Identifying strategies to maximise recruitment and retention of practices and patients in a multicentre randomised controlled trial of an intervention to optimise secondary prevention for coronary heart disease in primary care.

Background Recruitment and retention of patients and healthcare providers in randomised controlled trials (RCTs) is important in order to determine the effectiveness of interventions. However, failure to achieve recruitment targets is common and reasons why a particular recruitment strategy works for one study and not another remain unclear. We sought to describe a strategy used in a multicentre RCT in primary care, to report researchers’ and participants’ experiences of its implementation and to inform future strategies to maximise recruitment and retention. Methods In total 48 general practices and 903 patients were recruited from three different areas of Ireland to a RCT of an intervention designed to optimise secondary prevention of coronary heart disease. The recruitment process involved telephoning practices, posting information, visiting practices, identifying potential participants, posting invitations and obtaining consent. Retention involved patients attending reviews and responding to questionnaires and practices facilitating data collection. Results We achieved high retention rates for practices (100%) and for patients (85%) over an 18-month intervention period. Pilot work, knowledge of the setting, awareness of change in staff and organisation amongst participant sites, rapid responses to queries and acknowledgement of practitioners’ contributions were identified as being important. Minor variations in protocol and research support helped to meet varied, complex and changing individual needs of practitioners and patients and encouraged retention in the trial. A collaborative relationship between researcher and practice staff which required time to develop was perceived as vital for both recruitment and retention. Conclusions Recruiting and retaining the numbers of practices and patients estimated as required to provide findings with adequate power contributes to increased confidence in the validity and generalisability of RCT results. A continuous dynamic process of monitoring progress within trials and tailoring strategies to particular circumstances, whilst not compromising trial protocols, should allow maximal recruitment and retention.

Hot deformation characteristics of a nitride strengthened martensitic heat resistant steel

Constitutive equations including an Arrhenius term have been applied to analyze the hot deformation behavior of a nitride-strengthened (NS) martensitic heat resistant steel in temperature range of 900–1200 °C and strain rate range of 0.001–10 /s. On the basis of analysis of the deformation data, the stress–strain curves up to the peak were divided into four regions, in sequence, representing four processes, namely hardening, dynamic recovery (DRV), dynamic strain induced transformation (DSIT), and dynamic recrystallization (DRX), according to the inflection points in ∂θ/∂σ∂θ/∂σ and ∂(∂θ/∂σ)/∂σ∂(∂θ/∂σ)/∂σ curves. Some of the inflection points have their own meanings. For examples, the minimum of ∂θ/∂σ∂θ/∂σ locates the start of DRV and the maximum of it indicates the start of DRX. The results also showed that the critical strain of DRX was sensitive to ln(Z) below 40, while the critical stress of DRX was sensitive to it above 40. The final microstructures under different deformation conditions were analyzed in terms of softening processes including DRV, DRX, metadynamic crystallization (MDRX) and DSIT.

Analysis of deformation behavior and workability of advanced 9Cr-Nb-V ferritic heat resistant steels

Hot compression tests were carried out on 9Cr–Nb–V heat resistant steels in the temperature range of 600–1200 °C and the strain rate range of 10−2–100 s−1 to study their deformation characteristics. The full recrystallization temperature and the carbon-free bainite phase transformation temperature were determined by the slope-change points in the curve of mean flow stress versus the inverse of temperature. The parameters of the constitutive equation for the experimental steels were calculated, including the stress exponent and the activation energy. The lower carbon content in steel would increase the fraction of precipitates by increasing the volume of dynamic strain-induced (DSIT) ferrite during deformation. The ln(εc) versus ln(Z) and the ln(σc) versus ln(Z) plots for both steels have similar trends. The efficiency of power dissipation maps with instability maps merged together show excellent workability from the strain of 0.05 to 0.6. The microstructure of the experimental steels was fully recrystallized upon deformation at low Z value owing to the dynamic recrystallization (DRX), and exhibited a necklace structure under the condition of 1050 °C/0.1 s−1 due to the suppression of the secondary flow of DRX. However, there were barely any DRX grains but elongated pancake grains under the condition of 1000 °C/1 s−1 because of the suppression of the metadynamic recrystallization (MDRX).

Deformation and geochronology of syntectonic granitoids emplaced in the Major Gercino Shear Zone, southeastern South America

The Major Gercino Shear Zone is one of the NE-SW lineaments that separate the Neoproterozoic Dom Feliciano Belt, of Brazil and Uruguay, into two different domains: a northwestern supracrustal domain from a southeastern granitoid domain. The shear zone, striking NE, is composed of protomylonites to ultramylonites with mainly dextral kinematic indicators. In Santa Catarina State, southern Brazil, the shear zone is composed of two mylonite belts. The mylonites have mineral orientations produced under greenschist fades conditions at a high strain rate. Strong flattening and coaxial deformation indicate the transpressive character, while the role of pure shear is emphasized by the orientation of the mylonite belts in relation to the inferred stress field component. The quartz microstructures point out that different dynamic recrystallization regimes and crystal plasticity were the dominant mechanisms of deformation during the mylonitization process. Additionally, the fabrics suggest that the glide systems are activated for deformation conditions compatible with the metamorphism in the middle greenschist facies. Elongated granitoid intrusions belonging to two petrographically, geochemically and isotopically distinct rock associations occur between the two mylonite belts. The structures observed in the granites result from a deformation range from magmatic to solid-state conditions points to a continuum of magma straining during and just after its crystallization. Conventional U-Pb analysis of multi-crystal zircon fractions yielded essentially identical ages of 609 +/- 16 Ma and 614 +/- 2 Ma for the two granitic associations, and constrain the transpressive phase of the shear zone. K-Ar ages of biotites between 585 and 560 Ma record the slow cooling and uplift of the intrusions. Some K-Ar ages of micas in regional mylonites are similar, suggesting that thermo-tectonic activity was intense up to this time, probably related to the agglutination of the granite belt to the supracrustal belt NW of the MGSZ. (C) 2009 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Characterization of residential chimney conditions for flue gas flow measurements

A literature survey and a theoretical study were performed to characterize residential chimney conditions for flue gas flow measurements. The focus is on Pitot-static probes to give sufficient basis for the development and calibration of a velocity pressure averaging probe suitable for the continuous dynamic (i.e. non steady state) measurement of the low flow velocities present in residential chimneys. The flow conditions do not meet the requirements set in ISO 10780 and ISO 3966 for Pitot-static probe measurements, and the methods and their uncertainties are not valid. The flow velocities in residential chimneys from a heating boiler under normal operating condi-tions are shown to be so low that they in some conditions result in voiding the assumptions of non-viscous fluid justifying the use of the quadratic Bernoulli equation. A non-linear Reynolds number dependent calibration coefficient that is correcting for the viscous effects is needed to avoid significant measurement errors. The wide range of flow velocity during normal boiler operation also results in the flow type changing from laminar, across the laminar to turbulent transition region, to fully turbulent flow, resulting in significant changes of the velocity profile during dynamic measurements. In addition, the short duct lengths (and changes of flow direction and duct shape) used in practice are shown to result in that the measurements are done in the hydrodynamic entrance region where the flow velocity profiles most likely are neither symmetrical nor fully developed. A measurement method insensitive to velocity profile changes is thus needed, if the flow velocity profile cannot otherwise be determined or predicted with reasonable accuracy for the whole measurement range. Because of particulate matter and condensing fluids in the flue gas it is beneficial if the probe can be constructed so that it can easily be taken out for cleaning, and equipped with a locking mechanism to always ensure the same alignment in the duct without affecting the calibration. The literature implies that there may be a significant time lag in the measurements of low flow rates due to viscous effects in the internal impact pressure passages of Pitot probes, and the significance in the discussed application should be studied experimentally. The measured differential pressures from Pitot-static probes in residential chimney flows are so low that the calibration and given uncertainties of commercially available pressure transducers are not adequate. The pressure transducers should be calibrated specifically for the application, preferably in combination with the probe, and the significance of all different error sources should be investigated carefully. Care should be taken also with the temperature measurement, e.g. with averaging of several sensors, as significant temperature gradients may be present in flue gas ducts.

Quenched and annealed microstructures of hot worked magnesium AZ31

The microstructures of magnesium AZ31 are examined following hot compression testing and annealing. The grain size, fraction dynamically recrystallized and, in a couple of cases, the crystallographic texture are reported. The progress of dynamic recrystallization and the recrystallized grain size were sensitive to processing conditions, as expected. This effect was more marked in the former than in the latter, compared to other metals. It was also found that, for structures containing between 80 and 95% dynamic recrystallization, abnormal grain growth occurred during annealing. Irrespective of the whether or not abnormal grain growth occurred, the annealing step weakened the crystallographic texture.

Hot working microstructure map for magnesium AZ31

A thermomechanical processing (TMP) structure map is proposed that plots the critical strains required for dynamic recrystallization along with the grain sizes that result. These maps are useful in identifying the limits to grain refinement and designing hot working processes. They are readily constructed for well studied alloys such as plain carbon steel. In light of the recent interest in the hot working of magnesium, initial steps are taken here to construct a TMP structure map for the most common wrought magnesium alloy, AZ31. The completion of dynamic recrystallization is estimated using a geometrical approach and a twinning region is identified.

Influence of grain size on hot working stresses and microstructures in Mg-3A1-1Zn

The influence of the grain size on the deformation of Mg–3Al–1Zn was examined in compression at 300 °C. At low strains the flow stress increases with increasing grain size. This is interpreted in terms of dynamic recrystallization. Empirical models of dynamic recrystallization are developed and employed to generate a microstructure map.

The formation of ultrafine grained steel microstructures through thermomechanical processing.

The formation of ultrafine grained steels is an area of intense research around the World. There are a number of methods to produce grain sizes of approximately 1 µm, ranging from extreme thermal and deformation cycles to more typical thermomechanical processes. This paper reviews the status of the production of ultrafine grained steels through relatively simple thermomechanical processing. It is shown that this requires deformation within the Ae3 to Ar3 temperature range for a given alloy. The formation of ultrafine ferrite involves a dynamic transformation of a significant volume fraction of the austenite to ferrite. This dynamic strain induced transformation arises from the introduction of additional intragranular nucleation sites. It is possible that the deformation also hinders the growth or coarsening of the ferrite and may also lead to dynamic recrystallization of the ferrite. The most likely commercial exploitation of ultrafine ferrite would appear to rely on the formation of a critical volume fraction of dynamic strain induced ferrite followed by controlled cooling to ensure this is maintained to room temperature and to also form other secondary phases, such as martensite, bainite and/or retained austenite to improve the formability.

The influence of twinning on the hot working flow stress and microstructural evolution of magnesium alloy AZ31

The microstructural evolution during compression (at 350°C and a strain rate of 0.01s-1) was examined for magnesium alloy AZ31 received in the "as-cast" condition. It was revealed that at low strains, many twins are produced and dynamically recrystallized (DRX) grains form as a necklace along pre-existing grain boundaries. At higher strains, DRX stagnates, most likely due to the accommodation of deformation in the DRX fraction of the material. It was also observed that twin boundaries act as sites for the nucleation of DRX grains. The analysis was repeated for samples pre-compressed to a strain of 0.15 at room temperature prior to the hot deformation step. The idea of these additional tests was to increase the degree of twinning and therefore the density of sites for the nucleation of DRX. It was found that statically recrystallized (SRX) grains developed at the twins during heating to the test temperature. When these samples were deformed, the peak flow stress was reduced by approximately 20% and the development of DRX was enhanced. This can be attributed to the accelerated nucleation of DRX in the refined SRX structure.

Mapping the hot deformation microstructure of Ni-30Fe alloy

The evolution of structure during the hot working of an austenitic Ni-30%Fe alloy is studied using EBSD analysis of samples tested in torsion. A microstructural map in temperature-strain space that plots grain size, cell size, fracture and dynamic recrystallization is presented.

Influence of aging pre-treatment on the compressive deformation of WE54 alloy

The effect of aging pre-treatment on the compressive deformation of a commercial WE54 alloy is studied. Age hardening treatments were performed at 170 °C, 250 °C and 300 °C. Compression testing was then carried out for the peak aged samples at temperatures between ambient and 450 °C. Twinning dominated the deformation at lower temperatures for all initial microstructures. This behaviour was replaced by slip dominated flow when the temperature was raised. The temperature of the transition from twinning to slip dominated flow was only mildly sensitive to the pre-treatment. It is also evident that dynamic recrystallization is retarded in this alloy.

Microstructural evolution during hot deformation of duplex stainless steel

The microstructure evolution during hot deformation of a 23Cr-5Ni-3Mo duplex stainless steel was investigated in torsion. The presence of a soft δ ferrite phase in the vicinity of austenite caused strain partitioning, with accommodation of more strain in the δ ferrite. Furthermore, owing to the limited number of austenite/austenite grain boundaries, the kinetics of dynamic recrystallisation (DRX) in austenite was very slow. The first DRX grains in the austenite phase formed at a strain beyond the peak and proceeded to <15% of the microstructure at the rupture strain of the sample. On the other hand, the microstructure evolution in δ ferrite started by formation of low angle grain boundaries at low strains and the density of these boundaries increased with increasing strain. There was clear evidence of continuous dynamic recrystallisation in this phase at strains beyond the peak. However, in the δ ferrite phase at high strains, most grains consisted of δ/δ and δ/γ boundaries.

Grain refinement through controlled thermomechanical processing

The major challenge for thermomechanical processing is to extend grain refinement towards lower average grain sizes. However, there is also a need to provide a better understanding of the mechanisms through which the refinement processes proceed. Many recent proposals for advanced thermomechanical processing rely on the dynamic strain induced transformation (DSIT), and the dynamic recrystallisation of austenite as the main refinement mechanisms. These mechanisms are still not fully understood and their clarification can be expected to lead to even greater levels of refinement. The current review examines the roles of ferrite recrystallisation , DSIT and initial austenite grain size. It is shown that although the ferrite recrystallisation mechanism in DSIT has certain similarities with the well known continuous dynamic recrystallisation (CDRX), it is significantly affected by the transformed ferrite grain size. Also, reducing the initial austenite grain size increases the recrystallisation rate in the strain dependent as well as strain independent regions. These results show that the traditional concept of metadynamic recrystallisation is insufficient to explain the changes in grain size following deformation. An alternative explanation is presented.