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 science such as physics, astronomy, medicine, among many others. 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.
Modern science is typically divided into three major branches that consist of the natural sciences, which study nature in the broadest sense; the social sciences, which study people and societies; and the formal sciences (e.g., mathematics), 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 impacts 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.
A quantum dot
is a semiconducting crystal
in nanotechnology. Quantum dots confine electrons
, 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.
Lightning is a powerful natural electrostatic discharge of lighted streaks produced during a thunderstorm. This abrupt electric discharge is accompanied by the emission of visible light and other forms of electromagnetic radiation. The electric current passing through the discharge channels rapidly heats and expands the air into plasma, producing acoustic shock waves (thunder) in the atmosphere.
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