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Forearc and back-arc processes in subduction zones. (a) Cross section of a nonaccretionary (typically Mariana-type) subduction zone, with ocean crust being subducted beneath ocean crust and with extension in the back-arc region. (b) Cross section of…

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from article Electronic warfare

Fully automatic land-based ELINT system, which monitors and documents the nature and location of hostile electromagnetic emitters and detects any changes in their location. (Litton Applied Technology)

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from article Electronic warfare

Metallized glass chaff, which returns spurious radar echoes. (Lundy Electronics and Systems)

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from article Electronic warfare

Bulk-chaff dispensing pod which ejects chaff through six exit pipes.

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from article Electronic warfare

Countermeasures-dispensing system aboard an air transport used in humanitarian relief efforts ejecting flares to foil attacks by ground-launched infrared guided missiles. (Lockheed Aircraft Service Co.)

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from article Electronic warfare

Transmitter of infrared countermeasures system, providing 360° protection, mounted atop fuselage of UH-lH utility helicopter. (Sanders Associates)

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from article Electronic warfare

Typical pulse repeater jamming system.

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from article Electronic warfare

Programmable countermeasures-dispensing system, which can dispense chaff, flares, and active expendables to protect aircraft from threats. (Tracor)

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from article Electronic warfare

Antenna for shipborne deception ECM system mounted on vessel's superstructure. (Hughes Aircraft Co.)

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from article Underwater photography

Dolphin and underwater photographer—13-mm lens. The extreme wide angle of the 13-mm lens (170° diagonal coverage) was used here to capture a shot of an Atlantic bottlenose dolphin and diver. By using an extreme wide angle, it is possible to cover…

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from article Underwater photography

Over/under shot, Solomon Islands—16-mm lens. The over/under shot (one-half above the water and one-half below) is best done with a housed camera and dome port. An extreme wide-angle lens is typically used, although sometimes a split diopter is also…

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from article Underwater photography

Underwater photographer on a shipwreck—15-mm lens. Shipwrecks provide excellent subjects for wide-angle photography, and including a diver as an element of composition can add color to an otherwise monochromatic subject, as well as a sense of scale.…

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from article Underwater photography

Blue-cheeked butterflyfish, Red Sea—28-mm lens. Colorful tropical marine life is a fascinating subject for the underwater photographer. The challenge is to capture the composition in a natural, nonintrusive fashion. (Photograph by Stephen Frink)

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from article Underwater photography

Lionfish, Red Sea—60-mm macro lens. When capturing closeup photographs of subjects that might be frightened by using framers (closeup kit or extension tubes), the housed single-lens reflex camera is the perfect tool. Not only can the photographer…

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from article Underwater photography

Caribbean reef shark and diver—16-mm lens. The extraordinary depth of field of the full-frame fisheye lens is apparent here, as both the shark and the diver are in sharp focus. A little perspective distortion is evident: because the shark is nearer…

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from article Underwater photography

Bathypteroid fish photographed from the Westinghouse diving vehicle Deepstar at 4000 ft (1200 m) depth in the Gulf of Mexico. Tungsten lighting was used. (Photograph by R. Church)

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from article Underwater photography

Photograph taken (August 1956) in Romanche Trench, 0°10′S, 18°21′W, at depth of 25,000 ft (7625 m). A nylon cable was used from the deck of the Calypso. (National Geographic Magazine, March 1958)

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from article Unconformity

Four types of unconformity. (After C.O. Dunbar and J. Rodgers, Principles of Stratigraphy, John Wiley and Sons, 1957)

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from article Slate

Slaty cleavage in folded mica-rich rock near Walland, Blount County, Tennessee. (USGS)

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from article Orthoclase

Orthoclase. (Credit: Doug Sherman/Geofile)

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from article Polar meteorology

Composites of polar regions as photographed by meteorological satellites. (a) Arctic, May 1989. (b) Antarctic, November 4–25, 1986. (From U. S. Air Force Defense Meteorological Satellite Program film, NOAA/NESDIS, CIRES/National Snow and Ice Data…

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from article Polar meteorology

Automatic weather station on the Antarctic ice sheet. (Photo courtesy of G. Wendler)

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from article Polar meteorology

Mean streamlines of the katabatic wind over the Antarctic ice sheet (a) as constructed from sastrugi directions and (b) as computed with an atmospheric model by T. Parish. Note the streamline concentrations indicating very strong winds.

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from article Ovarian disorders

Illustrations displaying a normal ovary (bottom left), a polycystic ovary (bottom right), and the location of the ovaries in relation to the uterus (top). In the polycystic ovary, follicle development is stopped, so there is no ovulation. (Credit:…

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from article Ovarian disorders

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from article Foothill abortion

Near-term foothill abortions. The aborted calves show typical distended abdomens (resulting from edema) [labeled "a"] and skin lesions [labeled "b"]. (Credit: Jeffrey L. Stott)

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from article Foothill abortion

Classical lesions associated with a case of foothill abortion: (a) petechial hemorrhages on eyelid; (b) petechial hemorrhages on tongue and gums; (c) fluid- and fibrin-filled abdominal cavity, swollen liver, and enlarged spleen. (Credit: Jeffrey L.…

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from article Foothill abortion

Habitat and appearance of the Pajaroello tick: (a) typical terrain (sage, bitterbrush, and pinyon pine) inhabited by the Pajaroello tick; (b, c) collection of Pajaroello ticks using dry-ice traps (hungry ticks are attracted to carbon dioxide); (d)…

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from article Climatology

Arctic sea ice extent for March 2021 was 14.6 million km2 (5.6 million mi2) In comparison, the Arctic sea ice extent for March 2020 (not shown) was 15.05 million km2 (5.81 million mi2). The pink line shows the 1981 to 2010 average extent for March.…

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from article Climatology

The earth-atmosphere energy balance is the balance between incoming energy from the Sun and outgoing energy from the Earth, using 100 units of energy from the Sun as a baseline. (Credit: NOAA/National Weather Service)

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from article Climatology

Global map showing rainfall and snowfall. (Credit: NASA)

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from article Climatology

Annual variation of monthly mean temperature and precipitation at (a) Tatoosh Island, Washington, (b) Minneapolis, Minnesota, (c) New York, New York, and (d) Miami, Florida. °F = (°C × 1.8) + 32; 1 mm = 0.04 in.

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from article Climatology

Schematic illustration of the processes and interactions in the climate system. The colored arrows indicate externally applied conditions, and black arrows show internal processes that act to influence climate change.

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from article Climatology

Climate of the past half-million years. Oxygen isotope ratios are from ocean sediments, which reflect variations in the global volume of ice in glaciers and ice sheets.

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from article Nuclear explosion

The Grable nuclear explosion on May 25, 1953 at the Nevada Proving Grounds. The atomic bomb, with a yield of 15 kilotons, was fired from a 280-mm cannon, seen at right. It remains the only nuclear artillery shell tested by the United States…

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from article Nuclear explosion

The mushroom cloud from the first test of a thermonuclear device, code-named Ivy Mike, with a yield of about 10 megatons. Part of Operation Ivy by the United States military, Mike detonated on Elugelab island in the Eniwetok Atoll on October 31,…

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from article Nuclear explosion

The destruction in Hiroshima, captured in a photograph more than two months after the dropping of an atomic bomb in August 1945. (Credit: The National Archives)

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from article Circulation disorders

Illustration of the thickening and hardening of blood vessels prevalent in patients with arteriosclerosis. (Credit: Christoph Burgstedt/Shutterstock)

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from article Circulation disorders

Intestinal ischemia. Note the red discoloration of the wall of the ischemic segment of the colon (arrow). Colonic ischemia can result from a variety of causes; in this case, the patient had a thrombus that developed within the superior mesenteric…

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from article Biomass

Wood materials are common sources of biomass. They can be burned directly for energy or processed in industrial facilities to produce renewable biofuels. (Credit: alffoto/Getty Images)

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from article Biomass

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from article Biomass

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from article Carrier (communications)

Carriers. (a) Sinusoidal carrier. (b) Square-wave carrier.

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from article Leprosy

Delayed-type hypersensitivity lesions in a borderline lepromatous patient. Annular lesions are numerous and vary in size, but they have uniform morphology, with sharp interior and exterior margins, as well as central hypopigmentation. (Copyright ©…

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from article Toxicology

Toxicologists study the adverse effects of chemical and physical agents on living organisms. In this photograph, a turtle is covered in petroleum following an oil spill. (Credit: Getty Images)

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from article Toxicology

Fish killed by chemically contaminated waters. (Credit: National Oceanic and Atmospheric Administration)

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from article Toxicology

The movement of mercury in the environment. In nature, mercury vapor (Hg0) is a stable gas and evaporates from the Earth's surface (both soil and water). Moreover, anthropogenic sources are a significant contributor to atmospheric mercury, and these…

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from article Invasive forest species

The emerald ash borer (Agrilus planipennis) is a destructive invasive forest species. Native to northeastern Asia, this wood-boring beetle has devastated large areas of forests in North America and Europe. (Credit: Benjamin Smith)

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from article Invasive forest species

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from article Hail

Cross section of a large hailstone showing the structure of alternating rings of clear and white ice. (Alberta Research Council, Edmonton).

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from article Rift valley

Sketch showing several ways in which half-graben units can link to make rift zones. (a) Map view. (b) Cross sections. A-A′ and B-B′ show simple half-grabens that alternate polarity along strike. C-C′ shows a typical morphology across an overlapping,…

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from article Olivine

Olivine specimen. (RF Company/Alamy)

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from article Underwater vehicles

Two-person deep submersible vehicle Deep Rover with all-acrylic pressure hull. (Deep Ocean Engineering, Inc.)

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from article Underwater vehicles

Observation/work bell. (Comex Industries)

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from article Underwater vehicles

One-atmosphere tethered vehicle Mantis. (OSEL Group, Ltd.)

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from article Underwater vehicles

HARDSUIT atmospheric diving suit. (Oceanworks International)

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from article Underwater vehicles

Reef Ranger wet submersible. (Submersible Systems Technology)

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from article Underwater vehicles

Japan's 36,000-ft (11,000-m) Kaiko, a large working ROV. (Jamstec & Mitsui Engineering and Shipbuilding)

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from article Underwater vehicles

Components of a towed vehicle. (Marine Physical Laboratory, Scripps Institute of Oceanography)

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from article Underwater vehicles

Bottom-reliant vehicle. (Sonsub International)

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from article Underwater vehicles

Structurally reliant vehicle used for servicing seafloor oil well structures. (Kvaener Brug A/S)

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from article Underwater vehicles

REMUS is rated for continental shelf depths (355 ft; 200 m) and is compact and lightweight (40 kg; 88 lb). It is depicted with its laptop computer for downloading missions and uploading data, and one of the acoustic transponders used for navigation.…

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from article Underwater vehicles

Atlantis 48-passenger tourist submarine. (Atlantis Submarines International)

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from article Underwater vehicles

One of the two Russian Mir 20,000-ft (6,000-m) manned submersibles. (P.P. Shirshov Institute of Oceanology)

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from article Infrasound

Wavelength of subaudible acoustic waves as a function of frequency. Turbulent noise exists at the same frequency as acoustic signals, but at much shorter spatial scales. (Adapted from Alfred Bedard with permission)

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from article Infrasound

Annual mean sound speed (Equator to 80° N). The speed of sound tracks air temperature and varies with altitude. Sound speed decreases with increasing altitude in the troposphere as the air temperature decreases away from Earth's surface. Sound speed…

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from article Infrasound

Global infrasound network. Of the 60 planned operating stations, over half are built and recording data (dark color circles), several are under construction (light color circles), and a third have not yet been built (open circles).

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from article Autopilot

Basic elements of an autopilot system.

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from article Autopilot

Typical longitudinal autopilot control loop.

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from article Autopilot

Typical directional autopilot control loop.

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from article Streamgaging

A typical USGS streamgage structure showing its satellite antenna and solar panel. The electronic equipment inside the structure allows the USGS to monitor river water levels. (Courtesy of USGS)

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from article Streamgaging

USGS stilling-well streamgage. (Courtesy of USGS)

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from article Streamgaging

Example of a stage–discharge relation; here, the discharge is 40 cubic feet per second (cfs) when the stage is 3.30 ft. (Courtesy of USGS)

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from article Streamgaging

Current-meter streamflow measurements are made by determining the discharge in each subsection of a channel cross section and summing the subsection discharges to obtain a total streamflow. In each subsection, area = depth × width and discharge =…

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from article Streamgaging

Current measuring instruments. (a) Price AA current meter. (b) Price AA current meter attached to a wading rod. (c) Price AA meter suspended above a sounding weight. (Photos courtesy of M. Nolan, USGS, Menlo Park, CA)

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from article Streamgaging

Mechanical current meter with polymer rotor used for measuring velocity under ice. (Courtesy of USGS)

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from article Streamgaging

Acoustic Doppler current profiler mounted in a watercraft guided across a river channel from the bridge deck above using a tether. (Photos courtesy of Jeff Conaway, USGS, Anchorage, AK)

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from article Food microbiology

Pie chart showing the 14 major foodborne pathogens according to their economic costs (shown in terms of percent and U.S. dollars). The annual cost estimates are based on disease incidences in the United States. The five most costly foodborne…

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from article Food microbiology

A colorized scanning electron micrograph (SEM) of Salmonella enterica serovar Enteritidis. This foodborne pathogen can cause enteric (intestinal) infections. (Credit: Jean Guard-Petter/U.S. Department of Agriculture)

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from article Food microbiology

A digitally colorized scanning electron micrograph (SEM) depicting a number of mustard-colored, spheroid-shaped Staphylococcus aureus bacteria that were in the process of escaping their destruction by blue-colored human white blood cells. (Credit:…

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from article Food microbiology

Low-temperature electron micrograph of a cluster of E. coli bacteria. Each individual bacterium is oblong-shaped. (Credit: Eric Erbe/U.S. Department of Agriculture; digital colorization by Christopher Pooley/U.S. Department of Agriculture)

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from article Food microbiology

Confocal light micrograph of Campylobacter jejuni cells (fluorescent green) on chicken skin. (Credit: Anna Bates/U.S. Department of Agriculture)

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from article Kalahari Desert

Map of the Kalahari Desert.

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from article Fossil apes

Reconstructions and partial reconstructions of the craniums of fossil apes: (a) Proconsul, (b) Afropithecus, (c) Oreopithecus, (d) Ouranopithecus, (e) Sivapithecus, and (f) Ankarapithecus.

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from article Fossil apes

Cladogram of the evolutionary relationships of the key fossil and living apes. Broken lines indicate uncertain relationships.

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from article Plant

The kingdom Plantae contains a tremendous diversity of plants. The plants seen in the photograph are drought-tolerant varieties native to California and the Mediterranean region. (Credit: David Madison/Getty Images)

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from article Antisubmarine warfare

SQS-26 low-frequency hull sonar, the largest U.S. hull sonar (the version onboard current surface ships, SQS-53, uses much the same sonar dome). Nearby workers give idea of scale. (U.S. Navy)

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from article Antisubmarine warfare

Variable-depth sonar in streamlined housing (fish). (U.S. Navy)

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from article Antisubmarine warfare

Nuclear attack submarine USS San Francisco. The ridge running up the hull houses a towed array. (U.S. Navy)

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from article Antisubmarine warfare

Mark 46 lightweight homing torpedo aboard a helicopter. (U.S. Navy)

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from article Antisubmarine warfare

Swedish diesel submarine Gotland in the United States on loan from Sweden to help train U.S. naval crews against the type of submarine they are likely to encounter in littoral waters. During the Cold War, the U.S. Navy concentrated mainly on the…

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from article Antisubmarine warfare

Missile destroyer Forrest Sherman. With the demise of the Soviet Union, specialized antisubmarine ships no longer seem worthwhile. Forrest Sherman is a multirole destroyer designed to deal with air and underwater threats and to bombard land targets.…

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from article Optical information systems

Optical Fourier transform and correlation image processor. Lenses L1 and L2 have focal lengths fL1 and fL2.

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from article Optical information systems

Acoustooptic signal spectrum analyzer.

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from article Optical information systems

Optical matrix vector, crossbar, or neural net processor.

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from article Problem solving (psychology)

Composite view of a colorized magnetic resonance imaging (MRI) scan of a human brain blended with a cross-section illustration of a human head. Cognitive psychology attempts to understand the integral mental processes of the human brain involved in…

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from article Problem solving (psychology)

The game of chess involves many aspects of problem solving. In chess playing, a solution consists of an attempt to convert an initial state of a task (for example, a chessboard before the first move is made) into a final or goal state (checkmate)…

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from article Boracite

Boracite. (a) Specimen from Segeberg, Germany (specimen from Department of Geology, Bryn Mawr College). (b) Crystal habits (after C. S. Hurlbut, Jr., Dana's Manual of Mineralogy, 17th ed., John Wiley and Sons, 1959).

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from article Aurora

Ring-shaped auroral glow observed from above the north polar region by the Dynamics Explorer satellite. (L. A. Frank and J. D. Craven, University of Iowa)

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from article Aurora

Two curtain-shaped auroras stretching across the sky near Fairbanks, Alaska. (Courtesy Lee Snyder)

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