Letters : Pregnant brains
Cambridge
You suggest that reported changes in brain volume during pregnancy may
account for the fact that some pregnant women complain of problems with memory
and concentration (This Week, 11 January, p 5). But where has it been shown that
small differences in brain volume have any effect on behaviour? The profound
hormonal changes which take place during pregnancy are far more likely to
influence behaviour and these changes may also affect fluid retention and brain
volume.
As part of a national, longitudinal survey of health and lifestyle, we
conducted memory tests on over 100 pregnant women and compared their scores with
those of over 2000 nonpregnant women and over 1000 men of the same age (18 to 40
years). We found that pregnant women had marginally lower scores than
nonpregnant women, but this difference was significant only for those pregnant
women who reported adverse changes in mood.
Of particular interest is the fact that both pregnant and nonpregnant women
had higher scores than men on the memory test, although it is well known that
men on average have larger brains than women (because they have larger
bodies).
If pregnancy did cause a temporary impairment of memory, we would expect to
see an improvement in memory some time after childbirth. We tested the pregnant
women again some years after they had given birth and found no significant
improvement in their memory compared to women who remained nonpregnant or to
men.
We were also able to establish whether women who were pregnant in the second
part of our study, but had not been pregnant in the first, showed a
deterioration in their memory. Contrary to what your report would suggest, there
was no evidence that these women’s memories got worse when they became
pregnant.
We believe that the reported changes in brain volume in 10 pregnant women
have little or nothing to do with how women actually function in terms of their
memory. Hormonal changes during pregnancy may play a role in mood and wellbeing,
which may in turn influence memory and concentration. But even in the face of
such changes, pregnant women outperform men.
Letters : . . .
So women’s brains shrink when they are pregnant and a naive correlation is
made between brain size and cognitive function. It is a pity that nobody
involved has thought to look at the behavioural literature.
Our research has revealed little evidence of cognitive dysfunction in
healthy pregnant women, and objective evidence linking pregnancy and childbirth
with memory failure has remained elusive.
Problems with concentration and memory can be symptoms of puerperal
psychosis, a very rare disorder. And they are also symptoms of depression. The
incidence of depression is higher during pregnancy and after childbirth.
However, the explanations for this are, for the most part, rather more
mundane than brain shrinkage, and few women are severely affected.
Letters : Space nannies
Leeds
The US National Research Council’s report, which implies the postponement of
human expeditions to Mars, exemplifies how obsession with environmental health
risks can be taken to ridiculous extremes (This Week, 4 January, p 9, and
Letters, 25 January, p 50).
Astronauts to Mars will face a 15-month round trip and previously untried
landing and blast-off procedures on an alien planet, with a real prospect of
drifting off powerlessly into frozen space if things go wrong. Worries about
unknown and merely conjectural long-term health risks will pale into
insignificance for them, and if I were in their shoes I would far rather see
money spent on improving the prospect of a successful mission than on shielding
me from cosmic rays.
Astronauts, like the explorers of old, freely exchange safety and certainty
for excitement and the prospect of glory, and who are the NRC nannies to say
that this is wrong? Their demand for lengthy research or, in its absence, for
shielding costing $30 billion to “err on the side of caution”, is
therefore completely batty.
One-thousandth of that would provide very generous compensation for those who
may suffer bad effects from space exploration, but my bet is that even without
such a financial safety net, most astronauts would be quite prepared to risk
their lives to land on Mars.
Letters : Dredging it up
Swindon, Wiltshire
I strongly object to your misleading comments regarding the shoreline
management plan drawn up by Sir William Halcrow and Partners (“Crumbling away”,
21/28 December, p 14).
You have chosen to ignore that the plan puts forward a strategy for
stabilising the dune system in Hemsby to provide greater protection.
Historic data and maps were used to analyse both recent and long-term changes
to the coast. In many parts of Britain, the latest published Ordnance Survey
maps are a number of years old. It is therefore also necessary to consider more
recent information, and your suggestion that we have not done so is
inappropriate and incorrect. For the analysis of coastal evolution in this area,
Halcrow utilised aerial photography from both 1992 and 1994 (the latest
available at the time of the study in 1995), with the 1994 waterline indicated
on the maps in the plan to indicate the change from published information.
It is particularly disappointing that your report misses the fundamental
objective of shoreline management plans: they are being funded by both local and
national government precisely to avoid “ill-conceived coastal engineering and
offshore dredging” in the future, by adopting a strategic approach to coastal
management and by working with natural forces rather than attempting to resist
them.
This is a significant undertaking, planning the management of our coastlines
for the next few decades.
Letters : . . .
London
It is misleading to state that “offshore” dredging was responsible for the
loss of Hallsands in Devon, when in fact this dredging took place at the base of
the beach, causing the beach to collapse into the sea. Present-day aggregate
dredging off Norfolk takes place in an entirely different set of circumstances,
between 8 and 27 kilometres off the coast, with areas of deeper water and
shallower sandbanks in between the coast and the dredging areas.
For sand to move from the coast to the dredging area, or vice versa, would
entail sand grains travelling up and over sandbanks, then into deeper water than
the dredging areas and then over more sand banks, clearly a highly unlikely
scenario given the nature of the currents in this region.
It is important to appreciate that the coastline is, and always has been,
developing and dynamic, with sediment lost at one locality and sediment gained
at another. For example, the loss of the coastal town of Dunwich in Suffolk
during medieval times was due to marine erosion of sand and gravel cliffs. If
dredging occurred in medieval times, would this have been blamed for such
erosion?
Far from being the “villain” in coastal erosion, marine aggregate dredging is
helping to provide protection to the coast, supplying huge quantities of
material that could only otherwise be sourced from the land at a huge
environmental cost.
Letters : Well well
London
Your article on submerged oil waste contained a small number of inaccuracies
which in consequence painted an unduly pessimistic picture (This Week, 7
December, p 4).
In the first place, the number of fixed offshore installations throughout
British waters is some 220, with a like number in the Norwegian sector. The much
higher number of 1500 quoted in the article relates not to installations but to
the sites of individual wells drilled, including exploration sites.
At many well sites, and for over half the installations, there are no large
accumulated piles of well cuttings underneath them, for the simple reason that
seabed scour is so strong that cuttings have long since been wholly or partly
dissipated, to no apparent environmental ill effect. The dimensions of the
larger cuttings piles quoted from the Altra report relate only to the relatively
few larger installation sites.
Letters : Where are the jobs?
Rochdale
Adam Ingram asserts, “First, we need more young people to embrace science,
engineering, technology and design” (Forum, 4 January, p 42). Such assertions
are common.
Please, is there any empirical evidence to support them? The somewhat
unimpressive salaries offered for postdoctoral research jobs in the pages of
New 杏吧原创 itself don’t suggest any shortages in the
marketplace.
Letters : Uplifting
Norfolk
Why does a scientific periodical such as yourself persist in promulgating the
fallacy that a wing works solely by the fact that air moves faster over its top
than its bottom side, and that the resulting difference in pressure causes the
wing to provide lift (Technology, 14 December, p 18)?
The fact of the matter is that while the effect is there, the major reason a
wing generates lift is that it deflects air down. The wing achieves this because
it is presented at an angle to the flow of air through which it is moving
(called the angle of attack, or AoA).
When a wing is moving slowly it needs a (much) larger AoA to maintain the
same amount of lift compared to when it is moving quickly. But when a wing
reaches a certain critical AoA, the flow of air starts to detach from the top
surface of the wing, and because it isn’t being deflected as much any more you
lose a good half of your lift.
The point of the research reported on is to demonstrate a method of making
the flow of air “stick” to the wing at larger AoAs, thus allowing the wing to
move more slowly for a given lift (because it deflects the mass of air through a
greater angle). This, in turn, allows an aircraft to take off or land at slower
speeds or shorter distances, because it can safely use larger AoAs during these
phases of flight.
Letters : Wings of a Dove
Bembridge, Isle of Wight
I find it rather amusing that the picture that accompanies an article that
talks of borrowing from elsewhere and of all the computing that went into the
Boeing 777 is taken out of the window of a De Havilland Heron, which was
designed in about 1948 entirely without the aid of computers (Review, 4 January,
p 38).
What is more, the first aircraft was assembled largely using pieces of metal
“borrowed” from elsewhere鈥攆or example, from the Dove, with bits inserted
to stretch them where necessary. The wings of the Dove were moved out so that
the old wing root came between the Heron engines. The Dove tailplane was
enlarged by having pieces of wood “bolted” on the outside and a new skin wrapped
round it.
Bits of two Dove cabins were cut up and riveted together to make the bottom,
floor and sides of the longer cabin. The cockpit was a Dove cockpit, with only a
new roof to line up with the raised cabin roof.
Even the Dove assembly containing the pilot’s engine controls was used,
though twice as many engines had to be controlled. The outer levers that had
been the rpm (sorry, “engine speed” is the politically correct term nowadays)
controls became the throttles for the outer engines.
This lack of propeller control levers was made good by driving the propeller
controllers from the throttle levers by a cam. This produced a rather amusing
situation on the first takeoff, when the aircraft made a noise rather like a
whole formation of Harvards: the cams were reshaped pdq to reduce the rpm and
hence the propeller noise. Ah happy days, when engineering was fun.