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Article
Publication date: 4 January 2016

Xiayu Zheng, Yuhua Wang and Dongfang Lu

The purpose of this paper is to model the particle capture of elliptic magnetic matrices for parallel stream type high magnetic separation, which can be a guidance for the…

162

Abstract

Purpose

The purpose of this paper is to model the particle capture of elliptic magnetic matrices for parallel stream type high magnetic separation, which can be a guidance for the development of novel elliptic cylinder matrices for high-gradient magnetic separation (HGMS).

Design/methodology/approach

The magnetic field distribution around the elliptic matrices is investigated quantitatively and the magnetic field and gradient were calculated. The motion equations of the magnetic particles around the matrices were derived and the particle capture cross-section of elliptic matrices was studied and was compared with that of the conventional circular matrices.

Findings

Elliptic matrices can present larger particle capture cross-section than the conventional circular matrices and can be a kind of promising matrices to be applied to HGMS.

Originality/value

There is little literature investigating the magnetic characteristics and the particle capture of the elliptic matrices in HGMS, the study is of great significance for the development of novel elliptic magnetic matrices in HGMS.

Details

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, vol. 35 no. 1
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 4 February 2021

Easir Arafat Papon, Anwarul Haque and Muhammad Ali Rob Sharif

This paper aims to develop a numerical model of bead spreading architecture of a viscous polymer in fused filament fabrication (FFF) process with different nozzle…

Abstract

Purpose

This paper aims to develop a numerical model of bead spreading architecture of a viscous polymer in fused filament fabrication (FFF) process with different nozzle geometry. This paper also focuses on the manufacturing feasibility of the nozzles and 3D printing of the molten beads using the developed nozzles.

Design/methodology/approach

The flow of a highly viscous polymer from a nozzle, the melt expansion in free space and the deposition of the melt on a moving platform are captured using the FLUENT volume of fluid (VOF) method based computational fluid dynamics code. The free surface motion of the material is captured in VOF, which is governed by the hydrodynamics of the two-phase flow. The phases involved in the numerical model are liquid polymer and air. A laminar, non-Newtonian and non-isothermal flow is assumed. Under such assumptions, the spreading characteristic of the polymer is simulated with different nozzle-exit geometries. The governing equations are solved on a regular stationary grid following a transient algorithm, where the boundary between the polymer and the air is tracked by piecewise linear interface construction (PLIC) to reconstruct the free surface. The prototype nozzles were also manufactured, and the deposition of the molten beads on a flatbed was performed using a commercial 3D printer. The deposited bead cross-sections were examined through optical microscopic examination, and the cross-sectional profiles were compared with those obtained in the numerical simulations.

Findings

The numerical model successfully predicted the spreading characteristics and the cross-sectional shape of the extruded bead. The cross-sectional shape of the bead varied from elliptical (with circular nozzle) to trapezoidal (with square and star nozzles) where the top and bottom surfaces are significantly flattened (which is desirable to reduce the void spaces in the cross-section). The numerical model yielded a good approximation of the bead cross-section, capturing most of the geometric features of the bead with a reasonable qualitative agreement compared to the experiment. The quantitative comparison of the cross-sectional profiles against experimental observation also indicated a favorable agreement. The significant improvement observed in the bead cross-section with the square and star nozzles is the flattening of the surfaces.

Originality/value

The developed numerical algorithm attempts to address the fundamental challenge of voids and bonding in the FFF process. It presents a new approach to increase the inter-bead bonding and reduce the inter-bead voids in 3D printing of polymers by modifying the bead cross-sectional shape through the modification of nozzle exit-geometry. The change in bead cross-sectional shape from elliptical (circular) to trapezoidal (square and star) cross-section is supposed to increase the contact surface area and inter-bead bonding while in contact with adjacent beads.

Details

Rapid Prototyping Journal, vol. 27 no. 3
Type: Research Article
ISSN: 1355-2546

Keywords

Book part
Publication date: 18 January 2022

Arnab Bhattacharjee, Jan Ditzen and Sean Holly

The authors provide a way to represent spatial and temporal equilibria in terms of error correction models in a panel setting. This requires potentially two different…

Abstract

The authors provide a way to represent spatial and temporal equilibria in terms of error correction models in a panel setting. This requires potentially two different processes for spatial or network dynamics, both of which can be expressed in terms of spatial weights matrices. The first captures strong cross-sectional dependence, so that a spatial difference, suitably defined, is weakly cross-section dependent (granular) but can be non-stationary. The second is a conventional weights matrix that captures short-run spatio-temporal dynamics as stationary and granular processes. In large samples, cross-section averages serve the first purpose and the authors propose the mean group, common correlated effects estimator together with multiple testing of cross-correlations to provide the short-run spatial weights. The authors apply this model to the 324 local authorities of England, and show that our approach is useful for modeling weak and strong cross-section dependence, together with partial adjustments to two long-run equilibrium relationships and short-run spatio-temporal dynamics. This exercise provides new insights on the (spatial) long-run relationship between house prices and income in the UK.

Details

Essays in Honor of M. Hashem Pesaran: Panel Modeling, Micro Applications, and Econometric Methodology
Type: Book
ISBN: 978-1-80262-065-8

Keywords

Article
Publication date: 31 May 2022

Efe C. Balta and Atakan Altınkaynak

This paper aims to develop experimentally validated numerical models to accurately characterize the cross-sectional geometry of the deposited beads in a fused filament…

Abstract

Purpose

This paper aims to develop experimentally validated numerical models to accurately characterize the cross-sectional geometry of the deposited beads in a fused filament fabrication (FFF) process under various process conditions.

Design/methodology/approach

The presented numerical model is investigated under various fidelity with varying computational complexity. To this end, comparisons between the Newtonian, non-newtonian, isothermal and non-isothermal computational models are presented for the extrusion of polylactic acid material in an FFF process. The computational model is validated through an experimental study on an off-the-shelf FFF printer. Microscope images of experimentally printed FFF bead cross-sections corresponding to various printing conditions are digitally processed for the validation. In the experimental study, common practical printing conditions for an FFF process are tested, and the results are compared to the numerical model.

Findings

Microscope image analyses of the cross-sectional geometries of deposited beads show that the numerical model provides a precise characterization of the cross-sectional geometry under varying process parameters in terms of the cross-section outline, bead height and width. The results show that the nozzle-to-table distance has a great effect on the bead shape when compared to the extrusion rate at a given nozzle-to-table distance. Comparison of the various computational models show that the non-Newtonian isothermal model provides the best tradeoff between computational complexity and model accuracy.

Originality/value

The authors provide detailed computational models, including the extruder nozzle geometry for cases ranging from Newtonian isothermal models to non-Newtonian non-isothermal models with experimental validation. The validation study is conducted for practical process parameters that are commonly used in FFF in practice and show that the computational models provide an accurate depiction of the true process outputs. As the developed models can accurately predict process outputs, they can be used in further applications for process planning and parameter tuning.

Article
Publication date: 1 April 1993

Y. Pan

As the physical dimensions of the devices are reduced to the submicrometer regime, the hot‐carrier reliability has become an important issue in the scaling of the p‐MOSFET…

Abstract

As the physical dimensions of the devices are reduced to the submicrometer regime, the hot‐carrier reliability has become an important issue in the scaling of the p‐MOSFET as well as the n‐MOSFET. In this paper, we present a unified approach for p‐MOSFET degradation due to the trapping of the hot electrons in the gate oxide layers. A physical analytical model, based on the pseudo two‐dimensional model, is derived for the first time to describe the linear and saturation drain current degradation. The model has been verified by comparing the calculation and the measurement from submicron p‐MOSFET's with different channel lengths and oxide thickness. There are no empirical parameters in the model. Two physical parameters: the capture cross section and the density of states of electron traps, which can be determined independently from the measured degradation characteristics, are valid for both the linear current and the saturation current degradation. The simple expression is very suitable for the predicting of the circuit reliability.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 12 no. 4
Type: Research Article
ISSN: 0332-1649

Article
Publication date: 3 June 2019

Salman Ahmed Shaikh, Mohd Adib Ismail, Abdul Ghafar Ismail, Shahida Shahimi and Muhammad Hakimi Mohd. Shafiai

This paper aims to study the cross section of expected returns on Shari’ah-compliant stocks in Pakistan by using single- and multi-factor asset pricing models.

Abstract

Purpose

This paper aims to study the cross section of expected returns on Shari’ah-compliant stocks in Pakistan by using single- and multi-factor asset pricing models.

Design/methodology/approach

To estimate cross section of expected returns of Shari’ah-compliant stocks, the study uses capital asset pricing model (CAPM), Fama-French three-factor model and Fama-French five-factor model. Data for the period 2001-2015 on 217 companies are used. For the market portfolio, PSX-100 and Dow Jones Islamic Index for Pakistan are used.

Findings

The study could not find empirical support for CAPM using Lintner (1965), Black et al. (1972) and Fama and Macbeth (1973) approach. Nonetheless, the relation between beta and returns is positive in up-market and negative in down-market. The results of Fama-French three-factor and five-factor models suggest that size premium is positive and significant for explaining the cross section of stock returns of small size stocks, whereas value premium is positive and significant for explaining the cross section of returns of high value stocks.

Practical implications

The results suggest that fund managers can use Shari’ah-compliant stocks for portfolio diversification and for offering specialized investments given the positive market excess returns and the existence of size and value premium on Shari’ah-compliant stocks.

Originality/value

This is the first study on Fama-French (2015) five-factor model for Islamic capital markets in Pakistan.

Details

International Journal of Islamic and Middle Eastern Finance and Management, vol. 12 no. 2
Type: Research Article
ISSN: 1753-8394

Keywords

Article
Publication date: 1 October 2008

P. de Jager

Empirical accounting research frequently makes use of data sets with a time‐series and a cross‐sectional dimension ‐ a panel of data. The literature review indicates that…

Abstract

Empirical accounting research frequently makes use of data sets with a time‐series and a cross‐sectional dimension ‐ a panel of data. The literature review indicates that South African researchers infrequently allow for heterogeneity between firms when using panel data and the empirical example shows that regression results that allow for firm heterogeneity are materially different from regression results that assume homogeneity among firms. The econometric analysis of panel data has advanced significantly in recent years and accounting researchers should benefit from those improvements.

Details

Meditari Accountancy Research, vol. 16 no. 2
Type: Research Article
ISSN: 1022-2529

Keywords

Article
Publication date: 31 May 2013

Yaz Gulnur Muradoglu and Sheeja Sivaprasad

The purpose of this paper is to explore the effect of leverage mimicking factor portfolios in explaining stock return variations. This paper broadens the focus of the…

1808

Abstract

Purpose

The purpose of this paper is to explore the effect of leverage mimicking factor portfolios in explaining stock return variations. This paper broadens the focus of the current asset pricing literature by forming portfolios mimicking the leverage factor.

Design/methodology/approach

Following Fama and French's and Carhart's procedure in forming size, book‐to‐market and momentum mimicking portfolios, the authors of this paper form leverage mimicking factor portfolios to explain stock returns. A five factor model is constructed that explains the variations in stock returns better relative to the other asset pricing models including the Fama‐French‐Carhart four factor model.

Findings

The findings indicate that the leverage mimicking portfolio helps to explain stock return variations better relative to the other asset pricing models including the Fama‐French‐Carhart four factor model. Results are robust to other risk factors.

Research limitations/implications

The results lead us to explore further avenues in using other risk factors in asset pricing such as future work to consider other cross‐sectional attributes such as the stochastic behaviour of earnings or profitability that might also produce common variation in stock returns. There may be other risk factors that carry a premium and thus can be used for asset pricing.

Practical implications

The paper's findings are important in fund management when selecting or evaluating portfolio performance. The authors introduce an additional factor that has a sound theoretical appeal and show that leverage mimicking factor portfolios provide additional information in pricing assets, both in the cross section of all shares and in different sectors.

Originality/value

To the best of the authors' knowledge this is the first study of the effect of leverage mimicking factor portfolios in explaining stock return variations.

Details

Studies in Economics and Finance, vol. 30 no. 2
Type: Research Article
ISSN: 1086-7376

Keywords

Article
Publication date: 1 April 1986

G.V. GADIYAK, M.S. OBRECHT and S.P. SINITSA

In this paper we consider the effects of recombination during polarization on passing a current through SiN4 and SiO2. In the literature, some works have been devoted to…

Abstract

In this paper we consider the effects of recombination during polarization on passing a current through SiN4 and SiO2. In the literature, some works have been devoted to the problem of the passage of a current through MNOS‐structures. However, these studies related mainly to monopolar injection or bipolar injection but ignored recombination.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 5 no. 4
Type: Research Article
ISSN: 0332-1649

Article
Publication date: 14 October 2019

Muhammad Hanif, Abdullah Iqbal and Zulfiqar Shah

This study aims to understand and document the impact of market-based – market returns and momentum – as well as firm-specific – size, book-to-market (B/M) ratio…

Abstract

Purpose

This study aims to understand and document the impact of market-based – market returns and momentum – as well as firm-specific – size, book-to-market (B/M) ratio, price-to-earnings ratio (PER) and cash flow (CF) – factors on pricing of Shari’ah-compliant securities as explanation of variations in stock returns in an emerging market – Pakistan’s Karachi Stock Exchange.

Design/methodology/approach

Initially, the authors test Fama and French (FF) three-factor model – market risk premium, size and B/M – followed by modified FF model by including additional risk factors (PER, CF and momentum) over a 10-year period (2001-2010).

Findings

Our results support superiority of FF three-factor model over single-factor capital asset pricing model. However, addition of further risk factors – including PER, CF and momentum – improves explanatory power of the model, as well as refines the selection of risk factors. In this study, CF, B/M and momentum factors remain insignificant. Traditional B/M factor in FF model is replaced by PER.

Practical implications

Based on the modified FF model, the authors propose a stock valuation model for Shari’ah-compliant securities consisting of three factors: market returns, size and earnings, which explains 76per cent variations in cross sectional stock returns.

Originality/value

To the best of the authors’ knowledge, this is the first study (which combines market-based as well as fundamental factors) on pricing of Islamic securities and identification of risk factors in an emerging market – Karachi Stock Exchange.

Details

Journal of Islamic Accounting and Business Research, vol. 10 no. 5
Type: Research Article
ISSN: 1759-0817

Keywords

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