Have a deep view into what people are curious about.

🔗 Aviation 🔗 Physics 🔗 Aviation/aircraft

A vacuum airship, also known as a vacuum balloon, is a hypothetical airship that is evacuated rather than filled with a lighter-than-air gas such as hydrogen or helium. First proposed by Italian Jesuit priest Francesco Lana de Terzi in 1670, the vacuum balloon would be the ultimate expression of lifting power per volume displaced.

🔗 Computing 🔗 Computing/Computer hardware

The Dadda multiplier is a hardware binary multiplier design invented by computer scientist Luigi Dadda in 1965. It uses a selection of full and half adders to sum the partial products in stages (the Dadda tree or Dadda reduction) until two numbers are left. The design is similar to the Wallace multiplier, but the different reduction tree reduces the required number of gates (for all but the smallest operand sizes) and makes it slightly faster (for all operand sizes).

Dadda and Wallace multipliers have the same three steps for two bit strings ${\displaystyle w_{1}}$ and ${\displaystyle w_{2}}$ of lengths ${\displaystyle \ell _{1}}$ and ${\displaystyle \ell _{2}}$ respectively:

1. Multiply (logical AND) each bit of ${\displaystyle w_{1}}$, by each bit of ${\displaystyle w_{2}}$, yielding ${\displaystyle \ell _{1}\cdot \ell _{2}}$ results, grouped by weight in columns
2. Reduce the number of partial products by stages of full and half adders until we are left with at most two bits of each weight.
3. Add the final result with a conventional adder.

As with the Wallace multiplier, the multiplication products of the first step carry different weights reflecting the magnitude of the original bit values in the multiplication. For example, the product of bits ${\displaystyle a_{n}b_{m}}$ has weight ${\displaystyle n+m}$.

Unlike Wallace multipliers that reduce as much as possible on each layer, Dadda multipliers attempt to minimize the number of gates used, as well as input/output delay. Because of this, Dadda multipliers have a less expensive reduction phase, but the final numbers may be a few bits longer, thus requiring slightly bigger adders.

🔗 Novels 🔗 Novels/Science fiction 🔗 Science Fiction

A Canticle for Leibowitz is a post-apocalyptic science fiction novel by American writer Walter M. Miller Jr., first published in 1959. Set in a Catholic monastery in the desert of the southwestern United States after a devastating nuclear war, the book spans thousands of years as civilization rebuilds itself. The monks of the Albertian Order of Leibowitz preserve the surviving remnants of man's scientific knowledge until the world is again ready for it.

The novel is a fixup of three short stories Miller published in The Magazine of Fantasy & Science Fiction that were inspired by the author's participation in the bombing of the monastery at the Battle of Monte Cassino during World War II. The book is considered one of the classics of science fiction and has never been out of print. Appealing to mainstream and genre critics and readers alike, it won the 1961 Hugo Award for best science fiction novel, and its themes of religion, recurrence, and church versus state have generated a significant body of scholarly research. A sequel, Saint Leibowitz and the Wild Horse Woman, was published posthumously in 1997.

🔗 Environment 🔗 Disaster management 🔗 Energy 🔗 Pennsylvania 🔗 Mining

The Centralia mine fire is a coal-seam fire that has been burning underneath the borough of Centralia, Pennsylvania, United States, since at least May 27, 1962. Its original cause is still a matter of debate. It is burning in underground coal mines at depths of up to 300 feet (90 m) over an 8-mile (13 km) stretch of 3,700 acres (15 km²). At its current rate, it could continue to burn for over 250 years. It has caused most of the town to be abandoned: the population dwindled from around 1,500 at the time the fire started to 7 in 2013, and most of the buildings have been levelled.

🔗 Human rights 🔗 Military history 🔗 Military history/North American military history 🔗 Military history/United States military history 🔗 Military history/Military science, technology, and theory 🔗 Military history/Weaponry 🔗 Medicine 🔗 Biology 🔗 Military history/World War II 🔗 Military history/Cold War 🔗 United States History 🔗 Medicine/Society and Medicine

Unethical human experimentation in the United States describes numerous experiments performed on human test subjects in the United States that have been considered unethical, and were often performed illegally, without the knowledge, consent, or informed consent of the test subjects. Such tests have occurred throughout American history, but particularly in the 20th century. The experiments include: the exposure of humans to many chemical and biological weapons (including infection with deadly or debilitating diseases), human radiation experiments, injection of toxic and radioactive chemicals, surgical experiments, interrogation and torture experiments, tests involving mind-altering substances, and a wide variety of others. Many of these tests were performed on children, the sick, and mentally disabled individuals, often under the guise of "medical treatment". In many of the studies, a large portion of the subjects were poor, racial minorities, or prisoners.

Funding for many of the experiments was provided by the United States government, especially the United States military, the Central Intelligence Agency, or private corporations involved with military activities. The human research programs were usually highly secretive, and in many cases information about them was not released until many years after the studies had been performed.

The ethical, professional, and legal implications of this in the United States medical and scientific community were quite significant, and led to many institutions and policies that attempted to ensure that future human subject research in the United States would be ethical and legal. Public outrage in the late 20th century over the discovery of government experiments on human subjects led to numerous congressional investigations and hearings, including the Church Committee and Rockefeller Commission, both of 1975, and the 1994 Advisory Committee on Human Radiation Experiments, among others.

🔗 Biography 🔗 Australia 🔗 Crime 🔗 Death 🔗 Australia/Australian crime 🔗 Australia/Adelaide

The Somerton Man was an unidentified man whose body was found on 1 December 1948 on the beach at Somerton Park, a suburb of Adelaide, South Australia. The case is also known after the Persian phrase tamám shud (Persian: تمام شد), meaning "is over" or "is finished", which was printed on a scrap of paper found months later in the fob pocket of the man's trousers. The scrap had been torn from the final page of a copy of Rubaiyat of Omar Khayyám, authored by 12th-century poet Omar Khayyám.

Following a public appeal by police, the book from which the page had been torn was located. On the inside back cover, detectives read through indentations left from previous handwriting: a local telephone number, another unidentified number, and text that resembled a coded message. The text has not been deciphered or interpreted in a way that satisfies authorities on the case.

Since the early stages of the police investigation, the case has been considered "one of Australia's most profound mysteries". There has been intense speculation ever since regarding the identity of the victim, the cause of his death, and the events leading up to it. Public interest in the case remains significant for several reasons: the death occurred at a time of heightened international tensions following the beginning of the Cold War; the apparent involvement of a secret code; the possible use of an undetectable poison; and the inability of authorities to identify the dead man.

On 26 July 2022, Adelaide University professor Derek Abbott, in association with genealogist Colleen M. Fitzpatrick, claimed to have identified the man as Carl "Charles" Webb, an electrical engineer and instrument maker born in 1905, based on genetic genealogy from DNA of the man's hair. South Australia Police and Forensic Science South Australia have not verified the result, but South Australia Police said they were "cautiously optimistic" about it.

🔗 Physics

The Mpemba effect is a process in which hot water can freeze faster than cold water. The phenomenon is temperature-dependent. There is disagreement about the parameters required to produce the effect and about its theoretical basis.

The Mpemba effect is named after Tanzanian scientist Erasto Bartholomeo Mpemba (b.1950) who discovered it in 1963. There were preceding ancient accounts of similar phenomena, but these lacked sufficient detail to attempt verification.

🔗 United States/U.S. Government 🔗 United States 🔗 Espionage 🔗 Cats

Acoustic Kitty was a CIA project launched by the Central Intelligence Agency Directorate of Science & Technology, which in the 1960s intended to use cats to spy on the Kremlin and Soviet embassies. In an hour-long procedure a veterinary surgeon implanted a microphone in the cat's ear canal, a small radio transmitter at the base of its skull and a thin wire into its fur.

This would allow the cat to innocuously record and transmit sound from its surroundings. Due to problems with distraction, the cat's sense of hunger had to be addressed in another operation. Victor Marchetti, a former CIA officer, said Project Acoustic Kitty cost about $20 million.

The first Acoustic Kitty mission was to eavesdrop on two men in a park outside the Soviet compound on Wisconsin Avenue in Washington, D.C. The cat was released nearby, but was hit and allegedly killed by a taxi almost immediately. However, this was disputed in 2013 by Robert Wallace, a former Director of the CIA's Office of Technical Service, who said that the project was abandoned due to the difficulty of training the cat to behave as required, and "the equipment was taken out of the cat; the cat was re-sewn for a second time, and lived a long and happy life afterwards". Subsequent tests also failed. Shortly thereafter the project was considered a failure and declared to be a total loss. However, other accounts report more success for the project.

The project was cancelled in 1967. A closing memorandum said that the CIA researchers believed that they could train cats to move short distances, but that "the environmental and security factors in using this technique in a real foreign situation force us to conclude that for our (intelligence) purposes, it would not be practical." The project was disclosed in 2001, when some CIA documents were declassified.

🔗 Poetry

"Dane-geld" is a poem by British writer Rudyard Kipling (1865-1936). It relates to the unwisdom of paying "Danegeld", or what is nowadays called blackmail and protection money. The most famous lines are "once you have paid him the Danegeld/ You never get rid of the Dane."

🔗 Mathematics 🔗 Statistics

In statistics, the 68–95–99.7 rule, also known as the empirical rule, is a shorthand used to remember the percentage of values that lie within an interval estimate in a normal distribution: 68%, 95%, and 99.7% of the values lie within one, two, and three standard deviations of the mean, respectively.

In mathematical notation, these facts can be expressed as follows, where Pr() is the probability function, Χ is an observation from a normally distributed random variable, μ (mu) is the mean of the distribution, and σ (sigma) is its standard deviation:

${\displaystyle {\begin{aligned}\Pr(\mu -1\sigma \leq X\leq \mu +1\sigma )&\approx 68.27\%\\\Pr(\mu -2\sigma \leq X\leq \mu +2\sigma )&\approx 95.45\%\\\Pr(\mu -3\sigma \leq X\leq \mu +3\sigma )&\approx 99.73\%\end{aligned}}}$

The usefulness of this heuristic especially depends on the question under consideration.

In the empirical sciences, the so-called three-sigma rule of thumb (or 3σ rule) expresses a conventional heuristic that nearly all values are taken to lie within three standard deviations of the mean, and thus it is empirically useful to treat 99.7% probability as near certainty.

In the social sciences, a result may be considered "significant" if its confidence level is of the order of a two-sigma effect (95%), while in particle physics, there is a convention of a five-sigma effect (99.99994% confidence) being required to qualify as a discovery.

A weaker three-sigma rule can be derived from Chebyshev's inequality, stating that even for non-normally distributed variables, at least 88.8% of cases should fall within properly calculated three-sigma intervals. For unimodal distributions, the probability of being within the interval is at least 95% by the Vysochanskij–Petunin inequality. There may be certain assumptions for a distribution that force this probability to be at least 98%.