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DiracDelta - Science & Engineering encyclopedia Category: Sciences > Science & Engineering Date & country: 01/12/2007, UK Words: 4470

Yttrium
Yttrium is a lanthanide group metal which is found in most rare earth minerals, particularly yttrotantalite which, whilst containing yttrium and tantalum, also contains niobium, cerium, uranium, iron and calcium in varying amounts. The metal is stable in air due to the formation of an oxide film, but it will burn easily and will react with water to…

Yttrium Aluminium Garnet
A widely used solid-state crystal which is composed of yttrium and aluminium oxides which is doped with a small amount of the rare-earth neodymium. See also: Aluminium, Laser, Neodymium, Yttrium.

Zeeman Effect
The splitting of spectral lines when an external magnetic field is applied.Discovered in 1896 by P. Zeeman. In the normal Zeeman effect a single line is split into three if the field is perpendicular to the light path or two lines if the field is parallel to the light path. This effect can be explained by classical electromagnetic principles in ter…

Zener Diode
A diode that has been specially designed to break down at a particular voltage, consisting of a p-n junction with high doping concentrations on either side of the junction. It acts as a rectifier until the applied reverse voltage reaches a certain value, known as the Zener breakdown voltage, when the device becomes conducting. This effect occurs as…

Zener Voltage
reverse voltage at which breakdown occurs in a zener diode. See also: Zener Diode.

Zenith
Point in the Sky that is directly overhead. The direction to the zenith is perpendicular to the astronomical horizon. The point 180 degrees from the zenith is called the nadir. See also: Nadir, Zenithal.

Zenith Attraction
The effect of the earth's gravity on a meteoric body, which increases the velocity and moves the radiant toward the zenith. See also: Earth.

Zenith Telescope
Instrument for observing stars near the zenith (a point on the celestial sphere directly above the observer's position). See also: Zenith.

Zenithal
Of or pertaining to the zenith. See also: Zenith.

Zenographic
Referring to positions on Jupiter measured in latitude from Jupiter's equator and in longitude from a reference meridian.

Zero
In 876BC a symbol to represent zero was first used in India.

Zero Order Reaction
A reaction with a reaction rate that does not change when reactant concentrations change. See also: First Order Reaction, Reactants, Second Order Reaction.

Zero Point Energy
A minimum possible energy for an atom or molecule predicted by quantum mechanics. Electrons stay in motion and bonds continue to vibrate even at absolute zero because of zero point energy. See also: Quantum Mechanics.

Zero-Lift Chord
A chord taken through the trailing edge of an airfoil in the direction of the relative wind when the airfoil is at a zero-lift angle of attack. See also: Aerofoil, Airfoil.

Zero-Point Pressure
The pressure contributed by degenerate electrons, which do not come to rest even at absolute zero. See also: Absolute Zero, Electron.

Zeroth Law of Thermodynamics
If two bodies are each in thermal equilibrium with a third body, then all three bodies are in thermal equilibrium with each other. See also: First Law of Thermodynamics, Second Law of Thermodynamics, Thermal Equilibrium, Thermodynamics, Third Law of Thermodynamics.

Zeta Machine
An experimental thermonuclear device which generates a plasma inside a torus and employs the pinch effect for heating and compression. See also: Plasma.

Zeta Potential
Electric potential across all phase boundaries between solids and liquids. In colloids, the zeta potential is the potential across the ion layer around a charged colloidal particle. Neutralizing the zeta potential can cause the colloid to precipitate. Also known as the Electrokinetic Potential.

Zinc
Zinc is a brittle metal which has a blue cast. Extraction is achieved by heating the oxide with carbon and distilling out the metal. Zinc tarnishes in air and reacts with acids and alkalis. Zinc is used widely throughout industry; for example, it is used as a galvanic coating on steel to prevent corrosion, and is used as a constituent of various al…

Zinc Chloride
A white crystalline compound. The anhydrous salt, which is deliquescent, can be made by the action of hydrogen chloride gas on hot zinc. It has a relatively low melting point and sublimes easily, indicating that it is a molecular compound rather than ionic. Various hydrates also exist. Zinc chloride is used as a catalyst, dehydrating agent, and flu…

Zinc Chromate
Bright yellow pigment which chemically is substantially zinc chromate, although its precise composition is rather complex. Its chief use is in anti-corrosive paints and primers for steel.

Zinc Oxide
Used as a constituent of creams for its soothing qualities. White when cold and yellow when hot. It occurs naturally as a reddish orange ore - zincite, and can also be made by oxidizing hot zinc in air. It is amphoteric, forming zincates with bases. It is used as a pigment (Chinese white) in rubber, paint, and the plastic industries for its mildew …

Zinc Sulphate
Water soluble. Symbol ZnSO₄ Also known as White Vitriol, Goslarite

Zinc Sulphide
The commenest zinc ore. Symbol ZnS Also known as Sphalerite, Zinc Blende

Zincography
Process of etching unprotected parts of a zinc plate with strong acids to produce a printing surface. See also: Zinc.

Zip Fuel
A boron-base high-energy liquid propellant. See also: Boron.

Zirconium
Zirconium is a hard, lustrous, silvery coloured metal which is extracted from its ores (the oxide or zircon, ZrSiO₄) by conversion to the tetrahalide followed by reduction with magnesium. The metal is extremely corrosion resistant due to the formation of a stable oxide film and is unaffected by acids (with the exception of HF) and alkali…

Zirconium Oxide
Used in enamels and ceramic coatings. Symbol ZrO

Zodiac
The band of the sky extending 8 degrees either side of the ecliptic.The Sun, Moon, and navigational planets are always within this band, with the occasional exception of Venus. The zodiac is divided into 12 equal parts, called signs, each part being named for the principal constellation originally within it.

Zodiacal Light
A faint cone of light extending upward from the horizon in the direction of the ecliptic (zodiac). It is seen from tropical latitudes for a few hours after sunset or before sunrise.The spectrum of the zodiacal light is similar to that of sunlight, so it has been suggested that it is due to the scattering of sunlight by extraterrestrial dust particl…

Zoetrope
The zoetrope is an optical toy comprising a series of pictures on the inner surface of a cylinder. When the pictures are rotated and viewed through a slit, it gives the impression of continuous motion.

Zonal Wind
Atmospheric wind component which flows along the latitude.

Zone
Any group of crystal planes that are all parallel to one line, called the zone axis. See also: Crystal.

Zone of Avoidance
An irregular zone near the plane of the Milky Way where the absorption due to interstellar dust is so great that no external galaxies can be seen through it.

Zone Refining
Zone refining is a technique used to reduce the level of impurities in certain metals, alloys, semiconductors, and other materials. It is based on the observation that the solubility of an impurity may be different in the liquid and solid phases of a material. To take advantage of this observation, a narrow molten zone is moved along the length of …

Zone System
The zone system is a photographic system of exposure estimation invented by Ansel Adams that groups infinite tonal gradations into ten zones, zone 0 being black and zone 10 white. An f-stop change in exposure is required from zone to zone.

Zwicker Loudness
This is an objective method for measuring noise. It has primarily been used for steady state conditions, however, with increasing computer power, it is becoming increasingly common for it to be used for accelerations and decelerations. It is based on the use of the 25 1/3 octave bands between 20Hz and 12500Hz. The technique makes allowance for mask…

Zwitterion
A particle that contains both positively charged and negatively charged groups. This results in a net charge of zero.Such as an amino acid in neutral solution.amino acids (NH₂-CHR-COOH) can form zwitterions (+NH₃-CHR-COO-)

Zygote
A single living cell that results when a female egg is fertilized by sperm.

Zymase
Enzymes present in yeast that catalyze fermentation of sugar into alcohol and carbon dioxide.

Zymogen
An inactive precursor of an enzyme. See also: Enzyme.

Zymoscope
A zymosocope is an apparatus used for determining the fermenting power of yeast by measuring the amount of carbonic acid produced from a given quantity of sugar.

A-Pillar
The first, or most forward, roof support pillar located on either side of the windshield. Also known as A-post. See also: Wind Noise.

B Weighting
The B-weigthing curve approximately follows the 70 phon curve.The B-weighting curve follows the equation:

C Weighting
The C-weighting curve approximately follows the 100 phon curve.The C-weighting is described by the equation below:

D-Sub Connector
A connector whose male end has a D shaped raised shield that protects the connecting pins.

E-Type Thermocouple
Chromel-constantan thermocouple with a temperature range of 0 to 800 °C. See also: K-Type Thermocouple, N-Type Thermocouple, Thermocouple.

f-stop
The ratio of the focal length of the lens to diameter of the aperture. See also: Focal Length, Focal Point, Lens.

G Weighted Overall Level
G weighting purportedly reflects human response to infrasound. The curve is defined to have a gain of zero dB at 10Hz. Between 1Hz & 20Hz the slope is approximately 12dB per octave. The cut-off below 1Hz has a slope of 24dB per octave, and above 20Hz the slope is -24 dB per octave.On a logarithmic frequency scale this is:For further details refer t…

J-Type Thermocouple
Iron-constantan thermocouple with a temperature range of 0 to 750°C. See also: Celsius Temperature Scale, K-Type Thermocouple, N-Type Thermocouple, Thermometer, Thermometry, Ttype Thermocouple.

K-Type Thermocouple
Chromel-Alumel thermocouple with a temperature range of -200 to 1200°C. See also: Celsius Temperature Scale, E-Type Thermocouple, J-Type Thermocouple, N-Type Thermocouple, Thermometer, Thermometry, Ttype Thermocouple.

M-S Stereo
A method of removing imaging artefacts as well as exploiting stereo irrelevance or redundancy in stereophonic audio programmes based on coding the sum and difference signal instead of the left and right channels. Two channels are then encoded: the middle channel (computed by (l+r)/sqrt(2)) and the side channel (computed by (l-r)/sqrt(2)). Bits are …

N-Type Thermocouple
Nicrosil-Nisil thermocouple with a temperature range of -200 to 1200°C. See also: Celsius Temperature Scale, E-Type Thermocouple, J-Type Thermocouple, K-Type Thermocouple, Thermometer, Thermometry, Ttype Thermocouple.

Q-Switch
Used to build up a high population inversion within pulsed lasers.

S-Band
A band of radio frequencies extending from 1550 to 5200 MHz. See also: V-Band, X-Band.

T-Type Thermocouple
Copper-constantan thermocouple with a temperature range of -200 to 400°C. See also: Celsius Temperature Scale, J-Type Thermocouple, K-Type Thermocouple, N-Type Thermocouple, Thermometer, Thermometry.

t test
A hypothesis test based on Student's t distribution. Commonly used to test hypotheses about one or more population means or coefficients in a linear regression model.

V-Band
The V-band is the frequency band from 46,000 to 56,000 mhz employed in radar. See also: S-Band, X-Band.

V Engine
One with two banks of in-line cylinders mounted with an angular separation on a common crankcase. See also: Engine Configurations.

W Particles
Two subatomic particles, (W⁺ and W^-), discovered in experiments using powerful particle accelerators (c1983). Together with the electrically neutral Z particle, are the carriers of the electroweak force. See also: Electroweak Interaction.

X-Band
The X-band is the frequency band from 5200 to 10,900Mhz employed in radar. See also: S-Band, V-Band.

X-Intercept
The point at which a line crosses the x-axis.

X-Ray Crystallography
Determination of three dimensional arrangement of atoms in a crystal by analysis of x-ray diffraction patterns. See also: Crystal, X ray.

X-Ray Tube
A cathode ray tube that focuses energetic streams of electrons on a metal target, causing the metal to emit x-rays. See also: Electron.

x axis
The horizontal axis in the plane. See also: Axis, y axis.

X ray
A high-energy photon, usually produced by cathode rays or emitted by electrons falling to lower energy states in atoms. The range of frequencies in the electronic spectrum lying between the ultraviolet (3x10¹⁶Hz) and the gamma rays (10²¹Hz), wavelengths from a few picometers up to 20 nanometers.Some properties of X-rays:Travel…

Y-Intercept
The point at which a line crosses the y-axis.

y axis
The vertical axis in the plane. See also: Axis, x axis.

Z-Intercept
The point at which a line crosses the z-axis. See also: Y-Intercept.

Z Axis
Axis perpendicular to both X and Y axes.