Case for Casimir?
Steinn Sigurdsson’s search for a micro-gravity dependent on the inverse
fourth power of distance
(29 September, p 32)
might well turn up the Casimir force, which obeys just this rule.
Discovered by the Dutch Nobel prizewinner Hendrik Casimir in the 1920s, the
force is caused by the impact of virtual photons of all wavelengths pushing
against objects. When two objects are close together, photons with wavelengths
longer than the distance separating the objects cannot exist in the gap, so
there is an excess force pushing them together.
At short distances it is quite powerful. A separation of half a micron gives
a pressure of 0.02 newtons per square metre and might well be effective in
sweeping dust grains together.
Letter
One of the most commonly used processes in the waste water treatment industry
is the “activated sludge” process. In the typical installation, waste water is
fed into a large open tank containing a mixed microbial culture into which
compressed air is bubbled from the bottom. Biodegradable organic compounds are
converted mostly into carbon dioxide, water and more microbes.
It is standard safety training for workers to be told that if they fall into
such a tank, they will sink for exactly the reasons stated in this article, and
that shutting off the air supply is an important part of any rescue effort.
Letter
The oil industry has investigated this subject. Twenty years ago a few drill
ships sank following gas blowouts under water. One possible reason was the
decrease in water density caused by the blowout. Tests were performed using
models. The conclusion was that for the amount of gas expected from the blowout,
the expected increase in the ship’s draught was of the order of 30
centimetres鈥攏ot enough to sink a drill ship. However, if a low porthole
was left open, water could enter as the water bubbles. The porthole had to take
in a lot of water to increase the draught to start free flooding. So the change
in density did not cause the sinking.
Letter
I think it should be pointed out that for many years, British Admiralty
charts of areas with gas pipelines on the seabed have carried warnings regarding
the risks of damaging these pipelines. If that happened it would cause a release
of gas and a loss of buoyancy for vessels caught in the bubble stream.
Wrong font
Feedback reports on a drink supposedly containing a “fenilalanina’s font”
(29 September).
This sounds like a bit of computer mistranslation to me. Soft drinks
usually contain the artificial sweetener aspartame. This is labelled as being “a
source of phenylalanine”.
The presence of the amino acid phenylalanine is of concern to people with
phenylketonuria, who cannot metabolise it.
Pass the milk
Can I reassure Adam Quantrill
(15 September, p 51)
that there is currently no
scientific evidence that BSE can be transmitted through milk, as a number of
rigorous tests have proven since the disease was first recognised.
The World Health Organization has stated publicly that “Milk and dairy
products are considered safe, even in countries with a high incidence of BSE. No
evidence has been found from animal and human encephalopathies to suggest that
milk can transmit the disease.”
Britain’s Food Standards Agency is currently carrying out an 拢800,000
three-year study investigating whether there is any link between BSE and milk.
The results will be known in August 2003. The FSA has emphasised that this is a
purely precautionary measure, as all previous studies have shown that milk is
safe.
Opening the door on animal experimentation
Tam Dalyell falls into the usual trap of linking transparency about animal
experiments to “the actions of animal rights extremists”
(15 September, p 49).
There need be no such link. The British Union for the Abolition of
Vivisection, which unequivocally opposes the use or threat of violence, has long
accepted that the names and addresses of researchers and the places where they
work should not be disclosed. However, this does not prevent information about
the experiments themselves being made public, anonymously.
The system of regulation simply cannot work properly in the current
conditions of almost total secrecy. And this is why. The cost/benefit test that
lies at its heart is a moral judgement: in what circumstances is it justifiable
to inflict pain and distress on sentient creatures? As such, the judgement
should reflect informed public opinion. It’s obvious, however, that public
opinion cannot be informed unless the public has access to information. At
present, this moral judgement is made only by a handful of Home Office
inspectors.
There is also every reason to believe that the inspectorate has been
misapplying the law. Moreover, duplicate testing (a direct result of secrecy) is
acknowledged鈥攂y the European Commission, the government and even some
researchers鈥攖o be a real problem.
These are powerful reasons for much greater transparency. Public confidence
in the system of regulation鈥攕ome would say in science generally鈥攊s
at an all-time low. Animal researchers should have the courage of their
convictions and be open about their work with the public.
Bubbles sink boats
Bruce Denardo and colleagues could have saved themselves a lot of effort when
investigating whether bubbles can sink floating objects by visiting a hands-on
science centre
(29 September, p 12).
The device they built to see if neutrally
buoyant balls sank when on a column of rising bubbles sounds exactly like an
exhibit I developed with my colleague James Khan. It was shown in 1994 at a
British Interactive Group Fabricator’s event, following a TV documentary
proposing that subliming methane hydrates were responsible for the mysterious
disappearances of craft at sea.
“The Bermuda Triangle”, as the device is called, is a tall cylinder filled
with water upon which a solid, neutrally buoyant boat floats. If you pump air
into the water column, the boat promptly sinks. Stop pumping and it returns to
the surface for the next user. Versions of this exhibit can be found at my
centre, INSPIRE, in Norwich, at Snibston in Leicestershire, at Techniquest in
Cardiff and elsewhere.
Space giant
Japan’s National Space Development Agency and Institute for Laser Technology
propose a space-based laser to convert sunlight into 10 megawatts of laser light
(29 September, p 18).
I calculate that with 75 per cent conversion efficiency,
its mirrors would have to collect sunlight from an area of 12,500 square metres
and the satellite would have to dissipate 2.5 megawatts of waste heat.
While extremely lightweight mirrors can be made, a structure capable of
radiating away 2.5 megawatts of heat would have to be much more massive. This
would probably be the largest structure transported to space. I am not trying to
imply it would not work, just that a turbine wind farm and solar cell array
producing far more than 10 megawatts could be constructed on Earth for a
fraction of the price of the satellite. Also, a wind turbine farm is unlikely to
blow up on the launch pad.
Finally, has no one noticed that several lasers continuously beaming 10
megawatts to Earth could make an extremely powerful weapon if, for example, they
were aimed at an aircraft carrier or some unlucky city?
Floral headaches
As a child a few decades ago, I read a lot of stories containing helpful
hints for everyday life. One of these was to add an aspirin to the water if your
cut flowers were looking a bit droopy. Of course we never tried it, because it
was “obviously” impossible for a headache remedy to cure a flower.
However, since reading about the role of salicylic acid in triggering the
inducible defence mechanism in plants
(1 September, p 38),
I am having second thoughts. Has anyone tried it?
I do not think, though, that I will be trying the other two remedies I recall
from those stories: cold tea leaves for burns and scalds, and cotton wool soaked
in olive oil for toothache.
Trials on trial
Your editorial highlights important issues concerning the publication of the
results of clinical trials that were financed by the pharmaceuticals industry.
Several of the concerns raised may not, however, be as easy to solve as the
editors of major medical journals hope
(15 September, p 3).
Problems may exist with industry-financed trials in several respects: design,
overall analysis, selective reporting of data and selective reporting of whole
trials (the latter two cases are commonly referred to as “publication bias”).
While registries of trials will help to identify those that are unpublished or
partially published, they will do nothing to ensure that the right trials are
going ahead, nor that they are appropriately designed and conducted.
Taking a tougher stance on publishing will do nothing to “prevent unpalatable
results from being swept under the carpet”. That needs action regarding trials
that are not published, not action on trials that are published (or at least
submitted for publication).
“The results of [industry financed] clinical trials that prove negative are
only one-third as likely to appear…as the results of successful trials.”
Perhaps this is so, but this is a general problem of “publication bias”, and is
not limited to the pharmaceuticals industry. What proportion of non-industry
trials that yield negative results fail to be published? Your editorial implies
that none (or at least very few) go unpublished, but this is certainly not the
case. Yes, there is a problem here鈥攂ut not one limited to the
pharmaceuticals industry.
Requiring authors to sign a statement indicating their full responsibility
for conduct and findings of the trial will do nothing to prevent publication
bias, nor will it overcome the problem of not publishing results.
Progress, yes. A solution, no.
Howling to order
I agree with David Reby that the permanent descent of the human larynx may
have occurred independently of the evolution of language, but the suggestion
that it can be paralleled by laryngeal descent in the red deer is very hard to
swallow
(1 September, p 12).
Fellow primate roarers like the howler monkey do not display this feature.
The deer theory implies that the lowered larynx is a sex-linked feature, but in
humans it develops in boys and girls alike鈥攁nd not at puberty, but in the
first months of life. The only possible parallel with deer would be the
comparatively trivial additional drop in adolescent boys.
Moreover, the human larynx, quite unlike that of the deer, loses contact with
the palate entirely, necessitating a whole train of anatomical and behavioural
adaptations. The real prerequisite for speech was nothing to do with the larynx.
It was the voluntary breath control that humans share with all diving birds and
all diving mammals. Apes cannot talk because they lack this control: they cannot
say “Ah” to order.
If Reby and Tecumseh Fitch really want to find parallels with the human
condition, they might explore the descended larynx of the dugong, and (as
illustrated more than 60 years ago in Victor Negus’s The Mechanism of the
Larynx) of the walrus and the sea lion.
Many scientists remain unconvinced by the aquatic ape theory, but how long
can they continue to write as if they had never heard of it?
Complacency kills
Thank you for your compliment regarding the “ultimate product warning” label
on our KISS rebreather for scuba divers
(Feedback, 6 October).
Actually, though, there are three major hazards regarding rebreathers, of which
carbon dioxide is probably the least.
Carbon dioxide build-up (hypercapnia) tends to manifest as “air hunger”
before it reaches serious levels. The other hazards are hypoxia (caused by lack
of oxygen), which gives no warning whatsoever, and oxygen toxicity, which may or
may not give warnings of its onset.
Hypoxia may be preceded by a slight feeling of well-being, followed by
unconciousness. Oxygen toxicity results in convulsions that in themselves are
not fatal, though their occurrence underwater is not conducive to survival.
Although the warning may seem brutal, it is in fact the absolute truth.
Adding warning bells or alarms will not lessen the danger and may even increase
the risk through complacency.
Rebreathers by their very nature will never be “safe”. The only way to
enhance their safety is with a high degree of awareness鈥攅ven
paranoia鈥攊n the diver.
Not-so-tough glass
I refer to David Cohen’s excellent article about breaking glass
(22 September, p 38).
I am a consultant engaged by Eurostar to investigate the
seemingly spontaneous fractures of toughened glass in the roof and walls of the
Waterloo International Terminal and I question whether a passing bird of prey
dropping its dinner鈥攁 deer’s hoof鈥攐nto the roof caused the pane to
break.
The mass of the hoof in question was less than 25 grams. The possibility that
a leathery 2.5-centimetre lump, travelling at terminal velocity, could account
for the fracture of a sloping pane of 12-millimetre toughened glass is, I
believe, extremely remote.
Equally peculiar explanations have been offered in other instances of
spontaneous fracture. In the mid-1980s, an Australian glass manufacturer claimed
that a protracted series of spontaneous fractures in curtain wall glazing of an
office building in North Sydney was due to impact from pressed metal ashtrays
thrown discus-like by the drunk patrons of a nearby hotel beer garden.
Recurrent fractures of toughened glass in one prominent Bangkok office
building were long attributed to gunfire. The designer explained that some
heavily armed architectural critic was expressing dissatisfaction with the
reflective glass facade. However, no bullets or bullet holes were recorded.
Other popular but implausible explanations invoke manic window cleaners,
lightning, low orbital golf balls, ballistic kookaburras, building settlement
and membrane stresses caused by extreme, albeit unnoticed and short-lived, wind
forces.
Corrections
Our editing of Frank Fahy’s letter on snoring
(6 October, p 62)
wrongly changed the meaning of his last paragraph. This should have read: “Maybe
the article should have said ‘reduce loudness by between 2 and 11 dB’, the
latter figure corresponding approximately to a halving of loudness.” Our
apologies for this error.
Also, we should point out that, in the article on eradicating zebra mussels
(8 September, p 14)
and in a subsequent letter to the editor
(29 September, p 52),
frequencies of 50 hertz to 300 hertz were described as radio waves when in
fact they are too low in frequency to be radio waves, which are defined as 3000
hertz and up. Electric power (60 hertz in North America, 50 hertz in most other
places) is in the extremely low-frequency range, well below 3000 hertz.
Castrated, but…
In my experience, most vets recommend castration for dogs as a cure for
everything from ingrowing red corpuscles to a leg which seems willing to depart
(22 September, p 53).
It has also been my experience that castration has only one effect鈥攖he
dog becomes obese unless denied one of the few remaining pleasures in its life,
namely a satisfying meal.
The one thing it does not do for any species is cure the sex drive. My
daughter was obliged to rid her string of donkeys of two beautiful ladies
because the other 11 neutered males would not stay on the ground. It is
extremely dangerous if a male (or two) tries to mount a female while she is
carrying a child on her back.
Recursive Murphy
…and don’t forget, Murphy’s law is recursive
(6 October, p 63).
Washing the car to make it rain won’t work.
Smelly old us
We stink
(8 September, p 15).
That is why animals can smell us from a
kilometre away. Dogs love us. They really like a mobile stench.
The smell has nothing to do with hygiene. We are simply unable to detect it,
whereas most animals sniff and run. The Victorians knew this. Has the knowledge
been forgotten or are scientists too polite to mention it?
Extraterrestrials probably land, open their spacecraft hatch, breath in
deeply, gasp, close up and flee to other, more pleasant worlds.