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Balloons

Balloons

::For the impedance converter, see the article on balun. baluns.]] A balloon is a flexible bag normally filled with air or gas. Some balloons are purely decorative, others are used for specific purposes. Early balloons were made of dried animal bladders. Modern balloons can be made from materials such as rubber, latex, chloroprene or a nylon fabric.

Usage of Balloons

- small balloons (volume of a few litres)
- toy balloon
- decoration
- solar balloon
- balloon mail as part of a balloon flight competition or to spread information
- Balloon helicopter
- Demonstration of rocket propulsion by letting the gas stream away (balloon rocket)
- Ceiling balloon
- medium balloons (volume of hundreds to thousands of litres)
- transport of bombs (in World War II, FUGU-Balloon)
- transport of propaganda (in World War II and in the Cold War)
- Ceiling balloon
- Weather balloon used with a Radiosonde
- as fixed balloon
- for carrying advertising signs
- to carry antennae for LF and VLF
- party balloon
- large balloons (volume up to 12000 cubic metres)
- fixed balloon
- as manned observation post (before World War II)
- barrage balloon
- observation balloon for military reconnaissance
- positioning atomic bombs for bomb tests in the atmosphere
- free flying balloons
- lifting people, usually with a hot air balloon
- airship actually a buoyant aircraft rather than a balloon
- research balloon with instrumentation, also to carry telescopes
- rockoon
- balloon satellite for space research.
- espionage balloon for military reconnaissance espionage balloon

Balloons as flying machines

Large balloons filled with hot air or buoyant gas have been used as flying machines since the 18th century. See Balloon (aircraft) and Hot air balloon Such balloons, which lift a payload using buoyancy, should not be confused with balloons in space, launched with a rocket, which are simply large deployable structures. Balloons are sometimes used in form of a rockoon as carrier for rockets. Examples:
- Echo satellite
- Decoys accompanying ICBMs in midcourse, see also countermeasure

Balloons as decoration or entertainment

countermeasure Party balloons are mostly made of natural latex tapped from rubber trees and can be filled with air, helium, water, or any other suitable liquid or gas. The rubber makes the volume adjustable. Filling with air is done with the mouth or with a pump. When rubber balloons are filled with helium so that they float (restrained by ribbons or strings) they can hold their shape for only a few hours. The enclosed air or helium escapes through small pores in the rubber. If helium is used the gas escapes quicker than in the case of air because the helium atoms are much smaller than the nitrogen and oxygen molecules in air. Even a perfect rubber membrane eventually loses the gas to the outside, and its contents are contaminated by oxygen and nitrogen migrating inward from the outside. The gases in question actually dissolve in the rubber on one side and are released from solution on the other. The process by which a substance or solute migrates from a region of high concentration, through a barrier or membrane, to a region of lower concentration is called diffusion. The inside of balloons can be treated with a special gel (e.g. "Hi Float" brand) which coats the inside of the balloon to reduce the helium leakage, thus increasing float time. Latex rubber balloons are completely biodegradable, but cannot safely be released into the environment: they are a serious hazard to birds and wetland animals that confuse the balloons for food. Beginning in the early 1990s, some more expensive (and longer-lasting) helium balloons have been made of thin, unstretchable, impermeable metallized nylon films. These balloons are often mistakenly called Mylar balloons. These balloons have attractive shiny reflective surfaces and are often printed with colour pictures and patterns. The most important attributes of metallized nylon for balloons are its light weight, increasing buoyancy and its ability to keep the helium gas from escaping for several weeks. However, there has been some environmental concern, since the metallized nylon does not biodegrade or shred as a rubber balloon does, and a helium balloon released into the atmosphere can travel a long way before finally bursting or deflating. Release of these types of balloons into the atmosphere is harmful to the environment. Partygoers sometimes entertain each other by untying a balloon and inhaling the helium. Because the speed of sound in helium is about twice that in air, the helium causes the vocal tract to become more responsive to high-pitched sounds and less responsive to lower ones. The result is a voice that sounds high-pitched (and usually very funny). Balloon artists are entertainers who twist and tie inflated tubular balloons into sculptures (see also balloon animal). The balloons used for balloon sculpture are made of extra-stretchy rubber so that they can be twisted and tied without bursting. Since the pressure required to inflate a balloon is inversely proportional to the diameter of the balloon, these tiny tubular balloons are extremely hard to inflate initially. A pump is usually used to inflate these balloons. Decorators may use dozens of helium balloons to create balloon sculptures. Usually the round shape of the balloon restricts these to simple arches or walls, but on occasion more ambitious "sculptures" have been attempted with great success. The balloon decorating industry offers everything from simple balloon columns to stunning, very large and detailed sculptures. Water balloons are thin, small rubber balloons intended to be easily broken. They are usually used by children, who throw them at each other, trying to get each other wet - see practical joke.

Balloons in medicine

Angioplasty is a surgical procedure in which very small balloons are inserted into blocked or partially blocked blood vessels near the heart. Once in place, the balloon can be inflated to clear or compress arterial plaque, and to stretch the walls of the vein. A small stent can be inserted in its place to keep the vessel open after the balloon's removal. See myocardial infarction. Certain catheters have balloons at their tip to keep them from slipping out, for example the balloon of a Foley catheter is insufflated when the catheter is inserted into the urinary bladder and secures its position.

Records

Maximum flight heights

Manned Balloon The altitude record for manned balloons is 34668 metres. It was made by Malcolm D. Ross and Victor E. Prather over the Gulf of Mexico in 1961. Unmanned Balloon The altitude record for unmanned balloons is (1991 edition of Guinness Book) 51.8 kilometres. The vehicle was a Winzen-Balloon with a volume of 1.35 million cubic metres, which was launched in October 1972 in Chico, California, USA. This is the greatest altitude ever reached by a flying object requiring the surrounding air. Higher altitudes can only be reached by ballistic vehicles such as rockets, rocket planes or projectiles.

Balloon tank

See Atlas (rocket).

Usage of Balloons on other planets

In 1984 the Russian space probe Vega released two aerobots into the atmosphere of Venus, from which signals were received for two days.

Balloons in movies

- The Balloonatic (1923)
- The Wizard of Oz (1939)
- Trottie True (1949)
- Globex's messy break (1954)
- Around the World in Eighty Days (1956)
- The Red Balloon (1956)
- Stowaway in the Sky (1960)
- Mysterious Island (1961)
- Five Weeks in a Balloon (1962)
- The Great Race (1965)
- Those Magnificent Men in Their Flying Machines, or How I Flew from London to Paris in 25 hours 11 minutes (1965)
- Charlie Bubbles (1967)
- Chitty Chitty Bang Bang (1968)
- The Great Bank Robbery (1969)
- The Muppet Movie (1979)
- The Chipmunk Adventure (1987)
- Batman (1989)
- Around the World in 80 Days (2004)

External links

- [http://www.art-of-balloon-animals.ask-the-monkey.com Work of a typical balloon artist]
- [http://www.mbfloyd.com/ Balloon art instructions and gallery] Category:Parties ja:風船

Impedance

Electrical impedance or simply impedance is a measure of opposition to a sinusoidal electric current. The concept of electrical impedance generalizes Ohm's law in AC circuit analysis. Unlike electrical resistance, the impedance of an electric circuit can be a complex number. Oliver Heaviside coined the term impedance in July of 1886.

AC steady state

In general, the solutions for the voltages and currents in a circuit containing resistors, capacitors and inductors (in short, all linear behaving components) are solutions to a linear ordinary differential equation. It can be shown that if the voltage and/or current sources in the circuit are sinusoidal and of constant frequency, the solutions tend to a form referred to as AC steady state. Thus, all of the voltages and currents in the circuit are sinusoidal and have constant peak amplitude, frequency and phase. Let v(t) be a sinusoidal function of time with constant peak amplitude Vp, constant frequency f, and constant phase φ. :

v(t) = V_\mathrm cos \left( \omega  t + \phi \right) = \Re \left( V_\mathrm e^ e^ \right)

Where: v(t) is the voltage function

V_\mathrm

is the voltage maximum amplitude f is the constant frequency

\phi

is the constant phase ω is the angular speed (in radians per second).

\omega   = 2 \pi f \!\

j

represents the imaginary unit (

\sqrt

) and

\Re (z)

means the real part of the complex number z Now, let the complex number V be given by: :

V = V_\mathrm e^ \,

V is called the phasor representation of v(t). V is a constant complex number. For a circuit in AC steady state, all of the voltages and currents in the circuit have phasor representations as long as all the sources are of the same frequency. That is, each voltage and current can be represented as a constant complex number. For DC circuit analysis, each voltage and current is represented by a constant real number. Thus, it is reasonable to suppose that the rules developed for DC circuit analysis can be used for AC circuit analysis by using complex numbers instead of real numbers.

Definition of impedance

The impedance of a circuit element is defined as the ratio of the phasor voltage across the element to the phasor current through the element: :

Z_R = \frac

It should be noted that although Z is the ratio of two phasors, Z is not itself a phasor. That is, Z is not associated with some sinusoidal function of time. For DC circuits, the resistance is defined by Ohm's law to be the ratio of the DC voltage across the resistor to the DC current through the resistor: :

R = \frac

where the

V_R

and

I_R

above are DC (constant real) values. Just as Ohm's law is generalized to AC circuits through the use of phasors, other results from DC circuit analysis such as voltage division, current division, Thevenin's theorem, and Norton's theorem generalize to AC circuits.

Impedance of different devices

Resistor

For a resistor, we have the relation: :

\frac = R

That is, the ratio of the instantaneous voltage and current associated with a resistor is the value of the DC resistance denoted by R. Since R is constant and real, it follows that if v(t) is sinusoidal, i(t) is also sinusoidal with the same frequency and phase. Thus, we have that the impedance of a resistor is equal to R: :

Z_\mathrm = \frac

= R \,

Capacitor

For a capacitor, we have the relation: :

i_C(t) = C \frac

Now, Let :

v_C(t) = V_p sin \left( \omega  t \right)

It follows that :

\frac = \omega  V_p cos \left( \omega  t \right)

Using phasor notation and the result above, write our first equation as: :

I_c = j \omega  C V_c \,

It follows that the impedance of a capacitor is: :

Z_\mathrm = \frac = \frac

Inductor

For the inductor, we have: :

v_L(t) = L \frac

By the same reasoning used in the capacitor example above, it follows that the impedance on an inductor is: :

Z_\mathrm = j \omega  L \,

Reactance

See main article: Reactance The term reactance refers to the imaginary part of the impedance. Some examples: A resistor's impedance is R (its resistance) and its reactance is 0. A capacitor's impedance is j (-1/ωC) and its reactance is -1/ωC. An inductor's impedance is j ω L and its reactance is ω L. It is important to note that the impedance of a capacitor or an inductor is a function of the frequency f and is an imaginary quantity - however is certainly a real physical phenomenon relating the shift in phases between the voltage and current phasors due to the existance of the capacitor or inductor. Earlier it was shown that the impedance of a resistor is constant and real, in other words a resistor does not cause a phase shift between voltage and current as do capacitors and inductors. When resistors, capacitors, and inductors are combined in an AC circuit, the impedances of the individual components can be combined in the same way that the resistances are combined in a DC circuit. The resulting equivalent impedance is in general, a complex quantity. That is, the equivalent impedance has a real part and an imaginary part. The real part is denoted with an R and the imaginary part is denoted with an X. Thus: : $Z_\mathrm = R_\mathrm + jX_\mathrm \,$ $R_\mathrm$ is termed the resistive part of the impedance while $X_\mathrm$ is termed the reactive part of the impedance. It is therefore common to refer to a capacitor or an inductor as a reactance or equivalently, a reactive component (circuit element). Additionally, the impedance for a capacitance is negative imaginary while the impedance for an inductor is positive imaginary. Thus, a capacitive reactance refers to a negative reactance while an inductive reactance refers to a positive reactance. A reactive component is distinguished by the fact that the sinusoidal voltage across the component is in quadrature with the sinusoidal current through the component. This implies that the component alternately absorbs energy from the circuit and then returns energy to the circuit. That is, unlike a resistance, a reactance does not dissipate power. It is instructive to determine the value of the capacitive reactance at the frequency extremes. As the frequency approaches zero, the capacitive reactance grows without bound so that a capacitor approaches an open circuit for very low frequency sinusoidal sources. As the frequency increases, the capacitive reactance approaches zero so that a capacitor approaches a short circuit for very high frequency sinusoidal sources. Conversely, the inductive reactance approaches zero as the frequency approaches zero so that an inductor approaches a short circuit for very low frequency sinusoidal sources. As the frequency increases, the inductive reactance increases so that an inductor approaches an open circuit for very high frequency sinusoidal sources.
Combining Impedances
Combining impedances in series, parallel, or in delta-wye configurations, is the same as for resistors. The difference is that combining impedances involves manipulation of complex numbers.
In Series
Combining impedances in series is simple: $Z_ = Z_1 + Z_2 = (R_1 + R_2) + j(X_1 + X_2) \!\$
In Parallel
Combining impedances in parallel is much more difficult than combining simple properties like resistance or capacitance. In rationalized form the equivelant resistance is: $Z_ = R_ + j X_ \!\$ $R_ =$ $X_ =$
Circuits with general sources
Impedance is defined by the ratio of two phasors where a phasor is the complex peak amplitude of a sinusoidal function of time. For more general periodic sources and even non-periodic sources, the concept of impedance can still be used. It can be shown that virtually all periodic functions of time can be represented by a Fourier series. Thus, a general periodic voltage source can be thought of as a (possibly infinite) series combination of sinusoidal voltage sources. Likewise, a general periodic current source can be thought of as a (possibly infinite) parallel combination of sinusoidal current sources. Using the technique of Superposition, each source is activated one at a time and an AC circuit solution is found using the impedances calculated for the frequency of that particular source. The final solutions for the voltages and currents in the circuit are computed as sums of the terms calculated for each individual source. However, it is important to note that the actual voltages and currents in the circuit do not have a phasor representation. Phasors can be added together only when each represents a time function of the same frequency. Thus, the phasor voltages and currents that are calculated for each particular source must be converted back to their time domain representation before the final summation takes place. This method can be generalized to non-periodic sources where the discrete sums are replaced by integrals. That is, a Fourier transform is used in place of the Fourier series.
Magnitude and phase of impedance
Complex numbers are commonly expressed in two distinct forms. The rectangular form is simply the sum of the real part with the product of j and the imaginary part: : $Z = R + jX \,$ The polar form of a complex number is the product of a real number called the magnitude and another complex number called the phase: : $Z = \left|Z\right| e^ = \left|Z\right|\angle \phi \,$ Where the magnitude is given by: : $\left|Z\right|=\sqrt \,$ and the angle is given by: : $\phi = arctan \frac$ Alternately, the magnitude is given by: : $\left|Z\right|=\sqrt \,$ Where Z
- denotes the complex conjugate of Z: $R - jX\,$ .
Peak phasor versus rms phasor
A sinusoidal voltage or current has a peak amplitude value as well as an rms (root mean square) value. It can be shown that the rms value of a sinusoidal voltage or current is given by: : $V_\mathrm = V_\mathrm / \sqrt$ : $I_\mathrm = I_\mathrm / \sqrt$ In many cases of AC analysis, the rms value of a sinusoid is more useful than the peak value. For example, to determine the amount of power dissipated by a resistor due to a sinusoidal current, the rms value of the current must be known. For this reason, phasor voltage and current sources are often specified as an rms phasor. That is, the magnitude of the phasor is the rms value of the associated sinusoid rather than the peak amplitude. Generally, rms phasors are used in electrical power engineering whereas peak phasors are often used in low-power circuit analysis. In any event, the impedance is clearly the same whether peak phasors or rms phasors are used as the scaling factor cancels out when the ratio of the phasors is taken.
Matched impedances
When fitting components together to carry electromagnetic signals, it is important to match impedance, which can be achieved with various matching devices. Failing to do so is known as impedance mismatch and results in signal loss and reflections. The existence of reflections allows the use of a time-domain reflectometer to locate mismatches in a transmission system. For example, a conventional radio frequency antenna for carrying broadcast television in North America was standardized to 300 ohms, using balanced, unshielded, flat wiring. However cable television systems introduced the use of 75 ohm unbalanced, shielded, circular wiring, which could not be plugged into most TV sets of the era. To use the newer wiring on an older TV, small devices known as baluns were widely available. Today most TVs simply standardize on 75-ohm feeds instead.
Inverse quantities
The reciprocal of a non-reactive resistance is called conductance. Similarly, the reciprocal of an impedance is called admittance. The conductance is the real part of the admittance, and the imaginary part is called the susceptance. Conductance and susceptance are not the reciprocals of resistance and reactance in general, but only for impedances that are purely resistive or purely reactive.
Acoustic impedance
In complete analogy to the electrical impedance discussed here, one also defines acoustic impedance, a complex number which describes how a medium absorbs sound by relating the amplitude and phase of an applied sound pressure to the amplitude and phase of the resulting sound flux.
Data-transfer impedance
Another analogous coinage is the use of impedance by computer programmers to describe how easy or difficult it is to pass data and flow of control between parts of a system, commonly ones written in different languages. The common usage is to describe two programs or languages/environments as having a low or high impedance mismatch. =Application to physical devices= Note that the equations above only apply to theoretical devices. Real resistors, capacitors, and inductors are more complex and each one may be modeled as a network of theoretical resistors, capacitors, and inductors. Rated impedances of real devices are actually nominal impedances, and are only accurate for a narrow frequency range, and are typically less accurate for higher frequencies. Even within its rated range, an inductor's resistance may be non-zero. Above the rated frequencies, resistors become inductive (power resistors more so), capactiors and inductors may become more resistive. The relationship between frequency and impedance may not even be linear outside of the device's rated range.
See also

- Characteristic impedance
- Balance return loss
- Balancing network
- Bridging loss
- Damping factor
- Forward echo
- Harmonic oscillator
- Impedance bridging
- Impedance matching
- Loading
- Log-periodic antenna
- Physical constants
- Reflection coefficient
- Reflection loss, Reflection (electrical)
- Resonance
- Return loss
- Sensitivity
- Signal reflection
- Smith chart
- Standing wave
- Time-domain reflectometer
- Voltage standing wave ratio
- Wave impedance
- Reactance
- Inductance
- nominal impedance for a practical layman's introduction
- Mechanical impedance
External links

- [http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imped.html Explaining Impedance]
- [http://www.geocities.com/SiliconValley/2072/elecrri.htm Resistance, Reactance, and Impedance] Category:Antenna terminology Category:Electronics terms Category:Physical quantity ja:インピーダンス

Balun

A balun is a device designed to convert between balanced and unbalanced electrical signals, such as between coaxial cable and twin-lead (pronounced lēd like reed, not lĕd like red). This is almost always done through the use of a small isolation transformer, with the earth ground or chassis ground left floating or unconnected on the balanced side. This transformer can then also perform impedance matching at the same time. A balun generally has no other functional purpose except for compatibility between systems. The most common uses of baluns are:

Radio equipment

In television, amateur radio, and other antenna installations and connections, to convert between 300 ohm ribbon cable (balanced) and 75 ohm coaxial cable (unbalanced) or to directly connect a balanced antenna to (unbalanced) coax. To avoid EMC problems it is a good idea to connect a centre fed dipole antenna to coaxial cable via a balun.

Narrow band designs

- One easy to make balun is a (λ/2) length of coaxial cable, the inner core of the cable is linked at each end to the one of the balenced connections for a feeder or diople, one of these terminals should be connected to the inner core of the coaxial feeder. All three braids should be connected together. This then forms a 4:1 balun which works at only one frequency.
- Another narrow band design is to use a λ/4 length of metal pipe, the coaxial cable is placed inside the pipe, at one end the braid is wired to the pipe while at the other end no connection is made to the pipe. The balenced end of this balun is at the end where the pipe is wired to the braid. The λ/4 conductor acts as a transformer converting the infinite impedance at the unconnected end into a zero impedance at the end connected to the braid. Hence any current entering the balun through the conncetion which goes to the braid at the end with the connection to the pipe will flow into the pipe. This balun design is not good for HF becuase of the long length of pipe which will be needed. An easy way to make such a blaun is to paint the outside of the coax with conductive paint, then to connect this paint to the braid.

Wide band designs

- For instance two coils on a ferite rod can be used as a balun in the following way. The two windings need to be very tightly wound together, this can be done with enameled wire in two different ways, either the two windings are wound with great care so that the two form a single layer where each turn is touching each of the adjacent turns of the other winding or the two wires are twisted together before winding the coil. The start of the first winding then needs to be connected to the end of the second winding. This connection then needs to be attached to the braid of the coaxial feeder, the core of the coaxial feeder is wired to one of the remaining connections. The two conductors for the balenced feeder are then wired to the coil connections which are not wired dirrectly to the braid of the coax. This design can be thought of as a autotransformer. In addition to acting as a balun this design acts as a step up transformer which gives a 4:1 change in the impedance.
- A RF choke can be used in place of a balun. If a coil is made using coaxial cable near to the feed point of a balanced antenna then the RF current which flows on the outer surface of the coaxial cable can be attenuated. One way of doing this would be to wrap a lossy material, such as iron wool or ferrite around the coaxial cable, one method of doing this would be to use the plastic cylinderical container that curry powder is sold in to hold the iron wool, two holes would be needed in the ends of the plastic screw top jar to allow the coaxial cable to pass through.

Audio equipment

In audio applications, to convert between high impedance unbalanced and low impedance balanced lines.

Power line communications

In power line communications, baluns are used in coupling signals onto a power line.
- In electronic communications, baluns are used to convert TWIN-X cables to Category 5 cables, and back.

Pictures of baluns

RF designs

Category 5 cable Simple homemade 1:1 balun using a toroidal core and coaxial cable.
This is a simple RF choke which works as a balun by preventing signals passing along the outside of the braid. Such a device can be used to cure TeleVision Interferance by acting as a braid-breaker. braid-breakerThe baluns used for home television antennas have a 4:1 turns ratio, to match the standard 300-ohm ribbon cable to 75-ohm coaxial cable.

Audio designs

ohmThree audio transformers. Except for the connections, all three are electrically identical, but only the leftmost two can be used as baluns. The one at left would normally be used to connect a high impedance source, such as a guitar, into a balanced microphone input, serving as a passive DI unit. The one in the centre is for connecting a low impedance balanced source, such as a microphone, into a guitar amplifier. The one at the right is not technically a balun, as it provides only impedance matching.

References

- Building and Using Baluns and Ununs: Practical Designs for the Experimenter, Jerry Sevick, 1996.
- Radio communication handbook, Edition five, Radio Society of Great Britain (RSGB), 1976, pages 12.41 and 13.5 See also: Transmission line transformers Category:Transformers (electrical) ja:バラン (電子工学)

Rubber

:This article is about the material rubber, for other uses see Rubber (disambiguation) Rubber is an elastic hydrocarbon polymer which occurs as a milky emulsion (known as latex) in the sap of a number of plants but can also be produced synthetically. The major commercial source of natural latex used to create rubber is the Para rubber tree, Hevea brasiliensis (Euphorbiaceae). This is largely because it responds to wounding by producing more latex. Other plants containing latex include figs (Ficus elastica), euphorbias, and the common dandelion. Although these have not been major sources of rubber, Germany attempted to use such sources during World War II when it was cut off from rubber supplies. These attempts were later supplanted by the development of synthetic rubber. Its density is 920 kg/m³. density In places like Kerala, where coconuts are in abundance, the shell of half a coconut is used as the collection container for the latex. The shells are attached to the tree via a short sharp stick and the latex drips down into it overnight. This usually produces latex up to a level of half to three quarters of the shell. The latex from multiple trees are then poured into flat pans and this is mixed with formic acid, which serves as a coagulant. After a few hours, the very wet sheets of rubber are wrung out by putting them through a press before they are sent onto factories where vulcanization and further processing is done. Aside from a few natural product impurities, natural rubber is essentially a polymer of isoprene units, a hydrocarbon diene monomer. Synthetic rubber can be made as a polymer of isoprene or various other monomers. Rubber is believed to have been named by Joseph Priestley, who discovered in 1770 that dried latex rubbed out pencil marks. The material properties of rubber make it an elastomer.

History

In its native Central America and South America, rubber has been collected for a long time. The Mesoamerican civilizations used rubber mostly from Castilla elastica. The Ancient Mesoamericans had a ball game using rubber balls (see: Mesoamerican ballgame), and a few Pre-Columbian rubber balls have been found (always in sites that were flooded under fresh water), the earliest dating to about 1600 BCE. According to Bernal Díaz del Castillo, the Spanish Conquistadores were so astounded by the vigorous bouncing of the rubber balls of the Aztecs that they wondered if the balls were enchanted by evil spirits. The Maya also made a type of temporary rubber shoe by dipping their feet into a latex mixture. Rubber was used in various other contexts, such as strips to hold stone and metal tools to wooden handles, and padding for the tool handles. While the ancient Mesoamericans did not have vulcanization, they developed organic methods of processing the rubber with similar results, mixing the raw latex with various saps and juices of other vines, particularly Ipomoea alba, a species of Morning glory. In Brazil the natives understood the use of rubber to make water-resistant cloth. A story says that the first European to return to Portugal from Brazil with samples of such water-repellent rubberized cloth so shocked people that he was brought to court on the charge of witchcraft. Portugal When samples of rubber first arrived in England, it was observed that a piece of the material was extremely good for rubbing out pencil marks on paper. This was the origin of the material's English name of 'rubber'. Blocks of the material are still used for this purpose, and known as 'rubbers' in British English, causing occasional amusement to speakers of American English, to whom a 'rubber' is a condom (usually made from latex). (American English uses 'eraser' to refer to the rubber block.) The para rubber tree initially grew in South America, where it was the main source of what limited amount of latex rubber was consumed during much of the 19th century. About 100 years ago, the Congo Free State in Africa was a significant source of natural rubber latex, mostly gathered by forced labor. The Congo Free State was forged and ruled as a personal colony by the Belgian King Leopold II where millions of Africans died as a result of lust for rubber and rubber profits. After repeated efforts (see Henry Wickham) rubber was successfully cultivated in Southeast Asia, where it is now widely grown. Rubber, natural or synthetic substance characterized by elasticity, water repellence, and electrical resistance. Natural rubber is obtained from the milky white fluid called latex, found in many plants; synthetic rubbers are produced from unsaturated hydrocarbons.

Current sources of rubber

Today Asia is the main source of natural rubber. Over half of the rubber used today is synthetic, but several million tonnes of natural rubber are still produced annually, and is still essential for some industries, including automotive and military. Hypoallergenic rubber can be made from Guayule. Early experiments in the development of synthetic rubber led to the invention of Silly Putty. Natural rubber is often vulcanized, a process by which the rubber is heated and sulfur is added to improve resilience and elasticity. The process of vulcanization greatly improved the durability and utility of rubber from the 1830s on. The successful development of vulcanisation is most closely associated with Charles Goodyear. Carbon black is often used as an additive to rubber to improve its strength, especially in vehicle tires.

External links

- [http://www.irrdb.com/IRRDB/NaturalRubber/Default.htm International Rubber Research & Development Board]
- [http://astlettrubber.com/bulletins.shtml Astlett Rubber Inc]
- [http://www.sicom.com.sg Singapore Commodity Exchange] Category:Natural materials Category:Organic polymers Category:Terpenes and terpenoids ja:ゴム

LaTeX

L^AT_EX, written as LaTeX in plain text, is a document preparation system for the TeX typesetting program. It offers programmable desktop publishing features and extensive facilities for automating most aspects of typesetting and desktop publishing, including numbering and cross-referencing, tables and figures, page layout, bibliographies, and much more. LaTeX was originally written in 1984 by Leslie Lamport and has become the dominant method for using TeX —few people write in plain TeX anymore. The current version is LaTeX2ε.

Pronunciation

LaTeX is usually pronounced "LAY-tech" or "LAH-tech" (IPA: , ), where ch represents the sound of ch in German Bach or Scottish loch: the last character in the name is actually a capital chi, as the name of TeX derives from the Greek τεχνη (skill, art, technique). While TeX's creator Donald Knuth promoted the "tech" pronunciation, Lamport has said he doesn't favor or deprecate any pronunciation for LaTeX. It is traditionally printed with the special typographical logo shown on this page. In media where the logo cannot be precisely reproduced in running text, the word is typically given the unique capitalization LaTeX to avoid confusion with the word "latex".

The typesetting system

latex.]] LaTeX is based on the idea that authors should be able to concentrate on writing within the logical structure of their document, rather than spending their time on the details of formatting. It encourages the separation of formatting from content, whilst still allowing manual typesetting adjustments where needed. By keeping the formatting details in a separate file from the text, it is often regarded as superior to word processors and most other desktop publishing systems, which allow trivially easy visual layout changes but tend to intertwine content and form so tightly that consistency and automation are often difficult. LaTeX also provides great flexibility in formatting while maintaining the identity of structure, which purely structural systems like SGML and XML do not directly address. LaTeX can be arbitrarily extended by using the underlying macro language for developing custom formats. For example, there are numerous commercial implementations of the whole TeX system (which includes LaTeX), and vendors may offer extra features like phone support and additional typefaces. LyX is a free visual document processor that uses LaTeX for a back-end. TeXmacs is a free, WYSIWYG editor with similar functionalities as LaTeX, but a different typesetting engine. A number of popular commercial DTP systems use modified versions of the original TeX typesetting engine. The recent rise in popularity of XML systems and the demand for large-scale batch production of publication-quality typesetting from such sources has seen a steady increase in the use of LaTeX. The example below shows an example of a LaTeX input (left) and output (right): [http://sciencesoft.at/index.jsp?link=latex&lang=en&wiki=1 Online LaTex], which uses this example.

Community

batch production LaTeX was originally most commonly used by mathematicians and scientists, amongst whom it remains the favored tool for writing papers, preprints, and books. Because of the underlying TeX system, originally developed for documents with mathematics, laying out mathematical expressions is considered to be easier, and the resulting typesetting of higher quality, than any competing document-processing systems. Many scientific journals and other publishers provide free LaTeX packages which implement their "in-house" typesetting styles. The popularity of LaTeX in the technical and academic communities is perhaps partly due to its early availability on Unix systems, and the comparative unavailability of competing word processors on those platforms until recently. But from an early stage LaTeX was available on a wider range of hardware and software than any other program, and versions are now available for almost any system from PDAs to desktop PCs to supercomputers. LaTeX is less popular than mainstream desktop publishing software outside the technical communities for several reasons. It is regarded as hard to learn for people with no previous experience of markup languages. Although it is very easy to customise the appearance of articles, books, and reports, using only a handful of instructions, it remains basically a typesetter for automating document production, not a manual page design program, so performing complex visual layouts incorporating multiple images is difficult. Another barrier to usage for many is the asynchronous interface used in most free versions, where editing is done in a different window from the typeset display. Inverse search can be used to bridge this problem partially. Several commercial implementations, however, use a synchronous typographic display like other DTP systems (as does the non-commercial and open source LyX). Alternatively, GNU TeXmacs is a free WYSIWYG editor which offers features similar to LaTeX, but is based on a different typesetting engine.

Licensing issues

LaTeX is free software. It has a peculiar license called LPPL, not compatible with the GNU General Public License, that allows redistribution and modification, but requires that modified files carry a modified filename. This ensures that files that depend on other files will produce the expected behavior and avoids problems similar to DLL hell. A new version of the LPPL that will be compatible with the GPL is in the works.

Frontends

Because LaTeX markup code can be hard to remember and/or time consuming to learn, there are a few front ends to help:
- Kile: IDE designed mainly for KDE ([http://kile.sourceforge.net/ homepage]).
- LEd: A free environment for rapid TeX/LaTeX document development under MS Windows ([http://www.latexeditor.org homepage]).
- LyX: WYSIWYM (What you see is what you mean) IDE ([http://www.lyx.org/ homepage]).
- Scientific Letter: Commerce mail software with export to TeX/LaTeX ([http://www.sciletter.com/ homepage]).
- Texmaker: Free cross-platform LaTeX editor. Runs on Windows, Mac OS X and Unix (GNU/Linux binary). Is released under the GPL license ([http://www.xm1math.net/texmaker/index.html homepage]).
- TeXnicCenter: IDE designed for MS Windows users under GPL ([http://www.toolscenter.org/ homepage]).
- TeXShop: A free front end for Mac OS X, with editor and output window ([http://www.uoregon.edu/~koch/texshop/texshop.html homepage]).
- WebTex: A free MiKTeX/CGI driven web front end ([http://dev.baywifi.com/latex/ homepage]).
- WinEdt: Shareware IDE for Windows 9x/NT4.0/2000/XP ([http://www.winedt.com/ homepage]).
- WinShell: Freeware IDE for Windows 9x/NT4.0/2000/XP ([http://www.winshell.de/ homepage]).

External links

Community

- [http://www.latex-project.org/ Official LaTeX project site] web site for open development of LaTeX (you can also obtain a CVS snapshot of LaTeX3, the next version of LaTeX which is not yet released)
- [http://www.tug.org/ The TeX Users Group]
- [news:comp.text.tex comp.text.tex]. A Usenet newsgroup for (La)TeX related questions, comp.text.tex is an invaluable resource for (La)TeX. Search the archives with [http://groups.google.com/group/comp.text.tex Google Groups] before posting.
- [irc://irc.freenode.net/#latex #latex] IRC chat room on Freenode

Periodicals

- The PracTeX Journal. Online journal of the TeX Users Group.
- TUGBoat. Print journal of the TeX Users Group.

Tutorials/FAQs

- [http://www.lecb.ncifcrf.gov/~toms/latexforbeginners.html LaTeX for Beginners]
- [http://people.ee.ethz.ch/~oetiker/lshort/lshort.pdf The Not So Short Introduction to LaTeX2e], or LaTeX2e in 133 minutes (2.21 MiB PDF file).
- [http://www.tex.ac.uk/cgi-bin/texfaq2html?introduction=yes The UK TeX FAQ] List of questions and answers that are frequently posted at comp.text.tex.
- [http://www.ctan.org/tex-archive/info/beginlatex/ Formatting Information] Online book for beginners available in [http://www.ctan.org/tex-archive/info/beginlatex/html/index.html HTML] and [http://www.ctan.org/tex-archive/info/beginlatex/beginlatex-3.6.pdf PDF]
- [http://www.maths.tcd.ie/~dwilkins/LaTeXPrimer/ LaTeX Primer] A basic guide to LaTeX.
- [http://www.tug.org.in/tutorials.html Tutorials in LaTeX] Free manual distributed by the India TeX Users Group (TUG).
- [ftp://ftp.ams.org/pub/tex/doc/amsmath/short-math-guide.pdf The AMS Short Math Guide for LaTeX] A concise summary of math formula typesetting features (PDF file).
- [http://www.rna.nl/tex.html TeX on Mac OS X] Guide to using TeX and LaTeX on a Mac.
- [http://www-h.eng.cam.ac.uk/help/tpl/textprocessing/ Text Processing using LaTeX]
- [http://tex.loria.fr/index.html The (La)TeX encyclopaedia]
- [http://www.giss.nasa.gov/latex/ Hypertext Help with LaTeX]
- [http://www-h.eng.cam.ac.uk/help/tpl/textprocessing/ltxprimer-1.0.pdf LaTeX Tutorials: a Primer] (PDF file)
- [http://www.andy-roberts.net/misc/latex/index.html Getting to Grips with LaTeX] Latex tutorials taking you from the very basics towards more advanced topics.
- [http://www.math.auc.dk/~dethlef/Tips/preparation.html LaTeX, Emacs etc. for your PC] A useful and step-by-step guide to getting Miktex and Emacs working together on a Windows PC.

Add-on Packages

- [http://latex-beamer.sourceforge.net/ LaTeX-beamer] Create sophisticated, structured presentations and slides using LaTeX.
- [http://www.ctan.org/tex-archive/macros/latex/contrib/powerdot/ powerdot] Another very good class for presentations.
- [http://www.phil.cam.ac.uk/teaching_staff/Smith/LaTeX/nd.html bussproofs.sty (and others)] Setting natural deduction tree proofs.
- [http://www.mcnabbs.org/andrew/linux/latexres/ Making a Resume in LaTeX] A LaTeX template with instructions for making an easily-maintained resume.
- [http://latex2rtf.sourceforge.net/ LaTeX2RTF] Translator program which is intended to convert a LaTeX document into the RTF format.

Reference

- [http://www.ctan.org The Comprehensive TeX Archive Network] Latest (La)TeX-related packages and software
- [http://www.tug.org/tds/ TeX Directory Structure], used by many (La)TeX distributions
- [http://www.math.missouri.edu/~stephen/naturalmath/ Natural Math] converts natural language math formulas to LaTeX representation
- [http://www.ctan.org/tex-archive/info/l2tabu/english/l2tabuen.pdf Obsolete packages and commands]
- [http://www.miktex.org/ MiKTeX] A popular and up-to-date TeX (including LaTeX) implementation for Windows.
- . The Companion is an excellent resource for intermediate to advanced LaTeX users. For those already somewhat familiar with LaTeX, this is probably the single most useful available book on the subject. The book website has the complete Table of Contents and a sample chapter available for download. Category:Domain-specific programming languages Category:Free software Category:Page description languages Category:TeX Category:Typesetting programming languages Category:Typesetting ja:LaTeX ko:LaTeX

Chloroprene

Chloroprene is the common name for the organic compound 2-chloro-1,3-butadiene, which has the chemical formula ₄₅. The chemical structure is shown at right. It is used as monomer for the production of the polymer polychloroprene, a type of synthetic rubber. Polychloroprene is better known to the public as Neoprene, the trade name DuPont gave it when the company first developed it and currently used by DuPont Dow.

Production of chloroprene

The acetylene process was used to produce chloroprene until the 1960s. In this process, acetylene and hydrogen chloride were used as shown here: 554 px This process had disadvantages in that it was very energy-intensive and had high investment costs. The modern chloroprene process which is currently used by nearly all makers uses butadiene differently. 1,3-Butadiene undergoes addition of chlorine across one of its double bonds in its molecule to give 3,4-dichloro-1-butene. Then this compound undergoes an elimination of a hydrogen atom in the #3 position and the chlorine atom in the #4 position as HCl forming a double bond between the #3 and #4 carbon atoms in the molecule, yielding chloroprene.

References

[http://www.iisrp.com/WebPolymers/04FinalPolychloropreneIISRP.pdf Polychloroprene (CR), chloroprene rubber] category:dienes Category:Monomers ja:クロロプレン

Nylon

Nylon is a synthetic polymer, a plastic, invented on February 28, 1935 by Wallace Carothers at DuPont of Wilmington, Delaware, USA. The material was announced in 1938, and the first nylon products were a nylon bristled toothbrush made with nylon yarn (on sale on February 24, 1938) and more famously, women's stockings (on sale on May 15, 1940). Nylon fibres are now used to make many synthetic fabrics, and solid nylon is used as an engineering material.

Chemistry

Nylon is made of repeating units with amide linkages between them: hence it is frequently referred to as a polyamide. This is a more correct nomenclature, though still somewhat flawed. There are several different versions of these "nylons", which include various polyamides made using mono- or diacid and mono- or diamine monomers. The numbers usually appended to the "nylon" or "PA" part refer to the number of carbons in the reactive monomer. It was the first synthetic fibre to be made entirely from inorganic ingredients: coal, water and air. These are formed into two intermediate chemicals, known as monomers, which then react to form long polymer chains. Most types of nylon are condensation polymers, formed by reacting almost exactly equal parts of a diamine and a dicarboxylic acid, so that peptide bonds form on each end of a given monomer in a process analogous to biological polypeptide formation. The most common variant is nylon 6,6, also called nylon 66, which refers to the fact that both the diamine (hexamethylene diamine) and the diacid (adipic acid) have 6 carbon backbones. The diacid and diamine units alternate in the polymer chain. Therefore, unlike natural polyamides like proteins, the direction of the amide bond reverses at each bond. Another common nylon is nylon 6 or polycaprolactam. It is special because it's not a condensation polymer, but instead is formed by ring-opening polymerization of caprolactam. In this process, the peptide bond within the caprolactam molecule is broken, with the active groups on each side re-forming two new bonds as the monomer becomes part of the polymer backbone. In this polymer, all amide bonds lie in the same direction, but the properties of nylon 6 are almost indistinguishable from those of nylon 6,6. In keeping with this nomenclature, "Nylon 6,12" or "PA-6,12" consists of a polymer based upon a 6-carbon diamine, and a 12-carbon diacid. You can extrapolate from this to N-6,11; N-10,12; etcetera. Other "nylons" or "polyamides" include copolymerized carboxylic acid/diamine products that are NOT based upon the monomers listed above. For example, some "nylon" polymers are polymerized with the addition of diacids like terephthalic acid or isophthalic acid (more commonly associated with polyesters); copolymers of N66/N6; copolymers of N66/N6/N12; and others.

Historical uses

During World War II, nylon replaced Asian silk in parachutes. It was also used to make tires, tents, ropes, ponchos, and other military supplies. It was even used in the production of a high-grade paper for US currency. At the outset of the War, cotton accounted for more than 80 percent of all fibres used, and manufactured and wool fibres accounted for the remaining 20 percent. By August, 1945, manufactured fibres had risen to 25 percent, and cotton had dropped to 75 percent. Some conspiracy theorists surmise that cannabis sativa was made illegal because the fibres from the hemp plant, used for fabrics and ropes, were in strong competition with nylon. However, nylon fiber is more than twice as strong as hemp fiber and weighs 25% less. While hemp was originally used in climbing rope, it is now virtually unused in modern climbing, including countries where cannabis is legal. Therefore, it is unlikely that hemp makes better rope than nylon in the general case. Some of the terpolymers based upon nylon are used every day in packaging. One use of nylon polymers is in meat wrappings. This usage includes some sausage/meat sheaths.

Etymology

There is no evidence other than the places of origin for the popular belief that "nylon" is a contraction of "NY" (for "New York") and "Lon" for "London", the two cities where the material was first manufactured. In 1940 John W. Eckelberry of DuPont stated that the letters "nyl" were arbitrary and the "on" was copied from the names of other fibres such as cotton and rayon. A later publication by DuPont (Context, vol. 7, no. 2, 1978) explained that the name was originally intended to be "No-Run" ("run" in this context meaning "unravel"), but was then modified to avoid making such an unjustified claim and to make it sound better. The story goes that Carothers changed one letter at a time until DuPont's management were satisfied. However the facts are that Carothers was not involved in the nylon project over the last year of his life and had committed suicide well before the push to market began and the name nylon was coined. One legend holds that nylon stands for "now you, lazy old Nippon," as nylon was developed in the 1930s. In that decade, a chemical "war" was taking place between the United States and Japan (Nippon). Even though the word nylon was coined, it was never trademarked.

Uses

- nylon fiber
- stockings
- leggings
- pantyhose (called tights in the UK)
- toothbrush bristles
- fishing lines
- nets
- carpet fibre
- airbag fibre
- auto parts (intake manifolds, gas tanks)
- slings and rope used in climbing gear
- machine parts, such as gears and bearings
- parachutes
- metallized nylon balloons
- classical and flamenco guitar strings
- jacket
- paintball marker bolts
- tennis racquet strings

Litre

The litre (spelled litre in Commonwealth English and liter in American English) is a unit of capacity. There are two official symbols: lowercase l and uppercase L. The litre is not an SI unit but is accepted for use with the SI. The SI unit of volume is the cubic metre (m³).

Definitions and equivalents

A litre is defined as a special name for a cubic decimetre (1 L = 1 dm³).
- 1 L = 1000 cm³ (exactly)
- 1000 L = 1 m³ (exactly)

SI prefixes applied to the litre

The litre may be used with some SI prefixes.

Name origin

The word "litre" is derived from an older French unit, the litron, whose name came from Greek via Latin.

Other common metric equivalencies

- 1 µL (microlitre) = 1 mm³ (cubic millimetre)

Conversions

One litre :≈ 0.87987699 Imperial quart ::Inverse: One Imperial quart ≡ 1.1365225 litres :≈ 1.056688 US fluid quarts ::Inverse: One US fluid quart ≡ 0.946352946 litres :≈ 0.0353146667 cubic foot ::Inverse: One cubic foot ≡ 28.316846592 litres One millilitre :≈ 0.03519507972785404600 Imperial fluid ounce ::Inverse: One Imperial fluid ounce ≡ 28.4130625 mL :≈ 0.0338140227018429971686 US fluid ounce ::Inverse: One US fluid ounce ≡ 29.5735295625 mL :≈ 0.0000353146667 cubic foot ::Inverse: One cubic foot ≡ 28,316.846592 mL

Explanation

Litres are most commonly used for items measured by the capacity or size of their container (such as fluids and berries), whereas cubic metres (and derived units) are most commonly used for items measured either by their dimensions or their displacements. The litre is often also used in some calculated measurements, such as density (kg/L), allowing an easy comparison with the density of water. One litre of water weighs almost exactly one kilogram. Similarly: 1 ml of water weighs about 1 g; 1000 litres of water weighs about 1000 kg (1 tonne). This relationship is due to the history of the unit but since 1964 has not been part of the definition.

Symbol

Originally, the only symbol for the litre was l (lowercase letter l), following the SI convention that only those unit symbols that abbreviate the name of a person start with a capital letter. In many English-speaking countries, the most common shape of a handwritten Arabic digit 1 is just a vertical stroke, that is it lacks the upstroke added in many other cultures. Therefore, the digit 1 may easily be confused with the letter l. On some typewriters, particularly older ones, the l key had to be used to type the numeral 1. Further, in some typefaces the two characters are nearly indistinguishable. This caused some concern, especially in the medical community. As a result, L (uppercase letter L) was accepted as an alternative symbol for litre in 1979. The United States National Institute of Standards and Technology now recommends the use of the uppercase letter L, a practice that is also widely followed in Canada and Australia. In these countries, the symbol L is also used with prefixes, as in mL and µL, instead of the traditional ml and µl used in Europe. Prior to 1979, the symbol ℓ (script small l, U+2113), came into common use in some countries; for example, it was recommended by South African Bureau of Standards publication M33 in the 1970s. This symbol can still be encountered occasionally in some English-speaking countries, but it is not used in most countries and not officially recognised by the BIPM, the International Organization for Standardization, or any national standards body.

History

In 1793, the litre was introduced in France as one of the new "Republican Measures", and defined as one cubic decimetre. In 1879, the CIPM adopted the definition of the litre, and the symbol l (lowercase letter l). In 1901, at the 3rd CGPM conference, the litre was redefined as the space occupied by 1 kg of pure water at the temperature of its maximum density (3.98 °C) under a pressure of 1 atm. This made the litre equal to about 1.000 028 dm³ (earlier reference works usually put it at 1.000 027 dm³). In 1964, at the 12th CGPM conference, the litre was once again defined in exact relation to the metre, as another name for the cubic decimetre, that is, exactly 1 dm³. [http://ts.nist.gov/ts/htdocs/230/235/appxc/appxc.htm#footnote1 NIST Reference] In 1979, at the 16th CGPM conference, the alternative symbol L (uppercase letter L) was adopted. It also expressed a preference that in the future only one of these two symbols should be retained, but in 1990 said it was still too early to do so.

External links

- [http://www.bipm.org/en/si/si_brochure/ BIPM's "SI Brochure"]
- [http://www.bipm.org/en/si/si_brochure/chapter4/table6.html BIPM's "(Table 6 -) Non-SI units accepted for use with the International System"]
- [http://physics.nist.gov/cuu/Units/units.html NIST note on SI units]
- [http://physics.nist.gov/cuu/Units/outside.html NIST recommends uppercase letter L]
- [http://www.npl.co.uk/npl/reference/international.html UK National physical laboratory's "Internationally recognised non SI units" page] Category:Units of volume ko:리터 ja:リットル simple:Litre th:ลิตร

Solar balloon

A solar balloon is a black balloon that is filled with air. Due to the dark color of the balloon, it heats up in the sun. This causes the air present inside the solar balloon to expand and reduce in density compared with the surrounding air. As such, the balloon functions like a hot air balloon. Usage at the moment is currently restricted to the toy market, although it has been proposed that it be used in the investigation of planet Mars.

Balloon flight competition

A balloon flight competition is a competition with which it counts to send balloon postal service over as greatly as possible distances, because the flight of the related balloon is not susceptible, the result, as far as all started balloons well with hydrogen or helium filled are – of the wind conditions and of the probability is that the balloon is found at that decline plotted, dependent.

Balloon rocket

A balloon rocket is a balloon filled with air. To launch the rocket, a person releases the opening of the balloon. The balloon rocket is then propelled by the escape of the air which creates thrust. The flight altitude amounts to some meters. The balloon rocket is not by any means a technical machine, and can be used easily as a cheap and harmless way to demonstrate simple physics. A common variant of the balloon rocket uses a string, a drinking straw and adhesive tape. The string is threaded through the straw as is attached at both ends to objects of some kind, such as a doorknob on one end and a chair on the other. The straw is then taped to the top of the air-filled balloon, with the open end of the balloon touching one of the objects. When the balloon is released, the thrust from the opening propells it along the length of the string. The balloon can also be filled with gases other than air, with similar results. Category:Balloons

Ceiling balloon

A ceiling balloon is used by meteorologists to determine the height of the base of clouds above ground level during daylight hours.

How it is used

A ceiling balloon is a small, usually red, rubber balloon commonly measuring 76 mm (3 in) across prior to inflation. After inflation the balloon is taken outside and released. By timing the balloon from release until it enters the cloud a ceiling height can be obtained. When correctly inflated the balloon will rise at rate of 140 m/min (460 ft/min). The bases of clouds are very rarely flat and solid, so the ceiling height is not when the balloon disappears but when the colour begins to fade. The balloon can also be used to measure the vertical visibility into a layer of fog or blowing snow. In this case the balloon will begin to fade as soon as it is released, so the vertical visibility is when the balloon disappears. If the balloon is visible for a considerable distance into the cloud layer the observer should make note of it as it is of importance to aircraft. The ceiling balloon is a reliable, safe and simple way to get an indication of the height of clouds. However, it does suffer from some disadvantages that the observer must be aware of. Rain and wet snow may slow the ascent of the balloon, giving a falsely high ceiling and high winds and poor visibility may cause the balloon to appear to enter the cloud before it actually does. As the balloon rises at a rate of 140 m/min (460 ft/min) it will take over five minutes for the balloon to reach 700 m (2300 ft). Beyond this height the ability to follow the balloon, even with binoculars, is poor, as even the slightest movement of the eye off the balloon will almost certainly ensure that it vanishes. At night when it is not practical to use a balloon the ceiling projector is used. However, during twilight it may be impossible to use the ceiling projector and then a pibal (pilot balloon) light may be used. This is a simple flashlight bulb attached to a battery. To charge the battery it is immersed in water for three minutes and then tied to the balloon prior to inflation. These are rarely used today.

Technical details

The balloons and associated equipment are usually stored in a cabinet mounted on a wall close to the gas cylinders. The cabinet has three doors one of which opens down and to it the filler stand is attached. At the top of the filler stand is a "L" shaped pipe with two rings, a small one on the bottom and a larger one on the top called the inflation nozzle. The rings stop the tube from dropping through the stand or rising too far when the balloon is inflated. The top ring has several grooves cut into to help grip the balloon which is fitted to it. At the bottom of the pipe is a weight that, when the precise amount of gas has been added, will lift to indicate the balloon is full. A rubber hose is attached to this pipe and passes through the filler stand twice. The first hole is larger than the tube to permit movement, while the second is used to hold the tubing in place. From there the tube runs to a needle valve that controls the amount of gas flowing to the balloon. A second tube will then run from the valve to a regulator valve that is attached to the gas cylinder. This valve has two pressure gauges attached. One showing the total pressure remaining in the gas cylinder and the second showing the amount of gas flowing through the tubing. Typically the cylinder, which is made of steel and weighs about 140 lb (65 kg). It contains the equivalent of about 200 ft³ (5.7 m³) of gas at standard pressure, stored at a pressure of 2000 psi (14 megapascals) and will inflate approximately 120 balloons. On the opposite side of the cabinet is space to store balloons, string and pibal lights. The gas used to fill the balloon is usually helium but can also be hydrogen. However, due to its explosive nature in an oxygen atmosphere, hydrogen is rarely used. The balloon is attached to the inflation nozzle and a piece of string is wound around the neck. After donning safety glasses and hearing protection a check is made to ensure the needle valve is fully closed. The main valve on the cylinder is then opened, followed by the regulator valve. Next, the needle valve is opened and the balloon begins to inflate. As the balloon reaches the correct size the inflation nozzle will begin to lift. At this point the needle valve is closed along with the regulator valve and cylinder vale. The string is then used to tie off the balloon neck to ensure that no gas can escape. Caution must be used during inflation due to the occasional faulty balloon and its failure. If the person inflating the balloon is not wearing goggles or hearing protectors then eye or ear damage can result.

References

- Environment Canada - Atmospheric Environment Services, Technical Manual (TM07-01-01) Ceiling Balloon Equipment 76 mm (3 in). Category:Meteorology Category:Balloons

Weather balloon

, Canada]] , Canada]] A weather balloon is a balloon which carries instruments aloft to send back information on atmospheric pressure, temperature, and humidity by means of a small, expendable measuring device called a radiosonde. To obtain wind data, they can be tracked by radar, radio direction finding, or navigation systems (such as the satellite based Global Positioning System). The balloon itself produces the lift, and is usually made of a highly flexible latex material (though Chloroprene may also be used). The unit that performs the actual measurements and radio transmissions hangs at the lower end of the string, and is called a radiosonde. Specialized radiosondes are used for measuring particular parameters, such as determining the ozone concentration. In North America prior to release the balloon is usually filled with hydrogen (though helium can be used as a substitute) gas. The ascent rate can be controlled by the amount of gas the balloon is filled with. Weather balloons may reach altitudes of 40 km (25 miles) or more, limited by diminishing pressures causing the balloon to expand to such a degree (typically by a 100:1 factor) that it disintegrates. The instrument package is usually lost. Above that altitude sounding rockets may be used. Major manufacturers of balloons are Totex Corporation and Cosmopren in Japan, and Kaysam in the US.

External links

- [http://weather.uwyo.edu/upperair/sounding.html Atmospheric Soundings for Canada and the United States] - University of Wyoming
- [http://www.chem.hawaii.edu/uham/lift.html Balloon Lift With Lighter Than Air Gases] - University of Hawaii
- [http://www.nssl.noaa.gov/projects/telex/videos.html Examples of Launches of Instrumented Balloons in Storms] - NSSL
- [http://www.ofcm.gov/fmh3/text/default.htm Federal Meteorological Handbook No. 3 - Rawinsonde and Pibal Observations]
- [http://www.photolib.noaa.gov/historic/nws/kite1.html Kites and Balloons] - NOAA Photo Library
- [http://www.wff.nasa.gov/~code820/ NASA Balloon Program Office] - Wallops Flight Facility, Virginia
- [http://avc.comm.nsdlib.org/cgi-bin/wiki_grade_interface.pl?Weather_Balloons National Science Digital Library: Weather Balloons] - Lesson plan for middle school
- [http://www.pilotballoon.com/ Pilot Balloon Observation Theodolites] - Martin Brenner, CSULB Category:Balloons (aircraft) Category:Meteorology Category:Unmanned vehicles Category:Scientific observation

Party balloon

A party balloon is a little unmanned hot air balloon. For amusement, people let these small balloons fly at a party; they can be seen from some distance and are therefore suitable to mark the venue of the party. Much like a kite a party balloon should be tied on a rope, because there is some danger of setting fire: the balloon usually carries and is powered by a candle. In China these balloons are used to celebrate New Years Day. They are made of thin paper where the candle light comes shining through. In the streets, people let these usually cylindrical objects fly. It is 1.4 m high and 75 cm in diameter and has a bamboo and wire frame. The source of heat to create the motive power is a candle in the form of ring. At lift-off additional power has to be created by lighting some paper underneath the balloon. The balloons fly about 20 minutes on average. There should be no wind. In the winter and close to sea level it will fly best because it has more buoyancy. The danger that the balloon will cause a fire when it comes down is lowest under these conditions.

Cubic metre

The cubic metre (symbol m³) is the SI derived unit of volume. It is the volume of a cube with edges one metre in length.

History

Older equivalents were the stere and the kilolitre. The deprecation of the stere began in 1978, when the CIPM marked it (and several other metric units) as "undesirable" where not already in use, and strongly encouraged their discontinuation; in the United States, it was legally deprecated in 1982 (Federal Register, February 26, 1982, 47 FR 8399-8400) [http://physics.nist.gov/cuu/Units/register.html] [http://www.sizes.com/units/stegravere.htm].

Conversions

1 cubic metre is equivalent to:
- 1,000 litres (exactly)
- ~35.3 cubic feet (approximately). 1 cubic foot is 0.028 316 846 592 m³ (exactly)
- ~1.31 cubic yards (approximately). 1 cubic yard is 0.764 554 857 984 m³ (exactly)
- ~6.29 oil barrels (approximately). 1 barrel is 0.158 987 294 928 m³ (exactly) A cubic metre of pure water at a temperature of 3.98 °C (degrees Celsius) and standard atmospheric pressure has a mass of 999.972 kg (nearly one tonne). It is sometimes abbreviated m3 or m^3 when superscript characters are not available/accessible (i.e. in some typewritten documents and postings in Usenet newsgroups).

Multiples and submultiples

- A cubic decimetre (symbol dm³) is the volume of a cube of side length 1 decimetre (0.1 metre).
- 1 cubic decimetre is now equal to 1 litre. See 1 E-3 m³ for a comparison with other volumes.
- From 1901 to 1964 of the litre was defined as the volume of 1 kilogram of pure water at 4 degrees Celsius and 760 millimetres of mercury pressure. During this time, a litre was about 1.000028 dm³. In 1964 the original definition was reverted to.
- A cubic centimetre (cm³) is equal to the volume of a cube with side length of 1 centimetre. It was the base unit of volume of the CGS system of units, and is a legitimate SI unit.
- The colloquial abbreviations cc and ccm are not SI but are common in some contexts in English. For example 'cc' is commonly used for denoting displacement of car and motorbike engines "the Mini Cooper had a 1275 cc engine". In American medicine 'cc' is also common, for example "100 cc of blood loss".
- A cubic millimetre (mm³) is the volume equal to that of a cube with edges of 1 millimetre.
- A cubic kilometre (km³) is the volume equal to that of a cube of side length 1 kilometre.

External link

- [http://www.ex.ac.uk/trol/scol/index.htm Conversion Calculator for Units of VOLUME] Category:Orders of magnitude (volume) Category:Units of volume Category:SI derived units ko:세제곱미터 ja:立方メートル th:ลูกบาศก์เมตร

Barrage balloon

A barrage balloon is a large balloon used as a defence against aircraft. The balloon is attached to the ground with metal cables, which are intended to ensnare the aircraft, notably its propellers. Some versions carried small explosive charges that would be pulled up against the aircraft to ensure its destruction. Barrage balloons were only really successful for low-flying aircraft, the weight of a longer cable making them impractical for higher altitudes. In 1938 the British Balloon Command was established to protect cities and key targets such as industrial areas, ports and harbours. They were intended to serve as a defense against the dive bomber, flying at heights up to 5,000 feet, forcing the aircraft to fly higher and into the range of concentrated anti-aircraft fire. By the middle of 1940 there were 1,400 balloons, a third of them over the London area, where they proved largely useless against the German level bombers that flew right over them. Construction continued however, and in 1944 there were almost 3,000 such balloons. They proved to be particularly effective against the V-1 flying bomb, which tended to fly at 2,000 feet or lower, and claimed about 100 V-1s destroyed. Many bombers were equipped with devices to cut these cables. It was the British that employed the most barrage balloons, so correspondingly it was the Germans that developed the most capable cable cutters. Their systems consisted of small C-shaped devices attached to the leading edge of the wing, when a cable entered it after sliding down the wing it would trigger a small explosive charge that drove a blade through the cable. British bombers were also equipped with such devices, but the Germans tended not to use a balloon barrage. Some barrage balloons worked by allowing the part of their cable that was hit by a plane's wing to detach, after which parachutes at each end would open, breaking the plane's wing.

External Links

- [http://www.bbrclub.org/ Barrage Balloon Reunion Club (UK)]

Airship

1931]] An airship is a buoyant aircraft that can be steered and propelled through the air. Unlike aerodynamic aircraft which stay aloft by moving an airfoil through the air in order to produce lift, airships stay aloft primarily by means of a cavity (usually quite large) filled with a gas of lesser density than the surrounding atmosphere. Airships are also known as dirigibles from the French dirigeable, meaning "steerable". The term airship is sometimes informally used to mean a machine capable of atmospheric flight. The term zeppelin is a genericized trademark that originally referred to airships manufactured by the Zeppelin Company. In modern common usage, the terms zeppelin, dirigible and airship are used interchangeably for any type of rigid airship, with the terms blimp or airship alone used to describe non-rigid airships. In modern technical usage however, airship is the term used for all aircraft of this type with zeppelin referring only to aircraft of that manufacture and blimp referring only to non-rigid airships. In the early days of airships, the primary lifting gas was hydrogen. Until the 1950s, all airships, except for those in the United States continued to use hydrogen because it offered greater lift and was cheaper than helium. The United States (until then the sole producer) was also unwilling to export helium because of its rarity and the fact it was considered a strategic material. However, hydrogen is flammable when mixed with air, a quality that has caused disasterous effects. The buoyancy provided by hydrogen is actually only about 10% greater than that of helium. So the issue became one of safety versus cost. American airships have been filled with helium since the 1920s and modern passenger-carrying airships are, by law, now prohibited from being filled with hydrogen. Some small experimental ships still use hydrogen. Other small experimental airships are filled with hot air in a fashion similar to a hot air balloon. They are sometimes called hotships. In contrast to airships, balloons are buoyant aircraft that generally rely on wind currents for movement, though vertical movement can be controlled in both.

Types

balloon
- Rigid airships (for example, Zeppelins) have rigid frames containing multiple, non-pressurized gas cells or balloons to provide lift. Rigid airships do not depend on internal pressure to maintain their shape.
- Non-rigid airships (blimps) use a pressure level in excess of the surrounding air pressure in order to retain their shape.
- Semi-rigid airships, like blimps, require internal pressure to maintain their shape, but have extended, usually articulated keel frames running along the bottom of the envelope to distribute suspension loads into the envelope and allow lower envelope pressures.
- Metal-clad airships have characteristics of both rigid and non-rigid airships, utilizing a very thin, airtight metal envelope, rather than the usual rubber-coated fabric envelope. Only two ships of this type, Schwarz's aluminium ship of 1897 and the ZMC-2, have been built to date.
- Hybrid airship is a general term for an aircraft that combines characteristics of heavier-than-air (airplane or helicopter) and lighter than air technology. Examples include helicopter/airship hybrids intended for heavy lift applications and dynamic lift airships intended for long-range cruising. It should be noted that most airships, when fully loaded with cargo and fuel, are typically heavier than air, and thus must use their propulsion system and shape to generate aerodynamic lift, necessary to stay aloft; technically making them hybrid airships. However, the term "hybrid airship" refers to craft that obtain a significant portion of their lift from aerodynamic lift and often require substantial take-off rolls before becoming airborne.

History

The development of airships was necessarily preceded by the development of balloons. See balloon (aircraft) for details.

Airship Pioneers

Airships were among the first aircraft to fly, with various designs flying throughout the 19th century. They were largely attempts to make relatively small balloons more steerable, and often contained features found on later airships. These early airships set many of the earliest aviation records. In 1784 Jean-Pierre Blanchard fitted a hand-powered propeller to a balloon, the first recorded means of propulsion carried aloft. The first person to make an engine-powered flight was Henri Giffard who, in 1852, flew 27 km (17 miles) in a steam-powered airship. Charles F. Ritchel made a public demonstration flight in 1878 of his hand-powered one-man rigid airship and went on to build and sell five of his aircraft. Paul Haenlein flew an airship with an internal combustion engine on a tether in Vienna, the first use of such an engine to power an aircraft. In 1880, Karl Wölfert and Ernst Baumgarten attempted to fly a powered airship in free flight, but crashed. In the 1880's a Serb named Ogneslav Kostovic Stepanovic also designed and built an airship. However the craft was destroyed by fire before it flew. In 1883, the first electric-powered flight was made by Gaston Tissandier who fitted a 1-1/2 horsepower Siemens electric motor to an airship. The first fully controllable free-flight was made in a French Army airship, La France, by Charles Renard and Arthur Krebs in 1884. The 170 foot long , 66,000 cubic foot airship covered 8 km (5 miles) in 23 minutes with the aid of an 8-1/2 horsepower electric motor. In 1888, Wölfert flew a Daimler-built petrol engine powered airship at Seelburg. In 1896, a rigid airship created by Croatian engineer David Schwarz made its first flight at Tempelhof field in Berlin. After Schwarz's death, his wife, Melanie Schwarz, was paid 15,000 Marks by Zeppelin for information about the airship. In 1901, Santos Dumont, in his airship "Number 6", a small blimp, won the Deutsch de la Meurthe prize of 100,000 francs for flying from the Parc Saint Cloud to the Eiffel Tower and back in under thirty minutes. Many inventors were inspired by Santos-Dumont's small airships and a veritable airship craze began world-wide. Many airship pioneers, such as the American Thomas Scott Baldwin financed their activities through passenger flights and public demonstration flights. Others, such as Walter Wellman and Melvin Vaniman set their sights on loftier goals, attempting two polar flights in 1907 and 1909, and two trans-atlantic flights in 1910 and 1912. The beginning of the "Golden Age of Airships" was also marked with the launch of the Luftschiff Zeppelin LZ1 in July of 1900 which would lead to the most successful airships of all time. These Zeppelins were named after the pioneer Count Ferdinand von Zeppelin. Von Zeppelin began experimenting with rigid airship designs in the 1890's leading to some patents and the LZ1 (1900) and the LZ2 (1906). At the beginning of WW1 the Zeppelin airships had a cylindrical aluminium alloy frame and a fabric-covered hull containing separate gas cells. Multi-plane tail fins were used for control and stability, and two engine/crew cars hung beneath the hull driving propellers attached to the sides of the frame by means of long drive shafts. Additionally there was a passenger compartment (later a bomb bay) located halfway between the two cars.

Airships in the First World War

WW1 The prospect of using airships as bomb carriers had been recognised in Europe well before the airships themselves were up to the task. H. G. Wells described the obliteration of entire fleets and cities by airship attack in The War in the Air (1908), and scores of less famous British writers declared in print that the airship had altered the face of world affairs forever. On 5 March 1912, Italian forces became the first to use dirigibles for a military purpose during reconnaissance west of Tripoli behind Turkish lines. It was World War I, however, that marked the airship's real debut as a weapon. Count Zeppelin and others in the German military believed they had found the ideal weapon with which to counteract British Naval superiority and strike at Britain itself. More realistic airship advocates believed the Zeppelin was a valuable long range scout/attack craft for naval operations. Raids began by the end of 1914, reached a first peak in 1915, and then were discontinued after 1917. Zeppelins proved to be terrifying but inaccurate weapons. Navigation, target selection and bomb-aiming proved to be difficult under the best of conditions. The darkness, high altitudes and clouds that were frequently encountered by zeppelin missions reduced accuracy even further. The physical damage done by the zeppelins over the course of the war was trivial, and the deaths that they caused (though visible) amounted to a few hundred at most. The zeppelins also proved to be vulnerable to attack by aircraft and antiaircraft guns, especially those armed with tracer bullets. Several were shot down in flames by British defenders, and others crashed 'en route'. In retrospect, advocates of the naval scouting role of the airship proved to be correct, and the land bombing campaign proved to be disastrous in terms of morale, men and material. Many pioneers of the German airship service died bravely, but needlessly in these propaganda missions. They also drew unwanted attention to the construction sheds which were bombed by the British Royal Naval Air Service. Meanwhile the Royal Navy had recognised the need for small airships to counteract the submarine threat in coastal waters, and beginning in February 1915, began to deploy the SS (Sea Scout) class of blimp. These had a small envelope of 60-70,000 cu feet and at first utilised standard single engined planes (BE2c, Maurice Farman, Armstrong FK) shorn of wing and tail surfaces as an economy measure. Eventually more advanced blimps with purpose built cars, such as the C (Coastal), C
- (Coastal Star), NS (North Sea), SSP (Sea Scout Pusher), SSZ (Sea Scout Zero), SSE (Sea Scout Experimental) and SST (Sea Scout Twin) classes were developed. The NS class, after initial teething problems proved to be the largest and finest airships in British service. They had a gas capacity of 360,000 cu feet, a crew of 10 and an endurance of 24 hours. Six 230 lb bombs were carried, as well as 3-5 machine guns. British blimps were used for scouting, mine clearance, and submarine attack duties. During the war, the British built over 225 non-rigid airships, of which several were sold to the Russia, France, the US and Italy. Britain, in turn, purchased one M-type semi-rigid from Italy whose delivery was delayed until 1918. Eight rigid airships had been completed by the armistice, although several more were in an advanced state of completion by the wars end. The large number of trained crews, low attrition rate and constant experimentation handling techniques meant that at the wars end Britain was the world leader in non-rigid airship technology. Royal Navy Airplanes had essentially replaced airships as bombers by the end of the war, and Germany's remaining zeppelins were scuttled by their crews, scrapped or handed over to the Allied powers as spoils of war. The British rigid airship program, meanwhile, had been largely a reaction to the potential threat of the German one and was largely, though not entirely, based on imitations of the German ships.