Colloidal quantum dots incorporated in ionic salts (bottom, NaCl matrix) are more brightly photoluminescent than they are in solution (top, aqueous). Changing quantum dot size and/or composition yields different emission colors, allowing device makers to tune the optical properties of the material.
It’s quicksand. Quicksand is much thicker than water, which is why things sink so slowly. By that same logic, one can walk on its surface if you go fast enough and with little enough pressure, like skipping a stone on water.
Newton’s third law says that forces come in equal and opposite pairs. This means that when air exerts lift on an airplane, the airplane also exerts a downward force on the air. This is clear in the image above, which shows a an A380 prototype launched through a wall of smoke. When the model passes, air is pushed downward. The finite size of the wings also generates dramatic wingtip vortices. The high pressure air on the underside of the wings tries to slip around the wingtip to the upper surface, where the local pressure is low. This generates the spiraling vortices, which can be a significant hazard to other nearby aircraft. They are also detrimental to the airplane’s lift because they reduce the downwash of air. Most commercial aircraft today mitigate these effects using winglets which weaken the vortices’ effects. (Image credit: Nat. Geo./BBC2)
The heart-shaped pattern created by light rays when reflecting off a semi-circle. The rays are drawn imperfectly, with random variation as if they were drawn by hand. This type of pattern, the caustic, might be familiar from looking into a coffee cup in the Sun. [more] [coffee] [code]
The microgravity environment of space is an excellent place to investigate fluid properties. In particular, surface tension and capillary action appear more dramatic in space because gravitational effects are not around to overwhelm them. In this animation, astronaut Don Petit injects a jet of air into a large sphere of water. Some of the water’s reaction is similar to what occurs on Earth when a drop falls into a pool; the jet of air creates a cavity in the water, which quickly inverts into an outward-moving jet of water. In this case, the jet is energetic enough to eject a large droplet. Meanwhile, the momentum, or inertia, from the air jet and subsequent ejection causes a series of waves to jostle the water sphere back and forth. Surface tension is strong enough to keep the water sphere intact, and eventually surface tension and viscosity inside the sphere will damp out the oscillations. You can see the video in full here. (Image credit: Don Petit/Science off the Sphere)