Switchable opening and closing of a liquid marble via ultrasonic levitation

Liquid marbles have promising applications in the field of microreactors, where the opening and closing of their surfaces plays a central role. We have levitated liquid water marbles using an acoustic levitator and, thereby, achieved the manipulation of the particle shell in a controlled manner. Upon increasing the sound intensity, the stable levitated liquid marble changes from a quasi-sphere to a flattened ellipsoid. Interestingly, a cavity on the particle shell can be produced on the polar areas, which can be completely healed when decreasing the sound intensity, allowing it to serve as a microreactor. The integral of the acoustic radiation pressure on the part of the particle surface protruding into air is responsible for particle migration from the center of the liquid marble to the edge. Our results demonstrate that the opening and closing of the liquid marble particle shell can be conveniently achieved via acoustic levitation, opening up a new possibility to manipulate liquid marbles coated with non-ferromagnetic particles

Lost in transition: Forest transition and natural forest loss in tropical China

The term forest transition refers to a change in forest cover over a given area from a period of net forest area loss to a period of net gain. Whether transitioning from deforestation to reforestation can lead to improved ecosystem services, depends on the quality and characteristics of the newly established forest cover. Using publicly available data, we examine forest transition in two regions of tropical China: Hainan Island and Xishuangbanna. We found that the overall increase of forest cover in both areas during the 1980s was due to an increase in plantation forests rather than to increases in the area covered by natural forest. We also found a time lag between the increase in overall forest cover and an increase in natural forest. On Hainan Island, natural forest continued to decline beyond the point in time when overall forest cover had started to increase, and only began to recover ten years after the turning point in 1978. In Xishuangbanna, where the transition point occurred ten years later, the decline of natural forest cover is still going on. These divergent trends underlying forest transition are concealed by the continued practice to apply the term “forest” broadly, without distinguishing between natural forests and planted forests. Due to the use of undiscriminating terminology, the loss of natural forest may go unnoticed, increasing the risk of plantation forests displacing natural forests in the course of forest transition. Our findings are important for programs related to forest management and ecosystem services improvement, including reforestation and Payments for Ecosystem Services programs

Effect of WC content on microstructure, hardness, and wear properties of plasma cladded Fe–Cr–C–WC coating

The Q235 sample was coated with ball-milled Fe–Cr–C–WC powder using plasma cladding technology, and the influence of tungsten carbide (WC) content on the surface microstructure, hardness, and wear properties of the coated steel was evaluated. The single factor test of optimal WC content was carried out on DML-02BD plasma cladding machine, and the material after cladding was analyzed. The microstructure distribution, elemental composition and phase composition of the coating were observed by MIRA3-XMH scanning electron microscopy. The microhardness of cladding layer can indirectly reflect the properties of cladding layer to a certain extent, which is measured by the Vickers microhardness tester. The wear quality, friction coefficient and wear mark morphology can directly reflect the wear resistance of the test blocks. These are observed by the ring block friction and wear tester and the ultra depth of field microscope, respectively. With an increasing WC content, the microhardness of the cladding layer shows an upward trend. The main hard phases of the cladding layer after adding WC are (Cr, Fe) _7 C _3 , (Fe, Ni) _23 C _7 , and the other phases are γ -Fe, Fe _3 W _3 C, WCandFe _2 W. After 6 h friction and wear test, the cladding layer with 30%WC showed the best wear resistance. The total wear amount, wear volume, wear rate and friction coefficient were 0.01 g, 4.22 mm ^3 , 2.344 × 10 ^–4 mm ^3 /(N·m), and 0.35, which were 1/10, 1/5, 1/5, and 7/10 of those without WC cladding layer, respectively. It can be concluded that different WC contents affect the surface microstructure and properties of Fe–Cr–C alloy coating treated by plasma cladding technology. At a WC content of 30%, the microstructure and properties of the cladding layer reach the best