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The grain size effect is an important factor in determining the material removal behavior of polycrystalline silicon (p-Si). In the present study, to improve the understanding of nanoscale machining of p-Si, we performed molecular dynamics simulation of nanometric cutting on a p-Si workpiece and discussed the grain size effect on material removal behavior and subsurface damage formation. The simulation results indicate that when cutting on the polycrystal workpiece, the material removal process becomes unstable compared with single crystals. Higher removal efficiency, less elastic recovery and higher frictional coefficient are observed as the average grain size decreases. In the subsurface workpiece, when the grain size decreases, slip along grain boundaries merges as a nonnegligible process of the plastic deformation and suppresses the elastic deformation ahead of the cutting tool. It is also revealed that when cutting on a polycrystal workpiece with smaller grains, the average stress decreases while the workpiece temperature increases due to the impediment of heat transfer by grain boundaries. These results could provide a fundamental understanding in the material deformation mechanism of p-Si during nanoscale machining.

Leaf vein drip irrigation emitter is a new type of drip irrigation emitter. The flow channel achieves energy dissipation through flow diversion, turning, and sudden contraction. In this study, three design schemes (B1, B2, and B3) were proposed by optimizing the flow channel structure to improve the hydraulic performance, and the feasibility of the schemes was verified by combining them with experiments. The results show that the flow index of the three structural optimization designs were 0.52, 0.51, and 0.50, with errors of less than 5% compared to the measured results. Compared to the original structure A1 (with a flow index of 0.53), the hydraulic performance was improved by 0.4%, 3.2%, and 5.7%. Compared with A1 and B1, the turbulence kinetic energy of the main flow region of the B2 and B3 structures was significantly increased, and the proportion of low turbulence kinetic energy area had decreased. The increase in turbulent kinetic energy drove the liquid to remain turbulent, increasing the ability of particulate matter to flow out of the flow channel. The irregular changes in the velocity field in the high-speed zone result in a large velocity gradient, which maximizes the turbulent kinetic energy and entropy generation in the area. Among the four flow channel structures, the region with the highest turbulence dissipation was located in the upper part of the internal structure of the flow channel. There were apparent vortex regions in flow channels A1, B1, and B3 for energy dissipation, with energy dissipation coefficients being 6.07–8.51. However, the average flow velocity in this region was only about 0.2 m/s, and particulate matter was easily trapped. When the particle diameter increased, compared with the other three design structures, B2 had the best particle passage ability. Combined with the muddy water experiment, the optimized flow channel B2 anti-clogging performance improved by 30.8%. This study can provide a reference for further improving the hydraulic performance of drip irrigation emitters.

BackgroundThe subarachnoid space is continuous with the perivascular compartment in the central nervous system. However, whether the topography and severity of enlarged perivascular spaces (EPVS) correlates with spontaneous subarachnoid hemorrhage (SAH) remains unknown. Based on the underlying arteriopathy distributions, we hypothesized that EPVS in basal ganglia (BG-EPVS) are more closely associated with aneurysmal subarachnoid hemorrhage (aSAH) than other SAH without aneurysm.MethodsMagnetic resonance imaging (MRI) scans of 271 consecutive SAH survivors with and without aneurysm were analyzed for EPVS and other markers of imaging data. In the subgroup analysis, we compared the clinical characteristics and EPVS of SAH participants with and without pre-existing known risk factors (hypertension, diabetes, and smoking history) using multivariable logistic regression.ResultsPatients with aSAH (n = 195) had a higher severity of BG-EPVS and centrum semiovale EPVS (CSO-EPVS) than those without aneurysm (n = 76). Importantly, BG-EPVS predominance pattern (BG-EPVS>CSO-EPVS) only existed in aSAH survivors rather than other SAH without aneurysm. In the subgroup analysis, interestingly, we also found that a high degree of BG-EPVS showed an independent relationship with aSAH in patients without pre-existing risk factors (e.g., hypertension).ConclusionIn this cohort study, BG-EPVS predominance pattern was associated with aSAH patients compared with those without aneurysm. Moreover, BG-EPVS still showed a strong association with aSAH survivors without pre-existing vascular risk factors. Our present study suggested the BG-EPVS as a potential MRI-visible characteristic would shed light on the pathogenesis of glymphatic function at the skull base for aSAH.