Have a deep view into what people are curious about.

🔗 Visual arts

The Voyage of Life is a series of four paintings created by Thomas Cole in 1842, representing an allegory of the four stages of human life. The paintings, Childhood, Youth, Manhood, and Old Age, depict a voyager who travels in a boat on a river through the mid-19th-century American wilderness. In each painting the voyager rides the boat on the River of Life accompanied by a guardian angel. The landscape, each reflecting one of the four seasons of the year, plays a major role in conveying the story. With each installment the boat's direction of travel is reversed from the previous picture. In childhood, the infant glides from a dark cave into a rich, green landscape. As a youth, the boy takes control of the boat and aims for a shining castle in the sky. In manhood, the adult relies on prayer and religious faith to sustain him through rough waters and a threatening landscape. Finally, the man becomes old and the angel guides him to heaven across the waters of eternity.

🔗 Military history

🔗 International relations 🔗 Ancient Egypt 🔗 Politics 🔗 Sociology 🔗 Asia

A hydraulic empire, also known as a hydraulic despotism, hydraulic society, hydraulic civilization, or water monopoly empire, is a social or government structure which maintains power and control through exclusive control over access to water. It arises through the need for flood control and irrigation, which requires central coordination and a specialized bureaucracy.

Often associated with these terms and concepts is the notion of a water dynasty. This body is a political structure which is commonly characterized by a system of hierarchy and control often based on class or caste. Power, both over resources (food, water, energy) and a means of enforcement such as the military, is vital for the maintenance of control.

🔗 Philosophy 🔗 Philosophy/Philosophy of religion

The self-referencing doomsday argument rebuttal is an attempt to refute the doomsday argument (that there is a credible link between the brevity of the human race's existence and its expected extinction) by applying the same reasoning to the lifetime of the doomsday argument itself.

The first researchers to write about this were P. T. Landsberg and J. N. Dewynne in 1997; they applied belief in the doomsday argument to itself, and claimed that a paradox results.

🔗 Physics

A Halbach array (German: [ˈhalbax]) is a special arrangement of permanent magnets that augments the magnetic field on one side of the array while cancelling the field to near zero on the other side. This is achieved by having a spatially rotating pattern of magnetisation.

The rotating pattern of permanent magnets (on the front face; on the left, up, right, down) can be continued indefinitely and have the same effect. The effect of this arrangement is roughly similar to many horseshoe magnets placed adjacent to each other, with similar poles touching.

This magnetic orientation process replicates that applied by a magnetic recording tape head to the magnetic tape coating during the recording process. The principle was further described by James (Jim) M. Winey of Magnepan in 1970, for the ideal case of continuously rotating magnetization, induced by a one-sided stripe-shaped coil.

The effect was also discovered by John C. Mallinson in 1973, and these "one-sided flux" structures were initially described by him as a "curiosity", although at the time he recognized from this discovery the potential for significant improvements in magnetic tape technology.

Physicist Klaus Halbach, while at the Lawrence Berkeley National Laboratory during the 1980s, independently invented the Halbach array to focus particle accelerator beams.

🔗 Business 🔗 Engineering 🔗 Japan 🔗 Japan/Science and technology 🔗 Japan/Business and economy

Poka-yoke (ポカヨケ, [poka yoke]) is a Japanese term that means "mistake-proofing" or "inadvertent error prevention". A poka-yoke is any mechanism in any process that helps an equipment operator avoid (yokeru) mistakes (poka). Its purpose is to eliminate product defects by preventing, correcting, or drawing attention to human errors as they occur. The concept was formalised, and the term adopted, by Shigeo Shingo as part of the Toyota Production System. It was originally described as baka-yoke, but as this means "fool-proofing" (or "idiot-proofing") the name was changed to the milder poka-yoke.

The Electro Gyro-Cator was claimed to be the world's first automated commercially available automotive navigation system. It was co-developed by Honda, Alpine, and Stanley Electric Co..

Unlike most navigation systems of today, it did not use GPS Satellites to maintain its position and discern movement of the vehicle. Rather, it was an Inertial navigation system, because it contained a helium gas gyroscope that could detect both rotation and movement. A special servo gear was also attached to the transmission housing to feed information to the Gyro-Cator to help maintain position, map speed and distance traveled.

Transparent maps were placed inside the unit and it would scroll them past a 6 inch monochrome CRT illuminated screen as the car traveled along. The monitor would indicate by a series of circles (or cross hairs) on the screen to show the vehicle's current location or display lines for path of travel. A marking pen was also included to help make personal indicators on the map if needed. Adjustments could be made to change the display scale, position, rotation, brightness, and contrast. In its only year of production in 1981, it was announced as an option on that year's Honda Accord and Honda Vigor, but at ¥300,000 ($2,746 USD), it was almost a quarter of the value of the car. It is not clear how many units were actually sold to customers as a "dealer option". A patent for gyroscope design was introduced to the US in design patent D274332.

Documented weight for the unit was roughly 20 lb (9 kg). A display unit, with a cutaway of the Gyroscope, is currently shown at the Honda Collection Hall at Twin Ring Motegi, Japan.

🔗 Physics 🔗 Astronomy

A Jacobi ellipsoid is a triaxial (i.e. scalene) ellipsoid under hydrostatic equilibrium which arises when a self-gravitating, fluid body of uniform density rotates with a constant angular velocity. It is named after the German mathematician Carl Gustav Jacob Jacobi.

🔗 African diaspora 🔗 Oklahoma 🔗 Oklahoma/Task-force Tulsa

The Tulsa race massacre (also called the Tulsa race riot, the Greenwood Massacre, or the Black Wall Street Massacre) of 1921 took place on May 31 and June 1, 1921, when mobs of white residents attacked black residents and businesses of the Greenwood District in Tulsa, Oklahoma. It has been called "the single worst incident of racial violence in American history." The attack, carried out on the ground and from private aircraft, destroyed more than 35 square blocks of the district – at that time the wealthiest black community in the United States, known as "Black Wall Street".

More than 800 people were admitted to hospitals and as many as 6,000 black residents were interned at large facilities, many for several days. The Oklahoma Bureau of Vital Statistics officially recorded 36 dead, but the American Red Cross declined to provide an estimate. A 2001 state commission examination of events was able to confirm 39 dead, 26 black and 13 white, based on contemporary autopsy reports, death certificates and other records. The commission gave overall estimates from 75–100 to 150–300 dead.

The massacre began over Memorial Day weekend after 19-year-old Dick Rowland, a black shoeshiner, was accused of assaulting Sarah Page, the 17-year-old white elevator operator of the nearby Drexel Building. He was taken into custody. A subsequent gathering of angry local whites outside the courthouse where Rowland was being held, and the spread of rumors he had been lynched, alarmed the local black population, some of whom arrived at the courthouse armed. Shots were fired and twelve people were killed: ten white and two black. As news of these deaths spread throughout the city, mob violence exploded. White rioters rampaged through the black neighborhood that night and morning killing men and burning and looting stores and homes, and only around noon the next day Oklahoma National Guard troops managed to get control of the situation by declaring martial law. About 10,000 black people were left homeless, and property damage amounted to more than $1.5 million in real estate and $750,000 in personal property (equivalent to $32.25 million in 2019).

Many survivors left Tulsa. Black and white residents who stayed in the city were silent for decades about the terror, violence, and losses of this event. The massacre was largely omitted from local, state, and national histories.

In 1996, seventy-five years after the massacre, a bipartisan group in the state legislature authorized formation of the Oklahoma Commission to Study the Tulsa Race Riot of 1921 (renamed Oklahoma Commission to Study the Tulsa Race Massacre, in November 2018). Members were appointed to investigate events, interview survivors, hear testimony from the public, and prepare a report of events. There was an effort toward public education about these events through the process. The Commission's final report, published in 2001, said that the city had conspired with the mob of white citizens against black citizens; it recommended a program of reparations to survivors and their descendants. The state passed legislation to establish some scholarships for descendants of survivors, encourage economic development of Greenwood, and develop a memorial park in Tulsa to the massacre victims. The park was dedicated in 2010. In 2020, the massacre became part of the Oklahoma school curriculum.

🔗 Computer science 🔗 Databases 🔗 Databases/Computer science

R-trees are tree data structures used for spatial access methods, i.e., for indexing multi-dimensional information such as geographical coordinates, rectangles or polygons. The R-tree was proposed by Antonin Guttman in 1984 and has found significant use in both theoretical and applied contexts. A common real-world usage for an R-tree might be to store spatial objects such as restaurant locations or the polygons that typical maps are made of: streets, buildings, outlines of lakes, coastlines, etc. and then find answers quickly to queries such as "Find all museums within 2 km of my current location", "retrieve all road segments within 2 km of my location" (to display them in a navigation system) or "find the nearest gas station" (although not taking roads into account). The R-tree can also accelerate nearest neighbor search for various distance metrics, including great-circle distance.