Search results
11 – 20 of over 32000Jiangtao Xu, Na Luo, Shaojie Liu, Baoshan Zhao, Fang Qi, Yinjun Lian and Litong Wang
The purpose of this paper is to design a component synthesis method to suppress the vibration of the flexible spacecraft, which has the constant amplitude force/moment actuator.
Abstract
Purpose
The purpose of this paper is to design a component synthesis method to suppress the vibration of the flexible spacecraft, which has the constant amplitude force/moment actuator.
Design/methodology/approach
The authors proposed a method to construct constant amplitude of time delay and composite coefficient sequences based on the principles of the component synthesis vibration suppression (CSVS). The associated design strategy of the CSVS torque control is also developed. The dynamic model consisting of a single axis rotating rigid central body and a fixed flexibility panel is used to validate the proposed method. Constraint modal and free modal method are both tested to analyse the natural frequencies of the panel and dynamic properties of rigid–flexible decoupling system, under the conditions of known and unknown frequencies. The feasibility of constructing CSVS control force based on the constraint modal frequency is also analysed.
Findings
The proposed method can suppress multistage vibration and has arbitrary order robustness for each order frequencies simultaneously. Simulation results show that only the duration time of the actuator has to be set for the proposed method, reasonable vibration suppression effect can be achieved.
Practical implications
The method can be used in spacecraft, especially flexible spacecraft to suppress the vibration; the approach is convenient for engineering application and can be easily designed.
Originality/value
The authors proposed a method to construct constant amplitude of time delay and composite coefficient sequences based on the principles of the CSVS.
Details
Keywords
Li Fan, Min Hu and Mingqi Yang
The purpose of this paper is to develop a theoretical design for the attitude control of electromagnetic formation flying (EMFF) satellites, present a nonlinear controller for the…
Abstract
Purpose
The purpose of this paper is to develop a theoretical design for the attitude control of electromagnetic formation flying (EMFF) satellites, present a nonlinear controller for the relative translational control of EMFF satellites and propose a novel method for the allocation of electromagnetic dipoles.
Design/methodology/approach
The feedback attitude control law, magnetic unloading algorithm and large angle manoeuvre algorithm are presented. Then, a terminal sliding mode controller for the relative translation control is put forward and the convergence is proved. Finally, the control allocation problem of electromagnetic dipoles is formulated as an optimization issue, and a hybrid particle swarm optimization (PSO) – sequential quadratic programming (SQP) algorithm to optimize the free dipoles. Three numerical simulations are carried out and results are compared.
Findings
The proposed attitude controller is effective for the sun-tracking process of EMFF satellites, and the magnetic unloading algorithm is valid. The formation-keeping scenario simulation demonstrates the effectiveness of the terminal sliding model controller and electromagnetic dipole calculation method.
Practical implications
The proposed method can be applied to solve the attitude and relative translation control problem of EMFF satellites in low earth orbits.
Originality/value
The paper analyses the attitude control problem of EMFF satellites systematically and proposes an innovative way for relative translational control and electromagnetic dipole allocation.
Details
Keywords
Mark P. Pritchard, Daniel C. Funk and Kostas Alexandris
The reason patrons cease to attend sporting events is not well understood. The purpose of this paper is to examine how factors motivate and inhibit patronage from continuing.
Abstract
Purpose
The reason patrons cease to attend sporting events is not well understood. The purpose of this paper is to examine how factors motivate and inhibit patronage from continuing.
Design/methodology/approach
A random sample of a sport franchise's fan database (n=308) is drawn. First, respondent data refines measures and tests a structural equation model of direct and indirect links to patronage. Next, content analysis classifies spectators according to self‐stated barriers to continuance. These groupings then check the moderating role constraints have on patron attitude and behaviour.
Findings
Structural work confirms both direct and indirect links but notes that consumption primarily took an indirect route, with motivational desires rousing fan involvement and media use before increasing attendance. Group differences verify constraints and limit patronage but do not dampen product‐related attitude.
Research limitations/implications
The study helps clarify the connection between media use and attendance, describing how constraints impede spectator consumption. Study limitations include a focus on one hedonic service setting and the use of cross‐sectional data to examine ongoing phenomena.
Practical implications
Negotiating barriers to repeat purchase remains largely overlooked as a foundation for guiding strategy. Practical implications consider integrating both motives and constraints when marshalling efforts that build continuance.
Originality/value
Despite early interest from marketing practitioners, factors that inhibit patronage have drawn little attention. This study employs content and path analysis to address the matter.
Details
Keywords
The Pupil Control Ideology (PCI) concept has been used extensively to describe the school organization. Teachers hate been described as either “custodial” or “humanistic” in their…
Abstract
The Pupil Control Ideology (PCI) concept has been used extensively to describe the school organization. Teachers hate been described as either “custodial” or “humanistic” in their belief orientation to control of pupils. But clarification of the nature of pupil control and the teacher attitudes which lie at the base of control, has not been investigated adequately. The first section of the present investigation indicates the attitudes of teachers which are associated with high levels of custodialism. These attitudes include emphasis on, content to be taught, teacher direction, rigid classroom procedures and social disengagement from pupils. The second part of the study shows that while operational measures of control may be similar, attitudes underlying control may differ. In schools serving higher socio‐economic communities, teachers exhibit an “emotional disengagement—non‐teacher direction” form of ideology. The conclusion is drawn that unless future investigations both identify attitudes and explain the interactions of attitudes of teachers in each school system, Pupil Control Ideology may be an inadequate descriptor of the school as a social system.
Manuela Naldini and Cristina Solera
During the transition to parenthood, the gender division of paid and unpaid work undergoes a profound redefinition in response to both attitudes and resources. These attitudes may…
Abstract
During the transition to parenthood, the gender division of paid and unpaid work undergoes a profound redefinition in response to both attitudes and resources. These attitudes may be concordant or discordant between two partners, they may or may not clash with perceived financial or labour market constraints, and they may or may not provoke explicit conflicts and negotiations. In this study, by combining quantitative and qualitative data, we focus on Italian couples with young children or in transition to first child, and we explore what happens when partners have discordant views. The findings show that the division of domestic and care work seems more resistant to change and more responsive to the husband’s attitudes than does the division of paid work, as the latter is mainly driven by the woman’s education and attitudes. The findings also show that very few couples overtly disagree. If they do so, the main issue in dispute is the allocation of domestic work and the main solution consists more in hiring external help than in obtaining the husband’s greater participation. Compared with domestic work, the allocation of care is a less disputed and more flexible issue: when women start negotiations on a more equal sharing, men are more willing to increase their participation. However, when a more equal sharing is not attained, couples’ narratives tend to give the “cause” to the constraints of the man (typically his work) than of the woman, while they point at a redefinition (for the best of the family) of her rather than his preferences.
Details
Keywords
Zhi Chen, Daobo Wang, Ziyang Zhen, Biao Wang and Jian Fu
This paper aims to present a control strategy that eliminates the longitudinal and lateral drifting movements of the coaxial ducted fan unmanned helicopter (UH) during autonomous…
Abstract
Purpose
This paper aims to present a control strategy that eliminates the longitudinal and lateral drifting movements of the coaxial ducted fan unmanned helicopter (UH) during autonomous take-off and landing and reduce the coupling characteristics between channels of the coaxial UH for its special model structure.
Design/methodology/approach
Unidirectional auxiliary surfaces (UAS) for terminal sliding mode controller (TSMC) are designed for the flight control system of the coaxial UH, and a hierarchical flight control strategy is proposed to improve the decoupling ability of the coaxial UH.
Findings
It is demonstrated that the proposed height control strategy can solve the longitudinal and lateral movements during autonomous take-off and landing phase. The proposed hierarchical controller can decouple vertical and heading coupling problem which exists in coaxial UH. Furthermore, the confronted UAS-TSMC method can guarantee finite-time convergence and meet the quick flight trim requirements during take-off and landing.
Research limitations/implications
The designed flight control strategy has not implemented in real flight test yet, as all the tests are conducted in the numerical simulation and simulation with a hardware-in-the-loop (HIL) platform.
Social implications
The designed flight control strategy can solve the common problem of coupling characteristics between channels for coaxial UH, and it has important theoretical basis and reference value for engineering application; the control strategy can meet the demands of engineering practice.
Originality/value
In consideration of the TSMC approach, which can increase the convergence speed of the system state effectively, and the high level of response speed requirements to UH flight trim, the UAS-TSMC method is first applied to the coaxial ducted fan UH flight control. The proposed control strategy is implemented on the UH flight control system, and the HIL simulation clearly demonstrates that a much better performance could be achieved.
Details
Keywords
Gordon Wills, Sherril H. Kennedy, John Cheese and Angela Rushton
To achieve a full understanding of the role ofmarketing from plan to profit requires a knowledgeof the basic building blocks. This textbookintroduces the key concepts in the art…
Abstract
To achieve a full understanding of the role of marketing from plan to profit requires a knowledge of the basic building blocks. This textbook introduces the key concepts in the art or science of marketing to practising managers. Understanding your customers and consumers, the 4 Ps (Product, Place, Price and Promotion) provides the basic tools for effective marketing. Deploying your resources and informing your managerial decision making is dealt with in Unit VII introducing marketing intelligence, competition, budgeting and organisational issues. The logical conclusion of this effort is achieving sales and the particular techniques involved are explored in the final section.
Details
Keywords
Amirreza Kosari, Alireza Sharifi, Alireza Ahmadi and Masoud Khoshsima
Attitude determination and control subsystem (ADCS) is a vital part of earth observation satellites (EO-Satellites) that governs the satellite’s rotational motion and pointing. In…
Abstract
Purpose
Attitude determination and control subsystem (ADCS) is a vital part of earth observation satellites (EO-Satellites) that governs the satellite’s rotational motion and pointing. In designing such a complicated sub-system, many parameters including mission, system and performance requirements (PRs), as well as system design parameters (DPs), should be considered. Design cycles which prolong the time-duration and consequently increase the cost of the design process are due to the dependence of these parameters to each other. This paper aims to describe a rapid-sizing method based on the design for performance strategy, which could minimize the design cycles imposed by conventional methods.
Design/methodology/approach
The proposed technique is an adaptation from that used in the aircraft industries for aircraft design and provides a ball-park figure with little engineering man-hours. The authors have shown how such a design technique could be generalized to cover the EO-satellites platform ADCS. The authors divided the system requirements into five categories, including maneuverability, agility, accuracy, stability and durability. These requirements have been formulated as functions of spatial resolution that is the highest level of EO-missions PRs. To size, the ADCS main components, parametric characteristics of the matching diagram were determined by means of the design drivers.
Findings
Integrating the design boundaries based on the PRs in critical phases of the mission allowed selecting the best point in the design space as the baseline design with only two iterations. The ADCS of an operational agile EO-satellite is sized using the proposed method. The results show that the proposed method can significantly reduce the complexity and time duration of the performance sizing process of ADCS in EO-satellites with an acceptable level of accuracy.
Originality/value
Rapid performance sizing of EO-satellites ADCS using matching diagram technique and consequently, a drastic reduction in design time via minimization of design cycles makes this study novel and represents a valuable contribution in this field.
Details
Keywords
Tugrul Oktay, Harun Celik and Ilke Turkmen
The purpose of this paper is to examine the success of constrained control on reducing motion blur which occurs as a result of helicopter vibration.
Abstract
Purpose
The purpose of this paper is to examine the success of constrained control on reducing motion blur which occurs as a result of helicopter vibration.
Design/methodology/approach
Constrained controllers are designed to reduce the motion blur on images taken by helicopter. Helicopter vibrations under tight and soft constrained controllers are modeled and added to images to show the performance of controllers on reducing blur.
Findings
The blur caused by vibration can be reduced via constrained control of helicopter.
Research limitations/implications
The motion of camera is modeled and assumed same as the motion of helicopter. In model of exposing image, image noise is neglected, and blur is considered as the only distorting effect on image.
Practical implications
Tighter constrained controllers can be implemented to take higher quality images by helicopters.
Social implications
Recently, aerial vehicles are widely used for aerial photography. Images taken by helicopters mostly suffer from motion blur. Reducing motion blur can provide users to take higher quality images by helicopters.
Originality/value
Helicopter control is performed to reduce motion blur on image for the first time. A control-oriented and physic-based model of helicopter is benefited. Helicopter vibration which causes motion blur is modeled as blur kernel to see the effect of helicopter vibration on taken images. Tight and soft constrained controllers are designed and compared to denote their performance in reducing motion blur. It is proved that images taken by helicopter can be prevented from motion blur by controlling helicopter tightly.
Details
Keywords
Information and communications technology (ICT) offers enormous opportunities for individuals, businesses and society. The application of ICT is equally important to economic and…
Abstract
Information and communications technology (ICT) offers enormous opportunities for individuals, businesses and society. The application of ICT is equally important to economic and non-economic activities. Researchers have increasingly focused on the adoption and use of ICT by small and medium enterprises (SMEs) as the economic development of a country is largely dependent on them. Following the success of ICT utilisation in SMEs in developed countries, many developing countries are looking to utilise the potential of the technology to develop SMEs. Past studies have shown that the contribution of ICT to the performance of SMEs is not clear and certain. Thus, it is crucial to determine the effectiveness of ICT in generating firm performance since this has implications for SMEs’ expenditure on the technology. This research examines the diffusion of ICT among SMEs with respect to the typical stages from innovation adoption to post-adoption, by analysing the actual usage of ICT and value creation. The mediating effects of integration and utilisation on SME performance are also studied. Grounded in the innovation diffusion literature, institutional theory and resource-based theory, this study has developed a comprehensive integrated research model focused on the research objectives. Following a positivist research paradigm, this study employs a mixed-method research approach. A preliminary conceptual framework is developed through an extensive literature review and is refined by results from an in-depth field study. During the field study, a total of 11 SME owners or decision-makers were interviewed. The recorded interviews were transcribed and analysed using NVivo 10 to refine the model to develop the research hypotheses. The final research model is composed of 30 first-order and five higher-order constructs which involve both reflective and formative measures. Partial least squares-based structural equation modelling (PLS-SEM) is employed to test the theoretical model with a cross-sectional data set of 282 SMEs in Bangladesh. Survey data were collected using a structured questionnaire issued to SMEs selected by applying a stratified random sampling technique. The structural equation modelling utilises a two-step procedure of data analysis. Prior to estimating the structural model, the measurement model is examined for construct validity of the study variables (i.e. convergent and discriminant validity).
The estimates show cognitive evaluation as an important antecedent for expectation which is shaped primarily by the entrepreneurs’ beliefs (perception) and also influenced by the owners’ innovativeness and culture. Culture further influences expectation. The study finds that facilitating condition, environmental pressure and country readiness are important antecedents of expectation and ICT use. The results also reveal that integration and the degree of ICT utilisation significantly affect SMEs’ performance. Surprisingly, the findings do not reveal any significant impact of ICT usage on performance which apparently suggests the possibility of the ICT productivity paradox. However, the analysis finally proves the non-existence of the paradox by demonstrating the mediating role of ICT integration and degree of utilisation explain the influence of information technology (IT) usage on firm performance which is consistent with the resource-based theory. The results suggest that the use of ICT can enhance SMEs’ performance if the technology is integrated and properly utilised. SME owners or managers, interested stakeholders and policy makers may follow the study’s outcomes and focus on ICT integration and degree of utilisation with a view to attaining superior organisational performance.
This study urges concerned business enterprises and government to look at the environmental and cultural factors with a view to achieving ICT usage success in terms of enhanced firm performance. In particular, improving organisational practices and procedures by eliminating the traditional power distance inside organisations and implementing necessary rules and regulations are important actions for managing environmental and cultural uncertainties. The application of a Bengali user interface may help to ensure the productivity of ICT use by SMEs in Bangladesh. Establishing a favourable national technology infrastructure and legal environment may contribute positively to improving the overall situation. This study also suggests some changes and modifications in the country’s existing policies and strategies. The government and policy makers should undertake mass promotional programs to disseminate information about the various uses of computers and their contribution in developing better organisational performance. Organising specialised training programs for SME capacity building may succeed in attaining the motivation for SMEs to use ICT. Ensuring easy access to the technology by providing loans, grants and subsidies is important. Various stakeholders, partners and related organisations should come forward to support government policies and priorities in order to ensure the productive use of ICT among SMEs which finally will help to foster Bangladesh’s economic development.
Details