Competing Lengthscales in Colloidal Gelation with Non-Sticky Particles

Colloidal gels are widely applied in industry due to their rheological character -- no flow takes place below the yield stress. Such property enables gels to maintain uniform distribution in practical formulations; otherwise, solid components may quickly sediment without the support of gel matrix. Compared with pure gels of sticky colloids, therefore, the composites of gel and non-sticky inclusions are more commonly encountered in reality. Through numerical simulations, we investigate the gelation process in such binary composites. We find that the non-sticky particles not only confine gelation in the form of an effective volume fraction, but also introduce another lengthscale that competes with the size of growing clusters in gel. The ratio of two key lengthscales in general controls the two effects. Using different gel models, we verify such scenario within a wide range of parameter space, suggesting a potential universality in all classes of colloidal composites

Two-Stage Bagging Pruning for Reducing the Ensemble Size and Improving the Classification Performance

Ensemble methods, such as the traditional bagging algorithm, can usually improve the performance of a single classifier. However, they usually require large storage space as well as relatively time-consuming predictions. Many approaches were developed to reduce the ensemble size and improve the classification performance by pruning the traditional bagging algorithms. In this article, we proposed a two-stage strategy to prune the traditional bagging algorithm by combining two simple approaches: accuracy-based pruning (AP) and distance-based pruning (DP). These two methods, as well as their two combinations, “AP+DP” and “DP+AP” as the two-stage pruning strategy, were all examined. Comparing with the single pruning methods, we found that the two-stage pruning methods can furthermore reduce the ensemble size and improve the classification. “AP+DP” method generally performs better than the “DP+AP” method when using four base classifiers: decision tree, Gaussian naive Bayes, K-nearest neighbor, and logistic regression. Moreover, as compared to the traditional bagging, the two-stage method “AP+DP” improved the classification accuracy by 0.88%, 4.06%, 1.26%, and 0.96%, respectively, averaged over 28 datasets under the four base classifiers. It was also observed that “AP+DP” outperformed other three existing algorithms Brag, Nice, and TB assessed on 8 common datasets. In summary, the proposed two-stage pruning methods are simple and promising approaches, which can both reduce the ensemble size and improve the classification accuracy

Location Determination of Optimal Emergency System for Hurricane Disaster Based on Mathematical Modeling

This article first introduces the current research status of space optical communication, and gives a brief overview of the development and application prospects of space optical communication, explaining its important research significance. Then, the working principle of ATP in space optical communication system is studied, the mathematical model of ATP control system is established according to the actual needs, and the ATP control system design of space optical communication is designed. By selecting appropriate motors and gyroscopes as the actuators and detection elements of the system, substituting the actual parameters for simulation analysis, and correcting and verifying the results, some useful results are obtained. The simulation results show the rationality and effectiveness of the ATP design scheme

Rheology of a binary suspension

Suspensions are widely encountered in industrial processes. So it is important to fundamentally understand how they ow. While progress has been made on monodisperse suspensions, most realistic suspensions are composed of multiple constituent particles. Among a variety of multi-component suspensions, this work concerns a specific class consisting of large repulsive grains suspended in a viscoelastic gel. In such system, we highlight a unique solid-liquid transition which is triggered by external flow. Rheo-imaging reveals the correlation between the rheological transition and the structural change. This state transition is the focus of this thesis. We first establish a model binary suspension of large repulsive particles and small attractive particles. We mix two species of silica particles together, with the smaller (Brownian) ones being hydrophobically attractive and the larger (non- Brownian) ones stabilised via surface charge. Using a water-glycerol-ethanol mixture as the suspending solvent, we match the refractive index which, along with the fluorescent labelling of both particles and solvent, enables confocal microscopy. Remarkably, this model system is well-characterised, tuneable and transparent (imageable). Through extensive rheological studies, we observe a ow-switched transition between a solid state and a liquid state. Specifically, the binary suspension solidi es upon cessation of vigorous flow, while prolonged gentle flow results in a liquid state which permanently persists at rest. We demonstrate that this state transition is reversible and has memory. Rheo-confocal microscopy reveals distinct structure in the two states. The solid state consists of a gel matrix of small particles with large particles embedded inside, whereas in the liquid state, the small particles phase separate into disjoint, globular blobs. While there exists two states, detailed observation identi es three ow regimes. By varying the particle composition, we construct a state diagram to map out the extent of these regimes. The three regimes are demarcated by two transition boundaries, which are closely related to the macroscopic property of each state. We verify that the solid state is essentially a particle-fi lled gel and the lower boundary is its yield stress. Moreover, we show that the blobs in the liquid state are solid `droplets' whose strength directly determines the upper transition boundary. Beyond the state diagram, we further explore the parameter space of the binary system. We con rm that the small-small attraction and the large particle size are two key factors to the state transition. However, we still do not understand the microscopic mechanism. We illustrate several possible research lines, whose results may ll important gaps for the fundamental understanding. Our system contributes more than a model system. By comparing the rheology and microstructure, we reveal the similarity between a Li-ion battery slurry and our suspension. Moreover, the ow-switched solid-liquid transition, which is reversible and has memory, sheds new light on the smart material design. We identify our suspensions as a memory mechanorheological (McR) uid, whose rheology is mechanically tuneable and can persist upon removal of mechanical stimuli

How Surface Roughness Affects the Interparticle Interactions at a Liquid Interface

Shapes of colloids matter at liquid interfaces. We explore the interactions between rough-surfaced nanocolloids at the air--water interface through the compaction of monolayers experimentally and numerically. Sufficiently rough systems exhibit a non-trivial intermediate state between a gas-like state and a close-packed jamming state due to roughness-induced capillary attraction. We also find that roughness-induced friction lowers the jamming point, and the tangential contact force owing to surface asperities can cause a gradual off-plane collapse of the compressed monolayer.Comment: 6+6 pages, 4+3 figures, 4 video

Identification of Benzo[a]pyrene-metabolizing bacteria in forest soils by using DNA-based stable-isotope probing

DNA-based stable-isotope probing (DNA-SIP) was used in this study to investigate the uncultivated bacteria with benzo[a]pyrene (BaP) metabolism capacities in two Chinese forest soils (Mt. Maoer in Heilongjiang Province and Mt. Baicaowa in Hubei Province). We characterized three different phylotypes with responsibility for BaP degradation, none of which were previously reported as BaP-degrading microorganisms by SIP. In Mt. Maoer soil microcosms, the putative BaP degraders were classified as belonging to the genus Terrimonas (family Chitinophagaceae, order Sphingobacteriales), whereas Burkholderia spp. were the key BaP degraders in Mt. Baicaowa soils. The addition of metabolic salicylate significantly increased BaP degradation efficiency in Mt. Maoer soils, and the BaP-metabolizing bacteria shifted to the microorganisms in the family Oxalobacteraceae (genus unclassified). Meanwhile, salicylate addition did not change either BaP degradation or putative BaP degraders in Mt. Baicaowa. Polycyclic aromatic hydrocarbon ring-hydroxylating dioxygenase (PAH-RHD) genes were amplified, sequenced, and quantified in the DNA-SIP (13)C heavy fraction to further confirm the BaP metabolism. By illuminating the microbial diversity and salicylate additive effects on BaP degradation across different soils, the results increased our understanding of BaP natural attenuation and provided a possible approach to enhance the bioremediation of BaP-contaminated soils

Filled Colloidal Gel Rheology: Strengthening, Softening, and Tuneability

Filler-induced strengthening is ubiquitous in material science and is particularly well-established in polymeric nanocomposites. Despite having similar constituents, colloidal gels with solid filling exhibit distinct rheology, which is poorly understood. We show using experiments and simulations that filling monotonically enhances the yield stress of colloidal gels, while the elastic modulus first increases before decreasing. The latter effect results from a disturbed gel matrix at dense filling, evidenced by a growing inter-phase stress. This structural frustration is, however, not detrimental to yielding resistance. Instead, fillers offer additional mechanical support to the gel backbone via percolating force chains, at the same time decreasing the yield strain. We develop a mechanistic picture of this phenomenology that leads us to a novel `filler-removal protocol,' making possible individual control over the strength and brittleness of a composite gel