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from article Set theory
Sets of points on a plane.
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from article Set theory
Vertical projection of set X onto segment Y.
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from article Polygon
Triangle ABC with nine-point circle. Symbols are explained in text.
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from article Polygon
Regular pentagon, showing approximate construction without a protractor. Symbols are explained in text.
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from article Polygon
Polar triangles A, B, C and A′, B′, C′. The center of the sphere is at O. AQ and PB are 90° arcs, so angle C′ = arc PQ is the supplement of AB.
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from article Star
A view of the night sky from Cerro Paranal in the Atacama Desert in Chile. The bright star at top left is Sirius, the brightest star other than the Sun as seen from Earth. The bright star at right is Canopus, which happens to be the second brightest…
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from article Star
Looking toward the core of Milky Way, along a line of sight holding millions of stars in the disk of the Galaxy and obscuring dark bands of dust. (Credit: NASA)
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from article Star
The Hertzsprung-Russell (HR) diagram, which plots stars' temperatures (x axis) against their luminosities (y axis). Numerous examples of stars in the Milky Way are included in this sample diagram. (Credit: ESO)
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from article Star
An artist's impression of the sizes and appearances of a typical Sunlike star, a low-mass star, a brown dwarf, and a gas giant planet. (Credit: NASA’s Goddard Space Flight Center)
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from article Star
The Jewel Box open cluster (Kappa Crucis), which lies next to the Crux (Southern Cross) constellation. (Credit: ESO)
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from article Star
Globular cluster 47 Tucanae, one of the grandest in the Milky Way Galaxy, containing over 1 million stars, seen here by the Hubble Space Telescope. [Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration. Acknowledgment: J.…
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from article Star
Hubble Space Telescope images of the star known as V1, which U.S. astronomer Edwin Hubble (the telescope's namesake) discovered in 1923. Hubble used this Cepheid variable to show that a faint, fuzzy patch in the constellation Andromeda is actually…
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from article Star
Hubble Space Telescope image of the Ring Nebula in Lyra, a planetary nebula made of glowing ionized gas that surrounds a hot blue star. [Credit: H. Bond et al., Hubble Heritage Team (STScI /AURA), NASA]
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from article Star
A multi-wavelength view of the Crab Nebula. The pulsar at its heart appears as a white dot in this image. The image compiles observations in radio waves via the Karl G. Jansky Very Large Array (VLA), infrared light via the Spitzer Space Telescope.…
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from article Star
An artist's impression of a cutaway into an aged, high-mass star, offering a simplified depiction of its internal elemental layering. Elements are identified by their periodic table symbol. (Credit: NASA/CXC/M.Weiss)
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from article Epicycloid
Diagram of an epicycloid.
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from article Mass spectrometry
Mass spectra of creatine (molecular weight 131) obtained by (a) electron impact, (b) chemical ionization, (c) field ionization, and (d) field desorption with moderate heating. Both the molecular ion (not observed in a) and the M + 1 ion in b, c, and…
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from article Mass spectrometry
Representative gas-phase proton affinities of molecules.
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from article Mass spectrometry
Potential well of a molecule: (a) undistorted, with ionization potential I near a metal with work function ϕ in the absence of a field gradient; and (b) in a strong field gradient. Near the metal surface the external field raises the most weakly…
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from article Mass spectrometry
Use of isotope distribution to determine elemental composition. (a) Molecular ion for a compound containing one bromine atom. (b) Molecular ion for a compound containing two bromine atoms. (c) Molecular ion for a compound containing neither bromine…
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from article Mass spectrometry
Mass spectra of (a) acetophenone and (b) valerophenone, using electron impact.
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from article Mass spectrometry
Scale-expanded portion of acetophenone spectrum showing a broad metastable ion at m/e 56.5.
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from article Supramolecular chemistry
Schematic representation of the self-assembly of a tricompartmental cagelike architecture by coordination of 7 ligands of two different types and 12 Cu(I) metal ions: R groups are omitted for clarity on the assembled entity (right). (After P. N. W.…
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from article Sidereal time
Diagram of the Earth's motions, illustrating the concepts of sidereal time, hour angle, and right ascension. Symbols are explained in text.
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from article Centrifugation
Laboratory centrifuge. (Credit: McGraw-Hill Education)
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from article Centrifugation
Centrifuge used in the development of new therapeutic molecules based on human antibodies for the treatment of infectious and inflammatory diseases, Biotherapix, Grupo Genetrix, Madrid, Spain. (Credit: Pixtal/AGE Fotostock)
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from article Sleep-dependent memory processing
The sleep cycle, memory systems, and memory stages. (a) The human sleep cycle. Across the night, rapid eye movement (REM) sleep and non-REM (NREM) sleep cycle every 90 minutes in an ultradian manner (that is, occurring in cycles that are repeated…
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from article Sleep-dependent memory processing
Sleep-dependent motor skill learning. (a) Wake first. After morning training (10 a.m., clear bar), subjects showed no significant change in performance when tested after 12 hours of wake time (10 p.m., clear bar). However, when tested again…
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from article Sleep-dependent memory processing
Sleep-dependent integration of human relational memory. (a) Delayed inference (associative) memory performance (% correct) in a relational memory task following different offline delays. Immediate testing after just a 20-min offline delay…
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from article Territoriality
The tiger (Panthera tigris) is highly territorial in its behavior. (Credit: Safique Hazarika Photography/Getty Images)
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from article Celestial mechanics
Major bodies of the solar system, shown not to scale. The application of celestial mechanics has constrained their observed motions to an extremely high degree of precision, sufficient for plotting intercepts and flybys with spacecraft launched from…
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from article Celestial mechanics
Elliptical orbit of a satellite. (a) The orbit in a plane. (b) Orientation of the orbit in space.
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from article Celestial mechanics
Elements that are the basis of the celestial coordinate system most commonly used by astronomers.
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from article Celestial mechanics
Hohmann transfer, an interplanetary trajectory that connects two planetary orbits, enabling a spacecraft to travel from one to the other.
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from article Boron
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from article Diamond thin films
Diamond thin films. (a) Nucleation and growth of a diamond thin film. (b) Scanning electron microscope side view image of a 400-nm-thick diamond thin film grown on a silicon substrate. (Wensha Yang, University of Wisconsin-Madison)
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from article Diamond thin films
Scanning electron microscope images of two diamond films, showing the individual diamond crystallites that agglomerate into a continuous film. (a) Very small diamond grains. (b) Film with larger diamond crystals. (Bin Sun, University of…
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from article Metallochaperones
A family of copper metallochaperones direct the trafficking of copper ions inside the cell. The schematic shows three distinct pathways of copper movement within a eukaryotic cell. Copper is first transported into the cell by the cell-surface copper…
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from article Color index
Responses of the U, B (close to photographic), and V (close to visual) filters are superimposed onto blackbody curves for 3400, 5800, and 23,000 K (5660, 9980, and 40,940°F). The higher-temperature body is brighter in the blue and has a lower…
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from article Color index
Graph of the color index B-V versus the logarithm of the temperature T (in kelvins). As temperature climbs, the B-V color index decreases. (Courtesy of P. J. Flower, Transformations from theoretical Hertzsprung-Russell diagrams to color-magnitude…
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from article Zodiacal light
Morning zodiacal light as it typically appears at a low, northern latitude site, Mount Haleakala, Hawaii, at an altitude of 10,000 ft (3300 m). The outcropping of rock at the base of the zodiacal cone is approximately 20° from the Sun. (P. B.…
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from article Zodiacal light
All-sky photograph, taken from Mount Komagatake, Japan, showing the zodiacal band and Gegenschein, and the Milky Way.
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from article Hunger
Principles of appetite regulation by gut–brain peptides. Tissues and organs, including the pancreas, stomach, small intestine, adipose tissue, and large intestine, are sources of peptides that stimulate or inhibit appetite-regulating neurons in the…
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from article Rhenium
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from article Astronomical transit instrument
Six-inch (15-cm) transit circle, U.S. Naval Observatory. (Official U. S. Naval Observatory photograph)
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from article Astronomical transit instrument
Carlsberg Meridian Circle, La Palma, Canary Islands. (University of Copenhagen)
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from article Infrared spectroscopy
Mid-infrared absorption spectra recorded on a Fourier-transform spectrometer at a resolution of 1 cm−1. (a) Polystyrene film, 0.05 mm thick. The weak intensity fluctuations between 2000 and 2800 cm−1 are interference fringes, caused by reflections…
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from article Infrared spectroscopy
Basic single-beam recording infrared prism spectrometer. The monochromator (the portion from the entrance slit S1 to the exit slit S2) is a Littrow mounting, a common arrangement for infrared instruments.
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from article Infrared spectroscopy
Spectrum of the ν1 + ν5 rotation–vibration band of acetylene recorded with a grating spectrometer, resolution 0.05 cm−1; gas at 25°C and 100-torr (13.3-kPa) pressure, 25-cm (10-in.) path length. The letters indicate features that are discussed in…
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from article Xenon
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from article Star clouds
Hubble Space Telescope image of the center of the Sagittarius star cloud. (Hubble Heritage Team; Association of Universities for Research in Astronomy; Space Telescope Science Institute; NASA)
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from article Difference equation
Numerical solution of Eq. (32) for a = 0.05, b = 0.1, c = 0.01, and a step input. The solution uses the state-variable representation of Eq. (33) and the difference-equation approximation of Eq. (36) with h = 0.1.
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from article Symbiotic star
Hubble Space Telescope image of the Southern Crab Nebula, about 4400 parsecs (14,000 light-years) away. It contains a symbiotic system with a Mira-type star and a white dwarf, too close together to be visible as separate objects. The inset shows a…
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from article Symbiotic star
Hubble Space Telescope image of R Aquarii, the closest symbiotic system, about 200 parsecs (650 light-years) away. Its highly collimated bipolar jets are ejected from the central stars, which are too close together to be seen as separate objects.…
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from article Cycloid
Diagram of cycloid; symbols explained in text.
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from article Dialysis
Equipment for dialysis.
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from article Field theory (mathematics)
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from article Field theory (mathematics)
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from article Carbon
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from article Carbon
Graphene, an allotrope of carbon in which carbon atoms are arranged in a monolayer and bonded covalently forming a hexagonal structure. (Copyright © Science Photo Library/Alamy Stock Photo)
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from article Carbon
Carbon nanotube. (Copyright © Science Photo Library/Alamy Stock Photo)
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from article Speech perception
The perception of speech (as well as the production of speech) involves interactive processes occurring in various regions of the brain. Researchers also have noted the important contribution that vision makes to normal speech perception. (Copyright…
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from article Speech perception
An auditory spectrogram of the word "telephone." (a) The vertical striations in the bands represent amplitude modulation at the frequency of the voice pitch. Such striations are absent from the initial noise portion corresponding to the voiceless…
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from article Occultation
Schematic light curve of a central occultation by a ringed planet with substantial atmosphere. The relative brightness of the star, π(r), is plotted as a function of time or distance from the center of the planet, r. The decrease in stellar…
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from article Nuclear explosion
The Grable nuclear explosion on May 25, 1953 at the Nevada Proving Grounds. The atomic bomb, with a yield of 15 kilotons, was fired from a 280-mm cannon, seen at right. It remains the only nuclear artillery shell tested by the United States…
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from article Nuclear explosion
The mushroom cloud from the first test of a thermonuclear device, code-named Ivy Mike, with a yield of about 10 megatons. Part of Operation Ivy by the United States military, Mike detonated on Elugelab island in the Eniwetok Atoll on October 31,…
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from article Nuclear explosion
The destruction in Hiroshima, captured in a photograph more than two months after the dropping of an atomic bomb in August 1945. (Credit: The National Archives)
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from article Information theory (biology)
Human information processing. The estimates of channel capacity are based on the number of rods in the retina of the eye and the number of hair cells in the inner ear's organ of Corti.
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from article Information theory (biology)
Flow diagram of communication.
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from article Information theory (biology)
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from article Information theory (biology)
Coupling diagram of communication.
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from article Solution
Fugacity and mole fraction. Line A, ideal. Line B, typical nonideal. Line C, Henry's law.
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from article Adsorption
Particle adsorption on polymer hydrogel surface. [Credit: N. Sato et al., Sci. Rep., 2017 (CC BY 4.0)]
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from article Adsorption
One-dimensional potential energy curves typical for hydrogen molecules (H2) and atoms (H) as they approach the surface of a metal substrate. The solid curve, which involves a crossing from the molecular curve to the atomic curve, shows the type of…
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from article Adsorption
Analogy between the bonding of (a) the ethylidyne ligand (CCH3) to a rhodium (Rh) single crystal surface and (b) to a cobalt carbonyl cluster [H3CC(Co)2(CO)7]. The bond lengths and angles, as determined by diffraction techniques, are virtually…
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from article Adsorption
Scanning tunneling micrographs of 5× 2.25 nanometer areas of (a) the basal plane of a graphite surface and (b) the same surface after being covered with a liquid drop of 1-triacontanol. The bright spots in (a) correspond to every other carbon atom…
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from article Radiation chemistry
Variation of G with linear energy transfer (LET) for the products solvated electron (e−aq), OH, H2O2, H, and H2. (After R. C. Cooper and R. W. Wood, eds., Physical Mechanisms in Radiation Biology, National Technical Information Service, 1974)
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from article Radiation chemistry
Growth and decay of the signal of naphtholate anion in the pulse irradiation of a naphthol solution. Deter- mination of the decay rate gives a spontaneous lifetime of 30 milliseconds for loss of the naphthol proton in aqueous solution.
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from article Radiation chemistry
Time dependence of the electron spin resonance signals of hydrogen atoms in the presence of 50–600-micromolar azide ion. The signal intensities and decay periods decrease with increasing azide ion concentration.
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from article Transition elements
Portion of periodic table showing transition elements, their atomic number, symbol, and electron configurations in valence shells; heavy border indicates the more restricted classification.
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from article Transition elements
Physical properties of transition elements as function of their atomic number.
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from article Toxicology
Toxicologists study the adverse effects of chemical and physical agents on living organisms. In this photograph, a turtle is covered in petroleum following an oil spill. (Credit: Getty Images)
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from article Toxicology
Fish killed by chemically contaminated waters. (Credit: National Oceanic and Atmospheric Administration)
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from article Toxicology
The movement of mercury in the environment. In nature, mercury vapor (Hg0) is a stable gas and evaporates from the Earth's surface (both soil and water). Moreover, anthropogenic sources are a significant contributor to atmospheric mercury, and these…
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from article Surface (geometry)
Part of a dihedron (the rest has been torn away), showing dihedral angle.
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from article Surface (geometry)
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from article Surface (geometry)
Some quadric surfaces, with parameters a, b, and c. (a) Ellipsoid; 0 < c < b < a. (b) Hyperboloid of one sheet; 0 < a < b < c. (c) Elliptic paraboloid; 0 < a < b and c > 0. (d) Hyperboloid of two sheets; 0 < a < b < c. (e) Hyperbolic paraboloid; c >…
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from article Surface (geometry)
Surface of revolution. The generating curve (in the yz plane) is f(y,z) = 0. The axis of revolution is the z axis.
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from article Surface (geometry)
Sphere, with a zone and a lune.
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from article Surface (geometry)
Catenoid. The axis of revolution is the y axis.
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from article Interpolation
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from article Interpolation
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from article Interpolation
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from article Gas and atmosphere analysis
Collection devices for monitoring air in the workplace. (a) Solid sorbent (charcoal) sampling tube. (b) Midget impinger. (c) Cowled cassette and its filter. (d) Passive monitor, used for nitrogen dioxide. (e) Piston-type detector tube pump.
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from article Gas and atmosphere analysis
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from article Gas and atmosphere analysis
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from article Gas and atmosphere analysis
Evacuated-flask sampling system.
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from article Zirconium
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from article Controlled/living radical polymerization
Free-radical polymerization.
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from article Controlled/living radical polymerization
Active and dormant radical equilibrium.
