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For example, a photon has frequency of 1 THz, and 1.2345 cycle. What's its energy?E = hf
After a second thought, I realized that determining the direction of positron-electron collisions can be done better using a small ball of positron source and a small ball of electron source, separated by some distance inside the PET scanner. We can observe if the gamma rays coming out from the target still have random direction.The emitted positrons in a solid or liquid have a range of about 0.5 mm which limits the spatial resolution of PET. Havoing an energy of between 0.5 and 2 MeV (depending on the nuclide) you would need a very strong electric field to determine which way they move before annihilating, and since the p-e pair is electrically neutral, there's no much you can do to orient it in space. What we do know is that the coincident photon pairs are spherically distributed and randomly timed, so the hypothesis that they are randomly distributed seems to be supported.
The birds, as usual, know better than the pilot.An interesting clip, but one wing beat doesn't equate to sustained inverted flight. Some pigeons tumble in flight (it's a genetic defect), and swifts in particular are unstable in roll (negative glide dihedral) which makes them very agile, but they don't spend more than a beat inverted.
The initial concept dates back to 1897, when English engineer Frederick W. Lanchester patented wing end-plates as a method for controlling wingtip vortices.Practical implementation, as with all things aviational, depends on compromise and getting a nice smooth curve with an acceptable strength/weight ratio does require some clever materials engineering. I can't find your "20%" figure but Cessna certainly fitted droop tips in the 1950s to improve low speed handling.
When birds fly their wings move like the motion of pedaling a boat.Exactly the error that led to the deaths of many aviation pioneers. All birds flap their wings to take off, but those that fly furthest and longest hardly move their wings at all once they are airborne. Whilst brave but unobservant souls played with ornithopters, Cayley, Chanute and Lilienthal experimented with rigid gliders, as did the Wrights until they had developed a sufficiently light engine.
Not really.So if we have a flat upper surface, the wing will generate as much lift as a curved one? Why don't airplane designers (or birds) know this?
Bingo, see that's the basic fundamentals of any wing only the increased aerofoil is for lower speed but still can work when pushed in the inverted with the increased angle of attack.Except that single-surface and steep-camber foils (Rogallo wing, yacht sail, Wright airfoil, most bird wings, wind turbine) may stall before they produce positive lift if inverted.
The upper surface does not push anything down, but contributes 60 - 70% of the lift.Planes actually fly by pushing air down.Anything that deflects the wind is an airfoil,Snap!
The curved surface of the aerofoil is corrupted in inverted flight and acts as a flat surface
There is no such thing as a negative pressure;There is no such thing as negative money, but lots of people and businesses have overdrafts, or commitments greater than their current asset values. The concept of negative numbers is very useful.