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Disadvantages of electric traction include high capital costs that may be uneconomic on lightly trafficked routes; a relative lack of flexibility since electric trains need electrified tracks or onboard supercapacitors and charging infrastructure at stations; and a vulnerability to power interruptions. Different regions may use different supply voltages and frequencies, complicating through service. The limited clearances available under catenaries may preclude efficient double-stack container service. The lethal voltages on contact wires and third rails are a safety hazard to track workers, passengers and trespassers. Overhead wires are safer than third rails, but they are often considered unsightly.

What is a safer alternative to third rails?
Answer: Overhead wires
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The theoretical difficulties arise from the fact that all of the methods except the X-ray crystal density method rely on the theoretical basis of the Josephson effect and the quantum Hall effect. If these theories are slightly inaccurate – though there is no evidence at present to suggest they are – the methods would not give accurate values for the Planck constant. More importantly, the values of the Planck constant obtained in this way cannot be used as tests of the theories without falling into a circular argument. Fortunately, there are other statistical ways of testing the theories, and the theories have yet to be refuted.

Other than the X-ray crystal density method, other methods rely on what two effects?
Answer: the Josephson effect and the quantum Hall effect
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At the east end of the Lady Chapel is a memorial chapel to the airmen of the RAF who were killed in the Second World War. It incorporates a memorial window to the Battle of Britain, which replaces an earlier Tudor stained glass window destroyed in the war.

Where is the memorial chapel of the airmen of the RAF?
Answer:
At the east end of the Lady Chapel