Text E. Surface treatments of light alloys
Other than ferrous materials, the most widely used metals in race engines are aluminium and titanium. Magnesium comes some way down the pecking order (неофициальная иерархия), this having something to do with rules that deem magnesium not good for racing, although production engine manufacturers are very keen on it. The most common surface treatments applied to aluminium alloys are the anodising processes of which there is a great variety. Many of these are simply to improve the surface appearance of the material, and such thin-oxide films can be successfully dyed to produce some quite attractive coloured parts. Where race engines are used over long periods between rebuilds, thin anodised films can offer a very useful degree of corrosion resistance compared to untreated parts.
Thicker anodised surface treatments, called hard anodising, are rarely coloured but are more functional in bringing real improvements to the surface which go beyond corrosion resistance and improved aesthetics. The thicker oxidised layer allows aluminium parts to be used in more aggressive surface contact applications. By replacing a soft aluminium surface with one of aluminium oxide, which is much harder, problems such as cold welding (сварка) of aluminium to parts that are in contact with it can be eliminated (исключать, устранять). One common use of the process in race engines is on piston ring grooves (канавка поршневого кольца) to prevent ‘ring sticking’ (залипание, залегание компрессионного кольца, пригорание поршневых колец). Hard anodising processes can cause a significant decrease in endurance limit for aluminium alloys, although the percentage decrease depends both on the particular grade of aluminium and the hard anodising method being used. The porous nature of the thick anodised film allows it to be further treated with polymer materials such as PTFE (политетрафторэтилен, т.е. тефлон), giving a low coefficient of friction.
Anodising processes are also applicable to titanium, with thin oxides providing a degree of corrosion resistance and some attractive 'interference colour’ effects without the need to resort to dyed films. The anodising of titanium can help to prevent the serious problem of galling (задир, наволакивание металла, истирание), where surface seizure can result in sliding contacts under very low speeds and pressures. It finds particular use on special-purpose titanium studs (винт, болт, шпилька, штырь, цапфа) and threaded (thread – резьба) components for this reason.
Source: http://www.ret-monitor.com/articles/pdf/surface-treatments.pdf pages 47-48 Symbols: 2 133
ПР
Digital Signal Processing 1 (DSP)
Digital signal processing is one of the most powerful technologies that shape science and engineering in the twenty-first century. Revolutionary changes have already been made in a many fields: communications, medicine, radar and sonar2, music reproduction, oil prospecting, etc. Each of these areas has developed a deep DSP technology, with its own algorithms, mathematics3, and specialized techniques4. This combination of breadth and depth makes it impossible for any one individual to master all of the DSP technology that has been developed.
Digital Signal Processing is distinguished from other areas in computer science by the unique type of data it uses: signals. In most cases, these signals originate as sensory data from the real world: seismic vibrations, visual images, sound waves, etc. DSP is the mathematics, the algorithms, and the techniques used to manipulate these signals after they have been converted into a digital form.
The roots of DSP are in the 1960s and 1970s when digital computers first became available. Computers were expensive at that time, and DSP was limited to only a few applications. The first efforts were made in four key areas:
1) radar and sonar, where national security was at risk;
2) oil exploration, where large amounts of money could be made;
3) space exploration, where the data are irreplaceable5;
4) and medical imaging, where lives could be saved.
The personal computer revolution of the 1980s and 1990s caused new applications of DSP. Besides being used in military and government areas, DSP was suddenly offered by the commercial marketplace. Anyone who thought they could make money in the rapidly expanding field became suddenly a DSP vendor6. DSP reached the public in such products as: mobile telephones, compact disc players, and electronic voice mail.
Today, DSP is a basic skill7 needed by scientists and engineers in many fields. As an analogy, DSP can be compared to a previous technological revolution: electronics. In the field of electrical engineering nearly every scientist and engineer has some skill in basic circuit design. Without it, they would be lost in the technological world. DSP has the same future. (1862p.s)
Vocabulary
1)Digital Signal Processing – цифровая обработка сигнала
2)Sonar – гидролокация
3)mathematics – зд. математические символы
4)techniques – методы
5)irreplaceable – незаменимые
6)a vendor – продавец, торговец
7)skill – умение
I. Answer the question:
What bind of data does DSP manipulate?
a)Radiation coming from space.
b)Data used in military and government spheres.
c)Signals which originate in nature.
d)Sensory images produced by computers.
II. Decide which statement matches the text:
a)DSP is limited to only a few applications at present.
b)DSP does not have any commercial application.
c)DSP is one of the leading technologies of the nearest future.
d)DSP can never reach public.
III. Decide which statement does not match the text:
a)Any person is capable of gaining command of DSP.
b)DSP has altered a lot of spheres of science and technology.
c)DSP is vital in the matters of national defense.
d)DSP has been widely used in information technology since the 1980s.
IV. Decide which definitions match the following terms:
1.oil prospecting a) symbols used to write formulas
2.digital signal processing b) geological search of oil and gas fields
3.circuit design c) an area of electronics dealing with
production of integral circuits
4.mathematics d) turning sensory signals into a digital form
V. Fill in the gaps with the words from the list below:
skill, techniques, irreplaceable, mathematics, DSP, a vendor
1.The new device has proved __________________in our research programme.
2.We use a set of specialized __________________in our research.
3.Basie computer literacy is probably the main_________________ required in this activity.
4._____________________ is a universal language used by scientists and engineers in the rapidly developing area of digitization.
5._____________________ has originated as purely scientific technology, but it is widely offered by commercial market nowadays.
6.He has made his way up to the top manager of a well- known retail company, but he started his career as a street ___________________.
VI. Match the words in the right and left columns to make up a word expression from the text:
1.seismic a) design
2.commercial b) engineering
3.basic c) vibrations
4.circuit d) marketplace
5.electrical e) skill
6.revolutionary f) signals
7.sensory g) changes
Sonar
Sonar is an acronym1 for Sound Navigation and Ranging2. It is divided into two categories, active and passive. In active sonar, sound pulses between 2 kHz and 40 kHz are transmitted into the water, and the resulting echoes are detected and analyzed. Uses of active sonar include: detection and localization of undersea bodies, navigation, communication, and mapping the sea floor. A maximum operating range2 of 10 to 100 kilometers is typical. In comparison, passive sonar simply listens to underwater sounds, which includes: natural turbulence, marine life, and mechanical sounds from submarines and surface vessels. Since passive sonar emits no energy, it is ideal for covert3 operations. The most important application of passive sonar is in military surveillance systems4 that detect and track5 submarines. Passive sonar typically uses lower frequencies than active sonar because they propagate6 through the water with less absorption. Detection ranges2 can be thousands of kilometers.
Digital Signal Processing has revolutionized sonar in many of the same areas: pulse generation, pulse compression, and filtering of detected signals. On the one hand, sonar is simpler than radar because of the lower frequencies. On the other hand, sonar is more difficult than radar because the environment is much less uniform and stable. Sonar systems usually use many ways of transmitting and receiving elements, rather than just a single channel. By properly controlling and mixing the signals in these many elements, the sonar system can steer7 the emitted pulse to the desired location and determine the direction that echoes are received from. To handle these multiple channels, sonar systems require the same massive Digital Signal Processing computing power. (1497 p.s.)
Vocabulary
1)an acronym – аббревиатура, сокращение
2)Ranging – определение расстояния
operating range – диапазон действия
ranges – дальность, диапазон
3)covert – секретный
4)surveillance systems – разведывательные системы
5)to track – следить, преследовать
6)to propagate – распространяться
7)to steer – направлять
I. Answer the question:
What is the main application of passive sonar?
a)Detection and tracking of herds of fish.
b)Localization of dead civilizations.
c)Military tracking systems for binding submarines.
d)Location of underwater volcanoes.
II. Decide which statement matches the text:
a)A minimum operating range of 10 to 100 kilometres is typical of active sonar.
b)Low frequency sound pulses spread through the water with great absorption.
c)Sonar can only be used in unchangeable environments.
d)Passive sonar emits no radiation.
III. Decide which statement does not match the text:
a)Active sonar transmits sound waves into the water and listens to the echoes.
b)Passive sonar merely analyzes undersea sounds.
c)Detection ranges of passive sonar are very limited.
d)DSP has not had any influence on sonar.
IV. Decide which definitions match the following terms:
1.surveillance systems a) distance at which a system words
2.operating range b) military organization for collecting and
processing information
3.sonar c) sonic waves of different frequencies
4.sound pulses d) sound detection and tracking of various undersea
objects
V. Fill in the gaps with the words from the list below:
to track, operating range, covert, to steer, surveillance systems
1.____________________ of the new generation missile is 150-200 kilometres.
2.Computer crime is so common these days that it is hard ____________________ the culprit sometimes.
3.The whole team have worked undercover; no one has had the slightest idea of their ____________________ mission.
4.____________________ of this bind are extremely sophisticated and very expensive at present.
5.Usually built-in electronic equipment guides big ships in the ocean, but one needs a basic skill and a firm hand ____________________ to steer a smaller vessel.
VI. Match the words in the right and left columns to make up a word expression from the text:
1.surveillance a) ranges
2.detection b) (the) water
3.propagate through c) operations
4.undersea d) systems
5.covert e) bodies
6.natural f) turbulence
Radar
Radar is an acronym1 for Radio Detection and Ranging2. In the simplest radar system, a radio transmitter produces a pulse of radio frequency energy a few microseconds long. This pulse is fed into a highly directional antenna3, where the resulting radio wave propagates away4 at the speed of light. Aircraft in the path of this wave will reflect a small portion of the energy back toward a receiving antenna, situated near the transmission site. The distance to the object is calculated from the time between the transmitted pulse and the received echo. The direction to the object is found more simply; you know where you pointed the directional antenna when the echo was received.
The operating range5 of a radar system is determined by two parameters: how much energy is in the initial pulse, and the noise level of the radio receiver. Unfortunately, increasing the energy in the pulse usually requires making the pulse longer. In turn, the longer pulse reduces the accuracy and precision of the time measurement. This results in6 a conflict between two important parameters: the ability to accurately determine an object's distance.
Digital Signal Processing (DSP) has revolutionized radar in three areas. First, DSP can compress the pulse after it is received, providing better distance determination without reducing the operating range. Second, DSP can filter the received signal to decrease the noise. This increases the range, without degrading the distance determination. Third, DSP enables the rapid selection and generation of different pulse shapes and lengths. Among other things, this allows the pulse to be optimized for a particular detection problem. Now the impressive part: much of this is done at a rate comparable to the radio frequency used, as high as several hundred megahertz! (1591p.s.)
Vocabulary
1)an acronym – аббревиатура, сокращение
2)Ranging – определение расстояния
3)directional antenna – направленная антенна
4)to propagate away – распространяться
5)operating range – диапазон действия
6)to result in – приводить к чему-то
I. Answer the question:
What is the basic principle of radar operation?
a)An aircraft propagates away the radio pulse.
b)The directional antenna produces the radio pulse.
c)The radio transmitter emits the radio pulse concentrated and sent away by the directional antenna.
d)The distance to the object is calculated by the frequency of the reflected wave.
II. Decide which statement matches the text:
a)The radio pulse is fed directly into the aircraft which reflects it back.
b)The distance to the object is calculated from the time between the impulses propagated and reflected.
c)The more energy one puts into the pulse, the greater is the accuracy of time measurement.
d)The operating range of a radar is determined by two parametres: by the speed of the aircraft and by the wavelength of the impulse sent away.
III. Decide which statement does not match the text:
a)It is very simple to find the direction to the object: remember where you pointed the antenna.
b)One can make the pulse more powerful by making it longer.
c)The longer pulse increases the precision of time measurement.
d)The DPS system is equipped with a special filter to reduce the noise.
IV. Decide which definitions match the following terms:
1.propagate away a) distance at which a system works
2.radar b) a special device for concentrating a radio
impulse
3.operating range c) the system for radio location and ranging of the
object
4.directional antenna d) to transmit the energy impulse to the necessary
direction
V. Fill in the gaps with the words from the list below:
a radio transmitter, directional antenna, ranging, result in, compress
1.One of the most important parametres of any radar system is the accuracy and precision of _________________ .
2.It is not a problem to create a powerful source of energy, but only _________________ sends away a concentrated radio impulse.
3.A good efficient _________________ is the basic element of any radar system.
4.The ability of DSP _________________ the impulse _________________ the greater precision of ranging.
VI. Match the words in the right and left columns to make up a word expression from the text:
1.propagate a) measurement
2.directional b) in
3.time c) range
4.result d) site
5.transmission c) away
6.operating f) accuracy
7.reduce g) antenna
Computed Tomography
In 1895, Wilhelm Conrad Röntgen discovered that x-rays could pass through great amounts of matter. Medicine was revolutionized by the ability to look inside the living human body. Medical x-ray systems spread throughout the world in only a few years. In spite of its obvious success, medical x-ray imaging1 was limited by four problems until Digital Signal Processing2 appeared in the 1970s. First, overlapping3 structures in the body can hide behind each other. For example, portions of the heart might not be visible behind the ribs4. Second, it is not always possible to distinguish between similar tissues5. Third, x-ray images show anatomy, the body's structure, and not physiology, the body's operation. The x-ray image of a living person looks exactly like the x-ray image of a dead one! Fourth, x-ray exposure can cause cancer.
The problem of overlapping structures was solved in 1971 with the introduction of the first computed tomography. Computed tomography is a classic example of Digital Signal Processing. X-rays from many directions are passed through the section of the patient's body being examined. Instead of simply forming images with the detected x-rays, the signals are converted into digital data and stored in a computer. The information is then used to calculate images that appear to be slices6 through the body. These images show much greater detail than conventional techniques, allowing much better diagnosis and treatment. The impact of computed tomography was nearly as large as the original introduction of x-rays. Within only a few years, every major hospital in the world had access to computed tomography. In 1979, two of computed tomography' principle contributors, Godfrey N. Hounsfield and Allan M. Cormack, shared the Nobel Prize in Medicine.
The last three x-ray problems have been solved by using penetrating energy, such as radio and sound waves. Digital Signal Processing plays a key role in all these techniques. For example, Magnetic Resonance Imaging uses magnetic fields in conjunction7 with radio waves to probe the interior of the human body. (1780 p.s.)
Vocabulary
1)imaging – изображение
2)Digital Signal Processing – цифровая обработка сигнала
3)overlapping – частично совпадающие, частично
закрывающие
4)ribs – ребра
5)tissues – ткани
6)slices – части
7)in conjunction – вместе
I. Answer the question:
How is DSP used in computed tomography?
a)X- rays from only one direction are passed through a part of a human body.
b)Images formed by X- rays are stored in the computer.
c)Images formed by X- rays overlap each other giving a clear view of the patient's body.
d)Images formed by X- rays are converted into digital data and stored in the computer.
II. Decide which statement matches the text:
a)X-ray images show the clear distinction between the body of a living person and a dead one.
b)X-ray images always show the clear distinction even between very similar tissues.
c)DSP allows to calculate the digitized images of human body processed by a computer.
d)The two contributors of a computer tomography principle have never gained any recognition.
III. Decide which statement does not match the text:
a)X-ray imaging is very simple due to the fact that there are no overlapping structures within our body.
b)X-ray imaging does not show the details of the body's operation.
c)X-ray exposure is extremely dangerous for a human body.
d)It was quite easy for the major hospitals to gain access to computed tomography.
IV. Decide which definitions match the following terms:
1.tissues a) long parallel bones in the upper part of a body
2.ribs b) crossing each other, intersecting
3.DSP c) turning sensory signals into a digital form
4.overlapping d) soft structures of a body
V. Fill in the gaps with the words from the list below:
physiology, slices, computed, tomography, anatomy,
to calculate, overlapping
1.Digitized information is stored in the computer and then used ________________ the images of the living organism.
2._______________________ allows better diagnosis and treatment.
3.X- ray imaging gives a full picture of human________________ , the structure, not of its ________________, the work of the body.
4.Computed tomography allows us to see the difference between _________________ organs and ________________of the body.
VI. Match the words in the right and left columns to make up a word expression from the text:
1.cause a) structures
2.overlapping b) fields
3.X- ray c) tomography
4.magnetic d) cancer
5.computed e) data
6.digital f) images
7.calculate g) exposure
Telecommunications
Telecommunications is transferring information from one location to another. It includes many forms of information: telephone conversations, television signals, computer files, and other types of data. To transfer the information, you need a channel between the two locations. This may be a wire pair, radio signal, optical fiber, etc. Telecommunications companies receive payment for transferring their customer's information, while they must pay to establish and maintain the channel. The financial strategy of the company is simple: the more information they can pass through a single channel, the more money they make. Digital Signal Processing1 has revolutionized the telecommunications industry in many areas.
There are approximately one billion telephones in the world. At the press of a few buttons, any one may be connected to any other in only a few seconds. Until the 1960s, a connection between two telephones required passing the analog voice signals through mechanical switches and amplifiers. One connection required one pair of wires. In comparison, Digital Signal Processing converts audio signals into a stream of serial digital data. Thus, many telephone conversations can be transmitted on a single channel. For example, a telephone standard known as the T-carrier system can simultaneously transmit 24 voice signals. The financial advantage of digital transmission is enormous. Wire and analog switches are expensive; digital logic elements are cheap.
Echoes are a serious problem in long distance telephone connections. When you speak into a telephone, a signal representing your voice travels to the connecting receiver2, where a portion of it returns as an echo. If the connection is within a few hundred miles, the elapsed time3 for receiving the echo is only a few milliseconds. The human ear is usually hears echoes with these small time delays, and the connection sounds quite normal. As the distance becomes larger, the echo becomes rather noticeable4 and irritating. The delay can be several hundred milliseconds for intercontinental communications. Digital Signal Processing attacks this type of problem5 by measuring the returned signal and generating an appropriate antisignal to cancel6 the offending echo. (1922 p.s.)
Vocabulary
1)Digital Signal Processing – цифровая обработка сигнала
2)the connecting receiver – приемное устройство
3)the elapsed time – истекшее время, период времени
4)noticeable – заметный
5)attacks this type of problem – подходить к решению проблемы
6)to cancel – устранить
I. Answer the question:
How did DSP revolutionize telephone conversations?
a)A lot of analog voice signals pass through a lot of pairs of wires.
b)A lot of analog voice signals pass through a lot of mechanical switches and amplifiers.
c)Audio signals are converted into serial digital data and transmitted through a single channel.
d)A single audio signal can be transmitted through 24 channels.
II. Decide which statement matches the text:
a)The more information can be transmitted through a single channel, the more money the customers of the company make.
b)The T- carrier system allows to send 24 different audio signals through a single channel.
c)It is better to use wires and switches than serial digital data in telecommunications.
d)DSP converts voices into electrical impulses.
III. Decide which statement does not match the text:
a)Before the 1960 s, one pair of wires was used to send one analog voice signal to the receiver.
b)The two main tasks of telecommunication companies are transferring their customer's information and maintaining the channel.
c)DSP has made telecommunications cheaper.
d)DSP technology allows to convert audio signals into electric impulses.
IV. Decide which definitions match the following terms:
1.the elapsed time a) an impulse into which the audio signal turns
during the telephone conversation
2.DSP b) converting sensory signals into digital form
3.the analog voice signal c) to eliminate
4.to cancel d) a period of time during which the echo
travels back to the transmitter
V. Fill in the gaps with the words from the list below:
the analog voice signals a channel, advantage,
telecommunications, the connecting receiver
1.Establishing and maintaining __________________________ for transferring their clients’ information is the main task of ____________________________companies.
2.Before DSP, _______________________ were used in the telephone conversations instead of digital data.
3.__________________________usually returns apart of your voice signal as an echo.
4.DSP technology offers a financial ______________________ to telecom companies.
VI. Match the words in the right and left columns to make up a word expression from the text:
1.telecommunications a)fiber
2.optical b) signal
3.receive c) time
4.establish d) industry
5.audio e) the channel
6.elapsed f) strategy
7.financial g) payment
Laser
A laser is a device that emits light (electromagnetic radiation) through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation.The emitted laser light is notable for its high degree of spatial and temporal coherence, unattainable using other technologies.
Spatial coherence typically is expressed through the output being a narrow beam which is diffraction-limited, often a so-called "pencil beam." Laser beams can be focused to very tiny spots, achieving a very high irradiance. Or they can be launched into a beam of very low divergence in order to concentrate their power at a large distance.
Temporal (or longitudinal) coherence implies a polarized wave at a single frequency whose phase is correlated over a relatively large distance (the coherence length) along the beam. A beam produced by a thermal or other incoherent light source has an instantaneous amplitude and phase which vary randomly with respect to time and position, and thus a very short coherence length.
Most so-called "single wavelength" lasers actually produce radiation in several modes having slightly different frequencies (wavelengths), often not in a single polarization. And although temporal coherence implies monochromaticity, there are even lasers that emit a broad spectrum of light, or emit different wavelengths of light simultaneously. There are some lasers which are not single spatial mode and consequently their light beams diverge more than required by the diffraction limit. However all such devices are classified as "lasers" based on their method of producing that light: stimulated emission. Lasers are employed in applications where light of the required spatial or temporal coherence could not be produced using simpler technologies.
Terminology
The word laser started as an acronym for "light amplification by stimulated emission of radiation"; in modern usage "light" broadly denotes electromagnetic radiation of any frequency, not only visible light, hence infrared laser, ultraviolet laser, X-ray laser, and so on. Because the microwave predecessor of the laser, the maser, was developed first, devices of this sort operating at microwave and radio frequencies are referred to as "masers" rather than "microwave lasers" or "radio lasers". In the early technical literature, especially at Bell Telephone Laboratories, the laser was called an optical maser; this term is now obsolete.
A laser which produces light by itself is technically an optical oscillator rather than an optical amplifier as suggested by the acronym. It has been humorously noted that the acronym LOSER, for "light oscillation by stimulated emission of radiation," would have been more correct.With the widespread use of the original acronym as a common noun, actual optical amplifiers have come to be referred to as "laser amplifiers", notwithstanding the apparent redundancy in that designation.
The back-formed verb to lase is frequently used in the field, meaning "to produce laser light," especially in reference to the gain medium of a laser; when a laser is operating it is said to be "lasing." Further use of the words laser and maser in an extended sense, not referring to laser technology or devices, can be seen in usages such as astrophysical maser and atom laser.
Design
A laser consists of a gain medium inside a highly reflective optical cavity, as well as a means to supply energy to the gain medium. The gain medium is a material with properties that allow it to amplify light by stimulated emission. In its simplest form, a cavity consists of two mirrors arranged such that light bounces back and forth, each time passing through the gain medium. Typically one of the two mirrors, the output coupler, is partially transparent. The output laser beam is emitted through this mirror.
Light of a specific wavelength that passes through the gain medium is amplified (increases in power); the surrounding mirrors ensure that most of the light makes many passes through the gain medium, being amplified repeatedly. Part of the light that is between the mirrors (that is, within the cavity) passes through the partially transparent mirror and escapes as a beam of light.
The process of supplying the energy required for the amplification is called pumping. The energy is typically supplied as an electrical current or as light at a different wavelength. Such light may be provided by a flash lamp or perhaps another laser. Most practical lasers contain additional elements that affect properties such as the wavelength of the emitted light and the shape of the beam.
1. Answer the questions:
1.What way does the light go when laser is in action?
2.What process is called pumping?
3.What such light may be provided by?
4.What additional elements do practical lasers contain?
5.What acronym would have been more precise than” laser”?
2. Fill in the gaps:
1.A laser is technically…rather than…as suggested by the acronym.
2.… is frequently used in the field, meaning “to produce laser light.”
3.A beam … has an instantaneous amplitude and phase which … with respect to time and position.
4.Because … device of this sort operating at microwave and radio frequencies are referred to as “masers” rather than … or “radio lasers.”
5.Most so-called “single wavelength” lasers actually produce … in several modes having …, often not in a single polarization.
6.The gain medium is a material with properties that allow it ….
7.The energy is typically supplied as ….
8.… may be provided by a flash lamp or perhaps another laser.
3. Match parts of the notions:
1.Laser beams can be focused …
2.Most “single wavelength” lasers actually produce radiation in several modes …
3.The gain medium is a material with properties that …
4.A beam produced by a thermal or other incoherent light source …
5.A laser which produces light by itself …
6.The energy is typically supplied as …
a)has an instantaneous amplitude and phase which vary randomly.
b)is technically an optical oscillator rather than an optical amplifier.
c)to very tiny spots, achieving a very high irradiance.
d)having slightly different frequencies, often not in a single polarization allow it to amplify light by stimulated emission as light at a different wavelength
e)an electrical current or
4. Say what is true and what is false:
1.The energy is supplied as an electrical current or as light at the some wavelength.
2.Most lasers do not contain additional elements that affect properties such as the wavelength of the emitted light and the shape of the beam.
3.Water is a material with properties that allow laser to amplify light by stimulated emission.
4.There are some lasers which are not single spatial mode and their light beam diverge as much as required by the diffraction limit
5.Temporal coherence implies a polarized wave at a single frequency whose phase is correlated our relatively large distance along the beam.
Optical instruments
Single lenses have a variety of applications including photographic lenses, corrective lenses, and magnifying glasses while single mirrors are used in parabolic reflectors and rear-view mirrors. Combining a number of mirrors, prisms, and lenses produces compound optical instruments which have practical uses. For example, a periscope is simply two plane mirrors aligned to allow for viewing around obstructions. The most famous compound optical instruments in science are the microscope and the telescope which were both invented by the Dutch in the late 16th century.
Microscopes were first developed with just two lenses: an objective lens and an eyepiece. The objective lens is essentially a magnifying glass and was designed with a very small focal length while the eyepiece generally has a longer focal length. This has the effect of producing magnified images of close objects. Generally, an additional source of illumination is used since magnified images are dimmer due to the conservation of energy and the spreading of light rays over a larger surface area. Modern microscopes, known as compound microscopes have many lenses in them (typically four) to optimize the functionality and enhance image stability. A slightly different variety of microscope, the comparison microscope, looks at side-by-side images to produce a stereoscopic binocular view that appears three dimensional when used by humans.
The first telescopes, called refracting telescopes were also developed with a single objective and eyepiece lens. In contrast to the microscope, the objective lens of the telescope was designed with a large focal length to avoid optical aberrations. The objective focuses an image of a distant object at its focal point which is adjusted to be at the focal point of an eyepiece of a much smaller focal length. The main goal of a telescope is not necessarily magnification, but rather collection of light which is determined by the physical size of the objective lens. Thus, telescopes are normally indicated by the diameters of their objectives rather than by the magnification which can be changed by switching eyepieces. Because the magnification of a telescope is equal to the focal length of the objective divided by the focal length of the eyepiece, smaller focal-length eyepieces cause greater magnification.
Since crafting large lenses is much more difficult than crafting large mirrors, most modern telescopes are reflecting telescopes, that is, telescopes that use a primary mirror rather than an objective lens. The same general optical considerations apply to reflecting telescopes that applied to refracting telescopes, namely, the larger the primary mirror, the more light collected, and the magnification is still equal to the focal length of the primary mirror divided by the focal length of the eyepiece. Professional telescopes generally do not have eyepieces and instead place an instrument (often a charge-coupled device) at the focal point instead.
1. Answer the questions:
1.Why is additional source of illumination used in some cases?
2.What are the characteristic features of professional telescope?
3.Why do smaller focal-length eyepieces cause greater magnification?
4.What are the most famous compound optical instruments is science?
5.What does periscope consist of?
6.With what lenses were microscope first developed?
2. Fill in the gaps:
1.The objective lens of the telescope was designed with … to avoid optical aberrations
2.The larger the primary mirror, … .
3.Modern microscopes … to optimize the functionality and enhance image stability.
4.The comparison microscope looks … to produce a stereoscopic binocular view.
5.Since crafting large lenses is much more difficult then crafting large mirrors, most modern telescopes are … , that is, telescopes that use … rather than … .
3. Say what is false and what is true:
1.A periscope is two mirrors aligned to allow for viewing around obstructions.
2.Microscopes were first developed with four lenses.
3.Modern microscopes have few lenses in them to optimize the functionality and enhance image stability.
4.Because the magnification of a telescope is more than the focal length of the objective divided by the focal length of the eyepiece, smaller focal-length eyepiece causes greater magnification.
4. Match the halves of the sentences:
1.The main goal of a telescope is …
2.The absolute value for the exposure time required depends on …
3.Modern compound microscopes have many lenses in them …
4.A periscope …
5.Microscopes were first developed with two lenses …
6.The most famous compound optical instruments are …
7.The build of view changes …
8.This is any lens with a local length …
a)to optimize the functionality and enhance image stability.
b)is simply two plane mirrors.
c)the microscope and the telescope collection of light an objective lens and an eyepiece.
d)larger than the diagonal measure of the film or sensor.
e)how sensitive to light the medium is.
f)with the local length of the lens.
some extra texts to enjoy and ponder on
Text 1. In Space and On Earth, Why Build It,
When a Robot Can Build It for You?
Like something straight out of "Star Wars," armies of robots could nimbly be crawling up towers and skyscrapers to make repairs in the not-so-distant future, so humans don't have to.
That's just one thing researchers in Hod Lipson's Creative Machines Lab envision with their latest robot prototype. It can autonomously traverse and manipulate a 3-D truss structure, using specially designed gears and joints to assemble and disassemble the structure as it climbs. Lipson is an associate professor of mechanical and aerospace engineering, and of computing and information science at Cornell University.
The robot's design is detailed in a paper accepted by IEEE Robotics and Automation, to appear soon online and in print. Its co-authors include former visiting scientist Franz Nigl, former visiting Ph.D. student Shuguang Li, and undergraduate Jeremy Blum.
"What gets me most excited is this idea of safety," said Blum, a student researcher working on the project. Having a robot able to climb and reconfigure building structures, even just to deliver materials, would be a step toward making construction zones safer for humans, he said.
The researchers also point to space-exploration applications. Instead of sending astronauts out on a dangerous spacewalk at the International Space Station, a robot could be deployed to repair a damaged truss.
The robot is equipped with an onboard power system, as well as reflectivity sensors so it can identify where it is on the structure. This allows it to maneuver accurately without explicit commands, Blum added.
Lipson said he envisions transforming the built environment with the help of these kinds of technologies. Instead of making buildings out of concrete or other non-recyclable materials, components designed specifically for robots could be used to build or reconfigure structures more efficiently -- for example, after an earthquake, or if an outdated building needed to be torn down in favor of something better.
"Right now, we are very bad at recycling construction materials," Lipson said. "We are exploring a smarter way to allow the assembly, disassembly and reconfiguration of structures."
The project is part of a National Science Foundation Emerging Frontiers in Research and Innovation grant jointly awarded to Lipson at Cornell, Daniela Rus of the Massachusetts Institute of Technology, Mark Yim of the University of Pennsylvania, and Eric Klavins of the University of Washington.
Text 2. Controlling Light at Will: