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PostSubject: , Ernest Mercadier[   , Ernest Mercadier[ Icon_minitimeSat Dec 11, 2010 1:01 pm

Harmonic telegraph
Mechanical filter design was developed by applying the discoveries made in electrical filter theory to mechanics. However, a very early example (1870s) of acoustic filtering was the "harmonic telegraph", which arose precisely because electrical resonance was poorly understood but mechanical resonance (in particular, acoustic resonance) was very familiar to engineers. This situation was not to last for long; electrical resonance had been known to science for some time before this, and it was not long before engineers started to produce all-electric designs for filters. In its time, though, the harmonic telegraph was of some importance. The idea was to combine several telegraph signals on one telegraph line by what would now be called frequency division multiplexing thus saving enormously on line installation costs. The key of each operator activated a vibrating electromechanical reed which converted this vibration into an electrical signal. Filtering at the receiving operator was achieved by a similar reed tuned to precisely the same frequency, which would only vibrate and produce a sound from transmissions by the operator with the identical tuning.[8][9]
Versions of the harmonic telegraph were developed Elisha Gray, Alexander Graham Bell, Ernest Mercadier[n 2] and others. Its ability to act as a sound transducer to and from the electrical domain was to inspire the invention of the telephone.[8][9]
[edit]Mechanical equivalent circuits
Once the basics of electrical network analysis began to be established, it was not long before the ideas of complex impedance and filter design theories were carried over into mechanics by analogy. Kennelly, who was also responsible for introducing complex impedance, and Webster were the first to extend the concept of impedance into mechanical systems in 1920.[10] Mechanical admittance and the associated mobility analogy came much later and are due to Firestone in 1932.[11][12]
It was not enough to just develop a mechanical analogy. This could be applied to problems that were entirely in the mechanical domain, but for mechanical filters with an electrical application it is necessary to include the transducer in the analogy as well. Poincaré in 1907 was the first to describe a transducer as a pair of linear algebraic equations relating electrical variables (voltage and current) to mechanical variables (force and velocity).[13] These equations can be expressed as a matrix relationship in much the same way as the z-parameters of a two-port network in electrical theory, to which this is entirely analogous:

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PostSubject: Re: , Ernest Mercadier[   , Ernest Mercadier[ Icon_minitimeThu Dec 16, 2010 1:29 pm

Turkey tries army officers over Sledgehammer 'plot'

By Jonathan Head
BBC News, Istanbul

Officers allegedly plotted to blow up mosques and provoke clashes with historic rival Greece
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Turkey's religious-secular divide
Turkish military at uncomfortable crossroads
Latest Turkish 'plot' trial opens
A trial of nearly 200 retired and serving military officers has begun near Istanbul.

They face charges of plotting to bring down the government of the Islamically rooted Justice and Development Party seven years ago.

The alleged conspiracy, one of several being investigated, has divided opinion in Turkey.

The armed forces say that the plot was no more than a seminar to discuss hypothetical scenarios.

Twenty-eight serving generals or officers of equivalent rank are among those in the dock, and the trial could go on for months.

Thousands of documents confiscated from military bases will be used by prosecutors in this trial to try to prove their charge that the plan drafted in 2003, code-named Sledgehammer, was a real plot to bring down the government.

Some of the documents - which have been published by Turkish newspapers - describe dramatic schemes to plant bombs in mosques and provoke clashes with the Greek air force, allegedly to justify a military takeover.

But this is only the latest of a series of alleged anti-government conspiracies so confusing that few people are able to make sense of them.

Continue reading the main story

June 2007: Cache of explosives discovered; ex-soldiers detained
July 2008: 20 arrested, including two ex-generals and a senior journalist, for "planning political disturbances and trying to organise a coup"
July 2008: Governing AK Party narrowly escapes court ban
October 2008: 86 go on trial charged with Ergenekon coup plot
July 2009: 56 in dock as second trial opens
Nov 2009: Taraf newspaper reports "cage" plot, arrests begin
Jan 2010: Taraf reports 2003 Sledgehammer plot
Feb 2010: More than 40 officers arrested over Sledgehammer plot; several charged
December 2010: 196 current or former officers go on trial over Sledgehammer plot
One, known as Ergenekon, has already put more then 400 people on trial, in hearings that have lasted for over two years.

People here tend to judge the truth of these conspiracies according to whether they support or mistrust the governing party, which has been in power for eight years and is on track to win a third election victory next year.

It has long been at odds with the military and the judiciary, but now appears to be winning the upper hand, following September's referendum that approved its proposals for constitutional and judicial reform.

One of the judges who was supposed to hear the Sledgehammer case was removed by the recently restructured judicial supervisory board earlier this week.

And while the once-powerful armed forces commanders have at times complained about their colleagues being put on trial, the fact that they have done nothing else has convinced many Turks that the era of military intervention in politics is now over.

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