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from article Superacid
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from article Superacid
Hammett acidity function (H0) values for some solutions in 100% H2SO4. (After E. F. Caldin and V. Gold, eds., Proton Transfer Reactions, Chapman and Hall, 1975)
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from article Superacid
Hammett acidity function (H0) values for acids of the fluorosulfuric acid solvent system. (After E. F. Caldin and V. Gold, eds., Proton Transfer Reactions, Chapman and Hall, 1975)
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from article Superacid
Hammett acidity function (H0) values for some HF−MF5 systems.
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from article Marjoram
Close-up view of marjoram (Majorana hortensis; alternatively Origanum majorana). (Photo courtesy of Forest and Kim Starr)
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from article Stress (psychology)
Dimensions of stressful experiences. (Credit: National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health)
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from article Stress (psychology)
Diagram of the hypothalamic-pituitary-adrenal axis. The thicker arrow indicates that the feedback of glucocorticoids on ACTH is most potent. Abbreviations: ACTH, adrenocorticotropic hormone; CRH, corticotropin-releasing hormone. (Copyright ©…
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from article Tooth
Stages in the development of a tooth.
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from article Tooth
Schema showing tooth replacement in lower vertebrates. (a, b) Horizontal lines represent the strand of tissue which connects the tooth germs in most vertebrates; vertical lines indicate the distance from the tooth germs to the surface of the jaw. In…
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from article Colloid
Examples of colloid particles. (a) Zinc sulfide (sphalerite). (b) Cadmium carbonate, with an enlargement of the boxed section (courtesy of Egon Matijević).
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from article Emulsion polymerization
Process of emulsion polymerization.
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from article Emulsion polymerization
Entry in emulsion polymerization.
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from article Emulsion polymerization
Spontaneous packing of low-polydispersity polystyrene particles about 200 nm in diameter.
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from article Emulsion polymerization
Monomers used in emulsion polymerization.
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from article Emulsion polymerization
Amphiphilic RAFT in emulsion polymerization.
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from article Bioterrorism
Civilians are the prime targets in bioterrorist attacks. During World War II, gas masks with filters were distributed to British civilians because of fears of a chemical agent attack. (Credit: Ingram Publishing/SuperStock)
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from article Bioterrorism
A color-enhanced scanning electron micrograph (SEM) showing splenic tissue from a monkey with inhalation anthrax. Rod-shaped bacilli of Bacillus anthracis (yellow) and an erythrocyte (red) are shown. (Credit: Arthur Friedlander/National Institute of…
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from article Qualitative chemical analysis
A qualitative analysis test-tube method for separating cations into ion groups. (Copyright © McGraw-Hill Education/Stephen Frisch)
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from article Chestnut
American chestnut (Castanea dentata). (Photo courtesy of Forest and Kim Starr)
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from article Chestnut
Nuts of the Allegheny chinquapin (Castanea pumila). (Photo courtesy of Steve Hurst, USDA–NRCS PLANTS Database)
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from article Genetic mapping
A genetic map shows the relative locations of genes in a linear arrangement. The map is based on the idea of linkage (that is, the closer that two genes are to each other on the chromosome, the greater is the probability that they will be inherited…
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from article Genetic mapping
The process of genetic mapping involves analyses of how traits and genetic markers segregate in experimental or natural populations to determine whether traits and markers (collectively, loci) are inherited together or independently from one…
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from article Genetic mapping
Genetic map of chromosome X showing some of the disorders that are possible. (Copyright © McGraw-Hill Education)
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from article Amphetamine
Molecular structures of amphetamine and methamphetamine (a chemical derivative of amphetamine). (Copyright © McGraw-Hill Education)
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from article Caraway
Caraway (Carum carvi) fruits (often called “seeds”). Scale bar = 1 mm. (Photo by Steve Hurst; USDA–NRCS PLANTS Database)
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from article Air navigation
Typical wind triangle, drawn to scale. 1 knot = 1 nmi/h = 0.514 m/s.
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from article Air navigation
Electronic map display developed by a flight management computer on the pilot's instrument panel of a Boeing 767 airplane. (United Airlines)
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from article Air navigation
Loran C chain GRI 7980 in the southeastern United States, comprising primary station M and secondary stations W, X, Y, and Z. A position fix is shown at point A, where the lines of position 7980-Y-45000 and 7980-Z-61000 intersect.
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from article RNA World theory
Biochemical functions of the known natural ribozyme classes. Ribozymes are ribonucleic acid (RNA) molecules that can catalyze specific biochemical reactions. The self-cleaving ribozyme classes promote an internal phosphoester transfer reaction to…
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from article RNA World theory
Examples of possibly ancient riboswitches that bind RNA-derived compounds. Riboswitches for the essential cofactor thiamin (thiamine) pyrophosphate (TPP) are present in some species from all domains of modern life, whereas riboswitches for cyclic…
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from article Flame
Structure of a premixed laminar flame front.
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from article Flame
Structure of a laminar diffusion flame front.
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from article Purkinje cell
Purkinje cells (shown in red) are one of the main types of nerve cells found in the brain. These cells have elaborate branching structures called dendrites that receive signals from other nerve cells. (Credit: Yinghua Ma and Timothy…
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from article Dallis grass
Dallis grass (Paspalum dilatatum). (Photo courtesy of Larry Allain, USGS National Wetlands Research Center)
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from article Carnauba wax
Carnauba wax palm (Copernicia prunifera). The leaves of this palm are the source of carnauba wax. (Photo courtesy of Scott Zona)
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from article Electron spectroscopy
Excitation of electron spectra recorded with high-resolution instruments. (After H. Siegbahn and L. Karlsson, Photoelectron spectroscopy, Handbuch der Physik, vol. 31, 1982)
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from article Electron spectroscopy
The system of levels of an atom in a molecule can be divided into a valence electron region and an atomic-core region. Excitation of electron lines from the various regions can be made at different photon energies.
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from article Electron spectroscopy
Valence-band electron spectrum of gold excited by monochromatized Al Kα radiation (solid curve). Comparison is made with a theoretically calculated density of states (broken curve) which has been folded with a 0.25-eV gaussian corresponding to the…
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from article Electron spectroscopy
Benzene valence electron spectrum excited by Hel radiation at 21.22 eV, showing vibrational structures.
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from article Electron spectroscopy
ESCA spectrum of cesium fluoride (CsF) in glycol (HOCH2CH2OH) solution. Comparison is made with the corresponding electron-binding energies in the gas phase. (After H. Siegbahn et al., Phys. Scripta, 27:431, 1983)
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from article Electron spectroscopy
Electron spectrum from the 1s level of carbon in ethyl trifluoroacetate; binding energy = 291.2 eV.
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from article Electron spectroscopy
Binding-energy shifts for the sulfur 2p electrons versus the calculated charge. The points indicate averages from more than 100 compounds.
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from article Eye (vertebrate)
Diagram of the human eye. (Credit: Shutterstock)
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from article Eye (vertebrate)
Histological section of the vertebrate retina with a light-sensitive area and surrounding tissue. (Credit: Al Telser; copyright © McGraw-Hill Education)
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from article Eye (vertebrate)
Cross section of the vertebrate retina. (Copyright © McGraw-Hill Education)
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from article Eye (vertebrate)
Types of rods and cones found in different vertebrates: (a) goldfish, (b, c) frog, (d) squirrel, (e) human, (f) gecko, (g) goldfish, (h) frog, (i) turtle, (j) human, (k) frog, (l) turtle, (m) snake, and (n) fish. (Copyright © McGraw-Hill Education)
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from article Eye (vertebrate)
The Philippine tarsier (Carlito syrichta) is a nocturnal animal and possesses the largest eyes of any primate. (Credit: William Flaxington)
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from article Eye (vertebrate)
Development of the eye in the human embryo at (a, b, c) 3.5 weeks, (d, e, f) 4 weeks, (g) 4.5 weeks, and (h) 5 weeks. (Credit: Based on an original illustration by Ronan O'Rahilly)
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from article Colloidal crystal
Arrangement of particles and distribution of electrical charges in a charged stabilized body-centered-cubic colloidal crystal. Spheres indicated by broken lines show extent of positive counterion clouds.
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from article Colloidal crystal
Reflection of white light from a polycrystalline colloidal crystal suspension. The crystals are body-centered cubic, with a particle diameter of 0.1 μm and interparticle spacing of 1.5 μm.
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from article Colloidal crystal
Inverse opal structure formed by filling the void space of a face-centered cubic colloidal crystal emulsion of oil drops in water and then condensing silica in the aqueous void spaces. (D.J. Pine, University of California at Santa Barbara)
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from article Seasonal affective disorder
Exposure to bright light via a light-therapy box during winter is an effective treatment for individuals suffering from seasonal affective disorder. (Credit: Getty Images)
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from article Seasonal affective disorder
Individuals suffering from seasonal affective disorder often exhibit a variety of symptoms of depression, including increased sleep length, weight gain, and craving for carbohydrates, as well as sexual and social problems, anxiety, lethargy, and…
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from article Plant development
Stages of plant development for a daisy (genus Gerbera) showing the progression from a seedling to a blooming plant. (Credit: Hue Photography/Getty Images)
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from article Plant development
The aboveground body of the plant (shoot) comprises a stack of plant segments termed phytomers. Phytomers consist of a leaflike lateral organ (attached to the stem at a node), a stem (internode), and a lateral meristem or bud. All cells that are…
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from article Plant development
The root (a, b) is built by files of cells and contains three distinct zones of maturation (c). In contrast, the shoot apical meristem (d, e) gives rise to all aboveground plant tissues and comprises zones of cells. The central zone (CZ) maintains…
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from article Plant development
Much of plant morphological diversity can be explained by variations in (a) branching order/pattern, (b) phyllotaxy, and/or (c) leaf shape. (Copyright © McGraw-Hill Education)
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from article Plant development
The ABCE model for floral development. (a) Plants can regulate which type of floral organ is produced in each whorl by restricting the expression pattern of ABCE transcription factors. (b) The four whorls of the flower are shown (stamen, sepal,…
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from article Bromegrass
Smooth bromegrass (Bromus inermis). (Photo by Roselyn Heil, Yellowstone National Park, National Park Service)
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from article ENCODE project
More than one protein can be produced from a gene. RNAs can be produced from different promoters (blue and pink chevrons on the DNA helix), with longer transcripts incorporating additional coding exons (colored barrels). Different proteins also can…
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from article ENCODE project
The majority of the human genome is involved in a biochemical event. Studies from the ENCODE project indicate that approximately 80% of the human genome is “in use”; approximately 60% of the genome is transcribed into coding or noncoding RNAs, and…
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from article Respiratory pigments (invertebrate)
Electron micrograph of hemocyanin molecules from the snail Helix pomatia, showing “pillbox” subunit structure. Circular forms show subunits in a tenfold symmetrical array. There are six parallel rows of subunits in the rectangular forms.
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from article Cerebral palsy
The spastic forms of cerebral palsy include diplegia, hemiplegia, and quadriplegia. Diplegia refers to greater involvement of the legs and lesser involvement of the arms, hands, and trunk. Hemiplegia refers to involvement of one side of the body…
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from article Potassium
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from article Wavelets
Members of a wavelet family: an original and two shifted and dilated copies. (a) Original wavelet ψ with width w. (b) Large-scale wavelet ψa,b, with width aw that is larger than the original width w. (c) Fine-scale wavelet ψa,b with narrow width.
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from article Wavelets
Two examples of wavelets which generate an orthonormal basis, and which are associated with fast algorithms.
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from article Logic
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from article Logic
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from article Mitosis
Close-up microscopic view (colorized) of a two-cell embryo going through mitosis. (Credit: Andrii Vodolazhskyi/Shutterstock)
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from article Mitosis
Changes in microtubule distribution and chromosome position as an animal cell enters into and proceeds through mitosis. (a) Mid-prophase: chromosomes are condensing within the nucleus. (b) Late prophase/early prometaphase: centrosomes separate; the…
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from article Mitosis
Schematic representation of a mitotic cell, showing the spindle pole (centrosome), spindle microtubule, kinetochore, and chromosome structures. (Copyright © McGraw-Hill Education)
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from article Mitosis
Representation of the stages of mitosis for a typical animal cell: (a) prophase; (b) prometaphase; (c) metaphase; (d) anaphase; (e) early telophase; (f) late telophase. (Copyright © McGraw-Hill Education)
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from article Mitosis
Mitotic metaphase. Once all of the chromosomes have acquired a bipolar attachment and have become positioned on the spindle equator, the cell is considered to be in metaphase of mitosis. At this time, the spindle is fully mature and the cell is…
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from article Nicotine alkaloids
Ball and stick structure for nicotine.
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from article Nicotine alkaloids
Structures of nicotine and some other alkaloids found in tobacco.
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from article Corn
Corn (Zea mays) growing in a field. (Credit: Bob Nichols, Agricultural Research Service/U.S. Department of Agriculture)
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from article Corn
Ear of field corn on a stalk. The husk has been peeled back to display the kernels (seeds). (Credit: Howard F. Schwartz, Colorado State University)
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from article Corn
The corn leaf at the top is more resistant against leaf blight than the severely damaged leaf on the bottom. (Credit: Keith Weller, Agricultural Research Service/U.S. Department of Agriculture)
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from article Corn
Gall of corn smut, caused by Ustilago maydis, on a stalk of corn. (Credit: H. J. Larsen)
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from article Corn
White ear rot and seedling blight on a corn ear. The pathogen responsible for the afflicted corn is Stenocarpella maydis. (Credit: U.S. Department of Agriculture Cooperative Extension Slide Series/Clemson University)
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from article Vertebra
Lateral view of a human thoracic vertebra. Anterior is toward the right. (After C. M. Goss, ed., Gray's Anatomy of the Human Body, 28th ed., Lea and Febiger, 1964)
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from article Vertebra
Diagrammatic cross section through one side of the back of a 4-week-old human embryo. Migration of mesenchymal cells from the sclerotome is shown by arrows. (After L. B. Arey, Developmental Anatomy, 6th ed., Saunders, 1954)
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from article Vertebra
Representative vertebrae of a dog. (a) Atlas and axis articulated, cranial lateral aspect. (b) Fifth cervical, cranial lateral aspect. (c) Sixth thoracic, cranial lateral aspect. (d) Fifth lumbar, caudal lateral aspect. (e) Sacrum caudal, lateral…
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from article Vertebra
Lateral view of cat skeleton to illustrate Slijper's views on biomechanics of trunk skeleton. The brackets indicate lines of action of certain muscles upon the neural spines. (After W. F. Walker, Vertebrate Dissection, 4th ed., Saunders, 1970)
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from article Fennel
Fennel (Foeniculum vulgare). (Photo courtesy of Forest and Kim Starr)
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from article Chemical dynamics
Schematic of a molecular-beam experiment; the entire apparatus is under high vacuum.
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from article Chemical dynamics
Contour map of the DCl intensity. (a) Center-of-mass angular distribution of DCl from the reaction D + Cl2. (b) Angular distribution of Cl atoms from photodissociation of Cl2 molecules. Broken lines correspond to the second Cl atom.
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from article Chemical dynamics
Two-dimensional projection of CH3+ ions produced by ionizing CH3 radicals from CH3I dissociation. (Credit: Reprinted with permission from P. L. Houston, Snapshots of chemistry: Product imaging of molecular reactions, Acc. Chem. Res., 28:453–460,…
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from article Chemical dynamics
Schematic molecular-potential surfaces for ICN in the stable ground state (lower) and unstable excited state (upper). (Credit: Reprinted with permission from A. H. Zewail, Femtochemistry: Atomic-scale dynamics of the chemical bond, J. Phys. Chem. A,…
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from article Chemical dynamics
Fluorescence signals versus time delay for excitation of CN at 389.7, 389.8, 390.4, and 391.4 nm (from top to bottom). The longest wavelength excites CN when the reaction is nearly over, but the shortest excites CN when the reaction has just…
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from article Chemical dynamics
Contour plot of the potential-energy surface for the reaction F + H2 → HF + H, with a typical reactive trajectory indicated.
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from article Invertebrate embryology
Spermatozoa and fertilizable eggs. (a) Sea urchin spermatozoon. (b) Marine annelid (Nereis) egg, with intact germinal vesicle containing a nucleolus. Spheres surrounding germinal vesicle are oil droplets. (c) Marine mussel (Mytilus) egg, germinal…
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from article Invertebrate embryology
Formation of the fertilization membrane in the sea urchin egg. (a) Surface of the unfertilized egg. (b) Explosion of the cortical granules: the vitelline membrane begins to be lifted up while the dark bodies are extruded, and the egg plasma membrane…
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from article Invertebrate embryology
Symmetry of cleavage patterns and invertebrate blastulae. (a, b) Spiral cleavage. (c) Bilateral cleavage. (d) Radial cleavage. (e) Irregular cleavage. (f) Sea urchin blastula. Relatively uniformly sized blastomeres and large blastocoele. (g) Annelid…
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from article Invertebrate embryology
Gastrulation and larval mesoderm formation. (a) Early and (b) later stage in nonyolky eggs. (c) Late blastula, (d) early gastrula, and (e) late gastrula in yolky egg of the snail. (f) Mesoderm formation in the limpet (Patella) shown in sections…
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from article Invertebrate embryology
Maturation and early cleavage in the mussel (Mytilus). (a) First polar body being formed at animal pole; polar lobe at vegetal pole. (b) First polar body completely extruded; polar lobe withdrawn. (c, d) Second polar body formation. (e–g) First…
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from article Invertebrate embryology
Stages in the development of Patella and gastrulation in a tunicate. (a) Late blastula of Patella; macromeres being covered by micromeres, and blastopore at vegetal pole. (b) Early trochophore of Patella; blastopore shifted forward. (c) Matured…
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from article Invertebrate embryology
Cleavage and gastrulation in the sea urchin. (a) Zygote. (b) Two-cell stage. (c) Four-cell stage. (d) Eight-cell stage. (e) Sixteen-cell stage. (f) Thirty-two–cell stage. (g) Vegetal region of blastula flattened; primary mesenchymal cells in…
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from article Invertebrate embryology
Larval stages. (a) Ventral and (b) side view of pluteus larva of sea urchin. (c) Section through tunicate gastrula. (d) Tadpole stage of tunicate larva.
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from article Invertebrate embryology
Young echinoid Peronella japonica, after metamorphosis. (After K. Okazaki and J. C. Dan, Metamorphosis of partial larvae of Peronella japonica Morteusen, a sand dollar, Biol. Bull., 106:83–99, 1954)
