An internal-combustion engine is a heat engine that burns fuel and air inside a combustion
chamber located within the engine proper. Simply stated, a heat engine is an engine that
converts heat energy to mechanical energy. The internal- combustion engine should be
distinguished from the external- combustion engine, for example, the steam engine and the
Stirling engine, which burns fuel outside the prime mover, that is, the device that actually produces mechanical motion. Both basic types produce hot, expanding gases, which may then be employed to move pistons, turn turbine rotors, or cause locomotion through the reaction principle as they escape through the nozzle.
Most people are familiar with the internal-combustion reciprocating engine, which is used to
power most automobiles, boats, lawn mowers, and home generators. Based on the means of
ignition, two types of internal-combustion reciprocating engines can be distinguished:
spark-ignition engines and compression-ignition engines. In the former, a spark ignites a
combustible mixture of air and fuel; in the latter, high compression raises the temperature of the
air in the chamber and ignites the injected fuel without a spark. The diesel engine is a
compression-ignition engine. This article emphasizes the spark-ignition engine.
The invention and early development of internal-combustion engines are usually credited to
three Germans. Nikolaus Otto patented and built (1876) the first such engine; Karl Benz built
the first automobile to be powered by such an engine (1885); and Gottlieb Daimler designed the
first high-speed internal-combustion engine (1885) and carburetor. Rudolf Diesel invented a
successful compression-ignition engine (the diesel engine) in 1892.
The operation of the internal-combustion reciprocating engine employs either a four-stroke
cycle or a two-stroke cycle. A stroke is one continuous movement of the piston within the
cylinder.
In the four-stroke cycle, also known as the Otto cycle, the downward movement of a piston
located within a cylinder creates a partial vacuum. Valves located inside the combustion
chamber are controlled by the motion of a camshaft connected to the crankshaft. The four
strokes are called, in order of sequence, intake, compression, power, and exhaust. On the first
stroke the intake valve is opened while the exhaust valve is closed; atmospheric pressure forces a
mixture of gas and air to fill the chamber. On the second stroke the intake and exhaust valves are
both closed as the piston starts upward. The mixture is compressed from normal atmospheric
pressure (1 kg/sq cm, or 14.7 lb/sq in) to between 4.9 and 8.8 kg/sq cm (70 and 125 lb/sq in).
During the third stroke the compressed mixture is ignited--either by compression ignition or by
spark ignition. The heat produced by the combustion causes the gases to expand within the
cylinder, thus forcing the piston downward. The piston's connecting rod transmits the power from
the piston to the crankshaft. This assembly changes reciprocating--in other words, up-and-down
or back-and-forth motion--to rotary motion. On the fourth stroke the exhaust valve is opened so
that the burned gases can escape as the piston moves upward; this prepares the cylinder for
another cycle. Internal-combustion spark-ignition engines having a two-stroke cycle combine intake and compression in a single first stroke and power and exhaust in a second stroke.
The internal-combustion reciprocating engine contains several subsystems: ignition, fuel,
cooling, and exhaust systems.
The ignition system of a spark-ignition engine consists of the sparking device (the spark plug);
the connecting wire from the plug to the distributor; and the distributor, which distributes the
spark to the proper cylinder at the proper time. The distributor receives a high-energy spark from
a coil, or magneto, that converts low-voltage energy to high-voltage energy. Some ignition systems employ transistorized circuitry, which is generally more efficient and less troublesome than the mechanical breaker-point system used in the past. Most ignition systems require an external electrical energy source in the form of a battery or a magneto.
Spark-ignition engines require a means for mixing fuel and air. This may be either a carburetor or fuel injection. A carburetor atomizes the fuel into the engine's incoming air supply. The mixture is then vaporized in the intake manifold on its way to the combustion chamber. fuel injection sprays a controlled mist of fuel into the airstream, either in the intake manifold or just before the intake valve or valves of each cylinder. Both carburetors and fuel injectors maintain the correct fuel- to-air ratio, about one part fuel to fifteen parts air, over a wide range of air temperatures, engine speeds, and loads. Fuel injection can compensate for changes in altitude as well.
Internal-combustion engines require some type of starting system. Small engines are generally
started by pulling a starting rope or kicking a lever. Larger engines may use compressed air or
an electric starting system. The latter includes a starter--a high-torque electric motor--to turn the
crankshaft until the engine starts. Starting motors are extremely powerful for their size and are
designed to utilize high currents (200 to 300 amperes). The large starting currents can cause a
battery to drain rapidly; for this reason a heavy- duty battery is usually used. Interrupting this
connection is an electrical switch called a solenoid, which is activated by the low- voltage starting
switch. In this way the ignition switch can be located away from the starter and yet still turn the
starter on and off.
The cooling system is important because internal-combustion engines operate at high
temperatures of combustion--spark- ignition engines at approximately 2,760 degrees C (5,000
degrees F) and diesel engines at even higher temperatures. If it were not for the cooling system,
these high temperatures would damage and melt many parts of the engine. The cooling system
essentially dissipates the heat of combustion in metal, water, or air and automatically regulates
the temperature so that the engine can operate at its optimum temperature--about 93 degrees C
(200 degrees F).
Air-cooled engines, popularly used to power small lawn mowers, chain saws, power generators, and motorcycles, as well as small cars and airplanes, often require no moving parts, and therefore little or no maintenance, for the cooling system. The head, or uppermost part, of the cylinder and the cylinder block have fins cast into them; these fins increase the surface exposed to the surrounding air, allowing more heat to be radiated. Usually a cover or shroud channels the air
flow over the fins. A fan is sometimes included if the engine is located away from a stream of fast-moving air.
Water-cooled engines have water jackets built into the engine block. These jackets surround
the cylinders. Usually a centrifugal water pump is used to circulate the water continuously through the water jackets. In this way the high heat of combustion is drawn off the cylinder wall into the circulating water. The water must then be cooled in a radiator that transfers the heat energy of the water to the radiator's cooler surrounding fluid. The surrounding fluid can be air or water, depending on the application of the engine.
Internal-combustion engines include an exhaust system, which allows the hot exhaust gases to
escape efficiently from the engine. In some small engines the exhaust gases can exit directly into
the atmosphere. Larger engines are noisier and require some type of muffler or sound deadener,
usually a canister with an inner shell that breaks up the sound waves, dissipating their energy
within the muffler before the exhaust gases are permitted to escape.
The power capacity of an engine depends on a number of characteristics, including the volume
of the combustion chamber. The volume can be increased by increasing the size of the piston
and cylinder and by increasing the number of cylinders. The cylinder configuration, or
arrangement of cylinders, can be straight, or in-line (one cylinder located behind the other); radial
(cylinders located around a circle); in a V (cylinders located in a V configuration); or opposed
(cylinders located opposite each other). Another type of internal-combustion engine, the Wankel engine, has no cylinders; instead, it has a rotor that moves through a combustion chamber.
An internal-combustion engine must also have some kind of transmission system to control and direct the mechanical energy where it is needed; for example, in an automobile the energy
must be directed to the driving wheels. Since these engines are not able to start under a load, a
transmission system must be used to "disengage" the engine from the load during starting and
then to apply the load when the engine reaches its operating speed.
Sunday 1 September 2013
Impacto de la Fisica en el medio ambiente
IMPACTO DE LA FÍSICA EN EL MEDIO AMBIENTE
La física, al igual que muchas otras ciencias se encarga de explicar como funcionan o como pasan muchas de las cosas que nos rodean, entre las que destacamos todos los procesos naturales, estos estudios son útiles para permitir al ser humano duplicar ciertos fenómenos que son útiles para otras labores en beneficio de la comunidad. En este ensayo trataremos de mostrar algunos de los beneficios e influencias que tiene la física sobre la naturaleza en general.
En lo personal me parece poco apropiado decir que la física tiene cierto impacto en el ambiente, ya que creo que la física en su mayoría se dedica a averiguar el porqué de todo lo que pasa en el medio , que es su fin primordial. Una vez que el medio ya está estudiado entonces ahora si la labor se redirecciona a utilizar ese nuevo conocimiento en pro del ser humano, la mayoría de las veces, y es allí cuando se tiene un efecto de retroalimentación sobre el ambiente.
La ciencia física en escencia, como ya dijimos se encarga de averiguar el porqué y el cómo. Ejemplo de estos son todas las leyes que la describen, como de Newton o los diversos teoremas que se encargan de modelar situaciones para describir el comportamiento de diversos sistemas. Es gracias a todos estos estudios que sabemos cosas como ¿porqué se mueven las cosas?, ¿cómo vemos los colores?, ¿qué efecto magnético produce convierte la energía?, ¿cómo se lleva a cabo desprendimiento de calor y cómo se puede aprovechar?, entre otras muchas cuestiones que después se pueden utilizar para ciertas actividades en pro de la especies humana.
Los problemas empiezan cuando estas acciones en pro de la humanidad tienen ciertos efectos secundarios que ocasionan daños que muchas de las veces son irreparable. Como ejemplo de esto podemos citar el uso del petróleo, cuando se obtuvieron los primeros resultados gracias a su capacidad calorífica fue un sorprendente descubrimiento que vino a facilitar un sin número de tareas, pero ¿qué pasó cuando se descubrieron los productos contaminantes de su combustión?, se empezó a generar un caos incrementándose brutalmente los niveles de contaminación en gran parte por la combustión de este y además como era un recurso no renovable llegaría un tiempo en donde existiera escasez.
De esto surgieron formas alternativas como la energía nuclear, que aunque en algunos aspectos era menos contaminante y no llegaría a escasearse, tenía como resultados ciertos residuos radiactivos que serían difíciles de desechar en cualquier medio. Además existe un potencial riesgo de accidente por un descontrol en el sistema que podría ocasionar un desastre natural. El descubrimiento de este tipo de energía tuvo ciertos otros usos, como por ejemplo los médicos que llegaron para el tratamiento de ciertas enfermedades aumentando el tiempo de vida de la población. Aunque también existieron otras aplicaciones como las militares capaces de desaparecer miles de metros cuadrados de superficie generando consecuencias demasiado brutales para cualquier medio ambiente.
Debido a esto y gracias a ciertos otros avances de la física se han podido aprovechar ciertos otros tipos de energía como la solar, que gracias a materiales semiconductores y aprovechando la física de estado sólido, se han podido crear celdas capaces de convertir los fotones en electrones, o más bien la luz solar en electricidad, eliminando así problemas como riegos, desperdicios contaminantes o contaminación causada por productos de combustión. Cabe mencionar que dentro de la física de estado sólido también se ha estado desarrollando el concepto de superconductores, que son elementos que mínimas pérdidas al momento de la conducción de electrones, los que serán capaces, además de desperdiciar menos electricidad, de crear una forma mucho más eficiente que las actuales de almacenamiento de ésta para poder hacer un mejor uso, como por ejemplo utilizar la energía del sol durante la noche.
Existen además ciertos otros avances a los que se están tratando de llegar, como la separación del Hidrógeno del agua, lo que provocaría el abastecimiento casi interminable de un medio de combustión muy limpio que podría ser utilizado para diversas aplicaciones sin las desventajas de otros combustibles.
Durante la realización de este ensayo se me ocurre pensar que la física se ha enfocado al estudio del medio ambiente, en su mayoría, y además, en escala considerablemente menor, se ha utilizado esta información en beneficio de la humanidad. Desgraciadamente en el transcurso y alcance de este beneficio se ha pasado a través de diferentes etapas donde se notan los costos en el ambiente que tuvieron ciertas ganacias en el ser humano, por lo que entonces se busca un método de llagar a tener el mismo efecto sin tener que pagar ese precio. Debido a este sistema de aplicación de tecnología la física, al igual que todas las otras ciencias, se ha visto en una posición con ciertas prioridades al momento de su aplicación, primero el obtener el funcionamiento del medio, posteriormente aplicar esa información en beneficio de la humanidad con dos consideraciones importantes, la primera crear formas que afecten cada vez menos el medio ambiente mediante la planeación más estratégica y consciente de la creación de tecnología y desarrollando nuevos sistemas capaces de corregir ciertos errores que tecnologías capaces han ocasionado, reduciendo en una pequeña escala los efectos negativos y catástrofes originadas.
En mi punto de vista la física ha tomado un papel trascendental para sobrevivir al medio, si bien es cierto que la Tierra si no hubiera sido expuesta al ser humano con cambios en contra de la naturaleza sería un organismo autosustentable sin problemas considerables como los que se tienen ahora, debemos también aceptar los beneficios que han causado tales impactos sobre el ambiente, en especial para nuestra especie. Por lo que la comunidad científica debe comprometerse en encontar cada vez formas mejores, tanto más eficientes, económicas y menos contaminantes, de obtener beneficios para todos, siempre planeando detenidamente todos sus posibles efectos para minimizar las pérdidas. Y además debe tratar de divulgar sus descubrimientos lo más que se pueda para evitar que intereses localizados sean los causantes del continuo deterioro del sistema, logrando así la existencia de un mejor mundo por más tiempo el cual todos podamos disfrutar.
La física, al igual que muchas otras ciencias se encarga de explicar como funcionan o como pasan muchas de las cosas que nos rodean, entre las que destacamos todos los procesos naturales, estos estudios son útiles para permitir al ser humano duplicar ciertos fenómenos que son útiles para otras labores en beneficio de la comunidad. En este ensayo trataremos de mostrar algunos de los beneficios e influencias que tiene la física sobre la naturaleza en general.
En lo personal me parece poco apropiado decir que la física tiene cierto impacto en el ambiente, ya que creo que la física en su mayoría se dedica a averiguar el porqué de todo lo que pasa en el medio , que es su fin primordial. Una vez que el medio ya está estudiado entonces ahora si la labor se redirecciona a utilizar ese nuevo conocimiento en pro del ser humano, la mayoría de las veces, y es allí cuando se tiene un efecto de retroalimentación sobre el ambiente.
La ciencia física en escencia, como ya dijimos se encarga de averiguar el porqué y el cómo. Ejemplo de estos son todas las leyes que la describen, como de Newton o los diversos teoremas que se encargan de modelar situaciones para describir el comportamiento de diversos sistemas. Es gracias a todos estos estudios que sabemos cosas como ¿porqué se mueven las cosas?, ¿cómo vemos los colores?, ¿qué efecto magnético produce convierte la energía?, ¿cómo se lleva a cabo desprendimiento de calor y cómo se puede aprovechar?, entre otras muchas cuestiones que después se pueden utilizar para ciertas actividades en pro de la especies humana.
Los problemas empiezan cuando estas acciones en pro de la humanidad tienen ciertos efectos secundarios que ocasionan daños que muchas de las veces son irreparable. Como ejemplo de esto podemos citar el uso del petróleo, cuando se obtuvieron los primeros resultados gracias a su capacidad calorífica fue un sorprendente descubrimiento que vino a facilitar un sin número de tareas, pero ¿qué pasó cuando se descubrieron los productos contaminantes de su combustión?, se empezó a generar un caos incrementándose brutalmente los niveles de contaminación en gran parte por la combustión de este y además como era un recurso no renovable llegaría un tiempo en donde existiera escasez.
De esto surgieron formas alternativas como la energía nuclear, que aunque en algunos aspectos era menos contaminante y no llegaría a escasearse, tenía como resultados ciertos residuos radiactivos que serían difíciles de desechar en cualquier medio. Además existe un potencial riesgo de accidente por un descontrol en el sistema que podría ocasionar un desastre natural. El descubrimiento de este tipo de energía tuvo ciertos otros usos, como por ejemplo los médicos que llegaron para el tratamiento de ciertas enfermedades aumentando el tiempo de vida de la población. Aunque también existieron otras aplicaciones como las militares capaces de desaparecer miles de metros cuadrados de superficie generando consecuencias demasiado brutales para cualquier medio ambiente.
Debido a esto y gracias a ciertos otros avances de la física se han podido aprovechar ciertos otros tipos de energía como la solar, que gracias a materiales semiconductores y aprovechando la física de estado sólido, se han podido crear celdas capaces de convertir los fotones en electrones, o más bien la luz solar en electricidad, eliminando así problemas como riegos, desperdicios contaminantes o contaminación causada por productos de combustión. Cabe mencionar que dentro de la física de estado sólido también se ha estado desarrollando el concepto de superconductores, que son elementos que mínimas pérdidas al momento de la conducción de electrones, los que serán capaces, además de desperdiciar menos electricidad, de crear una forma mucho más eficiente que las actuales de almacenamiento de ésta para poder hacer un mejor uso, como por ejemplo utilizar la energía del sol durante la noche.
Existen además ciertos otros avances a los que se están tratando de llegar, como la separación del Hidrógeno del agua, lo que provocaría el abastecimiento casi interminable de un medio de combustión muy limpio que podría ser utilizado para diversas aplicaciones sin las desventajas de otros combustibles.
Durante la realización de este ensayo se me ocurre pensar que la física se ha enfocado al estudio del medio ambiente, en su mayoría, y además, en escala considerablemente menor, se ha utilizado esta información en beneficio de la humanidad. Desgraciadamente en el transcurso y alcance de este beneficio se ha pasado a través de diferentes etapas donde se notan los costos en el ambiente que tuvieron ciertas ganacias en el ser humano, por lo que entonces se busca un método de llagar a tener el mismo efecto sin tener que pagar ese precio. Debido a este sistema de aplicación de tecnología la física, al igual que todas las otras ciencias, se ha visto en una posición con ciertas prioridades al momento de su aplicación, primero el obtener el funcionamiento del medio, posteriormente aplicar esa información en beneficio de la humanidad con dos consideraciones importantes, la primera crear formas que afecten cada vez menos el medio ambiente mediante la planeación más estratégica y consciente de la creación de tecnología y desarrollando nuevos sistemas capaces de corregir ciertos errores que tecnologías capaces han ocasionado, reduciendo en una pequeña escala los efectos negativos y catástrofes originadas.
En mi punto de vista la física ha tomado un papel trascendental para sobrevivir al medio, si bien es cierto que la Tierra si no hubiera sido expuesta al ser humano con cambios en contra de la naturaleza sería un organismo autosustentable sin problemas considerables como los que se tienen ahora, debemos también aceptar los beneficios que han causado tales impactos sobre el ambiente, en especial para nuestra especie. Por lo que la comunidad científica debe comprometerse en encontar cada vez formas mejores, tanto más eficientes, económicas y menos contaminantes, de obtener beneficios para todos, siempre planeando detenidamente todos sus posibles efectos para minimizar las pérdidas. Y además debe tratar de divulgar sus descubrimientos lo más que se pueda para evitar que intereses localizados sean los causantes del continuo deterioro del sistema, logrando así la existencia de un mejor mundo por más tiempo el cual todos podamos disfrutar.
Hologram Essay
Holograms
Toss a pebble in a pond -see the ripples? Now drop two
pebbles close together. Look at what happens when the two sets
of waves combine -you get a new wave! When a crest and a trough
meet, they cancel out and the water goes flat. When two crests
meet, they produce one, bigger crest. When two troughs collide,
they make a single, deeper trough. Believe it or not, you've
just found a key to understanding how a hologram works. But what
do waves in a pond have to do with those amazing three-
dimensional pictures? How do waves make a hologram look like the
real thing?
It all starts with light. Without it, you can't see. And
much like the ripples in a pond, light travels in waves. When
you look at, say, an apple, what you really see are the waves of
light reflected from it. Your two eyes each see a slightly
different view of the apple. These different views tell you
about the apple's depth -its form and where it sits in relation
to other objects. Your brain processes this information so that
you see the apple, and the rest of the world, in 3-D. You can
look around objects, too -if the apple is blocking the view of
an orange behind it, you can just move your head to one side.
The apple seems to "move" out of the way so you can see the
orange or even the back of the apple. If that seems a bit
obvious, just try looking behind something in a regular
photograph! You can't, because the photograph can't reproduce
the infinitely complicated waves of light reflected by objects;
the lens of a camera can only focus those waves into a flat, 2-D
image. But a hologram can capture a 3-D image so lifelike that
you can look around the image of the apple to an orange in the
background -and it's all thanks to the special kind of light
waves produced by a laser.
"Normal" white light from the sun or a lightbulb is a
combination of every colour of light in the spectrum -a mush of
different waves that's useless for holograms. But a laser shines
light in a thin, intense beam that's just one colour. That means
laser light waves are uniform and in step. When two laser beams
intersect, like two sets of ripples meeting in a pond, they
produce a single new wave pattern: the hologram. Here's how it
happens: Light coming from a laser is split into two beams,
called the object beam and the reference beam. Spread by lenses
and bounced off a mirror, the object beam hits the apple. Light
waves reflect from the apple towards a photographic film. The
reference beam heads straight to the film without hitting the
apple. The two sets of waves meet and create a new wave pattern
that hits the film and exposes it. On the film all you can see
is a mass of dark and light swirls -it doesn't look like an
apple at all! But shine the laser reference beam through the
film once more and the pattern of swirls bends the light to re-
create the original reflection waves from the apple -exactly.
Not all holograms work this way -some use plastics instead
of photographic film, others are visible in normal light. But
all holograms are created with lasers -and new waves.
All Thought Up and No Place to Go
Holograms were invented in 1947 by Hungarian scientist
Dennis Gabor, but they were ignored for years. Why? Like many
great ideas, Gabor's theory about light waves was ahead of its
time. The lasers needed to produce clean waves -and thus clean
3-D images -weren't invented until 1960. Gabor coined the name
for his photographic technique from holos and gramma, Greek for
"the whole message. " But for more than a decade, Gabor had only
half the words. Gabor's contribution to science was recognized
at last in 1971 with a Nobel Prize. He's got a chance for a last
laugh, too. A perfect holographic portrait of the late scientist
looking up from his desk with a smile could go on fooling
viewers into saying hello forever. Actor Laurence Olivier has
also achieved that kind of immortality -a hologram of the 80
year-old can be seen these days on the stage in London, in a
musical called Time.
New Waves
When it comes to looking at the future uses of holography,
pictures are anything but the whole picture. Here are just a
couple of the more unusual possibilities. Consider this: you're
in a windowless room in the middle of an office tower, but
you're reading by the light of the noonday sun! How can this be?
A new invention that incorporates holograms into widow glazings
makes it possible. Holograms can bend light to create complex 3-
D images, but they can also simply redirect light rays. The
window glaze holograms could focus sunlight coming through a
window into a narrow beam, funnel it into an air duct with
reflective walls above the ceiling and send it down the hall to
your windowless cubbyhole. That could cut lighting costs and
conserve energy. The holograms could even guide sunlight into
the gloomy gaps between city skyscrapers and since they can bend
light of different colors in different directions, they could be
used to filter out the hot infrared light rays that stream
through your car windows to bake you on summer days.
Or, how about holding an entire library in the palm of
your hand? Holography makes it theoretically possible. Words or
pictures could be translated into a code of alternating light
and dark spots and stored in an unbelievably tiny space. That's
because light waves are very, very skinny. You could lay about
1000 lightwaves side by side across the width of the period at
the end of this sentence. One calculation holds that by using
holograms, the U. S. Library of Congress could be stored in the
space of a sugar cube. For now, holographic data storage remains
little more than a fascinating idea because the materials needed
to do the job haven't been invented yet. But it's clear that
holograms, which author Isaac Asimov called "the greatest
advance in imaging since the eye" will continue to make waves in
the world of science.
Toss a pebble in a pond -see the ripples? Now drop two
pebbles close together. Look at what happens when the two sets
of waves combine -you get a new wave! When a crest and a trough
meet, they cancel out and the water goes flat. When two crests
meet, they produce one, bigger crest. When two troughs collide,
they make a single, deeper trough. Believe it or not, you've
just found a key to understanding how a hologram works. But what
do waves in a pond have to do with those amazing three-
dimensional pictures? How do waves make a hologram look like the
real thing?
It all starts with light. Without it, you can't see. And
much like the ripples in a pond, light travels in waves. When
you look at, say, an apple, what you really see are the waves of
light reflected from it. Your two eyes each see a slightly
different view of the apple. These different views tell you
about the apple's depth -its form and where it sits in relation
to other objects. Your brain processes this information so that
you see the apple, and the rest of the world, in 3-D. You can
look around objects, too -if the apple is blocking the view of
an orange behind it, you can just move your head to one side.
The apple seems to "move" out of the way so you can see the
orange or even the back of the apple. If that seems a bit
obvious, just try looking behind something in a regular
photograph! You can't, because the photograph can't reproduce
the infinitely complicated waves of light reflected by objects;
the lens of a camera can only focus those waves into a flat, 2-D
image. But a hologram can capture a 3-D image so lifelike that
you can look around the image of the apple to an orange in the
background -and it's all thanks to the special kind of light
waves produced by a laser.
"Normal" white light from the sun or a lightbulb is a
combination of every colour of light in the spectrum -a mush of
different waves that's useless for holograms. But a laser shines
light in a thin, intense beam that's just one colour. That means
laser light waves are uniform and in step. When two laser beams
intersect, like two sets of ripples meeting in a pond, they
produce a single new wave pattern: the hologram. Here's how it
happens: Light coming from a laser is split into two beams,
called the object beam and the reference beam. Spread by lenses
and bounced off a mirror, the object beam hits the apple. Light
waves reflect from the apple towards a photographic film. The
reference beam heads straight to the film without hitting the
apple. The two sets of waves meet and create a new wave pattern
that hits the film and exposes it. On the film all you can see
is a mass of dark and light swirls -it doesn't look like an
apple at all! But shine the laser reference beam through the
film once more and the pattern of swirls bends the light to re-
create the original reflection waves from the apple -exactly.
Not all holograms work this way -some use plastics instead
of photographic film, others are visible in normal light. But
all holograms are created with lasers -and new waves.
All Thought Up and No Place to Go
Holograms were invented in 1947 by Hungarian scientist
Dennis Gabor, but they were ignored for years. Why? Like many
great ideas, Gabor's theory about light waves was ahead of its
time. The lasers needed to produce clean waves -and thus clean
3-D images -weren't invented until 1960. Gabor coined the name
for his photographic technique from holos and gramma, Greek for
"the whole message. " But for more than a decade, Gabor had only
half the words. Gabor's contribution to science was recognized
at last in 1971 with a Nobel Prize. He's got a chance for a last
laugh, too. A perfect holographic portrait of the late scientist
looking up from his desk with a smile could go on fooling
viewers into saying hello forever. Actor Laurence Olivier has
also achieved that kind of immortality -a hologram of the 80
year-old can be seen these days on the stage in London, in a
musical called Time.
New Waves
When it comes to looking at the future uses of holography,
pictures are anything but the whole picture. Here are just a
couple of the more unusual possibilities. Consider this: you're
in a windowless room in the middle of an office tower, but
you're reading by the light of the noonday sun! How can this be?
A new invention that incorporates holograms into widow glazings
makes it possible. Holograms can bend light to create complex 3-
D images, but they can also simply redirect light rays. The
window glaze holograms could focus sunlight coming through a
window into a narrow beam, funnel it into an air duct with
reflective walls above the ceiling and send it down the hall to
your windowless cubbyhole. That could cut lighting costs and
conserve energy. The holograms could even guide sunlight into
the gloomy gaps between city skyscrapers and since they can bend
light of different colors in different directions, they could be
used to filter out the hot infrared light rays that stream
through your car windows to bake you on summer days.
Or, how about holding an entire library in the palm of
your hand? Holography makes it theoretically possible. Words or
pictures could be translated into a code of alternating light
and dark spots and stored in an unbelievably tiny space. That's
because light waves are very, very skinny. You could lay about
1000 lightwaves side by side across the width of the period at
the end of this sentence. One calculation holds that by using
holograms, the U. S. Library of Congress could be stored in the
space of a sugar cube. For now, holographic data storage remains
little more than a fascinating idea because the materials needed
to do the job haven't been invented yet. But it's clear that
holograms, which author Isaac Asimov called "the greatest
advance in imaging since the eye" will continue to make waves in
the world of science.
History of Space Shuttle Program
The shuttle, a manned, multipurpose, orbital-launch space plane, was designed to carry payloads of up to about 30,000 kg (65,000 lb) and up to seven crew members and passengers. The upper part of the spacecraft, the orbiter stage, had a theoretical lifetime of perhaps 100 missions, and the winged orbiter could make unpowered landings on returning to earth. Because of the shuttle's designed flexibility and its planned use for satellite deployment and the rescue and repair of previously orbited satellites, its proponents saw it as a major advance in the practical exploitation of space. Others, however, worried that NASA was placing too much reliance on the shuttle, to the detriment of other, unmanned vehicles and missions.
The first space shuttle mission, piloted by John W. Young and Robert Crippen aboard the orbiter Columbia, was launched on April 12, 1981. It was a test flight flown without payload in the orbiter's cargo bay. The fifth space shuttle flight was the first operational mission; the astronauts in the Columbia deployed two commercial communications satellites from November 11 to 16, 1982. Later memorable flights included the seventh, whose crew included the first U.S. woman astronaut, Sally K. Ride; the ninth mission, November 28-December 8, 1983, which carried the first of the European Space Agency's Spacelabs; the 11th mission, April 7-13, 1984, during which a satellite was retrieved, repaired, and redeployed; and the 14th mission, November 8-14, 1984, when two expensive malfunctioning satellites were retrieved and returned to earth.
Despite such successes, the shuttle program was falling behind in its planned launch program, was increasingly being used for military tests, and was meeting stiff competition from the European Space Agency's unmanned Ariane program for the orbiting of satellites. Then, on January 28, 1986, the shuttle Challenger was destroyed about one minute after launch because of the failure of a sealant ring on one of its solid boosters. Flames escaping from the booster burned a hole in the main propellant tank of liquid hydrogen and oxygen and caused the booster to nose into and rupture the tank. This rupture caused a nearly explosive disruption of the whole system. Seven astronauts were killed in the disaster: commander Francis R. Scobee, pilot Michael J. Smith, mission specialists Judith A. Resnik, Ellison S. Onizuka, and Ronald E. McNair, and payload specialists Gregory B. Jarvis and Christa McAuliffe. McAuliffe had been selected the preceding year as the first "teacher in space," a civilian spokesperson for the shuttle program. The tragedy brought an immediate halt to shuttle flights until systems could be analyzed and redesigned. A presidential commission headed by former secretary of state William Rogers and former astronaut Neil Armstrong placed much of the blame on NASA's administrative system and its failure to maintain an efficient system of quality control.
In the aftermath of the Challenger disaster, the O-ring seals on the solid rocket booster (SRB) were redesigned to prevent recurrence of the January 28 failure. The shuttle launch program resumed on September 29, 1988, with the flight of Discovery and its crew of five astronauts. On this mission, a NASA communications satellite, TDRS-3, was placed in orbit and a variety of experiments were carried out. The success of this 26th mission encouraged the United States to resume an active launch schedule. One more flight was planned for 1988, and a total of 39 were scheduled through 1992. The long-delayed $1.5-billion Hubble Space Telescope was deployed by space shuttle in 1990 but, because of an optical defect, failed to provide the degree of resolution it was designed to have until it was repaired in December 1993. On February 2, 1995, Lieutenant Colonel Eileen M. Collins became the first woman to pilot the space shuttle. On March 18 the space shuttle Endeavor, piloted by Stephen Oswald, landed after a record 16 days, 15 hours in space.
The first space shuttle mission, piloted by John W. Young and Robert Crippen aboard the orbiter Columbia, was launched on April 12, 1981. It was a test flight flown without payload in the orbiter's cargo bay. The fifth space shuttle flight was the first operational mission; the astronauts in the Columbia deployed two commercial communications satellites from November 11 to 16, 1982. Later memorable flights included the seventh, whose crew included the first U.S. woman astronaut, Sally K. Ride; the ninth mission, November 28-December 8, 1983, which carried the first of the European Space Agency's Spacelabs; the 11th mission, April 7-13, 1984, during which a satellite was retrieved, repaired, and redeployed; and the 14th mission, November 8-14, 1984, when two expensive malfunctioning satellites were retrieved and returned to earth.
Despite such successes, the shuttle program was falling behind in its planned launch program, was increasingly being used for military tests, and was meeting stiff competition from the European Space Agency's unmanned Ariane program for the orbiting of satellites. Then, on January 28, 1986, the shuttle Challenger was destroyed about one minute after launch because of the failure of a sealant ring on one of its solid boosters. Flames escaping from the booster burned a hole in the main propellant tank of liquid hydrogen and oxygen and caused the booster to nose into and rupture the tank. This rupture caused a nearly explosive disruption of the whole system. Seven astronauts were killed in the disaster: commander Francis R. Scobee, pilot Michael J. Smith, mission specialists Judith A. Resnik, Ellison S. Onizuka, and Ronald E. McNair, and payload specialists Gregory B. Jarvis and Christa McAuliffe. McAuliffe had been selected the preceding year as the first "teacher in space," a civilian spokesperson for the shuttle program. The tragedy brought an immediate halt to shuttle flights until systems could be analyzed and redesigned. A presidential commission headed by former secretary of state William Rogers and former astronaut Neil Armstrong placed much of the blame on NASA's administrative system and its failure to maintain an efficient system of quality control.
In the aftermath of the Challenger disaster, the O-ring seals on the solid rocket booster (SRB) were redesigned to prevent recurrence of the January 28 failure. The shuttle launch program resumed on September 29, 1988, with the flight of Discovery and its crew of five astronauts. On this mission, a NASA communications satellite, TDRS-3, was placed in orbit and a variety of experiments were carried out. The success of this 26th mission encouraged the United States to resume an active launch schedule. One more flight was planned for 1988, and a total of 39 were scheduled through 1992. The long-delayed $1.5-billion Hubble Space Telescope was deployed by space shuttle in 1990 but, because of an optical defect, failed to provide the degree of resolution it was designed to have until it was repaired in December 1993. On February 2, 1995, Lieutenant Colonel Eileen M. Collins became the first woman to pilot the space shuttle. On March 18 the space shuttle Endeavor, piloted by Stephen Oswald, landed after a record 16 days, 15 hours in space.
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