Yak

The yak (Bos grunniens and Bos mutus) is a long-haired bovid found throughout the Himalaya region of southern Central Asia, the Tibetan Plateau and as far north as Mongolia and Russia. Most yaks are domesticated Bos grunniens. There is also a small, vulnerable population of wild yaks, Bos mutus.

Etymology

The English word "yak" derives from the Tibetan gyag (Tibetan: གཡག་, Wylie: g.yag ) – in Tibetan this refers only to the male of the species, the female being called a dri or nak. In English, as in most other languages which have borrowed the word, "yak" is usually used for both sexes.

Taxonomy

Yaks belong to the genus Bos, and are therefore related to cattle (Bos primigenius taurus, Bos primigenius indicus). Mitochondrial DNA analyses to determine the evolutionary history of yaks have been somewhat ambiguous.

The yak may have diverged from cattle at any point between one and five million years ago, and there is some suggestion that it may be more closely related to bison than to the other members of its designated genus. Apparent close fossil relatives of the yak, such as Bos baikalensis, have been found in eastern Russia, suggesting a possible route by which yak-like ancestors of the modern American bison could have entered the Americas.

Yaksha

Yaksha (Sanskrit यक्ष yakṣa, Pali yakkha) is the name of a broad class of nature-spirits, usually benevolent, who are caretakers of the natural treasures hidden in the earth and tree roots. They appear in Hindu, Jain and Buddhist texts. The feminine form of the word is yakṣī) or Yakshini (yakṣiṇī).

In Hindu, Jain, and Buddhist texts, the yakṣa has a dual personality. On the one hand, a yakṣa may be an inoffensive nature-fairy, associated with woods and mountains; but there is also a darker version of the yakṣa, which is a kind of ghost (bhuta) that haunts the wilderness and waylays and devours travelers, similar to the rakṣasas.

In Kālidāsa's poem Meghadūta, for instance, the yakṣa narrator is a romantic figure, pining with love for his missing beloved. By contrast, in the didactic Hindu dialogue of the Yakṣapraśnāḥ "Questions of the Yakṣa", it is a tutelary spirit of a lake that challenges Yudhiṣṭhira. The yakṣas may have originally been the tutelary gods of forests and villages, and were later viewed as the steward deities of the earth and the wealth buried beneath.

Yakovlev Yak-36

Yakovlev Yak-38

The Yakovlev Yak-38 (Russian: Яковлев Як-38; NATO reporting name: "Forger") was Soviet Naval Aviation's only operational VTOL strike fighter aircraft, in addition to being its first operational carrier-based fixed-wing aircraft. It was developed specifically for and served almost exclusively on the Kiev-class aircraft carriers.

Design and development

Designed by the A.S. Yakovlev Design Bureau JSC, the first drawings showed a supersonic aircraft strongly resembling the Hawker P.1154 in study in the United Kingdom, but with two R27-300 engines. Supersonic performances would have implied many difficulties of development, and it was decided to initially develop a relatively simple aircraft limited to Mach 0.95. Although the Yak-38 and Yak-38M were developed from the land-based Yakovlev Yak-36, the aircraft had almost nothing in common.

The prototype VM-01 was finished on 14 April 1970. Though outwardly similar to the British Hawker Siddeley Harrier, it followed a completely different configuration. Together with a vectorable thrust engine in the rear used during flight, two smaller, and less powerful, engines were housed in the front portion of the fuselage and used purely for take-off and landing. The aircraft used a similar layout to the German experimental VTOL strike fighter, the VFW VAK 191B, which began development in 1961, and the contemporary Dassault Mirage IIIV.

Air cycle machine

An air cycle machine (ACM) is the refrigeration unit of the environmental control system (ECS) used in pressurized gas turbine-powered aircraft. Normally an aircraft has two or three of these ACM. Each ACM and its components are often referred as an air conditioning pack. The air cycle cooling process uses air instead of a phase changing material such as Freon in the gas cycle. No condensation or evaporation of a refrigerant is involved, and the cooled air output from the process is used directly for cabin ventilation or for cooling electronic equipment.

History

Air cycle machines were first developed in the 19th century for providing chilling on ships. The technique is a reverse Brayton cycle (the thermodynamic cycle of a gas turbine engine) and is also known as a Bell Coleman cycle or "Air-Standard Refrigeration Cycle".

Technical details

The usual compression, cooling and expansion seen in any refrigeration cycle is accomplished in the ACM by a centrifugal compressor, two air-to-air heat exchangers and an expansion turbine.

List of Gargoyles characters

In the animated television series Gargoyles and the spinoff comic books Gargoyles (SLG comic) and Gargoyles: Bad Guys, Gargoyles are a species of winged humanoid creatures that are the focus of the show.

Gargoyles

Several clans of gargoyles exist worldwide (although until recently, they were unaware of each other's existence), and each clan has distinct cultural and morphological characteristics. All gargoyle clans are alike in that each has a particular item, area, or concept that they strive to protect. They are fierce warriors and are incredibly powerful and resilient; their appearance and ferocity (along with the fact that they are nocturnal creatures) often means that humans vilify them as demons and monsters. Most of the world's gargoyle clans do not peacefully co-exist with humans.

Gargoyles are particularly notable for entering a sort of stone hibernation, called "stone sleep", during the day, during which they resemble Gothic statues. During daylight, they can quickly heal from injury and illness, and are protected from most natural threats. However, this state makes them easy targets for destruction by their enemies and humans who hate them. The character Anton Sevarius postulated that, in this hibernation, they absorb solar radiation that allows them to store energy; otherwise, he concluded, the strenuous activity of gliding would require a nutritional intake equivalent to eating three cows a day. Damage during stone sleep can be fatal to a gargoyle. If a gargoyle dies during its hibernation, its body will remain stone.

Pack (canine)

Pack is a social group of conspecific canids. Not all species of canids form packs; for example, small canids like the red fox do not. Pack size and social behaviour within packs varies across species.

Pack behavior in specific species

African wild dogs (Lycaon pictus) live and hunt in packs. Males assist in raising the pups, and remain with their pack for life, while the females leave their birth pack at about the age of two and a half years old to join a pack with no females. Males outnumber the females in a pack, and usually only one female breeds, with all of the males. African wild dogs are not territorial, and they hunt cooperatively in their packs, running down large game and tearing it apart. They cooperate in caring for wounded and sick pack members as well as the young.

Gray wolves (Canis lupus) usually live in packs which consist of the adult parents and their offspring of perhaps the last 2 or 3 years. The adult parents are usually unrelated and other unrelated wolves may sometimes join the pack.