Loop Diagrams Research Articles

Light-light scattering in Very Special Relativity Quantum Electrodynamics and cosmic anisotropies

We consider scattering of light by light in Very Special Relativity (VSR) Quantum Electrodynamics (QED) with a non-zero photon mass. In order to preserve gauge invariance and Sim(2) symmetry we made use of a recently introduced infrared regularization of VSR theories. Additionally, we show that all one loop diagrams with any number of photon external legs and zero fermion legs reduce to the standard QED result with the effective electron mass, as required by unitarity. It follows that the Euler-Heisenberg Lagrangian is the same as in QED. The total cross section of scattering of light by light exhibits tiny anisotropies that could be detected at cosmological scales. In particular, they should be looked at the Cosmic Microwave Background (CMB) Radiation for low photon frequencies.

Connecting the dots in green food purchasing behavior literature: A system thinking approach for systematic literature reviews

AbstractRecent years have been characterized by an ever‐growing interest in consumers' behavior while purchasing green food products. Although existing research has produced a great number of papers on this topic, the knowledge generated in the field appears fragmented and, in certain cases, ambiguous. The main reasons can be traced back to the lack of reference frameworks that clarify the most used concepts, thus providing a shared language in this research domain. Despite other literature reviews that have been carried out on the domain of green food purchasing behavior, these works mainly rely on narrative summaries and qualitative analyses, which can overlook the complexity and interdependencies inherent in this research domain. The complexity of interconnected factors within this research domain poses challenges in effectively understanding and representing the underlying dynamics. To overcome these limitations, this paper proposes the use of a System Thinking based approach as a valuable method to provide a complete view of dynamics occurring in the green consumption behavior domain. In particular, we propose the integration of causal loop diagrams as a powerful visual tool to augment the conventional Systematic Literature Review process to provide a view at a glance of dynamics and capture the complex interdependencies occurring in a specific research domain. We carried out a systematic literature review by analyzing a set of 67 papers. We find nine relevant themes in the investigated research domain. Besides a descriptive picture of the scientific activity, a map of the main dynamics occurring in green food purchasing behavior has been provided.

A systems approach to improving health consideration in UK urban development: a real estate perspective

ABSTRACT This research investigates how population health is considered in urban development decision-making by developing a causal loop diagram from 21 interviews with senior real estate actors. It classifies variables in the model in structural, attitudinal, and transactional dimensions, links them to relevant decision-making actors, and identifies key feedback loops. This enhances understanding of the system and informs intervention strategies for improving the consideration of health. Structural and attitudinal variables are powerful leverage points but are more challenging to influence directly and slower to change. Yet, when activated through a transactional variable, such as enhancing a data-led health metric to increase the ability of stakeholders to include health in planning, investment and development decisions, they generate virtuous feedback loops. These drive and sustain decision-making that shapes a healthier built environment.

A system dynamics approach to plan strategy for managing factors influencing safety hazards on construction sites in developing countries

In order to improve site performance, this research paper seeks to identify safety-related risks related to construction workers on construction sites and to design a system dynamics model to handle the complexities of these hazards. The study uses causal loop diagrams (CLDs) to show how different elements that contribute to safety concerns are related to one another. The system dynamics (SD) model was built with the help of the five reinforcing and two balancing loops that the CLD analysis revealed. “Lack of Managerial Interest,” “Unforeseen Circumstances,” “Lack of Personal Protective Equipment,” “Knowledge Regarding Appropriate Hazards,” and “Innovative Technologies on Safety Measures” are the five main stocks that make up the SD model. The results show that two important factors impacting safety dangers are the sluggish adoption of innovative safety technologies and the lack of personal protective equipment. This study offers construction companies a methodology for quickly and effectively identifying and addressing safety issues.

Systems Thinking, Causal Loop Diagram, and Systems Dynamic in Public Health Challenges: Navigating Long COVID Syndrome and Sense of Smell in LGBTQIA+ Communities

ABSTRACTBackgroundThe coronavirus pandemic has profoundly affected global health, economic stability, and environmental sustainability. Despite these challenges, significant gaps in data remain, particularly in effectively assessing and engaging diverse communities such as color, LGBTQIA+ individuals, and low‐income groups. This shortage of comprehensive research limits our capacity to undertake sensitive studies, specifically in dealing with the complexities of long COVID, which some individuals continue to suffer from after their initial recovery.ObjectiveThis review delves into the ongoing repercussions of long‐term COVID‐19, a postinfectious syndrome marked by neurological symptoms such as cognitive deficits and sensory impairments, which may last well beyond the acute phase of the illness. These symptoms frequently overlap with mental health issues (e.g., anxiety and depression), which can aggravate the socioeconomic challenges faced by vulnerable populations, especially within the LGBTQA+ communities.MethodsTo tackle these complex interactions, we have introduced a novel public health framework: model‐based systems thinking (MBST), which incorporates System Dynamics and causal loop diagrams (CLD).Results and DiscussionThe articles were selected on the basis of their discussion of COVID‐19‐associated anosmia, exploration of olfactory dysfunction alongside neurocognitive disorders, and the challenges experienced in LGBQA+ communities. This approach offers a robust framework for dissecting the intricate ties between socioeconomic factors, health outcomes, and the extended recovery trajectories associated with long‐term COVID‐19, with a particular focus on olfactory dysfunction. We also explore strategies to make our models more accessible to healthcare providers and the LGBTQA+ communities, encouraging its broader adoption.ConclusionLong COVID's impact on public health and marginalized communities highlights the urgent need for adopting systems thinking models. Additionally, this article calls for a concerted effort from all experts to foster multidisciplinary, team‐based research and implement effective support measures for COVID‐19 survivors across all communities, mainly focusing on the scientific, social, and behavioral challenges LGBTQIA+ and low‐income individuals face.

Investigating the Impacts of Carbon Pricing Mechanism on CCS development in ASEAN countries

Abstract Carbon Capture and Storage (CCS) is a technology that contributes toward a reduction in carbon dioxide (CO2) emissions from large point sources. It has been proven to be a crucial technology to decarbonise ASEAN’s hard-to-abate industry sector. ASEAN countries are a concentrated cluster, contributing to significant emissions, and provides the potential for suitable geological storage for CCS according to current studies. This paper discusses the impact of carbon pricing on the CCS development in ASEAN countries, through studying factors that enable or disable successful CCS projects. Causal Loop Diagram (CLD), as a part of system dynamics, was employed as an analytical tool to identify and visualize the key variables, system’s structure, the network of existing carbon pricing mechanisms and other financing instruments needed in CCS deployment. The results of this study indicate that strong public and private finance, the development of carbon markets, and carbon pricing policies are the key enablers for CCS projects in ASEAN. Carbon pricing should be viewed as an effective catalyst that helps the growth of CCS with the right policies in place, government and regulatory support, and market forces.

Qualitative system dynamics modelling to support the design and implementation of tuberculosis infection prevention and control measures in South African primary health care facilities.

Tuberculosis infection prevention and control (TB IPC) measures are a cornerstone of policy, but measures are diverse and variably implemented. Limited attention has been paid to the health system environment which influences successful implementation of these measures. We used qualitative system dynamics and group-model-building methods 1) develop a qualitative causal map of the interlinked drivers of Mycobacterium tuberculosis (Mtb) transmission in South African primary health care facilities which in turn, helped us to 2) identify plausible IPC interventions to reduce risk of transmission. Two one-day participatory workshops were held in 2019 with policy- and decision-makers at national and provincial level, and patient advocates and health professionals at clinic and district level. Causal loop diagrams were generated by participants and combined by investigators. The research team reviewed diagrams to identify the drivers of nosocomial transmission of Mtb in primary health care facilities. Interventions proposed by participants were mapped onto diagrams to identify anticipated mechanisms of action and effect. Three systemic drivers were identified: 1) Mtb nosocomial transmission is driven by bottlenecks in patient flow at given times; 2) IPC implementation and clinic processes are anchored within a staff "culture of nominal compliance"; and 3) limited systems-learning at policy level inhibits effective clinic management and IPC implementation. Interventions prioritised by workshop participants included infrastructural, organisational, and behavioural strategies that target three areas: 1) improve air quality; 2) improve use of personal protective equipment; and 3) reduce the number of individuals in the clinic. In addition to core mechanisms, participants elaborated specific additional enablers that would help sustain implementation. Qualitative system dynamics modelling (SDM) methods allowed us to capture stakeholder views and potential solutions to address the problem of sub-optimal TB IPC implementation. The participatory elements of SDM facilitated problem-solving and inclusion of multiple factors frequently neglected when considering implementation.

Understanding Socio-Ecological Complexity of Mangrove-Crocodile-Fisher System of Bugsuk Island, Balabac, Palawan, the Philippines

The mangrove forest in Palawan has the most extensive distribution in the Philippines. The fisher community's perception of the mangrove forest as a known habitat for saltwater crocodiles (Crocodylus porosus) and its fishery benefits in Bugsuk Island were gathered using a participatory systems mental modeling framework for the coastal social-ecological system. From the causal loop diagram, six reinforcing and one balancing feedback loop were derived. The respondents observed a positive growth in the interaction between mangroves and crocodiles in Bugsuk Island, with both populations expanding and providing support to fishery resources. Bugsuk Island represents a unique diversity with great potential for resource conservation and economic benefit.

Evaluating the dynamics of fee-free higher education in South Africa: a causal loop diagram approach

Background This research investigated the dynamics of fee-free higher education in South Africa, aiming to elucidate the complexities surrounding its implementation and impact. By employing a causal loop diagram approach, the study examined the interplay of socioeconomic, political, and institutional factors influencing the provision of fee-free higher education. Method A participatory approach to developing the CLD was used. Through an extensive literature review, the research contextualised fee-free higher education enabling a preliminary CLD to be developed. Discussions were held to improve the preliminary model based on stakeholder and expert opinion. The model was then validated by stakeholders and experts. Results The CLD has explicitly mapped out the causal relationships which play a fundamental role in fee-free higher education in South Africa. Key findings revealed that fee-free higher education initiatives, such as managing funding constraints and administrative complexities, hold promise for fostering inclusivity and socioeconomic development but are hindered by bureaucratic policy establishments and inefficiencies. These challenges underscore the gap between policy formulation and implementation, highlighting the need for comprehensive reforms to streamline administrative processes and enhance financial sustainability within the higher education sector. Conclusion This research thoroughly examined the dynamics of fee-free higher education in South Africa, highlighting both the challenges and opportunities in its implementation. The study emphasized the need for systemic reforms to improve accessibility and effectiveness, while also underscoring the potential of such initiatives to promote social mobility and economic empowerment, aligning with global goals like the SDGs and the African Agenda 2063.

Modeling with a municipality: Exploring robust policies to foster climate-neutral mobility

Many European cities are investigating how to transition to climate-neutral transport systems. Due to the transport system’s complexity and uncertainty about the future, identifying drivers and choosing effective policies to make the city more sustainable is challenging. Additionally, the chosen policies need to be supported by relevant actors. This study aims to support the municipality of The Hague in generating robust policies supported by and within the municipality. We build on participatory modeling and decision-making under deep uncertainty to create a novel approach to address this goal. In two workshops, the participants formulated goals and objectives, created Causal Loop diagrams, and identified potential interventions. Using a set of possible futures, the interventions were then stress-tested to evaluate their robustness. By explicitly linking, for the first time, participatory modeling and decision-making under deep uncertainty approaches, the participants could understand the system better and deal with uncertainty. Participants gained insight into systemic complexity and methods to deal with it, the inter-relatedness of interventions and their effects, and a shared understanding of the problem and its scope. This study demonstrates the potential of a novel approach to generate supported robust interventions to achieve the goal of a climate-neutral transport system.

Towards sustainable urban logistics: Exploring the implementation of city hubs through system dynamics

The urban logistics system causes negative externalities, such as pollution, noise and congestion. This study focuses on city hubs as a concept to reduce these externalities by improving consolidation and adopting zero-emission vehicles. Our research employs system dynamics as a method to uncover the dynamics and mechanisms related to the barriers and potentials of city hub implementation in Stockholm from the perspectives of the Logistic Service Providers (LSPs), the receivers and the public sector. Moreover, a mixed method approach is used for data collection, allowing us to extract the knowledge from the real implementation case, co-create a qualitative model as a Causal Loop Diagram (CLD) with the stakeholders involved in the system, and generalise the model. The mixed method approach includes a group model-building workshop, literature review, existing city hub analysis and stakeholder interviews. The main result is a CLD, visualising the dynamics of the introduction of city hubs. The CLD explores three potential incentives and policies: (i) the receivers change address; (ii) shippers oblige LSPs to use the hubs; (iii) the public sector gives monetary incentives to LSPs. The CLD presented in this paper establishes a validated system structure for the urban logistic system and facilitates the policymakers’ understanding of the barriers to implementing city hubs and what policies could help their implementation.

Loops in AdS: from the spectral representation to position space. Part III

We study loop amplitudes in anti de-Sitter space via the spectral representation. We consider loops of spinning fields and in particular gauge fields, and derive various identities connecting different families of loop diagrams, at different number of loops, different spins, different masses. Such identities are useful for the computation of Witten diagrams. Considering the theory of large-Nf conformal scalar QED defined on AdS space, we derive an analytic expression for the exact 4-point correlation function at sub-leading order in 1Nf\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\frac{1}{N_f} $$\\end{document}. Additionally, we derive analytic expressions for bulk 2-point functions and boundary 4-point functions for various families of diagrams, which we denote as “blob diagrams”. Finally we study 4-point ladder diagrams with spinning fields, and we derive integral expressions for the spectral representation of a k-loop ladder diagram.

Role of the short-distance interaction in e+e−→γX(3872)

In this study, we analyze the cross-section data from the e+e−→γJ/ψω process to explore both short-distance and long-distance interactions for the radiative transition Y(4200)→γX(3872). We investigate the short-distance effects through the E1 transition among the cc¯ components, and the long-distance effects via hadronic loop diagrams. Our numerical analysis reveals that short-distance interactions play a significantly larger role in the radiative transition than that of the long-distance interactions. This finding underscores the importance of the compact cc¯ components in both the initial and the final states for accurately understanding the cross-section σ[e+e−→γJ/ψω]. Furthermore, with the help of relative branch ratio R we estimate the Γ[Y(4200)→γX(3872)] implied in the experimental study. Finally, we also discuss the possible existence of the ψ(4040) signal within the cross-section data. Published by the American Physical Society 2024

Everlasting interaction: Polarization summation without a Landau pole

We propose an external field approach to evaluating effective action allowing the interaction to act everywhere at all times (everlasting). Requiring that the asymptotic gauge fields are always interacting, we implement displacement fields encoding polarization corrections into the derivation of effective action. The result is a novel polarization summation for one-cut reducible loop diagrams, which can be applied to two cases: transient quasiconstant electromagnetic fields and everlasting interactions. In the first case, a perturbative expansion of our result recovers the Schwinger-Dyson reducible diagram series with a Landau pole. The everlasting summation evaluated in nonperturbative fashion removes the Landau pole, providing a new avenue for modeling strongly interacting theories. Published by the American Physical Society 2024

ACL Injury Etiology in Its Context: A Systems Thinking, Group Model Building Approach.

Background/Objectives: Given the complex nature of Anterior Cruciate Ligament (ACL) injury, it is important to analyze its etiology with suitable approaches in order to formulate intervention strategies for effective prevention. The present study employs system thinking techniques to develop a Causal Loop Diagram (CLD) Model for investigating the risk factors for ACL Injury (CLD-ACLI), through a Group Model Building approach. Methods: A two-stage procedure was applied involving a comprehensive literature review followed by several systems thinking group-modeling co-creation workshops with stakeholders. Results: Based on input from experts and stakeholders, combined with the latest scientific findings, the derived CLD-ACLI model revealed a series of interesting complex nonlinear interrelationships causal loops between the likelihood of ACL injury and the number of risk factors. Particularly, the interaction among institutional, psychological, neurocognitive, neuromuscular, malalignment factors, and trauma history seem to affect neuromuscular control, which subsequently may alter the biomechanics of landing, predisposing the ACL to injury. Further, according to the proposed CLD-ACLI model, the risk for injury may increase further if specific environmental and anatomical factors affect the shear forces imposed on the ACL. Conclusions: The proposed CLD-ACLI model constitutes a rigorous useful conceptual presentation agreed upon among experts on the dynamic interactions among potential intrinsic and extrinsic risk factors for ACL injury. The presented causal loop model constitutes a vital step for developing a validated quantitative system dynamics simulation model for evaluating ACL injury-prevention strategies prior to implementation.

A systems thinking framework for understanding rising childhood obesity in the Caribbean

ObjectiveThe aim of this study is to develop a systems thinking framework to describe the common complexities of childhood obesity in the Caribbean region and identify potential areas of intervention.MethodsGroup model building (GMB) is a form of systems science. Trained GMB facilitators in Puerto Rico, the US Virgin Islands, Barbados, and Trinidad and Tobago convened a group of multi-disciplinary stakeholders in a series of virtual meetings in 2021 to elaborate a hypothesis of the system driving childhood obesity represented by causal loop diagrams (CLD). Commonalities and differences between the CLDs from each island were identified and reconciled to create a synthesized CLD.ResultsA single explanatory CLD across the islands was developed and includes nine reinforcing loops. These loops addressed the interconnected role of schools, policy, commercial determinants, community and the personal experience of the child in rising childhood obesity rates.ConclusionsDespite differences across settings, there is a core system driving childhood obesity in the Caribbean, as described by stakeholders in GMB workshops. Policy solutions to the problem must be multi-faceted and multi-level to address the interlinked reinforcing loops of the complex system and reduce rates of childhood obesity.

Impact of digital logistics platforms to facilitate more regional food in the hospitality sector and communal catering

PurposeThis paper studies digitalization projects aiming to increase the share of regional food in the hospitality sector and communal catering. The focus is set on influencing factors and underlying feedback structures that arise through the digitalization of regional food supplies. The results can guide stakeholders to get a better understanding of key influencing factors and complexities from a holistic perspective.Design/methodology/approachA systems thinking approach is employed to model regional food networks. The influencing factors were found in the literature and in two model regions. Feedback loops and underlying structures were explained and validated through semi-structured interviews. Findings are visualized in causal loop diagrams (CLDs) and are used for theory development.FindingsThe presentation in CLDs helps understanding the influence of digital logistics platforms on the entire system of regional food supply and not just on isolated parts. Among others, cooperation, trust and digital solutions were identified as key success factors when aiming to increase the share of regional food in the hospitality sector and communal catering.Research limitations/implicationsThe work focused on the underlying feedback structures occurring in regional food supply in two, rural Bavarian regions in Germany with their unique geographical settings. Findings may, consequently, not be entirely transferable to other regions with varying characteristics. Further research needs to be done to see how much these regional parameters influence digital logistics platforms.Originality/valueThe paper contributes to the existing scientific literature by showing the impact coming from digital logistics platforms on regional food supply systems. Developing CLDs provides a basis for future work and facilitates discussion for researchers and practitioners to support future real-world implementations.

Identifying vulnerabilities in essential health services: Analysing the effects of system shocks on childhood vaccination delivery in Lebanon

Shocks effects are under-theorised in the growing literature on health system resilience. Existing work has focused on the effects of single shocks on discrete elements within the health system, typically at national level. Using qualitative system dynamics, we explored how effects of multiple shocks interacted across system levels and combined with existing vulnerabilities to produce effects on essential health services delivery, through the prism of a case study on childhood vaccination in Lebanon. Lebanon has experienced a series of shocks in recent years, including large-scale refugee arrivals from neighbouring Syria, the COVID-19 pandemic and a political-economic crisis. We developed a causal loop diagram (CLD) to explore the effects of each shock individually, and in combination. The CLD was developed and validated using qualitative data from interviews with 38 stakeholders working in Lebanon's vaccination delivery system, in roles ranging from national level policy to facility-level service delivery, conducted between February 2020 and January 2022.We found that each of the shocks had different effects on service demand- and supply-side dynamics. These effects cascaded from national through to local levels. Both Syrian refugee movement and the COVID-19 pandemic primarily exposed vulnerabilities in service demand, mainly through slowly emerging knock-on effects on vaccination uptake behaviour among host communities, and fear of contracting infection in crowded health facilities respectively. The economic crisis exposed wider system vulnerabilities, including demand for vaccination as household income collapsed, and supply-side effects such as reduced clinic time for vaccination, declining workforce retention, and reduced availability of viable vaccine doses, among others. Finally, important pathways of interaction between shocks were identified, particularly affecting the balance between demand for vaccination through publicly supported facilities and private clinics. Future research should incorporate dynamic approaches to identifying within-system vulnerabilities and their potential impacts under different scenarios, as a precursor to improved resilience measurement, system preparedness, and intervention targeting.

Sustainable Transportation Solutions for Intelligent Mobility: A Focus on Renewable Energy and Technological Advancements for Electric Vehicles (EVs) and Flying Cars

(1) Introduction: Transportation logistics play a pivotal role in facilitating both individual mobility and supply chain operations on a global scale. However, conventional transportation systems have contributed significantly to urban congestion and environmental degradation. In response to these challenges, there is growing momentum to investigate the potential of renewable energy to power electric vehicles (EVs) and flying automobiles, aiming to reduce fossil fuel dependence and carbon emissions. (2) Objectives: By analyzing key drivers and opportunities for integrating flying vehicles into existing infrastructure through dynamic modeling, this study seeks to accelerate the transition to sustainable transportation. (3) Methodology: A mixed-method approach, combining literature review and causal loop diagram analysis, is employed to understand the factors influencing EV and flying car adoption. (4) Results: Findings highlight the significant potential of renewable energy in reducing emissions and reliance on fossil fuels through widespread EV and flying vehicle adoption. The major drivers and challenges in infrastructure, safety, and airspace management are also identified. In addition, this research emphasizes the importance of sustainable transportation in addressing urban congestion, pollution, and energy security. (5) Conclusions: By leveraging renewable energy and embracing technological advancements, a low-carbon future for transportation can be achieved, benefiting both the environment and society.

Systems thinking for local food environments: a participatory approach identifying leverage points and actions for healthy and sustainable transformations

BackgroundCurrent local food environments encourage poor diets, posing a significant threat to public and planetary health. Acknowledging and addressing its inherent complexity is vital to making meaningful improvements to the food environment. Using a participatory approach with local stakeholders, this study aims to gain insight into the factors and mechanisms underlying the local food environment and to identify leverage points and system-based actions to foster healthy and sustainable local food environments.MethodsA systems-thinking approach was used in a Dutch municipality in 2022. Two group model building (GMB) workshops were held with community stakeholders (e.g. local policymakers, retailers and residents). During the first workshop (June 2022), factors and mechanisms influencing the local food environment were identified and visualized through a causal loop diagram (CLD). During the second workshop, leverage points and system-based actions to improve food environments were identified by the stakeholders. Four months after (October 2022), an action-implementation meeting was organized to stimulate the implementation of selected actions. Progress was monitored through brief telephone interviews 6 and 12 months after the second workshop.ResultsThe CLD visualises the factors and mechanisms influencing the local food environment from the point of view of the community stakeholders. The CLD consists of 46 factors shaping the local food environment, which were categorized into four identified subsystems: societal factors, individual, socio-economic factors, commercial factors and political factors. Eight leverage points were identified within the CLD, for example, ‘lobby from food industry’, ‘governmental food policies’ and ‘e-commerce and platform economy’. Stakeholders formulated 20 actions targeting the identified leverage points. During the action-implementation meeting, long-term plans were created for five actions. After 1 year, only one participant (policy advisory role) remained actively engaged in three of these actions.ConclusionsThis study yields insight into the numerous factors and mechanisms underlying the local food environment and identified system-based actions as perceived by local stakeholders to improve this food environment locally. The CLD offers stakeholders valuable insights on employing a systems approach when enhancing food environments. More research is necessary, especially into the long-term processes and effects of implementing system-oriented actions to improve local food environments.