In the Tait conjectures, a knot diagram is called "reduced" if all the "isthmi", or "nugatory crossings" have been removed.
|
|
This list of isthmuses is an appendix to the article isthmus. The list is sorted by the region of the world in which the isthmus is located. An isthmus ( or ; plural: isthmuses, or occasionally isthmi; from ) is a narrow piece of land connecting two larger areas across an expanse of water that otherwise separates them. A tombolo is an isthmus that consists of a spit or bar.
|
|
A reduced diagram is one in which all the isthmi are removed. Tait came up with his conjectures after his attempt to tabulate all knots in the late 19th century. As a founder of the field of knot theory, his work lacks a mathematically rigorous framework, and it is unclear whether he intended the conjectures to apply to all knots, or just to alternating knots. It turns out that most of them are only true for alternating knots.
|
|
The brachium of superior colliculus (or superior brachium) is a branch that extends laterally from the superior colliculus, and, passing between the pulvinar and medial geniculate body, is partly continued into an eminence called the lateral geniculate body, and partly into the optic tract. The superior colliculus is associated with a nearby structure called the parabigeminal nucleus, often referred to as its satellite. In the optic tectum this nearby structure is known as the nucleus isthmi.
|
|
Falmouth's southern shore is notable for a series of ponds and rivers spaced very closely together, all of which travel some distance into the town. These include, from west to east, Falmouth Inner Harbor, Little Pond, Great Pond (which leads to the Dexter and Coonamesset rivers), Green Pond, Bourne's Pond, Eel Pond (which leads to the Childs River), and Waquoit Bay, which lies along the Mashpee town line. The Buzzards Bay side of the town is primarily bays divided by necks, peninsulas connected to land by isthmi. The largest inlet is Megansett Cove along the Bourne town line.
|
|
Other aspects are highly variable, such as the total number of layers (from 3 in the African lungfish to 15 in the goldfishNorthcutt, 2002), and the number of different types of cells (from 2 in the lungfish to 27 in the house sparrow). The optic tectum is closely associated with an adjoining structure called the nucleus isthmi, which has drawn a lot of interest because it evidently makes a very important contribution to tectal function. (In the superior colliculus the like structure is termed the parabigeminal nucleus). The nucleus isthmii is divided into two parts, called isthmus pars magnocellularis (Imc; "the part with the large cells") and isthmus pars parvocellularis (Ipc; "the part with the small cells").
|
|
The sandy isthmus or tombolo "The Neck" connecting North and South Bruny Island in Tasmania, Australia An isthmus ( or ; plural: isthmuses or isthmi; from )LSJ entry ισθμός is a narrow piece of land connecting two larger areas across an expanse of water by which they are otherwise separated. A tombolo is an isthmus that consists of a spit or bar, and a strait is the sea counterpart of an isthmus. Canals are often built across isthmuses, where they may be a particularly advantageous shortcut for marine transport. For example, the Panama Canal crosses the Isthmus of Panama, connecting the North Atlantic and Pacific Oceans; the Suez Canal connects the Mediterranean Sea and the Red Sea, cutting across the western side of the Isthmus of Suez, formed by the Sinai Peninsula; and the Crinan Canal crosses the isthmus between Loch Crinan and Loch Gilp, which connects the Kintyre peninsula with the rest of Scotland.
|
|