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🔗 Computer science 🔗 Mathematics

A negative base (or negative radix) may be used to construct a non-standard positional numeral system. Like other place-value systems, each position holds multiples of the appropriate power of the system's base; but that base is negative—that is to say, the base b is equal to −r for some natural number r (r ≥ 2).

Negative-base systems can accommodate all the same numbers as standard place-value systems, but both positive and negative numbers are represented without the use of a minus sign (or, in computer representation, a sign bit); this advantage is countered by an increased complexity of arithmetic operations. The need to store the information normally contained by a negative sign often results in a negative-base number being one digit longer than its positive-base equivalent.

The common names for negative-base positional numeral systems are formed by prefixing nega- to the name of the corresponding positive-base system; for example, negadecimal (base −10) corresponds to decimal (base 10), negabinary (base −2) to binary (base 2), negaternary (base −3) to ternary (base 3), and negaquaternary (base −4) to quaternary (base 4).

🔗 Physics 🔗 Physics/Acoustics

In acoustics, a beat is an interference pattern between two sounds of slightly different frequencies, perceived as a periodic variation in volume whose rate is the difference of the two frequencies.

With tuning instruments that can produce sustained tones, beats can be readily recognized. Tuning two tones to a unison will present a peculiar effect: when the two tones are close in pitch but not identical, the difference in frequency generates the beating. The volume varies like in a tremolo as the sounds alternately interfere constructively and destructively. As the two tones gradually approach unison, the beating slows down and may become so slow as to be imperceptible. As the two tones get further apart, their beat frequency starts to approach the range of human pitch perception, the beating starts to sound like a note, and a combination tone is produced. This combination tone can also be referred to as a missing fundamental, as the beat frequency of any two tones is equivalent to the frequency of their implied fundamental frequency.

🔗 Biography 🔗 Chicago 🔗 Biography/Actors and Filmmakers 🔗 College Basketball

John Michael Crichton (; October 23, 1942 – November 4, 2008) was an American author, screenwriter, film director, and film producer. His books have sold over 200 million copies worldwide, and over a dozen have been adapted into films. His literary works are usually within the science fiction, techno-thriller, and medical fiction genres, and heavily feature technology. His novels often explore technology and failures of human interaction with it, especially resulting in catastrophes with biotechnology. Many of his novels have medical or scientific underpinnings, reflecting his medical training and scientific background. He wrote, among other works, The Andromeda Strain (1969), The Great Train Robbery (1975), Congo (1980), Sphere (1987), Jurassic Park (1990), Rising Sun (1992), Disclosure (1994), The Lost World (1995), Airframe (1996), Timeline (1999), Prey (2002), State of Fear (2004), and Next (2006). Films he wrote and directed included Westworld (1973), Coma (1978), The Great Train Robbery (1979), Looker (1981), and Runaway (1984).

🔗 Norse history and culture 🔗 Ancient Germanic studies

The sequence alu (ᚨᛚᚢ) is found in numerous Elder Futhark runic inscriptions of Germanic Iron Age Scandinavia (and more rarely in early Anglo-Saxon England) between the 3rd and the 8th century. The word usually appears either alone (such as on the Elgesem runestone) or as part of an apparent formula (such as on the Lindholm "amulet" (DR 261) from Scania, Sweden). The symbols represent the runes Ansuz, Laguz, and Uruz. The origin and meaning of the word are matters of dispute, though a general agreement exists among scholars that the word represents an instance of historical runic magic or is a metaphor (or metonym) for it. It is the most common of the early runic charm words.

The word disappears from runic inscriptions shortly after Migration Period, even before the Christianization of Scandinavia. It may have lived on beyond this period with an increasing association with ale, appearing in stanzas 7 and 19 of the Old Norse poem Sigrdrífumál, compiled in the 13th century Poetic Edda, where knowledge of invocative "ale runes" (Old Norse ölrúnar) is imparted by the Valkyrie Sigrdrífa. Theories have been suggested that the unique term ealuscerwen (possibly "pouring away of alu"), used to describe grief or terror in the epic poem Beowulf, recorded around the 9th to 11th century, may be directly related.

🔗 United States 🔗 Biography 🔗 Biography/science and academia 🔗 United States/Ohio 🔗 University of California

Elwyn Ralph Berlekamp (September 6, 1940 – April 9, 2019) was an American mathematician known for his work in computer science, coding theory and combinatorial game theory. He was a professor emeritus of mathematics and EECS at the University of California, Berkeley.

Berlekamp was the inventor of an algorithm to factor polynomials, and was one of the inventors of the Berlekamp–Welch algorithm and the Berlekamp–Massey algorithms, which are used to implement Reed–Solomon error correction.

Berlekamp had also been active in money management. In 1986, he began information-theoretic studies of commodity and financial futures.

🔗 Spaceflight 🔗 Physics 🔗 Astronomy 🔗 Solar System

The Pioneer anomaly or Pioneer effect was the observed deviation from predicted accelerations of the Pioneer 10 and Pioneer 11 spacecraft after they passed about 20 astronomical units (3×10⁹ km; 2×10⁹ mi) on their trajectories out of the Solar System. The apparent anomaly was a matter of much interest for many years but has been subsequently explained by an anisotropic radiation pressure caused by the spacecraft's heat loss.

Both Pioneer spacecraft are escaping the Solar System but are slowing under the influence of the Sun's gravity. Upon very close examination of navigational data, the spacecraft were found to be slowing slightly more than expected. The effect is an extremely small acceleration towards the Sun, of (8.74±1.33)×10⁻¹⁰ m/s², which is equivalent to a reduction of the outbound velocity by 1 km/h over a period of ten years. The two spacecraft were launched in 1972 and 1973. The anomalous acceleration was first noticed as early as 1980 but not seriously investigated until 1994. The last communication with either spacecraft was in 2003, but analysis of recorded data continues.

Various explanations, both of spacecraft behavior and of gravitation itself, were proposed to explain the anomaly. Over the period from 1998 to 2012, one particular explanation became accepted. The spacecraft, which are surrounded by an ultra-high vacuum and are each powered by a radioisotope thermoelectric generator (RTG), can shed heat only via thermal radiation. If, due to the design of the spacecraft, more heat is emitted in a particular direction by what is known as a radiative anisotropy, then the spacecraft would accelerate slightly in the direction opposite of the excess emitted radiation due to the recoil of thermal photons. If the excess radiation and attendant radiation pressure were pointed in a general direction opposite the Sun, the spacecraft's velocity away from the Sun would be decreasing at a rate greater than could be explained by previously recognized forces, such as gravity and trace friction due to the interplanetary medium (imperfect vacuum).

By 2012 several papers by different groups, all reanalyzing the thermal radiation pressure forces inherent in the spacecraft, showed that a careful accounting of this explains the entire anomaly; thus the cause is mundane and does not point to any new phenomenon or need for a different physical paradigm. The most detailed analysis to date, by some of the original investigators, explicitly looks at two methods of estimating thermal forces, concluding that there is "no statistically significant difference between the two estimates and [...] that once the thermal recoil force is properly accounted for, no anomalous acceleration remains."

🔗 India 🔗 Numismatics 🔗 India/Indian politics workgroup

A zero-rupee note is a banknote imitation issued in India as a means of helping to fight systemic political corruption. The notes are "paid" in protest by angry citizens to government functionaries who solicit bribes in return for services which are supposed to be free. Zero rupee notes, which are made to resemble the regular 50 rupee banknote of India, are the creation of a non-governmental organization known as 5th Pillar which has, since their inception in 2007, distributed over 2.5 million notes as of August 2014. The notes remain in current use and thousands of notes are distributed every month.

🔗 California 🔗 California/San Francisco Bay Area 🔗 Internet

The "PayPal Mafia" is a group of former PayPal employees and founders who have since founded and developed additional technology companies such as Tesla Motors, LinkedIn, Palantir Technologies, SpaceX, YouTube, Yelp, and Yammer. Most of the members attended Stanford University or University of Illinois at Urbana–Champaign at some point in their studies.

🔗 Politics 🔗 Psychology 🔗 Marketing & Advertising

Fearmongering, or scaremongering, is the act of exploiting feelings of fear by using exaggerated rumors of impending danger, usually for personal gain.