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Article

Marie Björk and Gunilla Pettersson-Berggren

The purpose of this paper is to investigate what might be relevant to younger children’s understanding of a number line and how teaching can be designed according to…

Abstract

Purpose

The purpose of this paper is to investigate what might be relevant to younger children’s understanding of a number line and how teaching can be designed according to variation theory to give pupils the opportunity to develop an understanding of the number line as a tool for mathematical thinking.

Design/methodology/approach

A Learning Study was conducted by mathematics teachers at Sjöstadsskolan in Stockholm. Variation theory was used as a theory of learning. In order to use the number line as a tool in mathematical thinking, pupils have to discern what is important for this form of representation of the numeral system. Critical aspects from other studies with similar learning objects have been taken into consideration for pre-test design. These aspects supplemented and enhanced the analysis of the results and the results were consistent with earlier learning studies’.

Findings

Four critical features, for younger pupils’ understanding of how the number line can be constructed, have been established in the study: the number line can have a different range (e.g. 0-20 or 30-60), correlation between the distance and value, two reference points are needed to place a third number and determine the scale, and the correlation between a part and whole.

Originality/value

Learning Study is emphasized as a powerful and structured model for teacher driven research aiming to develop the praxis. The use of experiences and results from other studies is recommended.

Details

International Journal for Lesson and Learning Studies, vol. 4 no. 4
Type: Research Article
ISSN: 2046-8253

Keywords

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Article

Shantanu Pramanik and Manab Kumar Das

The purpose of the present study is to investigate the flow and turbulence characteristics of a turbulent wall jet flowing over a surface inclined with the horizontal and…

Abstract

Purpose

The purpose of the present study is to investigate the flow and turbulence characteristics of a turbulent wall jet flowing over a surface inclined with the horizontal and to investigate the effect of variation of the angle of inclination of the wall on the flow structure of the wall jet.

Design/methodology/approach

The high Reynolds number two-equation κ− model with standard wall function is used as the turbulence model. The Reynolds number considered for the present study is 10,000. The Reynolds averaged Navier-Stokes (RANS) equations are used for predicting the turbulent flow. A staggered differencing technique employing both contravariant and Cartesian components of velocity has been applied. Results for distribution of wall static pressure and skin friction, decay of maximum streamwise velocity, streamwise variation of integral momentum and energy flux have been compared for the cases of α=0°, 5°, and 10°.

Findings

Flow field has been represented in terms of streamwise and lateral velocity contours, static pressure contour, vorticity contour and streamwise velocity and static pressure profiles at different locations along the oblique offset plate. Distribution of Reynolds stresses in terms of spanwise, lateral and turbulent shear stresses, and turbulent kinetic energy and its dissipation rate have been presented to describe the turbulent characteristics. Similarity of streamwise velocity and the velocity parallel to the oblique wall has been observed in the developed region of the wall jet flow. A decaying trend is observed in the variation of total integral momentum flux in the developed region of the wall jet which becomes more evident with increase in oblique angle. Developed flow region has indicated trend of similarity in profiles of streamwise velocity as well as velocity component parallel to the oblique wall. A depression in wall static pressure has been observed near the nozzle exit when the wall is inclined and the depression increases with increase in inclination. Effect of variation of oblique angles on skin friction coefficient has indicated that it decreases with increase in oblique angle. Growth of the outer and inner shear layers and spread of the jet shows linear variation with distance along the oblique wall. Decay of maximum streamwise velocity is found to be unaffected by variation in oblique angle except in the far downstream region. The streamwise variation of spanwise integral energy shows increase in oblique angle and decreases the magnitude of energy flux through the domain. In the developed flow region, streamwise variation of centreline turbulent intensities shows increased values with increase in oblique angle, while turbulence intensities along the jet centreline in the region X<12 remain unaffected by change in oblique angles. Normalized turbulent kinetic energy distribution highlights the difference in turbulence characteristics between the wall jet and reattached offset jet flow. Near wall velocity distribution shows that the inner region of boundary layer of the developed oblique wall jet follows a logarithmic profile, but it shows some difference from the standard logarithmic curve of turbulent boundary layers which can be attributed to an increase in skin friction coefficient and a decrease in thickness of the wall attached layer.

Originality/value

The study presents an in-depth investigation of the interaction between the jet and the inclined wall. It is shown that due to the Coanda effect, the jet follows the nearby wall. The findings will be useful in the study of combined flow of wall jet and offset jet and dual offset jet on oblique surfaces leading to a better design of some mechanical jet flow devices.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 24 no. 2
Type: Research Article
ISSN: 0961-5539

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Article

Maria Doubenskaia, Sergey Grigoriev, Ivan Zhirnov and Igor Smurov

This paper aims to propose methods for on-line monitoring and process quality assurance of Selective Laser Melting (SLM) technology as a competitive advantage to enhance…

Abstract

Purpose

This paper aims to propose methods for on-line monitoring and process quality assurance of Selective Laser Melting (SLM) technology as a competitive advantage to enhance its implementation into modern manufacturing industry.

Design/methodology/approach

Monitoring of thermal emission from the laser impact zone was carried out by an originally developed pyrometer and a charge-coupled device (CCD) camera which were integrated with the optical system of the PHENIX PM-100 machine. Experiments are performed with variation of the basic process parameters such as powder layer thickness (0-120 μm), hatch distance (60-1,000 μm) and fabrication strategy (the so-called “one-zone” and “two-zone”).

Findings

The pyrometer signal from the laser impact zone and the 2D temperature mapping from HAZ are rather sensible to variation of high-temperature phenomena during powder consolidation imposed by variation of the operational parameters.

Research limitations/implications

Pyrometer measurements are in arbitrary units. This limitation is due to the difficulty to integrate diagnostic tools into the optical system of a commercial SLM machine.

Practical implications

Enhancement of SLM process stability and efficiency through comprehensive optical diagnostics and on-line control.

Originality/value

High-temperature phenomena in SLM were monitored coaxially with the laser beam for variation of several operational parameters.

Details

Rapid Prototyping Journal, vol. 22 no. 1
Type: Research Article
ISSN: 1355-2546

Keywords

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Book part

André van Hoorn and Robbert Maseland

The purpose of this chapter is to make sense of the cultural distance paradox through a basic assessment of the cross-cultural comparability of cultural distance measures…

Abstract

Purpose

The purpose of this chapter is to make sense of the cultural distance paradox through a basic assessment of the cross-cultural comparability of cultural distance measures. Cultural distance between a base country and partner countries is a key construct in international business (IB). However, we propose that what exactly is measured by cultural distance is unique for each country that is chosen as the base country to/from which cultural distance to a set of partner countries is calculated.

Methodology/approach

We use a mathematical argument to establish that cultural distance may correlate rather differently with the culture of partner countries depending on which base country one considers, for example, the United States or China. We then use empirical analysis to show the relevance of this argument, using Hofstede’s data on national culture for 69 countries.

Findings

Results show that cultural distance indeed has very different correlations with partner country culture, depending on which country one selects as the base country in one’s distance calculations.

Practical implications

Implication of our findings is that measured cultural distance is not equivalent across different base countries. The effect of cultural distance on such issues as foreign market entry mode or market selection, therefore, lacks international generalizability.

Originality/value

This chapter presents the first assessment of the cross-cultural comparability of cultural distance. Paradoxical findings that plague extant cultural distance research may be understood from the found lack of measurement equivalence.

Details

Multinational Enterprises, Markets and Institutional Diversity
Type: Book
ISBN: 978-1-78441-421-4

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Article

In studies of engines and engine lubricants, it is often desirable to measure clearances between shafts and sleeve—or journal‐type bearings during operation. However, it…

Abstract

In studies of engines and engine lubricants, it is often desirable to measure clearances between shafts and sleeve—or journal‐type bearings during operation. However, it is usually rather difficult to obtain such measurements without affecting the operation, particularly at high speeds. A method recently developed by M. L. Greenough and associates of the National Bureau of Standards for the Navy Bureau of Ships appears to offer a satisfactory solution of the problem. The heart of the new system is a mutual‐inductance type of electrical distance‐measuring element; variation of the distance of the rotating shaft from two small fixed coils results in a readily measurable variation in the coupling between the coils.

Details

Industrial Lubrication and Tribology, vol. 3 no. 11
Type: Research Article
ISSN: 0036-8792

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Article

M. Saadat and C. Cretin

The introduction of automation for the assembly of aircraft wing box structures will require individual components to conform closely to the CAD design specification with…

Abstract

The introduction of automation for the assembly of aircraft wing box structures will require individual components to conform closely to the CAD design specification with regard to shape geometry and dimensional tolerances. Often, due to a variety of previous manufacturing processes, the 3D shape of these large components lose the accuracy of their designed dimensional specifications. Under these circumstances part‐to‐part assembly becomes tedious and it would be impossible to rely on robots to achieve precise assembly in an automated system. For this reason, variations need to be accurately quantified in order to provide a reliable prediction model in aid of any future automated assembly. This paper describes the measurement method used to record the possible variations occurring during the assembly process. The measurements were made using a laser tracker where the results are expected to offer some explanations as to the causes of the variation. The suitability of a laser tracker in a large assembly jig environment is then assessed. This study is based on the work that was carried out at BAE Systems UK, where the Airbus commercial aircraft wings are manufactured.

Details

Assembly Automation, vol. 22 no. 3
Type: Research Article
ISSN: 0144-5154

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Article

Marcel Bolos, Ioana Bradea and Camelia Delcea

The purpose of this paper is to focus on the adjustment of the GM(1, 2) errors for financial data series that measures changes in the public sector financial indicators…

Abstract

Purpose

The purpose of this paper is to focus on the adjustment of the GM(1, 2) errors for financial data series that measures changes in the public sector financial indicators, taking into account that the errors in grey models remain a key problem in reconstructing the original data series.

Design/methodology/approach

Adjusting the errors in grey models must follow some rules that most often cannot be determined based on the chaotic trends they register in reconstructing data series. In order to ensure the adjustment of these errors, for improving the robustness of GM(1, 2), was constructed an adaptive fuzzy controller which is based on two input variables and one output variable. The input variables in the adaptive fuzzy controller are: the absolute error ε i 0 ( k ) [ % ] of GM(1, 2), and the distance between two values x i 0 ( k ) [ % ] , while the output variable is the error adjustment A ε i 0 ( k ) [ % ] determined with the help of the above-mentioned input variables.

Findings

The adaptive fuzzy controller has the advantage that sets the values for error adjustments by the intensity (size) of the errors, in this way being possible to determine the value adjustments for each element of the reconstructed financial data series.

Originality/value

To ensure a robust process of planning the financial resources, the available financial data are used for long periods of time, in order to notice the trend of the financial indicators that need to be planned. In this context, the financial data series could be reconstituted using grey models that are based on sequences of financial data that best describe the status of the analyzed indicators and the status of the relevant factors of influence. In this context, the present study proposes the construction of a fuzzy adaptive controller that with the help of the output variable will ensure the error’s adjustment in the reconstituted data series with GM(1, 2).

Details

Grey Systems: Theory and Application, vol. 6 no. 3
Type: Research Article
ISSN: 2043-9377

Keywords

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Article

Aloysio Arthur Becker Fogliatto, Carlos Henrique Ahrens, Paulo Antônio Pereira Wendhausen, Edson Costa Santos and Daniel Rodrigues

Porous structures have been widely used in filtration, medical implants and aerospace field. In the filtration field, the study of permeability of the porous structures is…

Abstract

Purpose

Porous structures have been widely used in filtration, medical implants and aerospace field. In the filtration field, the study of permeability of the porous structures is of great importance. This paper aims to study the influence of selective laser sintering/melting (SLS/SLM) process parameters on porosity and permeability of stainless steels filters with gradient porosity (FGM).

Design/methodology/approach

AISI 316L stainless steel powder was used to manufacture FGM filters by varying the hatch distance while other process parameters were fixed. The relationship between porosity and permeability of such FGM filters was investigated by means of Archimedes’ and Forchheimer’s laws. The gradient of porosity was also analyzed by means of micro-computed tomography.

Findings

The results have confirmed the ability of SLS/SLM in controlling porosity of the final product by varying the hatch distance. Further, the results allow to assume that FGM filters will have particle retention capacity related to lowest porosity value (which in turn is associated with the lowest hatch distance value used), while it will work at lower pressure drops – or at higher flow rates for equal pressure drop – when compared to a filter without gradient porosity.

Originality/value

Some research found in recent literature has showed the relationship between SLS/SLM process parameters and permeability of stainless steel porous structures. However, this paper fulfils the need to understand the relationship between SLS/SLM process parameters, porosity and permeability behavior of functionally graded porous structures (FGM filters).

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Article

Kh. Lotfy

This paper aims to investigate the transient disturbances created by an internal line heat source that suddenly starts moving uniformly inside a visco‐elastic half‐space.

Abstract

Purpose

This paper aims to investigate the transient disturbances created by an internal line heat source that suddenly starts moving uniformly inside a visco‐elastic half‐space.

Design/methodology/approach

Generalised theory of thermo‐elasticity with relaxation time proposed by Lord‐Shulman is applied. The material of the semi‐infinite medium is an isotropic visco‐elastic solid of Kelvin‐Voight type. Fourier and Laplace transform techniques are used.

Findings

Applying the Fourier and Laplace transform techniques, expressions for displacement components in the transformed domain are found. These expressions prove the existence of three waves – a modified thermal wave, a visco‐elastic wave of defused nature and a transverse visco‐elastic wave.

Research limitations/implications

Surface displacement components were evaluated on the boundary for only a short time.

Originality/value

The paper provides numerical results that are illustrated graphically to highlight the variations of surface displacement components with distance for different values of time, source depth and velocity of the source.

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Article

Tongli Lu, Chunsheng Ni and Jianwu Zhang

The purpose of this paper is to present a magnetic contactless displacement sensor with liftoff compensation. The sensor consists of two‐axis Hall sensor, moving permanent…

Abstract

Purpose

The purpose of this paper is to present a magnetic contactless displacement sensor with liftoff compensation. The sensor consists of two‐axis Hall sensor, moving permanent magnet (PM) and ferromagnetic substrate which is considered as a magnetic flux concentrator.

Design/methodology/approach

The two Hall‐effect sensors are used to detect the BX and BY induced by the moving PM. The BX and BY curves reflect the nature of the liftoff and the displacement of the inducing PM, respectively. Then the model of the displacement sensor, based on the facing current method, is constructed. Finally, the finite element method is used to compute the characteristics of BX and BY.

Findings

The BY curve can be corrected according to the liftoff distance of Hall‐effect sensor distinguished by the BX trough value. Therefore, the influence of the liftoff on the output signal can be eliminated when BY curve is corrected.

Originality/value

The paper focused on the design of a contactless displacement sensor with compensated liftoff performance for the control measurement technology in general and for automotive engineering in particular.

Details

Sensor Review, vol. 30 no. 4
Type: Research Article
ISSN: 0260-2288

Keywords

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