Dust reduction
Following the article on PM10s (21 September, Inside Science) and Max Wallis’s timely warning on fine particles (19 October, p 28), let me offer some hope based on our own experience.
I have recently recorded, in ordinary office environments in London, a horrifying range of between 250,000 and 410,000 particles per cubic foot of air (equivalent to between 9 million and 15 million particles per cubic metre of air) at 0.5 micrometres in size. This is a size that can enter the bloodstream through the alveoli of the lungs.
These tiny menaces have various origins: not just vehicle fumes but also the skin cells that we all shed, printer toner, delaminating carpets, and even fragments of cellulose from paper.
The hope comes from the fact that I have recorded reductions in these particles of more than 90 per cent by using a combination of negative ionisation and HEPA (High Efficiency Particulate Air) filtration. This results in a significant reduction in upper respiratory problems, especially where a lot of time is spent in any indoor environment.
The negative ionisation has the added benefit of removing the positive charge of the particles, so they sink to the floor.
Coloured for the cold
It seems odd to me that there are not more (apparently) obvious explanations of skin colour than those put forward in your article (12 October, p 34). For example, has no one considered the radiative properties of skin to explain why people from northerly latitudes are fair-skinned?
The main requirement for survival at high latitudes is to be able to live through long, cold winters with (historically) limited food. So people must conserve as much energy as possible during this period.
Now consider “black body” radiation. It is well known that darker bodies radiate (or lose) energy at a higher rate than paler ones. So a black person is likely to radiate more than a white person.
This is an advantage at tropical latitudes (for people who stay in the shade). But it will be a burden during a high-latitude winter as it will mean that more food would have to be consumed to maintain body temperature.
A simple back-of-envelope calculation, assuming a difference in skin emmissivity of only 2 per cent between light-skinned and dark-skinned people, shows that a dark-skinned person will radiate an extra 77 megajoules of energy over 120 days. As I understand it, that means an extra nine days’ worth of food will have to be consumed just to keep warm. I suggest that difference could mean life or death.
Letter
Adrian Barnett reports an association between varying levels of melanin in skin and the balance between contradictory requirements for protection and synthesis in the skin. These, he notes, vary seasonally in regions away from the equator. He also notes that the number of melanin reservoirs does not vary greatly with skin colour.
These observations, taken together, would suggest that in temperate regions skin colour should vary seasonally. Tanning fits with this theory, but not perfectly. The time lag is great, and the range of the change is small compared with the observed regional variation in skin colour.
Worth the risk
I would like to comment on the controversy surrounding the hazards of gene therapy, highlighted by the case of the French boy who developed leukaemia after being treated with a retrovirus (12 October, p 5)
The genetic condition that the boy was being treated for is fatal in every case, while I understand that nowadays the commoner childhood leukaemias kill 2 or 3 of every 10 victims. So even in the worst-case scenario it is worth pressing on with the treatment, although of course there should also be research into how to avoid the negative side effects.
All new medical technology, and indeed all technology in general, has negative side effects. For instance, the first smallpox inoculation was introduced into Britain from Turkey by Lady Mary Wortley Montagu in the early 18th century. It killed 1 recipient in 50 but the inoculation continued because in those days smallpox killed such a high proportion of the population. It then paved the way for Jenner’s much safer smallpox vaccination.
PCs on planes
The letter on “lethal laptops” raises a good but scary point (5 October, p 28). The writer goes on to ask if there is an alternative to banning electronics on planes.
Passengers bring laptops aboard because they want the data and memory, the processing power and the interfaces. They want them on the plane and at their destination.
But which of those elements is unique to the passenger? Only the data. If the airplanes offered the processing power, the screens, keyboards and the network connections 鈥� preferably built into each seat 鈥� the passenger need bring only a data store. And if hotels and businesses offer the same, or if laptops could be rented at each destination, then the laptops could be left at home.
The same is true of CD players and video games. With the cost of electronics, including computers, going down and the risks of electronics on airplanes going up, it is only a matter of time.
Caring about krypton
Concerning the idea of spending some 拢335 million reducing emissions of radioactive krypton in order to prevent 80 cancer deaths over 10 years (12 October, p 7), I think we should ask the following question: how much suffering and early death could be prevented if the 拢335 million were spent on improving health care in poor countries?
Letter
The report on krypton-85 arising from nuclear fuel reprocessing at Sellafield reminded me of the neat idea developed by Derek Whitmell and co-workers at the UK Atomic Energy Research Establishment at Harwell in the late 1970s.
The krypton storage problem was dealt with by incorporating the gas into copper, layer by layer, using a deposition/sputter technique, to produce a centimetre-thick material containing about 5 per cent krypton. Electron microscopy showed the gas was present in a high concentration of nanometre-sized bubbles, but later these bubbles were shown to consist of krypton precipitates, held in the solid phase by the immense internal pressures (New 杏吧原创, 7 February 1985, p 22). Moreover, the precipitates were completely stable well above room temperature.
It seemed at the time that this material (perhaps the original “kryptonite” from the Superman stories!) had many advantages for krypton-85 storage over the alternative of holding it for 100 years in high-pressure gas cylinders where the complete retention of the gas might have been hard to guarantee.
A bit of understanding
It seems that Grigori Volovik has found what readers of the Hitchhiker’s Guide have known for years 鈥� that you can learn about the Universe from small bits of it (12 October, p 28). It is just that Volovik uses helium rather than fairy cake.
Need not to know
At the moment it may seem like fun to hold your own genome sequence, but have Craig Venter and colleagues considered the task of telling someone that they will develop Parkinson’s disease, or end their life in a wheelchair, or simply await the day that their medication may fail and they might be struck down with a stroke or heart attack (12 October, p 12)?
My first heart attack seven years ago came out of the blue and I would not have had it otherwise. True, had the possibility or probability been known, my doctor would have advised various precautions. Equally, two hours before the onset of pain, I would not have been 10 metres up a large sycamore tree. But it is also true that my life would have been blighted by the knowledge.
My second heart attack was not detected until I had an angiogram this year. I now know that I need a triple-bypass operation. And I also know that my consultant considers it too risky. In fiction, foreknowledge is doubtless great fun; in real life, it is a certain path to misery. Swap places anyone?
For the record
鈥� Thanks to the many learned readers who reminded us that “octopi” (5 October, p 10) could not possibly be the correct plural of “octopus” as it is derived from Greek. But we got it right when we referred to octopuses the following week (12 October, p 24).
鈥� In “Sea lion scores top marks in memory test” (26 October, p 25) we reported that “sea lions may have the best memory of all non-human creatures”. We should add that, as yet, no other animal has been tested for this length of time.
鈥� In “Who are we?” (26 October, p 44) we stated that there were no volcanoes to provide ash for carbon dating. That should have read radiometric dating.
鈥� The picture of Titan with “Titan probe could find a world of weirdness” (19 October, p 25) should have been credited to Mark Robertson-Tessi of the Arizona Space Grant program, working in collaboration with Ralph Lorenz, who emphasises that because of its thick atmosphere, Titan would appear dark red, not blue as shown.
Focusing on gravity
The goal of detecting gravitational waves is, as Stephen Battersby writes, truly breathtaking (7 September, p 26). But we strongly reject the suggestion implicit in his article that our project, known as LIGO, offers an inefficient route to this goal.
LIGO’s task is daunting. It must monitor the separation of mirrors 4 kilometres apart to an accuracy of 1/1000th the diameter of an atomic nucleus, while protecting the mirrors from all forces except gravitational waves. But the reported claim of one critic that we “could have developed better technology first on a smaller machine” overlooks the fact that all the technologies required for LIGO had been invented and tested by the early 1990s.
The key challenge is to make these technologies robust and work together in a complex gravitational-wave detector 100 times larger than our 1990s test beds. That is why we formulated a staged plan to scale up the equipment.
Step one was to build LIGO’s 4-kilometre-long vacuum systems and install initial detectors. These are not “pushed to the limits of current technology” but use simplified designs and the most robust of our technologies.
Step two, where we are now, is to perfect the interactions of these technologies and look for gravitational waves for several years at a sensitivity where the most optimistic estimates say waves will be seen. For step three, in about 2007, we will upgrade to our complex designs and delicate technologies in detectors sensitive enough for even the most pessimistic estimates.
LIGO is an international collaboration of 440 scientists from 16 countries, and includes the smaller British-German GEO detector. GEO takes part in the initial LIGO wave searches while testing the interactions of LIGO’s advanced technologies. GEO’s mirrors are kept still by hanging them from fused quartz fibres attached to cascaded pendulums. The fibres, developed in the early 1990s, were too delicate for the initial LIGO while the pendulums, developed in the 1980s, were too complex. But both will be used in LIGO’s 2007 upgrade, as will “signal recycling”, described by Battersby as a “new” technology even though it was invented in the 1980s.
LISA, the Laser Interferometer Space Antenna (planned for launch in 2011), will look for gravitational waves with wavelengths 10,000 times as long as those LIGO seeks, so its view of the sky will be radically different. LIGO and LISA are pricey, but extensive and repeated peer reviews have concluded that their pay-offs are worth it. Through the new windows they open onto the dark side of the Universe we will probe curved space and warped time in ways not even imagined a few decades ago.
We have named gravitational waves correctly