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The disease is caused by the bacterium Yersinia pestis and spread by fleas and through the air. [4] [5] One of the most significant events in European history, the Black Death had far-reaching population, economic, and cultural impacts. It was the beginning of the second plague pandemic. [6] .
Hydrothermal vents exist because the earth is both geologically active and has large amounts of water on its surface and within its crust. Under the sea, they may form features called black smokers or white smokers, which deliver a wide range of elements to the world's oceans, thus contributing to global marine biogeochemistry.
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Humans have always been aware of visible light and radiant heat but for most of history it was not known that these phenomena were connected or were representatives of a more extensive principle. The ancient Greeks recognized that light traveled in straight lines and studied some of its properties, including reflection and refraction. Light was int...
Electromagnetic waves are typically described by any of the following three physical properties: the frequency f, wavelength λ, or photon energy E. Frequencies observed in astronomy range from 2.4×1023 Hz (1 GeV gamma rays) down to the local plasma frequency of the ionized interstellar medium (~1 kHz). Wavelength is inversely proportional to the wa...
The types of electromagnetic radiation are broadly classified into the following classes (regions, bands or types): 1. Gamma radiation 2. X-ray radiation 3. Ultraviolet radiation 4. Visible light (light that humans can see) 5. Infrared radiation 6. Microwave radiation 7. Radio waves This classification goes in the increasing order of wavelength, wh...
Radio waves
Radio waves are emitted and received by antennas, which consist of conductors such as metal rod resonators. In artificial generation of radio waves, an electronic device called a transmitter generates an alternating electric current which is applied to an antenna. The oscillating electrons in the antenna generate oscillating electric and magnetic fields that radiate away from the antenna as radio waves. In reception of radio waves, the oscillating electric and magnetic fields of a radio wave...
Microwaves
Microwaves are radio waves of short wavelength, from about 10 centimeters to one millimeter, in the SHF and EHF frequency bands. Microwave energy is produced with klystron and magnetron tubes, and with solid state devices such as Gunn and IMPATT diodes. Although they are emitted and absorbed by short antennas, they are also absorbed by polar molecules, coupling to vibrational and rotational modes, resulting in bulk heating. Unlike higher frequency waves such as infrared and visible light whic...
Infrared radiation
The infraredpart of the electromagnetic spectrum covers the range from roughly 300 GHz to 400 THz (1 mm – 750 nm). It can be divided into three parts: 1. Far-infrared, from 300 GHz to 30 THz (1 mm – 10 μm). The lower part of this range may also be called microwaves or terahertz waves. This radiation is typically absorbed by so-called rotational modes in gas-phase molecules, by molecular motions in liquids, and by phonons in solids. The water in Earth's atmosphere absorbs so strongly in this r...
Canadian Table of Frequency Allocations Archived 2008-12-09 at the Wayback Machine (from Industry Canada)U.S. Frequency Allocation Chart – Covering the range 3 kHz to 300 GHz (from Department of Commerce)UK frequency allocation table (from Ofcom, which inherited the Radiocommunications Agency's duties, pdf format)Typhoid fever, also known simply as typhoid, is a disease caused by Salmonella enterica serotype Typhi bacteria, also called Salmonella typhi. [2] [3] Symptoms vary from mild to severe, and usually begin six to 30 days after exposure. [4] [5] Often there is a gradual onset of a high fever over several days. [4] .
Wikipedia is a free content online encyclopedia written and maintained by a community of volunteers, known as Wikipedians, through open collaboration and the wiki software MediaWiki.Wikipedia is the largest and most-read reference work in history, and is consistently ranked among the ten most visited websites; as of May 2024, it was ranked fifth by Semrush, and sixth by Similarweb.
Ebola. Two nurses standing near Mayinga N'Seka, a nurse with Ebola virus disease in the 1976 outbreak in Zaire. N'Seka died a few days later. Ebola, also known as Ebola virus disease ( EVD) and Ebola hemorrhagic fever ( EHF ), is a viral hemorrhagic fever in humans and other primates, caused by ebolaviruses. [1]
Top: Lightning and neon lights are commonplace generators of plasma. Center left: A plasma globe, illustrating some of the more complex plasma phenomena, including filamentation. Center right: A plasma trail from the Space Shuttle Atlantis during re-entry into Earth's atmosphere, as seen from the International Space Station. Bottom left: A ...
