Multiple Regimes Research Articles

Describing a landscape mosaic: Forest structure and composition across community types and management regimes in inland northeastern pitch pine barrens

Pitch pine (Pinus rigida Mill.) barrens are a globally rare, fire-dependent ecosystem of great ecological, social, and cultural significance found primarily in the northeastern US. In many cases, fire has been excluded from these systems leading to habitat degradation and biodiversity loss as pine barrens landscapes homogenize into closed-canopy forests of shade-tolerant, mesophytic species. This study aims to support the adaptive management of pine barrens ecosystems in the face of mesophication by contributing baseline information on their structure and composition. Specifically, we (1) assessed how stand conditions differ between community types and management strategies at the two sites and (2) placed this work in the broader context of pine barrens ecology and management. We sampled overstory structure and composition across five community types (successional northern sandplain grasslands, pitch pine-scrub oak barrens, pitch pine-scrub oak thicket, pitch pine-scrub oak woodland, and pitch pine-oak forest) and four management strategies (burning, thinning, burning and thinning, and no management). Differences in structure and composition between communities supported the concept of pine barrens as a landscape mosaic maintained by multiple unique disturbance regimes. Results suggest that burning, thinning, and their combination are all effective in maintaining conditions historically associated with pine barrens communities, and that a lack of active management may lead to a transition away from these characteristics. The range of pine barrens conditions documented in this and previous studies underscores the importance of management regimes that utilize a diversity of treatments applied at frequencies and intensities consistent with historic disturbance regimes for each pitch pine community type. Such strategies would maintain the mosaic of habitat conditions required to support the suite of species endemic to these communities, and would confer resilience to emerging stressors, such as southern pine beetle (Dendroctonus frontalis), which often generates greatest impacts in unmanaged, homogeneous forests.

Study on Multiscale Fluid–Solid Coupling Theoretical Model and Productivity Analysis of Horizontal Well in Shale Gas Reservoirs

In order to study the productivity dynamic evolution laws of shale gas horizontal well, a multiscale seepage theoretical model considering the fluid–solid coupling effect is proposed first in this paper, which introduces an anisotropic matrix permeability model that comprehensively considers multiple flow regimes and an artificial hydraulic fracture conductivity model that considers proppant deformation and embedment. Then the reliability of the theoretical model is verified by the field production data obtained from the Marcellus shale. Based on the established productivity model, the evolution laws of pore pressure and permeability in different areas of the reservoir with different production periods are studied first, and then the shale gas production rate and cumulative production under different physical mechanisms, different shale gas flow regimes, and different reservoir parameters are quantified and analyzed. The simulation results show that the pore pressure in the hydraulic fracture area decreases rapidly at the initial stage of production, resulting in large deformation, and the fracture conductivity tends to be stable gradually at the later stage of production. The desorption effect will increase shale gas production, while the stress sensitivity is just the opposite. When only real gas flow is considered, the gas cumulative production is the highest. The fluid–solid coupling of hydraulic fractures has a great impact on the production, while the fluid–solid coupling in the matrix area has a small impact on the production, which can be ignored if appropriate. During the sensitivity analysis of reservoir parameters, it is observed that the influence of parameters of hydraulic fractures on production is much higher than that of matrix regional parameters. During the production process, these influencing factors can be adjusted according to the change of production data to achieve the optimization of shale gas production. In a word, the new model proposed in this paper provides a more accurate method to estimate the impact of multiple physical mechanisms, especially the fluid–solid coupling effect, on shale gas production compared with the existing model. The research results of this study can provide some reference and guidance for the dynamic prediction of shale gas production and optimization of production parameters.

Signatures of Gate-Driven Out-of-Equilibrium Superconductivity in Ta/InAs Nanowires.

Understanding the microscopic origin of the gate-controlled supercurrent (GCS) in superconducting nanobridges is crucial for engineering superconducting switches suitable for a variety of electronic applications. The origin of GCS is controversial, and various mechanisms have been proposed to explain it. In this work, we have investigated the GCS in a Ta layer deposited on the surface of InAs nanowires. Comparison between switching current distributions at opposite gate polarities and between the gate dependence of two opposite side gates with different nanowire-gate spacings shows that the GCS is determined by the power dissipated by the gate leakage. We also found a substantial difference between the influence of the gate and elevated bath temperature on the magnetic field dependence of the supercurrent. Detailed analysis of the switching dynamics at high gate voltages shows that the device is driven into the multiple phase slips regime by high-energy fluctuations arising from the leakage current.

A non-homogeneous model of chromosome-number evolution to reveal shifts in the transition patterns across the phylogeny.

Changes in chromosome numbers, including polyploidy and dysploidy events, play a key role in eukaryote evolution as they could expediate reproductive isolation and have the potential to foster phenotypic diversification. Deciphering the pattern of chromosome-number change within a phylogeny currently relies on probabilistic evolutionary models. All currently available models assume time homogeneity, such that the transition rates are identical throughout the phylogeny. Here, we develop heterogeneous models of chromosome-number evolution that allow multiple transition regimes to operate in distinct parts of the phylogeny. The partition of the phylogeny to distinct transition regimes may be specified by the researcher or, alternatively, identified using a sequential testing approach. Once the number and locations of shifts in the transition pattern are determined, a second search phase identifies regimes with similar transition dynamics, which could indicate on convergent evolution. Using simulations, we study the performance of the developed model to detect shifts in patterns of chromosome-number evolution and demonstrate its applicability by analyzing the evolution of chromosome numbers within the Cyperaceae plant family. The developed model extends the capabilities of probabilistic models of chromosome-number evolution and should be particularly helpful for the analyses of large phylogenies that include multiple distinct subclades.

Tabulated Chemistry Approach for the Simulation of MILD Combustion: Effects of Scalar Mixing and Chemistry Tabulation.

MILD (moderate and intense low-oxygen dilution) combustion is a highly promising technology to deliver clean and efficient thermal energy. However, because of its unconventional reaction nature, the optimization of the MILD combustion in various industrial burners is still challenging, for which the design tool based on accurate and cost-effective numerical simulation is most desirable. To this end, the tabulated chemistry approach (TCA) is thoroughly assessed for the modeling of MILD combustion by simulations of the Adelaide Jet in Hot Coflow (JHC) burner. The sensitivities to the submodel accounting for the scalar micromixing and the canonical flame configurations (i.e., flamelet and PSR-based reactors), being relevant for MILD regime characterization in TCA, are studied. It is found that the scalar mixing enhanced through the dynamic adjustment of model parameter C s leads to an improved prediction, and the optimal value of C s = 8 is identified for the current flames. The proper parametrization of the detailed chemical structures in TCA is found to affect the accurate prediction of the MILD flame profiles, especially the mass fraction of minor species (e.g., OH, CO). Furthermore, the endothermic reaction path of O + C2H2 ⇒ CO + CH2 is indicated as the main contributing step to the disparities in the CO predictions. This implies that the multiple reaction regimes in complex MILD burning should be accounted for by the use of either flamelet or PSR structures, depending on the local microscale diffusion/chemistry competitions. Overall, the results highlight the influential role of multiscale mixing and its intercoupling with the finite-rate chemistry, the accurate determination of which is important for MILD combustion modeling.

Two slip regimes in sheared granular fault

In the stick-slip cycles of faults, the evolving contact state inside the gouge is a major contribution to the evolution of fault friction. However, the microscopic contact changes within stick-slip cycles associated with the possible existence of multiple fault slip regimes are still obscure. By simulating a sheared fault containing a granular gouge, we examine the particle-level contact evolution inside the gouge and the corresponding gouge stress field heterogeneity at fault slip. We find two regimes of fault slip driven by the heterogeneity of the gouge stress field: in the case of weak gouge stress field heterogeneity, local contact rearrangements give rise to macroscopic friction coefficient drop and accumulated gouge stress field heterogeneity (dispersive regime); in the instance of strong stress field heterogeneity, catastrophic failure occurs via contact rearrangement sweeping the whole fault and homogenizes the stress field distribution in the gouge (pervasive regime). In the language of self-organized criticality, the accumulation of gouge stress field heterogeneity is an inevitable consequence of increased entropy in the preparation stage of a large earthquake, which eventually destroys the long-range stress field correlations in the gouge and resets at the beginning of a new cycle of a large earthquake.

Linear logistic regression with weight thresholding for flow regime classification of a stratified wake

• Build a DNS database with O(100) realizations for stratified wake. • Develop a machine learning tool to classify the flow regimes in a stratified wake. • The physics governing stratified wake is universal with respect to Re and Fr. • The classifier captures the universal physics and generalize well. A stratified wake has multiple flow regimes, and exhibits different behaviors in these regimes due to the competing physical effects of momentum and buoyancy. This work aims at automated classification of the weakly and the strongly stratified turbulence regimes based on information available in a full Reynolds stress model. First, we generate a direct numerical simulation database with Reynolds numbers from 10000 to 50000 and Froude numbers from 2 to 50. Order (100) independent realizations of temporally evolving wakes are computed to get converged statistics. Second, we train a linear logistic regression classifier with weight thresholding for automated flow regime classification. The classifier is designed to identify the physics critical to classification. Trained against data at one flow condition, the classifier is found to generalize well to other Reynolds and Froude numbers. The results show that the physics governing wake evolution is universal, and that the classifier captures that physics.

On regime changes of COVID-19 outbreak

The COVID-19 pandemic has had a very serious impact on societies and caused large-scale economic changes and death toll worldwide. The first cases were detected in China, but soon the virus spread quickly worldwide and the intensity of newly reported infections grew high during this initial period almost everywhere. Later, despite all imposed measures, the intensity shifted abruptly multiple times during the two-year period between 2020 and 2022 causing waves of too high infection rates in almost every part of the world. To target this problem, we assume the data heterogeneity as multiple consecutive regime changes. The research study includes the development of a model based on automatic regime change detection and their combination with the linear birth-death process for long-run data fits. The results are empirically verified on data for 38 countries and US states for the period from February 2020 to April 2022. Finally, the initial phase (conditions) properties of infection development are studied.

An improved cavitation model with thermodynamic effect and multiple cavitation regimes

Mechanical feed pumps in organic Rankine cycle (ORC) power plants can suffer from cavitation to lose their normal feeding performance or even damage. Cavitation models for organic fluids in ORC systems are lacking presently. Hence, a new cavitation model with thermodynamic effect was proposed. Surface tension-controlled, inertia-controlled, intermediate and heat transfer-controlled cavitation regimes, and two key elements: vapour bubble growth rate and vapour bubble number density are included in the model. A known air or non-condensable gas concentration in the liquid was employed to determine cavitation nuclei number density. The model was coded in ANSYS CFX as user defined model and validated with cavitating flows of organic fluid R114 in a venturi, liquid nitrogen and liquid hydrogen on a tapered hydrofoil and warm water around a hydrofoil NACA 0015 in cavitation tunnels based on visualised cavity length. Two model constants, temperature depression, and minimal cavitation number were correlated to bulk liquid temperature, Reynolds number, and Jakob number. The temperature and pressure profiles of liquid nitrogen and hydrogen on hydrofoil surface were examined against the experimental data. The model was applied to simulate unsteady cavitating flows of organic fluid R245fa in a diaphragm pump. It was shown that the temperature depression and minimal cavitation number cannot be correlated to bulk liquid temperature, Reynolds number and Jakob number. Two model constants can be correlated fairly to Reynolds number. The model underestimates the thermodynamic effect by 43% for R114, 18.6% for liquid nitrogen and 32.6% for liquid hydrogen based on temperature depression. The predicted temperature and pressure profiles on hydrofoil surface agree with the experimental data for liquid nitrogen. The model can produce an expected curve of mean pump flow rate against net positive suction head available.

Study of nonlinear characteristics in hollow cathode discharge in unmagnetized plasmas

AbstractParametric study and nonlinear dynamical analysis of the discharge parameter variations are presented here for a hollow cathode source in the glow discharge regime and later in the radio frequency (RF) discharge regime. A plasma source consisting of a semi‐transparent hollow cathode leads to the generation of nonthermal energetic charged particles and the formation of multiple potential regimes in the plasma column during both the glow discharge as well as the RF discharge regimes. The hollow cathode discharge obtained using this single plasma source exhibits significant mixed‐mode oscillations (MMOs) during the glow discharge regime. Various regular and irregular sequences of MMOs evolved during the progressive change of discharge voltage in the glow discharge regime. During the RF power application across the hollow cathode source, the charged particles oscillate and appear in bursts in the time series. The present study investigates energy distribution among the coherent modes of discharge through the application of the Empirical Mode Decomposition technique. Multiple coherent modes are identified during both discharge regimes that carry most of the discharge energy.

Mutual impact of thermal radiations and temperature dependent thermal conductivity on non-Newtonian multiple flow regimes

The transfer of thermal energy is a specialized discipline of thermal engineering and hence own practical applications in an industrial thermal systems like refineries, air-conditioning plants, automotive engines, power plants, jet engines, refrigeration, food processing, and chemical processing plants to mention just a few. Owning such importance we have reported the collective impact of thermal radiations and temperature-dependent thermal conductivity for heat transfer in stagnation point magnetized Casson fluid flow field. The thermal flow regime of Casson fluid is manifested with a viscous dissipation effect as well. The flow equations are tackled numerically by the use of the shooting method. The outcomes are debated comparatively by considering various flow regimes namely (I) Thermal flow regime with thermal radiations (II) Thermal flow regime without thermal radiations (III) Heat flow with heat generation and (IV) Heat flow in the absence of heat generation. We believe that the present thermal comparative analysis will be helpful for the preceding studies which own thermal engineering standpoints for the transfer of thermal energy by means of fluid flow.

Spatiotemporal Patterning Enabled by Gene Regulatory Networks.

Spatiotemporal pattern formation plays a key role in various biological phenomena including embryogenesis and neural network formation. Though the reaction-diffusion systems enabling pattern formation have been studied phenomenologically, the biomolecular mechanisms behind these processes have not been modeled in detail. Here, we study the emergence of spatiotemporal patterns due to simple, synthetic and commonly observed two- and three-node gene regulatory network motifs coupled with their molecular diffusion in one- and two-dimensional space. We investigate the patterns formed due to the coupling of inherent multistable and oscillatory behavior of the toggle switch, toggle switch with double self-activation, toggle triad, and repressilator with the effect of spatial diffusion of these molecules. We probe multiple parameter regimes corresponding to different regions of stability (monostable, multistable, oscillatory) and assess the impact of varying diffusion coefficients. This analysis offers valuable insights into the design principles of pattern formation facilitated by these network motifs, and it suggests the mechanistic underpinnings of biological pattern formation.

A European Credit Council for Consistent and Informed Policymaking

Abstract In Banque Providence Eric Monnet draws on the history of central banking to investigate the problem of insufficient democratic anchoring of monetary policy. It is a very timely contribution, especially as the choices that the central bankers will face in the near future are bound to get ever more political. This article discusses Monnet’s proposals to increase central bank legitimacy through common deliberation of monetary policy authorities and economic policymakers, in particular in relation to EU’s credit policy. I draw on the rich literature on interinstitutional accountability to identify conditions for such an EU Credit Council to be fit for purpose. I further identify two specific EU contexts where further deliberation would be particularly called for: the differentiated monetary and internal market (credit) policies and the Green Deal. With regard to the first, I show how an EU Credit Council could help deepen our understanding of the mutual impact of advancing EU banking integration and continued existence of multiple currency regimes. With regard to the second, I discuss clarifications and adjustments needed in the EU legal framework to ensure that further policy coordination on financing the transition within such a Credit Council would facilitate the achievement of EU’s sustainability goals.

Estimation of Multiflier Effect of Public Spending on Economic Growth under Multiple Regimes Regime

The paper estimates the multiplier effect of public spending (total government spending) on economic growth (RGDP) from 44 years long time-series database of macro-economic variables from 1974-75 to 2018-19 (Panchayat Regime (1975-1990), Democracy I: Ceremonial Monarch (1991-2005) and Democracy II: Federal (2006-2019)) through structure vector auto-regressive (SVAR) model with tests. The paper provides the above three political regimes based on relationships between public spending and economic growth and the multiplier of public spending on economic growth. As a result, in the three different regimes, their nature, behavior, and dynamics are stationary. Except for real regular spending (RRS) in Democracy I: Ceremonial Monarch (1991-2005) and real capital spending (RCS) in Democracy II: Federal (2006-2019), all coefficient values of SVAR estimate shows a significantly positive relationship between the government spending and economic growth. It indicates a positive multiplier effect of public spending; recurrent spending and capital spending are positive to economic growth, except for GRRE in Democracy I: Ceremonial Monarch (1991-2005) and RCS in Democracy II: Federal (2006-2019). Likewise, in the different political regimes, higher multiplier of total public spending, regular public spending and capital public spending in the Panchayat Regime (1975-1990) are better than successive democratic regimes so-called the people’s centric political regimes: Democracy I: Ceremonial Monarch (1991-2005) and Democracy II: Federal (2006-2019). Besides, except for the Panchayat Regime (1975-1990), the multiplier value of public spending; recurrent spending, and capital spending are lower in Democracy I: Ceremonial Monarch (1991-2005) and then Democracy II: Federal (2006-2019). It indicates the low efficiency of the government spending and budgetary system. Therefore, the government should improve the efficiency of public spending, the ratio of the capital spending, and private investment for improving the higher multiplier variable in long run.

Geometric Programming Assisted Conversion Time Reduction Technique Applied to a Multiregime-Based Digitizer for Wide Span Resistive Sensors

This manuscript proposes a geometric-programming (GP)-aided approach for reducing the conversion time of digitizers for resistive sensors. The digitizer, comprising a relaxation oscillator circuit, partitions the sensor span into multiple regimes. An optimization problem with the objective of minimizing the maximum conversion time for the multiple regimes, while maintaining lower limits to on and off durations is formulated. This constrained optimization problem is shown to be a GP and solved numerically. Optimal thresholds for partitioning the span as well as the optimal circuit parameters have been derived from the GP-based solution. It has been shown that the usage of GP, in the digitizer, can reduce the conversion time by at least a factor of three. The performance of the digitizer, designed with GP-solutions, has been evaluated in simulation and experimental studies. Results show that the digital interface circuit requires only around 17 ms during the measurement range of 1 kΩ to 1 MΩ and provides a nonlinearity of 0.2 %.

A switching Gaussian process latent force model for the identification of mechanical systems with a discontinuous nonlinearity

Abstract An approach for the identification of discontinuous and nonsmooth nonlinear forces, as those generated by frictional contacts, in mechanical systems that can be approximated by a single-degree-of-freedom model is presented. To handle the sharp variations and multiple motion regimes introduced by these nonlinearities in the dynamic response, the partially known physics-based model and noisy measurements of the system’s response to a known input force are combined within a switching Gaussian process latent force model (GPLFM). In this grey-box framework, multiple Gaussian processes are used to model the unknown nonlinear force across different motion regimes and a resetting model enables the generation of discontinuities. The states of the system, nonlinear force, and regime transitions are inferred by using filtering and smoothing techniques for switching linear dynamical systems. The proposed switching GPLFM is applied to a simulated dry friction oscillator and an experimental setup consisting of a single-storey frame with a brass-to-steel contact. Excellent results are obtained in terms of the identified nonlinear and discontinuous friction force for varying: (i) normal load amplitudes in the contact; (ii) measurement noise levels, and (iii) number of samples in the datasets. Moreover, the identified states, friction force, and sequence of motion regimes are used for evaluating: (1) uncertain system parameters; (2) the friction force–velocity relationship, and (3) the static friction force. The correct identification of the discontinuous nonlinear force and the quantification of any remaining uncertainty in its prediction enable the implementation of an accurate forward model able to predict the system’s response to different input forces.

Social effects of neoliberal policy in post-Soviet Saint Petersburg: Urban space contestation revisited

Neoliberal city policy has become central for urban planning and (re)development in postsoviet St. Petersburg. Competing views on how urban space should be organized make citizens consolidate and buck the decisions of strong advocacy groups. This paper considers the contestation of urban space by urban dwellers and city elites in the early times of establishment and spread of neoliberal rhetoric and policy. It focuses on four cases of local communities struggling against spot construction, demolition, and renovation of historical areas (2005–2012). Empirically, the paper relies on a series of semi-structured interviews with local residents and activists as well as materials of semi-formalized observations at local gatherings and rallies. We use theories of urban political regimes to analyze the decisions on urban futures made by administrations and developers, and the theories of Lefebvre, Scott, and de Certeau providing insights into everyday grassroots resistance of citizens to structural pressures, domination and exploitation — to describe the responses of urbanites. Our data shows that these theories need to be adapted to the local context, where struggles over urban space unfolded under the conditions of total uncertainty including multiple property regimes, unstable legal frameworks, non-transparent decision-making by city authorities and investors, and rising tradition of civic participation. As a result, we question the scholarly convention about the paternalistic relations between urbanites and powerholders, and problematize the boundaries between the core concepts of urban theory: in particular, we demonstrate the relative nonbinary character of the opposition of spatial strategies vs. spatial tactics.

Properties of Flare-imminent versus Flare-quiet Active Regions from the Chromosphere through the Corona. II. Nonparametric Discriminant Analysis Results from the NWRA Classification Infrastructure (NCI)

A large sample of active-region-targeted time-series images from the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA), the AIA Active Region Patch database (Paper I) is used to investigate whether parameters describing the coronal, transition region, and chromospheric emission can differentiate a region that will imminently produce a solar flare from one that will not. Parameterizations based on moment analysis of direct and running-difference images provide for physically interpretable results from nonparametric discriminant analysis. Across four event definitions including both 24 hr and 6 hr validity periods, 160 image-based parameters capture the general state of the atmosphere, rapid brightness changes, and longer-term intensity evolution. We find top Brier Skill Scores in the 0.07–0.33 range, True Skill Statistics in the 0.68–0.82 range (both depending on event definition), and Receiver Operating Characteristic Skill Scores above 0.8. Total emission can perform notably, as can steeply increasing or decreasing brightness, although mean brightness measures do not, demonstrating the well-known active-region size/flare productivity relation. Once a region is flare productive, the active-region coronal plasma appears to stay hot. The 94 Å filter data provide the most parameters with discriminating power, with indications that it benefits from sampling multiple physical regimes. In particular, classification success using higher-order moments of running-difference images indicate a propensity for flare-imminent regions to display short-lived small-scale brightening events. Parameters describing the evolution of the corona can provide flare-imminent indicators, but at no preference over “static” parameters. Finally, all parameters and NPDA-derived probabilities are available to the community for additional research.

From Goldilocks to twin peaks: multiple optimal regimes for quantum transport in disordered networks.

Understanding energy transport in quantum systems is crucial for an understanding of light-harvesting in nature, and for the creation of new quantum technologies. Open quantum systems theory has been successfully applied to predict the existence of environmental noise-assisted quantum transport (ENAQT) as a widespread phenomenon occurring in biological and artificial systems. That work has been primarily focused on several 'canonical' structures, from simple chains, rings and crystals of varying dimensions, to well-studied light-harvesting complexes. Studying those particular systems has produced specific assumptions about ENAQT, including the notion of a single, ideal, range of environmental coupling rates that improve energy transport. In this paper we show that a consistent subset of physically modelled transport networks can have at least two ENAQT peaks in their steady state transport efficiency.

Frequency multiplication in a high-current relativistic gyrotron for obtaining high-power THz-band radiation

Using averaged equations and 3D particle-in-cell simulations, we investigate the frequency multiplication regime in a high-current relativistic gyrotron operating in 0.1 THz frequency band. We demonstrate that the ratio of the 3rd harmonic power and the fundamental cyclotron resonance power can reach 0.4–0.8%, which aloows for obtaining the 0.3 THz radiation with sub-MW output power level.