In terms of radar, electronics and even weapons, China's Sukhois are increasingly able to match the F-15C.

CENTERFORSECURITYPOLICY: Center For Security Policy

Snow fell overnight in Scotland - where temperatures were -15C (5F) in places - in north Wales and northern England.

BBC: Snow and ice leads to travel delays and school closures

Last night temperatures in England, Wales and Northern Ireland averaged between minus 5C and minus 10C, whilst in Scotland they typically fell to between minus 15C and minus 20C.

BBC: Heavy snow and ice bring travel chaos across UK

In severe cold, below -15C, before you turn the ignition key flash your main beams - this takes a bit of battery power and thaws it a bit inside.

BBC: Your tips for coping in a colder UK climate

At key points, components will go through further careful cleaning with ethanol and a thorough sterilisation with hydrogen peroxide vapour which, to add to the challenges, has to kept above 15C.

BBC: Key tests in search for life in frozen Antarctic lake

The helium, which by then will have risen to about minus 15C, is pushed through a liquid nitrogen "boiler" to bring it back down to its run temperature, before looping back into the pre-cooler.

BBC: Key tests for Skylon spaceplane project

Franco Aloisio, President of the Parada Foundation created in the mid 90s to help children living in the sewers in Bucharest, said the problem still existed in the city particularly in winter when temperatures drop to minus 15C but there had been an improvement.

UNESCO: WORLDWIDE

It is opening up a resort city where temperatures reach 40C in summer, and will be as warm as 10-15C by the sea when the Olympics take place from February 7-23 next year -- with organizers already stockpiling snow due to sporadic falls, Black says.

CNN: February 8, 2013 -- Updated 1159 GMT (1959 HKT)