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🔗 Physics 🔗 Physics/relativity

The Gödel metric is an exact solution of the Einstein field equations in which the stress–energy tensor contains two terms, the first representing the matter density of a homogeneous distribution of swirling dust particles (dust solution), and the second associated with a negative cosmological constant (see lambdavacuum solution). It is also known as the Gödel solution or Gödel universe.

This solution has many unusual properties—in particular, the existence of closed timelike curves that would allow time travel in a universe described by the solution. Its definition is somewhat artificial in that the value of the cosmological constant must be carefully chosen to match the density of the dust grains, but this spacetime is an important pedagogical example.

This solution was found in 1949 by Kurt Gödel.

🔗 United States 🔗 Disaster management 🔗 Crime 🔗 Death 🔗 Lists 🔗 Politics 🔗 Politics/American politics 🔗 Years 🔗 United States/U.S. history 🔗 Current events 🔗 Politics/Gun politics

This is a list of shootings in the United States that have occurred in 2022. Mass shootings are incidents involving several victims of firearm-related violence. The precise inclusion criteria are disputed, and there is no broadly accepted definition.

Gun Violence Archive, a nonprofit research group, run by Tracy Holtan, that tracks shootings and their characteristics in the United States, defines a mass shooting as an incident in which four or more people, excluding the perpetrator(s), are shot in one location at roughly the same time. The Congressional Research Service narrows that definition, limiting it to "public mass shootings", defined by four or more victims killed, excluding any victims who survive. The Washington Post and Mother Jones use similar definitions, with the latter acknowledging that their definition "is a conservative measure of the problem", as many shootings with fewer fatalities occur. The crowdsourced Mass Shooting Tracker project has the most expansive definition of four or more shot in any incident, including the perpetrator in the victim inclusion criteria.

A 2019 study of mass shootings published in the journal Injury Epidemiology recommended developing "a standard definition that considers both fatalities and nonfatalities to most appropriately convey the burden of mass shootings on gun violence." The authors of the study further suggested that "the definition of mass shooting should be four or more people, excluding the shooter, who are shot in a single event regardless of the motive, setting or number of deaths."

🔗 United States 🔗 Disaster management 🔗 Crime 🔗 Lists 🔗 Politics 🔗 Schools 🔗 Politics/American politics 🔗 United States/U.S. history 🔗 Politics/Gun politics

This chronological list of school shootings in the United States includes any school shootings that occurred at a K-12 public or private school, as well as at colleges and universities, and on school buses. Excluded from this list are the following:

1. Incidents that occurred during wars
2. Incidents that occurred as a result of police actions
3. Murder-suicides by rejected suitors or estranged spouses
4. Suicides or suicide attempts involving only one person.

Shootings by school staff, where the only victims are other employees, are covered at workplace killings.

🔗 Biology 🔗 Physics 🔗 Biophysics

Magnetosomes are membranous structures present in magnetotactic bacteria (MTB). They contain iron-rich magnetic particles that are enclosed within a lipid bilayer membrane. Each magnetosome can often contain 15 to 20 magnetite crystals that form a chain which acts like a compass needle to orient magnetotactic bacteria in geomagnetic fields, thereby simplifying their search for their preferred microaerophilic environments. Recent research has shown that magnetosomes are invaginations of the inner membrane and not freestanding vesicles. Magnetite-bearing magnetosomes have also been found in eukaryotic magnetotactic algae, with each cell containing several thousand crystals.

Overall, magnetosome crystals have high chemical purity, narrow size ranges, species-specific crystal morphologies and exhibit specific arrangements within the cell. These features indicate that the formation of magnetosomes is under precise biological control and is mediated biomineralization.

Magnetotactic bacteria usually mineralize either iron oxide magnetosomes, which contain crystals of magnetite (Fe₃O₄), or iron sulfide magnetosomes, which contain crystals of greigite (Fe₃S₄). Several other iron sulfide minerals have also been identified in iron sulfide magnetosomes—including mackinawite (tetragonal FeS) and a cubic FeS—which are thought to be precursors of Fe₃S₄. One type of magnetotactic bacterium present at the oxic-anoxic transition zone (OATZ) of the southern basin of the Pettaquamscutt River Estuary, Narragansett, Rhode Island, United States is known to produce both iron oxide and iron sulfide magnetosomes.

🔗 Iran 🔗 Cities

Ramsar (Persian: رامسر, also Romanized as Rámsar and Ránsar; formerly, Sakht Sar) is the capital of Ramsar County, Mazandaran Province, Iran. In 2012 its population was 33,018, in 9,421 families.

Ramsar lies on the coast of the Caspian Sea. It was also known as Sakhtsar in the past. The climate of Ramsar is hot and humid in summer and mild in winter. The proximity of the forest and the sea in this city has given a special beauty to this city and this attracts tourists in all seasons. Ramsar has an airport. The city of Ramsar was a small village in western Mazandaran until the Qajar period, and during the first Pahlavi period, with the rule of Reza Shah and with the support of the government, it became a beautiful city with many tourist facilities.

Ramsar is the westernmost county and city in Mazandaran. It borders the Caspian Sea to the north, Gilan province to the west, Qazvin Province to the south, and Tonekabon to the east.

🔗 New York City 🔗 Engineering

The Citicorp Center engineering crisis was the discovery, in 1978, of a significant structural flaw in Citicorp Center, then a recently completed skyscraper in New York City, and the subsequent effort to quietly make repairs over the next few months. The building, now known as Citigroup Center, occupied an entire block and was to be the headquarters of Citibank. Its structure, designed by William LeMessurier, had several unusual design features, including a raised base supported by four offset stilts, and diagonal bracing which absorbed wind loads from upper stories.

In the original design, potential wind loads for the building were calculated incorrectly. The flaw was discovered by Diane Hartley, an undergraduate student at Princeton University who was writing a thesis on the building, and was communicated to the firm responsible for the structural design. LeMessurier was subsequently lauded for acknowledging his error and orchestrating a successful repair effort. Estimates at the time suggested that the building could be toppled by a 70-mile-per-hour (110 km/h) wind, with possibly many people killed as a result. The crisis was kept secret until 1995 and Hartley had no knowledge of the significance of her work until after that time.

🔗 Technology 🔗 Medicine

The Corsi–Rosenthal Box, also called a Corsi–Rosenthal Cube or a Comparetto Cube, is a design for a do-it-yourself air purifier that can be built comparatively inexpensively. It was designed during the COVID-19 pandemic with the goal of reducing the levels of airborne viral particles in indoor settings.

🔗 Computing

QB64 (originally QB32) is a self-hosting BASIC compiler for Microsoft Windows, Linux and Mac OS X, designed to be compatible with Microsoft QBasic and QuickBASIC. QB64 is a C++ emitter, which is integrated with a C++ compiler to provide compilation via C++ code and GCC optimization.

QB64 implements most QBasic statements, and can run many QBasic programs, including Microsoft's QBasic Gorillas and Nibbles games. Furthermore, QB64 has been designed to contain an IDE resembling the QBASIC IDE. QB64 also extends the QBASIC programming language to include 64-bit data types, as well as better sound and graphics support. It can also emulate some DOS/x86 specific features such as INT 33h mouse access, and multiple timers.

Since version 2.0, QB64 now offers debugging abilities, with the new $DEBUG metacommand.

🔗 Economics 🔗 Lists

This is a list of some of the major unsolved problems, puzzles, or questions in economics. Some of these are theoretical in origin and some of them concern the inability of orthodox economic theory to explain an empirical observation.