure. The study provides insights into the dynamics of shock–bubble interactions under MHD conditions, contributing to the broader understanding of flow instability mechanisms in such complex environments.

Assessing the ionospheric scintillations occurrence on L-band in the southern Mediterranean sector

We assess the ionospheric scintillation occurrence on Global Navigation Satellite Signals (GNSSs) over the Mediterranean sector under the rising phase of the current solar cycle. To the scope, we leverage on a network of three Ionospheric Scintillation Monitoring Receivers (ISMRs), being part of the electronic Space Weather upper atmosphere (eSWua: eswua.ingv.it) system (Pica et al., 2021). Such ISMRs are located in Lampedusa Island (Italy, Lat: 35.52°N–Lon: 12.63°E), Chania (Crete, Greece, Lat: 35.52°N, Lon: 24.04°E) and Nicosia (Cyprus, Lat: 35.18°N–Lon: 33.38°E). To our knowledge, this is the first thorough assessment of the scintillation patterns in the Southern Mediterranean sector, aimed at depicting how small-scale irregularities that form in the area can potentially affect the GNSS-based positioning and related application and services. We analyse the period from January 2021 to December 2023, reporting that the bulk of the scintillation occurrence is due to small-scale irregularities forming in the southernmost area of the field of view of the network. Irregularities of such a scale are formed during the evolution of the Rayleigh-Taylor instability featuring the Equatorial Plasma Bubbles (EPB), which may spill-over in the field of view (FoV) of the receivers, i.e. at low elevation angles in the southernmost azimuthal range. As observations at low elevation angles are subject to multipath mimic weak to moderate scintillation conditions, we focus exclusively on severe amplitude scintillation occurrence (S4 > 0.7) in the azimuthal range 110–250°, w.r.t the FoV of the receivers, subsequently reaching down to the Saharian ionosphere. To further confirm the nature of the detected GNSS scintillation occurrence, we compare the results with the Swarm Level-2 Ionospheric Bubble Index (IBI) evaluated within the same period. In the context of the April 2023 geomagnetic storm, a worst-case scenario is also documented, illustrating the potential impact of ionospheric disturbances associated with EPBs in the Southern Mediterranean area.

Optimization of pyroelectric figure of merit of PNN-PZ-PT composition at morphotropic phase boundary

Ternary compounds are proven to be a more fascinating, owing to their potential to span a broader composition region of morphotropic phase boundary (MPB) – enhanced piezoelectric, electrostrictive, dielectric and ferroelectric properties. To activate defects dipoles, we perform MnO2 doping in ternary MPB compound 0.55Pb(Ni1/3Nb2/3)O3-0.135PbZrO3-0.315PbTiO3 [PNN-PZ-PT]. Temperature dependent dielectric spectroscopy reveals relaxor-ferroelectric nature of the synthesized ceramics. With the poling treatment, P-E loop of xMn-PNN-PZ-PT is softened, which emphasizes that the poling introduces higher order structural instability in MPB structure. The evolution of structural instability is as evidenced by the emergence of additional anomaly in thermal profile of dielectric constant due to electrical poling of xMn-PNN-PZ-PT and no systematic difference between polarizing behaviour of poled and unpoled specimen (Arrott plots). In association with defects dipoles, pyroelectric response based figure of merits (FOMs) of PNN-PZ-PT are improved. FOMs are characteristics of pyroelectric materials that insights about their suitability for specific application. Fi is suppressed with MnO2 doping and Fv, Fe and increases with MnO2 doping. Our study reveals that tailored and precise acceptor doping is crucial for the simultaneous optimization of all pyroelectric FOMs.

Structural modulation in colored polymer bands of methacrylic acid-based frontal polymerization

The periodic colored polymer bands have been investigated in frontal polymerization (FP) reaction containing methacrylic acid (MAA), hydroquinone, Benzoyl peroxide (BP), and N, N Dimethyl aniline (DMA) system. The MAA acts as a monomer, which was diluted adequately with methanol (MeOH), ethanol (EtOH), and butanol (BuOH) separately to observe the patterning characteristics in different reaction schemes. The structural modulations that include the periodicity of colored polymer bands, morphological changes, and spacings between two adjacent layers were studied. The colored variations of polymer bands and their dependency on the concentration of BP, hydroquinone and alcoholic compositions have been studied. The highly consistent pink-white colored polymer bands, loosely-packed band structures, and perfectly ordered band structures resulted in MeOH, EtOH, and BuOH systems, respectively, as discussed. The evolution of tiny bubbles and convection-type instability has been observed in different conditions of the FP reactions that significantly affect the planar movement of the polymer fronts. The hot spots, which usually represent the high-temperature regions of a typical frontal surface, have also been demonstrated in all reacting systems, which may cause spin mode propagation of the fronts and change the surface geometry, as described. The materials characterization was carried out using UV-visible spectrophotometer, NMR, FTIR, and FESEM techniques, providing information about the polymer phases involved in band structures, composition, and surface properties. The analytical data and results obtained during the study further emphasized that two different coloured polymers, namely 1, 4-dihydroxy anthraquinone methacrylic acid and poly-methacrylic acid dihydroxy, anthraquinone produced simultaneously and crystallized periodically, results in the development of a coloured polymer band structures. The possible reactions and associated chemical mechanisms concerning the observations, the nature of the monomer, and solvent characteristics have been proposed, which show a close agreement with the analytical data and results obtained during the study

Marangoni-driven pattern formation in an absorbing binary mixture

We investigate the evolution of convective instability in a LiBr–water binary mixture, driven by thermal and solutal Marangoni stresses, through numerical simulations. A small perturbation in absorption at the surface disturbs the equilibrium, generating surface tension gradients that drive Marangoni flows. To isolate and better understand the interplay between the Marangoni effect and absorption, we extended the previous study by investigating the LiBr–water binary system in the absence of gravity. For the first time, we observed the formation of a stable rim in an absorbing binary mixture, which underwent a slight contraction followed by rapid Marangoni spreading. This behavior shows similarities with the flow patterns seen in the “coffee-ring” and Marangoni spreading phenomena in evaporating binary mixtures. On the subsurface, convective motion breaks into several vortices, accompanied by the formation of plumes with reduced mass fraction. As the system evolves, the symmetry of the flow pattern around the cell center breaks down. The absence of buoyancy-driven forces eliminates a key counterforce to Marangoni flows, transforming the previously ordered patterns into non-periodic oscillations, followed by the development of non-stationary but regular patterns. These results complement our earlier findings [P. F. Arroiabe et al., Phys. Fluids 36, 022119 (2024)] where gravitational forces obscured these phenomena.

Flow stability and permeability in a nonrandom porous medium analog

The estimation of the permeability of porous media to fluids is of fundamental importance in fields as diverse as oil and gas industry, agriculture, hydrology, and medicine. Despite more than 150 years since the publication of Darcy's linear law for flow in porous media, several questions remain regarding the range of validity of this law, the constancy of the permeability coefficient, and how to define the transition from Darcy flow to other flow regimes. This study is a numerical investigation of the permeability and flow stability in a nonrandom quasi-tridimensional porous medium analog. The effect of increasing pressure gradient on the velocity field and on the estimation of Darcy and Darcy–Forchheimer coefficients is investigated for three different obstacles radius. The transition from Darcy flow to nonlinear behavior is associated with the formation of jets in the outlet of the porous medium and development of flow instabilities. Different representations of the Reynolds number proved adequate to detect deviation from the linear law. The instantaneous permeability calculated at each pressure gradient was sensitive to flow velocity, in agreement with previous studies stating that permeability cannot be conceptualized as a constant for real flows.

Effect of gas viscosity on the interfacial instability development in a two-phase mixing layer

The interfacial instability in a two-phase mixing layers between parallel gas and liquid streams is important to two-phase atomization. Depending on the inflow conditions and fluid properties, interfacial instability can be convective or absolute. The goal of the present study is to investigate the impact of gas viscosity on the interfacial instability. Both interface-resolved simulations and linear stability analysis (LSA) have been conducted. In LSA, the Orr–Sommerfeld equation is solved to analyze the spatio-temporal viscous modes. When the gas viscosity decreases, the Reynold number (Re) increases accordingly. The LSA demonstrates that when Re is higher than a critical threshold, the instability transitions from the absolute to the convective (A/C) regimes. Such a Re-induced A/C transition is also observed in the numerical simulations, though the critical Re observed in simulations is significantly lower than that predicted by LSA. The LSA results indicate that the temporal growth rate decreases with Re. When the growth rate reaches zero, the A/C transition will occur. The Re-induced A/C transition is observed in both confined and unconfined mixing layers and also in cases with low and high gas-to-liquid density ratios. In the transition from typical absolute and convective regimes, a weak absolute regime is identified in the simulations, for which the spectrograms show both the absolute and convective modes. The dominant frequency in the weak absolute regime can be influenced by the perturbation introduced at the inlet. The simulation results also show that the wave propagation speed can vary in space. In the absolute instability regime, the wave propagation speed agrees well with the absolute mode celerity near the inlet and increases to the Dimotakis speed further downstream.