Transition Path Research Articles

Behavioral Transition Path and Pivotal Nodes Regulating Attack in Initial Encounters between Unfamiliar Pigs.

This study leverages the inherent curiosity of pigs and their competitive nature among conspecifics to explore behavioral transition paths and critical nodes that govern aggression during initial encounters between unfamiliar individuals. Two consecutive experiments were designed to investigate these dynamics under controlled conditions. In Experiment 1, unfamiliar pigs engaged in one-on-one fights with quick retreats, displaying a simple behavioral sequence of looking followed by attacking. In Experiment 2, the addition of new pigs to resident groups resulted in a more complex and structured behavioral sequence. Resident pigs exhibited a 'four-step' exploratory behavior pattern: looking, sniffing, touching, and attacking. Further analysis revealed distinct exploratory pathways. In Experiment 1, only short behavioral paths were observed, while Experiment 2 revealed both long and short paths. Specifically, Experiment 2 uncovered seven types of behavioral transition paths, four of which were long and three short, highlighting different combinations of the basic behaviors. The transition paths involving aggression were more varied in Experiment 2 compared to Experiment 1. Overall, the 15 most frequent and obvious behavioral transition paths were identified across both experiments. Eight types of paths were categorized based on the transitions between the basic behaviors. These findings enhance our understanding of the behavioral dynamics in unfamiliar pig encounters, emphasizing the complexity of social interactions and the conditions under which aggression occurs.

Theoretical study of the mechanism of 2F-molecular sieve domain chiral transition of Asn molecules

Abstract Using density functional theory at the level of oniom (b3lyp/6-31g (d, p): uff), we investigated the chiral transition process of the Asparagine molecule in 2F-MOL. Furthermore, a complete chiral transition path reaction potential energy surface was drawn by looking for the extreme value point structures including the transition state and intermediate. The results show that the hydrogen atom on the chiral carbon atom of S-Asparagine molecule can transfer to the other side of the carbon atom via the oxygen atoms of carboxyl atoms as a bridge, to achieve the chiral transition of Asparagine molecule from S-type to R-type. On this path there is four intermediate and five transition states. The biggest reaction energy barrier is 243.9089KJ/mol derived from the fourth transition state TS1-R-Asn@2F-MOL.

Transition path properties for one-dimensional non-Markovian models

Transition path properties for one-dimensional non-Markovian models

‘You never get a livelihood out of going to school’: the crisis of urban modernity and the education-employment nexus in Harare, Zimbabwe

The economic crisis and informalisation in Zimbabwe from the late 1990s had many consequences, including the unattainability of the early postcolonial modernist lifestyle and the collapse of the robust education-employment nexus and steady transition pathway from school to work for graduates in urban areas. Education in Zimbabwe played social mobility and social transformation and reproduction functions from colonial times and continued to have an inherent value to Zimbabweans in the postcolonial period. However, with the collapse of the education-employment nexus and structural changes in the opposition movement which offered a transition path from university into party politics until the late 2000s, many school and university graduates did not get to experience social mobility. Accompanied by the wider frustrating conditions, such as bad governance, corruption and economic decline, this resulted in young people reconsidering the social mobility function of education and challenging modernist premises about education. These premises had been reproduced at different levels from family to wider society, and young people started rethinking and challenging them through their narratives, considering curriculum changes to include entrepreneurship education, participation in the informal economy and protest movements, all of which challenge the postcolonial modernity framework.

The future of renewable energy in Iran's energy policy

Renewable energy has become a very important issue in the world. Access problems, high prices, and environmental issues of fossil fuels have caused the world to turn to renewable energy. Using the quantitative-qualitative combined methodology and the theoretical framework of energy security, this research has tried to answer the question of what the future of renewable energy in Iran is. The hypothesis of this research is that despite the adoption of programs and policies for the productivity and development of renewable energy in Iran, sanctions and investment problems make the development of renewable energy in Iran a structural problem. The findings of the research indicate that in the long term, solving structural challenges such as sanctions and investment and encouraging investment in renewable energy can provide a transition path by diversifying energy sources. So, the article tries to analyze the situation of renewable energy in terms of opportunities and challenges and show a vision of the future of this energy in Iran.

Empirical evidence on digitization enabling the transition to a green economy in China.

In the context of the new normal, enhancing digitalization to empower the transition to a green economy is a critical instrument to promote China's economic transition from virtual to real sectors. It is also a necessary approach to realize the high-quality economic development in China. Based on panel data of 282 prefecture-level and above cities in China from 2011 to 2020, the study employs panel regression, spatial metrics, and other methods to explore the impact of urban digitization on the transition to a green economy from the dimensions of direct and indirect transmission mechanism, as well as heterogeneous effects. The findings reveal that digitalization not only exerts a positive effect on the green transition but also generates significant spatial spillover effects. The influence of digitization level on green economic transition exhibits notable regional heterogeneity. Advancement in digitization can foster green economic transition by catalyzing green technological innovation. While digitalization contributes to the green transition by optimizing the structure of energy consumption, its mediating effect is relatively modest. Therefore, it is essential to fortify the supply of digital innovative technology and strengthen digitalization and green technology innovation to jointly facilitate the transition to a green economy. This necessitates the implementation of differentiated development paths for digitization-enabled green economic transition in various regions.

Splitting probabilities as optimal controllers of rare reactive events.

The committor constitutes the primary quantity of interest within chemical kinetics as it is understood to encode the ideal reaction coordinate for a rare reactive event. We show the generative utility of the committor in that it can be used explicitly to produce a reactive trajectory ensemble that exhibits numerically exact statistics as that of the original transition path ensemble. This is done by relating a time-dependent analog of the committor that solves a generalized bridge problem to the splitting probability that solves a boundary value problem under a bistable assumption. By invoking stochastic optimal control and spectral theory, we derive a general form for the optimal controller of a bridge process that connects two metastable states expressed in terms of the splitting probability. This formalism offers an alternative perspective into the role of the committor and its gradients in that they encode force fields that guarantee reactivity, generating trajectories that are statistically identical to the way that a system would react autonomously.

Climate finance-driven feasibility study of a green ammonia and urea production plant in Italy

Ammonia is an essential feedstock widely used in the chemical sector with interesting new potential uses as fuel and hydrogen vector. Most of the produced ammonia is utilized in the manufacturing of urea. Industrial scale production relies on fossil fuels but, considering the energy transition path, a decarbonization of the sector is required. The proposed study developed a techno-economic assessment with an integrated climate finance analysis of a medium scale green ammonia and urea plant located in the South of Italy. Five different scenarios of production, all based on the electrolysis of desalinated water, were evaluated in terms of levelized cost of product, levelized cost of carbon abatement and emission intensity. Based on the output of the analysis, an enhanced scenario was further proposed to maximize the reuse and the monetization of the by-products: this scenario resulted in a competitive levelized cost of products of 640 EUR/ton of ammonia and 415 EUR/ton of urea respectively. A substantial decarbonization of ammonia and urea, with emission intensities well below the limitations set out by the new European standards, was obtained. The methodological approach developed proved climate finance to be a key economic instrument to enable decarbonization.

Calculating the Soil Freezing Characteristic Curve of Saline Soil With Equivalent State of Bulk Solution

AbstractThe relationship between unfrozen water content and temperature, called as soil freezing characteristic curve (SFCC), is of importance for hydrologic, engineering, environmental issues related to frozen soil. The SFCC of saline soil is essentially a result of phase equilibrium of pore solution, which is similar but not identical to that of bulk solution. However, there is still a vacancy of study on the phase equilibrium of pore solution in frozen soil. In this study, image transformation was used to establish the relationship of phase equilibrium between bulk solution and pore solution, with four introduced parameters. Then, the new model of SFCC for saline soil was proposed based on the equivalent state of bulk solution with Pitzer model and SFCC of nonsaline soil. The model was validated by the experimental data from published articles and showed good performance in calculating SFCC of saline soils regardless of soil type, phase transition path, and soil initial water‐salt condition, and some advantages when compared to other three models. All the four introduced parameters have clear physical meanings and their relationships with soil type and initial salt concentration were discussed. Finally, the evolution of phase diagram from bulk solution to pore solution at icing stage was figured out. Further studies are needed for their relationship at salt crystallization stage. Shifting the research perspective from unfrozen water content to pore solution, this study gives a new approach to research of freezing characteristic of saline soil and could promote hydrological and engineering research in cold regions.

Dynamic trade, education and intergenerational inequality

I present a dynamic trade model spanning many countries to explore the transitional paths of trade-induced inequality. By incorporating capital-skill complementarity, human capital accumulation, and capital accumulation, this paper examines the exact transitional path following a shift from autarky to trade. It reveals that trade increases the skill premium, skill share, and real wages for both skilled and unskilled workers in the majority of countries at the steady state. However, the short-term impact of trade on inequality is more pronounced. The exact transitional path indicates that the dynamic of trade-induced inequality is influenced by the flexibility in adjusting factor supplies during the transition at different stages, and education alleviates approximately 50% of trade-induced inequality in the long run. Furthermore, the analysis illuminates the observed patterns of skill premium in recent trade liberalization episodes in Mexico, China, and South Korea, and raises the possibility that globalization may intensify intergenerational inequality.

Techno-productive experiences for climate action in Argentina: Insights from renewable energy projects

The main purpose of this research is to analyze techno-productive experiences within the framework of renewable energy projects based on the use and exploitation of solar energy in a region defined by favorable bioclimatic conditions. Following a primarily qualitative method, the research has been based on four case studies of working groups and their experiences. Stakeholders from diverse origin and background, interested in developing their technologies (processes, inputs, components, equipment) for the use of solar energy have managed to enhance the links among such developments, the productive sector and the communities in the territorial area where they carry out their activities. As a possible path of sociotechnical transition, these specific processes materialize energy transition with the progressive change of production and consumption patterns in favor of climate action.

Transiting toward sustainable development: stochastic convergence of energy diversification using a newly constructed index.

An optimal energy mix is a sine qua non for sustainable development. However, the global energy mix is sub-optimally dominated by fossils which endangers energy security and threatens the attainment of sustainable development. Understanding the convergence of energy series can assist the transition path to optimal energy mix and sustainable development. Thus, research on the convergence of several energy series has gained prominence in recent years. This study extends this important niche in the literature on the convergence of natural resources and environmental series by examining the convergence in energy diversification along several dimensions for a panel of 79 lower-middle, higher-middle, and high-income countries. As a departure from the existing studies, the study employs a novel methodology that allows abrupt or smooth changes through the Fourier approximation of smooth breaks, while including factor structures to test for the presence of unit roots in the relative energy diversification series. The results provide evidence of convergence of the energy diversification series in the majority of the considered countries, with 90% of the sample demonstrating convergence. A disaggregated country analysis was conducted and the findings show that 93% of the lower-middle-income countries are converging, while 95% of the upper-middle-income countries and 87% of the high-income countries are converging. Policy implications of the findings are also discussed.

From sustainability to resilience: tracing the transition path for spatial planning policy in Greece

Sustainability and resilience are currently key analytical concepts with wide acceptance among different disciplines. This study initially attempts a comprehensive analysis of the current policy to specify the meaningful elements for integrating these concepts into spatial planning theory and practice. Then, a critical review of the Greek spatial planning policy aims to shed light on its evolution in relation to the two paradigms. The findings show that the actual shift from sustainability to resilience remains to be observed and that more attention should be focused on the political rather than the administrative aspect of planning.

A first-principles study of the phase transitions in ultrahigh temperature shape memory alloy RuNb

Ultrahigh temperature shape memory alloys (UHT-SMAs) have transition temperatures above 600 °C. They are needed for sensing and actuating devices in aerospace applications. However, very few such UHT-SMAs have been found. Among them are Ru-based alloys such as RuNb and RuTa, whose martensite structures and phase transitions are totally different from those of NiTi-based SMAs and were poorly understood. In this work, we carried out a systematical study of RuNb using first-principles total energy calculations and molecular dynamics (MD) simulations. We revealed the transition paths and mechanisms in cubic → tetragonal → monoclinic transitions. We determined the transition sequence and martensitic transition temperatures (MTTs) by evaluating the Gibbs free energies using thermodynamic integration. The calculated MTTs are in very good agreement with the experimental data. We also found that the monoclinic phase at the second transition has the P21/m symmetry instead of experimentally identified P2/m. The insights gained by this study and the verified ab initio methods for accurate MTT calculations can be applied to fast screen and quantitatively design novel UHT-SMAs having similar properties with desirable MTTs and much reduced cost.

Divergent paths for green transition: regional disparities in technology diversification

ABSTRACT This study explores the regional diversification processes into green technologies (2000–17) for different types of regions. Utilising patent and Eurostat data, we analyse these processes along the economic strength of regions and the nature of their knowledge base. Our findings reveal that both structurally strong and weak regions can successfully diversify into green technologies if they possess related technological capabilities. However, brown regions cannot do so, but regions specialised in both technologies can. While green relatedness density is important for green diversification on average, it becomes less effective in regions with strong specialisation in brown or both technologies.

Dynamical Reweighting for Biased Rare Event Simulations.

Dynamical reweighting techniques aim to recover the correct molecular dynamics from a simulation at a modified potential energy surface. They are important for unbiasing enhanced sampling simulations of molecular rare events. Here, we review the theoretical frameworks of dynamical reweighting for modified potentials. Based on an overview of kinetic models with increasing level of detail, we discuss techniques to reweight two-state dynamics, multistate dynamics, and path integrals. We explore the natural link to transition path sampling and how the effect of nonequilibrium forces can be reweighted. We end by providing an outlook on how dynamical reweighting integrates with techniques for optimizing collective variables and with modern potential energy surfaces.

Agroecological Pathways of Family Farmers in Northern Uruguay

In Uruguay, to address the socio-environmental problems generated by the production model resulting from the Green Revolution, several civil society organizations promoted the creation of a National Agroecology Plan (NAP) in 2015. The enactment of Law No.19.717, declaring a general interest and establishing a National Honorary Commission and a National Plan for the Promotion of Production with Agroecological Bases, along with recent calls from the “Senda Agroecológica” initiative, provide a favorable scenario to envision new production systems with agroecological foundations and pose a challenge for agronomic research. Despite this law defining family farmers as its main beneficiaries and the majority being livestock producers, there are few studies on the role of their technical and organizational practices in agroecological transition and the definition of agroecology. To contribute to filling this gap, the research aimed to identify the role of these practices, both individually and collectively, in defining agroecology and its trajectory. A theoretical framework and methodology were developed to analyze the practices and strategies of family livestock farmers and their relationships with technicians. Situations of change were identified, such as tick biological control and natural field management, through interviews and group work with farmers and technicians. Agroecological transition trajectories were analyzed, considering the role of territories in coordinating actions among diverse actors and establishing new identities and action devices, such as public policies and institutional projects. Results at both individual and collective levels indicate multiple transition paths, dependent on the specific situation of farms and projects. The analyzed cases reveal diversity in transitions without any prevailing. The challenge lies in turning these transformations into drivers of processes towards a strong agroecology, requiring support, assistance and guidance actions in the implementation of public policies.

Convergence analysis for minimum action methods coupled with a finite difference method

Abstract The minimum action method (MAM) is an effective approach to numerically solving minima and minimizers of Freidlin–Wentzell (F-W) action functionals, which is used to study the most probable transition path and probability of the occurrence of transitions for stochastic differential equations (SDEs) with small noise. In this paper, we focus on MAMs based on a finite difference method with nonuniform mesh, and present the convergence analysis of minimums and minimizers of the discrete F-W action functional. The main result shows that the convergence orders of the minimum of the discrete F-W action functional in the cases of multiplicative noises and additive noises are $1/2$ and $1$, respectively. Our main result also reveals the convergence of the stochastic $\theta $-method for SDEs with small noise in terms of large deviations. Numerical experiments are reported to verify the theoretical results.

Longitudinal dynamic envelope solution and transition path optimization based on reachability analysis for fixed-wing VTOL UAVs

Flight velocity and tilt angle are commonly employed to define the safe region for fixed-wing vertical take-off and landing (FW-VTOL) UAVs as they undergo tilting, referred to as the transition corridor. Nevertheless, the transition corridor only considers the aircraft's limitations in a quasi-stationary condition and ignores the additional constraints introduced by the aircraft's kinematic behavior. To obtain a more accurate safe state space, the concept of the dynamic envelope was proposed by previous researchers. The dynamic envelope of UAV represents the safe state space taking into account aerodynamic constraints and kinematic constraints. Solving the dynamic envelope has consistently remained a focal point of research in the field. This study introduces an innovative approach that employs reachability analysis to solve the dynamic envelope of the FW-VTOL UAV during the transition stage. Building upon this, it proposes a safety index for the transition path, optimized to determine the safest transition path. Subsequently, specific case studies verified the effectiveness of the solution process and optimization method. The designed optimal path enhances safety by 9.71% compared to the basic path, signifying its practical significance in mitigating risk during the transition stage of FW-VTOL UAVs. Furthermore, the attributes of the transition path are analyzed based on two aspects: (A) a comparison between the optimal transition path and the two-dimensional transition path with a constant angle of attack; (B) an examination of how key UAV design parameters influence the transition path's safety. Overall, the methodology and general rules proposed in this study provide a theoretical basis and technical support for improving the security of FW-VTOL UAVs in the transition stage.

Kinetic Network in Milestoning: Clustering, Reduction, and Transition Path Analysis.

We present a reduction of the Milestoning (ReM) algorithm to analyze the high-dimensional Milestoning kinetic network. The algorithm reduces the Milestoning network to low dimensions but preserves essential kinetic information, such as local residence time, exit time, and mean first passage time between any two states. This is achieved in three steps. First, nodes (milestones) in the high-dimensional Milestoning network are grouped into clusters based on the metastability identified by an auxiliary continuous-time Markov chain. Our clustering method is applicable not only to time-reversible networks but also to nonreversible networks generated from practical simulations with statistical fluctuations. Second, a reduced network is established via network transformation, containing only the core sets of clusters as nodes. Finally, transition pathways are analyzed in the reduced network based on the transition path theory. The algorithm is illustrated using a toy model and a solvated alanine dipeptide in two and four dihedral angles.