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Semi-solid metal alloys, as used in thixoforming, have a special microstructure of globular grains suspended in a liquid metal matrix. The complex rheological properties are strongly influenced by the local solid fraction, particle shape, particle size and state of agglomeration. There is a high demand for models and software tools allowing the simulation of semi-solid casting processes. The material under investigation is a tin-lead alloy (Sn-15%Pb) which exhibits a similar microstructure to aluminium alloys. The experiments were performed with a concentric cylinder rheometer of the Searle type. Initially, the liquid alloy is cooled down to the semi-solid range under constant shearing and then kept under isothermal conditions for further experimentation. Based on the experimental data, a single-phase model has been derived where the semi-solid alloy is regarded as a homogeneous material with thixotropic properties and the microstructure is characterised by a structural parameter. The model consists of two parts: the equation of state, including a finite yield stress, and a rate equation for the structural parameter. The model equations are employed in numerical software and used for the simulation of characteristic filling cases and the comparison with the conventional filling.
A suspension of PMMA spheres in a density matched saccharose solution is investigated with a classical Searle rheometer and a NMR (Nuclear Magnetic Resonance) spectrometer. Here the NMR is used to measure the radial distribution of the PMMA spheres in the rotating cell, in addition to the local velocity profile of the suspension. The influence of particle concentration on the wall depletion is studied. Further analysis are carried out with computational fluid dynamics software. The velocity field as well as the solid distribution in the couette flow is simulated with a two-phase model including the Darcy law and compared to the experimental data.
Semi-solid metal alloys, as used in thixoforming, have a special microstructure of globular grains suspended in a liquid metal matrix. The material under investigation is a tin–lead alloy (Sn–15% Pb) which exhibits a similar microstructure as aluminum alloys. The experiments were performed with concentric cylinder rheometers. Initially, the liquid alloy is cooled down to the semi-solid range under constant shearing and then kept under isothermal conditions for further experimentation. The microstructure is characterized in dependence of the shearing time. The rheological techniques consisted of step change of shear rate and shear stress ramp experiments for different solid fractions (40–50%). Based on the experimental data a single phase model has been derived, where the semi-solid alloy is regarded as a homogeneous material with thixotropic properties and the microstructure is characterized by a structural parameter. The model consists of two parts: the equation of state, including a finite yield stress, and a rate equation for the structural parameter. The model equations are employed into numerical software and used for the simulation of a characteristic thixocasting process. The results are compared to real experiments.
Semi-solid metal alloys, as used in industrial thixoforming, have a special microstructure of globular grains suspended in a liquid metal matrix. The complex rheological properties are strongly influenced by the local solid fraction, particle shape, particle size and state of agglomeration. It was analysed how the microstructure develops in dependence of the shear rate and cooling rate during the solidification and it was observed that the average particle size increased with increasing shear rate and decreasing cooling rate. In order to account for those phenomena, the rate of crystal growth and the relationship between average particle diameter and viscosity was modelled by applying the Sherwood two-film model for the mass transport. The dependence of the viscosity from the particle size were modelled with a modified Krieger–Dougherty model. Based on the rheological and microstructural observations an evaluation method was elaborated that allows for the construction of objective master curves that are independent of the particle growth during the experimentation. The isothermal experiments for the characterisation of the rheological behaviour consisted of step-change of shear-rate and yield-stress experiments. From the experimental data the steady-state flow curves could be determined as well as the time-dependent relaxation of the shear stress after a change of shear rate. The steady-state rheological behaviour was found to be shear thinning. Nevertheless, immediately after a shear-rate change an overshoot was observed that resulted from a short-time shear-thickening behaviour. The yield stress was found to strongly depend on the microstructure and the degree of agglomeration of the solid phase. With increasing rest time the yield stress was increasing strongly, because of the agglomeration of the solid particles. Based on the step-change of shear-rate experiments a single-phase flow has been developed that consists of a modified Herschel–Bulkley approach and accounts for the thixotropic as well as for the yield-stress behaviour of the alloys.
Companies and R&D institutions increasingly collaborate not only in isolated projects but also in knowledge-based networks. In those networks, participants combine expertise and applied problems to generate both ‘problem-solving knowledge’ and specialized knowledge: during the process of common problem-solving each partner acquires some of the specialized knowledge of the other partners as well as the newly generated problem-solving knowledge. This article examines the basic principles involved and provides a simple mathematical description of the step-by-step accumulation of knowledge through the solving of applied problems in a knowledge-based network. The rate of increase of the total amount of available knowledge in the network is derived and implications for the orientation of R&D institutes and companies are set out.
Purpose
– The purpose of this paper is to present the current empirical research examining communication, compensation and logistics as elements of product crises management in retailing.
Design/methodology/approach
– The advantages and disadvantages of these three elements of crises response strategies are juxtaposed drawing on relevant empirical research. For each element of crises response the major findings of research are summarized and shown how it relates to crisis management. Needs for further research that would be necessary to solidify recommendations to retail managers are derived.
Findings
– The investigation finds that both communicative and compensatory response elements as well as the retailer's logistics can positively influence evaluations of customers directly and indirectly affected by product problems thus enhancing brand equity. This in turn will serve to increase consumers' trust in the retailer that could win him new customers and generally benefit his reputation.
Research limitations/implications
– Most of the discussed research rests on the assumption of a given (extraneous) crisis response strategy of the manufacturer. Potential problems concerning the co‐ordination or implementation of manufacturer and retailer strategies remain open to question. Additionally, further research should examine which strategies are appropriate to which crisis situation.
Practical implications
– Materially, over‐compensating customers often has a detrimental effect on solving the crisis. The impact of different compensation types on crisis resolution mostly depends on their respective signalling capabilities, the product problem constituting the crisis and consumer attributions. The use and the effects of a communicative crisis response largely depend on moderating factors such as the retailer's reputation or the existence of strong retail brands and consumer expectations. Elements of logistics seem to support the effects of communication and compensation on crisis resolution but are hardly capable of solving a product‐harm crisis.
Originality/value
– The role of retailers in product‐harm crisis management has been widely neglected in research although such crises are predominant. This paper outlines the current empirical work on how different crises response elements may contribute to solving a product‐harm crisis for retailers. It derives relevant avenues for further research as well as useful insights to practitioners considering to using such response elements in their own crisis management strategy.
This research paper analyzes the role of pre-crisis
reputation for quality on consumers ’ perceptions of
product-related dangers and company responsibility
in product-harm crises with varying risk information.
We consider (non-) substantiated public
complaints incorporating low and moderate product-
related risks, as well as product-recall situations
involving serious risks to the health and safety of
consumers. Hypotheses are derived from theories
and concepts of consumer behavioural psychology.
These are then tested empirically by using an
online experiment. The effects of reputation are
analyzed across different crises contexts to derive
some general insights useful for crisis management.
In order to shed light on situational differences of
the reputation mechanism its effect on individual
crisis level will also be considered. In general, the
analysis fi nds that reputation for quality is capable
of positively infl uencing the perceptions of company
responsibility and thereby shielding the
manufacturer from receiving blame. However, an
established reputation for high product quality
prior to the crisis fails to positively impacting
consumers ’ perceptions of problem severity. The
crisis-specifi c effects of reputation turn out to be
ambivalent. On the basis of these fi ndings, recommendations
to crisis managers and relevant avenues
for future research are derived.
The candidate list of substances subject to authorisation is an instrument provided by the EU chemicals regulation (REACH) to publicly announce and prioritize chemical substances of very high concern (SVHC) as a first step of imposing an obligation of authorisation on them, i.e. including them into the authorisation list (Annex XIV of REACH). As a consequence of inclusion into the “candidate list”, a variety of obligations concerned with intensifying risk communication apply. Article producers, importers and distributors of articles have to communicate information about SVHCs contained in articles and necessary risk management measures to the recipients of the articles and provide this information to consumers on request (Art. 33 REACH). This research paper analyzes the reputational mechanism of the candidate list showing a potential to stigmatize not only the substances as such but also various actors of the supply chain associated with these substances and their brands. Drawing on behavioral psychology theories, hypotheses on the reputational impacts of the candidate list on substance manufacturers, downstream users (including formulators and manufacturers of articles) and distributors are derived. These are discussed on the basis of current empirical data surveyed by the European Commission.
Incidence of Tube Feeding in 7174 Newly Admitted Nursing Home Residents With and Without Dementias
(2015)
Background:
Tube feeding is a common form of long-term nutritional support, especially for nursing home residents, of whom many have dementia.
Objective:
Estimating the incidence of feeding tube placement in nursing home residents with and without dementia.
Methods:
Using claims data, we studied a cohort of newly admitted nursing home residents aged 65 years and older between 2004 and 2009. Analyses were stratified by dementia. We estimated incidence rates and performed multivariate Cox regression analyses.
Results:
The study cohort included 7174 nursing home residents. Over a mean follow-up of 1.3 years, 273 people received a feeding tube. The incidence per 1000 person-years was 28.4, with higher estimates for patients with dementia. When adjusting for age, sex, and level of care as a time-dependent covariate, influence of dementia decreased to a nonsignificant hazard ratio.
Conclusion:
It seems that not dementia itself but the overall clinical condition might be a predictor of tube feeding placement.