Investigation of microstructure and corrosion in Al-Cu and Al-Mg alloys with and without Li additions

The corrosion performance of Al-Cu and Al-Mg alloys with and without Li additions have been investigated. These include; AA2024-T3, AA2099-T8E77 (coarse and fine grain structure), AA5083-T351, spray formed Al-Mg-Li and spray formed Al-Mg-Li-Cu-Zn alloy. Atmospheric corrosion was investigated for up to 12 months of exposure in a rural-urban environment, prolonged immersion testing in 3.5 wt.% NaCl for up to 96 hr s and potentiodynamic polarisation in 3.5 wt.% NaCl were examined. This was to answer whether Li additions, spray forming and grain size impacted on the corrosion resistance. Atmospheric exposure showed Al2(CO3)3, NOx, SOx and NaCl compounds being deposited. Cathodic intermetallic compounds (Fe, Si, Mn and Cu rich) were shown to be associated with pitting corrosion, whereas anodic intermetallic compounds (Mg rich) offered sacrificial protection to the matrix. The Al-Cu alloys showed more corrosion compared to the Al-Mg alloys in all three corrosion investigations. The Al-Cu alloys showed pitting corrosion and intergranular corrosion, compared to primarily pitting corrosion on the Al-Mg alloys. AA2024-T3 developed a weakened, friable layer on the surface, consisting of a network of intergranular corrosion and numerous shallow pits. The Al-Cu-Li alloys also showed intergranular corrosion and pitting corrosion, but also developed selective grain dissolution, leading to extensive sub-surface cavities. This showed that Li additions in the Al-Cu alloys was detrimental and was primarily associated with the T type phases likely to be; T1 phase (Al2CuLi). Li additions in the Al-Mg alloys did not show any measurable improvement or reduction in corrosion resistance. Spray forming also did not appear to improve the corrosion resistance. Grain size in turn was shown to impact on corrosion resistance, with the general consensus being that finer grains offer increased corrosion resistances. Al-Cu alloys showed fine grain structures developed easy path propagation for intergranular corrosion, whereas fine grain structures on Al-Mg alloys promoted increased corrosion resistance

Corona Threshold of Single and Multiple Conductor Lines

Corona is a self sustaining, often luminous discharge due to ionization adjacent to charged conductors, characterized by the electrodes having a small radius of curvature compared with the interelectrode gap. The display on a power transmission line is accompanied by a current between the conductors which to an engineer mean a power loss that should be minimized if unavoidable

“Waves of Edema” seem implausible

No abstract available

Risk assessment in patients with an acute ST-elevation myocardial infarction

ST-elevation myocardial infarction (STEMI) is one of the leading causes of mortality and morbidity worldwide. While the survival after acute STEMI has considerably improved, mortality rate still remains high, especially in high-risk patients. Survival after acute STEMI is influenced by clinical characteristics such as age as well as the presence of comorbidities. However, during emergency care increasing access to tools such as the electrocardiogram, chest x-ray and echocardiography can provide additional information helping to further risk stratify patients. In the invasive setting, this can also include coronary angiography, invasive hemodynamic recordings and angiographic assessments of coronary flow and myocardial perfusion. We outline the common investigations used in STEMI and their role in risk assessment of patients with an acute STEMI

Dynamic finite-strain modelling of the human left ventricle in health and disease using an immersed boundary-finite element method

Detailed models of the biomechanics of the heart are important both for developing improved interventions for patients with heart disease and also for patient risk stratification and treatment planning. For instance, stress distributions in the heart affect cardiac remodelling, but such distributions are not presently accessible in patients. Biomechanical models of the heart offer detailed three-dimensional deformation, stress and strain fields that can supplement conventional clinical data. In this work, we introduce dynamic computational models of the human left ventricle (LV) that are derived from clinical imaging data obtained from a healthy subject and from a patient with a myocardial infarction (MI). Both models incorporate a detailed invariant-based orthotropic description of the passive elasticity of the ventricular myocardium along with a detailed biophysical model of active tension generation in the ventricular muscle. These constitutive models are employed within a dynamic simulation framework that accounts for the inertia of the ventricular muscle and the blood that is based on an immersed boundary (IB) method with a finite element description of the structural mechanics. The geometry of the models is based on data obtained non-invasively by cardiac magnetic resonance (CMR). CMR imaging data are also used to estimate the parameters of the passive and active constitutive models, which are determined so that the simulated end-diastolic and end-systolic volumes agree with the corresponding volumes determined from the CMR imaging studies. Using these models, we simulate LV dynamics from end-diastole to end-systole. The results of our simulations are shown to be in good agreement with subject-specific CMR-derived strain measurements and also with earlier clinical studies on human LV strain distributions

Estimating prognosis in patients with acute myocardial infarction using personalized computational heart models

Biomechanical computational models have potential prognostic utility in patients after an acute ST-segment–elevation myocardial infarction (STEMI). In a proof-of-concept study, we defined two groups (1) an acute STEMI group (n = 6, 83% male, age 54 ± 12 years) complicated by left ventricular (LV) systolic dysfunction; (2) an age- and sex- matched hyper-control group (n = 6, 83% male, age 46 ± 14 years), no prior history of cardiovascular disease and normal systolic blood pressure (SBP < 130 mmHg). Cardiac MRI was performed in the patients (2 days & 6 months post-STEMI) and the volunteers, and biomechanical heart models were synthesized for each subject. The candidate parameters included normalized active tension (ATnorm) and active tension at the resting sarcomere length (Treq, reflecting required contractility). Myocardial contractility was inversely determined from personalized heart models by matching CMR-imaged LV dynamics. Compared with controls, patients with recent STEMI exhibited increased LV wall active tension when normalized by SBP. We observed a linear relationship between Treq 2 days post-MI and global longitudinal strain 6 months later (r = 0.86; p = 0.03). Treq may be associated with changes in LV function in the longer term in STEMI patients complicated by LV dysfunction. Further studies seem warranted

CROP HEIGHT ESTIMATION WITH UNMANNED AERIAL VEHICLES

An unmanned aerial vehicle (UAV) can be configured for crop height estimation. In some examples, the UAV includes an aerial propulsion system, a laser scanner configured to face downwards while the UAV is in flight, and a control system. The laser scanner is configured to scan through a two - dimensional scan angle and is characterized by a maxi mum range. The control system causes the UAV to fly over an agricultural field and maintain, using the aerial propulsion system and the laser scanner, a distance between the UAV and a top of crops in the agricultural field to within a programmed range of distances based on the maximum range of the laser scanner. The control system determines, using range data from the laser scanner, a crop height from the top of the crops to the ground

An evaluation of cattle types for the east Kimberley

The first cattle to be introduced to Western Australia\u27s Kimberley region arrived at Ord River Station in 1884, after Nathaniel Buchanan had walked 4000 head of Shorthorn cattle overland from Queensland, on behalf of the owners, Osmond and Panton. In the early years of the Kimberley pastoral industry the virgin pastures allowed stock numbers to increase rapidly. Little consideration was given to stock or rangeland management, or to whezther other types of cattle could be raised for improved production. The Department of Agriculture started a comprehensive trail at Ord Regeneration Research Station (previously Ord River Station) in 1980 to evaluate the fertility, mortality and growth rate of Brahman and Africander cattle and their crosses. This article discusses some of the highlights of this eight-year trial, and the implications for the industry

Myocardial haemorrhage revealed by magnetic resonance imaging mapping in acute ST-elevation myocardial infarction: relationship with heart function and health outcomes

ST-elevation myocardial infarction (STEMI) management has evolved dramatically, with improved pharmacological treatment, rapid achievement of reperfusion with percutaneous coronary intervention (PCI) and advanced secondary prevention programmes, resulting in a decline in morbidity and mortality. However, it is well recognised that myocardial perfusion remains compromised in up to 50% of STEMI patients, despite rapid and successful mechanical revascularisation of the epicardial artery. This occurrence is called the “no-reflow” phenomenon and as a result, a substantial proportion of acute STEMI patients develop chronic cardiac failure, owing to poor microvascular function and myocardial perfusion. Although pathological and clinical observations initially seemed to support the theory that no-reflow was a consequence of microvascular obstruction (predominantly from distal embolisation of athero-thrombotic debris), irreversible microvascular injury and subsequent intramyocardial haemorrhage (IMH) are now also thought to play important factors in this process. T2*-CMR is the reference diagnostic method for imaging myocardial haemorrhage in-vivo, however technical issues have limited T2* imaging in clinical practice. The largest cohort studies of myocardial haemorrhage in STEMI patients to date, have not used T2* CMR, but instead used qualitative T2-weighted imaging methods to detect haemorrhage, which are hampered by image artefact. Because of the different CMR techniques, uncertainties have arisen surrounding the pathophysiology and clinical significance of myocardial haemorrhage, and its relationships with microvascular obstruction (MVO). In some studies, myocardial haemorrhage is associated with adverse remodelling and adverse clinical outcome, however other studies have shown that myocardial haemorrhage does not have prognostic significance beyond MVO. Recent developments in CMR imaging techniques have enabled clinically feasible, rapid parametric mapping, which allows direct determination of myocardial magnetic relaxation times (T1, T2 and T2*). These quantitative, novel mapping methods, address many of the inherent limitations associated with dark blood T2-weighted techniques, for a more objective assessment of the infarct core. The principal aim of this thesis is to define the clinical significance of myocardial haemorrhage using quantitative CMR mapping techniques and to determine whether detection of haemorrhage might improve risk stratification in STEMI survivors. In addition, I aim to characterise the evolution and inter-relationships between IMH and MVO in STEMI survivors to inform and implement targeted therapeutic interventions. Methods (1) Natural history study: We performed a single centre cohort study in 324 reperfused STEMI patients treated predominantly by emergency percutaneous coronary intervention (PCI) (The BHF MR-MI study; Clinicaltrials.gov NCT02072850). The index of microcirculatory resistance (IMR), a prognostically validated invasive microcirculatory biomarker, was measured acutely in the culprit coronary artery at the end of PCI using guidewire based-thermodilution. Infarct zone IMH and MVO were delineated as hypointense zones on T2* mapping CMR (T2* value <20 ms) and contrast-enhanced-CMR at 1.5 Tesla, respectively, 2 days and 6 months post-MI. T1- and T2-mapping techniques were also used to assess the infarct core and evaluate IMH. (2) Time-course study: 30 patients underwent serial CMR at 4 time-points: <1 day (4 to 12 hours), 3 days, 10 days and 6-7 months post-reperfusion. Adverse remodelling was defined as an increase in left ventricular end-diastolic volume (LVEDV) ≥ 20% at 6 months. Adverse cardiovascular events were pre-specified and defined according to internationally accepted criteria. All-cause death or heart failure were independently assessed during follow-up blind to other data. (3) Randomised proof-of-concept trial: We hypothesised that brief deferral of stenting after initial reperfusion, associated with the benefits of normal coronary flow and anti-thrombotic therapies, would reduce microvascular injury and increase myocardial salvage. We implemented a randomised proof-of-concept clinical trial of deferred PCI vs. immediate stenting (NCT01717573) (Carrick et al., 2014). In summary, the main findings of this thesis are: • Myocardial haemorrhage (defined by T2* CMR) is an independent predictor of adverse remodelling and all cause death or heart failure in the longer-term post STEMI. • Myocardial hemorrhage occurs in primary and secondary phases within the first 10 days post-MI and is a secondary phenomenon to the initial occurrence of microvascular obstruction. • Myocardial haemorrhage peaked at day 3 post-MI in reperfused STEMI patients, and the temporal changes in oedema may be a secondary process. • A hypointense infarct core on T2-mapping always occurred in the presence of microvascular obstruction and commonly in the absence of myocardial haemorrhage within 12 hours and 3 days post-MI, indicating that the presence of T2-core is more closely associated with microvascular obstruction than myocardial haemorrhage. • Infarct core pathology revealed by T2 (ms) was independently associated with all-cause death or heart failure hospitalisation during longer term follow-up. • Native T1 values (ms) within the infarct core were independently associated with adverse remodelling and adverse clinical outcome and had similar prognostic value when compared to microvascular obstruction. • IMR measured in the culprit coronary artery after reperfusion is more strongly associated with myocardial haemorrhage than microvascular obstruction in STEMI survivors 2 days later. • The proof-of-concept pilot deferred stenting trial showed that compared with standard of care with immediate stenting, brief deferral of stenting after initial reperfusion; reduced angiographic no-reflow, tended to reduce IMH and MVO, and increased myocardial salvage. The findings of this PhD are novel and have important clinical implications. Firstly, we found that myocardial haemorrhage occurs commonly and is a biomarker for prognostication in STEMI survivors. Secondly, IMR adds early prognostic information at the time of emergency reperfusion and has potential to stratify patients at risk of IMH for more intensive therapy. Thirdly, our results confirm that infarct pathologies are evolving dynamically and potentially, may be amenable to targeted therapeutic interventions. Finally, IMR has the potential to stratify STEMI patients acutely and deferred PCI is a simple intervention that could be practice changing, if the planned Phase 3 trial DEFER-STEMI confirms the hypothesis

Assessment of the relationships between myocardial contractility and infarct tissue revealed by serial magnetic resonance imaging in patients with acute myocardial infarction

Imaging changes in left ventricular (LV) volumes during the cardiac cycle and LV ejection fraction do not provide information on regional contractility. Displacement ENcoding with Stimulated Echoes (DENSE) is a strain-encoded cardiac magnetic resonance (CMR) technique that measures strain directly. We investigated the relationships between strain revealed by DENSE and the presence and extent of infarction in patients with recent myocardial infarction (MI). 50 male subjects were invited to undergo serial CMR within 7 days of MI (baseline) and after 6 months (follow-up; n = 47). DENSE and late gadolinium enhancement (LGE) images were acquired to enable localised regional quantification of peak circumferential strain (Ecc) and the extent of infarction, respectively. We assessed: (1) receiver operating characteristic (ROC) analysis for the classification of LGE, (2) strain differences according to LGE status (remote, adjacent, infarcted) and (3) changes in strain revealed between baseline and follow-up. 300 and 258 myocardial segments were available for analysis at baseline and follow-up respectively. LGE was present in 130/300 (43 %) and 97/258 (38 %) segments, respectively. ROC analysis revealed moderately high values for peak Ecc at baseline [threshold 12.8 %; area-under-curve (AUC) 0.88, sensitivity 84 %, specificity 78 %] and at follow-up (threshold 15.8 %; AUC 0.76, sensitivity 85 %, specificity 64 %). Differences were observed between remote, adjacent and infarcted segments. Between baseline and follow-up, increases in peak Ecc were observed in infarcted segments (median difference of 5.6 %) and in adjacent segments (1.5 %). Peak Ecc at baseline was indicative of the change in LGE status between baseline and follow-up. Strain-encoded CMR with DENSE has the potential to provide clinically useful information on contractility and its recovery over time in patients with MI