Book 2 Listening (1108796), страница 7
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The polyglycolicacid degrades spontaneously over the course of a few weeks with the consequence that it is,in effect, replaced by the collagen. The result is a tube of the length and diameter of theoriginal scaffold, that is composed of collagen and smooth-muscle cells- a structure similar toa natural blood vessel.Transplanting that into a patient, however, would risk provoking an immune reaction,since the muscle cells are "foreign" tissue.
To get around this, Dr Dahl and her colleagueswash the muscle cells away with a detergent, leaving just the collagen.Though the end product is a nonliving simulacrum of a blood vessel rather than anartificial version of the real, biologically active thing, experiments on animals suggest that itworks well enough to substitute for a diseased natural vessel (for example, a cloggedcoronary artery that might otherwise cause a heart attack). It can also act as a "tap" fromwhich the blood of people whose kidneys have failed might be drawn for dialysis.At the moment, the options for either of these things are limited.
The best approach is touse a length of vessel taken from elsewhere in the patient's body (commonly, his leg). Butthat requires such transplants to be healthy themselves - and each length of transplantedvessel can be used only once.
Synthetic vessels made of Teflon exist, but they are prone toinfection and blockage by blood clots, and tend to work for only a few months.The animal experiments suggest the new, all-collagen vessels are capable of lasting atleast a year without noticeable deterioration. They are also, once implanted, able to remodelthemselves in ways that improve their function- changing shape in response to blood flow,being colonized by cells from the patient's body, and showing signs of incorporating elastin,another structural protein found in natural vessels.Also, if kept in a suitable saline buffer at 4"C, they can be transplanted a year after theywere made without a perceptible degradation of their properties.
So, if human trials confirmthese results, the surgical-repairer's toolkit will have acquired a useful additional instrument and the age of the cyborg will be just that little bit nearer. (From The Economist, February 5,2011)34Unit 2. WaterScript 3. ObesityDrink till you dropConsume more water and you will become much healthier, goes an old wives’ tale.Drink a glass of water before meals and you will eat less, goes another.
Such prescriptionsseem sensible, but they have little rigorous science to back them up.Until now, that is. A team led by Brenda Davy of Virginia Tech has run the firstrandomised controlled trial studying the link between water consumption and weight loss. Areport on the 12-week trial, published earlier this year, suggested that drinking water beforemeals does lead to weight loss.
At a meeting of the American Chemical Society in Bostonthis week, Dr Davy unveiled the results of a year-long follow-up study that confirms andexpands that finding.The researchers divided 48 inactive Americans, aged 55 to 75, into two groups.Members of one were told to drink half a litre of water (a bit more than an American pint)shortly before each of three daily meals. The others were given no instructions on what todrink.
Before the trial, all participants had been consuming between 1,800 and 2,200 caloriesa day. When it began, the women’s daily rations were slashed to 1,200 calories, while themen were allowed 1,500. After three months the group that drank water before meals hadlost about 7kg (15,5 lb) each, whereas those in the thirsty group lost only 5 kg.Dr Davy confidently bats away some obvious doubts about the results. There is noselection bias, she observes, since this is a randomised trial.
It is possible that the waterdisplaced sugary drinks in the hydrated group, but this does not explain the weight lossbecause the calories associated with any fuzzy drinks consumed by the other group had tofall within the daily limits.Moreover, the effect seems to be longlasting.
In the subsequent 12 months theparticipants have been allowed to eat and drink what they like. Those told to drink waterduring the trial have, however, stuck with the habit – apparently, they like it. Strikingly, theyhave continued to lose weight (around 700g over the year), whereas the other participantshave put it back on.Why this works is obscure. But work it does. It’s cheap.
It’s simple. And unlike so muchdietary advice, it seems to be enjoyable too. (From The Economist, August 28, 2010)Script 4. Water purificationAny old iron?A little-known chemical may provide a new way to clean waterIron in water is normally regarded a pollutant. Luke Daly, the boss of Ferrate TreatmentTechnologies of Orlando, Florida, however, plans to turn that thought on its head.
He intendsto use a chemically unusual form of iron to clean water up, not make it dirty.Iron is found in the part of the periodic table known as the transition metals. Like allmetals, these react with other elements by giving up electrons to form positively chargedions. Transition metals, though, give up different numbers of electrons in differentcircumstances, and thus have ions of various charges. Usually, iron loses two or threeelectrons.
But in ferrates, which are compounds of iron and oxygen with non-transition metalslike sodium and calcium, it loses six. That makes ferrates extremely reactive, and it is thisreactivity which Mr Daly hopes to exploit.First, ferrates are strong oxidizing agents. That means they destroy bacteria andviruses, and break up organic molecules with alacrity.
Second, they are coagulants andflocculating agents. They attract other chemicals in the water, including dissolved metals, andprecipitate them for easy removal. Moreover, once it has done its job, the iron in ferratesprecipitates too, as iron oxide, leaving pure water behind.35The reason these wonder materials have not been used as water purifiers before is thattheir reactivity makes them unstable and thus difficult to store. Thomas Waite of the FloridaInstitute of Technology, an academic scientist on whose work the company has drawn, jokesthat in the early days of his research he kept the whole world's supply of ferrates in a cabinetin his laboratory.Ferrate Treatment Technologies' trick is to make ferrates on site, for instant use, ratherthan attempting to transport them to where they are needed.
The firm's "Ferrator" uses threecheap raw materials bleach, ferric chloride and caustic soda- to produce sodium and calciumferrate at a price competitive, in terms of oxidizing power, with more familiar water-cleanerslike chlorine and ozone.A machine small enough to be carried around in a pickup truck, Mr Daly claims, couldgenerate enough ferrates to purify 75m litres (20m American gallons) of water a day. Thesystem is now being tested at two plants in Florida. If all goes well, the first commercialFerrators will be up and running later this year.
(From The Economist, January 22, 2011)36Unit 3. FungiScript 5. Plant communicationsBeans' talkVegetables employ fungi to carry messages between themThe idea that plants have developed a subterranean internet, which they use to raisethe alarm when danger threatens, sounds more like the science-fiction of James Cameron'sfilm "Avatar" than any sort of science fact. But fact it seems to be, if work by David Johnsonof the University of Aberdeen is anything to go by. For Dr Johnson believes he has shownthat just such an internet, with fungal hyphae standing in for local Wi-Fi, alerts bean stalks todanger if one of their neighbours is attacked by aphids.The experiment which suggests this was following up the discovery, made in 2010 by aChinese team, that when a tomato plant gets infected with leaf blight, nearby plants startactivating genes that help ward the infection off - even if all airflow between the plants inquestion has been eliminated.
The researchers who conducted this study knew that soil fungiwhose hyphae are symbiotic with tomatoes (providing them with minerals in exchange forfood) also form a network connecting one plant to another. They speculated, though theycould not prove, that molecules signaling danger were passing through this fungal network.Dr Johnson knew from his own past work that when broad-bean plants are attacked byaphids they respond with volatile chemicals that both irritate the parasites and attract aphidhunting wasps.
He did not know, though, whether the message could spread, tomato-like,from plant to plant. So he set out to find out - and to do so in a way which would show if fungiwere the messengers.As they report in Ecology Letters, he and his colleagues set up eight "mesocosms",each containing five beanstalks. The plants were allowed to grow for four months, and duringthis time every plant could interact with symbiotic fungi in the soil.Not all of the beanstalks, though, had the same relationship with the fungi. In eachmesocosm, one plant was surrounded by a mesh penetrated by holes half a micron across.Gaps that size are too small for either roots or hyphae to penetrate, but they do permit thepassage of water and dissolved chemicals. Two plants were surrounded with a 40-micronmesh.
This can be penetrated by hyphae but not by roots. The two remaining plants, one ofwhich was at the centre of the array, were left to grow unimpeded.Five weeks after the experiment began, all the plants were covered by bags thatallowed carbon dioxide, oxygen and water vapour in and out, but stopped the passage oflarger molecules, of the sort a beanstalk might use for signalling. Then, four days from theend, one of the 40-micron meshes in each mesocosm was rotated to sever any hyphae thathad penetrated it, and the central plant was then infested with aphids.At the end of the experiment Dr Johnson and his team collected the air inside the bags,extracted any volatile chemicals in it by absorbing them into a special porous polymer, andtested those chemicals on both aphids (using the winged, rather than the wingless morphs)and wasps.
Each insect was placed for five minutes in an apparatus that had two chambers,one of which contained a sample of the volatiles and the other an odourless control.The researchers found, as they expected from their previous work, that when thevolatiles came from an infested plant, wasps spent an average of 312 minutes in thechamber containing them and 112 in the other chamber. Aphids, conversely, spent 114minutes in the volatiles' chamber and 314 in the control. In other words, the volatiles from aninfested plant attract wasps and repel aphids.Crucially, the team got the same result in the case of uninfested plants that had been inuninterrupted hyphal contact with the infested one, but had had root contact blocked. If bothhyphae and roots had been blocked throughout the experiment, though, the volatiles fromuninfested plants actually attracted aphids (they spent 312 minutes in the volatiles' chamber),while the wasps were indifferent.
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