Mode Dynamics Research Articles

Synchronization modes of triple flickering buoyant diffusion flames: Experimental identification and model interpretation.

The synchronization modes of a nonlinear oscillator system consisting of three identical flickering buoyant diffusion flames in isosceles triangles were studied experimentally and theoretically. Five synchronization modes, such as the in-phase, flickering death, partially flickering death, partially in-phase, and rotation modes, were experimentally observed and identified by systematically adjusting the flame distance and fuel flow rates. Two toy models were adopted to interpret the experimentally identified dynamical modes: one is the classical Kuramoto model, and the other is a complexified Stuart-Landau model, which was proposed through the introduction of the complex coupling term. The theoretical results show that the Kuramoto model successfully interpreted the dynamical modes except for those associated with amplitude death, and the complexified Stuart-Landau model well interpreted all the dynamical modes identified in our experiment. Remarkably, the proposed complexified Stuart-Landau model breaks a new path in the investigation of globally coupled nonlinear dynamical systems with identical oscillators, especially for the study of amplitude death mode.

Exploring poly-crystallization in semiconductors through assumption-less growth simulations: CdTe/CdS case study

Crystal growth is a complex process with far-reaching implications for high-performance materials across various fields. Recent advancements in structural analysis methods such as polyhedral template matching, which allows semiconductor-specific analysis, coupled with simulation technology, have enabled the comprehensive study of crystallization dynamics in semiconductors. However, the exploration of polycrystalline semiconductors created with minimal external intervention of the crystallization processes is relatively uncharted in comparison with metals. In this study, we employ molecular dynamics to simulate the growth of polycrystalline CdTe/CdS with the assumptions of classical mechanics, a Stillinger–Weber potential, an amorphous substrate, and common vapor growth conditions to allow the polycrystalline structures to evolve naturally. Post-simulation, we identify and analyze impactful structures and events, comparing them to theory and experiment to gain insight into various modes of crystallization dynamics. Two research questions guided the study: (1) How realistic are assumption-less simulated polycrystalline semiconductor structures? (2) To what extent can the approach provide insight into crystallization? The simulations, performed with minimal external control, yield polycrystalline structures mirroring experimental findings. The analysis reveals key crystallization insights, such as the role of amorphous atoms in the transition from nucleation to grain growth and the transformative impact of single events, such as dislocations, on crystallization dynamics. The method paves the way for reproducing and analyzing realistic polycrystalline semiconductor structures with minimal simulation assumptions across various growth modes.

The Optimal Size of a Heterogeneous Air Taxi Fleet in Advanced Air Mobility: A Traffic Demand and Flight Scheduling Approach

Introducing Advanced Air Mobility (AAM) as a novel transportation mode poses unique challenges due to limited practical and empirical data. One of these challenges involves accurately estimating future passenger demand and the required number of air taxis, given uncertainties in modal shift dynamics, induced traffic patterns, and long-term price elasticity. In our study, we use mobility data obtained from a Dresden traffic survey and modal shift rates to estimate the demand for AAM air taxi operations for this regional use case. We organize these operations into an air taxi rotation schedule using a Mixed Integer Linear Programming (MILP) optimization model and set a tolerance for slight deviations from the requested arrival times for higher productivity. The resulting schedule aids in determining the AAM fleet size while accounting for flight performance, energy consumption, and battery charging requirements tailored to three distinct types of air taxi fleets. According to our case study, the methodology produces feasible and high-quality air taxi flight rotations within an efficient computational time of 1.5 h. The approach provides extensive insights into air taxi utilization, charging durations at various locations, and assists in fleet planning that adapts to varying, potentially uncertain, traffic demands. Our findings reveal an average productivity of 12 trips per day per air taxi, covering distances from 13 to 99 km. These outcomes contribute to a sustainable, business-focused implementation of AAM while highlighting the interaction between operational parameters and overall system performance and contributing to vertiport capacity considerations.

Weakly nonlinear analysis of thermoacoustic oscillations in can-annular combustors

Can-annular combustors feature clusters of thermoacoustic eigenvalues, which originate from the weak acoustic coupling between $N$ identical cans at the downstream end. When instabilities occur, one needs to consider the nonlinear interaction between all $N$ modes in the unstable cluster in order to predict the steady-state behaviour. A nonlinear reduced-order model for the analysis of this phenomenon is developed, based on the balance equations for acoustic mass, momentum and energy. Its linearisation yields explicit expressions for the $N$ complex-valued eigenfrequencies that form a cluster. To treat the nonlinear equations semianalytically, a Galerkin projection is performed, resulting in a nonlinear system of $N$ coupled oscillators. Each oscillator represents the dynamics of a global mode that oscillates in the whole can-annular combustor. The analytical expressions of the equations reveal how the geometrical and thermofluid parameters affect the thermoacoustic response of the system. To gain further insights, the method of averaging is applied to obtain equations for the slow-time dynamics of the amplitude and phase of each mode. The averaged system, whose solutions compare very well with those of the full oscillator equations, is shown to be able to predict complex transient dynamics. A variety of dynamical states are identified in the steady-state oscillatory regime, including push–push (in-phase) and spinning oscillations. Notably, the averaged equations are able to predict the existence of synchronised states. These states occur when the frequencies of two (or more) unstable modes with nominally different frequencies lock onto a common frequency as a result of nonlinear interactions.

Stationary dynamics of planetary ring edge modes at Saturn’s B ring edge

Recent analyses of the structure of the B ring edge have revealed the existence of a rather large number of mode-like features11In this work the expression mode-like features refers to sinusoidal in azimuth (at least in first approximation), variations of the edge shape. of azimuthal wavenumber ranging from m=1 to m=5. Several such mode-like features are associated with each m. The presence of so many features is a puzzle in itself.The present work investigates whether these features can all be associated with independent edge modes and develops to this effect a formal extension of the still embryonic theory of edge modes as trapped waves. Based on this formal extension, forced and free edge modes are explored in some detail. The analysis explicitly shows how edge mode properties such as their resonance location (for free modes) and edge amplitude (for the m=2 forced mode) are related to the ring surface density. Furthermore, the apsidal misalignment of the forced m=2 mode has been known for some time to be related to the ring viscous dissipation in the edge region.This investigation leads to a number of conclusions:i/ Only one mode-like structure associated with a given m can be associated with an edge mode, except possibly for m=1 modes where each of the three detected features can be interpreted as an independent edge mode.ii/ The ring surface density at the edge is in the 200 g/cm2 range under the assumption of dynamically independent edge modes, but a preliminary crude account of collective mode effects brings this down to a more realistic value of ∼100 g/cm2. This applies in the last 20 or 30 kilometers to the edge (m≠1). Further inside (one to two hundred kilometers), the surface density is somewhat more modest, ∼60 g/cm2 (m=1).iii/ The viscous dissipation at the edge is constrained by the observed misalignment between the mean longitude of Mimas and the forced edge mode. The implied level of dissipation at the edge is consistent with the now predominant idea that transport in the B ring, away from the edge, is dominated by self-gravity wakes.iv/ The m=2 mode forced by Mimas is never nonlinear enough by itself to produce the viscous angular flux momentum reversal required to make the edge effectively confined by the associated satellite torque. This explains the failure of Hahn et al. (2009) to explain the confinement of the edge by Mimas except for unrealistic stress tensor properties. It is argued that the presence of so many modes and mode-like features provides a way to restore in a somewhat different form the edge confinement process of Borderies et al. (1982), thereby resolving the conundrum raised by Hahn et al. (2009).

The Binding Mode and Molecular Dynamics of Epigallocatechin and Epigallocatechin Gallate with Human Superoxide Dismutase 1 in Complex with a Naphthalene-Catechol Linked Compound

The Binding Mode and Molecular Dynamics of Epigallocatechin and Epigallocatechin Gallate with Human Superoxide Dismutase 1 in Complex with a Naphthalene-Catechol Linked Compound

Modal analysis of vortex rope using dynamic mode decomposition

The decelerating swirling flow in the draft tube of hydraulic turbines at part load conditions often results in a self-induced instability known as vortex rope. This phenomenon is associated with detrimental pressure pulsations in the hydropower system that need to be mitigated. A deep understanding of such instability is essential for developing effective mitigation and control strategies. The current article exploits the dynamic mode decomposition (DMD) algorithm to perform an in-depth modal analysis of the physical aspects of the vortex rope. DMD can efficiently identify distinct coherent structures with isolated frequencies. The sparsity-promoting variant of DMD is exploited to extract the most influential modes. The computational fluid dynamics (CFD) data is generated via a resolved improved delayed detached eddy simulation using OpenFOAM. Frequency analysis of the CFD data uncovered peaks at the normalized frequencies of f/fn=0.56 and 0.63, whose origins seemed initially unclear. Nevertheless, the DMD modal analysis elucidates that these excitations are associated with the rotation of the reunited vortex and fluctuations of the separated boundary layer, respectively. The non-linear dynamics of the flow field are unveiled through a modal decomposition revealing distinctive coherent structures with isolated frequencies. These include rotational and plunging modes of the vortex rope, traveling wakes of the blades, boundary layer separation due to strong adverse pressure gradient, and a reunited vortex core. The flow field reconstruction through time dynamics of DMD modes highlights while it is possible to achieve a perfect flow field reconstruction considering all recovered modes, the model typically fails to predict future behavior with an acceptable level of accuracy. The chaotic nature of the resolved turbulent flow field presents a substantial challenge for predicting the future through a model built based on prior events. The current modal analysis not only provides a more comprehensive understanding of the physics underlying the vortex rope phenomenon but also lays the groundwork for potential future applications in controlling mechanisms.

Predicting Surface Oscillations in Lake Superior from Normal Mode Dynamics

Abstract Satellite observation of sea surface height (SSH) may soon have sufficient accuracy and resolution to map geostrophic currents in Lake Superior. A dynamic atmosphere correction will be needed to remove SSH variance due to basinwide seiching. Here, the dynamics of rotating barotropic gravity modes are examined using numerical models and lake-level gauges. Gravity modes explain 94% of SSH variance in a general circulation model and evolve as forced, damped oscillators. These modes have significant SSH, but negligible kinetic energy (2 J m−2) and dissipation rates (0.01 mW m−2) relative to other motions in Lake Superior. Removing gravity modes from instantaneous SSH allows geostrophic currents to be accurately computed. Complex empirical orthogonal functions (CEOFs) from 50 years of data at eight lake-level gauges show patterns consistent with the first two gravity modes. The frequency spectra of these CEOFs are consistent with forced, damped oscillators with natural frequencies of 3.05 and 4.91 cycles per day (cpd) and decay time scales of 4.5 and 1.0 days. Modal amplitudes from the general circulation model and lake-level gauges are 80% coherent at 1 cpd, but only 50% coherent at 3 cpd, indicating that the atmospheric reanalysis used to force the general circulation model is not accurate at the high natural frequencies of the gravity modes. The results indicate that a dynamic atmosphere correction should combine modeled gravity modes below 1 cpd and observed mode-1 and mode-2 amplitudes (from lake-level gauges) at higher frequencies. An inverted barometer correction is also recommended to account for low-frequency atmospheric pressure gradients that do not project onto gravity modes.

Quasi-mode evolution in a stochastic magnetic field

We present a multi-scale model of quasi-mode evolution in a stochastic magnetic field. The similarity between a quasi-mode and a ballooning mode enables us to address the challenges arising from the disparate geometries in the theories of ballooning modes in the presence of resonant magnetic perturbations. We obtain useful insights into our understanding of ballooning mode dynamics in a stochastic background. To maintain quasi-neutrality at all scales, the beat between the quasi-mode and the stochastic magnetic field drives microturbulence, which drives the turbulent background that promotes mixing and damps the quasi-mode. As a result of the broad mode structure of the quasi-mode, the turbulent viscosity and the turbulent diffusivity produced by the microturbulence are larger than those in our related study on resistive interchange modes. The stochastic magnetic field can also enhance the effective plasma inertia and reduce the effective drive, thereby slowing the mode growth. A nontrivial correlation between the microturbulence and the magnetic perturbations is shown to develop. This could account for the reduction in the Jensen–Shannon complexity of pedestal turbulence in the Resonant Magnetic Perturbation Edge-Localized Mode suppression phase observed in recent experiments. Directions for future experimental and theoretical studies are suggested.

Switching dynamics of a Filippov memristive Hindmash–Rose neuron model with time delay

Considering the existence of magnetic induction effect with different intensities in the process of subthreshold and suprathreshold oscillations of bioelectrical activities, a non-smooth feedback strategy for memristive current with time delay is proposed, and then a four-dimensional Filippov Hindmarsh–Rose (HR) neuron model is established. The local stability and bifurcation patterns of delayed subsystems are qualitatively analyzed. Accordingly, the discriminant formula for the direction and stability of periodic solutions generated by Hopf bifurcation is obtained on the center manifold. Importantly, the stability of subsystems has switching behavior, which is accompanied by abundant hidden electrical activities under the effect of time delay. The theoretical analysis clarifies that the proposed feedback strategy leads to complex sliding mode dynamics, including sliding segments, various equilibrium points and sliding bifurcations. Meanwhile, the analytical conditions for motions of grazing, sliding, and crossing are developed and verified based on the flow switching theory. Moreover, the mechanism and evolutive rule of the self-excited and hidden sliding electrical activities are revealed by the fast-slow variable dissection method. Finally, it is verified that the time delay can not only induce bistable structures composed of the quiescent state and periodic bursting, but also eliminate the hidden sliding dynamics.

Loading Mode-Induced Enhancement in Friction for Microscale Graphite/Hexagonal Boron Nitride Heterojunction.

Classical friction laws traditionally assume that the friction between solid pairs remains constant with a given normal load. However, our study has unveiled a remarkable deviation from conventional wisdom. In this paper, we discovered that altering the loading mode of micro graphite flakes led to significant changes in the lateral friction under identical normal loads. By adding a cap onto a single graphite flake to disperse the normal load applied by an atomic force microscope (AFM) tip, we were able to distribute the concentrated force. Astonishingly, our results demonstrated a notable 4-7 times increase in friction as a consequence of load dispersion. Finite element analysis (FEA) further confirmed that the increase in compressive stress at the edges of the graphite flake, resulting from load dispersion, led to a significant increase in friction. This study underscores the critical role of the loading mode in microscale friction dynamics, challenging the prevailing notion that friction remains static with a given normal force. Importantly, our research sheds light on the potential for achieving macroscale structural superlubricity (SSL) by assembling microscale SSL graphite flakes by using a larger cap.

Reliability-based leading edge erosion maintenance strategy selection framework

Leading edge erosion has become one of the most prevailing failure modes of wind turbines. Its effects can evolve from an aerodynamic modification of the properties of the blade to a potential structural failure of the leading edge. The first produces a reduction of energy production and the second can produce a catastrophic failure of the blade. Considering the uncertainties and constraints involved in the design of optimal operation and maintenance (O&M) strategies for offshore assets and the influence of site-specific parameters on the dynamics of this particular failure mode, the task becomes complex. In this study, a framework to evaluate the influence of different maintenance strategies considering uncertainties in weather, material behaviour and repair success is presented. Monte Carlo Simulation (MCS) is used alongside a computational framework for Leading Edge Erosion (LEE) degradation to evaluate the lifetime cost distribution and probability of failure of the chosen maintenance strategies. The use of the framework is demonstrated in a case study considering a 5-MW offshore wind turbine located in the north of Germany. The influence of the modification of the maintenance interval or time between repairs and the comparison with maintenance activities executed only during months with milder weather is analysed in terms of cost and reliability. A Pareto front plot considering the probability of failure and the median of the cost is used to jointly compare strategies considering both aspects to provide a tool for risk-informed maintenance selection. Finally, the potential benefits of condition-based maintenance and autonomous decision-making systems are discussed. The case of study shows the benefits of repairs during summer months and the importance of the relation risk/O&M cost for different maintenance strategies.

FILIPPOV TYPE PREY–PREDATOR SYSTEM FOR SELECTIVE HARVESTING OF PREY

In this paper, the dynamics of a Filippov system with logistically growing prey and Holling Type II predation is explored. The selective nonlinear harvesting of prey is carried out when the ratio of prey to predator is above a specified threshold value. In order to prevent the extinction of both the species and sustainable economic gains, no harvesting is allowed when the ratio is below a threshold value. The equilibrium states and their stability for the individual smooth are analyzed. Filippov convex method is applied to determine the dynamics on the boundary. The sliding mode dynamics is scrutinized, and it is observed that there is no escaping region. The existence of boundary points, tangent points and pseudo-equilibrium points are established. The conditions are obtained for the visibility of the tangent points. The complex behavior within the sliding region is studied by experimenting with different initial conditions. The increase in harvesting effort may lead to extinction of both the species through the sliding region of the boundary. The change in the stability behavior of both the interior equilibrium states is investigated with respect to model parameters. Border cross bifurcates with threshold value as the bifurcation parameter is shown for both the interior equilibrium states.

Motivational profile and knowledge creation in eSports: examining the roles of mutualistic co-presence

PurposeResearch on knowledge creation within eSports learning is scarce. This study extends the understanding of competition-oriented collaborative learning in eSports by examining the relationship between the dynamics of knowledge creation modes and the continuum of the motivational profile, along with the moderating effects of mutualistic co-presence therein.Design/methodology/approachParticipants were recruited from the community of massively multiplayer online gamers (MMOGs). Through a quantitative survey, their motivations (i.e. self-extrinsic, self-intrinsic, peer-extrinsic and peer-intrinsic motivations), knowledge creation involvements (i.e. internalization, externalization, combination and socialization) and perception of mutualistic benefit of self and peers were captured for hypothesis testing.FindingsSignificant and positive direct relationships were observed between four motivations and four knowledge creation modes. The mutualistic co-presence positively moderated the positive relationship between the self-extrinsic, peer-extrinsic and peer-intrinsic motivations and socialization. When mutualistic self-benefit were outweighed, peer-extrinsic motivated gamers became less likely to perform internalization, whereas self-extrinsic and peer-extrinsic motivated gamers were less likely to perform combination.Originality/valueThis study is among the first to rationalize the relationship between motivational profile and the dynamics of knowledge creation in eSports learning. The conceptualization of the new construct – mutualistic co-presence – using the ecological concept of symbiosis is uncommon in prior literature. The findings also demonstrate that the four modes of knowledge creation in eSports learning are continuous and interwoven; they can be initiated at any point and do not necessarily occur in a specific sequence.

Fluid-structure interaction in phaco-emulsification based cataract surgery

Cataract scatters the light as it enters the eye, blurs images and severely interferes people's daily activities. The only effective therapy is cataract surgery, in which the clouded lens is phacoemulsified and removed. However, an aberrant iris distortion, namely intra-operative floppy iris syndrome (IFIS), is not uncommon in the phacoemulsification process, and it greatly degrades the surgical outcomes. Despite its great impact, the mechanism of IFIS has seldom been explored from the mechanics viewpoint. This study constitutes the first exploration into IFIS mechanism within the torsional-irrigation/aspiration (T-I/A) combined mode, from the perspective of fluid-structure coupling, employing our newly developed fluid-structure interaction (FSI) simulation framework. The impacts of several factors, including probe type and position, irrigation and aspiration (I/A), iris stiffness and lens presence, are evaluated in two different torsional-irrigation/aspiration (T-I/A) combined configurations, corresponding to the scenarios of coaxial and bimanual I/A operations. Results reveal that by altering the probe's location in anterior chamber, three distinct modes of iris dynamics are recognized and defined as repulsion (RP), attraction (AT), and adhesion (AH) modes according to the relative iris-probe location. Among them, RP mode, where the iris is repelled by the probe, is preferred to ensure the safety of the iris. Furthermore, IFIS could be alleviated by stiffening iris, reducing I/A strength and choosing coaxial I/A device. These interventions result in the contraction of the damaging AH zone towards the iris root, occurring at approximately one-fourth (coaxial case), one-fifth (coaxial case), and one-fourth of the iris length, achieved by quadrupling iris stiffness, ceasing I/A flow, and utilizing coaxial I/A device, respectively. However, the risk of IFIS is only marginally impacted by the lens presence. Our findings gain a deeper insight into the iris dynamics in T-I/A mode from fluid-iris interaction viewpoint, which may provide valuable guidance for the surgical protocol operation.

An adaptive dynamic programming method for observer‐based sliding mode control of connected vehicles subject to deception attacks

AbstractThis article investigates the problem of optimal observer‐based sliding mode control (SMC) of connected vehicles subject to deception attacks and disturbances with adaptive dynamic programming (ADP) method. For a group of vehicles with unknown nonlinear dynamics term and disturbance, this article aims to give a control methodology to achieve secure tracking of the desired spacing, velocity and acceleration. A neural network (NN) and an observer are constructed to estimate the unknown nonlinear term and the states, respectively. Then, a SMC scheme incorporating NN approximation is developed and an off‐policy ADP method is used to implement the optimal control of sliding mode dynamics. The proposed method can ensure individual stability and string stability of the set of vehicles. Numerical simulations are conducted to demonstrate the validity of the proposed controller.

MNEs Entry Mode Choices: The Impact of Past on Current. Evidence from an Emerging Economy

The paper examines the effect past entry strategies have on current ones on a country level, Turkey. It illustrates how international experience and institutional distance affect the way an entry-strategy is formed, and the procedure followed -mode learning, mode inertia, mode dynamics. To do so, it synthesizes the literature review within the framework of Benito et al. (2009). This paper’s modifications are empirically tested through a sample of 408 foreign equity investments. The econometric testing method implemented is that of Binary Logistic Regression. The period of investigation extends between 2011 and 2017. Results indicate that MNEs entering the Turkish secondary and tertiary Turkish sectors tend to utilize past entry mode strategies. Furthermore, the higher the past mode strategy is for an MNE, then it is 4.4 more possible for them to choose a wholly owned subsidiary.

Influence of Gaussian noise and Levy noise on the phase dynamics of the ensemble of Kuramoto-like oscillators of first and second

The purpose of this study is to determine the stability threshold of the dynamic modes of the ensemble of phase Kuramoto-like oscillators, describing the behavior of a simple power grid model with a ring topology, under the external influence of Gaussian noise and Levy noise, to evaluate the results and determine the threshold values of noise at which the considered dynamic model is the most sensitive to noise and demonstrates a change of the steady state. Methods. In this paper, two ensembles of Kuramoto-like phase oscillators with the same topology but different number of oscillators are investigated. The ensembles consist of second and first order phase oscillators modeling the dynamics of generators and consumers in the power grid, respectively. In this work, mode maps are computed and used, from which regions with different synchronous dynamics are selected. In the selected regions, a set of initial conditions is fixed and the ensemble under study is modeled in the presence of noise of different types and intensities. The obtained result is evaluated with the help of calculated spatio-temporal diagrams, values of the Kuramoto parameter and statistical characteristics estimated from the realizations of oscillations in time. Results. It has been shown that a power grid model consisting of Kuramoto-like phase oscillators exhibits different robustness to external noise disturbances depending on the type of noise disturbance and the steady-state dynamic regime. It was demonstrated that the frequency synchronization mode of all oscillators, independent of the initial conditions, is insensitive to the influence of white noise of high intensity, both Gaussian and Levy noise. Whereas, in the region of coexistence of synchronous and asynchronous behavior, depending on the initial conditions, a change of phase dynamics under the influence of different noise is observed. Numerical experiment has shown that the power grid model is more susceptible to Levy noise due to the noise features associated with random emissions, which in turn can be interpreted as random impulses. Conclusion. In a power grid model represented by two ensembles consisting of different numbers of Kuramoto-like phase oscillators of second and first order, different modes of frequency and phase dynamics of the oscillators are established. A numerical experiment with the influence of Gaussian noise and Levy noise is carried out for the obtained modes. It is shown that the model under study is more sensitive to Levy noise, the influence of which leads to a change of the dynamic mode due to the influence of strong random pulses.

Spatial-temporal dynamics of paddy productivity on the north coast of Java Island, Indonesia based on the principal component analysis of MODIS NDVI anomaly data

Comprehending the dynamics of paddy productivity is imperative for enhancing the efficacy of agricultural land developments. This study provides the application of principal component analysis (PCA) as a method for visualizing the spatial-temporal changes in paddy productivity. The analysis is conducted using the 8-day NDVI (normalized difference vegetation index) anomaly data of MODIS (Moderate Resolution Imaging Spectroradiometer) data spanning the period from 2000 to 2020. The regencies of Karawang, Subang, and Indramayu on the north coast of Java island are chosen as the study area because of their top rice production areas in Indonesia. The results show that the first leading PCA of the NDVI anomaly is related to the interannual variability of paddy productivity with 3-4 year cycles. The spatial and temporal dynamics of the first mode of eigenvectors and principal component time series can generally be grouped into nine categories. Two important categories to note are category-1 (1 January – 19 March) and category-8 (12 September – 16 December). In category-1, the NDVI anomalies move from north to middle and middle to north areas in Karawang and Subang regencies, respectively. In Indramayu Regency, the NDVI anomalies relatively remain in almost all areas. In contrast, in category-8 the NDVI anomalies move from the middle to northern areas in Karawang, Subang, and Indramayu regencies.

Tree regeneration and ontogenetic strategies of northern European hemiboreal forests: transitioning towards closer-to-nature forest management.

Tree ontogeny is the genetic trajectories of regenerative processes in trees, repeating in time and space, including both development and reproduction. Understanding the principles of tree ontogeny is a key priority in emulating natural ecological patterns and processes that fall within the calls for closer-to-nature forest management. By recognizing and respecting the growth and development of individual trees and forest stands, forest managers can implement strategies that align with the inherent dynamics of forest ecosystem. Therefore, this study aims to determine the ontogenetic characteristics of tree regeneration and growth in northern European hemiboreal forests. We applied a three-step process to review i) the ontogenetic characteristics of forest trees, ii) ontogenetic strategies of trees for stand-forming species, and iii) summarise the review findings of points i and ii to propose a conceptual framework for transitioning towards closer-to-nature management of hemiboreal forest trees. To achieve this, we applied the super-organism approach to forest development as a holistic progression towards the establishment of natural stand forming ecosystems. The review showed multiple aspects; first, there are unique growth and development characteristics of individual trees at the pre-generative and generative stages of ontogenesis under full and minimal light conditions. Second, there are four main modes of tree establishment, growth and development related to the light requirements of trees; they were described as ontogenetic strategies of stand-forming tree species: gap colonisers, gap successors, gap fillers and gap competitors. Third, the summary of our analysis of the ontogenetic characteristics of tree regeneration and growth in northern European hemiboreal forests shows that stand-forming species occupy multiple niche positions relative to forest dynamics modes. This study demonstrates the importance of understanding tree ontogeny under the pretext of closer-to-nature forest management, and its potential towards formulating sustainable forest management that emulates the natural dynamics of forest structure. We suggest that scientists and foresters can adapt closer-to-nature management strategies, such as assisted natural regeneration of trees, to improve the vitality of tree communities and overall forest health. The presented approach prioritizes ecological integrity and forest resilience, promoting assisted natural regeneration, and fostering adaptability and connectivity among plant populations in hemiboreal tree communities.