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Article
Publication date: 20 May 2020

Houzhe Zhang, Defeng Gu, Xiaojun Duan, Kai Shao and Chunbo Wei

The purpose of this paper is to focus on the performance of three typical nonlinear least-squares estimation algorithms in atmospheric density model calibration.

Abstract

Purpose

The purpose of this paper is to focus on the performance of three typical nonlinear least-squares estimation algorithms in atmospheric density model calibration.

Design/methodology/approach

The error of Jacchia-Roberts atmospheric density model is expressed as an objective function about temperature parameters. The estimation of parameter corrections is a typical nonlinear least-squares problem. Three algorithms for nonlinear least-squares problems, Gauss–Newton (G-N), damped Gauss–Newton (damped G-N) and Levenberg–Marquardt (L-M) algorithms, are adopted to estimate temperature parameter corrections of Jacchia-Roberts for model calibration.

Findings

The results show that G-N algorithm is not convergent at some sampling points. The main reason is the nonlinear relationship between Jacchia-Roberts and its temperature parameters. Damped G-N and L-M algorithms are both convergent at all sampling points. G-N, damped G-N and L-M algorithms reduce the root mean square error of Jacchia-Roberts from 20.4% to 9.3%, 9.4% and 9.4%, respectively. The average iterations of G-N, damped G-N and L-M algorithms are 3.0, 2.8 and 2.9, respectively.

Practical implications

This study is expected to provide a guidance for the selection of nonlinear least-squares estimation methods in atmospheric density model calibration.

Originality/value

The study analyses the performance of three typical nonlinear least-squares estimation methods in the calibration of atmospheric density model. The non-convergent phenomenon of G-N algorithm is discovered and explained. Damped G-N and L-M algorithms are more suitable for the nonlinear least-squares problems in model calibration than G-N algorithm and the first two algorithms have slightly fewer iterations.

Details

Aircraft Engineering and Aerospace Technology, vol. 92 no. 7
Type: Research Article
ISSN: 1748-8842

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Book part
Publication date: 18 March 2014

John Komlos and Leonard Carlson

We analyze heights of Indian scouts in the U.S. army born between ca. 1825 and 1875. Their average height of ca. 170 cm (67 in.) confirms that natives were tall compared…

Abstract

We analyze heights of Indian scouts in the U.S. army born between ca. 1825 and 1875. Their average height of ca. 170 cm (67 in.) confirms that natives were tall compared to Europeans but were nearly the shortest among the rural populations in the New World. The trend in their height describes a slightly inverted “U” shape with an increase between those born 1820–1834 and 1835–1839 of ca. 1.8 cm (0.7 in.) (p = 0.000) and a subsequent slight decline after the Civil War. This implies that they were able to maintain and perhaps even improve their nutritional status through the Civil War, though harder times followed for those born thereafter. We also recalculate the heights of Native Americans in the Boas sample and find that the Plains Indians were shorter than most rural Americans. The trend in the height of Indians in the Boas sample is similar to that of the scouts.

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Research in Economic History
Type: Book
ISBN: 978-1-78350-487-9

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Book part
Publication date: 30 September 2020

Gregori Galofré-Vilà

In this chapter, network analysis has been used to map out disciplinary areas of research and authorship in economic history. A total of 5,330 peer-reviewed articles…

Abstract

In this chapter, network analysis has been used to map out disciplinary areas of research and authorship in economic history. A total of 5,330 peer-reviewed articles published in the leading economic history journals has been surveyed. Since 1980, the number of publications has risen and then rapidly accelerated over the last 2 decades. This rise has been fueled by research being conducted within European universities instead of US or UK ones.

Details

Research in Economic History
Type: Book
ISBN: 978-1-83909-179-7

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Book part
Publication date: 19 November 2012

Sabrina Khanniche

Purpose – This chapter aimed to investigate hedge funds market risk. One aims to go further the traditional measures of risk that underestimates it by introducing a more…

Abstract

Purpose – This chapter aimed to investigate hedge funds market risk. One aims to go further the traditional measures of risk that underestimates it by introducing a more appropriate method to hedge funds. One demonstrates that daily hedge fund return distributions are asymmetric and leptokurtic. Furthermore, volatility clustering phenomenon and the existence of ARCH effects demonstrate that hedge funds volatility varies through time. These features suggest the modelisation of their volatility using symmetric (GARCH) and asymmetric (EGARCH and TGARCH) models used to evaluate a 1-day-ahead value at risk (VaR).

Methodology/Approach – The conditional variances were estimated under the assumption that residuals t follow the normal and the student law. The knowledge of the conditional variance was used to forecast 1-day-ahead VaR. The estimations are compared with the Gaussian, the student and the modified VaR. To sum up, 12 VaRs are computed; those based on standard deviation and computed with normal, student and cornish fisher quantile and those based on conditional volatility models (GARCH, TGARCH and EGARCH) computed with the same quantiles.

Findings – The results demonstrate that VaR models based on normal quantile underestimate risk while those based on student and cornish fisher quantiles seem to be more relevant measurements. GARCH-type VaRs are very sensitive to changes in the return process. Back-testing results show that the choice of the model used to forecast volatility has an importance. Indeed, the VaR based on standard deviation is not relevant to measure hedge funds risks as it fails the appropriate tests. On the opposite side, GARCH-, TGARCH- and EGARCH-type VaRs are accurate as they pass most of the time successfully the back-testing tests. But, the quantile used has a more significant impact on the relevance of the VaR models considered. GARCH-type VaR computed with the student and especially cornish fisher quantiles lead to better results, which is consistent with Monteiro (2004) and Pochon and Teïletche (2006).

Originality/Value of chapter – A large set of GARCH-type models are considered to estimate hedge funds volatility leading to numerous evaluation of VaRs. These estimations are very helpful. Indeed, public savings under institutional investors management then delegate to hedge funds are concerned. Therefore, an adequate risk management is required. Another contribution of this chapter is the use of daily data to measure all hedge fund strategies risks.

Details

Recent Developments in Alternative Finance: Empirical Assessments and Economic Implications
Type: Book
ISBN: 978-1-78190-399-5

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Article
Publication date: 1 February 1971

Peter Kyle

Looks at the problems and methods of providing companies with detailed information about their own sales and marketing costs. Shows how a database can be constructed using…

Abstract

Looks at the problems and methods of providing companies with detailed information about their own sales and marketing costs. Shows how a database can be constructed using the concept of marketing cost analysis. Describes profitability analysis for customers, products and any market segment required. Discusses potential problems with accuracy and the marginal cost approach, going on to show how the database should be expanded to form a complete marketing information system.

Details

European Journal of Marketing, vol. 5 no. 2
Type: Research Article
ISSN: 0309-0566

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Article
Publication date: 2 August 2019

Sokchea Lim and A.K.M. Mahbub Morshed

The purpose of this paper is to examine the dynamics and persistence of interpersonal trust among immigrants in the USA. More specifically, the authors investigate the…

Abstract

Purpose

The purpose of this paper is to examine the dynamics and persistence of interpersonal trust among immigrants in the USA. More specifically, the authors investigate the association between the levels of trust of US immigrants and the levels of trust in their home countries across different cohorts and generations of immigrants.

Design/methodology/approach

In order to quantify the extent of this relationship, the authors use two large sets of survey data, the General Social Survey and the World Value Survey, to construct the trust of immigrants in the USA and their levels of trust in their country of origin. The final sample size for the immigrants’ trust is 27,531 observations.

Findings

The examination of the two trust variables at different levels and for different cohorts show that there is an association between the levels of US immigrants’ trust and the levels of trust in the country of origin, suggesting that immigrants bring their culture with them and transmit it to the next generation. However, this association differs across various cohorts and generations of immigrants. The transmission of trust is strong in the second generation but becomes weaker in the third generation and seems to disappear in the fourth generation.

Social implications

Empirical estimates of how long the cultural traits embodied in a new immigrant are sustained in the newly adopted country are essential to the appraisal of the current apparent segregation of immigrants in the USA.

Originality/value

This paper focuses on the under-researched area of the dynamic properties of immigrants’ trust by using large data sets from social surveys. The authors examine this cultural assimilation across different cohorts and generations.

Details

Journal of Economic Studies, vol. 46 no. 3
Type: Research Article
ISSN: 0144-3585

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Article
Publication date: 6 June 2019

Joanne Roberts

Through a critical review of the impact of luxury international business, this study aims to contribute to an understanding of business activities that depend on an…

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Abstract

Purpose

Through a critical review of the impact of luxury international business, this study aims to contribute to an understanding of business activities that depend on an unequal distribution of income and wealth.

Design/methodology/approach

Drawing on a wide range of academic and practitioner literature, this study adopts a critical luxury studies approach to provide an assessment of the economic and social impact of luxury international business.

Findings

Luxury is an increasingly important sector of the economy, which contributes to the welfare of increasing numbers of people across the world. Alongside its dependence on an unequal distribution of income and wealth and the negative aspects to which this gives rise, luxury business generates significant benefits to the economy and society through promoting economic growth, innovation, cultural enrichment, improved quality of the built environment and environmentally sustainable business practices. Nevertheless, an appropriate level of regulation and taxation on the excesses of contemporary luxury consumption could improve the welfare of all. Hence, luxury international business warrants investigation by critical scholars who recognize the complexity of the benefits and dark sides arising from luxury.

Research limitations/implications

This study draws on an extensive review of academic and practitioner literature. However, primary research is required to investigate further the key issues identified.

Social implications

Through an exploration of the impact of the production and consumption of luxury, this study reveals how luxury businesses serving the super-rich can contribute to the welfare of society whilst also giving rise to negative outcomes.

Originality/value

By adopting a critical luxury studies approach, this study offers an original contribution to the field of international business and introduces avenues for future critical international business research.

Details

critical perspectives on international business, vol. 15 no. 2/3
Type: Research Article
ISSN: 1742-2043

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Article
Publication date: 1 June 2000

A. Savini

Gives introductory remarks about chapter 1 of this group of 31 papers, from ISEF 1999 Proceedings, in the methodologies for field analysis, in the electromagnetic…

Abstract

Gives introductory remarks about chapter 1 of this group of 31 papers, from ISEF 1999 Proceedings, in the methodologies for field analysis, in the electromagnetic community. Observes that computer package implementation theory contributes to clarification. Discusses the areas covered by some of the papers ‐ such as artificial intelligence using fuzzy logic. Includes applications such as permanent magnets and looks at eddy current problems. States the finite element method is currently the most popular method used for field computation. Closes by pointing out the amalgam of topics.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 19 no. 2
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 1 March 1991

Yu‐Kun FENG

A new method is derived for solving systems of ordinary differential equations of the first order. It is fully explicit, requires no matrix inversion, and shows relatively…

Abstract

A new method is derived for solving systems of ordinary differential equations of the first order. It is fully explicit, requires no matrix inversion, and shows relatively large time steps. The one‐ and two‐dimensional diffusion equations and the one‐dimensional electron transport equations of semiconductor devices are solved to demonstrate both the accuracy and the efficiency of the proposed method. This method is accurate and efficient when results are compared with analytical solutions.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 10 no. 3
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 6 June 2008

Heila Pienaar and Ina Smith

The purpose of this paper is to describe the development of a Library 2.0 service model for an African library.

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1549

Abstract

Purpose

The purpose of this paper is to describe the development of a Library 2.0 service model for an African library.

Design/methodology/approach

The paper focuses on the academic library at the University of Pretoria (UP), South Africa.

Findings

The UP is well on its way to becoming a Library 2/0 library.

Originality/value

This case study may pave the way for other academic libraries to integrate Library 2.0 within their service offering to the benefit of all.

Details

Library Hi Tech News, vol. 25 no. 5
Type: Research Article
ISSN: 0741-9058

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