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Posts : 24
Join date : 2010-12-03
|Subject: inductors, capacitors Sat Dec 11, 2010 12:58 pm|| |
The symbols x, t, and a represent their usual quantities; distance, time, and acceleration respectively.
The mechanical quantity compliance, which is the inverse of stiffness, can be used instead of stiffness to give a more direct correspondence to capacitance, but stiffness is used in the table as the more familiar quantity.
The scheme presented in the table is known as the impedance analogy. Circuit diagrams produced using this analogy match the electrical impedance of the mechanical system seen by the electrical circuit, making it intuitive from an electrical engineering standpoint. There is also the mobility analogy,[n 1] in which force corresponds to current and velocity corresponds to voltage. This has equally valid results but requires using the reciprocals of the electrical counterparts listed above. Hence, M → C, S → 1/L, D → G where G is electrical conductance, the inverse of resistance. Equivalent circuits produced by this scheme are similar, but are the dual impedance forms whereby series elements become parallel, capacitors become inductors, and so on. Circuit diagrams using the mobility analogy more closely match the mechanical arrangement of the circuit, making it more intuitive from a mechanical engineering standpoint. In addition to their application to electromechanical systems, these analogies are widely used to aid analysis in acoustics.
Any mechanical component will unavoidably possess both mass and stiffness. This translates in electrical terms to an LC circuit, that is, a circuit consisting of an inductor and a capacitor, hence mechanical components are resonators and are often used as such. It is still possible to represent inductors and capacitors as individual lumped elements in a mechanical implementation by minimising (but never quite eliminating) the unwanted property. Capacitors may be made of thin, long rods, that is, the mass is minimised and the compliance is maximised. Inductors, on the other hand, may be made of short, wide pieces which maximise the mass in comparison to the compliance of the piece.
Posts : 73
Join date : 2010-09-22
|Subject: Re: inductors, capacitors Thu Dec 16, 2010 1:30 pm|| |
Australia launches criminal probe into asylum shipwreck
The BBC's Nick Bryant said bad weather had caused particularly rough seas
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The human face of asylum debate
In pictures: Christmas Island sinking
The 'toxic' asylum issue
Australia is launching a criminal investigation into the Christmas Island shipwreck that killed at least 28 people, under people trafficking laws.
Prime Minister Julia Gillard said more bodies may be pulled from the sea after a boat carrying suspected asylum seekers crashed into jagged rocks.
She said the boat may have been carrying more than the 70 passengers originally thought.
Forty-two people were rescued from the heavy surf after the boat broke apart.
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BBC News, Sydney
Australia's asylum seeker debate is often conducted as if the people heading for its shores were an abstraction, with the term "boat people" almost shorn of its human meaning.
With such harrowing images from Christmas Island broadcast on early evening news shows, millions of Australians would have seen the anguished faces of those seeking to reach its shores, and witnessed the lengths to which they would go to get there. Put simply, it was shockingly real.
Tabloid sensationalism in Australia is normally turned against the asylum seekers. They are often regarded as "queue jumpers", unwilling to go through the normal channels to seek asylum. Asylum seekers arriving by plane do not attract the same attention, nor what refugee groups would call the same paranoiac reaction.
The disaster has already escalated the boat people debate, although the country's politicians have temporarily called a truce in respect for the dead. Whatever its outcome, after the tragedy on Christmas Island the debate has a human face.
Australia's asylum debate
"We do not know with any certainty how many people there were on the boat so we've got to prepare ourselves for the likelihood that more bodies will be found and that there has been further loss of life than we know now with the numbers available to us," said Ms Gillard.
Immigration Minister Chris Bowen said as many as 100 people may have been on board - some 30 more than originally believed.
The passengers of the flimsy wooden boat are believed to have been asylum seekers making their way to Australia via Indonesia.
The route of the vessel and the identity of who organised the journey are still unclear.
In recent years increasing numbers of people from countries such as Sri Lanka, Iran, Iraq and Afghanistan have been making their way to Australia in boats organised by people smugglers.
"It is an evil trade," said Ms Gillard. "But I believe Australians are responding to these events today as human beings."
The policy of how to handle immigration remains a sensitive one in Australia and Ms Gillard called on the opposition to join a bipartisan inquiry into the tragedy.
Julia Gillard: "We have got to prepare ourselves for the likelihood that more bodies will be found"
Ms Gillard's Labor Party only won a second term in August after securing the support of the Greens and independents.
Both the Greens and independent MP Rob Oakeshott have again called for a softer line on asylum policy.
Questions have been asked about how the boat managed to elude the Australian agencies charged with watching the country's sea approaches.
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Named by British sailor William Mynors, who sailed past on Christmas Day 1643
Annexed by British Crown in 1888, administered from Singapore
Australia paid Singapore £2.9m in compensation for the island in 1957
Australia opened its A$400m detention centre in 2006, and it now houses nearly 3,000 asylum seekers
Population of about 1,300, more than half of whom are ethnic Chinese
Christmas Island lies in the Indian Ocean about 2,600km (1,600 miles) from the Australian mainland, but only 300km south of Indonesia.
The boat approached the island early on Wednesday. The alarm was raised when residents heard the passengers' screams as heavy seas propelled the vessel onto the island's rocky shoreline.
Witnesses said the boat was smashed to pieces within an hour and survivors struggled to hang on to pieces of wreckage in the pounding surf.
It is believed the engine on the vessel failed, and island residents said the seas were the heaviest they had seen in months.
One resident, Simon Prince, told Associated Press: "The engine had failed. They were washing backward and forward very close to the cliffs here, which are jagged limestone cliffs, very nasty.
"When the boat hit the cliff there was a sickening crack. All the people on board rushed to the land side, which is the worst thing they could do."
Ms Gillard said the "extreme weather conditions" meant the boat was not detected "until seen from Christmas Island itself".
"In very rough and dangerous seas there is a limit to what can be achieved through radar and other surveillance mechanisms," she said.
Christmas Island is home to a detention centre housing nearly 3,000 asylum seekers who are waiting for their claims to be processed.
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