The macroscopic rheological properties of suspensions are often inextricably related to changes in their microstructure, and a number of experimental studies have demonstrated the significant ...influence of DLVO (Derjaguin-Landau-Verwey-Overbeek) interactions, namely microscopic repulsive and attractive forces due to surface charge on particles in suspensions, on the microstructure of suspensions, especially on cluster formation. In this study, the rheological properties of non-Brownian suspensions and their microstructures are investigated by numerical simulations combining DLVO interactions with hydrodynamics and frictional contacts. Different mechanisms have been identified to account for diverse rheological responses of repulsive and adhesive suspensions, revealing a significant association between the evolution of particle clusters and suspension rheology. In repulsive systems, competitions between repulsive and hydrodynamic forces and the resulting change in the distribution of minimum particle separation are responsible for the first shear thinning at low shear rates. Shear thickening is observed at high shear rates and is dominated by particles contacts. Enhancing attractive forces give rise to the viscosity of the suspensions while obscuring shear thickening, and particles make contacts even at the first shear thinning conditions. The second normal stress difference exhibit similar evolution with viscosity while the first normal stress difference is mainly dominated by fluctuations. Microstructure analysis shows frictional clusters appear in repulsive suspensions with growth in both quantity and size as shear rate increases. Clusters in strongly adhesive suspensions, on the other hand, break into smaller ones, resulting in a viscosity reduction. The calculation of the shape anisotropy indicates that frictional clusters in repulsive suspensions tend to expand uniformly in simulation box whereas at high attractive strength, clusters deform more cylindrical when strongly sheared. Our studies in microstructure can fundamentally help in bridging the gap between microscale evolution and macroscale rheological responses, thus contributing to the foundation of the constitutive model of non-Brownian suspensions.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Cell membrane (CM) coating technology is increasingly being applied in nanomedicine, but the entire coating procedure including adsorption, rupture, and fusion is not completely understood. ...Previously, we showed that the majority of biomimetic nanoparticles (NPs) were only partially coated, but the mechanism underlying this partial coating remains unclear, which hinders the further improvement of the coating technique. Here, we show that partial coating is an intermediate state due to the adsorption of CM fragments or CM vesicles, the latter of which could eventually be ruptured under external force. Such partial coating is difficult to self-repair to achieve full coating due to the limited membrane fluidity. Building on our understanding of the detailed coating process, we develop a general approach for fixing the partial CM coating: external phospholipid is introduced as a helper to increase CM fluidity, promoting the final fusion of lipid patches. The NPs coated with this approach have a high ratio of full coating (~23%) and exhibit enhanced tumor targeting ability in comparison to the NPs coated traditionally (full coating ratio of ~6%). Our results provide a mechanistic basis for fixing partial CM coating towards enhancing tumor accumulation.
•Suitability of DPD method for studying emulsion rheology is demonstrated.•Dilute and semi-dilute emulsion within more than 100 droplets have been simulated.•Shear-thinning and finite normal stress ...differences of emulsion have been captured.•Emulsion microstructures are related with its rheological behaviors.
The dissipative particle dynamics (DPD) method is used to simulate droplet suspension. The deformation of a single droplet is first studied to validate the method and a good agreement with previous theoretical, numerical and experimental results is obtained. Droplet-droplet interaction is calibrated by simulating the process of two droplets collision. A larger repulsion force is imposed between particles from different droplet to prevent two droplets from coalescing. Dilute to semi-dilute emulsions are simulated with more than a hundred droplets suspended in another immiscible fluid. Shear thinning and non-zero normal stress differences are captured in the simulations. These phenomena are related with the mean droplet deformation parameter and mean inclination angle. The droplet deformation contributes to the increasing of suspension viscosity. Decreasing the inclination angle aligns the droplets more with the flow direction, contributing more to shear thinning. Fluid inertia increases the suspension viscosity. A good agreement is achieved between our zero shear viscosity results and previous model/experimental work.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
Hummingbirds are flapping winged creatures with unique flight mechanisms. Their flight pattern is more similar to insects than other birds. Because their flight pattern provides a large lift force at ...a very small scale, hummingbirds can remain hovering while flapping. This feature is of high research value. In order to understand the high-lift mechanism of hummingbirds' wings, in this study a kinematic model is established based on hummingbirds' hovering and flapping process, and wing models imitating the wing of a hummingbird are designed with different aspect ratios. Therefore, with the help of computational fluid dynamics methods, the effect of aspect ratio changes on the aerodynamic characteristics of hummingbirds' hovering and flapping are explored in this study. Through two different quantitative analysis methods, the results of lift coefficient and drag coefficient show completely opposite trends. Therefore, lift-drag ratio is introduced to better evaluate aerodynamic characteristics under different aspect ratios, and it is found that the lift-drag ratio reaches a higher value when AR = 4. A similar conclusion is also reached following research on the power factor, which shows that the biomimetic hummingbird wing with AR = 4 has better aerodynamic characteristics. Furthermore, the study of the pressure nephogram and vortices diagram in the flapping process are examined, leading to elucidation of the effect of aspect ratio on the flow field around hummingbirds' wings and how these effects ultimately lead to changes in the aerodynamic characteristics of the birds' wings.
The viscometric behavior of laponite and bentonite suspensions at different concentrations in shear flow is studied. It is discovered that in the equilibrium state, a master curve of viscosity can be ...constructed when the applied shear stress is normalized by the respective suspension’s yield stress. The interparticle interaction controlling the yield behavior at the gel state also dominates the behavior of particles at the equilibrium flowing state. A constitutive framework is developed to describe the master curve of viscosity as a function of the shear stress normalized by the yield stress. Based on the proposed model, the effect of concentration on the viscosity of clay suspensions can be estimated via their yield stress.
A mono tiltrotor (MTR) design which combines concepts of a tiltrotor and coaxial rotor is presented. The aerodynamic modeling of the MTR based on blade element momentum theory (BEMT) is conducted, ...and the method is fully validated with previous experimental data. An automated optimization approach integrating BEMT modeling and optimization algorithms is developed. Parameters such as inter-rotor spacing, blade twist, taper ratio and aspect ratio are chosen as design variables. Single-objective (in hovering or in cruising state) optimizations and multi-objective (both in hovering and cruising states) optimizations are studied at preset design points; i.e., hovering trim and cruising trim. Two single-objective optimizations result in different sets of parameter selections according to the different design objectives. The multi-objective optimization is applied to obtain an identical and compromised selection of design parameters. An optimal point is chosen from the Pareto front of the multi-objective optimization. The optimized design has a better performance in terms of the figure of merit (FM) and propulsive efficiency, which are improved by 7.3% for FM and 13.4% for propulsive efficiency from the prototype, respectively. Further aerodynamic analysis confirmed that the optimized rotor has a much more uniform load distribution along the blade span, and therefore a better aerodynamic performance in both hovering and cruising states is achieved.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The effective control of infectious diseases, including Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection, depends on the availability of rapid and accurate monitoring ...techniques. However, conventional SARS-CoV-2 detection technologies do not support continuous self-detection and may lead to cross-infection when utilized in medical institutions. In this study, we introduce a prototype of a mask biosensor designed for the long-term collection and self-detection of SARS-CoV-2. The biosensor utilizes the average resonance Rayleigh scattering intensity of Au nanocluster-aptamers. The inter-mask surface serves as a medium for the long-term collection and concentration enhancement of SARS-CoV-2, while the heterogeneous-nucleation nanoclusters (NCs) contribute to the exceptional stability of Au NCs for up to 48 h, facilitated by the adhesion of Ti NCs. Additionally, the biosensors based on Au NC-aptamers exhibited high sensitivity for up to 1 h. Moreover, through the implementation of a support vector machine classifier, a significant number of point signals can be collected and differentiated, leading to improved biosensor accuracy. These biosensors offer a complementary wearable device-based method for diagnosing SARS-CoV-2, with a limit of detection of 103 copies. Given their flexibility, the proposed biosensors possess tremendous potential for the continuous collection and sensitive self-detection of SARS-CoV-2 variants and other infectious pathogens.
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