Mosquito mystery
Tangentially to your feature “Mosquitoes that kill malaria” (5 August): no one has yet shown that HIV can be transmitted by a nonhuman vector. But if the relatively huge malaria parasite can be transmitted by mosquitoes, why not the minuscule HIV molecule? Does this point to a potential means for combating HIV transmission or infection?
Wrong red
I read with great interest “Socotra’s misty future” (29 July). However, there appears to be some confusion regarding Dracaena cinnabari. The resinous exudation is indeed known as dragon’s blood and has been used for colouring spirit varnishes a deep red in earlier times, but in modern practice has been superseded by synthetic dyes.
Cinnabar, on the other hand, is mercury sulphide, which has been mined in Almad茅n, Spain, for some 2000 years. It was also made synthetically by the Chinese many centuries ago, the synthetic form being known as the red pigment vermilion.
But what's it for?
There’s a small snag with George Seaborn’s idea for a frozen (and thus tiltable) mercury mirror (Letters, 12 August). So far I haven’t managed to work out what precisely you would use a mirror covered in frozen water vapour for.
It seems that what is really needed is some material that is solid at room temperature and has a low coefficient of thermal expansion. It could then be melted, spun to the mirror profile, and allowed to cool. I think that an ideal material might be a mixture of fused silicates 鈥� or glass.
Anyone wishing to take up this idea has my permission.
Reading your article (“Spinning images from mercury mirrors”, 15 July), one would never know that it was Ermanno Borra of Laval University in Canada who was responsible for reviving the idea of liquid mirror telescopes. It was he who showed that one could overcome the difficulties of implementing an idea which had been abandoned as impossible over 50 years earlier. It was he who showed that this cheap technology can now be used to make mirrors suitable for studying a whole range of phenomena, from space junk to the distribution of galaxies.
As a sceptical member of NSERC, the agency that awards research grants in Canada, which supported his work, I saw the difficulty he had in convincing anyone that his idea had any merit. Now that the sceptics have been proven wrong, I find it unfortunate that a journal such as yours ignores his pioneering work.
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It ain't broke
For anybody familiar with the DC-X Space Clipper project it is quite clear that rather than being a “coming of age”, NASA’s takeover will mean the untimely death of this promising machine (“Space Clipper comes of age”, 12 August).
The whole thrust of the Delta Clipper project was for a “cheap and cheerful” craft using off-the-shelf technology and offering reliable, inexpensive access to orbit. To this end the designers used simpler and more reliable, albeit heavier, engines and other essential components.
The total cost of the current DC-X test model, which must have the most successful test flight record of any experimental rocket, was $59 million. According to your article, NASA is now going to spend a further $50 million turning this concept on its head by adding a variety of expensive, complex and experimental materials and components to produce a new DC-XA which it hopes will work as well as the one they’ve already got.
A 60 per cent weight saving on the liquid hydrogen tank sounds impressive, and indeed it would be if the Clipper could lift off with dry tanks. I wager the percentage sounds much less impressive when the weight of the fuel is included. Aluminium may be relatively heavy but I could buy tons of it for every kilo of epoxy composite, and its structural and thermal properties are already well understood.
Personally, I think a craft that gets five tons into orbit and costs (say) $50 million is infinitely preferable to one that gets six tons into orbit but costs $500 million plus extra launch insurance and lower reliability because of untried engineering.
Clearly NASA has no intention of developing the Delta Clipper into the cheap (to manufacture, operate and insure) spacecraft it could be, but rather to use the DC-X concept as a test-bed for a new generation of its own flying money pits. Seeing the elegant simplicity of the Delta Clipper suffocated under NASA’s hypocritical bureaucracy must sadden the hearts of all who truly care about expanding humanity into space.
Solar energy source
Recent measurements of the solar wind, which seem to show a strong correlation with the solar neutrino flux, suggest that a revolution in astrophysics may be at hand (New 杏吧原创, Science, 12 August).
Fusion in the solar core cannot fluctuate as rapidly as the putative variations in neutrino flux and solar wind unless the fusion reactions are driven by an altogether different process 鈥� perhaps an electromagnetic mechanism such as chaotic rotation of magnetic fields in the core.
The hypothesis that fusion is not, and has never been, the main source of solar energy could be tested by comparing the present abundance of helium-4 in the Sun with the initial abundance five billion years ago, known to be about 25 per cent by mass.
The Sun has been shining steadily for at least four billion years (enabling life on Earth). It is therefore easy to show that, if fusion alone has been responsible for the solar energy output up to the present time, the helium-4 enhancement must now be at least 4.5 per cent by mass. The current abundance therefore cannot be less than 29 to 30 per cent.
The amount of helium-4 in the core could be estimated, using solar seismology, from acoustic wave velocities. The big question is whether such measurements agree with the expected 20 to 30 per cent mass fraction. Clearly, if a significant discrepancy exists, fusion cannot be the only or even the main source of solar energy.
Remove the humans
Sanjay Kumar’s article on leopards attacking people in the Indian state of Himachal Pradesh highlights the pressures placed upon indigenous wildlife for the sake of human population expansion (This Week, 12 August). Humans are moving into the territories of big cats, destroying their habitats, and in return are losing their livestock, or worse their lives.
The immediate, and understandable feeling is that the leopard population should be culled, as proposed by the state’s chief conservator of forests, Gian Chand Gupta. However, the question must be asked: why?
There are two solutions to the problem 鈥� remove the leopards, or remove the humans and their livestock. As the latter are the invaders and the former are teetering on the verge of extinction, protected by the India’s Wildlife Protection Act, then the choice must be obvious. Although it may well be politically unpopular, the Indian government must bite the bullet and decide whether or not the act is to have any meaning. But what real hope is there of this when Himachal Pradesh’s chief conservator of forests is in favour of culling an endangered species?
Forests aren't sinks
Rigel Jenman in his article on the valuing of trees seeks to perpetuate the idea that the forest has a “capacity to maintain a stable atmosphere by fixing carbon dioxide and producing oxygen” (Letters, 29 July). We are taught this truism in school. Unfortunately it is taken by many as a reason for protecting virgin old-growth forests, including tropical rainforests, because people believe these forests have the ability to suck up great amounts of carbon dioxide while only giving back oxygen.
This, however, is not the case. Any climax (undisturbed and in balance) plant community is “carbon neutral” 鈥� that is, it puts back into the atmosphere as much carbon as it takes in through transpiration. The carbon is released when the plants die and are broken down on or in the soil. Both carbon dioxide and methane are released into the atmosphere. All of a plant community’s production 鈥� leaf fall, flowers, fruit and dead plants 鈥� are handled in this way.
The only time a plant community can be “carbon positive” is when it is dynamic, and a community is only dynamic following disturbance. This disturbance can be caused by nature, in the form of fire, flood, drought or storm, or by humans. When a forest is recovering from disturbance it is fixing carbon at a great rate.
It follows that the best way to use forests to remove carbon from the atmosphere is to harvest timber. Provided this timber is used for long-term products such as houses and quality furniture, then this carbon is tied up for many decades, maybe centuries. Harvesting trees for short-term uses, such as in paper, packaging and disposable chop sticks, does nothing for the atmosphere and, because of the low value of these products, encourages wasteful and destructive harvesting techniques.
There are many other good reasons for preserving the remaining areas of “pristine” vegetation, be they tropical rainforest, savanna grasslands or tundra, without trying to push the greenhouse argument.
Friendly farming
Ian Anderson tells only part of the story, and the gloomy part at that, in “Australia’s growing disaster” (29 July). While not disputing that timber clearing in some regions has resulted in salination problems, we believe that when there are positive aspects of agricultural development, these too need to be mentioned.
One of us (Bill Burrows) has recently described enormous, and hitherto unrecognised, carbon sinks in the grazed woodlands of northern Australia. This sink, the result of increases in woody plant density and biomass under grazing, is conservatively estimated to represent around 130 million tonnes CO2 equivalent per annum. Furthermore, this value is derived from substantial, hard-won, field observations at more than 20 sites in Queensland, not on data that has been theorised from the comfort of an armchair.
This figure of course presents agriculture in a far better light, rather than as an environmental demon. It needs to be acknowledged and lauded. Indeed, including this figure would reduce Australia’s net emissions on the world “greenhouse stage” by 23 per cent and correspondingly improve our net per capita emissions in comparison with other nations.
Our estimates of annual land clearing in Queensland are also at odds with those claimed by Anderson, who falls into the old trap of equating clearing permits with actual clearing. However, our main concern is that agriculture should be seen as an environmental necessity and not only as a scapegoat for a variety of environmental afflictions.
The numbat was once widespread in Western Australia, South Australia, Northern Territory, Victoria and New South Wales. It disappeared over much of this range in regions where no clearing had taken place. Rather, the major problem for the numbat was introduced animals, particularly the fox and feral cat.
This was shown dramatically when zoologists in Western Australia made a determined attack on these introduced pests. As a result, the numbers of numbats, woylies and other threatened small mammals increased to levels where they could be taken off the endangered list. It is important that culls of feral animals such as the goat, rabbit and pig, as well as the fox and feral cat, be carried out over the whole of Australia. Otherwise captive breeding, followed by restocking suitable habitats, will prove a waste of money.
Neil Clark, an agricultural consultant from Bendigo in Victoria, is quoted as saying that the cause of land conservation is suffering because the problems are being “researched to death 鈥� We need to divert money for a while into getting the solutions into place”.
We suffered the same problem with the Lord Howe Island woodhen. This species was reduced to a few dozen individuals. The only hope in our opinion was a captive breeding programme. However, at a seminar on the crisis the scientists claimed that more research was needed. Fortunately our society was able to force a breeding programme to be put in hand, with dramatic success.
Our society believes that where a need is urgent, scarce funds should be used to take the most scientifically accepted, practical solution, instead of creating more papers to add to the dossier of extinction.