Letter
Barry Fox writes: This is perfectly correct. Engineers in the industry
have been saying it privately for the past two years or so. But to say so
publicly would be tantamount to admitting liability for the alleged dangers of
the current system
Fuel guzzled
Lee Schipper quotes figures for fuel efficiency in cars, saying that the
improvement between 1973 and 1975 was 30 per cent in the US and only 10 per cent in Europe
(Letters, 23 May, p 56).
Once again we have statistics quoted with no framework mentioned. What were
the respective fuel efficiencies in 1973? I suspect, having some knowledge of
American vehicles of this time, that the European cars may have been around
twice as efficient.
So the American vehicles had twice the room for improvement and required much
less effort to produce a threefold improvement.
Pretty vacant
Nigel Henbest reports that the Wake Shield鈥攁 giant saucepan lid
free-flying behind the shuttle Columbia鈥�”has smashed all records for a
human-made vacuum”. This centrepiece of an otherwise engaging article is unfortunately wrong
(“Into the void”, 25 April, p 26). The figure quoted for the
vacuum created by the Wake Shield is greatly exaggerated. Moreover, it is easy
to make a vacuum on Earth that is much better even than that hoped for from the
Wake Shield.
Henbest correctly uses the average spacing between the residual molecules in
the vacuum as a measure of its quality and reports that the average spacing
between molecules behind the Wake Shield is about 1 millimetre. Actually this is
what was hoped for, not what was measured. A mass spectrometer similar to that
used to measure the vacuum on the Moon found that the average spacing of water
molecules varied during the flight, but was typically only 14
micrometres鈥攔ather a poor vacuum by normal Earth standards.
Moreover, vacuums are easily created here on Earth that are even better than
the unrealised hopes for the Wake Shield. A conventional vacuum pump is used to
pump the air out of a container, which is then closed and cooled to a
temperature of 4.2 kelvin (the boiling point of liquid helium at atmospheric
pressure). This creates a vacuum where the theoretical spacing between residual
molecules (neglecting the effect of occasional cosmic rays) is nearly 1
kilometre.
This way of obtaining a good vacuum is called cryopumping. By cooling to
below 0.1 kelvin, which is easily achieved with a dilution refrigerator, the
vacuum can be better still.
The real challenge on Earth, as in space, is to measure the spacing between
molecules when there are so few of them. The best commercial vacuum gauges are
not nearly sensitive enough.
Some years ago we used antiprotons, the antimatter counterpart of protons, as
an extremely sensitive vacuum gauge and showed that the average spacing of
molecules within our 4.2 kelvin container was greater than 2 millimetres. In
theory, the vacuum should be much better, but even our improved antiproton
vacuum gauge was not sensitive enough to tell.
Sexist truths
I am writing to complain about the cover story, “Hidden truths”
(23 May, p 28),
illustrated on the front cover by a photograph of a pouting woman wearing
only a bra. It saddens me that a respected journal such as New
杏吧原创, aimed at intelligent people, should have used such an
exploitative, sexist image that was totally irrelevant to the actual
article.
Similarly, within the article itself was a photograph of the lower half of a
woman, naked buttocks exposed, in a clich茅d “prostitute-and-car-door”
scenario. Was this tacky image really necessary to convey the fact that
prostitutes were referred to in the article?
We are about to enter the 21st century. Isn’t it time this sexist portrayal
of women stopped?
Badly bent ray
I read with interest John Casti’s summary of the principle of least effort
(“Easy does it”, 9 May, p 44).
It is fascinating that the principle’s influence
should be so widespread. Of course, I’ve always wondered why campus designers
don’t just let pedestrians determine where the walkways should go. Many of them
are unused, and spontaneous paths just crop up.
Now to the nitty-gritty: page 46 (figure 2) has a diagram of a plane-parallel
plate with a ray of (least-time) light passing through. With such a plate, the
entering and exiting directions are always parallel.
The ray does of course follow the least-time path. But the ray shown would be
correct only if the optic were a triangular section prism with the base at the
bottom, or perhaps the upper section of a converging lens.
Older ice
Jack Saxon describes the ancient glacial sediments at Hallett Cove near
Adelaide, South Australia, and assumes that they date from the Cretaceous and
are evidence of Cretaceous glaciation in Australia
(Letters, 16 May, p 53).
These glacial deposits, which include spectacular striated pavements formed by
rock-laden ice scraping across bedrock, are in fact Permian (about 280 million
years old) and were formed 180 million years before the Cretaceous.
During the Permian, Australia was covered by part of a huge icecap which
extended across the landmass of Gondwana during a glaciation that lasted for
nearly 80 million years.
Some like it hot
Vincent Piat-Kelly hopes that organisms might feed on radioactive waste
(Letters, 18 April, p 53). There are indications
that microbes can, at least indirectly, utilise energy from radioactive decay.
For example, radiolysis of water produces hydrogen and an oxidant (something
like H2O2) which can serve as an energy source for chemolithotrophic organisms
(see also “Some bugs like it hot”, 5 October 1996, p 42).
Unfortunately, utilisation of the energy released has no effect whatsoever on
the rate of decay of radionuclides and hence offers no neat alternative to
geological disposal.
Woollies for oil waters
Jeff Hecht’s story about the hairdresser in the US who hopes to clean up oil
spills with hair from his customers
(This Week, 16 May, p 16) reminds me of the
time of the Torrey Canyon disaster in 1967, when oil slicks were very much in
the news.
At one of the Shell laboratories some of my colleagues and I decided to do
some “under the table” experiments and discovered it was surprisingly easy to
mop up oil from water with natural greasy cotton wool or with shoddy wool. We
envisaged long sausages of shoddy wool being trailed through an oil slick and
the oil being recovered by passing the sausage through a giant mangle. In this
way oil could be soaked up rapidly without detergents.
This idea was not followed up. The Torrey Canyon was soon forgotten and we
probably thought it was a barmy idea anyway. But now that NASA seems to be
interested, I suggest we all send them our discarded woollen garments to
experiment with.
Dolphin delight
I work on a whalewatch boat and I am used to seeing dolphins swim in the bioluminescence
(In Brief, 2 May, p 23).
It is pure magic to see these dolphins shine like a Christmas tree. Sometimes
the light is bright enough to show up the patterns and the colours of the
animals. While dolphins are riding a bow wave you see both the glow and sparks
from the bioluminescent plankton. Jellies show up as very bright
sparks鈥攃aused by bacteria living inside them.
If you have ever swum in the sea on a dark night, you may have seen the same
thing happening to your own body.
I never considered telling the scientists we work with, or any others, about
this as I thought they already knew about it.
Pass, comrade
You mention that security at NASA Ames is “very tight”
(Feedback, 30 May). You bet it is.
They used to share the field with the Navy (who have now closed their base).
Going to see a scientist at NASA a few years ago, I sent a fax to the NASA PR
giving my name and that of my P.A. When we got there the NASA computer had my
name in it, but not that of my P.A.
It was Sunday and there was no way to get it changed. The scientist had it
sussed: “Get the car pass and put it on the dash, and we’ll go through the Navy
gate. They never check. The NASA guys always do.”
He was right. The Navy gate guard waved us through and once on the base we
drove across to the NASA section without hassle. I guess the Martians were felt
to be a greater threat than the Russians.
Empty words
The linguistic trick mentioned by
Feedback (2 May) to avoid printing an
unlucky page 13鈥攁s employed by an airline鈥攚as often used in
technical manuals for computers. One would be confronted by a page with the
words “This page is intentionally left blank”. But of course it was not
blank鈥攊t had the statement on it. So if they could misinform you about
that page how could you trust what was on the others? Readers might like to
suggest what words could be on a page that showed it held nothing of import.
Give them your kids
Congratulations to Debora MacKenzie for her witty article which advocated
training aspiring politicians by forcing them to care for young children
(Forum, 16 May, p 50).
Obviously the jobs have a lot in common: smiling when you don’t want to,
kissing smelly babies, diversionary tactics, lying and charm, not to mention
long hours and every chance of ending up with egg on your face.
I agreed completely with the conclusion: “After all, if we can’t trust
politicians with our toddlers, why on earth should we trust them with our
governments?”
Come on parents, offer your toddlers.
Prior cartoon
I believe there is something about there being “no prior art” for a patent to be
successful. The patent for a system that will tell you what your pet or baby is trying to say
(This Week, 23 May, p 11) certainly has prior
补谤迟鈥攍颈迟别谤补濒濒测.
In 1992 an episode of The Simpsons cartoon show entitled “Brother,
Can You Spare Two Dimes”, was first aired in the US (it was repeated on BBC2 a
few months ago). In the episode, Homer Simpson’s brother, Herb, invents a device
called a Baby Translator.
As Herb says: “It measures the pitch, the frequency, and the urgency of a
baby’s cry, and then tells whoever’s around, in plain English.” The cartoon also
made clear that Herb spent a good deal of time building up a “library” of cries
so that the machine would function correctly.
In the cartoon, the machine was a great success and restored Herb’s fortune
(which had been lost by Homer).
Chin up for health
Regarding the possible harmful effects of using cellphones
(This Week, 10 May 1997, p 4),
surely the simple and cheap answer to this would be to put the
aerial at the bottom rather than the top of the phone. This would place the
source of the radiation about five times farther away from the nearest brain
tissue. This tissue would consequently receive electromagnetic radiation at
around one twenty-fifth of the intensity from conventional designs.
Is there any reason for the aerial being at the top of cellphones or is this
(as I suspect) just a tradition perpetuated by the need for the user to have a
“cool” image?
Of course, if it subsequently becomes evident that cellphone radiation rots
the teeth, then it’s back to the drawing board.
Right to clone
Nell Boyce decries loopholes in various proposed laws to ban human cloning
(This Week, 9 May, p 6). What she fails to mention
is that in the US the Constitution will effectively block any such laws.
“Reproductive freedom” means much more than just the right to an abortion.
The US Supreme Court has also ruled that every American has a constitutional
right to have their own children, and to make all sorts of reproductive
decisions without government interference. Laws trying to stop people from
having children鈥攆or example by denying infertile people access to exotic
reproductive technologies such as IVF, or requiring the sterilisation of
convicted criminals鈥攈ave been struck down as unconstitutional.
Around 15 per cent of Americans are infertile, and most cannot be helped by
current medicine. Cloning technology, once perfected, will offer the only way
for many people to have their own genetic children. Denying such people access
to cloning technology would be the equivalent of forced sterilisation. To uphold
any cloning ban, a US court would have to rule that disabled people (as some
courts classify the infertile) have less of a right to have children than
convicted rapists and child molesters.
In the US, reproduction is a private matter, not a political one. Congress
and state legislatures lack the constitutional authority to interfere with human
cloning.