ICON Technology & Process Consulting (United Kingdom)

Abstract The melting behavior of aluminum alloy is crucial for spacecraft structure re-entry damage. This work performs the molecular dynamics simulations to investigate the amorphization behavior of polycrystalline AlMg alloys with different grain sizes and pre-deformations under high temperatures. The simulation results demonstrated that the melting rate slows down for the polycrystalline AlMg alloys with the larger grains. The melting process shifts from the grain-boundary-to-interior amorphization in small grains to both grain boundary and interior melting in large grains. Further simulations discovered that the elastic pre-deformation has little effect on melting behaviors of polycrystalline AlMg alloys, and the plastic pre-deformation leads to the significant impact on the amorphization process of the smaller grain size but less contribution for the larger grains. This is originated from the fact that the small grains experience grain-boundary sliding and the large grains generate dislocations when the pre-plastic deformation. Analysis of the differences between the pre-loading and non-pre-loading cases reveals that the difference under plastic pre-loading is more obvious than elastic pre-loading. Such difference first rises then falls with increasing the temperature. In addition, the relationship between the difference in amorphous-atom volume fraction (pre-loading vs non-pre-loading) and grain size is further discussed and the pre-stretched (pre-compressed) deformation makes the difference decrease (increase) with grain size. The findings in this work could be helpful to understand the melting process of Al alloys under the high temperature environment.

Efficient mixing of shear-thinning fluids is crucial in many industries, with micromixers playing a key role in improving fluid handling. This study introduces innovative passive micromixer designs aimed at enhancing chaotic advection through secondary flows, especially in curved channels. We examined various split-and-recombine (SAR) microchannels, including a flow-focusing straight type, using numerical simulations across a range of Reynolds numbers with carboxymethyl cellulose solutions of different power-law indices. Performance metrics such as mixing index, pressure drop, and mixing energy cost were evaluated. While SAR configurations induced higher pressure drops, their relatively higher mixing index values resulted in lower mixing energy costs compared to the straight-type channel. Dean flow analysis showed that the splitting and recombining mechanism in SAR configurations generated stronger secondary flows, promoting greater stretching and folding of fluid elements. This significantly enhanced chaotic advection in curved geometries, leading to superior mixing efficiency over the straight-type configuration. These findings offer valuable insights into optimizing micromixer designs, balancing enhanced mixing with energy efficiency for shear-thinning fluids.

Numerical optimization methods are being used increasingly with flow simulations to improve the performance of fluid flow systems.Through a series of cases studies, this presentation will describe how combining experimental, flow modelling and optimization methods enable practical flow systems to be designed effectively within feasible time-scales.A number of the limitations of current numerical approaches will be highlighted and important new research directions will be discussed.

PurposeThe aim of the study was to analyze early mortality after continuous-flow left ventricular assist device (LVAD) implantation which remains high.MethodsWe analyzed consecutive (n = 2689) patients from the European Registry for Patients with Mechanical Circulatory Support (EUROMACS) undergoing continuous-flow LVAD implantation. The primary outcome was early (< 90 days) mortality. Secondary outcomes were differential causes of early post-operative death following LVAD implantation.ResultsUnivariable and multivariable analysis as well as regression analysis were used to examine determinants and differential causes of early (< 90 days) mortality after LVAD implantation. During the first 90 days, 2160 (80%) patients were alive with ongoing LVAD support, 40(2%) patients underwent heart transplantation, and 487(18%) deceased. The main causes of early death were MOF (36%), sepsis (28%), cardiopulmonary failure (CPF; 10%), CVA (9%), and right-sided heart failure (RHF, 8%). Furthermore, MOF and sepsis are 70% of causes of death in the first week. Independent clinical predictors of early death were age, female sex, INTERMACS profile 1 to 3, and ECMO. Laboratory predictors included elevated serum creatinine, total bilirubin, lactate, and low hemoglobin. Furthermore, hemodynamic predictors included elevated RA-to-PCWP ratio, pulmonary vascular resistance, and low systemic vascular resistance. Longer total implantation time was also independent predictor of early mortality. A simple model of 12 variables predicts early mortality following LVAD implantation with a good discriminative power with area under the curve of 0.75.ConclusionsIn the EUROMACS registry, approximately one out of five patients die within 90 days after LVAD implantation. Early mortality is primarily dominated by multiorgan failure followed by sepsis. A simple model identifies important parameters which are associated with early mortality following LVAD implantation.

Tricuspid regurgitation (TR) is common in patients receiving a left ventricular assist device (LVAD). Controversy exists as to whether concomitant tricuspid valve surgery (TVS) is beneficial in currently treated patients. Therefore, our goal was to investigate the effect of TVS concomitant with a LVAD implant. The European Registry for Patients with Mechanical Circulatory Support was used to identify adult patients. Matched patients with and without concomitant TVS were compared using a propensity score matching strategy. In total, 3323 patients underwent LVAD implantation of which 299 (9%) had TVS. After matching, 258 patients without TVS were matched to 258 patients with TVS. In the matched population, hospital deaths, days on inotropic support, temporary right ventricular assist device implants and hospital stay were comparable, whereas stay in the intensive care unit was higher in the TVS cohort (11 vs 15 days; P = 0.026). Late deaths (P = 0.17), cumulative incidence of unexpected hospital readmission (P = 0.15) and right heart failure (P = 0.55) were comparable between patients with and without concomitant TVS. In the matched population, probability of moderate-to-severe TR immediately after surgery was lower in patients with concomitant TVS compared to patients without TVS (33% vs 70%; P = 0.001). Nevertheless, the probability of moderate-to-severe TR decreased more quickly in patients without TVS (P = 0.030), resulting in comparable probabilities of moderate-to-severe TR within 1.5 years of follow-up. In matched patients, TVS concomitant with LVAD implant does not seem to be associated with better clinical outcomes. Concomitant TVS reduced TR significantly early after LVAD implant; however, differences in probability of TR disappeared during the follow-up period.

Little is known about cerebral strokes in paediatric patients supported by intracorporeal continuous-flow ventricular assist devices. We retrospectively investigated patients younger than 19 years of age who were treated with an intracorporeal continuous-flow ventricular assist device in the European Registry for Patients with Mechanical Circulatory Support (EUROMACS) database. The patients were stratified by body surface area in Group 1 [<1.2 m2 (n = 13)] and Group 2 [≥1.2 m2 (n = 38)]. Cerebral strokes, both ischaemic and haemorrhagic, were studied. Of the 2941 patients with ventricular assist device (VAD) implants listed in the database, 124 (4%) patients were less than 19 years of age. Fifty-one of them (2%) were supported with a continuous-flow ventricular assist device. Group 1 (6 female and 7 male) had a mean age (±SD) of 9 ± 2.3 years compared with 15.6 ± 1.8 years in Group 2 (21 female and 17 male). Three (23%) patients died in Group 1 on VAD support, whereas 5 (13%) patients died in Group 2 (P = 0.21; log-rank test). Seven (54%) patients with a VAD in Group 1 and 17 (45%) patients in Group 2 underwent transplantation (P = 0.29); of these, 1 (8%) patient recovered (Group 1) with subsequent device explantation. The other patients, 2 in Group 1 and 16 in Group 2, were still on device support at the time of the analysis. There were no cerebral strokes in Group 1, but 4 cerebral strokes (11% of Group 2, 8% of a total of 51 patients in Groups 1 and 2 combined) occurred in Group 2 (3 patients died; P = 0.26; log-rank test). Taken together, the incidence of cerebral strokes in this paediatric cohort of patients with an intracorporeal VAD was 0.1 per patient-year. The incidence of cerebral strokes in children with intracorporeal VADs (0.1 per patient-year) seems to be low irrespective of the body surface area.