杏吧原创

Low-gravity lager

Question: Apparently NASA is aiming to brew a beer in space. The yeast can
neither sink nor rise as in traditional beer production and any carbon dioxide
that is produced will not rise to the surface. So how will the beer ferment and
will the final product be anything like Earth beer?

Answer: NASA is indeed interested in the questions raised by brewing beer in
a microgravity environment. 杏吧原创s who study the physics of gas-liquid
mixtures would like to understand, for example, what happens when there is no
buoyancy to bring the bubbles to the surface of a fizzy liquid, and the
characteristics of fermentation in microgravity.

Two separate space shuttle experiments tackled these questions. The first
investigated how well yeast performs in orbital free fall鈥攏ot only to see
if brewing space-beer might be possible, but also to provide valuable
information to pharmaceuticals companies with a keen interest in the biology of
orbiting microbes.

The space-beer turned out essentially the same as that brewed on Earth: its
specific gravity and the yeast鈥檚 performance when used to brew subsequent
batches of beer was comparable to that of control samples on Earth. However, the
total yeast cell count and the percentage of live cells in the space sample were
lower. Despite this, the fermentation was significantly more efficient. This
raises the question of whether we can modify the fermentation process, or the
yeast itself, to reproduce this effect on Earth.

The second experiment, flown on the shuttle by the Coca-Cola Company, was to
test its system for dispensing Coke in a weightless environment. The challenge
was to dispense a fizzy beverage yet keep the gas in solution until the cola is
drunk. Because bubbles don鈥檛 鈥渞ise鈥� in free-fall, changes in temperature,
pressure, or even physical agitation tend to cause the whole thing to degenerate
into a foamy mess.

A computer-controlled device adjusted the temperature of the drink during
mixing and dispensing, and minimised agitation by dispensing the drink into a
collapsible bag inside a pressurised bottle. The pressure around the bag was
slowly released as it filled with drink, keeping the drink under constant
pressure and preventing the gas from coming out of solution too quickly. The end
result was a space version of the world-famous fizzy drink.

Daniel Smith

Bath

Bad credit 1 & 2

Question: The Last Word has told us why wiping dust off malfunctioning credit
cards helps them to work, but a colleague showed me that covering a failing card
in plastic wrap or cling film always makes it work again. Transparent sticky
tape also makes it work again. Why?

Answer: As a card ages it gets worn down and is no longer as flat as it used
to be. This means that when it is swiped the magnetic strip may not run flush to
the sensor, and so it can鈥檛 be read. Wrapping cling film around the card makes
it thicker again, so that it sits tight in the slot in the swipe machine,
forcing it flat. This allows the sensor to read the magnetic strip.

Mark Clough

Hawera, New Zealand

Power blitz

Question: Considering the enormous amount of electrical energy contained in a
lightning strike, why has no one tried to tap it for domestic use? Lightning
energy is grounded by sending rockets into clouds, so could this energy be
used?

Answer: It might sound like quite a nice idea, but there are several reasons
why the answer is no. The first stems from the confusion of power with energy.
Lightning strikes have a lot of power, but very little energy.

Although a typical lightning strike can have a power of several gigawatts, it
lasts for only a fraction of a millisecond. Because energy = power x time, the
energy contained in a lightning strike is in fact a mere few megajoules, which
compares poorly with the 33.6 megajoules released by burning a litre of
petrol.

The second problem is the unpredictable and intermittent nature of lightning.
And even if you covered the whole of the British countryside with lightning
rods, you would still be faced with the problem of converting 5000-ampere direct
current DC pulses lasting less than half a millisecond into the 230-volt,
50-hertz alternating current supply we use in our homes.

Sergey Borovik

Manchester

Answer: Lightning is driven by potentials of several million volts and the
currents involved can peak at 20,000 amperes. This huge power of several hundred
megawatts combined with the spectacular visual display gives the illusion of
enormous energy. In fact the energy released is relatively modest.

So even disregarding the erratic nature of lightning and the enormous
engineering difficulty of harnessing this energy, it simply would not be worth
the effort.

Incidentally, the damage that lightning does to houses and trees arises
because the discharge energy is released extremely quickly in a relatively small
volume, consequently generating explosive and incendiary effects.

R. Barnes

Chartered engineer and electrical power engineering consultant

Hartley, Kent

This week鈥檚 questions

Fear of failure: I am a skydiver. Every 120 days we must have our reserve
(emergency) parachutes re-packed by a licensed parachute rigger. Because all
parachutes are now made of synthetic material鈥攑reviously they were cotton
and silk, which bugs loved to eat鈥攕ome have suggested the re-pack cycle
should be doubled to 240 days.

Riggers occasionally make mistakes such as leaving their tools in the
parachute, or simply packing it so badly that it won鈥檛 open. If this should
happen at the moment, your reserve parachute would be useless for the next 120
days until the mistake was spotted at the next re-pack. Many people say that the
new 240-day re-pack cycle would cut the chance of these mistakes by one half,
since you re-pack half as often.

On the other hand, if you should have a badly packed parachute on a 240-day
re-pack cycle, you would have it for twice as long before it was discovered.

Which option offers the best chance of survival?

By e-mail, no name and address supplied

Natal knots: Do midwives actually tie a knot in the umbilical cord after
birth. If not, what surgical procedure do they perform? And what happened in the
days before modern medicine standardised the process?

Jack Whyatt

Greenville, Michigan