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from article Wool
Sheep at a research facility near Dubois, Idaho. (Photo courtesy of the Agricultural Research Service, U.S. Department of Agriculture)
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Image
from article Wool
Longitudinal section of a completely developed nonmedullated wool follicle, including sebaceous and sweat glands.
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from article Wool
Cuticle, cortex, and medulla of a wool fiber.
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from article Wool
Scale formation of Delaine Merino wool fibers.
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from article Wool
Fine wool staples showing distinct crimp (wavy) patterns. The length shown is the minimum for each classification.
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from article Molybdenum
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from article Brazil nut
Unshelled Brazil nuts (Bertholletia excelsa). (Photo courtesy of C. E. Timothy Paine)
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from article Staining
Photomicrograph of Mycobacterium tuberculosis (the causative agent of tuberculosis) using the acid-fast Ziehl-Neelsen carbol fuchsin stain. In this case, the M. tuberculosis bacteria stain red (or reddish purple), whereas non-acid-fast species stain…
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from article Staining
Staining of Klebsiella bacteria using crystal violet. (Credit: Lisa Burgess/McGraw-Hill Education)
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from article Staining
Photomicrograph of a Gram-stained urethral exudate sample from a male who presented with a case of urethritis. Numerous extracellular Gram-negative Neisseria gonorrhoeae bacteria are evident. (Credit: Norman Jacobs/U.S. Centers for Disease Control…
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from article Castor plant
Seeds of the castor plant (Ricinus communis). These seeds, which are also known as castor beans, are processed to make castor oil. (Credit: Brian Prechtel/Agricultural Research Service, United States Department of Agriculture)
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from article Cowpea
Cowpea (Vigna unguiculata): pods and leaves. (Photo by Howard F. Schwartz, Colorado State University)
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from article Cowpea
Cowpea seeds, which are often called black-eyed peas. (Photo by Joseph Berger; Bugwood.org)
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from article Sulfur
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from article Telemetering
Functions of a generic aerospace telemetry system.
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from article Telemetering
Functions of a supervisory control and data acquisition (SCADA) system.
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from article Telemetering
Functions of a spacecraft telemetry and command system, using packet telemetry.
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from article Kumquat
Fruits and foliage of the Nagami kumquat (Fortunella margarita). (Photo by Forest and Kim Starr)
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from article Mulberry
White mulberry (Morus alba). (Photo courtesy of Forest and Kim Starr)
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from article Jawless vertebrate
Interrelationships of jawless and jawed vertebrates, showing the distribution of some major evolutionary steps. (Copyright © McGraw Hill)
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from article Beech
Leaf on top of bark of American beech (Fagus grandifolia). (Photo courtesy of Robert H. Mohlenbrock, USDA–NRCS PLANTS Database)
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from article Beech
Beechnuts of the American beech (Fagus grandifolia). (Photo courtesy of Steve Hurst, USDA–NRCS PLANTS Database)
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from article Schuler pendulum
Basic principles illustrated by (a) simple pendulum; (b) Earth-radius pendulum; (c) solid pendulous rod.
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from article Schuler pendulum
Behavior of pendulous rod when accelerated about Earth. (a) Short-period pendulous rod. (b) Schuler-period pendulous rod. (c) Nonpendulous rod.
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from article Schuler pendulum
Gyropendulum; thrust bearing provides extra freedom, necessary for gyroscopic action.
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from article Schuler pendulum
Principle of Schuler-tuned stable platform.
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from article Psocoptera
Valenzuela flavidus, male (family Caeciliusidae): habitus (general appearance). Body length: 2.02 mm (0.08 in.).
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from article Psocoptera
Metylophorus novaescotiae, female (family Psocidae): habitus. Body length: 5.24 mm (0.2 in.).
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from article Psocoptera
(a–e) Mouthparts of a typical psocid, Echmepteryx hageni (family Lepidopsocidae): a = labrum, b = maxilla (l = lacinia), c = hypopharynx (li = lingual sclerite), d = mandible, e = labium. Scale: 0.1 mm (0.004 in.). (f) Wing venation of a typical…
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from article Psocoptera
Liposcelis brunnea, female (family Liposcelididae): habitus of a cleared specimen. Body length: 1.1 mm (0.043 in.).
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from article Catalysis and catalysts
The Hoveyda-Grubbs catalyst, molecular formula C31H38Cl2N2ORu, is a ruthenium-based metathesis catalyst.
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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 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 Cellular automata
Cellular automata connections: (a) linear, (b) orthogonal, and (c) full.
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from article Cellular automata
Cellular automata in action.
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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 Devonian
Devonian, the fourth period of the Paleozoic Era.
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from article Devonian
Biostratigraphic zones based on conodonts (left) plotted to show approximate correspondence to the chronostratigraphic stages and series which compose the Devonian System (right) and relative sea-level changes (center) showing major fluctuations…
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from article Devonian
Reconstruction of Middle Devonian continental positions based on distribution of lithologic climatic indicators. Probable ocean currents derived from this paleogeography explain the biogeographic realms. Kolyma and Tarim are microcontinents of the…
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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 Malvales
A blooming hibiscus flower (genus Hibiscus, family Malvaceae, order Malvales). (Credit: Howard F. Schwartz/Colorado State University)
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from article Obolellida
Obolella. (a) Shell exterior (after J. Hall and J. M. Clarke, An introduction to the study of the Brachiopoda intended as a handbook for the use of students, Report of the N.Y. State Geologist for 1891, 1894). (b) Dorsal valve interior, and (c)…
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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…
Image
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 Enantiornithes
Protopteryx, the most primitive known enantiornithine bird, collected from the Early Cretaceous of Hebei Province, northern China.
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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 Information management
Information concept in a word tag cloud managed in the context of big data. (Credit: Shutterstock/Rafal Olechowski)
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from article Videotelephony
Video telephone call using a tablet computer. (Courtesy of Fotolia, https://us.fotolia.com)
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from article Mollusca
Higgins eye pearly mussels (Lampsilis higginsii). (Credit: U.S. Fish and Wildlife Service)
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from article Mollusca
Snails are assigned to the class Gastropoda in the phylum Mollusca. (Credit: Zuzha/Shutterstock)
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from article Mollusca
Generalized model of a stem mollusk (or archetype) in side view. There are three distinct regions in the molluscan body: head-foot, visceral mass, and mantle-shell. Water circulation through the mantle cavity, gills (ctenidia), and pallial complex…
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from article Mollusca
Arrangement of the mantle and shell layers in mollusks. The fleshy mantle margin is divided into three lobes, and the outer pallial lobe is largely responsible for secretion of the three layers of the shell. (Credit: W. D. Russell-Hunter)
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from article Mollusca
Aspidobranch ctenidium (feather or plume gill) as found in primitive gastropods and other molluscan groups. (a) Stereogram showing the water current from the ventral inhalant to the dorsal exhalant between adjacent gill plates; this current is…
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from article Mollusca
Common octopus (Octopus vulgaris). (Credit: Aerial-motion/Shutterstock)
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from article Frequency modulation
Examples of modulating signals and corresponding frequency-modulated waveforms. (a) Ramp modulating signal. (b) Periodic modulating signal.
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from article Frequency modulation
Example of direct method of frequency modulation.
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from article Frequency modulation
Example of indirect method of frequency modulation.
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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 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 Paleoecology
Zonation of Silurian (425 million year old) marine communities in the Welsh Basin, United Kingdom. Marine animal communities were typically arranged in belts parallel to the shoreline and related to water depth. A classic study using fossil…
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from article Paleoecology
Classification of shales in terms of percentages of three benthic habitat groups: epifaunal suspension-feeding bivalves (those living at the sediment-water interface and filtering seawater), infaunal (living within and feeding on the sediment), and…
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from article Paleoecology
Comparison of four developmental stages in four ancient reef masses. (After K. R. Walker and L. P. Alberstadt, Ecological succession as an aspect of structure in fossil communities, Paleobiology, 3:238–257, 1975)
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from article Paleoecology
Formation and burial sequence of Bobcaygeon hardground. (a) Soft-bottom community of strophomenid brachiopods and infaunal burrowers inhabiting carbonate mud. (b) Hardground community consisting of boring and encrusting organisms. (c)…
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from article Paleoecology
Tiering or vertical depth stratification in marine communities through time. Note the rapid rise of the highest-tier (level) organisms (crinoids or sea lilies, bryozoans) from a few centimeters to over a meter above the sea floor during the…
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from article Paleoecology
The three great marine evolutionary faunas of the Phanerozoic. The Cambrian fauna, composed of trilobites, primitive groups of brachiopods, and mollusks, arose early during that period to a diversity of about 50 families, and then dwindled during…
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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)
