This coaxial microwaveplasma source (MPS) generates plasma without using a magnetic field. It works like an inverse luminescent tube excited by microwaves. The coaxial microwave plasma generator consists of a copper rod (antenna) as inner conductor surrounded by quartz tube filled with argon gas, the plasma is the outer conductor. The inside of the tube is at atmospheric pressure whereas the outside is at low pressure. The plasma formed around the quartz tube acts as an outer conductor in such a way that a spatially extended surface wave is created, just in an equivalent (‘inverse’) situation to that found in the Surfatron source (where the plasma is inside the tube instead of outside).
The microwave with a frequency of 2.45 GHz generated by two magnetrons is fed into the copper rods at both ends. On the outside of the tube, in the low pressure, the microwave fields ignite the plasma. The plasma represents a conductive medium so by increasing microwave power the plasma grows from both ends along the tube, and a homogeneous plasma is formed. The high power microwave breakdown at atmospheric pressure leads to the formation of filamentary structures. These striations or string-like structures, also known as birkeland currents, are seen in many plasmas, like the plasma ball, the aurora,lightning,electric arcs, solar flares, and even supernova remnants.
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)