Search

Minimizing frictional resistance and preventing the attachment of marine organisms are extremely important for global ship navigation to reduce energy consumption and carbon emissions. However, there is still a lack of an effective and environmentally-friendly drag reduction and antifouling method. Here, we propose a spontaneous fast-moving air film to resolve this problem. We first developed a serial brachistochrone-shaped superhydrophobic pattern to easily capture underwater air bubbles and realize the spontaneous and directional transportation of bubbles with an average velocity of 444 mm s−1 that is the fastest in the whole world. Then, the continuous supply of air bubbles and serial brachistochrone-shaped superhydrophobic pattern were combined to form a spontaneous fast-moving air film, which not only prevents the escape of supplied air bubbles but also replenishes the air film on a superhydrophobic surface. The spontaneous fast-moving air film showed an amazing 27% drag reduction rate and simultaneous 80% antifouling rate, which was an outstanding capability that had never been reported before. This effective and environmentally-friendly drag reduction and antifouling method will minimize energy consumption and carbon emissions and has strong implications for global sustainable development. [ABSTRACT FROM AUTHOR]

Reducing the flexspline (FS) deformation is important for decreasing the alternating stress, flare angle in the axial direction, spatial deformation of teeth, and tube length. However, it may increase the probability of insufficient engagement depth and nonexistent conjugate tooth profiles. In this study, a mathematical model of the harmonic drive (HD) with a new tooth profile is proposed to reduce the FS deformation while satisfying the engagement depth and existence of a conjugated tooth profile. First, the generation mechanism of the new tooth profile is discussed in detail and the connection method of the circular arc tooth profile and transition tooth profile in the FS were presented. Then, two key parameters of the model, the translation distance and offset distance were studied to design the ideal tooth profile. Finally, a tooth root chamfer method was proposed to achieve smooth operation of the HD. Additionally, owing to the lack of a wear assessment of the new tooth profile, a sliding coefficient calculation model was presented. To verify the feasibility of the models, a prototype with a radial deformation coefficient of 0.8 was designed, processed, and tested. The experimental results were consistent with the theoretical analyzes. [ABSTRACT FROM AUTHOR]

Background. Vascular adventitia contains progenitor cells and is shown to participate in vascular remolding. Progenitor cells are recruited into the venous thrombi in mice to promote neovascularization. We hypothesized that the adventitial progenitor cells of human great saphenous vein (HGSV-AdPC) enhance the resolution of venous thrombosis via neovascularization. Methods. Human great saphenous vein (HGSV) was harvested from the patients with great saphenous vein varicose and sectioned for immunohistochemistry, or minced for progenitor cell primary culture, or placed in sodium dodecyl sulfate solution for decellularization. Human venous thrombi were collected from patients with great saphenous vein varicose and superficial thrombophlebitis. Infrarenal abdominal aorta of New Zealand white rabbits was replaced with interposing decellularized vessel, and the patency of the grafts was confirmed by ultrasonic examination. Animal venous thrombi in the left infrarenal vena cava of mice were produced with Prolene suture ligation and ophthalmic force clipping of this portion. After HGSVs were digested by collagenase, the CD34+CD117+ HGSV-AdPC were isolated on FACS system, labelled with CM-Dil, and transplanted into the adventitia of infrarenal vena cava of nude mice. The percentage of thrombus organization area to the thrombus area was calculated as the organization rate. The thrombus cell, endothelial cells, and macrophages in the thrombi were counted in sections. Cell smears and frozen sections of human saphenous veins and venous thrombi were labeled with Sca1, CD34, CD117, Flk1, CD31, and F4/80 antibodies. The CD34+CD117+ HGSV-AdPC were cultured in endothelial growth medium with vascular endothelial growth factor (VEGF) to induce endothelial cell differentiation and analyzed with real time-PCR, Western blotting, and tube formation assays. Results. Immunohistochemical staining showed that the CD34+CD117+ cells were located within the adventitia of HGSVs, and many CD34+ and CD117+ cells have emerged in the human venous thrombi. The number of progenitor cells within the marginal area of 7 days mice thrombi was shown to be Sca1+ ≈21%, CD34+ ≈12%, CD117+ ≈9%, and Flk1+ ≈5%. Many CD34+adventitial progenitor cells have migrated into the decellularized vessels. FACS showed that the number of CD34+CD117+ HGSV-AdPC in primary cultured cells as 1.2 ± 0.07 %. After CD34+CD117+HGSV-AdPC were transplanted into the adventitia of nude mice vena cava with venous thrombi, the organization rate, nucleate cell count, endothelial cells, and macrophage cells of thrombi were shown to be significantly increased. The transplanted CD34+CD117+ HGSV-AdPC at the adventitia have crossed the vein wall, entered the venous thrombi, and differentiated into endothelial cells. The CD34+CD117+ HGSV-AdPC in the culture medium in the presence of VEGF-promoted gene and protein expression of endothelial cell markers in vitro and induced tube formation. Conclusions. HGSV-AdPC could cross the vein wall and migrate from the adventitia into the venous thrombi. Increased HGSV-AdPC in the adventitia has enhanced the resolution of venous thrombi via differentiating into endothelial cells of neovascularization. [ABSTRACT FROM AUTHOR]

Previous studies found that the peripheral cutting edge and end cutting edge in micro end milling had different cutting phenomena considering the size effect in micro cutting processes. This paper is a further study on this point considering different workpiece materials and cutting edge radii. Finite element simulations have been conducted to determine the minimum undeformed chip thickness (MUCT) by the chip morphology and the results are verified by micromilling experiments. Both the simulations and experiments show that the MUCT of the peripheral cutting edge and the end cutting edge are different even if the cutting edge radii remain unchanged. The MUCT is directly proportional to the cutting edge radius. Material properties also have some effects on the MUCT of the peripheral cutting edge. But it has limited effects on that of the end cutting edge. The results indicate that the feed engagement other than the axial depth of cut should be carefully selected in micro end milling when considering different workpiece materials. [ABSTRACT FROM AUTHOR]

Dalian University of Technology, China (DLUT) successfully developed class-1 spur gear artefacts. However, the expanded uncertainty U95 of the existing instrument for measuring gear helix deviations is more than 1/3 of the class-1 gear helix tolerances, which cannot meet the measuring requirements of the helix deviations for the class-1 spur gear artefacts. In order to solve these problems, the influences of the mandrel locating error on the gear helix deviations are analysed, and a novel instrument for measuring spur gear helix deviations to submicron accuracy is designed. The instrument is optimized for the measurement of specific gear types (external teeth, medium module, with through-hole, reference diameter ≤126 mm). The expanded uncertainties U95 of the instrument for measuring the total helix deviation Fβ, the helix slope deviation fHβ and the helix form deviation ffβ are 0.23 µm, 0.20 µm and 0.18 µm respectively. This is less than 1/3 of the class-1 gear helix tolerances (the total helix tolerance FβT, the helix slope tolerance fHβT and the helix form tolerance ffβT are 2.4 µm, 1.6 µm and 1.8 µm respectively: ISO 1328-1:2013). Verification measurements with a calibrated measurement standard show the proficiency. [ABSTRACT FROM AUTHOR]

Self‐propelled autonomous devices have huge application prospects in the field of environmental protection and energy. Nonetheless, the requirement of special chemicals or external electric and thermal energy limits their practical application. Here, a green self‐propelling method based on Laplace pressure originated from water droplets is reported. First, a triangle‐shaped miniboat composed of a superhydrophobic plate with an inclined superhydrophilic pore is fabricated. Water droplets put on superhydrophilic pore pass through the pore and form a jellyfish‐like jet, which further propels the miniboat to move spontaneously and directionally. The propelling distance, propelling time, and instantaneous propelling velocity of the miniboat is greatly affected by the pore size and the initial water droplet volume. Then, two types of devices are designed and installed on the miniboat to successively provide small water droplets from the reservoir or rain to realize the continuous and long‐distance self‐propelled motion. Moreover, a spindle‐shaped miniboat with two or four symmetrical and inclined pores is designed. Under propelling by the torque, the spontaneous and continuous rotation motion is also achieved. This finding will open a new avenue for a wide range of applications ranging from a detecting minirobot on the water surface to a power generation device from rain. [ABSTRACT FROM AUTHOR]

This paper presents a miniature three-degree-of-freedom laser measurement (3DOFLM) system for displacement feedback and error compensation of a nanopositioning stage. The 3DOFLM system is composed of a miniature Michelson interferometer (MMI) kit, a wavelength corrector kit, and a miniature autocollimator kit. A low-cost laser diode is employed as the laser source. The motion of the stage can cause an optical path difference in the MMI kit so as to produce interference fringes. The interference signals with a phase interval of 90° due to the phase control are detected by four photodetectors. The wavelength corrector kit, based on the grating diffraction principle and the autocollimation principle, provides real-time correction of the laser diode wavelength, which is the length unit of the MMI kit. The miniature autocollimator kit based on the autocollimation principle is employed to measure angular errors and compensate induced Abbe error of the moving table. The developed 3DOFLM system was constructed with dimensions of 80 mm (x) × 90 mm (y) × 20 mm (z) so that it could be embedded into the nanopositioning stage. A series of calibration and comparison experiments were carried out to test the performance of this system. [ABSTRACT FROM AUTHOR]

The ultra-precision master gear with high pitch accuracy has important applications in the calibration of high-precision gear measuring instruments or coordinate measuring machines and in military industries. In order to improve pitch deviations of ultra-precision gear, two gear-grinding techniques to improve pitch deviations of ultra-precision gear were proposed. First, based on the indexing plate system, the working principle of indexing plate and error transferring rules were discussed, and the technical approaches of decreasing the geometric eccentricity were proposed. Then according to the error interference principle, the offset-compensated technique and the neighbour-tooth translocation technique were proposed to improve the pitch machining accuracy of ultra-precision master gear. Finally, precision gear-grinding experiments were conducted by adopting the neighbour-tooth translocation technique based on offset-compensated technique. And the single pitch deviation fp of the test specimen is reduced from 1.06 to 0.63μm and the total cumulative pitch deviation Fp is reduced from 3.11 to 1.98μm with measurement uncertainty U95 = 0.33μm, which both reach the highest class (class 1 defining in ISO 1328-1:2013). The results show the efficiency and practicability of the two gear-grinding techniques to machine ultra-precision master gear. [ABSTRACT FROM AUTHOR]

The accuracy requirement of ultra-precision involute artefacts and master gears, which are used to calibrate the gear measuring machines, is increasing as power density increases; however, the complexities and specificities in the involute processing and measuring have been the bottleneck of manufacturing technique for high-grade involute artefacts and ultra-precision master gears. In order to develop the ultra-precision involute gear profile, related researches were conducted in this study. First, the manufacturing level of high-grade involute artefacts was introduced. Then, the forming principle of the involute was discussed, and the roller–rail type and cam–baffle type of mechanical generating mechanism with little effects of driving accuracy on generating accuracy and less error sources were pointed out. Finally, the double roller–rail type of grinding and measuring devices for high-grade involute artefacts were designed according to the optimal forming principle of the involute, and a precision grinding experiment on an involute cam (a kind of high-grade involute artefacts) was conducted. The measured results show that the total profile deviation is not more than 0.6 µm and the profile form deviation is less than 0.4 µm in 105 mm generating length of the specimen. By using the refined involute cam and gear grinder with cam–baffle type of mechanical generating mechanism, a precision grinding experiment on the specimen of a master gear was conducted. The experimental results verify that the roller–rail type of mechanical generating mechanism has the processing capacity of high-grade involute artefacts with submicron-level profile accuracy and the refined gear grinder with cam–baffle type of mechanical generating mechanism has the processing capacity of ultra-precision master gear with grade-1 profile accuracy. [ABSTRACT FROM AUTHOR]

In order to improve the machining quality and reduce the dimensional errors of micro high-aspect-ratio straight thin walls, the on-line cutting parameter compensation device has been introduced and corresponding micromilling processes have been investigated. Layered milling strategies for the micromilling of thin walls have been modeled and simulated for thin walls with different thicknesses based on the finite element method. The radial cutting parameters compensation method is adopted to compensate the thin wall deformation by raising the radial cutting parameters since the thin wall deformation make the actual radial cutting parameters smaller than nominal ones. The experimental results show that the dimensional errors of the thin wall have been significantly reduced after the radial cutting parameter compensation. The average relative dimensional error is reduced from 6.9% to 2.0%. Moreover, the fabricated thin walls keep good shape formation. The reduction of the thin wall dimensional error shows that the simulation results are reliable, which has important guiding significance for the improvement of thin wall machining quality, especially the improvement of dimensional accuracy. The experimental results show that the developed device and the machining strategy can effectively improve the micromilling quality of thin walls. [ABSTRACT FROM AUTHOR]

K9 optical glass has superb material properties used for various industrial applications. However, the high hardness and low fracture toughness greatly fluctuate the cutting force generated during the grinding process, which are the main factors affecting machining accuracy and surface integrity. With a view to further understand the grinding mechanism of K9 glass and improve the machining quality, a new arithmetical force model and parameter optimization for grinding the K9 glass are introduced in this study. Originally, the grinding force components and the grinding path were analyzed according to the critical depth of plowing, rubbing, and brittle tear. Thereafter, the arithmetical model of grinding force was established based on the geometrical model of a single abrasive grain, taking into account the random distribution of grinding grains, and this fact was considered when establishing the number of active grains participating in cutting Nd-Tot. It should be noted that the tool diameter changed with machining, therefore this change was taking into account when building the arithmetical force model during processing as well as the variable value of the maximum chip thickness amax accordingly. Besides, the force analysis recommends how to control the processing parameters to achieve high surface and subsurface quality. Finally, the force model was evaluated by comparing theoretical results with experimental ones. The experimental values of surface grinding forces are in good conformity with the predicted results with changes in the grinding parameters, which proves that the mathematical model is reliable. [ABSTRACT FROM AUTHOR]

Wire electrochemical micromachining (WECMM) technology is regarded a promising method to fabricate high aspect ratio microstructures on hard-to-machining materials, however, the by-product accumulation in the machining gap limits its application. In this paper, a new method called ultrasonic-assisted wire electrochemical micromachining (UA-WECMM) is proposed to improve the machining performance of WECMM. Firstly, a flow-field simulation in the machining gap was carried out; the results showed that the ultrasonic vibration of electrode can remarkably enhance the mass transport in the machining gap and improve the machining condition. Secondly, experiments were performed to confirm the effect of ultrasonic vibration, which illustrated that the vibration with proper amplitude can reduce the slit width and improve the morphology of machined surface. Moreover, the influence of other machining parameters were also discussed. Finally, a T-type micro connector with good surface roughness (Ra 0.286 μm) was fabricated on a 300-μm-thick 304 stainless steel workpiece and a micro gear (diameter: 3.362 mm; Ra: 0.271 μm) with an aspect ratio of 7 was fabricated on a 2-mm-thick workpiece. It is proved that the proposed ultrasonic-assisted wire electrochemical micromachining method has considerable potential and broad application prospects. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of statins on risk of recurrent venous thromboembolism (VTE) was systematically analyzed. • Statins were associated with lower risks of recurrent VTE and its two forms, i.e. DVT and PE. • Statins were associated with a lower risk of mortality among patients with VTE. • Randomized clinical trials are warranted to corroborated these findings. Recent studies have suggested that statins may be associated with a lower risk of recurrent venous thromboembolism (VTE). We systematically searched PubMed, Web of Science and Cochrane Library from inception until May 2020 to identify any eligible studies that reported the association between statin use and the risk of recurrent VTE, and conducted a comprehensive systematic review and meta-analysis (PROSPERO registration number: CRD42020190169) on this matter. A total of 14 observational studies were included for qualitative review and 12 of them qualified for meta-analyses. The main meta-analysis found that statin use was associated with a lower risk of disease recurrence among patients with VTE (pooled adjusted HR: 0.76, 95% CI: 0.69−0.83), which was robust in sensitivity analyses and free of significant publication bias. Additionally, such association was present when restricting to periods after anticoagulation withdrawal (pooled adjusted HR: 0.78, 95% CI: 0.70−0.88) and when separately analyzing recurrent deep vein thrombosis (pooled adjusted HR: 0.71, 95% CI: 0.62−0.81) and recurrent pulmonary embolism (pooled adjusted HR: 0.80, 95% CI: 0.66−0.97; P = 0.027). Furthermore, statin use in patients with VTE was also found to be associated with a lower risk of all-cause mortality (adjusted HR: 0.65, 95% CI: 0.56−0.77), and possibly an even lower risk of bleeding (adjusted HR: 0.88, 95% CI: 0.73–1.07), albeit not statistically significant. Statins have the potential to reduce recurrent events among patient with VTE. Randomized clinical trials to better explore the effect of statins in secondary prevention of VTE are warranted. [ABSTRACT FROM AUTHOR]

Background: Venous thromboembolism (VTE) concomitant to acute limb ischemia (ALI) is rarely reported. The aim of the study was to investigate characteristics and identify clinical indicators of VTE in patients with ALI., Methods: Electronic medical record was used to identify patients diagnosed with ALI from January 2013 to June 2019. Eligible patients were categorized as VTE or non-VTE based on the presence or absence of concomitant VTE. Univariate analysis and multivariate analysis for indicators of VTE were performed., Results: A total of 153 patients with 161 ischemic limbs were enrolled. Venous duplex ultrasound (DUS) for 149 patients (157 ischemic limbs) revealed deep vein thrombosis (DVT) in 38 (24.2%) ischemic limbs of 37 (24.8%) patients. Five femoral DVTs were found intraoperatively. Six patients had pulmonary embolism (PE) and three of them died. In all, 43 (28.1%) ALI patients were diagnosed with VTE. They were treated with trans-arterial catheter-directed thrombolysis (N.=22), embolectomy (N.=9), primary amputation (N.=4) and anticoagulation alone (N.=8). The univariate analysis indicated that symptoms ≥ 2 days [odds ratio (OR): 3.42, 95%CI:1.54-7.62], Rutherford classification IIb-III (OR: 9.17, 95%CI: 2.10-40.12), leg swelling (OR: 4.44, 95%CI: 2.07-9.53), neutrophil ratio ≥0.80 (OR: 3.92, 95%CI: 1.72-8.93) and positive D-dimer (OR: 8.44, 95%CI: 3.65-19.53) were indicators of VTE concomitant to ALI. In the multivariate analysis, leg swelling and positive D-dimer appeared to be independent indicators., Conclusions: VTE commonly occurs to ALI. Venous DUS for DVT screening should be considered for ALI patients who present one or more of these indicators.