Have a deep view into what people are curious about.

🔗 Mathematics

In geometry, a ball is a region in a space comprising all points within a fixed distance, called the radius, from a given point; that is, it is the region enclosed by a sphere or hypersphere. An n-ball is a ball in an n-dimensional Euclidean space. The volume of a n-ball is the Lebesgue measure of this ball, which generalizes to any dimension the usual volume of a ball in 3-dimensional space. The volume of a n-ball of radius R is ${\displaystyle R^{n}V_{n},}$ where ${\displaystyle V_{n}}$ is the volume of the unit n-ball, the n-ball of radius 1.

The real number ${\displaystyle V_{n}}$ can be expressed by a expression involving the gamma function. It can be computed with several recurrence relations. It can be expressed in terms of ${\displaystyle A_{n},}$ the area of the unit n-sphere.

🔗 Systems 🔗 Robotics 🔗 Systems/Cybernetics

The Johns Hopkins Beast was a mobile automaton, an early pre-robot, built in the 1960s at the Johns Hopkins University Applied Physics Laboratory. The machine had a rudimentary intelligence and the ability to survive on its own. As it wandered through the white halls of the laboratory, it would seek black wall outlets. When it found one it would plug in and recharge.

The robot was cybernetic. It did not use a computer. Its control circuitry consisted of dozens of transistors controlling analog voltages. It used photocell optics and sonar to navigate. The 2N404 transistors were used to create NOR logic gates that implemented the Boolean logic to tell it what to do when a specific sensor was activated. The 2N404 transistors were also used to create timing gates to tell it how long to do something. 2N1040 Power transistors were used to control the power to the motion treads, the boom, and the charging mechanism.

The original sensors in Mod I were physical touch only. The wall socket was detected by physical switches on the arm that followed the wall. Once detected, two electrical prongs were extended until they entered the wall socket and made the electrical connection to charge the vehicle. The stairway, doors, and pipes on the hall wall were also detected by physical switches and recognized by appropriate logic.

The sonar guidance system was developed for Mod I and improved for Mod II. It used two ultrasonic transducers to determine distance, location within the halls, and obstructions in its path. This provided "The Beast" with bat-like guidance. At this point, it could detect obstructions in the hallway, such as people in the hallway. Once an obstruction was detected, the Beast would slow down and then decide whether to stop or divert around the obstruction. It could also ultrasonically recognize the stairway and doorways to take appropriate action.

An optical guidance system was added to Mod II. This provided, among other capabilities, the ability to optically identify the black wall sockets that contrasted with the white wall.

The Hopkins Beast Autonomous Robot Mod II link below was written by Dr. Ronald McConnell, at that time a co-op student and one of the designers for Mod II.

🔗 Germany 🔗 Motorcycling

The Daimler Petroleum Reitwagen ("riding car") or Einspur ("single track") was a motor vehicle made by Gottlieb Daimler and Wilhelm Maybach in 1885. It is widely recognized as the first motorcycle. Daimler is often called "the father of the motorcycle" for this invention. Even when the three steam powered two wheelers that preceded the Reitwagen, the Michaux-Perreaux and Roper of 1867–1869, and the 1884 Copeland, are considered motorcycles, it remains nonetheless the first petrol internal combustion motorcycle, and the forerunner of all vehicles, land, sea and air, that use its overwhelmingly popular engine type.

🔗 Brands 🔗 Chemistry 🔗 Invention 🔗 Polymers

Starlite is an intumescent material claimed to be able to withstand and insulate from extreme heat. It was invented by British amateur chemist and hairdresser Maurice Ward (1933-2011) during the 1970s and 1980s, and received significant publicity after coverage of the material aired in 1990 on the BBC science and technology show Tomorrow's World. The name Starlite was coined by Ward's granddaughter Kimberly.

The American company Thermashield, LLC claims to have acquired the rights to Starlite in 2013 and replicated it. It is the only company to have itself publicly demonstrated the technology and have samples tested by third parties.

🔗 Internet 🔗 Computing 🔗 Marketing & Advertising 🔗 Computing/Software 🔗 Computing/Computer Security 🔗 Israel

Download Valley is a cluster of software companies in Israel, producing and delivering adware to be installed alongside downloads of other software. The primary purpose is to monetize shareware and downloads. These software items are commonly browser toolbars, adware, browser hijackers, spyware, and malware. Another group of products are download managers, possibly designed to induce or trick the user to install adware, when downloading a piece of desired software or mobile app from a certain source.

Although the term references Silicon Valley, it does not refer to a specific valley or any geographical area. Many of the companies are located in Tel Aviv and the surrounding region. It has been used by Israeli media as well as in other reports related to IT business.

Download managers from Download Valley companies have been used by major download portals and software hosts, including Download.com by CNET, Softonic.com and SourceForge.

🔗 Education

Sloyd (Slöjd), also known as Educational sloyd, is a system of handicraft-based education started by Uno Cygnaeus in Finland in 1865. The system was further refined and promoted worldwide, and was taught in the United States until the early 20th Century. It is still taught as a compulsory subject in Finnish, Danish, Swedish and Norwegian schools.

🔗 Computing 🔗 Computing/Software 🔗 Linux

The magic SysRq key is a key combination understood by the Linux kernel, which allows the user to perform various low-level commands regardless of the system's state. It is often used to recover from freezes, or to reboot a computer without corrupting the filesystem. Its effect is similar to the computer's hardware reset button (or power switch) but with many more options and much more control.

This key combination provides access to powerful features for software development and disaster recovery. In this sense, it can be considered a form of escape sequence. Principal among the offered commands are means to forcibly unmount file systems, kill processes, recover keyboard state, and write unwritten data to disk. With respect to these tasks, this feature serves as a tool of last resort.

The magic SysRq key cannot work under certain conditions, such as a kernel panic or a hardware failure preventing the kernel from running properly.

🔗 Spaceflight

Mercury-Redstone 1 (MR-1) was the first Mercury-Redstone unmanned flight test in Project Mercury and the first attempt to launch a Mercury spacecraft with the Mercury-Redstone Launch Vehicle. Intended to be an unmanned sub-orbital spaceflight, it was launched on November 21, 1960 from Cape Canaveral Air Force Station, Florida. The launch failed in a peculiar fashion which has been referred to as the "four-inch flight".

🔗 United States 🔗 Numismatics 🔗 Numismatics/American currency 🔗 U.S. Congress

The United States Gold Reserve Act of January 30, 1934 required that all gold and gold certificates held by the Federal Reserve be surrendered and vested in the sole title of the United States Department of the Treasury. It also prohibited the Treasury and financial institutions from redeeming dollar bills for gold, established the Exchange Stabilization Fund under control of the Treasury to control the dollar’s value without the assistance (or approval) of the Federal Reserve, and authorized the president to establish the gold value of the dollar by proclamation.

Immediately following passage of the Act, the President, Franklin D. Roosevelt, changed the statutory price of gold from $20.67 per troy ounce to $35. This price change incentivized gold miners globally to expand production and foreigners to export their gold to the United States, while simultaneously devaluing the U.S. dollar by increasing inflation. The increase in gold reserves due to the price change resulted in a large accumulation of gold in the Federal Reserve and U.S. Treasury, much of which was stored in the United States Bullion Depository at Fort Knox and other locations. The increase in gold reserves increased the money supply, lowering real interest rates which in turn increased investment in durable goods.

A year earlier, in 1933, Executive Order 6102 had made it a criminal offense for U.S. citizens to own or trade gold anywhere in the world, with exceptions for some jewelry and collector's coins. These prohibitions were relaxed starting in 1964 – gold certificates were again allowed for private investors on April 24, 1964, although the obligation to pay the certificate holder on demand in gold specie would not be honored. By 1975 Americans could again freely own and trade gold.

🔗 Linguistics

Oi is an interjection used in various varieties of the English language, particularly Australian English, British English, Indian English, Irish English, New Zealand English, and South African English, as well as non-English languages such as Chinese, Tagalog, Tamil, Hindi/Urdu, Japanese, and Portuguese to get the attention of another person or to express surprise or disapproval. It is sometimes used in Canadian English and very rarely in American English. The word is also common in the Indian subcontinent, where it has varied pronunciations of "O-ee" and "O-ye".

"Oi" has been particularly associated with working class and Cockney speech. It is effectively a local pronunciation of "hoy" (see H-dropping), an older expression. A study of the Cockney dialect in the 1950s found that whether it was being used to call attention or as a challenge depended on its tone and abruptness. The study's author noted that the expression is "jaunty and self-assertive" as well as "intensely cockney".

A poll of non-English speakers by the British Council in 2004 found that "oi" was considered the 61st most beautiful word in the English language. A spokesman commented that "Oi is not a word that I would've thought turned up in English manuals all that often." "Oi" was added to the list of acceptable words in US Scrabble in 2006.