A
Abdomen (ant):
The
posterior segment of the body, behind the thorax or cephalothorax.
Aberration:
In microscopy, an effect which causes distortion
or blurring of the image.
Aberration, Chromatic:
An effect created by the dispersion of the material
from which the lens is
made. This causes different wavelengths of light to
be refracted to different
degrees. The name chromatic comes from the colors evident
with this type
of aberration.
Aberration, Spherical:
An aberration caused by a lens being spherical, instead
of the proper shape.
Spherical aberration is characterized by the edges
of the image being
magnified more than the center.
Achromat Doublet:
Two lenses of different refractive indices placed
next to each other to eliminate
chromatic aberration in a lens system. See Chromatic
Aberration.
Accommodate:
In opthalmology, to focus by contracting the crystalline
lens of the eye.
Acrylic fiber:
Any of the group of synthetic textile fibers made
by the polymerization of
acrylonitrile.
Acrylonitrile:
A colorless, flammable, poisonous, carcinogenic liquid,
C3H4N, used in the
production of polymers and copolymers, as rubbers,
fibers and clear plastics
for beverage containers.
Adjacent:
Lying near, close, or contiguous; adjoining.
Alleviate:
To make easier to endure; lessen; mitigate.
Alpha, a:
Greek symbol used to denote an alpha particle.
Alpha Particle:
A doubly charged positive helium ion, consisting of
two protons and two
neutrons. A term usually used in conjunction with radiation.
Alpha particles
can be ejected from certain radioactive isotopes.
Amorphous:
Lacking definite form; without crystalline structure.
Amplitude:
The measure of a wave from its lowest point to
its highest. In physical
manifestations of waves, such as in water, the
amplitude is a measure
of distance. With light, the amplitude is a measure
of the wave's energy.
Angstrom:
1 X 10^ -10 m. A convenient unit of measurement,
as atom diameters are
on the order of angstroms. Represented by the symbol
Å.
Antennae:
One of the jointed, movable sensory appendages occurring
in pairs on the heads
of insects and most other arthropods.
Antisolar Point:
The point 180 degrees from the Sun, relative to
an observer. The angular measure
of rainbows can be made from the antisolar point,
which corresponds to the shadow
of one's head.
Anti-twilight Arch:
The band of light above the horizon opposite a
rising or setting sun. This
phenomenon is due to an optical mix of Rayleigh-scattered
blue wavelength light
and red wavelength light reflected from larger
particles in the atmosphere. See
Rayleigh scattering.
Appendage:
A limb or other subsidiary part that diverges from
the central or principal structure.
Aperture:
A small hole through which light passes. Apertures
are used to form images or
mask undesired light from an image.
Aqueous Humor:
Liquid inside the cornea of the eye with a refractive
index of 1.376.
Arachnids:
Any of numerous wingless, carnivorous arthropods of
the class Arachnida,
comprising spiders, scorpions, mites, and ticks, characterized
by a two-segmented
body with eight appendages and no antennae.
Aragonite:
One of the two crystal forms of calcium carbonate,
the other being calcite.
Calcite is normally the stable phase. Both are present
in the shells of certain
sea creatures.
Arthropods:
Any invertebrate of the phylum Arthropoda, having a
segmented body, jointed limbs,
and a mineralized chitinous shell covering and including
insects, spiders, and other
arachnids, crustaceans, and myriapods.
Atom:
The smallest particle of an element, which cannot be
subdivided without
creating another element. Atoms have nuclei consisting
of positively charged
protons and neutrons which are not charged. The nucleus
is surrounded by
negatively charged electrons. Together, they make the
atom neutrally
charged. Almost all of the mass of an atom is in the
nucleus.
Atomic Number:
The number of protons in an atomic nucleus. For a neutral
atom, this also
corresponds to the number of electrons orbiting the
nucleus. For example,
carbon with symbol C on the periodic chart, has atomic
number of 6. This
means that it has 6 protons, and, the neutral carbon
atom has 6 electrons.
Attenuation:
Weakening in force or intensity: "attenuation
in the volume of sound."
B
Beta, b:
Greek
symbol used to denote electrons.
Beta Particles:
High-energy electrons.
Brackish:
Slightly salt; salty or briny; distasteful; unpleasant.
Bremsstrahlung Radiation:
An electric charge, as it is being accelerated or decelerated,
produces
radiation, which can be in the form of x-rays. This
radiation is called
Bremsstrahlung Radiation and usually creates an unwanted
background in
a spectrum.
C
Calcareous:
Of, containing, or like calcium carbonate; chalky.
Calcite:
A common mineral, calcium carbonate, CaCO3,
found in a great variety of
crystalline forms: a major constituent of limestone,
marble and chalk.
Camera Obscura:
A room or box containing a hole in at least one
of the walls that creates an
image of the outside objects on the opposite wall.
Cantilever:
A projecting structure, such as a beam, that is
supported at one end and
carries a load at the other end or along its length.
Catalyst:
A substance that causes or speeds a chemical reaction
without itself being affected.
Cathode Ray Tube (CRT):
A vacuum tube in which cathode rays, in the form
of a slender beam of electrons,
are projected on a fluorescent screen and produce
a luminous spot.
Cellulose:
An inert carbohydrate, (C6H10O5)n,
the chief constituent of the cell walls of plants
and of wood, cotton, hemp, paper, etc.
Chitin:
A nitrogen-containing polysaccharide, related chemically
to cellulose, that forms
a semitransparent horny substance and is a principal
constituent of the exoskeleton,
or outer covering, of insects, crustaceans, and arachnids.
Charged:
Having acquired a net electric charge. Objects
can become charged due to
a transfer of electrons from one object to another.
An example of this
transfer is that which occurs while shuffling across
a carpet or the rubbing
of a plastic rod with a piece of fur.
Combustible:
Capable of catching fire and burning.
Compound:
A substance consisting of atoms of different atomic
numbers.
Compton Scattering:
The change in direction and energy of a photon
due to the interaction
with an electron.
Compound Microscope:
A microscope containing at least two lenses to
form the image of a
specimen. Invented by Robert Hooke in the mid-17th
century.
Concave:
An inward curvature. A concave lens or mirror has at
least one surface that
curves inward. A concave lens causes light rays to
diverge, and a concave
mirror causes light rays to converge. A mnemonic device
to remember the
difference between concave and convex is that caves
are concave.
Cones:
The photosensitive cells in the eye's retina that
respond to changes in the
energy, or wavelength, of light. There are three types
of cones:
red-sensitive, blue-sensitive, and green-sensitive.
Contiguous:
Touching or in contact; being in close proximity without
touching; near.
Converge:
To come together or come to a single place or point.
Convex:
An outward curvature. A convex mirror curves outward
and a convex lens has
at least one side that curves outward. A convex lens
causes light rays to
converge and a convex mirror causes light rays to diverge.
See also Reflection
and Refraction.
Copal:
A resin obtained from various tropical trees and used
in making varnishes.
Cornea:
The outer layer of the eye. A major contributor
to the refraction of light
in the eye.
Coulomb:
A unit of electric charge. 6.25 x 10^18 electrons will
have a charge of one
coulomb. A Coulomb per second flowing through a wire
is defined as one
Ampere.
Count:
The electronic pulse created in a detector by one quantum
of radiation. Counts
are summed to make spectral peaks.
Counterfeit:
Make in imitation with intent to deceive; not genuine;
forged.
Critical Angle:
The angle beyond which light, traveling through
an optically dense medium and
incident on the interface with a less dense medium,
will totally internally reflect.
For light exiting glass to air, the critical angle
is 41 degrees.
Crustaceans:
Any chiefly aquatic arthropod of the class Crustacea,
typically having a body
covered with a hard shell, including lobster, shrimp,
crabs, barnacles and wood lice.
Crystal:
A regular arrangement of atoms in three dimensional
space. Sometimes this
regular arrangement gives the crystal a definite three
dimensional shape. For
example if the atoms arrange themselves in a cubic
lattice, the crystal might
be cubic.
Crystalline Lens:
The lens inside a human eye.
Currency:
Any form of money that is in circulation as a medium
of exchange in a country.
D
Denominations:
One of the grades in a series of designations of quantity,
value, measure, weight, etc.
Depth of Focus:
Same as depth of field.
Depth of Field:
The depth over which features can be considered in
focus. The distance along
the optic axis over which features are in focus.
Detector (Radiation):
Any device which detects incoming radiation and can
create an electronic
signal for every quantum of radiation, proportional
to the energy of the
quantum. Detectors can be of many types, Gas and solid
state. However,
the detectors referred to on this website are all solid
state, usually lithium
drifted silicon.
Deterrent:
Serving or tending to deter or discourage from acting
or proceeding.
Diffraction:
The bending of waves around corners. Sound can diffract
around buildings and
light can diffract around very small obstacles.
The obstacle must be of a size
similar to or smaller than the length of the wave involved.
Diffraction can lead
to interference phenomena.
Diffraction Grating:
A device which uses diffraction and interference phenomena
to disperse a
beam of light into its various wavelengths.
Diode:
A semiconductor device that emits light or can
produce power when used in a
solar cell.
Diopters:
A unit of measurement used in optometry. A diopter
is the inverse of a lens'
focal length, measured in meters.
Disintegration:
To separate into parts or lose intactness; break
up; decay.
Dispersion:
The change in refractive index with wavelength. Most
refractive materials
refract short wavelengths of light more than long wavelengths
of light. This
property is called the dispersion of the medium.
Diverge:
To cause to spread or move apart.
Dopant:
A substance mixed in exceedingly small quantities
with an otherwise pure
substance.
Ductile:
Able to undergo change of form without breaking; capable
of being molded or shaped.
E
Earth's Shadow:
The shadow of the Earth projected onto the atmosphere.
Often seen for several
minutes in a clear sky after sunset. The shadow
is low on the horizon, bluish in
color and rises as the sun sets lower beyond the
Western horizon.
Echinoderm:
Any marine invertebrate animal of the phylum Echinodermata,
including starfish
and sea urchins, characterized by a five part radially
symmetrical body and a
calcareous endoskeleton.
Eclipse:
A shadow, or the act of blocking light. In astronomy,
refers to the phenomenon
of the Moon blocking the Sun's light (solar eclipse),
or the Earth blocking the Sun's
light to the moon (lunar eclipse).
Elastic Collision:
A collision between two bodies during which kinetic
energy is conserved.
During an elastic collision the bodies do not stay
together.
Electromagnetic Radiation:
The type of radiation we know as light: X-rays, radio
waves, ultraviolet
and infrared, among others. Electromagnetic radiation
consists of
alternating electronic and magnetic fields at right
angles to each other.
Both of these fields consist of waves and impart electromagnetic
radiation
with a specific wavelength and frequency. Electromagnetic
radiation travels
at 3 x 10^8 meters per second in a vacuum. See Electromagnetic
Spectrum.
Electromagnetic Spectrum:
Refers to the entire range of wavelengths through which
electromagnetic
radiation can be manifested. The longest wavelengths
are the lowest
energies and the shortest wavelengths are the highest.
Starting at the
longest wavelengths, there are radio waves which proceed
through the
microwave region. The next highest energy radiation
is infrared followed
by visible light, then ultraviolet radiation, X-rays
and then gamma rays.
Electron:
An elementary particle having a rest mass of 9.11 X
10^-31 kilograms
and an electric charge of -1.602 X 10^-19 coulombs.
Electrons, being
negatively charged, cancel out the positive charge
of an atoms nucleus.
In the structure of an atom, electrons surround the
positively charged
nucleus.
Electron, Auger:
An electron which has been ejected from an atom by
the Auger process.
In this process, an inner shell electron is emitted
from an atom. an outer
shell electron then fills the inner shell vacancy,
and in the process, the
extra energy causes another outer shell electron to
be ejected. This outer
shell electron is referred to as the Auger electron
and the energy of this
electron is measured to determine elemental composition.
Electron, Backscattered:
An electron which has been scattered directly from
a nucleus.
Backscattered electrons loose very little energy as
a result of the
backscattering process and are usually used for compositional
or Z
contrast imaging in electron microscopy.
Electron, Secondary:
Secondary electrons are electron which have been ejected
from a sample
as a result of bombardment by an incident beam, and
are ejected only
after considerable scattering and energy loss inside
the material. Secondary
electrons are used for topographic imaging in electron
microscopy.
Electron Volt:
A unit of energy. An electron volt is equivalent to
the energy required move
an electron through a potential difference of one volt.
An electron volt is
equal to 1.602 x 10^-19 joules.
Element:
A substance consisting of atoms all of the same atomic
number. Elements
can combine to make compounds.
Energy:
A physical quantity defined as the ability to do work.
Some of the types of
energy Include heat, (the motion of atoms) kinetic,
(the movement of a
mass through space) potential, ( a mass with the capability
to move in
response to a force) as well as electrical chemical
and others. Energy can
be transformed from one form to another but not destroyed.
Epoch:
A period of time marked by distinctive features, noteworthy
events,
changed conditions, etc.
Extended Source:
A light source that emits froma finite area or
volume. The Sun is an
extended light source in the sky. See Point Source.
Exude:
To come out gradually in drops; ooze out; to emit through
small openings.
F
First Surface:
The surface of a lens or mirror that first encounters
incident light. A
household mirror has a first surface glass over
the layer of silver.
Fluorescence:
An ability that some transparent bodies have of
modifying incident light to
produce light lower in energy and different in color
form the mass of the material.
For example, the hyaline layer is a glassy translucent
material found in scorpions
causing fluorescence under ultraviolet light.
Focal Length:
The distance from a lens at which parallel rays converge
after they pass
through the lens or reflect from the mirror.
Focal Plane:
The plane at which a lens forms images. A movie screen
is at the focal plane
of the projector's lens.
Focal Point:
A point of convergence of parallel rays of light (
or other radiation) or a point
from which it diverges. The location at which rays
parallel to the optical axis
of an ideal mirror or lens converge to a point.
Frequency:
The number of waves passing a point in time. For light,
usually expressed in
Hertz (Hz), the number of waves per second. Related
to the wavelength by
the equation f = v/l,
where f is the frequency, v is the wave velocity, and
l
is the wavelength.
Fresnel Lens:
A lens in which only the outer layer of glass or plastic
is used to refract light.
Used in lighthouses, lanterns, and as flat lenses.
G
Gamma, g:
Greek symbol used to denote high-energy photons.
Gamma Radiation:
High-energy electromagnetic radiation emitted by excited
atomic nuclei.
Gauss:
A unit of magnetic field strength.
Grazing Incidence:
An object or light striking a surface at an highly
oblique angle. Light encountering
a surface at grazing incidence is nearly 100% reflected.
H
Habitats:
The natural environment of an organism; place that
is natural for the life and
growth of an organism; the place where one is usually
found.
Hereditary:
Passing or capable of passing, naturally from parent
to offspring through genes.
Hole:
A vacancy in the electron population of a semiconductor,
which acts as a
positively charged current carrier.
Hooke's Law:
An explanation of how springs behave. By applying force
(F) to the spring,
the spring will stretch by length (x). When you double
the force (F) you
double the length (x). Hooke's law applies to both
stretchable springs and
compressible springs. The only limit is that when the
spring is stretched beyond
its elasticity and becomes permanently deformed.
Hydrothermal:
Of or pertaining to the action of hot aqueous solutions
or gases within or on the
surface of the earth.
Hyperopia:
A malady of the eye in which the focal plane rests
behind the retina. Commonly
known as "farsightedness". Corrected with convex lenses.
I
Impurity:
The quality or state of being impure.
Incandescence:
Giving off light due to the attainment of an extremely
high temperature.
Incandescent:
See incandescence
Incident:
Refers to electromagnetic energy or ions which are
directed at and strike
a target or sample. As opposed to scattered or reflected
energy or
particles, which are leaving the target or sample.
Incident photons or
other particles can be scattered, reflected, or absorbed.
Inclusions:
A foreign body or inert structure within in cell.
Index of refraction:
See refractive index.
Inelastic collision:
A collision between two bodies in which kinetic energy
is not conserved,
but momentum is.
Infrared:
Radiation in the electromagnetic spectrum between visible
light and radio waves.
Inscriptions:
Something marked as words, characters, etc. carved
on stone or other hard surfaces.
Insulation:
Material used to cover, line or separate that prevents
or reduces the passage,
transfer, or leakage of heat, electricity, or sound.
Interference:
The constructive and destructive addition of waves.
Interference can
lead to patterns sometimes called diffraction patterns
as in Young's
double slit experiment.
Invertebrate:
Without a backbone or spinal column; not vertebrate.
Ion:
In general, any charged particle. In aqueous chemistry,
usually a
soluble charged particle. In physics, usually an atom
with an electron
added or removed. If an electron is added the ion is
negatively charged,
if an electron is removed, the ion is positively charged.
When this happens,
the atom is said to be ionized.
Ionization:
The creation of ions. In physics, the gain or
loss of an electron by an
atom. In chemistry, the gain or loss of an electron
by a group of atoms.
Gaining an electron creates a negative ion and losing
an electron creates
a positive ion.
Iridescence:
The property of producing colors due to the interference
effects of light
reflecting off of different layers at different angles.
See Interference.
Iris:
The network of muscle tissue in the eye that opens
and closes the pupil
and is responsible for the color of one's eyes. See
Pupil.
Irradiate:
To expose to any type of radiation.
Irritant:
A biological, chemical, or physical agent that stimulates
a characteristic function
or elicits a response, esp. an inflammatory response.
Isotope:
Indicates different forms of the same element. Isotopes
cannot differ in
the number of protons or electrons they possess, but
do differ in the
number of neutrons in the nucleus. See Radioisotope.
J
Joule:
A unit of energy. The amount of energy it takes to
exert a force of one
Newton through a distance of one meter. Also equal
to one Watt of
electrical energy expended for one second.
K
Keratin:
A protein which makes up most of the structure of hair
and fingernails.
L
Lambda, l:
Greek symbol used to denote wavelength.
Laser:
A device that utilizes the stimulated emission of light
to create and amplify
a beam of light. The laser-producing material is often
gallium arsenide,
helium-neon, or ruby.
Lattice:
An imaginary regular arrangement of points in three
dimensional space.
Any lattice point is equal to any other lattice point.
It will have the same
number of lattice points around it in the same directions
the same distance
away as any other lattice point.
Lattice Point:
An imaginary point in three-dimensional space that
defines a structure point
of a lattice. Any lattice point is equal to any other
lattice point. It will have
the same number of lattice points around it in the
same directions the same
distance away as any other lattice point.
LED:
Light Emitting Diode. A semiconductor device that emits
light of a specific energy
when electrical current flows through it.
Lepton:
Any of a class of elementary particles that consist
of the electron, neutrino,
muon, and tau particle.
Lithography:
A printing technique by which the image to be printed
is fixed on a stone,
silicon or metal plate with a combination of ink-absorbent
and ink-repellent vehicles.
M
Magnification:
The degree to which an image is larger than the object.
Calculated as image
length/ object length. Meter: An agreed upon unit of
length. One meter is
approximately 39 inches.
Malleable:
Capable of being extended or shaped as by hammering
or by pressure.
Meter:
A unit of length defined in 1800 as one ten-millionth
of the meridian distance
from the equator to the North Pole. Once meter, symbol
m, is approximately
39 inches in length.
Meteor:
The streak of light in the sky resulting from
the incandescent particles given
off by an incoming piece of space debris. The debris
itself before it strikes
the ground is called a meteoroid. After it has
struck the ground, it is called a
meteorite.
Meteorite:
An object from space which has entered the Earths
atmosphere and struck
the ground. Meteorites can be "Finds" or "falls". Finds
are found some some
unknown time after striking the Earth, and not seen
to strike the ground.
Falls are seen to fall to the Earth and then recovered
where they were seen
to fall.
Micro:
The Greek symbol m,
which denotes 10^-6.
Microbiology:
The study of microscopic organisms and single cells.
Micron:
1X10^-6 m. Symbol mm.
Microscope:
An arrangement of lenses deigned to view objects at
high magnification. A
simple microscope contains only one lens. A compound
microscope contains
more than one lens. Electron microscopes contain electron
lenses. By
extension, any device designed to view objects at larger
magnification,
even without lenses. (i.e.: Scanning Tunneling
Microscope, STM, Near Field
Scanning Optical Microscope, NSOM.)
Mirage:
An image distorted by light refracted through heated
or cooled air. Inferior mirages
are formed in layers of cool air over warm air - often
seen in the desert. Superior
mirages are formed in layers of warm air over cool
air - often seen over the ocean
or frozen landscapes.
Mitigate:
To lessen in force or intensity; make less severe;
make milder or more gentler.
Molecule:
The smallest particle of a substance that retains the
chemical and physical properties
of the substance and is composed of two or more atoms;
a group of like or different
atoms held together by chemical forces.
Momentum:
That property which is conserved during elastic or
inelastic collisions. It is
defined as the product of the mass and the velocity
of the body, and is
represented by p. p = mv. Also equal to a force over
a unit time. P = fDt. In
quantum mechanics, p = h/l
where h is Plancks constant and l
is wavelength.
Mylar:
A trademark used for a thin, strong polyester film.
Myopia:
A malady of the eye in which the focal plane rests
in front of the retina.
Commonly known as "nearsightedness". Corrected with
concave lenses.
Myriapods:
Any arthropod having an elongated segmented body with
numerous paired,
jointed legs, as a centipede or millipede.
N
Nanometer:
1 x 10 ^-9 meters. Symbol nm.
Neutron:
A particle having mass 1.675 X 10^ -27 kg, slightly
greater than that of the
proton, and no charge. The nuclei of atoms contain
protons and neutrons.
Newton:
A unit of force in the M.K.S. system. The force required
to impart to a mass
of one kilogram an acceleration of one meter per second
squared.
Normal:
Perpendicular, or at a right angle. Lines can be normal
or perpendicular,
planes can be normal, and lines can be normal to planes.
Nucleus:
The very small positively charged core of an atom.
The atomic nucleus
consists of positively charged protons and uncharged
neutrons. Most of
the mass of an atom is in the nucleus.
O
Oligocene:
Noting or pertaining to an epoch of the Tertiary Period,
occurring from 40 million
to 25 million years ago.
Ommatidium:
A single unit in the compound eye of an insect. It
consists of a facet, a
lens and a photoreceptor.
Opaque:
The property of blocking light. An opaque object passes
no light through it.
Oscillators:
An electrical circuit that produces an alternating
output current of a certain
frequency determined by the characteristics of the
circuit components.
P
Penumbra:
The part of a shadow where some of the light from an
extended light source is blocked.
In astronomy, the penumbra is the area on the ground
where observers see a partial
solar eclipse. See umbra, eclipse.
Period:
The time to complete one cycle of motion. The period
of the Earth's rotation is 24 hours.
Phosphor:
A material that emits lower energy light when illuminated
by high energy light. The insides
of fluorescent light bulbs are coated with phosphor.
Photon:
A quantum of electromagnetic radiation. Photons are
characteristic of all electromagnetic
radiation, from the longest radio waves up to the shortest
gamma rays. The shorter the
wavelength of the radiation, the more energetic the
photon.
Phylum:
The primary subdivision of taxonomic kingdom, grouping
together all classes of
organisms that have the same body plan.
Piezoelectric effect:
Certain crystals with asymmetric unit cells have this
property. When a
compressive stress is applied to these crystals, it
effectively shifts the
positive ions in one direction and the negative ions
in the other. This
will produce a temporary charge buildup on the opposite
surfaces of the
crystal. A tensile stress will reverse the charge.
The corollary effect can
occur, an applied potential difference can change the
shape of the crystal.,
or apply a force against a restraint.
Piezoelectricity:
Electricity or electric polarity due to pressure especially
in a crystalline
substance (as quartz).
Pinhole Camera:
A device used to record or view images of light caused
by a pinhole that
forces light rays to cross.
PIXE:
Particle Induced X-ray Emission. The process whereby
an incident ion causes
an inner shell electron to be ejected from an
atom. The resulting electron
transition causes a characteristic x-ray which
is analysed.
Plancks Constant:
A constant of proportionality between the wavelength
of electromagnetic
radiation and the energy by the equation E = hc/l.
Where E is the energy
of the photon of electromagnetic radiation, l
is the wavelength, c is the
velocity of light and h is Planks constant, 6.626.x
10^-34 Joule-seconds.
Point Source:
An ideal light source that emits from an infinitesimally
small area.
Stars as seen in the sky are essentially point sources.
See Extended Source.
Polarize:
To cause radiation to be polarized. If light passes
through a polarizing filter,
the alternating electric and magnetic fields will
no longer be oriented in all
directions perpendicular to the direction of motion,
but will be oriented more
strongly in specific directions. Light can also
be polarized by passage through
the atmosphere and by reflecting off of surfaces
at a very shallow angle.
See Electromagnetic Radiation.
Polymer:
A compound of high molecular weight derived either
by the addition of many other
small molecules, such as polyethylene, or by the condensation
of many smaller
molecules with the elimination of water, alcohol,
or the like, such as nylon.
Polymerization:
The act of forming a polymer or polymeric compound.
Positron:
Positively charged particles with the same mass as
an electron.
Presbyopia:
A malady of the eye in which the crystalline lens loses
the ability to focus properly.
Occurs commonly with age. Corrected with convex lenses.
Primary Rainbow:
The rainbow found 40-42° from the antisolar point.
Usually the only rainbow in the sky.
Sometimes seen with the secondary rainbow.
Prism:
A device which uses the dispersion property of
glass to split light into its
component wavelengths.
Probe:
A usually small object used especially for exploration
to obtain specific information.
Definition created in 1580.
Proboscis:
The trunk of an elephant; any long flexible snout;
the elongated, protruding process
on the head of certain insects or worms, used for feeding
or sensing food.
Proton:
An elementary particle of mass 1.673 x 10^-27 kg or
about 1,836 times that of an electron.
The proton has a charge equal in magnitude as that
on an electron only positive
instead of negative, being +1.602 x 10^-19 Coulombs.
The nuclei of atoms contain
protons and neutrons.
Pupil:
The aperture of the eye. See Iris.
Q
Quantum:
A discrete unit that exists at very small dimensions.
A quantum of
electromagnetic energy (light) is the photon.
R
Radiation:
The emission of particles from a source. The particles
may have mass,
as in the case of neutrons or alpha particles, or may
be massless as in
the case of photons, such as x-rays and gamma rays.
Radioisotope:
Some isotopes are radioactive, giving off radiation.
These are called
radioisotopes.
Raster:
A scan pattern (as of the electron beam in a cathode-ray
tube) in which
an area is scanned from side to side in line from top
to bottom; also: a pattern
of closely spaced rows of dots that form the image
on cathode-ray tube (as of a
television or computer display).
Rayleigh Scattering:
The scattering of light or electrons due to interactions
with particles whose
size roughly corresponds to the wavelength of the photons
or electrons.
The amount of scattering follows the inverse of the
wavelength to the fourth power.
Blue sky, smoke, and some animal coloring are due to
Rayleigh scattering.
Reflection:
When an incident photon leaves a surface on the same
side (as
opposed to the opposite side, being transmitted, or
being absorbed in
the material) it has been reflected. Different surfaces
reflect light to
different degrees and different surfaces reflect different
wavelengths
of light. For example, if a surface reflects light
of 4,500 Angstroms, we
say it reflects blue light.
Refraction:
When light passes from one transparent medium to another,
it may
change directions, or refract at the interface. The
degree to which light
refracts at an interface is determined by Snells law,
which states n1/n2
= sin Q2/Sin Q1 = v2/v1. Where n1 and n2 are the indices
of the two
materials, Q1 and Q2 are the angles of refraction of
the two materials,
and v1 and v2 are the velocities of light in the two
materials.
[illustration]
Refractive index:
A numerical measure of refraction, related to the velocity
of light in a
material. Denoted by the letter n. n = v0/vm, where
v0 is the velocity of
light in a vacuum, and vn is the velocity of light
in the medium of refractive
index n. N in a vacuum is 1. N of water is 1.33. See
refraction.
Resilient:
Able to spring back to an original form or position
after compression, stretching, etc.
Resin:
Any class of nonvolatile, solid or semisolid organic
substance, as copal or mastic,
that consists of amorphous mixtures of carboxylic acids.
Resolve:
The ability to discern two separate, closely spaced
objects. Related to resolving power,
the ability of a device to optically resolve distinct
objects.
Resolution:
The ability to discern two separate, closely spaced
objects.
Retina:
The layer of photosensitive cells at the rear of the
human eye.
Rods:
The photosensitive cells in the eye's retina that respond
to changes in
the brightness of light.
S
Secondary Rainbow:
The rainbow seen "outside of" a primary rainbow. This
rainbow is 49-51° from
the antisolar point and its colors are reversed relative
to the primary.
Selection Rules:
In X-ray emission from atoms, these rules determine
which electron transitions
between energy states are allowed.
SEM-EDS:
Scanning Electron Microscopy-Energy Dispersive
Spectroscopy. The process
whereby an incident electron causes an inner shell
electron to be ejected
from an atom. The resulting electron transition causes
a characteristic
x-ray which is analysed. This takes place in an electron
microscope as the
electrons used for imaging also cause the emission
of X-rays.
Semiconductor:
A material that can be an insulator in very pure form,
but is usually doped
with very small amounts of impurities in order to cause
it to conduct with
more or less resistance depending on the amount of
the dopant. silicon
and germanium are two elemental semiconductors. Unlike
a metal, the
resistance of a semiconductor decreases with an increase
in temperature.
Shoshone:
A member of an American Indian people or group of peoples
living mainly
in Nevada, N Utah, Idaho, and W Wyoming; a river in
NW Wyoming, flowing NE
into the Big Horn River. 120mi (193 km) long.
Simultaneously:
Existing, occurring, or operating at the same time;
concurrent.
Solar Cell:
A semiconductor device used to produce power when irradiated
by sunlight.
Sound:
Vibrations of air molecules, which we hear.
Spectrometer:
An instrument used for measuring the energies and wavelengths
of photons.
Spectroscope:
An optical instrument that produces a spectrum of the
wavelengths of light.
Spectrum:
Plural, Spectra. Any visible manifestation of radiation
which is arranged
according to wavelength or energy. Can refer to the
visible spread of
radiation caused by a prism or diffraction grating
in visible light, or the
graph created by any method of plotting radiation intensity
with photon
energy or wavelength.
Speed of Light:
The speed at which electromagnetic energy travels in
a vacuum, which is 3 x 10^8 m/s.
Nothing that carries information can travel faster
than the speed of light.
Substrate:
The foundation on which an integrated electronic circuit
is formed or
fabricated, usually silicon.
Sundog:
An atmospheric optical phenomenon that mimics the image
of the Sun.
Caused by light refracting through horizontal ice crystals
in the atmosphere,
which often disperse the light as well. Also known
as 'parhelia', sundogs are
found 22° from the solar disk in skies with cirrus
clouds.
Synchronous:
Occurring at the same time; same as simultaneously.
T
Tactile:
Pertaining to or affecting the sense of touch; perceptible
to the touch; tangible.
Thermocouple:
A device that measures temperature as a function of
the electromotive force
induced when heat is applied to two dissimilar metal
wires joined at both ends.
Thorax (Ant):
The portion of the body of an insect between the head
and abdomen.
Total Internal Reflection:
A phenomenon that occurs when light is incident on
an interface between
two media of different refractive indices. If the light
is traveling through a more
dense medium and strikes the surface at an angle greater
than the critical angle,
the light will be totally reflected inside the medium.
Optical fibers take advantage
of this property to propagate light through the fiber.
Translucent:
The property of passing light with some loss of the
light. One can
normally see part way into translucent objects, but
not all the way
through.
Transparent:
The property of passing light.
Ultraviolet:
A region of the electromagnetic spectrum where the
photons have
higher energy than the visible region, but lower energy
than X-rays.
Opinions vary on exactly where the ultraviolet region
begins and ends,
but the wavelengths are about 100 angstroms to about
4000 angstroms.
Umbra:
The central part of a shadow where all light from an
extended (or point) source
is blocked. See Penumbra, Eclipse
Unimpeded:
Not slowed or prevented; a good vacuum is necessary
to allow the electrons
to move unimpeded down the column of a scanning electron
microscope.
V
Vacuum:
A condition of rarified gas. A perfect vacuum can never
be attained, as
every surface has water and various other substances
on it in minute
quantities which will evaporate under conditions of
vacuum.
Vertebrate:
Belonging to the Vertebrata, a subphylum of chordate
animal having an
internal skeleton of bone or cartilage that includes
a brain case and a spinal
column, and comprising mammals, birds, reptiles, amphibians,
and fishes.
Visual Ray:
Theorized by Empedocles in the fifth century B.C. to
explain the visual perception.
An human eye would emit a visual ray to intercept a
light ray from an object;
the returning ray-combination would inform the observer
of the perceived object.
W
Watermark:
A figure or design impressed in some paper during manufacturing,
visible when the paper is held to light.
Wave number:
The number of waves in a given length. Equal to the
reciprocal of the
wavelength, 1/l.
Wavelength:
The distance between two successive peaks or troughs
on a wave.
Related to frequency by the equation f = v/l,
where f is the frequency,
v is the velocity of the wave and l
is the wavelength.
X
X-ray:
Any quantum of electromagnetic radiation between the
wavelengths
of 1 X 10^ -9 m and 1 X 10^-11 m or between the energies
of
approximately 1 keV and approximately 100 keV.
X-ray Diffraction:
The reflection of X-rays from planes of atoms.
XRF:
X-Ray Fluorescence. The process whereby an incident
photon causes
an inner shell electron to be ejected from an atom.
The resulting
electron transition causes a characteristic x-ray which
is analysed.