Cooling radio waves to their quantum ground state

Researchers at Delft University of Technology have found a new way to cool radio waves all the way down to their quantum ground state. To do so, they used circuits that employ an analog of the so-called laser cooling technique ...

The photoelectric properties of MAPbI3

Organic-inorganic hybrid perovskites (OIHPs) are promising in photovoltaic energy harvesting, electro-optic detection, and all-optical conversion. Understanding the atomic structure and structural instability of OIHPs is ...

First evidence of microtubules' mechanosensitive behavior

Inside cells, microtubules not only serve as a component of the cytoskeleton (cell skeleton) but also play a role in intracellular transport. In intracellular transport, microtubules act as rails for motor proteins such as ...

New record set for lowest temperature—38 picokelvins

A team of researchers affiliated with several institutions in Germany and two in France has set a new record for the lowest temperature ever recorded in a lab setting—38 picokelvins. In their paper published in the journal ...

Researchers unlock secret path to a quantum future

In 1998, researchers including Mark Kubinec of UC Berkeley performed one of the first simple quantum computations using individual molecules. They used pulses of radio waves to flip the spins of two nuclei in a molecule, ...

Challenging the big bang puzzle of heavy elements

It has long been theorized that hydrogen, helium, and lithium were the only chemical elements in existence during the Big Bang when the universe formed, and that supernova explosions, stars exploding at the end of their lifetime, ...

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Atom

The atom is a basic unit of matter consisting of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in the case of hydrogen-1, which is the only stable nuclide with no neutron). The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain bound to each other, forming a molecule. An atom containing an equal number of protons and electrons is electrically neutral, otherwise it has a positive or negative charge and is an ion. An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determine the isotope of the element.

The name atom comes from the Greek ἄτομος/átomos, α-τεμνω, which means uncuttable, something that cannot be divided further. The concept of an atom as an indivisible component of matter was first proposed by early Indian and Greek philosophers. In the 17th and 18th centuries, chemists provided a physical basis for this idea by showing that certain substances could not be further broken down by chemical methods. During the late 19th and early 20th centuries, physicists discovered subatomic components and structure inside the atom, thereby demonstrating that the 'atom' was divisible. The principles of quantum mechanics were used to successfully model the atom.

Relative to everyday experience, atoms are minuscule objects with proportionately tiny masses. Atoms can only be observed individually using special instruments such as the scanning tunneling microscope. Over 99.9% of an atom's mass is concentrated in the nucleus, with protons and neutrons having roughly equal mass. Each element has at least one isotope with unstable nuclei that can undergo radioactive decay. This can result in a transmutation that changes the number of protons or neutrons in a nucleus. Electrons that are bound to atoms possess a set of stable energy levels, or orbitals, and can undergo transitions between them by absorbing or emitting photons that match the energy differences between the levels. The electrons determine the chemical properties of an element, and strongly influence an atom's magnetic properties.

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