2-sided

In topology, a compact codimension one submanifold of a manifold is said to be 2-sided in when there is an embedding

with for each and

In other words, if its normal bundle is trivial.

This means, for example that a curve in a surface is 2-sided if it has a tubular neighborhood which is a cartesian product of the curve times an interval.

A submanifold which is not 2-sided is called 1-sided.

Examples

Surfaces

For curves on surfaces, a curve is 2-sided if and only if it preserves orientation, and 1-sided if and only if it reverses orientation: a tubular neighborhood is then a Möbius strip. This can be determined from the class of the curve in the fundamental group of the surface and the orientation character on the fundamental group, which identifies which curves reverse orientation.

Nox

Nox may refer to:

Science and technology

Entertainment

Other uses

See also

Mythology of Stargate

In the fictional universe of the Stargate franchise, the people of Earth have encountered numerous extraterrestrial races on their travels through the Stargate. In addition to a diversity of alien life, there is also an abundance of other humans, scattered across the cosmos by advanced aliens in the distant past. Some of the most significant species in Stargate SG-1 are the Goa'uld, the Asgard, and the Replicators. Stargate Atlantis, set in the Pegasus galaxy, introduced the Wraith and the Asurans. One of the most influential species in Stargate, the Ancients, have moved on to a higher plane of existence. For practical reasons of television productions, almost all of the alien and human cultures in the Stargate's fictional universe speak native English. Because of the time constraints of an hour-long episode, it would become a major hindrance to the story each week if the team had to spend a sizeable part of each episode learning to communicate with a new species.

Stargate SG-1 explains the human population in the Milky Way galaxy by revealing that the alien Goa'uld transplanted humans from Earth to other planets for slave labor. Many of these populations were subsequently abandoned, often when deposits of the precious fictional mineral naqahdah were exhausted, and developed into their own unique societies. Some of these extraterrestrial human civilizations have become much more technologically advanced than Earth, the in-show rationale being that they never suffered the setback of the Dark Ages. The most advanced of these humans were the Tollan, although they were destroyed by the Goa'uld in Season 5's Between Two Fires. The human populations of the Pegasus galaxy are the product of Ancient seeding. few human races in Pegasus are technologically advanced, as the Wraith destroy any civilization that could potentially pose a threat. There are also large numbers of humans in the Ori galaxy, where they empower the Ori through worship.

Nox (video game)

Nox is an action role-playing game developed by Westwood Studios and published by Electronic Arts in 2000 for Microsoft Windows. It details the story of Jack, a young man from Earth who is pulled into a high fantasy parallel universe and has to defeat the evil sorceress Hecubah and her army of Necromancers to return home. Depending on the player's choice of character class at the beginning of the game (warrior, conjurer, or wizard), the game follows three largely different linear storylines, each leading to its unique ending. In the multiplayer, players can compete against each other in various game modes such as deathmatch and capture the flag, while the freely downloadable expansion pack NoxQuest added a cooperative multiplayer mode. The game was generally well received by critics and the media.

Gameplay

The player controls Jack from oblique perspective with the mouse and a number of pre-defined hotkeys. The line of sight is limited by an innovative and well-receivedfog of war system named "TrueSight", which dynamically blacks out portions of the screen which Jack cannot see from his current position. The single-player campaign consists of multiple locations which Jack must explore, killing enemies and monsters and assisting his allies. Most of the game time is spent in dungeons and wilderness where Jack gathers experience points (the highest possible level in the game is 10) and collects items such as weapons, armor and spells, which can be equipped, learned, or sold to traders found on several locations throughout the game. The story is told through dialogue with non-player characters, cut scenes using the game engine, and a few pre-rendered full motion videos.