The effect of friction on indenter force and pile-up in numerical simulations of bone nanoindentation

Nanoindentation is a useful technique for probing the mechanical properties of bone, and finite element (FE) modeling of the indentation allows inverse determination of elasto-plastic constitutive properties. However, FE simulations to date have assumed frictionless contact between indenter and bone. The aim of this study was to explore the effect of friction in simulations of bone nanoindentation. Two dimensional axisymmetric FE simulations were performed using a spheroconical indenter of tip radius 0.6m and angle 90°. The coefficient of friction between indenter and bone was varied between 0.0 (frictionless) and 0.3. Isotropic linear elasticity was used in all simulations, with bone elastic modulus E=13.56GPa and Poisson’s ratio =0.3. Plasticity was incorporated using both Drucker-Prager and von Mises yield surfaces. Friction had a modest effect on the predicted force-indentation curve for both von Mises and Drucker-Prager plasticity, reducing maximum indenter displacement by 10% and 20% respectively as friction coefficient was increased from zero to 0.3 (at a maximum indenter force of 5mN). However, friction has a much greater effect on predicted pile-up after indentation, reducing predicted pile-up from 0.27m to 0.11m with a von Mises model, and from 0.09m to 0.02m with Drucker-Prager plasticity. We conclude that it is important to include friction in nanoindentation simulations of bone.

Internal audit department characteristics/activities and audit fees : some evidence from Hong Kong firms

This study provides preliminary support for the notion that internal audit function assists in reducing external audit effort and fees. Data on internal audit characteristics and activities are obtained from survey respondents of Hong Kong companies and audit fee model data are acquired from their annual reports. The results of this study suggest that the external auditor of firms in Hong Kong rely on the internal audit function and subsequently charge a lower fee. Lower external audit fees are associated with a larger internal audit department and certain activities carried out by the internal audit. Specifically, lower external audit fees are associated with more internal audit effort spent on activities relating to financial statements, systems development and maintenance, operating efficiency and effectiveness, fraud investigations and unlimited access to internal auditors’ working papers. The results of this study suggest that the contribution of the internal audit may substitute for some substantive external auditing processes and lower monitoring costs.

L'Impatto delle Condizioni Interne ed Esterne sul Ruolo del Cda : un'Analisi Empirica sulle Grandi Imprese Italiane [The impact of internal and external contingencies on board tasks performance : an empirical investigation of Italian companies]

Il Consiglio di Amministrazione (CdA) è il principale organo di governo delle aziende. La letteratura gli attribuisce tre ruoli: controllo, indirizzo strategico e collegamento con l’ambiente (networking). Precedenti studi empirici hanno analizzato se un Consiglio di Amministrazione è attivo o meno in tutti e tre i ruoli in un dato momento. Nel presente lavoro, invece, si propone un approccio «contingente» e si analizzano i ruoli svolti dal CdA al variare delle condizioni interne (aziende in crisi o di successo) ed esterne (aziende in settori competitivi o regolamentati).. L’indagine empirica è stata condotta su un campione di 301 imprese italiane di grandi dimensioni. I risultati supportano la tesi iniziale secondo cui le condizioni interne ed esterne incidono sul ruolo svolto dal CdA. In particolare i risultati evidenziano che il CdA non svolge sempre tutti e tre i ruoli nello stesso momento, ma esso si concentra sul ruolo o sui ruoli che assumono grande importanza nella situazione in cui si trova l’azienda. Con riferimento alle condizioni interne, nelle imprese in crisi il CdA è attivo in tutti e tre i ruoli, mentre in quelle di successo prevale un orientamento verso la funzione strategica. Nelle aziende che operano in settori competitivi il ruolo di controllo è più pressante mentre nei settori regolamentati prevale una funzione di networking.

Internal market orientation and market-oriented behaviours

Purpose: The purpose of this empirical paper is to investigate internal marketing from a behavioural perspective. The impact of internal marketing behaviours, operationalised as an internal market orientation (IMO), on employees’ marketing and other in-role behaviours (IRB) were examined. ---------- Design/methodology/approach: Survey data measuring IMO, market orientation and a range of constructs relevant to the nomological network in which they are embedded were collected from the UK retail managers. These were tested to establish their psychometric properties and the conceptual model was analysed using structural equations modelling, employing a partial least squares methodology. ---------- Findings: IMO has positive consequences for employees’ market-oriented and other IRB. These, in turn, influence marketing success. Research limitations/implications – The paper provides empirical support for the long-held assumption that internal and external marketing are related and that organisations should balance their external focus with some attention to employees. Future research could measure the attitudes and behaviours of managers, employees and customers directly and explore the relationships between them. ---------- Practical implications: Firm must ensure that they do not put the needs of their employees second to those of managers and shareholders; managers must develop their listening skills and organisations must become more responsive to the needs of their employees. ---------- Originality/value: The paper contributes to the scarce body of empirical support for the role of internal marketing in services organisations. For researchers, this paper legitimises the study of internal marketing as a route to external market success; for managers, the study provides quantifiable evidence that focusing on employees’ wants and needs impacts their behaviours towards the market.

The effect of friction on indenter force and pile-up in numerical simulations of bone nanoindentation

Nanoindentation is a useful technique for probing the mechanical properties of bone, and finite element (FE) modeling of the indentation allows inverse determination of elasto-plastic constitutive properties. However, all but one FE study to date have assumed frictionless contact between indenter and bone. The aim of this study was to explore the effect of friction in simulations of bone nanoindentation. Two dimensional axisymmetric FE simulations were performed using a spheroconical indenter of tip radius 0.6 m and angle 90°. The coefficient of friction between indenter and bone was varied between 0.0 (frictionless) and 0.3. Isotropic linear elasticity was used in all simulations, with bone elastic modulus E=13.56GPa and Poisson‟s ratio f 0.3. Plasticity was incorporated using both Drucker-Prager and von Mises yield surfaces. Friction had a modest effect on the predicted force-indentation curve for both von Mises and Drucker-Prager plasticity, reducing maximum indenter displacement by 10% and 20% respectively as friction coefficient was increased from zero to 0.3 (at a maximum indenter force of 5mN). However, friction has a much greater effect on predicted pile-up after indentation, reducing predicted pile-up from 0.27 to 0.11 m with a von Mises model, and from 0.09 to 0.02 m with Drucker-Prager plasticity. We conclude that it is potentially important to include friction in nanoindentation simulations of bone if pile-up is used to compare simulation results with experiment.

Application of an optimisation algorithm to configure an internal fixation device

Fractures of long bones are sometimes treated using various types of fracture fixation devices including internal plate fixators. These are specialised plates which are used to bridge the fracture gap(s) whilst anatomically aligning the bone fragments. The plate is secured in position by screws. The aim of such a device is to support and promote the natural healing of the bone. When using an internal fixation device, it is necessary for the clinician to decide upon many parameters, for example, the type of plate and where to position it; how many and where to position the screws. While there have been a number of experimental and computational studies conducted regarding the configuration of screws in the literature, there is still inadequate information available concerning the influence of screw configuration on fracture healing. Because screw configuration influences the amount of flexibility at the area of fracture, it has a direct influence on the fracture healing process. Therefore, it is important that the chosen screw configuration does not inhibit the healing process. In addition to the impact on the fracture healing process, screw configuration plays an important role in the distribution of stresses in the plate due to the applied loads. A plate that experiences high stresses is prone to early failure. Hence, the screw configuration used should not encourage the occurrence of high stresses. This project develops a computational program in Fortran programming language to perform mathematical optimisation to determine the screw configuration of an internal fixation device within constraints of interfragmentary movement by minimising the corresponding stress in the plate. Thus, the optimal solution suggests the positioning and number of screws which satisfies the predefined constraints of interfragmentary movements. For a set of screw configurations the interfragmentary displacement and the stress occurring in the plate were calculated by the Finite Element Method. The screw configurations were iteratively changed and each time the corresponding interfragmentary displacements were compared with predefined constraints. Additionally, the corresponding stress was compared with the previously calculated stress value to determine if there was a reduction. These processes were continued until an optimal solution was achieved. The optimisation program has been shown to successfully predict the optimal screw configuration in two cases. The first case was a simplified bone construct whereby the screw configuration solution was comparable with those recommended in biomechanical literature. The second case was a femoral construct, of which the resultant screw configuration was shown to be similar to those used in clinical cases. The optimisation method and programming developed in this study has shown that it has potential to be used for further investigations with the improvement of optimisation criteria and the efficiency of the program.

Investigating the development of the internal and external service tasks of non-executive directors: the case of the Netherlands (1997-2005)

During the last decade, globalisation and liberalisation of financial markets, changing societal expectations and corporate governance scandals have increased the attention for the fiduciary duties of non-executive directors. In this context, recent corporate governance reform initiatives have emphasised the control task and independence of non-executive directors. However, little attention has been paid to their impact on the external and internal service tasks of non-executive directors. Therefore, this paper investigates how the service tasks of non-executive directors have evolved in the Netherlands. Data on corporate governance at the top-100 listed companies in the Netherlands between 1997 and 2005 show that the emphasis on non-executive directors' external service task has shifted to their internal service task, i.e. from non-executive directors acting as boundary spanners to non-executive directors providing advice and counselling to executive directors. This shift in board responsibilities affects non-executive directors' ability to generate network benefits through board relationships and has implications for non-executive directors' functional requirements.