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Abstract In order to improve the quality of products during additive manufacturing, we developed a novel freezing sublimation-based method for inkjet-based three-dimensional (3D) printing technology, which can significantly improve the uniformity of material distribution in printed products. In our previous studies, we used a laboratory prototype with single droplets of inkjet solution containing colloidal particles to prove the concept of this study. However, understanding the interaction between droplets on the printing substrate surface is also crucial for determining the printing resolution and accuracy of this method, which cannot be fully investigated through single droplet-based experimental studies. To fill this knowledge gap, we conducted a series of experiments on colloidal droplet impingement, freezing, and sublimation on substrates using dual droplets. The experimental setup allowed the release of two droplets in quick succession from a modified nozzle with two needles. These droplets coalesced on the substrate surface due to spreading during their impingement processes. Observations revealed that the coalescence pattern of these two droplets varied depending on the time interval between their release. When the second droplet was released immediately after the first, their coalescence was governed by fluid dynamics. However, when the second droplet was released after the first droplet had frozen on the substrate, it spread above the ice surface of the first droplet in a relatively slower process. This observation provides new insights for the continued study and optimization of the proposed novel freezing sublimation-based 3D printing method. 

Abstract Aircraft icing, resulting from the freezing of supercooled water droplets on exposed surfaces, presents considerable hazards to flight safety by impairing aerodynamic performance and operating efficiency. This study empirically examines the interaction dynamics of supercooled water droplets and dielectric barrier discharge (DBD) plasma actuators, emphasizing electrical, thermal, and phase transition phenomena. Supercooled droplets were produced via sonic levitation in a freezer set at −10°C and subsequently deposited onto the plasma actuator surface at −5°C. Electrical diagnostics indicated a reduction in current intensity following droplet impact which inhibited plasma discharge activity. Thermal imaging detected localized heating at nucleation locations, indicating a temperature plateau during freezing caused by latent heat release. A study of spatial temperature along the droplet x-axis revealed a pronounced thermal gradient, with the most significant temperature rise occurring adjacent to the plasma-exposed area. High-speed imaging elucidated droplet dynamics, demonstrating spreading, descent towards the ground electrode, and subsequent retraction following stabilization. These discoveries improve the comprehension of plasma-droplet interactions, aiding in the improvement of plasma-based anti-icing technology. This research promotes the creation of effective and environmentally friendly solutions for aviation safety and other areas affected by icing hazards. 

Abstract Biodiversity underpins critical ecological processes, yet its relationship with phosphorus (P) remains poorly understood. Understanding the distinct responses of plant and soil microbial diversity to P availability changes is particularly crucial on a global scale. Integrating meta-analysis and natural gradient approaches, this study evaluates these responses globally. Specifically, we conducted a meta-analysis using 393 observations from 128 field P addition experiments and supplemented this with a natural gradient analysis of forest tree diversity and vascular plant diversity. Our meta-analysis results showed that P additions reduced plant species richness by 8.5% and Shannon index by 1.3% in global grasslands, while exerting minimal effects on soil bacterial and fungal diversity across major terrestrial ecosystems. Natural gradient analysis further demonstrated significant correlations between both forest tree richness and vascular plant richness with soil total P concentrations. Notably, partial correlation analyses showed negative correlations when controlling for gross primary productivity and edaphic variables, but positive correlations when controlling for climatic variables. These complementary approaches collectively suggest that plant diversity exhibits greater sensitivity to altered soil P availability than soil microbial diversity. Consequently, elucidating the differential responses of above- and below-ground biodiversity to nutrient supply changes provides a scientific foundation for sound management of terrestrial ecosystem functions and processes. 

Inkjet-based three-dimensional (3D) printing is widely used for fast and efficient non-contact manufacturing, yet it suffers from several drawbacks, such as coarse resolution, lack of adhesion, manufacturing inconsistency, and uncertain final part mechanical properties. These undesirable effects are related to complex flow phenomena in colloidal droplets in inkjet 3D printing, particularly the internal flows and droplet deformations during the deposition and drying processes. These challenges are due to the colloidal suspension droplets being kept in the liquid state during printing. To overcome these disadvantages, this paper presents a novel freezing-sublimation-based inkjet 3D printing concept that freezes the colloidal droplets upon impact followed by sublimation, eliminating the undesirable particle transport and fluid motions during deposition. A series of experiments were conducted to characterize the colloidal droplet behaviors during the impinging/freezing and sublimation processes and evaluate the effects of the freezing process on droplet impinging dynamics as well as the final deposition patterns through sublimation. It was demonstrated that the deposition patterns obtained from this new method are much more uniform than the conventional evaporation-based deposition method. Both qualitative and quantitative methods were applied to analyze the colloidal droplet profiles during the printing process (impinging, freezing, and sublimation), as well as the final deposition patterns. The study shows promising results of using this new method, providing a foundation for the development of the novel freezing-sublimation-based inkjet 3D printing technique. 

The Worthington jets from bursting bubbles at a gas-liquid interface can break up into small droplets, aerosolizing chemical and biological substances into the atmosphere and impacting both global climate and public health. Despite their importance in contaminant transport, the influence of adsorbed contaminants on bubble-bursting jet dynamics remains poorly understood. Here, we document how an immiscible compound contaminant layer impacts the jet radius, which deviates from the expected jetting dynamics produced by clean bubble bursting. We rationalize the deviation of the jet radius by characterizing the propagation of the capillary waves at the air-oil-water interface. We develop a linearized wave damping model based on the oil thickness profile and the wave dispersion, and we propose a revised Ohnesorge number with a scaling relation that captures the experimental results reasonably well. Our work not only advances the fundamental understanding of bubble bursting jets but also offers valuable insights for predicting bubble-mediated aerosol size distributions and transport of airborne contaminants in realistic environmental scenarios. 

We examine the collective behavior of single cells in microbial systems to provide insights into the origin of the biological clock. Microfluidics has opened a window onto how single cells can synchronize their behavior. Four hypotheses are proposed to explain the origin of the clock from the synchronized behavior of single cells. These hypotheses depend on the presence or absence of a communication mechanism between the clocks in single cells and the presence or absence of a stochastic component in the clock mechanism. To test these models, we integrate physical models for the behavior of the clocks in single cells or filaments with new approaches to measuring clocks in single cells. As an example, we provide evidence for a quorum-sensing signal both with microfluidics experiments on single cells and with continuousin vivometabolism NMR (CIVM-NMR). We also provide evidence for the stochastic component in clocks of single cells. Throughout this study, ensemble methods from statistical physics are used to characterize the clock at both the single-cell level and the macroscopic scale of 10⁶cells.