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Meissner effect

Meissner effect

Science (from Latin scientia, meaning "knowledge") is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe.

From classical antiquity through the 19th century, science as a type of knowledge was more closely linked to philosophy. In the West, the term natural philosophy encompassed fields of study that are currently associated with disciplines such as classical physics, astronomy and medicine and was a precursor of modern natural sciences (life science and physical science). In the 17th and 18th centuries, scientists increasingly sought to formulate knowledge in terms of laws of nature. Over the centuries, the term science became associated with the scientific method, a systematic way of studying the natural world and particularly in the 19th century, multiple distinguishing characteristics of contemporary modern science began to take shape.

Modern science is typically divided into three major branches that consist of the natural sciences (e.g. biology, chemistry, physics), which study nature in the broadest sense; the social sciences (e.g. psychology, sociology, economics), which study individuals and societies; and the formal sciences (e.g. mathematics, logic, theoretical computer science), which study abstract concepts. There is disagreement, however, on the formal sciences being a science as they do not rely on empirical evidence. Disciplines that use science, such as engineering and medicine, are described as applied sciences.

Science is related to research and is commonly organized by academic and research institutions as well as government agencies and companies. The practical impact of scientific research has led to the emergence of science policies that seek to influence the scientific enterprise by prioritizing the development of commercial products, armaments, health care, and environmental protection.

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Nanodevice that efficiently produces visible light, through energy transfer from quantum wells to quantum dots.
A quantum dot is a semiconducting crystal in nanotechnology. Quantum dots confine electrons, holes, electron-hole pairs, or excitons to zero dimensions in a region of the order of the electrons' Compton wavelength. This confinement leads to discrete quantized energy levels and to the quantization of charge in units of the elementary electric charge e. Quantum dots are particularly significant for optical applications due to their theoretically high quantum yield. Quantum dots have also been suggested as implementations of a qubit for 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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Sonoluminescence is the emission of light by bubbles in a liquid excited by sound.
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Sonoluminescence is the emission of short bursts of light from imploding bubbles in a liquid when excited by sound. The effect was first discovered at the University of Cologne in 1934 as a result of work on sonar. H. Frenzel and H. Schultes put an ultrasound transducer in a tank of photographic developer fluid. They hoped to speed up the development process. Instead, they noticed tiny dots on the film after developing, and realized that the bubbles in the fluid were emitting light with the ultrasound turned on. It was too difficult to analyze the effect in early experiments because of the complex environment of a large number of short-lived bubbles. (This experiment is also ascribed to N. Marinesco and J.J. Trillat in 1933).

Sonoluminescence may or may not occur whenever a sound wave of sufficient intensity induces a gaseous cavity within a liquid to quickly collapse. This cavity may take the form of a pre-existing bubble, or may be generated through a process known as cavitation. Sonoluminescence in the laboratory can be made to be stable, so that a single bubble will expand and collapse over and over again in a periodic fashion, emitting a burst of light each time it collapses.

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Portrait of Galilei Galileo by Giusto Sustermans.
Galileo Galilei (February 15, 1564 – January 8, 1642) was an Italian physicist, astronomer, and philosopher who is closely associated with the scientific revolution. His achievements include improvements to the telescope, a variety of astronomical observations, the first and second laws of motion, and effective support for Copernicanism. According to Stephen Hawking, Galileo has contributed more to the creation of the modern natural sciences than anybody else. He is the "father of modern astronomy," the "father of modern physics," and the "father of science." The work of Galilei is considered to be a significant break from that of Aristotle.

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