An AR-15-style rifle is any lightweight semi-automatic rifle based on or similar to the Colt AR-15 design. The original ArmaLite AR-15, its predecessor, was a scaled-down derivative of Eugene Stoner's ArmaLite AR-10 design and featured selective fire. ArmaLite sold the patent and trademarks to Colt's Manufacturing Company in 1959, resulting in the Colt AR-15, which removed the selective fire feature. After most of the patents for the Colt AR-15 expired in 1977, many firearm manufacturers began to produce copies of the Colt AR-15 under various names. While the patents are expired, Colt retained the trademark of the AR-15 name and is the sole manufacturer able to label their firearms as AR-15.The Federal Assault Weapons Ban restricted the sale of the Colt AR-15 and some derivatives in the United States from 1994 to 2004, although it did not affect rifles with fewer listed features. After the term modern sporting rifles was coined in 2009 by the US National Shooting Sports Foundation, a firearms trade association, it was quickly adopted by much of the industry.In the 2010s, AR-15-style rifles became one of the "most...

A look through HBR’s archives shows that business thinkers use the concept of a “business model” in many different ways, potentially skewing the definition. Many people believe Peter Drucker defined the term in a 1994 article as “assumptions about what a company gets paid for,” but that article never mentions the term business model. Instead, Drucker’s theory of the business was a set of assumptions about what a business will and won’t do, closer to Michael Porter’s definition of strategy. Businesses make assumptions about who their customers and competitors are, as well as about technology and their own strengths and weaknesses. Joan Magretta carries the idea of assumptions into her focus on business modeling, which encompasses the activities associated with both making and selling something. Alex Osterwalder also builds on Drucker’s concept of assumptions in his “business model canvas,” a way of organizing assumptions so you can compare business models. Introducing a better business model into an existing market is the definition of a disruptive innovation, as written about by Clay Christensen. Rita McGrath offers that your business model is failing when innovations yield smaller and smaller improvements. You can innovate a new model by altering the mix of products and services, postponing decisions, changing the people who make the decisions, or changing incentives in the value chain. Finally, Mark Johnson provides a list of nineteen types of business models and the organizations that use them.

Protein secondary structure is the local spatial conformation of the polypeptide backbone excluding the side chains. The two most common secondary structural elements are alpha helices and beta sheets, though beta turns and omega loops occur as well. Secondary structure elements typically spontaneously form as an intermediate before the protein folds into its three dimensional tertiary structure. Secondary structure is formally defined by the pattern of hydrogen bonds between the amino hydrogen and carboxyl oxygen atoms in the peptide backbone. Secondary structure may alternatively be defined based on the regular pattern of backbone dihedral angles in a particular region of the Ramachandran plot regardless of whether it has the correct hydrogen bonds. The concept of secondary structure was first introduced by Kaj Ulrik Linderstrøm-Lang at Stanford in 1952. Other types of biopolymers such as nucleic acids also possess characteristic secondary structures. Types The most common secondary structures are alpha helices and beta sheets. Other helices, such as the 310 helix and π helix, are calculated to have energetically...

Radiation therapy is a cancer treatment that uses high-energy x-ray or other particles to destroy cancer cells. A doctor who specializes in giving radiation therapy to treat cancer is called a radiation oncologist. A radiation therapy regimen, or schedule, usually consists of a specific number of treatments given over a set period.

A quasar is an extremely luminous active galactic nucleus (AGN). It is pronounced KWAY-zar, and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from a galaxy nucleus is powered by a supermassive black hole with a mass ranging from millions to tens of billions of solar masses, surrounded by a gaseous accretion disc. Gas in the disc falling towards the black hole heats up because of friction and releases energy in the form of electromagnetic radiation. The radiant energy of quasars is enormous; the most powerful quasars have luminosities thousands of times greater than that of a galaxy such as the Milky Way. Usually, quasars are categorized as a subclass of the more general category of AGN. The redshifts of quasars are of cosmological origin.The term quasar originated as a contraction of "quasi-stellar [star-like] radio source"—because quasars were first identified during the 1950s as sources of radio-wave emission of unknown physical origin—and when identified in photographic images at visible wavelengths, they resembled faint, star-like...

Assyrian sculpture is the sculpture of the ancient Assyrian states, especially the Neo-Assyrian Empire of 911 to 612 BC, which was centered around the city of Assur in Mesopotamia (modern-day Iraq) which at its height, ruled over all of Mesopotamia, the Levant and Egypt, as well as portions of Anatolia, Arabia and modern-day Iran and Armenia. It forms a phase of the art of Mesopotamia, differing in particular because of its much greater use of stone and gypsum alabaster for large sculpture. Much the best-known works are the huge lamassu guarding entrance ways, and Assyrian palace reliefs on thin slabs of alabaster, which were originally painted, at least in part, and fixed on the wall all round the main rooms of palaces. Most of these are in museums in Europe or America, following a hectic period of excavations from 1842 to 1855, which took Assyrian art from being almost completely unknown to being the subject of several best-selling books, and imitated in political cartoons.The palace reliefs contain scenes in low relief which glorify the king, showing him at war, hunting, and fulfilling other kingly roles. Many works left in situ, or...

Plinian eruptions or Vesuvian eruptions are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in 79 AD, which destroyed the ancient Roman cities of Herculaneum and Pompeii. The eruption was described in a letter written by Pliny the Younger, after the death of his uncle Pliny the Elder. Plinian/Vesuvian eruptions are marked by columns of volcanic debris and hot gases ejected high into the stratosphere, the second layer of Earth's atmosphere. The key characteristics are ejection of large amount of pumice and very powerful continuous gas-driven eruptions. According to the Volcanic Explosivity Index, Plinian eruptions have a VEI of 4, 5 or 6, sub-Plinian 3 or 4, and ultra-Plinian 6, 7 or 8. Short eruptions can end in less than a day, but longer events can continue for several days or months. The longer eruptions begin with production of clouds of volcanic ash, sometimes with pyroclastic surges. The amount of magma erupted can be so large that it depletes the magma chamber below, causing the top of the volcano to collapse, resulting in a caldera. Fine ash and pulverized pumice can deposit over large areas. Plinian eruptions are...

Water reclamation (also called wastewater reuse, water reuse or water recycling) is the process of converting municipal wastewater (sewage) or industrial wastewater into water that can be reused for a variety of purposes. Types of reuse include: urban reuse, agricultural reuse (irrigation), environmental reuse, industrial reuse, planned potable reuse, de facto wastewater reuse (unplanned potable reuse). For example, reuse may include irrigation of gardens and agricultural fields or replenishing surface water and groundwater (i.e., groundwater recharge). Reused water may also be directed toward fulfilling certain needs in residences (e.g. toilet flushing), businesses, and industry, and could even be treated to reach drinking water standards. The injection of reclaimed water into the water supply distribution system is known as direct potable reuse, however, drinking reclaimed water is not a typical practice. Treated municipal wastewater reuse for irrigation is a long-established practice, especially in arid countries. Reusing wastewater as part of sustainable water management allows water to remain as an alternative water source for human activities. This...

Dream SMP Zak Ahmed (born: January 17, 2000 (2000-01-17) [age 22]), better known online as Skeppy, is an American YouTuber known for his Minecraft challenge videos involving numerous contestants and his collaborations with fellow YouTuber BadBoyHalo. Before, Skeppy mostly made content on trolling players (the majority of hackers on Invadedlands and SkittleMC), trolling his staff, and his friends a6d and BadBoyHalo in Minecraft. However, there are exceptions, such as the Q&A series he adds to eve

Planet 51 is a 2009 computer-animated science fiction comedy film directed by Jorge Blanco and co-directed by Javier Abad and Marcos Martínez, from a script by Joe Stillman, based on an original idea by Javier Abad, Jorge Blanco, Marcos Martínez and Ignacio Pérez Dolset. Starring Dwayne Johnson, Jessica Biel, Justin Long, Gary Oldman, Seann William Scott and John Cleese, the film follows an astronaut who lands on an alien planet, as one of the aliens helps him return to his ship while evading the military. An international co-production by Spain, United Kingdom, United States, and Canada, with the studios Ilion Animation Studios based in Madrid, and HandMade Films in London, the film was originally acquired for North American distribution by New Line Cinema, but then sold to Sony Pictures before completion. Originally titled Planet One, and later named as an allusion to Area 51, the film was completed on a $70 million budget, which, as of 2010, was the most expensive film produced in Spain.Planet 51 was released on 20 November 2009 in the United States and Canada by Sony Pictures Releasing's TriStar Pictures...