Trapping Hydrogen Molecules between Perfect Graphene.

There is a lack of deep understanding of hydrogen intercalation into graphite due to many challenges faced during characterization of the systems. Therefore, a suitable route to trap isolated hydrogen molecules (H2) between the perfect graphite lattices needs to be found. Here we realize the formation of hydrogen bubbles in graphite with controllable density, size, and layer number. We find that the molecular H2 cannot be diffused between nor escape from the defect-free graphene lattices, and it remains stable in the pressurized bubbles up to 400 °C. The internal pressure of H2 inside the bubbles is strongly temperature dependent, and it decreases as the temperature rises. The proton permeation rate can be estimated at a specific plasma power. The producing method of H2 bubbles offers a useful way for storing hydrogen in layered materials, and these materials provide a prospective research platform for studying nontrivial quantum effects in confined H2.

Note: A contraction channel design for planar shock wave enhancement.

A two-dimensional contraction channel with a theoretically designed concave-oblique-convex wall profile is proposed to obtain a smooth planar-to-planar shock transition with shock intensity amplification that can easily overcome the limitations of a conventional shock tube. The concave segment of the wall profile, which is carefully determined based on shock dynamics theory, transforms the shock shape from an initial plane into a cylindrical arc. Then the level of shock enhancement is mainly contributed by the cylindrical shock convergence within the following oblique segment, after which the cylindrical shock is again "bent" back into a planar shape through the third section of the shock dynamically designed convex segment. A typical example is presented with a combination of experimental and numerical methods, where the shape of transmitted shock is almost planar and the post-shock flow has no obvious reflected waves. A quantitative investigation shows that the difference between the designed and experimental transmitted shock intensities is merely 1.4%. Thanks to its advantage that the wall profile design is insensitive to initial shock strength variations and high-temperature gas effects, this method exhibits attractive potential as an efficient approach to a certain, controllable, extreme condition of a strong shock wave with relatively uniform flow behind.

Note: A top-view optical approach for observing the coalescence of liquid drops.

We developed a new device that is capable of top-view optical examination of the coalescence of liquid drops. The device exhibits great potential for visualization, particularly for the early stage of liquid bridge expansion, owing to the use of a high-speed shadowgraph technique. The fluid densities of the two approaching drops and that of the ambient fluid are carefully selected to be negligibly different, which allows the size of the generated drops to be unlimitedly large in principle. The unique system design allows the point of coalescence between two drops to serve as an undisturbed optical pathway through which to image the coalescence process. The proposed technique extended the dimensionless initial finite radius of the liquid bridge to 0.001, in contrast to 0.01 obtained for conventional optical measurements. An examination of the growth of the bridge radius for a water and oil-tetrachloroethylene system provided results similar to Paulsen's power laws of the inertially limited viscous and inertial regimes. Furthermore, a miniscule shift in the center of the liquid bridge was detected at the point of crossover between the two regimes, which can be scarcely distinguished with conventional side-view techniques.