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Editorial Briefing
Cooling paint

Oct 2018

Cooling paint

In the journal Science (September 2018), researchers reported a method for making a coating that reflects sunlight and radiates heat. The coating can be used to cool buildings and reduce air-conditioning use, keeping surfaces painted with the material about 6 degrees Celsius cooler than the surrounding air temperature. The paint can be easily applied to most surfaces, including the exterior walls and roofs of existing buildings. The cooling effect is based on a phenomenon known as passive daytime radiative cooling, whereby a surface cools without any energy input by reflecting ultraviolet to near-infrared solar radiation (278- to 4600-nanometer wavelengths) and radiating long-wave radiation (8000- to 13,000-nanometer wavelengths) through the atmosphere to outer space. Cool roofs designed using metals (such as aluminum) or white-pigmented paints help keep building temperatures lower by reflecting sunlight but are less effective at emitting the heat they absorb because heat is reflected inside these materials. See also: Buildings; Emissivity; Heat transfer; Infrared radiation; Paint and coatings; Radiation; Reflection of electromagnetic radiation; Solar radiation

Editorial Briefing
Dark lightning linked to visible lightning

Jan 2013

Dark lightning linked to visible lightning

Until recent years, the research focus on the high-energy photons known as gamma rays has been on nuclear and cosmic sources for them. Now it has moved to the cloud—the thundercloud, that is—where short bursts of gamma rays, known as terrestrial gamma ray flashes (TGFs) or dark lightning, have been observed. In a thunderstorm, a gamma-ray burst occurs when electrons accelerated by a strong electric field to almost the speed of light collide with air molecules. See also: Electric field; Gamma-ray burst; Gamma rays; Photon; Thunderstorm

Editorial Briefing
A new realm of ultrafast physics at the zeptosecond scale

Oct 2020

A new realm of ultrafast physics at the zeptosecond scale

For the first time, researchers have measured a process that occurs in mere zeptoseconds, or trillionths of a billionth of a second (10-21 seconds). The process is the transit of a light particle, or photon, across the two atoms that compose a hydrogen molecule. The travel time of the photon was revealed through the fundamental light-matter interaction known as photoionization, which occurs when a light particle adds energy to an atom and causes the ejection of one or more electrons. In the new research, the measured time interval between the ejection of an electron from the first atom and the second atom in the molecule was 247 zeptoseconds on average. The study's approach could be used to learn more about photoionization and other ultrafast reactions. See also: Atom; Atomic structure and spectra; Electron; Energy; Hydrogen; Molecule; Photon

Editorial Briefing
Ultraviolet light for destroying coronaviruses and other pathogens in enclosed, occupied spaces

Nov 2020

Ultraviolet light for destroying coronaviruses and other pathogens in enclosed, occupied spaces

A form of ultraviolet (UV) light holds promise as an innovative way to neutralize airborne SARS-CoV-2 particles and other viruses, potentially helping slow the COVID-19 pandemic that, to date, has caused over 1.3 million deaths globally. More energetic than visible light, UV light is generally divided into three frequency bands: UVA, UVB, and UVC. The first two bands are commonly known for causing sunburns and cataracts as well as increasing the risk of skin cancer. The most energetic and thus potentially most dangerous of the three, UVC, is not naturally encountered at Earth's surface because it is absorbed by the ozone and oxygen in our planet's atmosphere. However, recent research has shown that a particular kind of UVC, known as far-UVC, does not harm humans while effectively destroying airborne virus particles. These results suggest that radiating human-occupied rooms with far-UVC could slash airborne virus counts and thus curb novel coronavirus infection rates. See also: Atmosphere; Coronavirus; Electromagnetic radiation; Stratospheric ozone; Ultraviolet radiation; Ultraviolet radiation (biology); Virus

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