Д о п о л н и т е л ь н ы е т е к с т ы
The history of carries goes back almost as far as airplanes. In 1910, only seven years after Orville Wright made the first machine-powered flight, naval aviators began experiments taking off from and landing on battleships. Carriers played a small role in World War 2 and since 1945 they have been involved in almost all major US military operations.
At present, only ten countries possess carries but the super carriers, or flattops, of the US Navy are the biggest in the world. With a crew of up to 6,000 people onboard, and with a length from bow to stern the size of three football pitches, the nuclear-powered Nimitz carriers can transport up to 80 aircraft, launch or land a plane every 25 seconds and generate between 140 and 160 sorties per day. A speed of more than 35 knots per hour, approximately 700 nautical miles per day, gives the United States the ability to deploy military forces to almost anywhere in the world in less than two weeks.
Carries are open to attack from enemy ships, missiles and aircraft. From this reason, carries are always escortedby a flotilla of other ships, called the carrier battle group (GBG). The GBG is capable of carrying out anti-aircraft, anti-submarine and anti-surface defence warfare. Although the GBG is formed according to the mission, a typical formation includes: the aircraft carrier, two guided-missile cruisers; two destroyers; one frigate; two submarines and a supply ship.
An aircraft carries is a type of warships fitted with a runway or flight deck which is used to launch and recover planes. The hull of the carrier is made of extremely strong steel plates. Below the waterline the hull is rounded and narrow but above the waterline the hull gets wider and forms the flight deck. When not in use, aircraft are secured in the hangar bay, located two decks below the flight deck. The aircraft are then lifted from the hangar bay to the flight deck by the elevator.
The flight deck is not long enough for most planes to make an ordinary takeoff, so they are launched with a machine. To prepare for launching an aircraft, the carrier sails into wind. This manoeuvre reduces the plane's minimum take off the speed by getting the wind moving over the flight deck and over plane's wings. A steam- powered catapult is then used for launching the aircraft. The power for the catapult comes from the carrier's nuclear reactor and the catapult is able to accelerate the aircraft from 0 to 240 kph in two seconds.
The flight deck only has about 150 metres of runway space for launching which is not enough for high-speed jets, so aircraft land in process known as an arrested landing. Thick metal cables, or arresting wires are stretched across the deck and the pilot's arm when he lands is to catch the cable with the tailhook - a long hook attached to the plane's tail. This system can stop 24.5 -ton aircraft travelling at 241 kph in a 96-metre landing area in only two seconds.
Cryptography's role has traditionally been to preserve the privacy of messages; to keep secrets hidden from prying eyes. But today's cryptography is more than secret writing, more than encryption and decryption. According to Merrill, today's concept of message security involves the fulfillment of five different objectives:
1. Confidentiality - to keep the contents of a massage secret so that the sender and receiver have the exclusive knowledge of it.
2. Authentication - to positively identify the origin of the message so that impersonation, known in techno-speak as spoofing, is not possible.
3. Message Integrity - to ensure that the message has not been modified in transit, whether by innocent computer glitch or malicious tampering by third parties.
4. Non-Repudiation - to provide assurance of the origin or delivery of data in order to protect the sender against false denial by the recipient that the data has been received, or to protect the recipient against false denial by the sender that the data has been sent.
5. Time-Date Stamping - the ability to accurately determine the time and date when the message was created, sent and/or received.
The objectives above are not new. Business people and lawyers in ordinary paper-based society have been applying such principles for many years in order to protect the sanctity of their transactions. It is now just a matter of using technological measures, such as cryptography, to achieve the same objectives in the virtual world. As commerce becomes more sophisticated, the role of cryptography in securing the information society follows accordingly. Recognizing this, the OECD defines cryptography as, "The discipline which embodies principles, means and methods for the transformation of data in order to hide its information content, establish its authenticity, prevent its undetected modification, prevent its repudiation, and/or prevent its unauthorized use". This is the new paradigm of cryptography and the foundation of digital signatures.
adjust (v) - приводить в порядок
adjustable (adj) - регулируемый, настраиваемый
alter (v) - измерять, менять, видоизменять
alteration (n) - изменение, перестройка, перемена, переделка
alternation (n) - чередование, периодическое изменение
amplitude (n) - диапазон, размах, полнота, амплитуда
board (n) - панель прибора, плата, борт ( корабля)
carrier (n) - носитель (заряда)
carrier wave (n) - несущая волна
comparatively (adj) - сравнительно
compare (v) - сравнивать
component (n) - составная часть
consist of (v) - состоять из
contain (v) - содержать, вмещать
cycle (n) - полный круг, цикл, период
desire (v) - желать, просить, требовать
desirable (adj) - желательный, подходящий
eliminate (v) - устранять, исключать
emerge (v) - появляться, показываться, возникать
employ (v) - использовать, применять, предоставлять работу, нанимать
explore (v) - исследовать, изучать, разведывать
exploration (n) - исследование, изучение, разведка, выявление
include (v) - включать, охватывать. иметь в своем составе
instantaneous (adj) - мгновенный, моментальный
intelligible (adj) - понятный, ясный, четкий, вразумительный
intense (adj) - сильный, значительный. интенсивный
intensity (n) - интенсивность, напряженность,
intensify (v) - усиливать
interfere (v) - мешать. служить препятствием
interference (n) - помехи, вмешательство
involve (v) - включать, содержать, подразумевать
ionosphere (n) - ионосфера
length (n) - длина, расстояние, долгота
line-of-sight (n) - зона прямой видимости
modify (v) - видоизменять
modification (n) -видоизменение
modulate (v) - модулировать; amplitude modulated signal - смодулированный по амплитуде сигнал
modulation (n) - модуляция
module (n) - элемент конструкции
motion (n) - движение, ход
prevent (v) - предотвратить, помешать
propagate (v) - распространять
proper (adj) - правильный, надлежащий
reflect (v) - отражаться, отражать
reflection (n) - отражение
range (n) - ряд, цепь, область, круг, сфера, зона, спектр, радиус действия
range (v) - выстраивать в ряд, располагать в порядке,
ranging (n) - измерение дальности, регулирование диапазона
retain (v) - удерживать, поддерживать, сохранять
return (n) - возвращение, отдача
series (n) - ряд, группа
sensitivity (n) - чувствительность, восприимчивость
sideband (n) - боковая полоса частот
transducer (n) - датчик
tube (n) - электронно-лучевая трубка
tuner (n) - механизм настройки
typical (adj) - типичный
variable (adj) - изменчивый, непостоянный
variation (n) - изменение, колебание, разновидность
variety (n) - разнообразие, ряд. множество
various (adj) - различный, разнообразный, разный
vary (v) - меняться, отличаться
vehicle (n) - средство передвижение, носитель, проводник
yield (v) - производить, являться причиной, вызывать
modify (v), modification (n)
(I) A most important phenomenon in nature is known to be the transmission1 of energy from one point to another by means of what is called “wave motion”. To understand this kind of motion precisely2 means to understand the principles underlying radio technique.
Radio communication is accomplished3 by means of propagation4 of radio waves. We must therefore try to understand what a wave is. For this purpose let us consider what happens5 if we drop a stone into still water. The surface of the water becomes covered with waves and these travel away from the splash in ever6 widening circles7. The water does not move outward from the central point (though it seems8 to do it), but it rises and then falls again. To be more exact, the particles of water are vibrating9 relative to their former position in the vertical plane. These vibrations spread10 further outward on the surface of the water. Motions of this kind are called wave motions.
There are different kinds of waves, such as heat waves, sound11 waves, light waves, radio waves, etc.
Consider a radio wave. Essentially a radio wave is not different from any other kind of wave as it is a sine12 wave. But a radio wave is found to travel long distances and can penetrate13 non-metallic objects. It travels at the speed of light, namely 186,000 miles per second.
(II) Because of the above-mentioned phenomena transmission through space became possible. If we want some information to be sent rapidly, we send it by radio. Radio allows us to communicate over long distances and there is hardly14 a locality15 outside the range of at least one powerful transmitting station.
What causes16 waves to appear?
Radio waves are caused by the to-and-fro surges of an alternating17 current in a conductor. These to-and-fro surges set up in the conductor are called electromagnetic waves, because they consist of electric and magnetic force components. When these electromagnetic waves escape18 from the conductor into space they are said to be radiated19 by the conductor, hence20 the name radio waves.
The number of complete vibrations in a unit of time is known as the frequency21 of the motion. If the number of waves per second is small such a wave is called a low-frequency wave, if the number of waves is great, the frequency will be higher.
The wavelength is the distance the wave will travel in the time required for one complete vibration. To find the wavelength one must know the frequency of the wave. It can be found from the relation: velocity equals frequency multiplied22 by wavelength (v = f ). Hence low-frequency waves have long wavelength, while high-frequency waves have short wavelength.
The shortest possible radio waves are found to be approximately23 several millimeters long. When short waves are sent out and meet an obstacle24 they are reflected25. This quality of radio waves can be used for many purposes.
Originally26 radio was brought into use to communicate with ships and then it gradually became the best means of communication. At the present time radio devices are being used to detect27 at distances, formerly considered impossible, the presence of enemy planes, submarines and surface vessels28, and enable29 us to determine30 exactly their location. This method by means of which one can determine the position of objects is known to be radio location.
In the future radio waves are likely to be used to perform tasks which now seem to be improbable to many people.