The construction of roads and bridges Roads
Although there were highway links in Mesopotamia from as early as 3500 BC, the Romans were probably the first road-builders with fixed engineering standards. At the peak of the Roman Empire in the first century AD. Rome had road connections totalling about 85,000 kilometres.
Roman roads were constructed with a deep stone surface for stability and load-bearing. They had straight alignments and therefore were often hilly. The Roman roads remained the main arteries of European transport tor many centuries, and even today many roads follow the Roman routes. New roads were generally of inferior quality, and the achievements of Roman builders were largely unsurpassed until the resurgence of road-building in the eighteenth century.
With horse-drawn coaches in mind, eighteenth-century engineers preferred to curve their roads to avoid hills. The road surface was regarded as merely a face to absorb wear, the load-bearing strength being obtained from a properly prepared and well-drained foundation. Immediately above this, the" Scottish engineer John McAdam (1756-1836) typically laid crushed stone, to which stone dust mixed with water was added, and which was compacted to a thickness of just five centimetres, and then rolled. McAdam’s surface layer - hot tar onto which a layer of stone chips was laid - became known as tarmacadam', or tarmac. Roads of this kind were known as flexible pavements.
By the early nineteenth century - the start of the railway age - men such as John McAdam and Thomas Telford had created a British road network totalling some 200.000 km, of which about one sixth was privately owned toll roads called turnpikes. In the first half of the nineteenth century, many roads in the US were built to the new standards, of which the National Pike from West Virginia to Illinois was perhaps the most notable.
In the twentieth century, the ever-increasing use of motor vehicles threatened to break up roads built to nineteenth-century standards, so new techniques had to be developed.
On routes with heavy traffic, flexible pavements were replaced by rigid pavements, in which the top layer was concrete, 15 to 30 centimetres thick, laid on a prepared bed. Nowadays steel bars are laid within the concrete. This not only restrains shrinkage during setting, but also reduces expansion in warm weather. As a result, it is possible to lay long slabs without danger of cracking.
The demands of heavy traffic led to the concept of high-speed, long-distance roads, with access - or slip-lanes - spaced widely apart. The US Bronx River Parkway of 1925 was followed by several variants - Germany’s autobahns and the Pan American Highway. Such roads - especially the intercity autobahns with their separate multi-lane carriageways for each direction - were the predecessors of today’s motorways.
Bridges
The development by the Romans of the arched bridge marked the beginning of scientific bridge-building; hitherto, bridges had generally been crossings in the form of felled trees or flat stone blocks Absorbing the load by compression, arched bridges are very strong. Most were built of stone, but brick and timber were also used. A fine early example is at Alcantara in Spain, built of granite by the Romans in AD 105 to span the River Tagus. In modern times, metal and concrete arched bridges have been constructed. The first significant metal bridge, built of cast iron in 1779, still stands at Ironbridge in England.
Steel, with its superior strength-to-weight ratio, soon replaced iron in metal bridge-work. In the railway age, the truss (or girder) bridge became popular. Built of wood or metal, the truss beam consists of upper and lower horizontal booms joined by vertical or inclined members.
The suspension bridge has a deck supported by suspenders that drop from one or more overhead cables. It requires strong anchorage at each end to resist the inward tension of the cables, and the deck is strengthened to control distortion by moving loads or high winds. Such bridges are nevertheless light, and therefore the most suitable for very long spans. The Clifton Suspension Bridge in the UK, designed by Isambard Kingdom Brunei (1806—59) to span the Avon Gorge in England, is famous both for its beautiful setting and for its elegant design. The 1998 Akashi Kaikyo Bridge in Japan has a span of I 1,991 metres, which is the longest to date.
Cantilever bridges, such as the 1889 Forth Rail Bridge in Scotland, exploit the potential of steel construction to produce a wide clearwater space. The spans have a central supporting pier and meet midstream. The downward thrust, where the spans meet, is countered by firm anchorage of the spans at their other ends. Although the suspension bridge can span a wider gap, the cantilever is relatively stable and this was important for nineteenth-century railway builders. The world’s longest cantilever span - 549 metres - is that of the Quebec rail bridge in Canada, constructed in 1918.
Call for Online Essays to Beat Internet Cheats
Jane Richardson
Academics are being encouraged to require all students to submit their essays and assignments electronically, to make it easier to beat web cheats at their own game. The University of Melbourne's academic board has approved a tough university-wide attack on the contemporary plague of electronic plagiarism. The Melbourne action follows other moves nationally that indicate the extent of university anxiety about online cheating in an era when a 'whatever you can get away with' attitude often prevails. The Australian Vice-Chancellors Committee is assessing plagiarism software that can detect whether student work has been downloaded in part or entirely from the net. And an Australian Universities Teaching Committee project is investigating the scale of the problem and issues in the online assessment of student work. The Melbourne academics want the university to set up its own anti-plagiarism website with constantly updated information on electronic checking software and an essay bank for cross-checking. The academic board's report on plagiarism says Melbourne has not tried to quantify the extent of electronic cheating, but states that it clearly exists and has the potential to undermine confidence in student assessment. | The board says that despite existing anti-cheating strategies, such as regular rewording of questions and changes to required reading and research, the problem of electronic plagiarism is acute where large numbers of students are doing the same exercise or where students are able to submit essays on questions of their own choice. The board's report lists existing plagiarism-detection methods such as the University of California's commercial website (www.plagiarism.org) where lecturers pay to have student essays checked against each other and a database of student papers and web materials. But Melbourne's academics believe it is possible for students to rephrase and restructure material to beat this type of system. 'Moreover, there is an increasing sophistication of electronic translators which paraphrase plagiarised material, hence making its detection more difficult,' the report says. 'This solution potentially requires the instructor to check up to five websites for each essay: a not insignificant task where large classes are concerned.' The Melbourne academics believe the knowledge that student work will be checked on cheat-detector websites will help to deter cheats. | The report says a holistic rather than 'catch and punish' approach works best and it sets out procedures and penalties for students caught cheating, ranging from redoing the assignment to facing academic misconduct charges. Melbourne's head of computer science Leon Sterling said yesterday electronic cheating was an issue in computer science departments worldwide. 'Sometimes people just don’t pose programming assignments because they worry it's too easy to copy. We think that’s the wrong way to teach. But we regularly run comparison software to check if students' assignments are similar,' he said. Professor Sterling's department already requires students to submit work electronically. He said it was often small, telltale signs that gave away the plagiarism-abnormal spacing, or changing the names of variables, but then including comment that referred to the old names. Professor Sterling said the university was making it clear to students that 'just taking someone's file, editing it and submitting it as your own isn't acceptable to us here'. |
Much ado about almost nothing
The public outcry over genetically modified foods offers several lessons for those working and investing in nanotechnology.
(1) "The time for discussion of the rights and wrongs of GM crops has passed. Intense and consistent economic sabotage and intimidation are what will make the commercialisation of GM crops an unattractive option."
(2) Words like these, from an article in the current edition of Earth First!, a radical environmental journal, send shivers down the spines of those involved in commercialising biotechnology. The strength of public disapproval of genetically modified organisms (GMOs) was a shock and a surprise to most of those involved. Now, some people are wondering whether nanotechnology - a term that covers the manipulation of matter at scales of a millionth of a millimetre - could be in for similar treatment and, if so, whether there are lessons that its protagonists can learn from the public backlash against biotechnology.
Profit of doom
(3) In a neglected corner, amid thousands of participants at a Nanotech conference held in Boston last week, Jeffrey Matsuura, a law professor at the University of Dayton, in Ohio, stood next to his unprepossessing poster of his work. His warning, however, was pertinent to everyone there - especially the investors who were scouring the conference for opportunities. And this is that several of the factors that created a public backlash against biotechnology are already at work within nanotechnology.
Dr. Matsuura says that biotechnologists assumed that the public would quickly recognise and appreciate biotech's potential for improving the quality of life. Instead, the risks captured the attention of the media and much of the general public. Well-fed European consumers met the suggestion of cheaper food, in particular, with scepticism. Many felt that the gains would accrue to the companies which had developed GMOs, while the risks of growing and consuming the crops would be taken on by the public.
(4) Dr. Matsuura believes that public perception of nanotechnology is developing along a similar track. Like those of biotechnology, the first applications of nanotechnology will bring little obvious benefit to consumers. Better, cheaper materials, and hidden manufacturing efficiencies that benefit producers first, are redolent of the 'advantages' of biotech - namely reduced applications of agricultural chemicals, which help to keep the cost down while raising yields. Obvious consumer benefits, such as improvements in medicine, are further away.
(5) This should not matter - consumers do benefit eventually, even from cost savings. And yet, in alliance with a feeling that there are hazards involved, an absence of immediate benefits could turn public opinion against nanotech quite rapidly. And potential hazards there are. Concerns over out-of-control, self - replicating 'nanobots' that would eventually consume and transform the entire planet into a 'grey goo'are absurd. And yet, it is true that novel 'nanoparticles' might have real toxicological risks.
(6) Nanoparticles are so small that, if inhaled, they could become lodged in the lungs. In theory, they are small enough to enter living cells and accumulate there. And in January Ken Donaldson, a professor of respiratory toxicology at the University of Edinburgh, told a Royal Institution seminar in London that, once inhaled, ultrafine carbon particles can move to the brain and blood.
(7) There are already several products that use nanoparticles already on the market, such as sunscreen and car parts. Though all this may sound alarming, people are already exposed to nanoparticles of many different kinds, and have been throughout history. Soot, for example, is composed of carbon nanoparticles. Nevertheless, nanoparticles from sources such as diesel soot, welding fumes and photocopier toner are already associated with ill-health.The prospect of more such particles is likely to worry many. No wonder that several people at the conference in Boston mentioned the need to address public fears over nanotechnology "aggressively".
(8) One of these was Clayton Teague, the director of America's National Nanotechnology Co-ordination Office. He says the American government is as sensitive to any indication of true health risk as any member of the public. Several large and well-funded studies on the environmental and health risks of nanotechnology are now under way.
(9) Dr. Teague adds that any decisions about nanotechnology will be made carefully and based on solid scientific data. But even if science gives the go-ahead, another one of Dr Matsuura's lessons is that this might not necessarily win the day, and that fear over potential abuses and accidents may dominate the debate.
(10) One piece of advice Dr. Matsuura gives is that everyone involved should have a consistent message. If investors are told a technology will change the world, someone who is concerned about the risks cannot then be told that the same technology is no big deal. It strikes a false note to say that something can be both revolutionary and nothing to worry about, he says. Such inconsistencies will breed public mistrust and fear.
Product placement
(11) Donald Reed is a senior consultant with Ecos, a business-advisory firm based in Sydney, Australia, that acts as an intermediary between corporations and activists. Mr Reed goes as far as to recommend that companies think about the early products they choose to pursue - in particular, whether they can demonstrate the "societal value" of these products. For example, it might be worth emphasising that one of the early products of nanotechnology could be cheap and efficient photovoltaic materials, which are used to generate electricity from sunlight.