Biodegradable mems. Vocabbox. A lot of machines made by physicists are used in medicine now, страница 3

The team sent the microwaves through a narrow ring-shaped slit and onto a large spherical mirror that focused the reflected waves beyond the source. The microwaves were modulated with rectangular pulses and were detected at various positions along the mirror axis, ranging from 30 - 140 cm from the source. By plotting the arrival time of the pulses versus distance, the team discovered that the microwaves travel up to 25% faster than the speed of light for distances less than a metre. Beyond one metre, however, the microwaves slowed down.

In a second experiment, Lijun Wang of the NEC Research Institute in Princeton, US, scientists  pushed the speed of an electromagnetic pulse to 300 times the speed of light by passing it through a chamber filled with optically excited caesium. Within the excited medium, the phase velocity can be negative – in other words, the waves that make up the pulse can travel backwards. The overall result is that the outgoing wave, travelling 300 times faster than the speed of light, can leave the chamber before the peak of the incoming wave has even arrived. Indeed, in the Princeton experiment the outgoing pulse travelled almost 20 metres before the incoming pulse reached the chamber. The results have been submitted to Nature.

Many physicists believe that causality has not been violated in the experiment because the peak of the incoming pulse was not pushed to superluminal speeds, only its leading edge. However, Ranfagni points out that there is no formal proof that an electromagnetic wavepacket cannot travel faster than the speed of light.

Comprehension check

Answer the following questions:

1.  What is one of the most fundamental laws in physics?

2.  What can travel faster than light? Over what distances?

3.  How much faster do the microwaves travel?

Discussion

Comment on the text using the following prompts: first of all... , secondly... , as I see it…, personally I feel..., I’m not sure about... , I’m convinced that... , I’d say... , I can’t side with the author….

Give your own project of making something travel faster than the speed of light.

UNIT 4

SUPERCONDUCTING  GAINS

Vocabbox

noun collocations

§  highly demanding applications

§  superconducting devices

§  large current amplification

§  negative current gain

§  quantum tunnelling

§  proximity effect

§  superconducting energy gap

verb collocations

§  make something attractive

§  amplify electrical current

§  exhibit current amplification

§  tunnel through the detector junction

Pre-reading task

1.  Superconducting materials are attractive for highly demanding applications. Do you agree? Give your examples.

2.  Before reading the text answer the following questions:

1)  What qualities make a superconducting device so attractive?

2)  How do you imagine the main parts of such a device?

3)  What application can it have today?

Reading

Read the text. Find some information about the main parts of a superconducting device and its operation.

Transistors are invariably made of semiconducting materials, but the special properties of superconducting materials make them attractive for some, highly demanding, applications. Indeed, physicists have been trying to build superconducting devices with transistor-like properties – in particular devices that can amplify electrical currents – for more than 20 years. Now Giampiero Pepe of the University of Naples in Italy and colleagues led by Antonio Barone, together with Norman Booth of Oxford University in the UK, Scientists have built a semiconducting device that exhibits large current amplification and other transistor-like properties. This device can also be operated to obtain negative current gain, which is not possible with semiconductor devices.