No abstract is provided for this article.
No abstract is provided for this article.
This paper presents a cement hydration model over time using the cemdata07 thermodynamic database and a series of derived discrete solid phases (DSPs) to represent calcium silicate hydrate (C-S-H) as a binary solid solution with two end-members. C-S-H in cement is amorphous and poorly crystalline with a range of molar Ca/Si ratios from 0.6 to 1.7. It displays strongly incongruent dissolution behaviour, where the release of calcium into solution is several orders of magnitude greater than silicon. It is, therefore, important that any cement hydration model provides a credible account of this behaviour. C-S-H has been described in the cemdata07 thermodynamic database as a number of solid solutions using different end-members with differing levels of complexity. While solid solutions can be included in most modern geochemical software programs, they often lead to a significant increase in computation time. This paper presents how an incongruent solid solution between two C-S-H end-members may be represented as a number of DSPs to model cement hydration over time using the PHREEQC geochemical software. By using DSPs rather than modelling C-S-H as a nonideal solid solution, this gives the user full control of the input for the model, reducing the computational demand and analysis time with no loss in accuracy in predicting stable-phase assemblages and their associated pore chemistry over time.
Acute coronary occlusion occurs in 4.3% to 8.3% of patients during coronary angioplasty. Its occurrence is difficult to predict in an individual patient. At high risk are patients with unstable angina, intracoronary thrombus, extreme age, long complex lesions, and diffuse disease. “Standard” management including redilation (prolonged perfusion) thrombolytic treatment and emergency bypass surgery is only successful in approximately 50% of the patients and is associated with a high mortality and myocardial infarction rate of <6% and 30%, respectively. Bail-out stent implantation appears to emerge as an effective alternative in suitable patients and might reduce mortality, the apparent progression to myocardial infarction, or might decrease the need for emergency bypass. New techniques including directional atherectomy, rotational ablation, or the excimer laser are associated with a similar frequency of acute occlusion. Immediate access to a surgical back-up facility remains necessary to treat refractory acute occlusions.
Leaching from cement can lead to a loss in performance and durability and can also have an environmental impact. Therefore, it is an important aspect to consider when new cements are being developed and where concrete is to be placed that could lead to the contamination of groundwater. Calibrated thermodynamic models can provide very useful predictions in a matter of seconds for any cement-based material. However, such models need to include accurate representations of the solid-solution nature of the C-S-H gels that are included for the incongruent dissolution of calcium and silica. This study presents the calibration of a thermodynamic model employing the pH-REdox-Equilibrium geochemical software 3.8.7, written in C (PHREEQC 3.8.7), to model the change in the pH and the leaching of calcium (Ca) and silica (Si) from cement against the Ca/Si ratio and over time. The predicted concentrations of Ca and Si and the pH in the leachate were calculated using three solid-solution C-S-H gel models that were taken from the cemdata18 database, namely, CSHQ, CSH3T, and tobermorite–jennite, which have not been analysed before and show good agreement. The calibrated model was used to predict leaching from a CEM II/A-L cement and a blended CEM I + fly-ash with a cement replacement level of 35%. The effect of a sulphate environment (Na2SO4) was also analysed.
Intravascular ultrasound (IVUS) is a catheter-based diagnostic tool that provides a real-time, high-resolution, tomographic view of coronary arteries. There are basically two types of commercially available IVUS imaging catheters: a single-element mechanically rotated transducer and a phased-array electronic system. Mechanical systems comprise a flexible cable with a single rotation transducer that revolves at 30 revolutions per second emitting and receiving ultrasound signals every 1º increment. Phased-array catheters contain a 64-element annular array that enables a coordinated emission of the ultrasound signal. Quantitative angiographic measurements can be misleading since this technique only allows the evaluation of the profile of the lumen. A meta-analysis of angiographic studies has concluded that the magnitude of the antiatherosclerotic effects is small compared with the effects of statins on the prevention of cardiovascular events. The relation between shear stress and plaque vulnerability is currently the subject of intensive research efforts.
The SYNTAX trial randomized patients equally eligible for coronary artery bypass grafting or percutaneous coronary intervention using the Heart Team approach. The SYNTAXES study achieved a follow-up rate of 93.8% and reported the 10-year vital status. Factors associated with increased mortality at 10 years were pharmacologically treated diabetes mellitus, increased waist circumference, reduced left ventricular function, prior cerebrovascular and peripheral vascular disease, western Europe and North American descent, current smoking, chronic obstructive pulmonary disease, elevated C-reactive protein, anemia, and an increase in HbA1c. Procedural factors associated with higher 10 years mortality include periprocedural myocardial infarction, extensive stenting, small stents, ≥1 heavily calcified lesion, ≥1 bifurcation lesion, residual SYNTAX score >8, and staged percutaneous coronary intervention. Optimal medical therapy at 5 years, use of statins, on-pump coronary artery bypass grafting, multiple arterial grafts, and higher physical component score and mental component score were associated with lower mortality at 10 years. Numerous scores and prediction models were developed to help individualize risk assessment. Machine learning has emerged as a novel approach for developing risk models.
