Resistors are used in many different ways. First of all, they are put in circuits to protect components from damage such as LEDs.
They also control the amount of current flowing in a circuit, for example, if you want less current to flow you would put in a resistor with a higher value. Resistors can also split voltage between different parts of a circuit and control time delay.
Electric heaters use very large resistors to turn electricity into heat. Usually, engineers try to make resistors heat up as little as possible to not waste power, but in a heater, this "waste" is a good thing. You can also use resistors for soldering electronics.
There are many different types of resistors you can find. They are all made with a resistive material encased in a non-conductive material, such as plastic. Fixed resistors are usually made of carbon encased in a plastic cylinder, with a connecting wire on either end. Most resistors used in electronics today are carbon resistors. Older resistors were made of other poorly conducting metals, in order to restrict the flow of charge.
Death Star
The Death Star is a fictional moon-sized space station and superweapon. It was invented for the "Star Wars" movies. It was a huge spherical space station which fired a ray of energy which could destroy a planet.
The details of the Death Star changed between different models during production of "". These changes include the position of the superlaser. The idea of the Death Star as a large, spherical space station was the same in all the models. The sound of the Death Star counting down until it fires comes from the "Flash Gordon" movies. Making a Death Star that was only partly built (but was still powerful) was a problem for Industrial Light & Magic's modelmakers for "". Only the front side of the 137-centimeter model was finished. The image was flipped horizontally for the final movie. Both Death Stars were created in the movies by using a full models, models of sections of the space station and matte paintings.
The first Death Star was shown in its finished form in "". It was commanded by Grand Moff Tarkin (Peter Cushing). The Death Star was the Galactic Empire's "ultimate weapon". The movie begins with Leia Organa (Carrie Fisher) attempting to take the station's plans to the Rebel Alliance, wanting to help them destroy the Death Star. Onboard her vessel, she was captured by an imperial ship and taken captive to the Death Star. There, Tarkin tries to make Leia reveal the location of the rebel base by threatening the use of the Death Star to destroy Leia's home world, Alderaan. She tells them a location but not the real one, but Tarkin has her planet destroyed anyway. Later, Luke Skywalker (Mark Hamill) and his small crew are also captured and taken to the station, escaping with Leia shortly after. In the movie's main battle scene, the force ghost of Obi-wan Kenobi tells Luke to use the "Force" to help him direct proton torpedoes from his x-wing into the Death Star' reactor core and not with his ship's targeting system. Luke obeys and successfully launches the torpedoes into the core. This ultimately resulted in the destruction of the battle station.
"Return of the Jedi" takes place four years later. At this time, the Empire is building a new Death Star. It is half-finished in the movie. Emperor Palpatine (Ian McDiarmid) and Darth Vader (David Prowse/James Earl Jones) send the Rebels false information with the intention of trapping the Rebels, saying that the station's weapons systems are not fully functional. They also want to get Skywalker on board so they can turn him to the dark side of the Force. In the movie's climax, Vader throws Palpatine down one of the station's reactor core, apparantly killing him. However, Palpatine fires a large amount of sith lightning during this process and critically damages the electronics on Vader's suit that keeps him alive. Luke tries to get his father out of the battle station but he dies shortly after. Luke then takes Vader's body and leaves the Death Star just before it is destroyed by Lando Calrissian onboard the "Millennium Falcon."
The first Death Star is also dealt with in the "Star Wars" prequel trilogy. Its schematics are shown in "". At the end of "", the Death Star is shown starting to be built.
Doctor of Philosophy
The Doctor of Philosophy, (PhD, Ph.D., DPhil or D.Phil.) is a degree a person gets from a university by finishing a doctorate program. In many areas of study, the PhD/DPhil is the highest degree that a person can earn (this is called the "terminal degree"). There are PhD/DPhil degrees for many different fields, such as PhDs/DPhils in literature, philosophy, history, science, mathematics, and engineering. Some PhD/DPhil degrees have existed for hundreds of years, such as the PhD/DPhil in Canon Law. Other PhD/DPhil degrees were developed in the 1970s and 1980s, such as the PhD/DPhil in Computer Science.
To be admitted to a PhD/DPhil program, a person usually has to have completed their Bachelor's degree or master's degree that is related to the PhD/DPhil degree. For example, a person applying to be admitted to a PhD/DPhil degree in Theater would normally have to have a master's degree such as a Master of Arts (MA) degree in Theater, English Literature, or a related area.
The PhD/DPhil degree usually takes between three and six years of full-time study to complete. They may or may not require a master's degree beforehand. Many PhD/DPhil degrees begin with a period of graduate courses. After the PhD/DPhil student has taken these courses, they take examinations to test what the student knows about their area of study. After the student passes the exams, they begin to do original research. The product is a long research report called a dissertation (or a "thesis"). Some PhD/DPhil degrees also require students to pass exams in languages (such as French, German, or other languages). Many PhD/DPhil students teach undergraduate students or assist professors with research during their PhD/DPhil studies.
Requirements for university teaching vary in different subjects and in different countries. A PhD/DPhil is necessary or usual to become a university professor in many fields, especially in science. However, many famous professors have not had higher degrees, though that is less common today. In some fields, there is no PhD/DPhil, and so another degree is required to become a university professor. For example, the highest degree in Fine Arts fields such as printmaking or graphic design is the Master of Fine Arts (MFA) degree. A person with an MFA degree can become a university professor in some Fine Arts fields.
Global 200
The Global 200 is the list of ecoregions identified by the World Wide Fund for Nature (WWF) as priorities for conservation. According to the WWF, an ecoregion is defined as a "relatively large unit of land or water containing a characteristic set of natural communities that share a large majority of their species, dynamics, and environmental conditions (Dinerstein et al. 1995, TNC 1997)."
The WWF assigns a conservation status to each ecoregion in the Global 200: critical or endangered; vulnerable; and relatively stable or intact. Over half of the ecoregions in the Global 200 are rated endangered.
Ecoregion
An ecoregion (ecological region), sometimes called a bioregion, is the next smallest ecologically and geographically defined area beneath "realm" or "ecozone". Ecoregions cover relatively large area of land or water, and contain characteristic, geographically distinct natural communities and species. When defined by the World Wide Fund for Nature (WWF), the boundaries of an ecoregion approximate the original extent of the natural communities prior to any major recent disruptions or changes. The WWF has identified 825 terrestrial ecoregions, and approximately 450 freshwater ecoregions across the Earth.