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Article
Publication date: 25 July 2019

Christopher Stroehlein, Hermann Landes, Andreas Krug and Peter Dietz

The purpose of this paper is to investigate magneto-mechanical coupling occurring in magnetic resonance imaging (MRI) systems. The authors study influence of the strength…

Abstract

Purpose

The purpose of this paper is to investigate magneto-mechanical coupling occurring in magnetic resonance imaging (MRI) systems. The authors study influence of the strength of the background field on the coupling of mechanically isolated, conductive cylindrical structures and the so-called shields. This coupling has a strong impact on frequency-dependent thermal losses occurring in the shield structures which are of high importance in MRI systems.

Design/methodology/approach

In the investigations, numerical methods are applied. First, finite element methods taking into account the full magneto-mechanical coupling are used to investigate the coupled physical phenomena. As these calculations may be time-consuming, several approximate predictive methods are derived. Modal expansion factors and participation factors are based on combinations of structural eigenmode calculations and eddy current calculations using Biot–Savart representations of the dynamic gradient field. In addition, a parallelism factor expressed in terms of the shield vibrations is defined to measure the coupling between the distinct cylinders.

Findings

It is found that the strength of the background field strongly influences the coupling of the distinct shields, which strongly increases the parallelism of the shield vibrations. Furthermore, modal expansion and participation factors are significantly influenced, caused by frequency shifts due to magnetic stiffening and increased magnetic coupling.

Research limitations/implications

The current work is limited to the modal expansions of a single shield. This needs to be extended in the future as comparison of modal expansion factors and finite element simulation indicate.

Originality/value

The defined factors estimating parallelism and modal participation in magneto-mechanical coupling are original work and studied for the first time.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering , vol. 38 no. 5
Type: Research Article
ISSN: 0332-1649

Keywords

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Article
Publication date: 22 August 2010

Sanja Kutnjak Ivković and Tara O'Connor Shelley

This paper aims to explore how police officer rank affects the relation between the extent of the code of silence and views of discipline fairness.

Abstract

Purpose

This paper aims to explore how police officer rank affects the relation between the extent of the code of silence and views of discipline fairness.

Design/methodology/approach

In 2005, 150 police supervisors and 450 line officers from East Bohemia, the Czech Republic were surveyed, regarding crucial components of police integrity.

Findings

Supervisor and line officer codes of silence are similar; whenever the codes differ, the supervisor code seems to be narrower. The majority of line officers and supervisors provided similar assessments of the expected discipline; they disagreed only regarding a small number of scenarios. The results clearly show a direct relation between how strongly police officers adhere to the code of silence and the way they view disciplinary fairness, regardless of their supervisory status.

Research limitations/implications

The survey included only police officers from East Bohemia in the Czech Republic.

Practical implications

The methodology can be utilized by police administrators to explore the contours of the code of silence in their agencies, police officers' views about appropriate and expected discipline, as well as the relation between the police officers' willingness to tolerate misconduct in silence, and their perceptions of the fairness of the expected discipline.

Originality/value

Studies exploring the relation between the code of silence and discipline fairness are rare. This study contributes to this scarce literature along two dimensions: first, it provides an in‐depth analysis of the relation between the extent of the code of silence and views of discipline fairness in an emerging democracy; and second, it explores the effect of police officer rank on this relation.

Details

Policing: An International Journal of Police Strategies & Management, vol. 33 no. 3
Type: Research Article
ISSN: 1363-951X

Keywords

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