814 resultados para Calculus of operations.


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Purpose: This paper aims to explore practices and technologies successfully servitised manufacturers employ in the delivery of advanced services. Design/methodology/approach: A case study methodology is applied across four manufacturing organisations successful in servitization. Through interviews with personnel across host manufacturers, their partners, and key customers, extensive data are collected about service delivery systems. Analyses identify convergence in their practices and technologies. Findings: Six distinct technologies and practices are revealed: facilities and their location, micro-vertical integration and supplier relationships, information and communication technologies (ICTs), performance measurement and value demonstration, people deployment and their skills, and business processes and customer relationships. These are then combined in an integrative framework that illustrates how operations are configured to successfully deliver advanced services. Research limitations/implications: The analyses are reductive and rationalising. Future studies could identify other technologies and practices. Case study as a method is inherently limited in the extent to which findings can be generalised. Practical implications: Awareness and interest in servitization is growing, yet adoption of a servitization strategy requires particular organisational capabilities on the part of the manufacturer. This study identifies technologies and practices that underpin these capabilities. Originality/value: This paper contributes to the understanding of the servitization process and, in particular, the implications to broader operations of the firm. © Emerald Group Publishing Limited.

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Purpose - It is important to advance operations management (OM) knowledge while being mindful of the theoretical developments of the discipline. The purpose of this paper is to explore which theoretical perspectives have dominated the OM field. This analysis allows the authors to identify theory trends and gaps in the literature and to identify fruitful areas for future research. A reflection on theory is also practical, given that it guides research toward important questions and enlightens OM practitioners. Design/methodology/approach - The authors provide an analysis of OM theory developments in the last 30 years. The study encompasses three decades of OM publications across three OM journals and contains an analysis of over 3,000 articles so as to identify which theories, over time, have been adopted by authors in order to understand OM topics. Findings - The authors find that the majority of studies are atheoretical, empirical, and focussed upon theory testing rather than on theory development. Some theories, such as the resource-based view and contingency theory, have an enduring relevance within OM. The authors also identify theories from psychology, economics, sociology, and organizational behavior that may, in the future, have salience to explain burgeoning OM research areas such as servitization and sustainability. Research limitations/implications - The study makes a novel contribution by exploring which main theories have been adopted or developed in OM, doing so by systematically analyzing articles from the three main journals in the field (the Journal of Operations Management, Production and Operations Management, and the International Journal of Operations and Production Management), which encompass three decades of OM publications. In order to focus the study, the authors may have missed important OM articles in other journals. Practical implications - A reflection on theories is important because theories inform how a researcher or practicing manager interprets and solves OM problems. This study allows the authors to reflect on the collective OM journey to date, to spot trends and gaps in the literature, and to identify fruitful areas for future research. Originality/value - As far as the authors are aware, there has not been an assessment of the main theoretical perspectives in OM. The research also identifies which topics are published in OM journals, and which theories are adopted to investigate them. The authors also reflect on whether the most cited papers and those winning best paper awards are theoretical. This gives the authors a richer understanding of the current state of OM research.

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This dissertation contributes to the rapidly growing empirical research area in the field of operations management. It contains two essays, tackling two different sets of operations management questions which are motivated by and built on field data sets from two very different industries --- air cargo logistics and retailing.

The first essay, based on the data set obtained from a world leading third-party logistics company, develops a novel and general Bayesian hierarchical learning framework for estimating customers' spillover learning, that is, customers' learning about the quality of a service (or product) from their previous experiences with similar yet not identical services. We then apply our model to the data set to study how customers' experiences from shipping on a particular route affect their future decisions about shipping not only on that route, but also on other routes serviced by the same logistics company. We find that customers indeed borrow experiences from similar but different services to update their quality beliefs that determine future purchase decisions. Also, service quality beliefs have a significant impact on their future purchasing decisions. Moreover, customers are risk averse; they are averse to not only experience variability but also belief uncertainty (i.e., customer's uncertainty about their beliefs). Finally, belief uncertainty affects customers' utilities more compared to experience variability.

The second essay is based on a data set obtained from a large Chinese supermarket chain, which contains sales as well as both wholesale and retail prices of un-packaged perishable vegetables. Recognizing the special characteristics of this particularly product category, we develop a structural estimation model in a discrete-continuous choice model framework. Building on this framework, we then study an optimization model for joint pricing and inventory management strategies of multiple products, which aims at improving the company's profit from direct sales and at the same time reducing food waste and thus improving social welfare.

Collectively, the studies in this dissertation provide useful modeling ideas, decision tools, insights, and guidance for firms to utilize vast sales and operations data to devise more effective business strategies.

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Increased complexity in large design and manufacturing organisations requires improvements at the operations management (OM)–applied service (AS) interface areas to improve project effectiveness. The aim of this paper is explore the role of Lean in improving the longitudinal efficiency of the OM–AS interface within a large aerospace organisation using Lean principles and boundary spanning theory. The methodology was an exploratory longitudinal case approach including exploratory interviews (n = 21), focus groups (n = 2), facilitated action-research workshops (n = 2) and two trials or experiments using longitudinal data involving both OM and AS personnel working at the interface. The findings draw upon Lean principles and boundary spanning theory to guide and interpret the findings. It was found that misinterpretation, and forced implementation, of OM-based Lean terminology and practice in the OM–AS interface space led to delays and misplaced resources. Rather both OM and AS staff were challenged to develop a cross boundary understanding of Lean-based boundary (knowledge) objects in interpreting OM requests. The longitudinal findings from the experiments showed that the development of Lean Performance measurements and lean Value Stream constructs was more successful when these Lean constructs were treated as boundary (knowledge) objects requiring transformation over time to orchestrate improved effectiveness and in leading to consistent terminology and understanding between the OM–AS boundary spanning team.

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Research has highlighted the relationship between vehicle speed and increased crash risk and severity. Evidence suggests that police speed enforcement, in particular speed camera operations, can be an effective tool for reducing traffic crashes. A quantitative survey of Queensland drivers (n = 852) was conducted to investigate the impact of police speed enforcement methods on self-reported speeding behaviour. Results indicate that visible enforcement was associated with significantly greater self-reported compliance than covert operations irrespective of the mobility of the approach, and the effects on behaviour were longer lasting. The mobility of operations appeared to be moderated the visibility of the approach. Specifically, increased mobility was associated with increase reported compliant behaviour, but only for covert operations, and increased longevity of reported compliant behaviour, but only for overt operations. The perceived effectiveness of various speed enforcement approaches are also analysed across a range of driving scenarios. Results are discussed in light of the small effect sizes. Recommendations for policy and future research are presented.

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Network induced delay in networked control systems (NCS) is inherently non-uniformly distributed and behaves with multifractal nature. However, such network characteristics have not been well considered in NCS analysis and synthesis. Making use of the information of the statistical distribution of NCS network induced delay, a delay distribution based stochastic model is adopted to link Quality-of-Control and network Quality-of-Service for NCS with uncertainties. From this model together with a tighter bounding technology for cross terms, H∞ NCS analysis is carried out with significantly improved stability results. Furthermore, a memoryless H∞ controller is designed to stabilize the NCS and to achieve the prescribed disturbance attenuation level. Numerical examples are given to demonstrate the effectiveness of the proposed method.

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Purpose: The purpose of this paper is to explore the role of cross-functional teams in the alignment between system effectiveness and operational effectiveness after the implementation of enterprise information systems (EIS). In addition, it aims to explore the contribution of cross-functional teams to improvement in operational performance. ---------- Design/methodology/approach: The research uses a combination of qualitative and quantitative methods, in a two-stage methodological approach, to investigate the influence of cross-functional teams on the alignment between system effectiveness and operational effectiveness and the impact of the stated alignment on the improvement in operational performance. ---------- Findings: Initial findings suggest that factors stemming from system effectiveness and the performance objectives stemming from operational effectiveness are important and significantly well correlated factors that promote the alignment between the effectiveness of technological implementation and the effectiveness of operations. In addition, confirmatory factor analysis has been used to find the structural relationships and provide explanations for the stated alignment and the contribution of cross-functional teams to the improvement in operational performance. ---------- Research limitations/implications: The principal limitation of this study is its small sample size. ---------- Practical implications: Cross-functional teams have been used by many organisations as a way of involving expertise from different functional areas in the implementation of innovative technologies. An appropriate use of the dimensions that emerged from this research, in the context of cross-functional teams, will assist organisations to properly utilise cross-functional teams with the aim of improving operational performance. ---------- Originality/value: The paper presents a new approach to measure the effectiveness of EIS implementation by adding new dimensions to measure it.

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The paper has a twofold purpose. First it highlights the importance of accounting information in the economic development of developing countries, with a particular focus on the nation of Libya. Secondly, using the case of Libya's General Company for Pipelines (GCP), it demonstrates that the use of accounting information to achieve economic development goals is determined to a large extent by the political/ideological setting in which it is generated. The study is based on a literature review and archival research, reinforced by a qualitative case study comprised of interviews, attendance at meetings and a study of internal documents. A study of The General Company for Pipelines (GCP) revealed that frequent politically driven changes in the structure and number of popular congresses and committees severely limited the use of accounting information, relegating it to a formal role. In consequence, accounting information had litle effect on stimulating economic development in Libya. This study focuses on one case study which does limit generalisability. However, it also suggests fruitful research areas considering the historic factors which have determined the accounting role in developing and planned economies. By providing insights about social factors which have determined the use of accounting in a planned economy, this study has implications for similar economies as they move towards a more globalised mode of operations which enhance the role of accounting in meeting economic development needs. If devleoping countries are to harness the potential of accounting aid in the achievement of their development plans, the social and political setting in which accounting has been conducted needs to be understood.

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Designing trajectories for a submerged rigid body motivates this paper. Two approaches are addressed: the time optimal approach and the motion planning ap- proach using concatenation of kinematic motions. We focus on the structure of singular extremals and their relation to the existence of rank-one kinematic reduc- tions; thereby linking the optimization problem to the inherent geometric frame- work. Using these kinematic reductions, we provide a solution to the motion plan- ning problem in the under-actuated scenario, or equivalently, in the case of actuator failures. We finish the paper comparing a time optimal trajectory to one formed by concatenation of pure motions.

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An autonomous underwater vehicle (AUV) is expected to operate in an ocean in the presence of poorly known disturbance forces and moments. The uncertainties of the environment makes it difficult to apply open-loop control scheme for the motion planning of the vehicle. The objective of this paper is to develop a robust feedback trajectory tracking control scheme for an AUV that can track a prescribed trajectory amidst such disturbances. We solve a general problem of feedback trajectory tracking of an AUV in SE(3). The feedback control scheme is derived using Lyapunov-type analysis. The results obtained from numerical simulations confirm the asymptotic tracking properties of the feedback control law. We apply the feedback control scheme to different mission scenarios, with the disturbances being initial errors in the state of the AUV.

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Autonomous underwater vehicles (AUVs) are increasingly used, both in military and civilian applications. These vehicles are limited mainly by the intelligence we give them and the life of their batteries. Research is active to extend vehicle autonomy in both aspects. Our intent is to give the vehicle the ability to adapt its behavior under different mission scenarios (emergency maneuvers versus long duration monitoring). This involves a search for optimal trajectories minimizing time, energy or a combination of both. Despite some success stories in AUV control, optimal control is still a very underdeveloped area. Adaptive control research has contributed to cost minimization problems, but vehicle design has been the driving force for advancement in optimal control research. We look to advance the development of optimal control theory by expanding the motions along which AUVs travel. Traditionally, AUVs have taken the role of performing the long data gathering mission in the open ocean with little to no interaction with their surroundings, MacIver et al. (2004). The AUV is used to find the shipwreck, and the remotely operated vehicle (ROV) handles the exploration up close. AUV mission profiles of this sort are best suited through the use of a torpedo shaped AUV, Bertram and Alvarez (2006), since straight lines and minimal (0 deg - 30 deg) angular displacements are all that are necessary to perform the transects and grid lines for these applications. However, the torpedo shape AUV lacks the ability to perform low-speed maneuvers in cluttered environments, such as autonomous exploration close to the seabed and around obstacles, MacIver et al. (2004). Thus, we consider an agile vehicle capable of movement in six degrees of freedom without any preference of direction.

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This paper is concerned with the design and implementation of control strategies onto a test-bed vehicle with six degrees-of-freedom. We design our trajectories to be efficient in time and in power consumption. Moreover, we also consider cases when actuator failure can arise and discuss alternate control strategies in this situation. Our calculations are supplemented by experimental results.

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This paper serves as a first study on the implementation of control strategies developed using a kinematic reduction onto test bed autonomous underwater vehicles (AUVs). The equations of motion are presented in the framework of differential geometry, including external dissipative forces, as a forced affine connection control system. We show that the hydrodynamic drag forces can be included in the affine connection, resulting in an affine connection control system. The definitions of kinematic reduction and decoupling vector field are thus extended from the ideal fluid scenario. Control strategies are computed using this new extension and are reformulated for implementation onto a test-bed AUV. We compare these geometrically computed controls to time and energy optimal controls for the same trajectory which are computed using a previously developed algorithm. Through this comparison we are able to validate our theoretical results based on the experiments conducted using the time and energy efficient strategies.

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This paper discusses control strategies adapted for practical implementation and efficient motion of underwater vehicles. These trajectories are piecewise constant thrust arcs with few actuator switchings. We provide the numerical algorithm which computes the time efficient trajectories parameterized by the switching times. We discuss both the theoretical analysis and experimental implementation results.

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In this paper we consider the implementation of time and energy efficient trajectories onto a test-bed autonomous underwater vehicle. The trajectories are losely connected to the results of the application of the maximum principle to the controlled mechanical system. We use a numerical algorithm to compute efficient trajectories designed using geometric control theory to optimize a given cost function. Experimental results are shown for the time minimization problem.