Ebook: Leveraging Transdisciplinary Engineering in a Changing and Connected World
Simple problems have become rare in today’s technologically advanced world. Problems are typically much more complex, and solving them requires integrative knowledge from several disciplines. Technology alone cannot be the answer. Collaborative teams equipped with knowledge and skills in various disciplines are indispensable to exploit technologies effectively and create new conceptual, theoretical, methodological, and translational innovations that integrate and move beyond discipline-specific approaches to address a common problem in the changing and connected world.
This book presents the proceedings of TE2023, the 30th International Conference on Transdisciplinary Engineering, held in Hua Hin Cha Am, Thailand from 11-14 July 2023. The theme of this year’s conference was Leveraging Transdisciplinary Engineering in a Changing and Connected World, and it provided a forum for more than 115 participants from academia and industry to exchange knowledge and ideas connected to this aspect of transdisciplinary engineering. A total 117 submissions were received for the conference, of which 93 were selected for presentation and publication here following a rigorous abstract and full-paper review process. They are arranged under 7 categories: product design and development; team working; smart operations for value chain management; transdisciplinary approaches; engineering education; critical issues in transdisciplinary engineering; and theoretical contributions.
Providing a comprehensive overview of the latest innovations and ideas in transdisciplinary engineering, the book will be of interest to all those working in the field.
We are delighted to disseminate through this proceedings a collection of peer-reviewed papers presented at the 30th ISTE International Conference on Transdisciplinary Engineering (TE2023), held during July 11–14, 2023, at Dusit Thani Hotel in Hua Hin Cha Am, Thailand. The conference was organized by the A-Cube Research Group at Asian Institute of Technology, Thailand, and in collaboration with the International Society of Transdisciplinary Engineering (ISTE) and ReCap 4.0 Consortium with the support of the Erasmus+ Program of the European Union.
TE2023 brought together more than 115 participants from reputed educational institutes and well-known global corporates located in twenty countries on five continents to set an international forum for academic people and interested industry professionals to exchange their knowledge and ideas connected to the conference theme “Leveraging Transdisciplinary Engineering in a Changing and Connected World.”
As we are experiencing, technological advancement has created a new landscape for how business functions and exposed individuals to an open, connected world. The unexpected pandemic has further expedited the need for change. All industrial, business, and education sectors have been challenged and have already begun to leverage technologies to improve operational performance. We all are experiencing a wind of change. An open, connected world allows us to access things in the blink of an eye. An open, connected world opens a door of opportunity for great ideas. An open, connected world can also turn those who remain in the status quo to be the history of tomorrow. It will no longer be a trade-off between quality and speed for a business in an open, connected world. They both must be there. Those who cannot deliver them will be gone with the wind because someone somewhere will. That is the power of an open, connected world.
Therefore, straightforward, simple problems have become rare in practice in today’s world. Problems that await us to solve are much more complex and require integrative knowledge from several disciplines. Technology alone cannot be the answer. Collaborative teams of people with an agile mindset, the ability to see a holistic picture and equipped with knowledge and skills in various disciplines are indispensable to exploit the technologies effectively to create new conceptual, theoretical, methodological, and translational innovations that integrate and move beyond discipline-specific approaches to address a common problem in the changing and connected world. That is how vital Transdisciplinary Engineering is today. That is why we were together to share experiences, brainstorm, and redraw our identity and boundary of belonging.
Besides parallel paper presentation sessions contributing to the proceedings, five prominent international and local speakers shared their valuable experiences and insights with our participants in the keynote sessions, covering different aspects, from economy to industry to technology to design and education. The ISTE also ran a panel discussion to solidify ideas to define Transdisciplinary Engineering. Some of our participants also offered their expertise in interesting workshop sessions, and some shared their recent works in a poster session. Contributions in all aspects from all parties made this TE2023 successful.
This proceedings contains 93 articles that passed through abstract and full paper review processes and were invited for oral presentation at TE2023. They were selected from among 117 submissions of full papers and are arranged according to the conference program covering 7 main categories: Product Design and Development, Team Working, Smart Operations for Value Chain Management, Transdisciplinary Approaches, Engineering Education, Critical Issues in Transdisciplinary Engineering, and Theoretical Contributions. According to the word cloud of the titles of the full papers submitted, design is the most popular word, followed by digital, transdisciplinary, and engineering. In fact, design and transdisciplinary have been in the top five of popular words for the last few TE conferences reflecting how transdisciplinary engineering strongly connects and contributes to support various aspects of design that have become much more complicated in today’s open, connected world. Digital, another popular word, reveals our community is pursuing digital technology-related research to support smart operations for value chain management. It is worth noting that words related to education appear more often in the titles. Few of them are in the top ten, however, which gives an insight into the importance of incorporating transdisciplinarity in modern engineering education.
Pisut Koomsap
Adam Cooper
Josip Stjepandić
Beatfit, a personal fitness app launched in 2018, had a problem with users not being able to find and continue with the best workout contents due to the increasing number of contents. This paper argues how personalization system on the mobile app has improved user engagement and changed consumer behaviors under the context of health care industry. The author found that: (1) “the time of day the app is opened and the theme of the content matches” influences behavior change. (2) For users who have played the app less than 5 times since they started using it, it is important that the titles and attributes of the content match the interests of the users obtained from the interviews system. (3) For users who have started using the app more than 5 times, it is important to recommend classes that are preferred by loyal users with similar tastes through collaborative filtering. Aristol Inc developed the recommendation system reflecting these findings and released to mobile applications, resulting in a 1.5x increase in engagement. In this study, we utilized data from Beatfit, a digital healthcare service, a fitness version of “Netflix” developed to prevent lifestyle-related diseases caused by lack of exercise. We believe that the recommendation system approach we developed can be used in the future not only to reduce inactivity, but also to address other health management issues such as smoking cessation, weight loss, and stress management.
Mobile application marketing has taken the approach of maximizing the time spent using the application. However, in the realization of exercise habits, the more important indicator is how habitually they use applications. This study proposes to develop a “habitation score”, a quantitative measure of application use habits in order to improve the persistence rate of application use. The authors calculated a “habitation score” from the following process. Firstly, feature extraction from profile data and behavioral data. Secondly, six variables including the indicator of habitation were selected from the data characteristics as explanatory variables. Finally based on the explanatory variables, a habitation score was calculated using logistic regression model. Through this development, the authors found two things. One is that the smaller the change in usage frequency, the closer it gets to habit formation. The other is that using the application at multiple times during the day and engaging in multiple categories of exercise had a positive impact on habit formation. Furthermore, we confirmed that “habituation score” had more influence on the subscription retention rate than the time spent during a certain period. This study examined the subject matter of “Beatfit”, on-demand fitness service on a smartphone application to help users achieve their exercise habits. This study is expected to be applied not only to the healthcare domain, but also to a variety of subscription-based services where habit formation is important.
Cyber-physical-human systems (CPHS) represent significant extensions of cyber-physical systems (CPS) to include aspects of human interactions and usage. A class of CPHS of interest here is smart products that offer services to their customers, supported by back-end systems (e.g., information, finance) and other infrastructure. We argue that although the domain of CPS relies on engineering and computer science as its foundations, the emerging field of CPHS does not have an underlying scientific foundation. Transdisciplinary teams of researchers are needed to integrate the engineering, computing, and human behavioral fields that are central to CPHS to develop new foundational theory and methodology. Furthermore, a new design methodology is needed for CPHS, given the transdisciplinary nature of the field, that anticipates human acceptability and usability considerations as well as emerging behaviors that result from human-system interactions. In this paper, we propose a framework for such a design methodology. The domain of assistive and rehabilitation technology is used in this paper to provide an example field of practice that could benefit from a systematic design methodology. A CPHS design example is provided to illustrate the application of the methodology framework.
A bill of materials (BOM) is a representation of the structure of parts and components in a product. The most well-known ones are the engineering (EBOM) and the manufacturing (MBOM). However, there are several more with various purposes throughout the lifecycle of the product. All BOMs are related to the part and component structure of the product but focus on different life cycle phases. They are often individually defined in product development creating a fragmented process. In this paper it is proposed to instead define a “master BOM” It is cross functional and includes all life cycle items. The master BOM has impact on the IT environment of a company as well as the organization of the work. In this paper, the creation and management of BOMs have been investigated in an industrial company. The IT environment of the company is currently heterogeneous, but there is a change towards a PLM centric environment. Results indicate that changing the IT environment and the structure of BOMs can integrate the different domains of the company better and facilitate the early phase assessment of the environmental impact of the products.
In recent decades industrial development has led to increasingly sophisticated machinery and systems, which require complex maintenance routines. Consequently, maintenance operators may not have the sufficient skills to perform recovery procedures properly and quickly, so that the need of assistance from the manufacturer’s after-sales service or companies specialized in maintenance services. Such actions usually lead to very long recovery times, high maintenance costs, and a temporary drop in production. In this scenario, we should consider that Industry 4.0 is making available innovative technologies, such as Augmented Reality (AR), suitable for improving the skills and competencies of operators without burdening their cognitive load, and consequently wellbeing. However, technologies must be selected, designed, and used according to the users’ needs to be effective and useful. The paper presents a user experience (UX)-driven methodology for designing user-centric AR applications for complex maintenance procedures. The methodology was applied to a real industrial case concerning the management of CNC machines in a plant producing tractors components, where a smartphone-based AR application was designed and tested with users. The satisfactory results highlighted the potential benefits of AR in industry and specifically in maintenance.
The main objective of this article is to structure and clarify the transdisciplinary reality of modularization as a foundation for handling business-driven modularization of smart products. Lately, the complexity has increased in the industry due to global manufacturing, different customer requirements, legal requirements, digitalization, new business models, and the evolvement of smart products. The increasingly complex reality has been acknowledged on an enterprise engineering level where complexity is one part of different grand challenges for enterprises. This complexity needs to be handled both horizontally (in the whole value chain) and vertically (on all management levels). It is therefore essential to clarify the modularization landscape by bringing together the business domain, and the engineering domain to cater for the future of modularization. The main contribution of this paper is to suggest a conceptualization of the modularization domain through a meta-model that covers essential aspects of business-driven modularization of smart products.
When designing light aircraft, the designer should take into account many different factors from various fields, such as aerodynamics, structural strength, flight mechanics, etc., from the conception stage. To perform advanced analyzes during development and optimisation work, it is usually necessary to quickly generate an aircraft model in the CAD environment. Such a primary geometric form is the input model for further analyses. The paper presents a method of quick generation of the CAD model including the conceptual form of the aircraft. The model is created on the basis of previously identified assumptions and construction rules used in the design of aircraft. The rules are based on integrated information from the fields of aircraft design, aerodynamics, and flight mechanics, as well as good engineering practises and aviation regulations. The structure of the information and the way of its integration into the CAD model were presented. Generative modelling is used to generate the CAD model. The model also includes strength verification algorithms, which are commonly used in conceptual design. The geometric model is based on a hierarchical structure adapted for reuse. The structure of the model is simplified for the purposes of preliminary model generation, but has the potential for further extensive development and refinement. This basic geometry can be used for further development and refinement. The paper also presents the verification of the method on the example of ready-made commercial aircraft and glider structures, starting from classic structures and ending with structures with the best performance used in air sports.
Product realization is inherently transdisciplinary, resulting in the need for different functions to collaborate. However, collaboration can be hindered by boundaries, arising from differences and dependencies in knowledge. One way to integrate knowledge across these boundaries is through the use of so-called boundary objects. However, boundary objects are situational, meaning that different aspects can affect whether an object functions as a boundary object or not. Based on a systematic literature review, this paper presents a comprehensive overview of different aspects that need to be considered for an object to function as a boundary object in the context of product realization. The aspects were divided into properties relating to the object, and situational aspects connecting to the situation in which the object is used. The paper further shows the role that interplay between aspects plays, and how it can be accounted for.
Adaptive automation, the scheme to allocate power of control between the automation system and the human operator dynamically and flexibly depending on situations, has been studied in multiple disciplines recently. It is expected to alleviate the Out-Of-The-Loop (OOTL) phenomenon of human operators through occasional handover. However, the effectiveness and impacts of adaptive automation on human pilots in aviation scenarios are still unrevealed. To partially fill this gap, this study will investigate how the preset handover affects pilots’ emergency-handling performance and psychophysiological alteration. The emergency-handling performance will be measured by the aircraft control behaviours recorded by the flight simulator, and the psychophysiological alteration will be assessed based on eye movements recorded by the eye-tracker. Twenty-six student pilots were recruited to participate in a comparative experiment consisting of two simulation flight tasks in a flight simulator. Compared with the control flight which performs autopilot during the whole cruising phase, the adaptive automation mode requires the pilots to conduct twice manual piloting at preset time points. Finally, an identical engine shutdown is triggered in each flight to assess the pilots’ emergency-handling performance. As a result, the aircraft control behaviours data of the adaptive automation mode demonstrates a significant superiority and the eye movements data also presents several indicative divergences. This study reveals the natural human responses to the handover between autopilots and human pilots. The results can serve as a foundation for further developing the autopilot into the adaptive automation paradigm.
It is well acknowledged that DfAM requires a comprehensive understanding of materials, processes and parameters, and the associated geometric opportunities and limitations. The holistic knowledge required for efficient DfAM poses a major challenge to the progression of industrial applications of additive manufacturing (AM). Whilst AM offers enhanced geometric freedom during the design process, the psychological inertia of long-standing subtractive approaches is retained in the design thinking of the engineering community and inherent in computer aided design (CAD). To create an axisymmetric form about a curved axis defined in 3D-space, the traditional method enabled by CAD is to define a centreline and/or a series of cross-sections. However, this process is constrained by the planar nature of the sketch function and can be highly time-consuming. This paper proposes a novel approach, using a mathematical framework that has proved useful in the modelling of living tissue, to enable the parametric design of axisymmetric forms. The mathematical methodologies will be presented as follows: a length-polar-projection description of the centreline and specification of the axisymmetric cross-sections. This transdisciplinary approach was developed between the disciplines of mathematics, biology and engineering. As such, it offers a completely novel, more efficient and insightful process than current commercial approaches. The results of this study offer two contributions to research knowledge: time-efficient, parametric generation of complex axisymmetric geometries defined in 3D and a process by which to upskill knowledge of the design engineer.
A vast body of research has described product platforms as strategic enablers for increased business competitiveness, but there is a lack of empirical research describing what types of assets that are used in industry as elements in a platform. Previous research has suggested a platform as a “collection of assets shared by a group of products” and also classified these assets into four transdisciplinary categories: Components, Processes, Knowledge and People and Relationships. This categorization is, however, too imprecise to identify the core assets needed to build a platform, and better guidance is needed. This paper presents a cross-case study of assets used in the product development process at two case companies. These represent two different product disciplines: Industrialized housebuilding, a sector within the construction trade, and Outdoor Power Equipment producing forest and gardening tools. The main contribution of the paper is a comparison of what formal and informal design assets that are used in the two disciplines.
Industrialized housebuilding (IHB) is a sector within the construction trade where product platforms have been introduced from the mechanical industry to manage the product architecture and allow mass customization. The aim of this study is to analyze product development projects connected to the product platform and the production. For IHB, the backbone is a technical platform where components are designed and combined. Clients are satisfied, avoiding compromising the technical platform and the product architecture of the different variants. However, the adaptation to production is decisive and production has increased automation, with less flexibility in relation to the products. Still, product development has focused on the engineering view and the development of building components which fit in the predefined or well-established production facility while at the same time satisfy customer demands, i.e., maintaining the balance between distinctiveness and commonality. The study has observed one IHB company and two of their development projects focusing on changes in the product architecture for components across several of their product families. The development has been carried out in a bottom-up fashion. The results indicate difficulties in finding solutions, which fit production. An integrated design of production obstructs product development; the selection of project participants may affect the project results, both in terms of prior experience but also the problem-solving ability; the lack of project documentation is costly since experience is not captured, which could be recycled in future developments.
Much like how plants grow via the expansion and multiplication of cells, a 3D printed component is formed via the bonding of material point-by-point from the bottom-up. Exploiting this analogy, this work employs mathematical models of three-dimensional plant growth to further understand and aid implementation of additive manufacturing (AM) technologies (otherwise known as 3D printing). The resolution of these printed structures is of the upmost importance in the fabrication of tissue scaffolds or constructs that mimic the mechanical properties of tissues. As such, the overarching aim is to derive a generalised mathematical model to simulate the extrusion-based bioprinting process via manipulation of the underlying physics of the system. Such a model has the potential to theoretically identify which combinations of printing process parameters generate a successful resolution: the ‘window of printability’ of a bioink. A hydrogel typically presents a shear-thinning behaviour. In this paper we consider the simplest case: a Newtonian fluid flow far from any edge effects. An initial steady-state model for a viscous thread under extrusion using an arc-length-based coordinate system is presented. As such, this research presents a significant milestone toward representing the non-Newtonian system. This uniquely transdisciplinary methodology seeks to optimise the comparability and transferability of results across materials and laboratories and, above all, increase the efficiency of extrusion-based bioprinting and enhance design creativity by devising a user-friendly, sustainable tool for engineers to visualise AM as a process of growth.
Although offshore wind energy is one of the promising renewable energy sources, there are some opponent opinions due to some reasons, including “disturbance of landscape.” Such opinions should not be ignored for public facilities. However, landscape is a value that cannot be quantified easily. Array patterns of wind turbines are determined due to terrains, wind conditions, avoidance of wake, etc., not because of the landscape. The authors apply a method called “induction field of vision” to wind turbine arrays to extract numerical features of the shape. Correlation of the numerical features and the observer’s preferences were calculated. The preliminary results showed that the regular pattern has a weaker impression than the irregular pattern, and more preferred to. Although the tendency itself is natural, the important fact is that the reason of preference can be explained numerically. This paper investigates the observer’s preferences more precisely by the photos combining practical landscapes with virtual wind turbine arrays using Virtual Reality. Through this effort, the study clarifies which array patterns can ease disturbance of landscape. Since there are many offshore wind farm projects following the approved three projects, the obtained information will be useful in considering the acceptable array designs of the next offshore wind farms, which have less impacts on landscape and are symbiotic with local communities.
With the arrival of industry 4.0, it is possible to transform from traditional factories to smart factories. During the transformation, building a communication channel between customer requirements and production capacity in the product manufacturing stage, realizing the customized order service with low volume and high-mix production are critical. To achieve this potential, this study aims to understand the requirements of customers through the Kano model, which can classify the product attributes into one-dimensional, attractive, must-be, indifferent, reverse, and questionable requirements. Then, a design strategy for a conceptualization of the “Quick customized order configuration system” was proposed based on the Kano analysis results. Thus, an empirical case study of this product configuration system is illustrated as verification in this work.
Although most studies use data analysis models as a solution for SPSS, a single model cannot handle multiple tasks at the same time, and errors in model analysis can easily make the system unstable, resulting in unsatisfactory services provided to customers. In addition, most studies extract potential customer needs through textual data, while ignoring the information possessed by image data. In order to make up for the lack of research, this study proposes a method, which includes: (1) Constructing a suitable model to optimize the existing PSS, in which the customer preference is extracted from the image data through the Object Detection model. (2) Analyze customer feedback through Natural Language Processing (NLP) methods to optimize the system. (3) Integrate multiple deep learning models to build a recommendation system to provide customers with personalized services. The main purpose of this research is to integrate multiple models into an SPSS, and to provide a more stable system through the interactive operation of the models. Among them, it analyzes user preferences through image assistance, improves customer satisfaction, and establishes a feedback system to provide personalized services based on user comments. In this study, the customer journey map is used to verify the feasibility of this attraction recommendation system, and experiments show that this system can improve customer satisfaction.
In a changing and connected world, people are surrounded by an increasing number of smart devices in a complex system. Intelligent technology has revolutionised the way we interact with these devices, and has resulted in improved user experiences through the integration of physical status and digital applications. However, this transition has also presented new challenges and demands for transdisciplinary adaptation in traditional approaches to design education. Many existing design methods and frameworks have not kept pace with the level of automation now seen in intelligent interactive products, nor have they addressed human-machine interdependence in a system-thinking context. The aim of this study is to gain insights from the younger generation of design students to inform the development of a more suitable design course. Using smart home products as the case scenario, 39 industrial design students evaluated the user experience with the products through hands-on interaction. The individual product reviews of the robot cleaner, smart speaker and smart lightbulb were then analysed and consolidated. Thus, this study contributes to the elucidation of design students’ perspectives on intelligent user interfaces. Furthermore, a comparative analysis of user insights was conducted through peer assessments, focus groups and large language models to explore their potential and difference in terms of the design process. Overall, the goal of this analysis is to advance the field of design practice and education.
Service innovation is a new service or a renewal of an existing service that is put into practice and provides benefit to the organization that should be transdisciplinary. The customer experience (CX) design is the process design teams follow to optimize customer experiences at all touchpoints before, during, and after conversion. With the rise of the Internet, online passenger reviews are of great importance to airlines because electronic word-of-mouth (eWOM) from real-world experiences significantly impacts the decisions of potential consumers and repurchasing customers. Passengers fill in their flight experience on the Skytrax website, a professional survey website covering 350 airlines. This study selects Star Alliance, OneWorld, and SkyTeam as the targets and extracts Skytrax reviews to analyze each airline affiliated with the three alliances. The data-driven transdisciplinary methods, TF-IDF, association rule mining, and sentiment analysis, are used to analyze passengers’ online opinions. The result finds that alliances provide services supported via cross airlines and divisions to create benefits for stakeholders.
Electric vehicles (EVs) are emerging as a feasible solution to combat emissions, reduce reliance on fossil fuels, and gradually replace internal combustion engine (ICE) vehicles. The primary purpose of the traction battery in EVs is to provide energy to power the electric motor. However, the design of these batteries is complex, which presents one of the significant challenges in reducing the cost of vehicle electrification. This article discusses the obstacles a transdisciplinary team faces in developing a lithium-ion battery with a battery management system (BMS) for a small urban vehicle under the “Rota 2030 Program. The case study focuses on the collaboration between researchers from Brazilian technology institutions and two subsidiaries of multinational automotive companies based in Brazil. The team encountered difficulties locating information regarding commercial electric vehicle systems, such as battery sizing details, cell configurations, the chemical composition used, and developing BMS hardware and software, which are constantly evolving. The initial results reveal the complexity and challenges involved in designing a battery that meets the requirements of an EV.
In automated production industries, qualified maintenance is important. Planning and executing complex practical maintenance training scenarios on real machines can be expensive. To reduce cost, virtual training simulations in Virtual Reality (VR) are slowly being established in the virtual commissioning sector, but implementation times can be long and costly when each new training scenario needs to be implemented manually. This paper describes the outcome of a three-year research project, which addressed an automated generation of gamified maintenance training in VR based on existing virtual commissioning scenarios instead of manually configuring the machine logic on an example in the automotive industry. With the project partners from the automotive and gaming industry, a demonstrator was created. The result is a transdisciplinary setup guide for three different user types: the commissioner, the trainer, and the trainee. The users are supported with a combination of automated functions and included descriptions to utilize VR without being VR experts. The first user, the commissioner, can generate a VR scene from virtual commissioning and connects them so that the real machine behavior of the virtual Programmable Logic Controller (PLC) and Numerical Control (NC) can be used in VR over the virtual Human Machine Interfaces (HMI) like touchscreens, buttons, and other machine parts. The trainer can configure training in this virtual commissioning scene for the maintenance trainee to use for virtual machine training. The demonstrator received positive feedback from key users of the automotive industry and should be tested for their training in the next steps.
Air traffic controllers (ATCers) typically work under fixed team schedules, and the interaction of group members may significantly impact their behaviors. To understand the mechanism by which group characteristics affect the safety behaviors of individual ATCer, this study problematizes the variables of group dynamics and self-efficacy in this setting and proposes a mediation model in which group dynamics impact safety behaviors through self-efficacy. Data were collected using a self-reported questionnaire survey from 85 Chinese ATCers in two Air Traffic Administrations. The results revealed that the indirect effects of two subdimensions of group dynamics (group cohesion and group infectivity) on safety behaviors via self-efficacy were salient, whereas group pressure was not correlated with safety behaviors. This finding implied the partial mediation role of self-efficacy, which was expected to redress an omission in the influence path from group dynamics to safety behaviors from the cognitive mechanism perspective. The results can facilitate a better understanding of how group characteristics impact safety behaviors and also help develop efficient measures to reduce ATCers’ safety performance at the group level.
The topic of team composition, recomposition, and role selection in long-term educational programs that comprise of multiple smaller courses, such as coding bootcamps, has received limited attention in the literature, despite its importance. However, the rise of large-scale online learning environments such as MOOCs has highlighted the need for effective strategies to address the high drop-out rates and low quality graduates observed in these contexts. In this paper, we propose to build a theoretical framework by using a multiple-criteria technique that incorporates personalities, agile, and gamification to address this problem. This framework will be used to better understand the dynamics of team composition, recomposition, and role selection in virtual teams within such educational programs.