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from article Ordovician
Ordovician, the second period of the Paleozoic Era.
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from article Ordovician
Early Ordovician (Arenig) paleogeography, major rock suites and potential ocean surface currents; based on remanent magnetism data supplemented by plots of the positions of shelf sea carbonates and reefs.
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from article Lipidomics
Components of phosphoinositides. (a) General structure of phospholipids, showing positions sn-1 and sn-2, where various fatty acids may attach. X represents a phosphate-linked group; FA represents a fatty acid. (b) Space-filling models of four…
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from article Lipidomics
Selected MS ion chromatograms of synthetic 1,2-diacyl-sn-3-glycerol (DAG) molecular species from polymorphonuclear neutrophilic leukocytes (PMNs) of patients with local aggressive periodontal disease. DAG species were resolved and identified by…
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from article Lipidomics
Families of bioactive lipids. (a) Arachidonic acid is the precursor for many of the known bioactive mediators, such as EETs, prostaglandins, leukotrienes, and lipoxins. (b) Eicosapentanoic acids (C20:5 and C22:6) are precursors to potent new…
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from article Lipidomics
Functional-mediator lipidomics approach to evaluate and profile compounds during experimental inflammation and its resolution.
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from article Thrombosis
Organized thrombus in an artery with recanalization.
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from article Thrombosis
Organized thrombus in an artery with scar formation; the artery is completely occluded by the fibrotic mass.
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from article Mitochondria
A mitochondrion is a specialized compartment (organelle) of a eukaryotic cell (upper left). The electron micrograph (upper right) and the accompanying illustration (bottom) indicate the outer and inner membranes, cristae, and matrix. [Credit…
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from article Mitochondria
Three-dimensional reconstruction of a rat liver mitochondrion produced by electron microscopic tomography. During imaging, the sample is tilted around one or more axes to generate different projections that are later digitally combined to produce a…
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from article Mitochondria
Guard cells of a transgenic tobacco plant expressing green fluorescent protein (GFP) targeted to mitochondria. Chloroplasts (cell plastids) show red chlorophyll autofluorescence and mitochondria show green protein fluorescence. (Credit: Rainer…
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from article Mitochondria
Mitochondria are the powerhouses of the cell, being responsible for energy generation in the form of adenosine triphosphate (ATP). ATP is produced by the coupled processes of electron transport and oxidative phosphorylation in mitochondria.…
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from article Eye (invertebrate)
Pigment spot ocellus, the simplest invertebrate eye. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)
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from article Eye (invertebrate)
Simple open eye of the marine limpet Patella. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)
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from article Eye (invertebrate)
Large, complex eye of the marine snail Murex. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)
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from article Eye (invertebrate)
Simple pigment cup ocellus of flatworm. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)
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from article Eye (invertebrate)
Large, complex eye of the clam worm Nereis. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)
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from article Eye (invertebrate)
Simple eye of Ranzania, a marine annelid. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)
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from article Eye (invertebrate)
Highly developed eyes at anterior end of pelagic marine annelid Alciopidae. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)
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from article Eye (invertebrate)
Scallop Argopecten with one valve removed showing ocelli along the margin of the mantle. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)
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from article Eye (invertebrate)
Longitudinal section through the tubelike anterior median eye of jumping spider Salticus. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)
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from article Eye (invertebrate)
Octopus eye. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)
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from article Eye (invertebrate)
Two ommatidia from compound eye of crayfish Astacus. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)
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from article Eye (invertebrate)
Compound eye adapted for opposition image formation. Light rays from points a, b, and c. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed., Brooks/Cole Thomson, Belmont, CA, 2004)
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from article Eye (invertebrate)
Compound eye adapted for superposition image formation. The light from points a, b, and c is concentrated on an ommatidium. (After E. E. Ruppert, R. S. Fox, and R. D. Barnes, Invertebrate Zoology: A Functional Evolutionary Approach, 7th ed.,…
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from article Ferret
An endangered black-footed ferret (Mustela nigripes). (Photo copyright © Joseph Dougherty)
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from article Physiological acoustics
Schematic outline of the central auditory pathways. Numbers indicate the number of neurons from the cochlea. (After S. S. Stevens, ed., Handbook of Experimental Physiology, John Wiley and Sons, 1951)
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from article Physiological acoustics
Distribution of frequency maxima along the basilar membrane. Numbers give frequencies in hertz. Length of basilar membrane = 32 mm, width = 0.04 mm at base, 0.50 mm at apex. (After O. Stuhlmann, An Introduction to Biophysics, John Wiley and Sons,…
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from article Physiological acoustics
Isoamplitude curves of the dc receptor potential within one guinea pig inner hair cell of the basal region. Q10 is a measure of the width of each curve, equal to the center frequency divided by the bandwidth at 10 dB above threshold. (After I. J.…
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from article Physiological acoustics
Intensity/rate functions of two cat cochlear nerve fibers tuned to (a) 2.2 kHz and (b) 10.6 kHz. (After W. D. Keidel and W. D. Neff, eds., Handbook of Sensory Physiology, Springer, 1975)
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from article Physiological acoustics
Tuning curves of a number of nerve fibers in the cat cochlear nerve. (After N. Y.-S. Kiang, Discharge Patterns of Single Fibers in the Cat's Auditory Nerve, MIT Res. Monogr. 35, MIT Press, 1965)
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from article Physiological acoustics
PST histograms for a number of nerve fibers in a cat with various characteristic frequencies, showing response to click stimulation. Each histogram represents 1 minute of data (600 clicks at click rate of 10 per second). (After N.Y.-S. Kiang,…
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from article Physiological acoustics
Response patterns of cells in cat cochlear nuclei, with characteristic frequencies indicated. (a) Primarylike response, 3.5 kHz. (b) Chopper response, 7.0 kHz. (c) Pauser response, 6.6 kHz. (d) “On” pattern, 2.1 kHz. (After R. R. Pfeiffer,…
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from article Physiological acoustics
Ascending (afferent) and descending (efferent) auditory nerve systems. Number labels in the ascending system indicate the number of neurons from the cochlea, while those in the descending system indicate the number of neurons from the auditory…
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from article Granite
Classification of granitic rocks by the IUGS scheme. All proportions are by volume percentages.
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from article South America
Map of South America.
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from article South America
Andes Mountains, Chile. The Andes, which parallel the Pacific coast, constitute one of the Earth's most majestic features. Only the Himalayas exceed them in elevation and mass. (United Press International)
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from article South America
Representative view of the hilly uplands and low mountain country of the Guiana Highlands. One of five waterfalls on the Canaima River, Gran Sabana in southern Venezuela. (Venezuelan Information Service)
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from article South America
Uplifted beaches on desert coast, east side of San Juan Bay, Departmento de Ica, Peru. The sea cliff is about 100 ft (30 m) high. Each horizontal line represents a former beach. (Photograph by F. Atchley)
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from article South America
Port of Matarani on the desert coast of southern Peru. This oblique aerial view looks coastwise southward over one of the world's driest and most barren coastal zones. (Servicio Aerofotográfico Nacional)
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from article Zosterophyllopsida
Examples of Devonian Zosterophyllopsida. (a) Reconstruction of the Early Devonian Zosterophyllum rhenanum, here depicted as an aquatic plant (after R. Kräusel and H. Weyland, Neue Pflanzenfunde im rheinischen Unterdevon, Palaeontographica B,…
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from article Sexually transmitted diseases
Acquired immune deficiency syndrome (AIDS) is a sexually transmitted disease caused by the human immunodeficiency virus (HIV). In this image, a human T cell (blue) is under attack by HIV (yellow), hampering the effectiveness of the body's immune…
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from article Sexually transmitted diseases
Prevalence of Chlamydia trachomatis (the most-common sexually transmitted bacterial pathogen) among individuals aged 14 to 39. The prevalence varies by sex, race/ethnicity, and age. Error bars indicate 95% confidence intervals. (Credit: U.S. Centers…
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from article Sexually transmitted diseases
Age-related incidence of hospitalized cases of acute pelvic inflammatory disease (salpingitis) in sexually experienced females in the United States. (Copyright © McGraw-Hill Education)
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from article Bytownite
Bytownite, from Crystal Bay, Minnesota. (Specimen from Department of Geology, Bryn Mawr College)
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from article Excretion
Sequence of breakdown from nucleic acid to ammonia. Reverse pathways broken indicate either lack of knowledge of the mechanism or that other enzymes than those shown are involved. (After M. Florkin, Biochemical Evolution, Academic Press, 1949)
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from article Excretion
Chart of the principle of excretion of a common nitrogenous waste, whether derived from protein or nucleic acid. (After M. Florkin and G. Duchateau, Arch. Int. Physiol., 53:267–307, 1943)
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from article Ophiuroidea
Representative ophiuroids, which have a quite distinctive shape. (a) Ophiopeza cylindrica (alternatively, Pectinura cylindrica). (b) Asteroporpa australiensis (alternatively, Astroporpa wilsoni). (c) Gorgonocephalus chilensis.
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from article Ophiuroidea
External features of the ophiuroid Amphiura. (a) Aboral view. (b) Adoral view.
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from article Tetanus
Photomicrograph showing endospores forming at the ends of Clostridium tetani bacterial cells, which are shaped like small tennis rackets. Clostridium tetani is the causative agent of tetanus. (Credit: Lisa Burgess; copyright © McGraw Hill)
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from article Syphilis
Syphilis is caused by Treponema pallidum, which is a corkscrew-shaped motile bacterium (spirochete). (Credit: National Institute of Allergy and Infectious Diseases, National Institutes of Health)
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from article Rabies
Negri bodies (cytoplasmic inclusion bodies) in infected nerve cells in a dog brain are characteristic cellular changes that occur as a result of rabies encephalitis. (Credit: G. Heid/Centers for Disease Control and Prevention)
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from article Rabies
Schematic model of a rabies virus showing the surface glycoprotein spikes (projections) extending from the lipid envelope that surrounds the internal nucleocapsid and the matrix protein lining the envelope. The nucleocapsid comprises the single RNA…
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from article Metamorphic rocks
Fabrics of metamorphic rocks under microscope. (a) Mortar fabric; (b) flaser or mylonitic fabric; (c) granoblastic fabric (after E. E. Wahlstrom, Petrographic Mineralogy, John Wiley and Sons, 1955). (d) Lepidoblastic fabric; (e) nematoblastic…
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from article Metamorphic rocks
Diagram showing the general relationship between deformation folding and slaty cleavage caused by pressure PP or the couple ScSc. Heavy black lines denote the original bedding deformed into folds. Thin lines indicate slaty cleavage which may grow…
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from article Metamorphic rocks
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from article Metamorphic rocks
Mineral facies groups of regional metamorphic rocks showing the temperature and pressure of metamorphism. °F = (°C × 1.8) + 32.1 km = 0.6 mi.
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from article Geographic information systems
Comparison of (a) raster and (b) vector data models at the boundary of a residential housing subdivision. Raster data files consist of rows of uniform cells coded according to data values. Raster files are easily manipulated, but are less detailed…
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from article Geographic information systems
Overlay analysis using raster data files.
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from article Chaos
Graphic depicting extreme rainfall totals in the state of South Carolina in early October, 2015, which according to National Weather Service statistics represented a 1,000-year rainfall event, meaning such an event is expected to occur about once…
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from article Chaos
Transition from order to chaos (turbulence) in a rising column of cigarette smoke. The initial smooth streamline flow represents order, while the erratic flow represents chaos.
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from article Chaos
Three-dimensional visualization of the Lorenz butterfly as traced out by the trajectory of the original simulation reported by Lorenz in 1963 (σ = 10, b = 8/3, r = 28) with initial conditions (X, Y, Z) = (0, 1, 0). The integration was performed with…
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from article Chaos
Separation of solutions on the Lorenz attractor. The two trajectories starting from the nearby initial points indicated by the balls in the right lobe of the attractor stay together for several circuits around both lobes and then separate as they…
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from article Chaos
Examples of fractal (self-similar) sets. (a) The Mandelbrot set in the complex plane, with origin indicated by the cross. A single point in the complex plane (in this case C = 0.314 − 0.537 i, where 1 = 1 ) generates (b) an associated Julia set.
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from article Chaos
Representations of pendulum motion corresponding to a periodic variation in angular position θ whose amplitude is just less than π radians (180°). (a) Phase-space representation (plot of momentum p versus θ). (b) Time plots of θ and of p = Θ. (c)…
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from article Chaos
Example of a pendulum in which gravity and a torsional ribbon act in opposition. The oscillating mass is a thin semicircular metal plate that is rigidly attached to the ribbon at its midpoint. The ribbon is fixed at each end but twists where the…
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from article Chaos
Simple fractal geometry attractors generated by computer. (a) Attractor generated using the Chirikov map defined by Eqs. (15), with c = 1.6 and initial values p0 = θ0 = 2. (b) Attractor generated using the torsion-gravity pendulum map defined by…
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from article Chaos
Examples of the period-doubling route to chaos for two vastly different iterative expressions. (a) The logistic map, defined by Eq. (18). (b) The Chebyshev root-finding algorithm applied to Kepler's equation, defined by Eqs. (20) and (21) with…
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from article Chaos
Power spectra of acoustic cavitation noise at four different excitation levels, showing the successive filling of the spectrum by period doubling (frequency halving) when the sound input intensity is raised. Numbers at tops of the graphs indicate…
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from article Chaos
Dependence of the scaled threshold field n40 F (10%) that produces an ionization probability of 10% after weakly bound hydrogen atoms are exposed to about 300 microwave field oscillations, on the scaled frequency n30ω.
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from article Spermatogenesis
Cellular events in human spermatogenesis. Cell types are labeled.
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from article Echocardiography
Two-dimensional echocardiogram from a position near the apex of the ventricles of a human heart. The left ventricle is on the right, separated from the left atrium below by the mitral valve. The right ventricle is on the left, and the right atrium…
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from article Microbiology
Two important types of microbes are bacteria (Mycobacterium tuberculosis; left) and fungi (Histoplasma capsulatum; right). [Credit: Janice Haney Carr/Centers for Disease Control and Prevention (left); Libero Ajello/Centers for Disease Control and…
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from article Microbiology
Viruses (Herpes simplex; left) and protozoa (Oxytricha trifallax; right) are microorganisms studied by microbiologists. [Credit: Centers for Disease Control and Prevention (left); National Human Genome Research Institute (right)]
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from article Bean
Pods of soybean plants (Glycine max). (Credit: Howard F. Schwartz/Colorado State University)
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from article Bean
Red dry bean pods (Phaseolus vulgaris). (Credit: Howard F. Schwartz/Colorado State University)
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from article Bean
Different stages of maturity of the seeds of light red kidney beans in opened pods. (Credit: Howard F. Schwartz/Colorado State University)
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from article Bean
Symptoms of Pythium disease on Phaseolus vulgaris (common bean) plants. (Credit: University of Georgia Plant Pathology Archive)
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from article Bean
Anthracnose, caused by Colletotrichum lindemuthianum, on bean pods. (Credit: U.S. Department of Agriculture Cooperative Extension Series, Clemson University)
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from article Chronic fatigue syndrome
Chronic fatigue syndrome is more widespread among women. (Credit: Sirikorn Thamniyom/Shutterstock)
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from article Formation
Geological units of Paleozoic age recognized in the walls of the Grand Canyon, Arizona. (Modified from S. S. Beus, Geology along the South Kaibab Trail, eastern Grand Canyon, Arizona, in S. S. Beus, ed., Geological Society of America Centennial…
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from article Precipitation measurement
Automatic gages. (a) Tipping-bucket rain gage. (b) Weighing rain gage. (Belfort Instrument)
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from article Precipitation measurement
Comparison of rainfall rates measured with gages and radar using (a) the R, Z relation and (b) the R, KDP relation. Each data point (+) is the rainfall rate for a single storm.
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from article Forensic document analysis
Dots appearing in the background of documents produced by Xerox 5750 digital color copiers and printers.
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from article Forensic document analysis
An illustrative chart showing similar features that appear in both the questioned and specimen handwriting.
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from article Forensic document analysis
The signature on a photocopied contract that was inserted by cutting and pasting a genuine signature from item K5 into position on the contested document. The overlaid ruled graphs confirm that the signatures on items Q1 and K5 are duplicates of one…
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from article Forensic document analysis
The D and LLR values among three examples of the letter “e” written by two writers.
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from article Forensic document analysis
Histograms and parametric probability density functions: (a) same and different histograms for the letter “e” and (b) same and different probability density functions for letter “e.”
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from article Forensic document analysis
Three black ballpoint pen inks analyzed for dating tags using thin layer chromatography. The tag found in ink 1 was added to writing inks manufactured during 1981 and 1991, while no dating tags were detected in inks 2 and 3.
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from article Trypanites
Trypanites borings in a carbonate hardground from the Upper Ordovician of northern Kentucky. The borings descend from the top of the rock surface perpendicularly to the bedding. Each boring is filled with tiny dolomite crystals, making them stand…
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from article Coenzyme
Nicotinamide adenine dinucleotide (NAD+) is a coenzyme that functions as a hydrogen acceptor for a large number of dehydrogenase enzymes, including alcohol dehydrogenase (ADase). The coenzyme NAD+ needs to be present in order for the oxidation of…
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from article Nervous system (invertebrate)
Electrical potentials and synaptic arrangements. (a) An action potential recorded from the giant axon of the squid. (b) Electrical synapse (two-way). (c) Chemical synapse (one-way).
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from article Nervous system (invertebrate)
Neuron types. (a) Multipolar, isopolar neurons (primitive invertebrate). (b) Unipolar, heteropolar neurons (common invertebrate); arrow indicates direction of information flow. (c) Bipolar neuron (common invertebrate). (d) Multipolar, heteropolar…
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from article Nervous system (invertebrate)
Electrical responses and nervous systems in the lowest invertebrates. (a) Recording from Paramecium illustrates a graded action potential which uses Ca2+ ions in the upswing phase and K+ ions during repolarization; three responses of varying size…
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from article Nervous system (invertebrate)
Nervous systems of the intermediately advanced invertebrates (various worms). (a) Turbellarian flatworm (Notoplana) illustrating nerve cells coming together to form ganglia and nerve tracts (centralization) and nerve cells concentrated in the head…
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from article Nervous system (invertebrate)
Advanced invertebrates as represented by the crustacean nervous system. (a) Crayfish central nervous system (after W. C. Curtis and M. J. Guthrie, Textbook of General Zoology, 3d ed., John Wiley and Sons, 1938). (b) Photomicrograph of cross section…
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from article Nervous system (invertebrate)
Advanced invertebrate nervous system as represented in the marine gastropod mollusk Aplysia. (a) General arrangement of nervous system. (b) Map of the dorsal and ventral surfaces of the abdominal, or parietovisceral, ganglion, indicating the many…
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from article Vegetation and ecosystem mapping
Terrestrial major habitat types.
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from article Notoungulata
Skull and jaw of Adinotherium ovinum, an early Miocene toxodontid notoungulate from the Santa Cruz formation of Patagonia, Argentina.
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from article Notoungulata
Examples of molars of Adinotherium ovinum from the Santa Cruz formation of Patagonia, Argentina. (a) Upper molar. (b) Lower molar.
