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from article Chemistry
Periodic table. (Jaap Hart/Getty Images)
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from article Aspidorhynchiformes
Aspidorhynchus acutirostris, Upper Jurassic, Bavaria; a typical fish of the order Aspidorhynchiformes.
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from article Paleobotany
Compression specimen of the Triassic leaf type Dicroidium.
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from article Paleobotany
Permian pollen grain macerated from Antarctic coal.
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from article Paleobotany
Cross section of a permineralized stem from a Carboniferous coal ball.
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from article Paleobotany
Thin section of a petrified Rhynie chert stem.
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from article Paleobotany
Several coprolites found within the tissues of a Carboniferous plant.
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from article Paleobotany
Cuticle of a fossil (Eocene) leaf showing the outline of the epidermal cells and fungus with specialized hyphae.
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from article Paleobotany
Several Glossopteris leaves from the Permian of Antarctica. Leaves of this type were some of the first evidence that at one time the southern continents were all physically linked into a major continental plate called Gondwana.
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from article Paleobotany
Section showing tree rings from a temperate plant, showing change in cell size and wall thickness.
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from article Paleobotany
Section showing rings from a tree with uniform cell size and wall thickness, but growing at approximately 82° South during the Triassic.
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from article Osteolepiformes
Schematic phylogeny (family tree) of the osteolepiforms, based on arguments presented by P. Ahlberg and Z. Johanson (1998). The fishes within the gray zone are conventionally designated as Osteolepiformes (the formal group name), but they actually…
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from article Osteolepiformes
The tristichopterid Eusthenopteron foordi. (a) A close-up of its pectoral fin skeleton. (b) An illustration of the full specimen. Eusthenopteron reached approximately 50–70 cm in length. Its pectoral fin skeleton contains structures equivalent to…
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from article Magellanic Clouds
Large Magellanic Cloud; the large red patch is the 30 Doradus nebula, one of the largest H II regions known. (Copyright © Australian Astronomical Observatory; photograph by David Malin from AAT plates)
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from article Magellanic Clouds
Small Magellanic Cloud. This image is composed from two images of the Digitized Sky Survey 2. (ESA/Hubble; Digitized Sky Survey 2)
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from article Magellanic Clouds
Large Magellanic Cloud. (Harvard Observatory photograph by P. Hodge)
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from article Magellanic Clouds
Giant gas cloud centered on 30 Doradus in the Large Magellanic Cloud. (Cerro Tololo Inter-American Observatory photograph by P. Hodge)
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from article Parasympathetic nervous system
Overview of parasympathetic pathways of the human autonomic nervous system. Preganglionic axons from the brain and spinal cord innervate the viscera in the head, neck, and trunk. (Copyright © McGraw Hill)
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from article Fertilization (animal)
Photomicrograph (tinted green) of mouse sperm bound to the zona pellucida of an unfertilized egg under laboratory conditions (in vitro). (Credit: K. O. Kalthoff)
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from article Fertilization (animal)
Mammalian sperm (a) adhering to the zona pellucida, (b, c) undergoing the acrosome reaction, and (c, d) penetrating the zona pellucida on its way to the egg cell proper. (Copyright © McGraw Hill)
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from article Chemical senses
The sense of smell (olfaction) is a key chemical sense in vertebrates. (Left) Taste buds of the oral cavity, especially the tongue, are composed of modified epithelial cells responsive to chemicals in solution. (Right) Bitter, sour, salty, and sweet…
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from article Mercury (element)
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from article Mercury (element)
Mercury droplets exhibiting non-wetting of the surface. (Credit: A. Cerar/Getty Images)
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from article Mercury (element)
Tooth with a silver-amalgam filling. (Credit: Szasz-Fabian Jozsef/Shutterstock.com)
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from article Universe
An image from a computer simulation of large-scale structure formation in the universe, with vast filaments of relatively dense matter separated by even larger voids with low matter density. Each dot indicates an individual galaxy. (Credit: Max…
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from article Universe
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 Universe
A mosaic of the central star-forming region of the Orion Nebula, otherwise known as M42. Here the emission from young stars (pointlike sources) lights up the surrounding gas, mostly composed of hydrogen atoms. (Credit: C. R. O'Dell and S. K. Wong,…
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from article Universe
The Hubble Ultra Deep Field. The image represents a nearly 12-day exposure of a small patch of sky, about a tenth of the diameter of the full Moon, that is “empty” to the naked eye from Earth. Taken by the Advanced Camera for Surveys (ACS; optical)…
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from article Universe
Galaxies. (a) Spiral galaxy M81 (NGC 3031). The flat disk, spiral arms, and central bulge are visible. The spherical halo that surrounds both is too sparsely populated to be evident (Credit: NASA, ESA, JPL-Caltech, Harvard-Smithsonian Center for…
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from article Universe
Heart of the Virgo Cluster, the nearest moderately rich cluster of galaxies, including the giant elliptical galaxies M84, M86, and M87. (Credit: Anglo-Australian Observatory; photograph by David Malin)
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from article Universe
The Sloan Digital Sky Survey's map of the universe, compiled via redshift surveys. Each dot represents a galaxy, while a color bar represents local density. (Credit: SDSS)
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from article Universe
The Hubble diagram for type Ia supernovae, from a compilation of well-observed type Ia supernovae, showing the linear relationship between distances and recession velocities. The slope of the best-fit line gives the Hubble constant H0. The scatter…
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from article Universe
Full-sky projection map of temperature variations in the cosmic background radiation, as measured by the Planck spacecraft. (Credit: ESA/Planck Collaboration)
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from article Universe
Timeline of the universe, a representation of the evolution of the universe. The far left depicts the earliest moment we can now probe, when a period of “inflation” produced a burst of exponential growth in the universe. (Size is depicted by the…
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from article Pigmentation
Colorful flower of Mirabilis jalapa. The colors of the flowers of this plant can vary as a result of different plant pigments. (Credit: F. D. Richards)
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from article Pigmentation
Zebrafish are often studied as model organisms for research dealing with skin pigmentation. (Credit: Lynn Ketchum/Oregon State University)
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from article Coronoidea
Stephanocrinus gemmiformis, Middle Silurian, Tennessee; side view of the theca.
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from article Neurohypophysis hormone
Structure of neurohypophysial hormones. Each neurohypophysial hormone is made up of nine amino acid residues with two half cysteines joined by a disulfide bridge to form a ring structure. Vasotocin is found in fishes and fetal pituitaries, while…
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from article Peroxisome
Electron micrograph of a cell of Yarrowia lipolytica (a type of yeast) grown in fatty acid–containing medium. (Copyright © McGraw Hill)
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from article Bipolar disorder
Prevalence of bipolar disorder in adults. The bar graph shows the percent of the U.S. adult population affected by bipolar disorder as it relates to age. (Credit: National Institute of Mental Health)
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from article Enzyme inhibition
Enzyme inhibition often works by preventing a substrate from attaching to an active enzyme. In this example, E1 is one of three sequential enzymes that will convert a substrate (S) into a product (P). However, the product that is created can then…
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from article Enzyme inhibition
Two types of reversible enzyme inhibition. (Left) In competitive inhibition, the inhibitor interferes with the active site of the enzyme, so the substrate is unable to bind to it. (Right) In noncompetitive inhibition, the inhibitor changes the…
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from article Organic conductor
Structures of organic conductors. (a) Electron donors. (b) Acceptor molecule (TCNQ) and two monovalent anions. Abbreviations are explained in the text.
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from article Organic conductor
Stacking of charge-transfer compounds. (a) Segregated stacking of TTF-TCNQ-like materials. (b) Typical zigzag stacking of the (TMTSF)2X series.
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from article Organic conductor
Comparison of the range of electrical conductivities of some AsF5-doped conducting polymers with some metals, semiconductors, and nonconducting polymers.
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from article Organic conductor
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from article Docodonta
Restoration of the skull of the Late Jurassic docodont Haldanodon in lateral view. Arrow points to dentary-squamosal articulation; the articular-quadrate articulation lies directly behind it (toward the midline of the skull). (Illustration by…
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from article Docodonta
Upper and lower molars of Docodon, a Late Jurassic docodont. (a) Occlusal view of an upper molar. (b) Internal and (c) occlusal views of a lower molar.
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from article Atomic clock
A cesium fountain clock at the National Physical Laboratory in the United Kingdom. (Credit: National Physical Laboratory, United Kingdom)
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from article Atomic clock
Basic schematic of a cesium atomic-beam clock.
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from article Atomic clock
Basic schematic of a hydrogen maser.
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from article Atomic clock
Basic schematic of a rubidium gas cell.
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from article Atomic clock
Electrodes used to create the confining electric potential for a Penning ion trap or a Paul ion trap. An electric potential V, which is static for a Penning trap and oscillating for a Paul trap, is applied between the ring electrode and the end-cap…
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from article Atomic clock
Cesium atomic fountain clock. A sample of cesium atoms is trapped and laser-cooled at the intersection of six laser beams. The atoms are then launched upward, passing through the microwave cavity, then falling back through the cavity. After passing…
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from article Geometrization theorem
Making a 2-D torus.
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from article Geometrization theorem
Life in Seifert-Weber dodecahedral space. (Courtesy of Geometry Center, University of Minnesota)
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from article Geometrization theorem
Hyperbolic dodecahedron of infinite diameter. The infinite spikes are rounded off “chimneys,” which are here triangular rather than rectangular. (Courtesy of Paul Nylander from http://bugman123.com/)
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from article Geometrization theorem
Neck pinching, resulting in infinite curvature.
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from article Geometrization theorem
Ricci flow with surgery.
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from article Neuroeconomics
Neuroeconomics applies neuroscientific tools and methodologies to investigate the decision making that occurs inside the brain. (Credit: James Steidl/SuperStock)
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from article Lysosome-related organelle
Recruitment of cargo molecules into protein-coated (clathrin-coated) vesicles at the trans-Golgi network (TGN) for delivery to incipient lysosomes or lysosome-related organelles. In the TGN, soluble lysosomal or lysosome-related organellar proteins…
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from article Matrix theory
Vector rotation that rotates any vector v in the plane counterclockwise through 45° to a new vector Tv.
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from article Paleopathology
The fused spine and ribs in a case of ankylosing spondylitis from an adult male human found at a burial site near the Kuskokwim River, Alaska. (Credit: Department of Anthropology, National Museum of Natural History, Smithsonian Institution Catalog…
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from article Paleopathology
Pottery figurine of an achondroplastic dwarf from an archeological site in Tachina, Esmeraldas, Ecuador, dated between 500 BCE and 500 CE. (Credit: Department of Anthropology, National Museum of Natural History, Smithsonian Institution Catalog No.…
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from article Paleopathology
Sword trauma that removed part of the left upper jaw and the right lower jaw so that no remaining teeth were in contact between the jaws. The adult male human survived this injury. The skull is from an archeological burial site near the Stewart…
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from article Paleopathology
Destruction of the lower portion of the fourth lumbar vertebra (arrow), probably caused by tuberculosis, from a young male human skeleton found at the archeological burial site of Bâb edh-Dhrâ in Jordan, dated to approximately 3300 BCE. (Credit:…
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from article Paleopathology
The effect of scurvy on the right side of the cranium of an 11-year-old human child from the archeological site of Pachacamac, Peru. (Credit: Department of Anthropology, National Museum of Natural History, Smithsonian Institution Catalog No. 266599)
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from article Boolean algebra
A portrait of George Boole.
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from article Equation of time
Graph of the equation of time, showing how the equation results from combining the effects of the inclination of the Earth's axis and the eccentricity of its orbit. (After B. M. Oliver, The shape of the analemma, Sky Telesc., 44:20–22, July 1972)
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from article Equation of time
Analemma recorded in a multiple-exposure, year-long photograph obtained with an east-facing, permanently mounted camera that made an exposure approximately once a week at exactly 8:30 a.m. Eastern Standard Time. On three occasions the shutter was…
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from article Psychological resilience
Psychological resilience refers to positive adaptation among individuals at risk for maladjustment. There are three classes of protective factors that help people to thrive in the face of significant adversities: support from close family and…
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from article Psychological resilience
The strongest predictor of resilient adaptation is the quality of an individual's close, personal relationships. In general, positive relationships help individuals to combat adversity through collective problem solving and through the sharing of…
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from article Calculus of variations
Weierstrass condition. Symbols explained in text.
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from article Calculus of variations
Example of an area-minimizing surface that cannot be written as the graph of a single function. (a) Nonconvex domain C. (b) Minimal graph over C that is not area-minimizing. (c) Second surface over C that has less area. (After F. Morgan, Geometric…
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from article Calculus of variations
Comparison of surfaces. (a) Surface with no handles. (b) Surface with one handle and less area. (c) Surface with two handles and still less area. (d, e, f) These three surfaces are deformed to show that they do have zero, one, and two handles,…
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from article Calculus of variations
Examples of surfaces minimizing the integral of a nonelliptic integrand among all bodies having the same volume (the surface at upper left) and among all surfaces having the same boundary (the saddle-shaped surface). Surfaces were computed as part…
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from article Herschel Space Observatory
An artist’s impression of Herschel against a backdrop of the Rosette Nebula observed in the instrument’s infrared and submillimeter range, assigned scientifically representative, visible-light colors. (Credit: ESA - C. Carreau)
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from article Herschel Space Observatory
Herschel satellite. (a) Artist's impression. (b) Assembled satellite under test. (Credit: ESA)
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from article Herschel Space Observatory
Composite 70/160/250–μm image of the Rosette Nebula, showing a 2 × 2° area of sky, part of the Herschel-HOBYS Key Project. (Credit: ESA; SPIRE and PACS Consortia)
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from article Herschel Space Observatory
Composite 250/350/500–μm image of a 4 × 4° area of sky, part of the Herschel-ATLAS Key Project. (Credit: ESA; H-ATLAS Consortium)
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from article Herschel Space Observatory
Small portion of a HIFI spectrum (signal strength versus frequency in GHz) of the Orion Nebula. Spectral lines from numerous interstellar molecules are seen. The numbered lines are from methanol (CH3OH). (Credit: ESO, Adapted from S. Wang et al.,…
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from article Suicide
Methods of suicide in (left) males and (right) females. The three most prevalent methods of suicide involve firearms, suffocation, and poisoning. Males are much more likely to use firearms, whereas the preferred method in females is poisoning.…
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from article Suicide
Age-adjusted suicide rates in males and females from 1999 to 2017 in the United States. (Credit: National Vital Statistics System, National Center for Health Statistics, Centers for Disease Control and Prevention)
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from article Linear algebra
Geometric representation of a vector OP.
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from article Hydrido complexes
Structure of ReH92−.
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from article Hydrido complexes
Structure of [HMn(CO)5].
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from article Hydrido complexes
Structure of [HRe(C5H5)2]. The aromatic C5H5 groups are represented by pentagons.
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from article Hydrido complexes
Hydridophosphine structures, with the C6H5 groups not shown. (a) [HRuCl(P{C6H5 }3)3]. (b) [H3Ir(P{C6H5 }3)3].
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from article Hydrido complexes
Reaction scheme for hydrogenation of an olefin using Wilkinson's catalyst.
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from article Hydrido complexes
Structure of [HCr2(CO)10]−.
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from article Hydrido complexes
Structure of [H2W2(CO)8]2−.
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from article Hydrido complexes
Core of the [H8Re2(P{C2H5 }2C6H5)4] molecule. All organic groups are omitted for clarity.
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from article Hydrido complexes
Structure of [H2Th(C5 {CH3 }5)2]2. The hydrogen atoms of the methyl groups are omitted for clarity.
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from article Gastrointestinal tract disorders
The major organs and associated anatomical structures of the gastrointestinal tract. (Copyright © McGraw-Hill Education)
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from article Gastrointestinal tract disorders
A cross section of a peptic ulcer, illustrating the four layers: fibrin (black arrowhead), neutrophils (black arrow), granulation tissue (white arrowhead), and fibrosis (white arrow). (Copyright © McGraw-Hill Education)
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from article Gastrointestinal tract disorders
Small intestine biopsy showing villous atrophy, which is found in individuals affected by celiac disease. (Credit: Ed Uthman/National Institutes of Health)
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from article Lepisosteiformes
Spotted gar (Lepisosteus oculatus). (Photo by Brian Montague, U.S. Fish and Wildlife Service)
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from article Extremophile
Extremophile (psychrophile) bacteria (Carnobacterium pleistocenium) retrieved from the ice of a frozen Alaskan pond dating back approximately 32,000 years. (Credit: Marshall Space Flight Center, National Aeronautics and Space Administration)
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from article Tommotian fauna
Tube-dwelling animals of the Tommotian fauna. (a) Cloudina, one of the earliest animals with a mineralized skeleton. (b) Aculeochrea, an anabaritid showing the three-rayed symmetry typical of the group. (c) Hyolithellus, an animal reinforcing its…
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from article Tommotian fauna
Reconstruction of life cycle of the probably scyphozoan Olivooides, based on fossilized embryos and polyps.
