雅思 文章

20 September 2012 by Will Ferguson, Navajo Nation, Arizona Magazine issue 2883. Subscribe(预定 订阅 捐助) and save For similar stories, visit the Field Notes Topic Guide

A scheme in Arizona using solar energy to power a water desalination（脱盐作用 海水淡化） plant aims to bring running water to thousands of people

THE sun beats down on sand dunes（小沙丘） and cracked （裂缝）red soil as we rumble（察觉 识破) through the desert in a heavy-duty pickup truck. It is monsoon (雨季)season in the Navajo Nation but the scenery looks as if it never got the memo（备忘录）. Two decades of severe drought have left the land parched.（焦干的 干透的）

\"It's hard to imagine that 30 years ago this was all covered in knee-high grass,\" says Kevin Black, a Native American affairs specialist for the US Bureau of Reclamation. \"Clean water has become the Navajo's most precious commodity.\"

Arizona's largest aquifer lies 120 metres beneath us, but the water is not drinkable. It's half as salty as seawater, and a 2008 study found that it contains dangerous levels of uranium（铀） and arsenic.（砷 砒霜）

Black says piping（滚烫的） water from a tribe-owned purification（净化 纯净 ）facility to homes scattered （消散 使四散）across an area the size of West Virginia is an economic impossibility. For 80,000 Navajo, this means no running water at home.

Instead, Navajo families drive hundreds of kilometres every month to collect water. \"It is called water hauling(搬运 牵引),\" Black says. \"It is an expensive and time-consuming journey that has become part of the Navajo way of life.\" The Bureau of Reclamation and engineers at the University of Arizona think they have come up with a way to help, by building a self-sufficient, solar-powered desalination plant.

Black points out the budding facility perched on a hill in the south-western corner of the reservation (see map). Construction began in mid-August. On completion in 2013, it will produce close to 4000 litres of clean water a day, he says. With sufficient funding, the facility could be the first of a series across the reservation. That could halve the cost of hauling water.

Wendell Ela, the project's lead engineer, has been testing prototypes for the past year in Tucson. He says the process uses electricity from solar panels to pump contaminated water up from the aquifer and boil it.

The steam then passes through a series of membranes that filter out salt and other contaminants. As it cools, the difference in vapour pressure it creates draws more hot water vapour through the system. Purified water is then collected in an external condenser.

Although commercial desalination plants have been used in the Middle East and Australia since the early 1990s, they rely on reverse osmosis or multistage distillation - processes that are technically challenging and expensive to maintain.

By contrast, the team's membrane desalination system is ideal for an isolated population that does not have access to an electrical grid, Ela says. It is built using simple, low-tech, off-the-shelf components. The team is aiming to build a system lasting 30 to 40 years that would require only periodic maintenance. \"We had to design the system to be within the capacity and budget of the water-users,\" he says.

Such reliability isn't guaranteed, says John Lienhard, an engineer at the Massachusetts Institute of Technology, who says the technology hasn't been around long enough to have much of a track record. And the systems cost up to $100,000 to build. But he says that should fall steeply as they gain wider adoption.

The impact on Navajo life would be profound. If the other planned desalination plants are built in the reservation, they could provide running water to tens of thousands of Navajo who have never had it.

\"People always ask, 'If it is so bad why don't they leave?'\" Black says. \"My response is, 'Who are we to question them?' Their livelihood and culture has been intertwined with this place for thousands of years. We are trying to help them hold on to their identity in a world that is changing very fast.\"

Arctic ice low heralds end of 3-million-year cover

Updated 10:49 31 August 2012 by Catherine Brahic Magazine issue 2880. Subscribe and save

For similar stories, visit the Climate Change Topic Guide

Editorial: \"Arctic melt, smash and grab ahead\"

IT IS smaller, patchier and thinner than ever - and rotten in parts. The extent of the Arctic ice cap has hit a record low, and the consequences of what is arguably the greatest environmental change in human history will extend far

beyond the North Pole.

For at least 3 million years, and most likely 13 million, says Louis Fortier of the University of Laval in Quebec City, Canada, the Arctic Ocean has been covered by a thick, floating ice cap, the breadth of which fluctuates with the seasons and currents. Each summer, the cap shrinks to an annual minimum in mid-September before growing out again, fuelled by plummeting winter temperatures and long nights.

Climate change has had more of an impact here than anywhere else on Earth. Air temperatures are rising twice as fast as the global average, and models predict ...

To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content.

A real fMRI high: My ecstasy brain scan

16:49 18 September 2012 by Graham Lawton Magazine issue 2883. Subscribe and save

For similar stories, visit the Field Notes , The Human Brain and Drugs and Alcohol Topic Guides

Our reporter experience the highs, lows and psychedelic purple doors involved in taking MDMA while having his brain scanned

Editorial: \"MDMA TV: Turn on, tune in, do the research\"

See more in our gallery: \"A wide-eyed view on being high inside an fMRI\" My usual pick-me-up on a Monday morning is a cup of coffee. Today it's going to be something very different.

I've been up since 6 am. I've had a breath test for alcohol, a urine test for drugs and a psychological test for mental health. Then I'm handed a red pill and a glass of water. I swallow it… and I'm told to relax. Which is easier said than done when you don't know if you've just taken vitamin C or 83 milligrams of pure MDMA.

Half an hour later I'm inside an fMRI brain scanner, my head clamped in place and a visor over my face. It's noisy and claustrophobic but I'm reassured by the panic button in my hand and a voice from the control room.

And then I start to feel it. A tingle of energy, like pins and needles, starts in the pit of my stomach and rises slowly, not unpleasant but not exactly pleasurable either. It builds in intensity, then breaks into a wave of bliss. The placebo effect can be powerful but when it happens again, I'm in no doubt. I'm coming up. I'm taking part in a groundbreaking study on MDMA, the drug commonly known as ecstasy. The research is run by David Nutt of Imperial College

London, a former government adviser and one of the few UK researchers licensed to study class-A drugs.

His main aim is to discover what MDMA does to the human brain, something that, remarkably, has never been done before. A second goal is to study MDMA as a therapy for post-traumatic stress disorder. The experiment is also being filmed for a Channel 4 documentary called Drugs Live: The Ecstasy Trial, which will be broadcast in the UK next week.

Over the next hour I ride ferocious surges of serotonin that balloon me higher and higher, while trying to focus on a series of tasks. The fMRI machine is going through its repertoire of rackets – rhythmic clankings, throaty roars and what sounds like organ music. At times I feel amazing, at others panicky. Keeping my head still is very, very hard. But I ride it out.

When I'm pulled out 90 minutes later, the drug effects have plateaued. My mind is clear, my movement feels smooth and, aside from some jaw clenching, I feel content and sociable. And surprisingly psychedelic: a purple door is throbbing before my eyes.

I perform psychological tests, but my heart isn't in it. I'm more interested in chatting to the psychologists, doctors, nurses and porters. Finally I head home, and wake up the following day feeling pretty good.

Robin Carhart-Harris, a member of Nutt's team, later tells me they have now scanned 23 brains and have some preliminary results. While inside the machine, one of the tasks involved thinking about five of my most positive and negative memories. I rated these in terms of their vividness and associated emotion during the high and later that day.

The hypothesis was that MDMA would make the negative memories less painful. \"We saw a boosted brain response to positive memories, and a weaker response to negative ones,\" says Carhart-Harris. \"It fits the idea that MDMA can help people access negative memories without being overwhelmed by them and they might be able to change the way they feel about what happened.\"

A week after my first scan I return to go through the same procedure. As I swallow the pill I wonder briefly if last week was some kind of amazing placebo effect. It wasn't.

How to defuse sub-Saharan Africa's population bomb

00:01 26 April 2012 by Eliya Zulu Read full article

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Will there be 15.8 billion people inhabiting the world in 2100, or 6.2 billion? The first scenario might trigger harsh resource shortages, unrest and war; the latter features a stable planet with hope for all.

As this century proceeds, more and more of the population growth will be driven by the least developed countries. Most are in Africa, which has an average family size of 4.7 children per woman. It is the only continent where population is predicted to keep growing beyond 2100.

If Africa's population increases according to the UN's medium prediction, the continent will have about 3.6 billion people by the end of the century – raising its current share of global population from 12 per cent to about one-third. Nevertheless, its population could reach 5.2 billion or 2.4 billion by 2100, depending on whether fertility is 0.5 children above or below the UN's medium estimate.

The population of the Sahel – those semi-arid countries bordering the Sahara – will double or more by 2050 at exactly the time that global warming is likely to have the harshest effects. As population growth and global warming coincide, the hunger and refugee problems in the Horn of Africa, and type of resource battles seen in Darfur or South Sudan, will multiply.

Worldwide, the UN predicts 15.8 billion humans by the end of the century if average family size remains around 2.6 children per woman, but 6.2 billion if it stabilises at 1.6 children. If fertility levels drop to the replacement level of 2.1, then there will be 10 billion people. This week the Royal Society launched a new report called People and the Planet. It reviews the evidence on the link between population and global challenges, underscoring the need to move to a biologically sustainable economy as well as lifting the poorest 1.3 billion people out of abject poverty.

The report explores the impacts of population changes on general wellbeing, urbanisation, food and water security, and the risk of conflict. It also emphasises the need to reduce excessive consumption in developed countries and emerging economies. Crucially, the report calls for investment in voluntary family planning, and in the education and wellbeing of girls in the least developed countries in order to slow population growth.

Changing habits

Africa remains the region with the lowest use of contraceptives (29 per cent of married women of reproductive age versus the global average of 69 per cent) and a high demand for children. However, things are changing. It is possible to manage population growth if local governments, the international community and others make the right decisions and provide the right support.

In developing countries between the 1970s and 1990s, cultural sensitivity surrounding childbearing was prevalent, as were suspicions over the intentions of western development partners in promoting family planning. Such sentiments, however, have largely dissipated.

Leaders are becoming more receptive to addressing population issues due to the growing evidence that high growth undermines efforts to ease poverty and hunger, and that investing in quality human capital is needed to transform their economies.

The economic turbulence experienced by most developing countries since the 1980s also

makes it clear that it will be difficult or impossible to break their development shackles without curbing rapid population growth.

Leaders who were once reluctant to promote family planning have joined the family planning bandwagon, thanks to scrutiny of their progress towards the Millennium Development goals (including poverty, equality and sustainability), coupled with the increasing evidence that family planning plays a central role in improving maternal and child health.

Furthermore, although leaders embrace big populations as symbols of political power, a source of global influence and a potential economic asset, it is increasingly apparent that development goals are better met through high quality populations rather than big ones. The political will and commitment to promote family planning and reduce population growth is not as entrenched in the highly populated countries of central and west Africa as it is in northern, southern and parts of eastern Africa. But it is instructive that virtually all African countries now acknowledge rapid population growth as one of the key impediments to development.

For example, Rwanda has seen one of the fastest increases in history in use of modern contraceptives – from 6 per cent of married women of reproductive age in 2000 to 45 per cent in 2010. Malawi, which banned family planning between 1969 and 1984, has one of Africa's highest levels of modern contraceptive use – 42.2 per cent – in 2010.

And while many African leaders could once argue that it was against African culture to promote family planning, the evidence over the past two decades shows that most women are having more children than they would like, and many would like to postpone their next birth.

Across the globe, 215 million women report unmet need for family planning. In most African countries, the majority of women of reproductive age have unmet family planning needs. In sub-Saharan Africa, 42 of the 78 million women who need family planning are not using modern contraception. About two in five women in Ghana, Zambia, Malawi and Togo recently reported that their last birth was unplanned.

This is due to a lack of services, disapproval of family planning, misinformation, misconceptions and medical barriers, such as limiting oral contraceptive use to medical prescription. These barriers can be addressed through voluntary family planning programmes that are well-planned, appropriately funded, with strong community involvement and mobilisation.

Girls who stay in school longer have fewer children because they marry later. They are also more likely to want fewer children as they want to pursue a career and enjoy greater power to negotiate contraception use.

Governments should legislate against child marriages, and young people deserve youth-friendly reproductive health services. Unfortunately, family planning is not high on the development priority list in many least developed countries and is subsequently under-funded. The international community needs to step in. Evidence shows that in such cases, governments slowly assume funding responsibility.

The Royal Society report suggests that offering family planning through appropriate clinical, commercial and community channels could cost about $6 to 7 billion per year. It would cost perhaps another $1 billion to keep half of 15 to 19-year-old girls in the

fastest-growing least developed countries in school instead of entering into child marriage. An overall investment of $10 billion a year today could begin to move global population towards 6 billion in 2100. Taking no action will cost many times more. The pace of technical change, global warming, competition for resources and short-term national rivalries point to problems in the future.

There is no way to guarantee a safe future, but the commonsense view is that a world of 6 or 7 billion people with reasonable living standards for most is a better bet than one with 12 to 16 billion in which 5 to 6 billion struggle to survive on a few dollars a day while the richest continue to consume too much, and women are still denied their freedom.

At less than one thousandth of global GDP, $10 billion dollars per year could potentially change the course of the 21st century.

Author Profile: Eliya Msiyaphazi Zulu is the founder and executive director of the African Institute for Development Policy, which promotes use of research and related evidence in decision-making processes related to population change, reproductive health and sustainable development in Africa. He was a member of the Royal Society study group that produced the report People and the Planet

Cameras know you by your walk

20 September 2012 by Jim Giles Magazine issue 2883. Subscribe and save For similar stories, visit the Crime and Forensics Topic Guide

Improvements in gait analysis mean your characteristic way of walking could soon be used to identify you – wherever you are

EVERYONE knows how easy it is to recognise a friend or family member from their walk - even from a distance.

But despite more than three decades of research, using gait analysis as a biometric has never taken off. Until now, perhaps. Recent advances in the accuracy of automated gait recognition suggest the technology could soon form the basis for a new generation of security systems.

Gait analysis has attracted attention because of the shortcomings of other biometric security techniques. Iris scans and face recognition require reasonably high-quality images, for example. They also generally require a cooperative subject, as do fingerprints. By contrast, a person's gait can be recognised from low-quality CCTV footage.

In one leading technique, known as the gait energy image, computer vision techniques use video images of a person to create a blurred silhouette that is characteristic of their gait. A human operator links this gait \"signature\" to a person's identity, allowing the system to automatically spot that person when they are next caught on film.

This technique uses just a blank silhouette, but Martin Hofmann and colleagues at the Technical University of Munich in Germany have developed a version that also extracts information from the person's image, such as the shadows on their clothing, which leads to a more detailed signature. Hofmann also used Microsoft's gaming sensor Kinect to

measure depth, allowing him to better separate the target from the background. The result is a system that is better at tackling tasks that cause problems for the standard version of the technique, such as recognising a person carrying a briefcase. In tests using videos of several hundred people the system achieved a recognition rate of almost 80 per cent, outperforming 13 other gait analysis methods, including the one using gait energy images. Another problem that has troubled researchers is finding a way to identify a person captured at different camera angles, and Daigo Muramatsu and colleagues at Osaka University in Japan are now working on a solution. They filmed 20 people on a treadmill using 24 cameras ranged around them and used this data to write software that can model the appearance of a person's gait when viewed from different angles. In preliminary tests, the system led to lower identification error rates at almost all angles, results Muramatsu describes as \"promising\".

Muramatsu and Hofmann will present their work this week at the BTAS biometrics conference in Washington DC.

These and other developments suggest that automated gait analysis might be ready for commercial use in the near future. Muramatsu says his group is already working with forensic scientists in Japan and has also developed gait analysis software that can be used by non-experts.

At the National Physical Laboratory in Teddington, UK, researchers have developed a demonstration system that can track people as they move through the laboratory building by their gait alone.

Hofmann cautions against thinking gait recognition will ever rival fingerprints for accuracy. Accuracy rates can plummet if a person walks more rapidly than normal, for example. But that does not mean it won't prove useful. \"Gait has potential for commercial applications,\" he says. \"Imagine a bank robber who has covered his fingers and face, but can be identified by the way he walks out of the bank.\"

Ministry of suspicious walks

Could you tell if a phone has been stolen by a change in the walking pattern of the person carrying it? An Android app developed by Marios Savvides and colleagues at Carnegie Mellon University in Pittsburgh, Pennsylvania, uses data from the accelerometer and gyroscope that come as standard on modern smartphones to record the movements that a phone makes as its owner walks. In a study to be presented this week at the BTAS biometrics conference in Washington DC, Savvides shows the app can identify a particular gait with over 95 per cent accuracy. The technology could one day be used to shut a device down if it registers a gait that does not match that of its owner.

Duck river

The idea was to place Liittschwager's standard cube frame in this river in Lillard's Mill, Tennessee – home to 54 different species of mussel and 32 species of fish – and photograph everything within. But algae made the water too murky to get clear shots. Last-minute improvisation, after Liittschwager made a trip to the local hardware store, converted the frame into a mini-aquarium: he and collaborators then simply scooped up a sample from the river.

Sperm stem cells restore male fertility

17:35 05 November 2012 by Will Ferguson For similar stories, visit the Stem Cells Topic Guide

Men who lose the ability to produce sperm after chemotherapy might one day be able to regain their fertility. That's because, for the first time, infertility has been reversed in a male primate using an injection of stem cells.

Cancer drugs often work by destroying rapidly dividing cells, as these are a typical feature of cancer. Unfortunately, the drugs can also kill other rapidly dividing cells, including those that produce sperm. Some men choose to freeze sperm samples before therapy so they can use them for artificial insemination at a later date, but this is not an option for boys who have not yet reached puberty.

Kyle Orwig at the University of Pittsburgh School of Medicine in Pennsylvania may have a solution. He says that while boys don't make sperm cells, they do possess \"spermatogonial\" stem cells that will eventually produce them.

To see if these stem cells could be used to restore fertility, Orwig and his team took samples of the cells from the testes of prepubescent and adult male rhesus macaques, and froze them. The monkeys were then given chemotherapy agents known to shut down sperm production. A few months later, the researchers injected each monkey's own spermatogonial stem cells back into its testes.

Sperm production was re-established in nine of the 12 adult animals and started normally in three out of five prepubescent animals once they reached maturity. The resulting sperm were used to fertilise eggs and produce healthy embryos.

\"I think this is the best option we have ever had,\" says Renee Reijo Pera, director of Stanford University's Center for Human Embryonic Stem Cell Research and Education, who wasn't involved in the study. \"I know a lot of people have thought about doing this before but no has ever been able to successfully demonstrate this in a clinical setting with a species genetically very similar to us.\"

Orwig says there are some concerns that implanting stem cells could reintroduce cancer

cells that may have been present in the original tissue. However, centres in the US and Europe are already banking testicular tissue for boys in the hope that new stem cell-based therapies will become available.

\"In the most optimistic scenario our research suggests a man could have his own stem cells transplanted, giving him the opportunity to have children via natural intercourse,\" Orwig says. It's not yet ready for clinical translation, he says, \"but it's an important step forward\".

Why I've built my own satellite

06 November 2012 byMaggie McKee Magazine issue 28. Subscribe and save For similar stories, visit the Interviews and Spaceflight Topic Guides

The technology-obsessed artist has built his own satellite, but is finding it much harder to sell T-shirts to pay for the launch

You have built your own satellite as part of your Open Source Satellite Initiative. What will it do?

It will communicate down to Earth and people can talk to it using amateur radio equipment. Anyone can send it a message, which it will transmit in Morse code using LED lights bright enough to be seen from Earth with bare eyes or binoculars. I'm trying to raise the attention of the general public about the space programme, and give them a chance to look at the sky one more time.

What has the experience been like?

The most difficult thing was knowing which components can work in space, where there are radiation and temperature fluctuations. For six years, I've been digging around the internet and reading papers about the kind of commercial components used in the space programme. There are also regulation problems. Each country is trying to be responsible for any foreign objects in space. I have to say exactly which radio frequency band I'm going to use and whether I can turn off the transmitter if my satellite is causing a problem. How much did the project cost?

The satellite cost around $600. The launching cost is $100,000. My original idea was to pay for this by selling T-shirts. If I sell 10,000 T-shirts at $35 each, then I can cover the costs. That was my plan, but making T-shirts and promoting them is much harder than launching a satellite!

Your satellite will launch on a Russian Soyuz rocket. When is the launch date?

It was meant to be 31 August this year, but it was postponed. Now it's April next year. That makes me sad. I want to finish it one way or the other. Why did you want to build a satellite?

There are lots of issues to talk about: individuals vs institutions or the government; amateurs vs professionals - the do-it-yourself culture. Which is more important, the art or

the science? I thought it would be nice to make the narratives, but still I had to build my satellite and not just fake it. Fifteen years ago, without the internet, it was almost impossible to build anything that uses extreme tech. These days, anything is possible. Do you plan to build more satellites?

The most important mission of my satellite is to test whether all those commercial components are functional in space or not, so then we can make a better satellite next time. I think the next step is more creativity, not just implementation. It would be nice if I can bring some people - artists or whoever - to build a satellite together. We can rent a whole rocket and put like 50 of them inside.

Tell me about some of your other art projects.

I made a uranium necklace for people who want to commit suicide. I put it on eBay, at almost $1 million. Someone commented to me that it's too expensive. I replied, it's the price of your life. Another one is the LED that blinks once every 100 years. By the time it lights, I will be gone but I think people will want to see whether the LED is blinking or not. It's putting eternity to the trivial.