Molecular Dynamics Simulations of Metal / Molten Alkali Carbonate Interfaces

Neutral and charged interfaces between molten alkali carbonates M2CO3 (M = Li, Na, and K) and planar solid walls have been investigated by molecular dynamics based on a rigid-ions force field. Simulations cover the temperature range 1200 K ≤ T ≤ 1500 K at a moderate (∼15 kbar) overpressure to compensate for the slight overestimate of the system volume by the force field model. The results provide an intriguing view of the interplay among ion packing, oscillating screening, anisotropic correlations, and ion dynamics at the interface. The mass and charge density profiles display prominent peaks at contact, and tend to their constant bulk value through several oscillations, whose amplitude decays exponentially moving away from the interface. Oscillations in the charge density profile extend screening to longer distances and limit the capacitance of the interface. Ion–ion correlations are enhanced in proximity of the interface but retain the exponentially decaying oscillatory form of their bulk counterpart. Diffusion is slower in the molecularly thin layer of ions next to the interface than in the bulk. The analysis of interfaces is completed by the computation of structural properties of bulk phases, and by the estimate of transport coefficients such as self-diffusion, electrical conductivity, and especially thermal conductivity, which is seldom computed by simulation. All together, the results of our simulations for homogeneous and inhomogeneous molten carbonates provide crucial insight on systems and properties relevant for advanced devices such as fuel cells, that, in turn, might play a prominent role in future power generation strategies

The effective subsidence capacity concept: How to assure that subsidence in the Wadden Sea remains within defined limits?

Subsidence caused by extraction of hydrocarbons and solution salt mining is a sensitive issue in the Netherlands. An extensive legal, technical and organisational framework is in place to ensure a high probability that such subsidence will stay within predefined limits. The key question is: how much subsidence is acceptable and at which rate? And: how can it be reliably assured that (future) subsidence will stay within these limits? To address the issue for the Wadden Sea area, the concept of ‘effective subsidence capacity’ is used. To determine the ‘effective subsidence capacity’, the maximum volumetric rate of relative sea-level rise, that can be accommodated in the long term, without environmental harm, is established first. The volume of sediment that can be transported and deposited by nature into the tidal basin where the subsidence is expected, ultimately determines this ‘limit of acceptable average subsidence rate’. The capability of the tidal basins to ‘capture’ sediment over the lunar cycle period of 18.6 years is the overall rate-determining step. Effective subsidence capacity is then the maximum average subsidence rate available for planning of human activities. It is obtained by subtracting the subsidence volume rate ‘consumed’ by natural relative subsidence in the area (sealevel rise plus natural shallow compaction) from the total long-term acceptable subsidence volume rate limit. In the operational procedure for mining companies, six-years-average expectation values of subsidence rates are used to calculate the maximum allowable production rates. This is done under the provision that production will be reduced or halted if the expected or actual subsidence rate (natural + man induced) is likely to exceed the limit of acceptable subsidence. Monitoring and management schemes ensure that predicted (6-year average) and actual (18.6-year average) subsidence rates stay within the limit of acceptable subsidence rate and that no damage is caused to the protected nature. A GPS based early warning system is used for early detection of unexpected behaviour. In support of SSM (State Supervision of Mines, the government regulator), TNO-AGE (an independent government advisory group) applies an independent Bayesian statistical analysis of all data, as they become available, to calculate the probability of scenario’s under which future subsidence will exceed the defined limits. It is external to the operator’s annual measurement and control loop and ensures that preventive actions can be taken in time in case such scenarios emerge. Regular communication keeps the authorities and the general public informed on the use of the effective subsidence capacity to demonstrate that the actual average subsidence rate stays strictly within the defined bounds and that, from a scientific point of view, there is no reasonable doubt that damage to the tidal system will not occur now or in the future

Increased levels of circulating platelet-monocyte complexes and platelet-neutrophil complexes are associated with myocardial infarction

Cardiolog

Hemodynamic Optimization in Cardiac Resynchronization Therapy: Should We Aim for dP/dtmax or Stroke Work?

Item does not contain fulltextOBJECTIVES: This study evaluated the acute effect of dP/dtmax- versus stroke work (SW)-guided cardiac resynchronization therapy (CRT) optimization and the related acute hemodynamic changes to long-term CRT response. BACKGROUND: Hemodynamic optimization may increase benefit from CRT. Typically, maximal left ventricular (LV) pressure rise dP/dtmax is used as an index of ventricular performance. Alternatively, SW can be derived from pressure-volume (PV) loops. METHODS: Forty-one patients underwent CRT implantation followed by invasive PV loop measurements. The stimulation protocol included 16 LV pacing configurations using each individual electrode of the quadripolar lead with 4 atrioventricular (AV) delays. Conventional CRT was defined as pacing from the distal electrode with an AV delay of approximately 120 ms. RESULTS: Compared with conventional CRT, dP/dtmax-guided optimization resulted in a one-third additional dP/dtmax increase (17 +/- 11% vs. 12 +/- 9%; p /=10% LVEF improvement). Although acute changes in SW were predictive for long-term CRT response (area under the curve: 0.78; p = 0.002), changes in dP/dtmax were not (area under the curve: 0.65; p = 0.112). CONCLUSIONS: PV-guided hemodynamic optimization in CRT results in approximately one-third SW improvement on top of conventional CRT, caused by a mechanism of enhanced VA coupling. In contrast, dP/dtmax optimization favored LV contractility. Ultimately, acute changes in SW showed larger predictive value for long-term CRT response compared with dP/dtmax