Search results

1 – 10 of over 77000
Article
Publication date: 4 August 2014

Krzysztof Górecki

The purpose of this paper is to present a new method of measuring thermal resistance of power light-emitting diodes (LEDs). Properties of power LEDs strongly depend on…

Abstract

Purpose

The purpose of this paper is to present a new method of measuring thermal resistance of power light-emitting diodes (LEDs). Properties of power LEDs strongly depend on their internal temperature. The value of this temperature depends on the cooling conditions characterized by thermal resistance.

Design/methodology/approach

The new method of measuring the value of this parameter belongs to the group of electric methods. In this method, the problem of estimating the value of electrical power converted into light is solved. By comparing the values of the case temperature obtained for the LED operating in the forward mode and the reverse-breakdown mode, the thermal power is estimated. On the basis of the measured value of the thermally sensitive parameter (the LED forward voltage) and the estimated value of the thermal power, thermal resistance is calculated.

Findings

The elaborated method was used to measure thermal resistance of the selected types of power LEDs operating at different cooling conditions. The correctness of the elaborated measurement method was proved by comparing the results of measurements obtained with the use of the new method and the infrared method.

Research limitations/implications

On the basis of the obtained results of measurements and the catalog data of the tested diodes, the dependence of the measurement error of thermal resistance of the LED on its luminous efficiency is discussed.

Originality/value

The new measurement method is easy to use and more accurate than the classical method of thermal resistance measurement of the diode.

Details

Microelectronics International, vol. 31 no. 3
Type: Research Article
ISSN: 1356-5362

Keywords

Book part
Publication date: 26 November 2014

Moses Acquaah

The purpose of this study is to review the literature on strategic management in Africa with special emphasis on how strategy constructs have been measured and present a…

Abstract

Purpose

The purpose of this study is to review the literature on strategic management in Africa with special emphasis on how strategy constructs have been measured and present a roadmap to help improve strategy research in Africa.

Design/methodology/approach

A content analysis of empirical research on strategic management published in journals using data from Africa from 2000 to 2013 is conducted to examine construct measurement practices.

Findings

The findings indicate that the average sample sizes in strategy research in Africa is not large as strategy research in general, and have low statistical power. While the studies rely heavily on single-indicator measures, there were also several studies using scale or multiple measures that report reliabilities.

Research limitations

Limitations of the research include small number of studies used, inability to examine journal effects’ of the findings due to few numbers of papers from many of the journals, and lack of examination of the influence of the context and topical areas of the articles on the use of the construct measurement techniques.

Practical implications

The study provides information about the use of construct measurement techniques and power analysis in strategy research in Africa. It further encourages the use of larger sample sizes, the examination of power, and more focus on variables which allow the assessment of reliabilities and validity.

Originality and value

Little is known about construct measurement practices of the empirical research in and about Africa in the discipline of strategic management. This chapter builds on extant research on construct measurement issues in strategic management research, but with the unique value-added contribution of focusing on the African environment where the discipline is beginning to take hold.

Details

Advancing Research Methodology in the African Context: Techniques, Methods, and Designs
Type: Book
ISBN: 978-1-78441-489-4

Keywords

Article
Publication date: 5 September 2016

Krzysztof Olasek, Maciej Karczewski, Michal Lipian, Piotr Wiklak and Krzysztof Józwik

A solution to increase the energy production rate of the wind turbine is proposed by forcing more air to move through the turbine working section. This can be achieved by…

Abstract

Purpose

A solution to increase the energy production rate of the wind turbine is proposed by forcing more air to move through the turbine working section. This can be achieved by equipping the rotor with a diffusing channel ended with a brim (diffuser augmented wind turbine – DAWT). The purpose of this paper is to design an experimental stand and perform the measurements of velocity vector fields through the diffuser and power characteristic of the wind turbine.

Design/methodology/approach

The experiments were carried out in a small subsonic wind tunnel at the Institute of Turbomachinery, Lodz University of Technology. An experimental stand design process as well as measurement results are presented. Model size sensitivity study was performed at the beginning. The experimental campaign consisted of velocity measurements by means of particle image velocimetry (PIV) and pneumatic pitot probe as well as torque and rotational velocity measurements.

Findings

Characteristics (power coefficient vs tip speed ratio) of the bare and shrouded wind turbine were obtained. The results show an increase in the wind turbine power up to 70-75 per cent by shrouding the rotor with a diffuser. The mechanisms responsible for such a power increase were well explained by the PIV and pneumatic measurement results revealing the nature of the flow through the diffuser.

Research limitations/implications

Experimental stand for wind turbine rotor testing is of a preliminary character. Most optimal methodology for obtaining power characteristic should be determined now. Presented results can serve as good input for choice of stable and reliable control system of wind turbine operational parameters.

Practical implications

A 3 kW DAWT is being developed at the Institute of Turbomachinery, Lodz University of Technology. Aim of the study is to design a compact and smart wind turbine optimised for low wind speed conditions. Developed wind turbine has a potential to be used as an effective element within a net of distributed generation, e.g. for domestic use.

Originality/value

Research carried out is the continuation of theoretical study began in 1970s. It was also inspired by practical solutions proposed by Japanese researchers few years ago. Presented paper is the summary of work devoted to optimisation of the DAWT for wind conditions in the region. Original solution has been applied, e.g. for experimental stand design (3D printing application).

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 26 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 15 May 2017

Shan Xue, Li Xiong, Zhao Lu and Jia Wu

This study aims to review the literature on graph-theoretic mining methods for node importance in both static and dynamic world city networks, which is correspondingly…

Abstract

Purpose

This study aims to review the literature on graph-theoretic mining methods for node importance in both static and dynamic world city networks, which is correspondingly categorised by graph-theoretic node importance mining on network topologies and transmission mechanisms.

Design/methodology/approach

The authors overview the graph-theoretic indicators of node importance: centrality and power. Then, the methods of graph-theoretic node importance mining on network topologies are assessed with node relevance, centrality- and power-based measurements, heterogeneous fusion and other miscellaneous approaches. The latest progress in transmission mechanisms is also reviewed in this study involving network evolution, node immunisation and robustness in dynamics. Finally, the findings are analysed and future directions in this field are suggested.

Findings

The method development of node importance mining is driven by complex application-based problems within a transmission mechanism. Fusion measurements, based on centrality and power, are extended by other graph mining techniques in which power has a significant role. In conclusion, the trends of node importance mining focus on power-embedded fusion measurements in the transmission mechanism-based complex applications.

Originality/value

This is the first systematic literature review of node importance from the view of graph-theoretic mining.

Details

Information Discovery and Delivery, vol. 45 no. 2
Type: Research Article
ISSN: 2398-6247

Keywords

Article
Publication date: 1 March 2004

Emilio Ghiani, Nicola Locci, Carlo Muscas and Sara Sulis

This paper deals with the uncertainty in digital measurement systems designed for power quality applications. The main goal of this work is to evaluate such uncertainty by…

Abstract

This paper deals with the uncertainty in digital measurement systems designed for power quality applications. The main goal of this work is to evaluate such uncertainty by means of a Monte Carlo method recently proposed in the literature. The accuracy of the measurement result obtained with a DSP‐based instrument for power quality metering depends on the behavior of the devices located in both the conditioning block and A/D conversion stage: it is thus necessary to consider the uncertainties introduced by each component of the system and the propagation of their effects through the measurement chain. Here, the uncertainty is estimated starting from the technical specifications provided by the manufacturers of these devices. Experimental results are reported to show the importance of some concerns about the practical implementation of the proposed methodology in a real instrument.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 23 no. 1
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 26 August 2014

Ping Yang and Guangzhen Xing

This article aims to propose a new measurement method for ultrasonic power based on self-reciprocity theorem which turns the estimation of ultrasonic power to the…

Abstract

Purpose

This article aims to propose a new measurement method for ultrasonic power based on self-reciprocity theorem which turns the estimation of ultrasonic power to the measurement of first echo current and open-circuit voltage of the driving source.

Design/methodology/approach

The formula for ultrasonic power is derived which has corrected the position of pressure reflection coefficient on the interface of water and steel. The diffraction correction for focusing transducers is evaluated using numerical computation of the Rayleigh integral. One way to estimate the reflection coefficient of focusing beams on heterogeneous interface is also depicted.

Findings

Comparison experiment with radiation force balance method demonstrates that ultrasonic power measurement using self-reciprocity is sound in theory and feasible in practice.

Originality/value

It has a better capability of anti-environmental interference and, thus, can be extended to low-level and high-frequency power measurements.

Details

Sensor Review, vol. 34 no. 4
Type: Research Article
ISSN: 0260-2288

Keywords

Article
Publication date: 5 September 2016

Amin Helmzadeh and Shahram M. Kouhsari

The purpose of this paper is to propose an efficient method for detection and modification of erroneous branch parameters in real time power system simulators. The aim of…

Abstract

Purpose

The purpose of this paper is to propose an efficient method for detection and modification of erroneous branch parameters in real time power system simulators. The aim of the proposed method is to minimize the sum of squared errors (SSE) due to mismatches between simulation results and corresponding field measurements. Assuming that the network configuration is known, a limited number of erroneous branch parameters will be detected and corrected in an optimization procedure.

Design/methodology/approach

Proposing a novel formulation that utilizes network voltages and last modified admittance matrix of the simulation model, suspected branch parameters are identified. These parameters are more likely to be responsible for large values of SSE. Utilizing a Gauss-Newton (GN) optimization method, detected parameters will be modified in order to minimize the value of SSE. Required sensitivities in optimization procedure will be calculated numerically by the real time simulator. In addition, by implementing an efficient orthogonalization method, the more effective parameter will be selected among a set of correlated parameters to avoid singularity problems.

Findings

Unlike state estimation-based methods, the proposed method does not need the mathematical functions of measurements to simulation model parameters. The method can enhance other parameter estimation methods that are based on state estimation. Simulation results demonstrate the high efficiency of the proposed optimization method.

Originality/value

Incorrect branch parameter detection and correction procedures are investigated in real time simulators.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 35 no. 5
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 25 January 2011

Sari Merilampi, Toni Björninen, Leena Ukkonen, Pekka Ruuskanen and Lauri Sydänheimo

The purpose of this paper is to develop a wireless strain sensor for measuring large strains. The sensor is based on passive ultra high‐frequency radio frequency…

1579

Abstract

Purpose

The purpose of this paper is to develop a wireless strain sensor for measuring large strains. The sensor is based on passive ultra high‐frequency radio frequency identification (RFID) technology and it can be embedded into a variety of structures.

Design/methodology/approach

Silver ink conductors and RFID tags were printed by the screen printing method on stretchable polyvinyl chloride and fabric substrates. The development of the strain‐sensitive RFID tag was based on the behavior of the selected antenna and substrate materials. Performance of the tags and the effect of mechanical strain on tag functioning were examined.

Findings

The results showed that large displacements can be successfully measured wirelessly using a stretchable RFID tag as a strain‐sensitive structure. The behavior of the tag can be modified by selection of the material.

Research limitations/implications

New tag designs, which are more sensitive to small levels of strain and which have a linear response will be the subject for future work. Tag performance under cyclic loading and in a real environment will also be investigated. Future work relating the investigation of practical applications and the system designing for the strain sensor will also be required.

Practical implications

Printing is fast and simple manufacturing process which does not produce much waste or material loss. The sensor is a new application of printed electronics. It also provides new opportunities for system designers.

Originality/value

The paper provides a new kind of wireless strain sensor which can be integrated into many structures (i.e. clothes). The sensor is a new application of printed electronics and it is made from novel materials.

Details

Sensor Review, vol. 31 no. 1
Type: Research Article
ISSN: 0260-2288

Keywords

Article
Publication date: 1 May 1988

John F. Gaski

The author sets out to achieve a better measurement of interorganisational power in distribution channels.

Abstract

The author sets out to achieve a better measurement of interorganisational power in distribution channels.

Details

International Journal of Physical Distribution & Materials Management, vol. 18 no. 5
Type: Research Article
ISSN: 0269-8218

Article
Publication date: 18 August 2021

Gowtham Venkatraman, Adam Hehr, Leon M. Headings and Marcelo J. Dapino

Ultrasonic additive manufacturing (UAM) is a solid-state joining technology used for three-dimensional printing of metal foilstock. The electrical power input to the…

Abstract

Purpose

Ultrasonic additive manufacturing (UAM) is a solid-state joining technology used for three-dimensional printing of metal foilstock. The electrical power input to the ultrasonic welder is a key driver of part quality in UAM, but under the same process parameters, it can vary widely for different build geometries and material combinations because of mechanical compliance in the system. This study aims to model the relationship between UAM weld power and system compliance considering the workpiece (geometry and materials) and the fixture on which the build is fabricated.

Design/methodology/approach

Linear elastic finite element modeling and experimental modal analysis are used to characterize the system’s mechanical compliance, and linear system dynamics theory is used to understand the relationship between weld power and compliance. In-situ measurements of the weld power are presented for various build stiffnesses to compare model predictions with experiments.

Findings

Weld power in UAM is found to be largely determined by the mechanical compliance of the build and insensitive to foil material strength.

Originality/value

This is the first research paper to develop a predictive model relating UAM weld power and the mechanical compliance of the build over a range of foil combinations. This model is used to develop a tool to determine the process settings required to achieve a consistent weld power in builds with different stiffnesses.

1 – 10 of over 77000