Stable Regime Research Articles

Air bubbles crossing a stratified water-diesel fuel interface

This study examines the behavior of a single air bubble moving through a stratified interface between two liquid phases: purified water as the denser liquid and diesel fuel as the lighter counterpart. The study investigates the impact of the upper liquid's height on bubble behavior, particularly under low gas flow rates, using high-speed video imaging. The experimental findings unveil two distinct scenarios: stable and unstable regimes. In stable conditions, the bubble follows a linear trajectory, simultaneously transferring some of the denser liquid into the lighter phase. Conversely, under unstable conditions, the bubble undergoes oscillations, navigating a zigzag or spiral path. The study also explores the correlation between the upper liquid height and the deformation and division of the dragged volume. This comprehensive investigation sheds light on the intricate interplay between liquid heights and bubble dynamics at liquid-liquid interfaces.

Observation of a new pedestal stability regime in MAST Upgrade H-mode plasmas

The first pedestal stability and structure analysis on the new MAST Upgrade (MAST-U) spherical tokamak H-mode plasmas is presented. Our results indicate that MAST-U pedestals are close to the low toroidal mode number (n) peeling branch of the peeling-ballooning instability, in contrast with MAST H-mode pedestals which were deeply in the high-n ballooning branch. This offers the possibility of reaching the ELM-free quiescent H-mode (Burrell et al 2005 Plasma Phys. Control. Fusion 47 B37–B52) or high-performance super H-mode (Snyder et al 2015 Nucl. Fusion 55 083026; Snyder et al 2019 Nucl. Fusion 59 086017) regimes. In addition, the coupling between the peeling and ballooning branches is weak in MAST-U, suggesting that a path to very high pedestal pressure gradient at high density may exist with sufficient heating power. A possible explanation for the differences between MAST and MAST-U pedestal stability is given in terms of plasma shaping parameters, in particular squareness and elongation, as well as the pedestal top temperature and collisionality.

Influence of binder content on gas-water two-phase flow and displacement phase diagram in the gas diffusion layer of PEMFC: A pore network view

Understanding the gas-water flow dynamics in the gas diffusion layer (GDL) is one of the keys to improving the proton exchange membrane fuel cell's (PEMFC) overall performance and avoiding water flooding. Yet, the relationship between the two-phase flow and micro-scale GDL structures (including binder, PTFE, and fiber skeleton) is not well understood. In this study, three-dimensional GDL structures with different fractions of binder contents (φb=0%∼50%) and a fixed porosity of 75.6 % are confidently reconstructed based on high-resolution images from the confocal microscope, implying that the addition of binder will increase the number of large pores and cause a bimodal throat size distribution through morphology analysis. Thereafter, drainage simulations are performed under a wide range of capillary number (−9 < log Ca <0) and viscosity ratio (−3 < log M < 2) by the pore network model (PNM), which robustly predicts the displacement phase diagram of viscous fingering, capillary fingering, stable displacement, and transitional regime. In the viscous fingering and stable displacement regime, the nonwetting phase saturation (Snw) is nearly the same for different φb, implying the fluid invading pathway does not change much with the addition of binder. However, in the capillary fingering regime (refer to the actual operating conditions), Snw increases rapidly with φbat the breakthrough time and its transient value continues to increase until the steady state, which may be attributed to the increased fractions of pores above the capillary threshold attributed by the bimodal throat size distribution. In addition, the effective water permeability increases sharply with φb, whereas the gas permeability remains almost constant, which means such pore structure alteration by adding the binder is beneficial to water disposal in PEMFC. This research provides insights into delineating the effect of pore and throat size distribution alteration by adding binder on two-phase dynamics in GDL.

Pentingnya Pemisahan Kekuasaan Dalam Mempertahankan Pemerintahan Yang Seimbang

The division of power into three branches put forward by two experts called trias politica which is generally divided into legislative, executive, and judicial powers, the fourth branch put forward by Hans Kelsen in the statement of ensuring regime stability requires a fourth branch referred to as the Constitutional Court which is believed to be the guardian of the stability of the other three branches by maintaining the constitution in the party government and with this function can determine many other characteristics. By using a normative method that aims to understand and interpret the rules of law contained in the constitution of state administration in Indonesia, ensuring the suitability of each rule of law with the norms that apply in the context of writing articles on constitutional law. The data used in this paper is secondary data. This existence of a balanced government in the state administration ensures that there is a fair contribution of power in each power-sharing system with the aim of monitoring and balancing each other to prevent abuse of power and ensure the fulfillment of citizens’ rights.

Ho:YLF regenerative amplifier delivering 22 mJ, 2.0 ps pulses at a 1 kHz repetition rate

We report on a high-energy, few-ps, continuous-wave pumped Ho:YLF regenerative amplifier (RA) operating in a chirped-pulse amplification arrangement. A three-stage optical parametric amplifier serves as versatile seed source emitting broadband pulses centered at 2050 nm. It provides seed pulses with 4 µJ energy within the Ho:YLF amplification bandwidth centered at 2051 nm. Thanks to the high seed pulse energy, bifurcation instabilities are mitigated and gain narrowing is reduced for such a high-gain Ho-doped RA operating at few kHz repetition rate. At 1 kHz the Ho:YLF RA emits 22.5 mJ energy pulses with a compressed pulse duration of 2.0 ps in the stable single-pulse regime. The water cooled RA features a high extraction efficiency of 31% and exhibits a remarkable stability of 0.11% rms. Doubling the repetition rate to 2 kHz, RA pulse energy reaches 15 mJ. The demonstrated 10 GW peak power at 1 kHz and the 30 W average power at 2 kHz are the highest values reported to date for few-ps RAs operating at 2 µm wavelength.

Constraint effects on fracture toughness of ductile cast iron in the ductile regime

To assess the effect of constraint loss on fracture toughness of ductile cast iron (DCI), GJS-400–15, in the ductile regime at 0 °C, the fracture toughness was characterised with two different types of fracture toughness specimens, compact tension (C(T)) and single edge tension (SE(T)) specimens. The constraint state in the specimens was quantified using finite element analysis. Overall, the constraint dependence of fracture toughness for DCI is comparable to typical ferritic structural steels. For the obtained J-R curves, the fracture toughness increases as the crack grows, and the crack growth is stable on macroscopic scale up to J = 290 kJ/m2. Independent of the constraint state in the stable crack growth regime, the global failure mechanism is ductile fracture, including occasional local brittle areas.

Physics-guided fuel-switching neural networks for stable combustion of low calorific industrial gas

Dual fuel combustion of low calorific industrial gas has been widely used in various types of burners for industrial production needs. Fuel switching rule is purely empirical lacking theoretic basis, potentially leading to flame extinction or excessive waste of ignition fuel. This study focuses on exploring physics-guided fuel-switching strategy for stable combustion of coke oven gas (COG) and blast furnace gas (BFG) in representative swirl burner. Stable operating regimes for COG and BFG are firstly identified with chemical eigen-analysis. The intrinsic propensity of flame extinction during fuel switching is revealed by positive chemical eigenvalues, and the key species and elementary reactions are identified. A clustered neural network with flag controller (CNNF) is then constructed to achieve stable combustion during fuel switching from COG to BFG as early as possible to reduce the use of COG. Results show that COG must be used to ignite and increase the ambient temperature to at least 673 K to avoid flame extinction. The chemical eigen-guided CNNF controller can adjust the switch speed to advance the fuel switching time by 14 % and can be further expanded to other fuel switching applications.

Rotating Stall Inception Prediction Using an Eigenvalue-Based Global Instability Analysis Method

The accurate prediction of rotating stall inception is critical for determining the stable operating regime of a compressor. Among the two widely accepted pathways to stall, namely, modal and spike, the former is plausibly believed to originate from a global linear instability, and experiments have partially confirmed it. As for the latter, recent computational and experimental findings have shown it to exhibit itself as a rapidly amplified flow perturbation. However, rigorous analysis has yet to be performed to prove that this is due to global linear instability. In this work, an eigenanalysis approach is used to investigate the rotating stall inception of a transonic annular cascade. Steady analyses were performed to compute the performance characteristics at a given rotational speed. A numerical stall boundary was first estimated based on the residual convergence behavior of the steady solver. Eigenanalyses were then performed for flow solutions at a few near-stall points to determine their global linear stability. Once the relevant unstable modes were identified according to the signs of real parts of eigenvalues, they were examined in detail to understand the flow destabilizing mechanism. Furthermore, time-accurate unsteady simulations were performed to verify the obtained eigenvalues and eigenvectors. The eigenanalysis results reveal that at the rotating stall inception condition, multiple unstable modes appear almost simultaneously with a leading mode that grows most rapidly. In addition, it was found that the unstable modes are continuous in their nodal diameters, and are members of a particular family of modes typical of a dynamic system with cyclic symmetries. This is the first time such an interesting structure of the unstable modes is found numerically, which to some extent explains the rich and complex results constantly observed from experiments but have never been consistently explained. The verified eigenanalysis method can be used to predict the onset of a rotating stall with a CPU time cost orders of magnitude lower than time-accurate simulations, thus making compressor stall onset prediction based on the global linear instability approach feasible in engineering practice.

Effects of a coup attempt on public attitudes under autocracy: quasi-experimental evidence from Russia

ABSTRACT Elite schisms are known to destabilize autocracies, but there is little scholarship that examines how such splits affect regime support or perceptions of regime stability. We utilize a unique survey that was in the field during a June 2023 coup attempt in Russia to examine this question. By comparing the responses of respondents interviewed before the coup with those interviewed after the coup, we estimate the effect of the coup on a number of attitudes. We find that the coup had no effect on regime support and only a limited (negative) effect on perceptions of regime stability. By contrast, we find that the coup caused a precipitous drop in support for the coup’s leader and that this effect is larger among those who watch state television. The findings suggest that the regime used its control of the information space to swiftly demonize the coup leader and avoid public fallout.

Extracting Atmospheric Stability Information from Dual-Doppler Radar Scans in the AWAKEN Campaign

Dual-Doppler (DD) derived wind direction (β) fields are used in a novel approach to assess atmospheric stability by way of power spectral density (PSD) and bulk statistical analyses. Data on atmospheric stability, thermodynamic profiles, and wind behavior, as acquired during the AWAKEN campaign, are examined for a measurement time period featuring two stability transitions to analyze differences in flow structure as a function of stability regime. Analysis of the β fields yielded promising results when compared to stability regime and can be applied to other cases.

Stability Maintenance and the ‘Three Evils’: Framing China’s Role in Central Asia

ABSTRACT This article analyzes 430 security-related press releases from meetings between officials from China and the Central Asian republics between 1991 to January 2023 to examine how its threat perceptions have evolved. First, China’s focus on the Three Evil Forces (terrorism, extremism, separatism) has won its support and cooperation from regimes across the region. Second, China has advanced a number of new security concepts over the years, most recently the Global Security Initiative. Each of these concepts, as well as frameworks such as the Shanghai Cooperation Organization (SCO) and China + Central Asia, advance China’s vision of a multipolar world order in which universal values are replaced with adherence to state sovereignty and cultural relativism. This article argues that China’s securitized approach to regional foreign policy-making has helped coordinate local responses to disparate challenges while granting them political buy-in and support to mobilize state resources to promote regime stability.

Wind farm power curve characterization under different atmospheric stability regimes

Wind farm power curves are particularly relevant in different applications. A better understanding of wind farm power curves under different atmospheric regimes is sought. In the present work, the atmospheric stability regime was identified by the vertical gradient of the potential temperature. Vertical profile of the wind velocity presented a clearly different pattern during the stable and unstable regimes. Analysis was performed considering 5 years of data from three wind farms, each corresponding to different mesoscale wind. Power curves are presented as a function of atmospheric stability. For each wind farm, we utilized wind velocity and temperature data measurements of a correspondent near the tower location. Clearly different patterns of wind farm power curves were observed as a function of the stability regime, with clear differences in the dependence of mesoscale wind regimes. For the same mean velocity, wind power production is greater for higher values of turbulence intensity TI.

Foreign Aid Allocation and Regime Stability: A Cross-National Study in Indonesia

Purpose: The aim of the study was to analyze the foreign aid allocation and regime stability: a cross-national study in Indonesia. Methodology: This study adopted a desk methodology. A desk study research design is commonly known as secondary data collection. This is basically collecting data from existing resources preferably because of its low cost advantage as compared to a field research. Our current study looked into already published studies and reports as the data was easily accessed through online journals and libraries. Findings: The study in Indonesia revealed that foreign aid allocation plays a crucial role in regime stability. Increased foreign aid, especially directed towards economic development and infrastructure, positively impacted regime stability. Conversely, political conditionality attached to aid often led to destabilization, fostering domestic opposition and unrest. Unique Contribution to Theory, Practice and Policy: Dependency theory, principal-agent theory &amp; institutional theory may be used to anchor future studies on foreign aid allocation and regime stability: a cross-national study in Indonesia. By pooling resources, sharing expertise, and aligning objectives, stakeholders can leverage synergies and address governance challenges more effectively. Donor countries should adopt more coherent and principled aid allocation policies that prioritize the promotion of democratic governance, human rights protections, and inclusive development.

From Myths, Ci and Fu Works to Temple Worship: A New Inquiry into the Evolution of Fu Fei 宓妃, the Goddess of the Luo River

Luo Shen 洛神 (The Goddess of the Luo River), also known as Fu Fei 宓妃 (Consort Fu), governed the Luo River and was a deity with distinctive representativeness and influence in the Luoyang area of China. To date, research has been centered around literary works and paintings, particularly Luoshen Fu 洛神賦, with little exploration into the belief of the Goddess of the Luo River. In this paper, specific and detailed textual research is made on the origins and historical transformations, as well as functional shifts, of the Goddess of the Luo River from the perspective of belief in the deity. Based on extant ancient documents and stele inscriptions and combined with anthropological field research, five new ideas are described. First, rituals honoring the Luo River were present in ancient times, yet the deity of the Luo River was initially a male entity called Luo Bo 洛伯, not the goddess Consort Fu. Second, Consort Fu first appears in Li Sao 離騷 as a goddess from the Kunlun Mountains. Third, during the Eastern Han dynasty (25–220), driven by the political and cultural needs of rulers to maintain regime stability, the Goddess of Kunlun, Consort Fu, became the Goddess of the Luo River. Fourth, in the medieval period, the image of the Goddess of the Luo River underwent a historic transformation, evolving from a deity governing the Luo River to a beauty yearning for secular love, merging with the historical figure of Zhen Fei 甄妃 (Consort Zhen) from the Cao Wei dynasty (220–266), forming a unified literary and artistic figure that significantly broadened the social influence of the Goddess of the Luo River. Fifth, the state-sponsored worship of the Goddess of the Luo River reached its peak during the Tang (618–907) and Song (960–1279) dynasties, and afterward, it gradually declined to a local folk belief due to a shift in the political center. The transition of the belief in the Goddess of the Luo River from official to folk realms, deeply intertwining with people’s lives, is a historical reflection of the eastward shift in the imperial center after the Tang dynasty. It also signifies a transformation of the function of the belief in the Goddess of the Luo River, from a political guardian deity ensuring the nation’s peace and the government’s stability to a protective deity for ordinary people’s family stability and prosperity of descendants.

Disinformation and Regime Survival.

Disinformation has transformed into a global issue and while it is seen as a growing concern to democracy today, autocrats have long used it as a part of their propaganda repertoire. Yet, no study has tested the effect of disinformation on regime stability and breakdown beyond country-specific studies. Drawing on novel measures from the Digital Society Project (DSP) estimating the levels of disinformation disseminated by governments across 148 countries between 2000-2022 and from the Episodes of Regime Transformation (ERT) dataset, we provide the first global comparative study of disinformation and survival of democratic and authoritarian regimes, respectively. The results show that in authoritarian regimes, disinformation helps rulers to stay in power as regimes with higher levels of disinformation are less likely to experience democratization episodes. In democracies, on the other hand, disinformation increases the probability of autocratization onsets. As such, this study is the first to provide comparative evidence on the negative effects of disinformation on democracy as well as on the prospects of democratization.

Flux‐gradient relations and their dependence on turbulence anisotropy

AbstractMonin–Obukhov similarity theory (MOST) is used in virtually all Earth System Models to parametrize the near‐surface turbulent exchanges and mean variable profiles. Despite its widespread use, there is high uncertainty in the literature about the appropriate parametrizations to use. In addition, MOST has limitations in very stable and unstable regimes, over heterogeneous terrain and complex orography, and has been found to represent the surface fluxes incorrectly. A new approach including turbulence anisotropy as a non‐dimensional scaling parameter has recently been developed and has been shown to overcome these limitations and generalize the flux‐variance relations to complex terrain. In this article, we analyze the flux‐gradient relations for five well‐known datasets, ranging from flat and homogeneous to slightly complex terrain. The scaling relations show substantial scatter and highlight the uncertainty in the choice of parametrization even over canonical conditions. We show that, by including information on turbulence anisotropy as an additional scaling parameter, the original scatter becomes well bounded and new formulations can be developed that drastically improve the accuracy of the flux‐gradient relations for wind shear () in unstable conditions and for temperature gradient () in both unstable and stable regimes. This analysis shows that both and are strongly dependent on turbulence anisotropy and allows us finally to settle the extensively discussed free convection regime for , which clearly exhibits a power law when anisotropy is accounted for. Furthermore, we show that the eddy diffusivities for momentum and heat and the turbulent Prandtl number are strongly dependent on anisotropy and that the latter goes to zero in the free convection limit. These results highlight the necessity to include anisotropy in the study of near‐surface atmospheric turbulence and lead the way for theoretically more robust simulations of the boundary layer over complex terrain.

‘Diffuse Support’ and Authoritarian Regime Resilience: Azerbaijanism vis-à-vis Azerbaijan’s Talysh Minority

Abstract This article asks what role does the official national identity discourse play in building authoritarian resilience in Azerbaijan, and how do alternative narratives of particular historical events impact such resilience-building efforts? The discourse of Azerbaijanism is a source of diffuse support legitimizing the authoritarian regime in Azerbaijan. This is largely due to the role played by the ruling family in Azerbaijanism and the emphasis that is placed upon that family’s ability to resolve internal and external threats to the developing nation-state. Alternative narrations of historical memories – such as those regarding the establishment of the Talysh-Mughan (Autonomous) Republic during the summer of 1993 – act as ‘hidden transcripts’ that shed light upon the cracks in the regime’s façade, challenging its claims to historical and other ‘truths’. In so doing, ‘hidden’ alternative transcripts challenge the legitimacy of the governing regime, testing the first of Gerschewski’s (2013) three pillars of authoritarian regime stability (i.e., legitimation, repression, and co-optation).

A switch in thermal and haline contributions to stratification in the Greenland Sea during the last four decades

Stratification and its thermal and haline contributions are important ocean properties of fundamental climatic influence. Upper-ocean stratification shapes marine ecosystems by regulating nutrient availability and deep-ocean stratification is important for carbon sequestration and ventilating the ocean interior. Here, we first assess the applicability of an ocean reanalysis product in representing stratification in the Nordic Seas and East Greenland Shelf. While the reanalysis performs well in most interior basins, it exhibits significant shortcomings on the East Greenland shelf, raising concerns about the reanalysis product in these areas. We then examine the development in the thermal and haline contributions to summer upper- (100 m) and winter intermediate- (1000 m) ocean stratification in the Greenland Sea from 1980 to 2020. We find that there has been a transition in the controls of winter stratification in the upper 1000 m of the Greenland Sea. The transition was associated with a westward migration of the boundary between salinity- and temperature-stratified waters and eventual switch from haline to thermal control of winter stratification. With that follows a change in the type of forcing that can lead to convection: The Greenland Sea is now less dependent on eroding salinity gradients but rather depends on cooling to overcome stratification. There has been a similar switch in summer stratification in the upper-ocean of the Greenland Sea where surface waters shifted from variable stratification, alternating between salinity and temperature dominance, to a stable temperature-stratified regime. This switch coincided with declining sea-ice concentrations related to the disappearance of the Odden ice tongue after 1997. The high sea-ice conditions previously characteristic of the Greenland Sea are now rare suggesting the transition will persist with potential implications for marine ecology and local sea-ice formation. Our findings reveal differences in how thermal and haline stratification has developed over the last 40 years, which may help explain or predict plankton production and carbon uptake and export.

(Digital Presentation) The Effect of Coating Quality on Water Transport in the Gas Diffusion Layer of PEM Fuel Cells

Present study examines the impact of the quality of the GDL non-wetting coating on water transport. It is found that there are two distinct regions defined by the coating quality which present fundamentally distinct behaviours, one region characterized by few coating defects with the second marked by significant coating degradation. Simulations consider the influence of heterogeneous wetting and pinning conditions on protruding water droplets in contact with the GDL fibrous matrix. The mixed-non-wetting behaviour for a uniform non-wetting coating having less than 25% defects is characterized by a high breakthrough pressure, yielding improved transport properties in the stable displacement regime. The coating degrades under normal operating conditions and it changes the water transport characteristics unfavorably through a significant decrease in breakthrough pressure, and an up to six-fold increase in droplet volume. Various degrees of coating degradation are considered and the corresponding Laplace pressure is determined as a function of droplet volumes at breakthrough.

Transition to plastic regime for Rayleigh-Taylor instability in soft solids.

Rayleigh-Taylor instability (RTI) is observed in soft materials that have significant resistance to yield. Estimating the instability threshold is critical to several engineering applications and has been the topic of several studies in past decades. However, limited attention has been given to the elastic-to-plastic (EP) transition threshold, where material properties vary significantly. This study explores the phase transition between the pure elastic and stable plastic regimes in RTI in a soft solid (mayonnaise) using a rotating wheel experimental setup with a time-varying acceleration profile. The material properties of the soft solid are characterized using rheological techniques. Different initial perturbation wavelength and amplitude combinations are used to analyze their role in the EP transition threshold and the subsequent maximum fully recoverable elastic strain. The effects of the initial perturbation dimensions, the steepness of the perturbation, and the mass of the perturbation on the stability of the samples, the EP transition thresholds, and the maximum fully recoverable elastic strains are analyzed. The samples with the largest full elastic recovery potentials and the parameters governing this phenomenon are identified, and the physics behind it is discussed. It is observed that increasing the initial perturbation wavelength decreases the required phase transition acceleration while increasing the maximum fully recoverable elastic strain. Finally, nondimensional parameters that involve the perturbation dimensions, as well as the mechanical properties of the material, are introduced to provide a generalized approach to the problem.