The slope model is established by Geo-Studio, and the deformation characteristics and stability of structural-soil slope in Zhanjiang area under different rainfall patterns are analyzed. The MK model was used basing on Morgenstern-price method. By setting monitoring points at the top, toe and slope surface of the slope, the variation rule of pore water pressure and displacement at the monitoring points under the four types of rainfall are gotten, and the shapes of different types of sliding surfaces are obtained. By the analysis of the most dangerous sliding surfaces, some suggestions are put forward. Those have important reference value for prevention or controlling the geological disasters such as landslides in Zhanjiang area.
The relationship between quality abnormality and anomalous causes in the assembly process of CNC machine was described by fuzzy relation equations, because they were not one to one. The fuzzy relation equations were established according to the fuzzy relation matrix and membership degree of abnormality mode and were translated into optimal solution problems by fuzzy deconvolution method. The interval solution of the fuzzy relation equation was obtained by minimal mean square error of BP algorithm, realizing section locating of the contribution of anomalous causes to quality abnormality for a given problem, thereby gaining the optimal solution. Finally, the viability and effectiveness of this method were verified by the quality abnormity diagnosis in the assembly process of a NC rotary table.
The droplet breakup technology can effectively increase the generation throughput and adjust the droplets size, which has an important impact on the performance of the double emulsion droplets in medical, chemical, and other applications. This work presents an experimental study on the breakup regimes of double emulsion droplets after their on-chip generation. Five distinct breakup regimes are categorized according to the breakup times and the existence of the coupling effect during breakup process. Evolutions of the neck widths and thinning rates of both inner droplets and outer droplets are provided to discuss the dynamics of different regimes as well as different stages. In particular, the influences of the coupling effect on the interfacial evolution, collapsing mechanism, force analysis, and breakup critical condition are confirmed by comparisons with the results of single emulsion droplets.
The droplet breakup technology can effectively increase the generation throughput and adjust the droplets size, which has an important impact on the performance of the double emulsion droplets in medical, chemical, and other applications. This work presents an experimental study on the breakup regimes of double emulsion droplets after their on-chip generation. Five distinct breakup regimes are categorized according to the breakup times and the existence of the coupling effect during breakup process. Evolutions of the neck widths and thinning rates of both inner droplets and outer droplets are provided to discuss the dynamics of different regimes as well as different stages. In particular, the influences of the coupling effect on the interfacial evolution, collapsing mechanism, force analysis, and breakup critical condition are confirmed by comparisons with the results of single emulsion droplets.
The flow topology inside a droplet acts directly on the cells or substances enclosed therein and is, therefore, of great significance in controlling the living environment of cells and the biochemical reaction process. In this paper, the flow characteristics inside droplets moving in rectangular microchannels are studied experimentally by particle image velocimetry for capillary numbers ranging from 10−5 to 10−2. In order to decouple the effects of total flow, droplet spacing, viscosity ratio, droplet size, and the depth-to-width ratio of the channel on the flow field, the droplet trains with a designed initial state are first produced by controlling the two-phase flow rate and setting up an auxiliary inlet, which is used to adjust the droplet size and spacing, and then run at a set flow rate. As the total flow increases, the flow topologies inside the plunger droplet gradually change from four eddies to two at relatively high viscosity ratios, whereas the opposite transition direction is observed in the low-viscosity-ratio system. The flow topology inside spherical droplets is unaffected by the total flow or capillary number, invariably producing double vortices. The effect of the channel wall on the droplet boundary decreases as the droplet spacing increases or the droplet size decreases. Assuming the continuity of the fluid mass, the competition between the gutter-flow driving stress and the oil-film resistance determines the boundary velocity of the droplet. The oil-film resistance dominates the motion of the droplet boundary in high-aspect-ratio channels, resulting in the negative rotation of the boundary velocity vectors and six vortices in the interior of the droplet. The results are conducive to the further development of microfluidic flow cytometry, particle concentration control, and droplet micromixers.
The teaching practice of cell biology experiments for oversea medical students in School of Medicine of Tongji University was reported in the present article, and the teaching principles of careful plan, clear contents, concise textbook, flexible scheme, full preparation, earnest triallecture, orderly implementation and formative assessment were put forward. Based on the different teaching object, the paper mainly explained the differences and the basis of the experimental teaching process of the foreign students and the domestic medical students to provide experience for improving the teaching mode of this kind of course.
Key words:
Oversea students; Bachelor of medicine and bachelor of surgery (MBBS); Cell biology experiments
In the fields of organ printing and drug preparation, high-precision and stable dispersion of high-viscosity biomaterials enable precise control of organ morphology and drug release rate. This paper proposes the use of an acoustic surface wave to overcome the problem of unstable interface breakup and weak size controllability when the traditional passive droplet microfluidics is applied to high-viscosity (higher than 0.4 Pa·s) dispersed phases. This paper studies the internal flow behavior of high-viscosity fluid under the influence of an acoustic field and realizes the accurate prediction of formation regime and droplet size. Experimental results show that with the increase in acoustic power, three unique droplet generation regimes (e.g., long jetting, transition, and dripping) exist. The transition regime is most suitable for high-throughput preparation of high-viscosity droplets, and its corresponding flow and acoustic conditions can be predicted by equation μd/μc = 4.8 × 10−8 (μc × vc/AP02 × w)−3.32. Affected by the regime transition, the droplet size increases with the increase in acoustic power. The droplet size prediction can be realized based on the capillary number Caf, which represents the intensity of the acoustic field.
The flow fields generated by the acoustic behavior of microbubbles can significantly increase cell permeability. This facilitates the cellular uptake of external molecules in a process known as ultrasound-mediated drug delivery. To promote its clinical translation, this study investigated the relationships among the ultrasound parameters, acoustic behavior of microbubbles, flow fields, and delivery results. SonoVue microbubbles were activated by 1 MHz pulsed ultrasound with 100 Hz pulse repetition frequency, 1:5 duty cycle, and 0.20/0.35/0.70 MPa peak rarefactional pressure. Micro-particle image velocimetry was used to detect the microbubble behavior and the resulting flow fields. Then HeLa human cervical cancer cells were treated with the same conditions for 2, 4, 10, 30, and 60 s, respectively. Fluorescein isothiocyanate and propidium iodide were used to quantitate the rates of sonoporated cells with a flow cytometer. The results indicate that (1) microbubbles exhibited different behavior in ultrasound fields of different peak rarefactional pressures. At peak rarefactional pressures of 0.20 and 0.35 MPa, the dispersed microbubbles clumped together into clusters, and the clusters showed no apparent movement. At a peak rarefactional pressure of 0.70 MPa, the microbubbles were partially broken, and the remainders underwent clustering and coalescence to form bubble clusters that exhibited translational oscillation. (2) The flow fields were unsteady before the unification of the microbubbles. After that, the flow fields showed a clear pattern. (3)The delivery efficiency improved with the shear stress of the flow fields increased. Before the formation of the microbubble/bubble cluster, the maximum shear stresses of the 0.20, 0.35, and 0.70 MPa groups were 56.0, 87.5 and 406.4 mPa, respectively, and the rates of the reversibly sonoporated cells were 2.4% ± 0.4%, 5.5% ± 1.3% and 16.6% ± 0.2%. After the cluster formation, the maximum shear stresses of the three groups were 9.1, 8.7, and 71.7 mPa, respectively. The former two could not mediate sonoporation, whereas the last one could. These findings demonstrate the critical role of flow fields in ultrasound-mediated drug delivery and contribute to its clinical applications.
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