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In order to increase erosion lifetime of the divertor target, in the 2nd design phase of R&D work package ‘Divertor’ for European DEMO, armor thickness of tungsten monoblock divertor target is increased from 5 mm to 8 mm. By increasing armor thickness, surface temperature increases nearly linearly, which makes effect of creep no longer negligible at slow transients of 20 MW/m2. In this work, structural impact of creep in tungsten monoblock divertor target is for the first time quantitatively analyzed with the aid of finite element method. The numerical simulations have revealed that creep results in an increase of inelastic strain accumulation. With increasing armor thickness, tensile surface stress along x-axis (the longer edge at the plasma-facing surface of tungsten monoblock) reduces, while surface stress along z-axis (axial direction of the cooling tube) changes from tensile to compressive. Creep will accelerate this change. With increasing grain size, creep strain accumulation at loading surface increases due to higher creep rates, while plastic strain accumulation decreases. Creep can mitigate the risk of deep cracking by reducing the driving force for crack opening, and has a positive impact for preventing the contact between the upper parts of neighboring monoblocks in high heat flux tests.

In this work, the surface cracking features of tungsten armor under thermal shock loads by edge-localized mode (ELM) were investigated by means of computational fracture mechanics analysis. For the simulation it was assumed that a small crack was initiated at low temperature after the shut-off of thermal load in contrast to the previous studies where the presence of a crack before thermal loading was assumed. The threshold power density for surface cracking was predicted to range between 0.3 and 0.6GW/m2 while the threshold of base temperature lay between 200 and 400°C. The theoretically predicted damage map agreed well with the experimental data from electron beam irradiation tests. The current simulation model turned out to match better to the real experimental observation than the previous predictions where the threshold base temperature lies roughly between 400 and 600°C.

In this work, the cracking behavior of tungsten under edge-localized mode (ELM)-like thermal shock loads was investigated on the basis of a rigorous computational fracture mechanical analysis combined with the finite element method. Typical transient thermal shock loads of ELM conditions were considered with a relevant range of power density and base temperature for a loading duration of 1 ms. Crack initiation and progressive growth were predicted using the extended finite element method and the J-integral was calculated for the assumed precrack by means of the virtual crack extension method. For a power density of 1 GW/m2 and higher, a crack is preferably initiated near the edge of the loading area and is then followed by a gradual horizontal kinking, parallel to the loading surface. The crack formation is predicted for the power density of 0.6 GW/m2 and above, and when the base temperature is higher than 600 °C, almost no cracks is predicted. The numerically predicted cracking behavior agrees in general with the experimental observations.

The algal community structure is vital for aquatic management. However, the complicated environmental and biological processes make modeling challenging. To cope with this difficulty, we investigated using random forests (RF) to predict phytoplankton community shifting based on multi-source environmental factors (including physicochemical, hydrological, and meteorological variables). The RF models robustly predicted the algal communities composed by 13 major classes (Bray-Curtis dissimilarity = 9.2 ± 7.0%, validation NRMSE mostly 0.74) in Norway's largest lake, Lake Mjosa. The importance analysis showed that the hydro-meteorological variables (Standardized MSE and Node Purity mostly >0.5) were the most influential factors in regulating the phytoplankton. Furthermore, an in-depth ecological interpretation uncovered the interactive stress-response effect on the algal community learned by the RF models. The interpretation results disclosed that the environmental drivers (i.e., temperature, lake inflow, and nutrients) can jointly pose strong influence on the algal community shifts. This study highlighted the power of machine learning in predicting complex algal community structures and provided insights into the model interpretability.

Introduction: A refractory cervical anastomotic fistula which postoperatively remains unhealed for more than 2 months under conservative care severely impacts the quality of life of the patient and potentially leads to anastomotic stricture after the fistula heals. It is widely accepted that, to avoid this complication, refractory cervical anastomotic fistulas should undergo more aggressive treatments. However, when and which surgical intervention should be considered is unclear. Objective: This study was designed to evaluate the role of the pectoralis major myocutaneous flap in the management of refractory cervical anastomotic fistulas based on our experience of 6 cases and a literature review. Methods: Six patients diagnosed with refractory cervical anastomotic fistula after esophagectomy treated using pectoralis major myocutaneous flap transfer were included in the study. The clinical data, surgical details, and treatment outcome were retrospectively analyzed. Results: All patients survived the operations. One patient who had a circumferential anastomotic defect resulting from surgical exploration developed a mild fistula in the neo-anastomotic site in the 5th postoperative day, which healed after 7 days of conservative care. This patient developed an anastomotic stricture which was partially alleviated by an endoscopic anastomotic dilatation. All the other 5 patients had uneventful recoveries after operations and restored oral intake on the 10th–15th days after operation, and they tolerated normal diets without subsequent sequelae on follow-up. One patient developed both local and lung recurrence and died in 15 months after operation, while the other 5 patients survived with good tumor control during the follow-up of 25–53 months. Conclusion: The satisfactory treatment outcome in our study demonstrates that pectoralis major myocutaneous flap reconstruction is a reliable management modality for refractory cervical anastomotic fistulas after esophagectomy, particularly for those patients who experienced persistent fistulas after conservative wound care and repeated wound closures.