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A lithophone is a musical instrument consisting of a rock or pieces of rock which are struck to produce musical notes. Notes may be sounded in combination (producing harmony) or in succession (melody). The lithophone is an idiophone comparable to instruments such as the glockenspiel, vibraphone, xylophone and marimba.

In the Hornbostel-Sachs classification system, lithophones are designated as '111.22' – directly-struck percussion plaques.

The free energy principle tries to explain how (biological) systems maintain their order (non-equilibrium steady-state) by restricting themselves to a limited number of states. It says that biological systems minimise a free energy function of their internal states, which entail beliefs about hidden states in their environment. The implicit minimisation of variational free energy is formally related to variational Bayesian methods and was originally introduced by Karl Friston as an explanation for embodied perception in neuroscience, where it is also known as active inference.

The free energy principle is that systems—those that are defined by their enclosure in a Markov blanket—try to minimize the difference between their model of the world and their sense and associated perception. This difference can be described as "surprise" and is minimized by continuous correction of the world model of the system. As such, the principle is based on the Bayesian idea of the brain as an “inference engine”. Friston added a second route to minimization: action. By actively changing the world into the expected state, systems can also minimize the free energy of the system. Friston assumes this to be the principle of all biological reaction.. Friston also believes his principle applies to mental disorders as well as to artificial intelligence. AI implementations based on the active inference principle have shown advantages over other methods.

The free energy principle has been criticized for being very difficult to understand, even for experts. Discussions of the principle have also been criticized as invoking metaphysical assumptions far removed from a testable scientific prediction, making the principle unfalsifiable. In a 2018 interview, Friston acknowledged that the free energy principle is not properly falsifiable: "the free energy principle is what it is — a principle. Like Hamilton’s Principle of Stationary Action, it cannot be falsified. It cannot be disproven. In fact, there’s not much you can do with it, unless you ask whether measurable systems conform to the principle."

Krista and Tatiana Hogan (born October 25, 2006) are Canadians who are conjoined craniopagus twins. They are joined at the head and share a skull and a brain. They were born in Vancouver, British Columbia, and are the only unseparated conjoined twins of that type currently alive in Canada. They live with their mother, Felicia Simms, in Vernon, British Columbia, have two sisters and a brother and often travel to Vancouver for care at BC Children's Hospital and Sunny Hill Health Centre for Children.

Coulombic explosions are a mechanism for transforming energy in intense electromagnetic fields into atomic motion and are thus useful for controlled destruction of relatively robust molecules. The explosions are a prominent technique in laser-based machining, and appear naturally in certain high-energy reactions.

Min Chiu Li (Chinese: 李敏求; pinyin: Lǐ Mǐnqiú; 1919–1980) was a Chinese-American oncologist and cancer researcher. Li was the first scientist to use chemotherapy to cure widely metastatic, malignant cancer.

The solar storm of 1859 (also known as the Carrington Event) was a powerful geomagnetic storm during solar cycle 10 (1855–1867). A solar coronal mass ejection (CME) hit Earth's magnetosphere and induced the largest geomagnetic storm on record, September 1–2, 1859. The associated "white light flare" in the solar photosphere was observed and recorded by British astronomers Richard C. Carrington (1826–1875) and Richard Hodgson (1804–1872). The storm caused strong auroral displays and wrought havoc with telegraph systems. The now-standard unique IAU identifier for this flare is SOL1859-09-01.

A solar storm of this magnitude occurring today would cause widespread electrical disruptions, blackouts and damage due to extended outages of the electrical grid. The solar storm of 2012 was of similar magnitude, but it passed Earth's orbit without striking the planet, missing by nine days.

Yuan Longping (Chinese: 袁隆平; September 7, 1930 – May 22, 2021) was a Chinese agronomist, member of the Chinese Academy of Engineering, known for developing the first hybrid rice varieties in the 1970s.

Hybrid rice has since been grown in dozens of countries in Africa, America, and Asia—providing a robust food source in areas with a high risk of famine. For his contributions, Yuan is always called the "Father of Hybrid Rice" by the Chinese media. On May 22, 2021, Yuan Longping died of multiple organ failure at the age of 90.

The Day of the Programmer is an international professional day that is celebrated on the 256th (hexadecimal 100th, or the 2⁸th) day of each year (September 13 during common years and on September 12 in leap years). It is officially recognized in Russia.

The number 256 (2⁸) was chosen because it is the number of distinct values that can be represented with a byte, a value well known to programmers. 256 is also the highest power of two that is less than 365, the number of days in a common year.

The nuclear football (also known as the atomic football, the president's emergency satchel, the Presidential Emergency Satchel, the button, the black box, or just the football) is a briefcase, the contents of which are to be used by the President of the United States to authorize a nuclear attack while away from fixed command centers, such as the White House Situation Room. It functions as a mobile hub in the strategic defense system of the United States. It is held by an aide-de-camp.