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A perpetual bond, also known colloquially as a perpetual or perp, is a bond with no maturity date, therefore allowing it to be treated as equity, not as debt. Issuers pay coupons on perpetual bonds forever, and they do not have to redeem the principal. Perpetual bond cash flows are, therefore, those of a perpetuity.

This is a list of notable active virtual communities with more than 1 million registered members.

Defunct

Valonia ventricosa, also known as bubble algae or sailor's eyeballs is a species of alga found in oceans throughout the world in tropical and subtropical regions. It is one of the largest – if not the largest – unicellular organisms.

The bus service from London, England to Calcutta, India (now Kolkata) was considered to be the longest bus route in the world. The bus service, which started in 1957, was routed to India via Belgium, Yugoslavia and North Western India. This route is also known as the Hippie Route. According to reports, it took about 50 days for the bus to reach Calcutta from London. The voyage was over 10,000 miles (16,000 km) one way and 20,300 miles (32,700 km) for the round trip. It was in service until 1976. The cost of the trip one-way was £85 in 1957 and £145 in 1973. This amount included food, travel and accommodation.

The Zero one infinity (ZOI) rule is a rule of thumb in software design proposed by early computing pioneer Willem van der Poel. It argues that arbitrary limits on the number of instances of a particular type of data or structure should not be allowed. Instead, an entity should either be forbidden entirely, only one should be allowed, or any number of them should be allowed. Although various factors outside that particular software could limit this number in practice, it should not be the software itself that puts a hard limit on the number of instances of the entity.

Examples of this rule may be found in the structure of many file systems' directories (also known as folders):

• 0 – The topmost directory has zero parent directories; that is, there is no directory that contains the topmost directory.
• 1 – Each subdirectory has exactly one parent directory (not including shortcuts to the directory's location; while such files may have similar icons to the icons of the destination directories, they are not directories at all).
• Infinity – Each directory, whether the topmost directory or any of its subdirectories, according to the file system's rules, may contain any number of files or subdirectories. Practical limits to this number are caused by other factors, such as space available on storage media and how well the computer's operating system is maintained.

In real-world software design, violations of this rule of thumb are common. For example, the FAT16 file system imposes a limit of 65,536 files to a directory.

The pirate game is a simple mathematical game. It is a multi-player version of the ultimatum game.

In medicine and medical anthropology, a culture-bound syndrome, culture-specific syndrome, or folk illness is a combination of psychiatric and somatic symptoms that are considered to be a recognizable disease only within a specific society or culture. There are no objective biochemical or structural alterations of body organs or functions, and the disease is not recognized in other cultures. The term culture-bound syndrome was included in the fourth version of the Diagnostic and Statistical Manual of Mental Disorders (American Psychiatric Association, 1994) which also includes a list of the most common culture-bound conditions (DSM-IV: Appendix I). Counterpart within the framework of ICD-10 (Chapter V) are the culture-specific disorders defined in Annex 2 of the Diagnostic criteria for research.

More broadly, an endemic that can be attributed to certain behavior patterns within a specific culture by suggestion may be referred to as a potential behavioral epidemic. As in the cases of drug use, or alcohol and smoking abuses, transmission can be determined by communal reinforcement and person-to-person interactions. On etiological grounds, it can be difficult to distinguish the causal contribution of culture upon disease from other environmental factors such as toxicity.

Mponeng is a gold mine in South Africa's Gauteng province. Previously known as Western Deep Levels #1 Shaft, the underground and surface works were commissioned in 1987. It extends over 4 kilometres (2.5 mi) below the surface, and is considered to be one of the most substantial gold mines in the world. It is also currently the world's deepest mine from ground level, reaching a depth of 4 km (2.5 mi) below ground level. The trip from the surface to the bottom of the mine takes over an hour.

Over 5400 metric tonnes of rock are excavated from Mponeng each day. At a price of $19.4 per gram of gold, the mine only needs to extract 10 grams of gold per ton excavated to remain profitable. The mine contains at least two gold reefs, with the deepest one metre thick.

Harmony Gold purchased Mponeng from AngloGold Ashanti in September 2020. Along with AGA's Mine Waste Solutions, Harmony paid approximately $300m.

This is a list of countries by hospital beds per 1000 or 100,000 people, as published by the local governments, international organisation (OECD, E.U.), academic sources or others. The number of beds per people is an important indicator of the health care system of a country. The basic measure focus on all hospital beds, which are variously split and occupied. The classic hospital beds are also called curative beds. For severe patients with risk of organ(s) failure, patients are provided intensive care unit beds (aka ICU bed) or critical care beds (CCB).

Among OECD countries, curative beds' occupancy rate average was 75%, from 94.9% (Ireland) to 61.6% (Greece), with half of the OECD's nation between 70% and 80%.

In 2009, European nations, most of them also part of OECD, had an aggregated total of 2,070,000 acute beds and 73,585 (2.8%) critical care beds (CCB) or 11.5CCB/100,000 inhabitants. Germany had 29.2, Portugal 4.2.Aging population leads to increased demand for CCB and difficulties to satisfy it, while both quantity of CCB and availability are poorly documented.

The name-letter effect is the tendency of people to prefer the letters in their name over other letters in the alphabet. Whether subjects are asked to rank all letters of the alphabet, rate each of the letters, choose the letter they prefer out of a set of two, or pick a small set of letters they most prefer, on average people consistently like the letters in their own name the most. Crucially, subjects are not aware that they are choosing letters from their name.

Discovered in 1985 by the Belgian psychologist Jozef Nuttin, the name-letter effect has been replicated in dozens of studies, involving subjects from over 15 countries, using four different alphabets. It holds across age and gender. People who changed their names many years ago tend to prefer the letters of both their current and original names over non-name letters. The effect is most prominent for initials, but even when initials are excluded, the remaining letters of both given and family names still tend to be preferred over non-name letters.

Most people like themselves; the name is associated with the self, and hence the letters of the name are preferred, despite the fact that they appear in many other words. People who do not like themselves tend not to exhibit the name-letter effect. A similar effect has been found for numbers related to birthdays: people tend to prefer the number signifying the day of the month on which they were born. Alternative explanations for the name-letter effect, such as frequent exposure and early mastery, have been ruled out. In psychological assessments, the Name Letter Preference Task is widely used to estimate implicit self-esteem.

There is some evidence that the effect has implications for real-life decisions. In the lab, people disproportionately favor brands matching their initials. An analysis of a large database of charity donations revealed that a disproportionately large number of people donate to disaster relief following hurricanes with names sharing their initial letter (e.g. Kate and Kevin following Hurricane Katrina). Studies that investigate the impact of name-letter matching on bigger life decisions (where to live, whom to marry, which occupation to take on) are controversial.