Regular pentagon, showing approximate construction without a protractor. Symbols are explained in text.
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.
from article Epicycloid
Diagram of an epicycloid.
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…
Representative gas-phase proton affinities of molecules.
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…
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…
Mass spectra of (a) acetophenone and (b) valerophenone, using electron impact.
Scale-expanded portion of acetophenone spectrum showing a broad metastable ion at m/e 56.5.
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.…
from article Centrifugation
Laboratory centrifuge. (Credit: McGraw-Hill Education)
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)
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…
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…
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…
from article Territoriality
The tiger (Panthera tigris) is highly territorial in its behavior. (Credit: Safique Hazarika Photography/Getty Images)
from article Boron
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)
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…
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…
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…
from article Rhenium
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…
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.
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…
from article Xenon
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.
from article Cycloid
Diagram of cycloid; symbols explained in text.
from article Dialysis
Equipment for dialysis.
from article Field theory (mathematics)
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)
Carbon nanotube. (Copyright © Science Photo Library/Alamy Stock Photo)
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…
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…
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…
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,…
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)
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.
Flow diagram of communication.
Coupling diagram of communication.
from article Solution
Fugacity and mole fraction. Line A, ideal. Line B, typical nonideal. Line C, Henry's law.
from article Adsorption
Particle adsorption on polymer hydrogel surface. [Credit: N. Sato et al., Sci. Rep., 2017 (CC BY 4.0)]
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…
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…
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…
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)
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.
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.
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.
Physical properties of transition elements as function of their atomic number.
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)
Fish killed by chemically contaminated waters. (Credit: National Oceanic and Atmospheric Administration)
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…
from article Surface (geometry)
Part of a dihedron (the rest has been torn away), showing dihedral angle.
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 >…
Surface of revolution. The generating curve (in the yz plane) is f(y,z) = 0. The axis of revolution is the z axis.
Sphere, with a zone and a lune.
Catenoid. The axis of revolution is the y axis.
from article Interpolation
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.
Evacuated-flask sampling system.
from article Zirconium
from article Controlled/living radical polymerization
Free-radical polymerization.
Active and dormant radical equilibrium.
Nitroxide-mediated radical polymerization of styrene or butylacrylate.
Atom transfer radical polymerization.
RAFT polymerization.
from article Antisubmarine warfare
SQS-26 low-frequency hull sonar, the largest U.S. hull sonar (the version onboard current surface ships, SQS-53, uses much the same sonar dome). Nearby workers give idea of scale. (U.S. Navy)
Variable-depth sonar in streamlined housing (fish). (U.S. Navy)
Nuclear attack submarine USS San Francisco. The ridge running up the hull houses a towed array. (U.S. Navy)
Mark 46 lightweight homing torpedo aboard a helicopter. (U.S. Navy)
Swedish diesel submarine Gotland in the United States on loan from Sweden to help train U.S. naval crews against the type of submarine they are likely to encounter in littoral waters. During the Cold War, the U.S. Navy concentrated mainly on the…
Missile destroyer Forrest Sherman. With the demise of the Soviet Union, specialized antisubmarine ships no longer seem worthwhile. Forrest Sherman is a multirole destroyer designed to deal with air and underwater threats and to bombard land targets.…
from article Menthol
Enantioselective synthesis of /(−) menthol.
from article Gel permeation chromatography
Gel permeation chromatograph.
Typical gel permeation chromatogram with a calibration curve.
Typical triple chromatogram obtained by using both light scattering and viscometric detectors in addition to a concentration detector.
from article Problem solving (psychology)
Composite view of a colorized magnetic resonance imaging (MRI) scan of a human brain blended with a cross-section illustration of a human head. Cognitive psychology attempts to understand the integral mental processes of the human brain involved in…
The game of chess involves many aspects of problem solving. In chess playing, a solution consists of an attempt to convert an initial state of a task (for example, a chessboard before the first move is made) into a final or goal state (checkmate)…
from article Morphine alkaloids
Biosynthesis of thebaine.
from article Osmoregulatory mechanisms
Various osmoregulatory mechanisms are utilized in a marine fish. The "0/00" term indicates units of parts per thousand. (Copyright © McGraw-Hill Education)
The kidney helps to eliminate water and waste products from the body. During osmoregulation in this organ, numerous smaller functional units, called urinary tubules or nephrons, allow water to be moved across cell membranes from a lower to a higher…
from article Carborane
Parent clusters from which carborane structures are determined. The diagonal lines define series of related closo, nido, and arachno structures.
Skeletal structures of the (a) 1,2-, (b) 1,7-, and (c) 1,12-isomers of C2B10H12.
Vertex boron atom with the three sp3 orbitals that it employs in cluster bonding. The BH unit contributes three orbitals and only two electrons to the bonding that holds the cluster together (framework bonding).
Three resonance structures of nido-C2B4H8.
Skeletal structures of the tetracarbon carboranes, R4C4B8H8.
Skeletal structures. (a) [nido-7,8-C2B9H12]−. (b) [nido-7,9-C2B9H12]−. (c) [nido-C2B10H12]2− anions. (d) (C2B9H11)2MN-4 complexes, where N = oxidation state of the metal.
from article Agricultural chemistry
Agricultural chemistry often involves the use of fertilizers to improve agricultural output and productivity. Urea (carbamide) fertilizers are notable sources of nitrogen, which is necessary for healthy plant growth and well-balanced soil…