THE SIZE EFFECT ON THE DISPERSION OF A PARTICLE IN A HOMOGENEOUS ISOTROPIC TURBULENCE

The mechanism of the response motion of a suspended particle to turbulent motion of its surrounding fluid is different according to si:e of turbulent eddies. The particle is dragged by the viscous force of large eddies, and meanwhile driven randomly by small eddies. Based on this understanding, the dispersion of a particle with finite size in a homogeneous isotropic turbulence is calculated in this study. Results show that there are two competing effects: when enhanced by the inertia of a particle, the long-term particle diffusivity is reduced by the finite size of the particle.

A homogenous solid polymer electrolyte prepared by facile spray drying method is used for room-temperature solid lithium metal batteries

The aggregation of inorganic particles with high mass ratio will form a heterogeneous electric field in the solid polymer electrolytes(SPEs),which is difficult to be compatible with lithium anode,leading to inadequate ionic conductivity.Herein,a facile spray drying method is adopted to increase the mass ratio of inorganic particles and solve the aggregation problems of fillers simultaneously.The polyvinylidene fluoride(PVDF)with lithium bis(trifluoromethanesulfonyl)imide(LiTFSI)covers the surface of each Li_(6.4)La_(3)Zr_(1.4)Ta_(0.6)O_(12)(LLZTO)granules during the nebulization process,then forming flat solid electrolytes via layer-by-layer deposition.Characterized by the atomic force microscope,the obtained solid electrolytes achieve a homogenous dispersion of Young’s modulus and surface electric field.As a result,the as-prepared SPEs present high tensile strength of 7.1 MPa,high ionic conductivity of 1.86×10^(−4)S·cm^(−1)at room temperature,and wide electrochemical window up to 5.0 V,demonstrating increased mechanical strength and uniform lithium-ion migration channels for SPEs.Thanks to the as-prepared SPEs,the lithiumsymmetrical cells show a highly stable Li plating/stripping cycling for over 1,000 h at 0.1 mA·cm^(−2).The corresponding Li/LCoO_(2)batteries also present good rate capability and excellent cyclic performance with capacity retention of 80%after 100 cycles at room temperature.

The spatial variation of soil bacterial community assembly processes affects the accuracy of source tracking in ten major Chinese cities

Urban soils harbor billions of bacterial cells and millions of species.However,the distribution patterns and assembly processes of bacterial communities remain largely uncharacterized in urban soils.It is also unknown if we can use the bacteria to track soil sources to certain cities and districts.Here,Illumina MiSeq sequencing was used to survey soil bacterial communities from 529 random plots spanning 61 districts and 10 major cities in China.Over a 3,000 km range,community similarity declined with increasing geographic distance(Mantel r=0.62),and community composition was clustered by city(R^(2)=0.50).Within cities(<100 km),the aforementioned biogeographic patterns were weakened.Process analysis showed that homogenizing dispersal and dispersal limitation dominated soil bacterial assembly at small and large spatial scales,respectively.Accordingly,the probabilities of accurately tracking random soil sources to certain cities and districts were 90.0% and 66.7%,respectively.When the tested samples originated from cities that were more than 1,265 km apart,the soil sources could be identified with nearly 100% accuracy.Overall,this study demonstrates the strong distance-decay relationship and the clear geographic zoning of urban soil bacterial communities among cities.The varied importance of different community assembly processes at multiple spatial scales strongly affects the accuracy of microbial source tracking.

High Performance Long Chain Polyamide/Calcium Silicate Whisker Nanocomposites and the Effective Reinforcement Mechanism

PA1012/calcium silicate whisker nanocomposites with contents of whisker ranging from 10 wt% to 40 wt%, are prepared by twin screw extruder without any additions of coupling agent. The effect of whisker on the matrix is analyzed by the studies of morphology, the mechanical properties, water absorption and thermal stabilities. SEM micrographs obviously demonstrate, even under the high filler content of 40 wt% and without surface treatment, calcium silicate whisker can be homogeneously dispersed in polyamide, directly leading to the enhanced mechanical properties. The mechanism of higher efficiency of reinforcement is needle-like shape whisker, having access to be intercalated, and mutual affinity caused by hydrogen bonding interaction between carbonyl group in polyamide chain and hydroxyl group in whisker surface. Both aspects attach matrix with excellent stress-transfer properties. In addition, with the assistance of whisker, the nanocomposite favors an improved water absorption as well as thermal stability, which is intimately associated with physical performance.

Melt emulsification-Is there a chance to produce particles without additives?

Melt emulsification is a well known process. Milk is thus homogenized for over 100 years. In the melt emulsification process, the future disperse phase is melted and dispersed into droplets, the size of which is controlled by an emulsification process. After emulsification, the droplets are cooled down and solid particles of spherical shape are formed. In order to realize melt emulsification processes, we developed the new SHM （Simultaneous Homogenizing and Mixing） nozzle, which enables us to mix separate phases directly into the droplet forming zone of homogenization nozzles. This molten milk fat globule can be homogenized at elevated fat content （up to 42 vol% instead of max. 17 vol%） and elevated temperatures （up to 150 ℃ instead of max. 70 ℃） without loosing product quality as for conventional homogenization processes. In addition, more than 80% of the energy costs can be saved and additional mixing units can be spared. This is realized by a controlled and quick dilution and cooling down of molten fat globules directly after their disruption in the nozzle itself. SHM-technology also allows for the dispersing of molten waxes. Instant cooling down after adjusting particle sizes also allows us to work without emulsifiers or other additives as absolutely required in conventional melt emulsification processes where molten droplets will coalesce upon their collisions in the homogenization nozzle. SHM-melt emulsification is thus an alternative to conventional milling processes, which are often limited by the stickiness of these products.