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Featured article 1

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Charles Darwin, whose theory of natural selection underpins Evolution
alleles from one generation to the next. The word "evolution" is often used as a shorthand for the modern theory of evolution of species based upon Charles Darwin's theory of natural selection, which states that all modern species are the products of an extensive process that began over three billion years ago with simple single-celled organisms, and Gregor Mendel's theory of genetics. As the theory of evolution by natural selection and genetics has become universally accepted in the scientific community, it has replaced other explanations including creationism and Lamarckism. Skeptics, often creationists, sometimes deride evolution as "just a theory" in an attempt to characterize it as an arbitrary choice and degrade its claims to truth. Such criticism overlooks the scientifically-accepted use of the word "theory" to mean a falsifiable and well-supported hypothesis
.
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Featured article 3

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New horizons (NASA)
gravity assist
.

The primary scientific objectives are to characterize the global geology and morphology and map the surface composition of Pluto and Charon, and study the neutral

atmosphere of Pluto and its escape rate. Other objectives include studying time variability of Pluto's surface and atmosphere; imaging and mapping areas of Pluto and Charon at high-resolution; characterizing Pluto's upper atmosphere, ionosphere
, and energetic particle environment; searching for an atmosphere around Charon; refining bulk parameters of Pluto and Charon; and searching for additional satellites and rings.

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Featured article 4

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Alanine, as used in NMR implementation of error correction. Qubits are dictated by spin states of carbon atoms.
A
quantum mechanical phenomena, such as superposition and entanglement, to perform operations on data. In a classical (or conventional) computer, the amount of data is measured by bits; in a quantum computer, it is measured by qubits. The basic principle of quantum computation is that the quantum properties of particles can be used to represent and structure data, and that devised quantum mechanisms can be used to perform operations with this data. For a generally accessible overview of quantum computing, see Quantum Computing with Molecules, an article in Scientific American by Neil Gershenfeld
and Isaac L. Chuang.

Experiments have already been carried out in which quantum computational operations were executed on a very small number of qubits. Research in practical areas continues at a frantic pace; see Quantum Information Science and Technology Roadmap for a sense of where the research is heading. Many national government and military funding agencies support quantum computing research, to develop quantum computers for both civilian and national security purposes, such as cryptanalysis.

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Featured article 5

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Nanodevice that efficiently produces visible light, through energy transfer from quantum wells to quantum dots.
A
quantum information processing
.

Because the quantum dot has discrete energy levels, much like an atom, they are sometimes called artificial atoms. The energy levels can be controlled by changing the size and shape of the quantum dot, and the depth of the potential. Like in atoms, the energy levels of small quantum dots can be probed by optical spectroscopy techniques. In contrast to atoms it is relatively easy to connect quantum dots by tunnel barriers to conducting leads, which allows the application of the techniques of tunneling spectroscopy for their investigation.

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Featured article 6

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Molecular model of hydrogen chloride
industry
. The name HCl often refers somewhat misleadingly to hydrochloric acid instead of the gaseous hydrogen chloride.

Hydrogen chloride forms corrosive hydrochloric acid on contact with body tissue.

burns. Hydrogen chloride may cause severe burns to the eye
and permanent eye damage.

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Featured article 7

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Carbon nanotube
nanometer scale, usually 1 to 100 nm (1/1,000 µm, or 1/1,000,000 mm). A possible way to interpret this size is to take the width of a human hair, and imagine something ten thousand times smaller. The term has sometimes been applied to microscopic
technology.

Nanotechnology is any technology which exploits phenomena and structures that can only occur at the nanometer scale, which is the scale of several atoms and small molecules. The United States's National Nanotechnology Initiative website defines nanotechnology as "the understanding and control of matter at dimensions of roughly 1 to 100 nanometers, where unique phenomena enable novel applications."

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Featured article 8

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Teflon is polytetrafluoroethylene (PTFE), a polymer of fluorinated ethylene.
Teflon is the brand name of the polymer polytetrafluoroethylene (PTFE) discovered by Roy J. Plunkett (1910–1994) of DuPont in 1938 and introduced as a commercial product in 1946. It is a fluoropolymer but not a thermoplastic
in the true sense.

PTFE has the lowest

coefficient of friction
of any known solid material. It is used as a non-stick coating for pans and other cookware. PTFE is very non-reactive and is often used in containers and pipework for reactive chemicals. Its melting point is 327°C, but its properties degrade above 260°C. At this point gaseous fluorine compounds are released that are dangerous to humans.

Other polymers with similar composition are known by the Teflon name: fluorinated ethylene-propylene (FEP) and perfluoroalkoxy polymer resin (PFA). They retain the useful properties of PTFE of low friction and non-reactivity, but are more easily formable. FEP is softer than PTFE and melts at 260°C; it is highly transparent and resistant to sunlight.

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Featured article 9

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Severe soil erosion in a wheat field near Washington State University.
Erosion is the displacement of solids (soil, mud, rock and other particles) by the agents of wind, water or ice, by downward or down-slope movement in response to gravity or by living organisms (in the case of bioerosion). Erosion is distinguished from weathering, which is the breaking down of rock and particles through processes where no movement is involved, although the two processes may be concurrent.

Erosion is a natural process, but in many places it is increased by human

terrace
-building and tree planting.

A certain amount of erosion is natural and, in fact, healthy for the ecosystem. For example, gravels continually move downstream in watercourses. Excessive erosion, however, can cause problems, such as receiving water sedimentation, ecosystem damage (including fish kills) and outright loss of soil.

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Featured article 10

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Hale-Bopp comet, February 23, 1997
A
coma (or atmosphere) and/or a tail — both due primarily to the effects of solar radiation upon the comet's nucleus
, which itself is a minor planet composed of rock, dust, and ices. Due to their origins in the outer solar system and their propensity to be highly affected (or perturbed) by relatively close approaches to the major planets, comets' orbits are constantly changing. Some are moved into sungrazing orbits that destroy the comets when they are too near the Sun, while others are thrown out of the solar system forever.

Most comets are believed to originate in a cloud (the

solar nebula; the outer edges of such nebulae are cool enough that water exists in a solid (rather than gaseous) state. Asteroids originate via a different process, but very old comets which have lost all their volatile
materials may come to resemble asteroids.

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Featured article 11

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A mirror neuron
A
Ramachandran
on their potential importance in imitation and language.

In humans, mirror neurons are found in the inferior frontal cortex, close to Broca's area, a language region. This has led to suggestions that human language evolved from a gesture performance/understanding system implemented in mirror neurons. However, like many theories of language evolution, there is little direct evidence either way.

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Featured article 12

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A ribbon diagram of Dihydrofolate reductase
enzymes. The study of an enzyme's kinetics provides insights into the catalytic mechanism of this enzyme, its role in metabolism, how its activity is controlled in the cell and how drugs and poisons can inhibit
its activity.

Enzymes are

substrates. These target molecules bind to an enzyme's active site and are transformed into products through a series of steps known as the enzymatic mechanism. Some enzymes bind multiple substrates and/or release multiple products, such as a protease cleaving one protein substrate into two polypeptide products. Others join substrates together, such as DNA polymerase linking a nucleotide to DNA
. Although these mechanisms are often a complex series of steps, there is typically one rate-determining step that determines the overall kinetics. This rate-determining step may be a chemical reaction or a conformational change of the enzyme or substrates, such as those involved in the release of product(s) from the enzyme.

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Featured article 13

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A potassium Faraday filter designed, built and photographed by Jonas Hedin for making daytime LIDAR measurements at Arecibo Observatory.
An
lines
of atomic vapors and so may also be designated an atomic resonance filter (ARF).

The three major types of atomic line filters are absorption-re-emission ALFs, Faraday filters and Voigt filters. Absorption-re-emission filters were the first type developed, and so are commonly called simply "atomic line filters"; the other two types are usually referred to specifically as "Faraday filters" or "Voigt filters". Atomic line filters use different mechanisms and designs for different applications, but the same basic strategy is always employed: by taking advantage of the narrow lines of absorption or resonance in a metallic vapor, a specific frequency of light bypasses a series of filters that block all other light.

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Featured article 14

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The Grand Canyon from Navajo Point
The
sand dunes from an extinct desert
.

Uplift of the region started about 75 million years ago in the

Colorado River to cut its channel into the four plateaus that constitute this area. But the canyon did not start to form until 5.3 million years ago when the Gulf of California opened up and thus lowered the river's base level (its lowest point) from that of large inland lakes to sea level
.

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Featured article 16

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Featured article 17

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Featured article 18

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Mean surface temperature anomalies during the period 1995 to 2004 with respect to the average temperatures from 1940 to 1980.
Earth's atmosphere and oceans
in recent decades.

The Earth's average near-surface atmospheric temperature rose 0.6 ± 0.2 

attributable to human activities"[2]
.

The increased amounts of carbon dioxide (CO2) and other greenhouse gases (GHGs) are the primary causes of the human-induced component of warming[3]. They are released by the burning of fossil fuels, land clearing and agriculture, etc. and lead to an increase in the greenhouse effect. The first speculation that a greenhouse effect might occur was by the Swedish chemist Svante Arrhenius in 1897, although it did not become a topic of popular debate until some 90 years later.

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Featured article 19

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The tectonic plates of the world were mapped in the second half of the 20th century.
sea floor spreading
developed during the 1960s.

The outermost part of the Earth's interior is made up of two layers: above is the lithosphere, comprising the crust and the rigid uppermost part of the mantle. Below the lithosphere lies the asthenosphere, which is a more viscous zone of the mantle. Although solid, the asthenosphere has very low shear strength and can flow like a liquid on geological time scales. The deeper mantle below the asthenosphere is more rigid again.

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Featured article 20

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According to the Big Bang(also known as the Large Boom), the universe emerged from an extremely dense and hot state (bottom). Since then, space itself has expanded with the passage of time, carrying the galaxies with it.
In
Robertson–Walker model of general relativity) as indicated by the Hubble redshift of distant galaxies taken together with the cosmological principle
.

Extrapolated into the past, these observations show that the universe has expanded from a state in which all the matter and energy in the universe was at an immense temperature and density. Physicists do not widely agree on what happened before this, although general relativity predicts a gravitational singularity (for reporting on some of the more notable speculation on this issue, see cosmogony).

The term Big Bang is used both in a narrow sense to refer to a point in time when the observed expansion of the universe (

Alpher–Bethe–Gamow theory
.

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Featured article 21

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Marine debris on the Hawaiian coastline
gyres and on coastlines. Some forms of marine debris, such as harmless driftwood, occur naturally, and human activities have been adding similar material into the oceans for thousands of years. Only recently, however, with the advent of plastic, has human influence become an issue as many types of plastics do not biodegrade. Waterborne plastic is both unsightly and dangerous; posing a serious threat to fish, seabirds, marine reptiles, and marine mammals
, as well as to boats and coastal habitations. Ocean dumping, accidental container spillages, and wind-blown landfill waste are all contributing to this growing problem.
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Featured article 22

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Scaled Composites SpaceShipTwo
Scaled Composites' Model 339
space tourists, under development by The Spaceship Company, a joint venture between Scaled Composites and Sir Richard Branson's Virgin Group, as part of the Tier 1b program. The spaceship was officially unveiled to the public on Monday, 7 December 2009, at the Mojave Air and Spaceport in California. The Virgin Galactic spaceline plans to operate a fleet of five of these craft in passenger-carrying private spaceflight
service. The destruction in a test flight of the first craft in 2014 has delayed the start of commercial operations.

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Featured article 23


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