Image
from article Messier Catalog
Search Results
Search Results
Refine this search
Search result paging links
12,550 results
Image
from article Red Sea
Division of the Red Sea into regions representing different stages in the formation of an ocean basin. (After F. Martinez and J. R. Cochran, Structure and tectonics of the northern Red Sea: Catching a continental margin between rifting and drifting,…
Image
from article Active sound control
Results of a computer simulation of the sound field produced by two sources of spherical sound waves in air that have identical source strengths and are separated by a distance of 10 m. The sources are out of phase and radiate sound at a frequency…
Image
from article Active sound control
Feed-forward active noise control system. Elements of the system below the broken line are entirely digital, the filter H operating on the input sequence x to produce the output sequence y. The characteristics of the filter are designed by using the…
Image
from article Active sound control
Active control system for the suppression of propeller-induced aircraft cabin noise. The digital filters H1 and H2 are designed to minimize the sum of the squared error signals e1–e4.
Image
from article Active sound control
Distribution of sound pressure level (in decibels on an arbitrary scale) at head height in a 48-seat propeller aircraft (a) before and (b) after the use of a multichannel active noise control system consisting of 16 loudspeakers and 32 microphones.…
Image
from article Active sound control
Multichannel feed forward active control system for suppressing noise from multiple primary sources.
Image
from article Active sound control
Performance of a multichannel feed forward system for the active suppression of road-induced noise in a small passenger car at a speed of 60 km/h (37 mi/h). Reference signals were taken from six vibration sensors on the vehicle suspension. The…
Image
from article Immunity
The immune response to an invading microbe can generate immunity via antibody production. Steps: (1) Antigen binds to a B cell receptor (antibody) on a B cell. (2) The B cell may also receive more information from a helper T cell about the presence…
Image
from article Immunity
Colored scanning electron micrograph of an activated human macrophage. Activation of macrophages is often an important aspect of the immune response. (Credit: Steve Gschmeissner/Science Photo Library/Alamy Stock Photo)
Image
from article Immunity
Colored scanning electron micrograph of B lymphocytes. These white blood cells are involved in the immune response. (Credit: Steve Gschmeissner/Science Photo Library/Alamy Stock Photo)
Image
from article Deforestation
View of an area of deforestation in Central Kalimantan, Indonesia. In this case, the land is being cleared to develop areas for intensive rice production. (Credit: Australian National University)
Image
from article Deforestation
The relationship between forest and nonforest (other) land. Preservation of forest lands includes reforestation and natural regeneration. However, deforestation and natural events can lead to nonforest land. Afforestation (the act or process of…
Image
from article Deforestation
Natural forest areas (in hectares; 1 hectare = 2.47 acres) in various climatic domains (boreal/polar, temperate, subtropical, and tropical) from 1990 to 2015. The data are derived from the Global Forest Resources Assessment 2015 by the Food and…
Image
from article Deforestation
Former rainforest in northern Queensland, Australia, that was deforested in the early 1900s and is now used for pasture. (Credit: Rodney Keenan)
Image
from article Deforestation
Aerial view of deforestation in the Amazon region of Brazil. Clearing of trees in the Amazon rainforest has resulted in the elimination of natural resources and numerous species. (Credit: Luoman/Getty Images)
Image
from article Polaron
An electron self-trapped by the displacements of equilibrium positions of atoms that surround it.
Image
from article Polaron
Energy levels of quasifree and self-trapped states when the polaron is energetically stable.
Image
from article Polaron
Polaron mobilities versus inverse temperature.
Image
from article Ionic crystals
Sodium chloride lattice. The darker circles represent positive ions and the lighter circles negative ions. (After F. Seitz, The Modern Theory of Solids, Dover, 1987)
Image
from article Ionic crystals
Cesium chloride lattice. (After F. Seitz, The Modern Theory of Solids, Dover, 1987)
Image
from article Ionic crystals
Wurtzite lattice. (After F. Seitz, The Modern Theory of Solids, Dover, 1987)
Image
from article Ionic crystals
Zinc blende lattice. (After F. Seitz, The Modern Theory of Solids, Dover, 1987)
Image
from article Ionic crystals
Calcium fluoride lattice. (After F. Seitz, The Modern Theory of Solids, Dover, 1987)
Image
from article Ionic crystals
Rutile lattice. (After F. Seitz, The Modern Theory of Solids, Dover, 1987)
Image
from article Ionic crystals
Image
from article Basalt
Devils Postpile, Mammoth Lakes, California, United States, which formed about 82,000 years ago, is a great example of columnar basalt. (Credit: U.S. National Park Service)
Image
from article Basalt
Thin section of upper crust of lava about 3 cm from top; black is microcrystalline groundmass. 0.5 mm = 0.02 in.
Image
from article Basalt
Thin section of interior of lava shown in Fig. 1, but 7.9 m (26 ft) below the top of the flow. Clear plagioclase crystals are ophitically enclosed in large pyroxene grains up to 1 mm in diameter. Crystals of black magnetite are minor. A few…
Image
from article Basalt
Growth of crystals as a function of temperature in basalt in Hawaiian lava. °F = (°C × 1.8) + 32.
Image
from article Basalt
Diagrams illustrating the compositions of basalts in terms of normative mineral formulas. Customarily, CaAl2Si2O8 (anorthite) is grouped together with NaAlSi3O8 (albite), and Fe2SiO4, FeSiO3, and CaFeSi2O6 are grouped with the corresponding Mg…
Image
from article Evolutionary computation
Typical flowchart for an evolutionary algorithm.
Image
from article Evolutionary computation
Traveling salesperson problem comprising 1000 cities. (a) Best-evolved solution after examination of 4 × 107 possible solutions. (b) Rate of evolutionary optimization.
Image
from article Evolutionary computation
Arrangement for distributing an evolutionary algorithm across multiple processors. Each processor holds its own population that undergoes random variation and selection. Occasionally, solutions will migrate from one population to another and begin…
Image
from article Symphyla
Scutigerella immaculata. This symphylan is a garden and greenhouse pest. (Photo by Ivo Antušek; BioLib.cz)
Image
from article Symphyla
Cercus (enlarged view). (Courtesy of Robert T. Allen, Academy of Natural Sciences, Philadelphia; Amanda Lawrence, Electron Microscope Center, Mississippi State University)
Image
from article Cestida
Structure of Cestum veneris.
Image
from article Cohesion (physics)
Calculated pressure-volume curves for molybdenum and xenon at absolute zero. Negative-pressure portions of curves are represented by broken lines because they cannot be directly measured. 1 kilobar = 0.1 GPa; 1 Å3 = 0.001 nm3.
Image
from article Ordovician
Ordovician, the second period of the Paleozoic Era.
Image
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.
Image
from article Precession of equinoxes
Illustration of the celestial sphere, an imaginary sphere of infinite radius centered on the Earth and projected using Earth's celestial poles and celestial equator. (Credit: NASA)
Image
from article Precession of equinoxes
Motion of the Earth's axis of rotation.
Image
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…
Image
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…
Image
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…
Image
from article Lipidomics
Functional-mediator lipidomics approach to evaluate and profile compounds during experimental inflammation and its resolution.
Image
from article Cephalochordata
European lancelet (Branchiostoma lanceolatum). (After J. E. Webb, On the populations of Branchiostoma lanceolatum and their relations with the West African lancelets, Proc. Zool. Soc. Lond., 127:131, 1956)
Image
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…
Image
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…
Image
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…
