A DVD (which means Digital Versatile Disc or a Digital Video Disc) is an optical disc capable of storing up to 4.7 GB of data, more than six times what a CD can hold. DVDs are often used to store movies at better quality than a VHS. DVDs can also have interactive menus and bonus features such as deleted scenes and commentaries. Like CDs, DVDs are read with a laser.
The disc can have one or two sides, and one or two layers of data per side; the number of sides and layers determines how much it can hold. A 12 cm diameter disc may have one of the following storage capacities:
There are also 8 cm DVDs with a storage capacity of 1.5 GB.
The capacity of a DVD-ROM can be visually determined by noting the number of data sides, and looking at the data side(s) of the disc. Double-layered sides are usually gold-colored, while single-layered sides are usually silver-colored, like a CD. One additional way to tell if a DVD contains one or two layers is to look at the center ring on the underside of the disc. If there are two barcodes, it is a dual layer disc. If there is one barcode, there is only one layer.
Both CD and DVD discs have equal sizes (diameter, thickness etc.). However, the amount of information they can store is different. These discs are made of the same materials and have the same methods of production.
CDs and DVDs use the same way of keeping information. Both CDs and DVDs have pits and bumps on the data track (the data track represents a path which has certain information). The information is read by a laser.
A DVD disk has several layers, which are made of plastic. All layers have a thickness of 1.2 millimeters. An injection used on a polycarbonate plastic leads to the creation of microscopic bumps. Today's production uses this type of plastic to create different things because it can resist very high and low temperatures.
When layers are made, the bumps appear. Many bumps form one continuous spiral that can include information. After that a spray of a special reflective layer covers the bumps.
Aluminum is applied behind inner layers and semi-reflective gold covers the outer layers. This helps the laser to concentrate through the outer layers onto the inner ones. Then, after applying a protective liquid (lacquer) and pressing the layers, they are treated with infrared light.
Every track on a DVD disk circles from its center to the edge. The distance between the tracks on a DVD disk is 740 nanometers. Only a very precise mechanism can read the bumps on the disk, because they are very small (320×400×120 nanometers).
The aluminum side of the disk has pits, but the side which is read by the laser has bumps. Because the size of the bumps are very small, a DVD track is very long. A data track of a DVD layer is about 7.5 miles long. This is the length of an ordinary DVD disk. The track of a disc with two sides would be about 30 miles long.
Submarine
A submarine (or Sub) is a vessel that goes underwater. Most large submarines are war vessels. Some small ones are used for scientific or business purposes. These are often called "submersibles" and cannot go far or stay long away from base. Some people buy their own to explore under the sea. A submarine is actually a boat, not a ship.
Early submarines were often powered by hand. This is because boat engines had not been invented yet. They were almost always made for war. Submarines would try to sink enemy ships by crude methods. These included drilling screws into their wooden hulls. Some tried to blow up a ship. This often destroyed the submarine, too. At the end of the 19th century, the Whitehead torpedo and electrical systems allowed much better submarines.
These better submarines were much used during the First and Second World Wars. Many of these better submarines were created by Germany, called U-boats. The submarines were powered by a diesel-electric system. A diesel motor would be used to turn a generator. The generator would charge a large battery while the submarine was on the surface. The power in the battery was then used by the submarine when it went underwater. These submarines were dangerous to enemies. They were hard to see while underwater but it was easy to attack them when they surfaced to recharge. Many modern boats still use this diesel-electric propulsion system.
The First Battle of the Atlantic was the first major battle that was mainly fought between submarines and their enemies. As in later wars, the main jobs of submarines were to enforce a blockade and to sink enemy warships. They usually attacked freighters at night, shooting with their deck guns and then hiding under the water. Sometimes they used their torpedoes, which they could fire while underwater, especially against larger ships and warships. During World War II The US Navy lost around 52 submarines due to combat and non-combat causes.
After World War II better sonar helped the enemies of submarines to find and destroy them. New subs were more streamlined and had no deck guns because water dragging against the guns made noise underwater and slowed the subs.
Most large modern military submarines are powered by nuclear reactors. These submarines often have a system which can get air from the seawater. These two things allow them to stay underwater for long periods of time. Their most important uses are attacking ships or launching missiles. These include cruise missiles and nuclear missiles. There are two main kinds of subs. Attack submarines are small and fast. They attack other subs and surface ships with torpedos. Missile subs are larger and slower. They are built to shoot missiles at far-away targets on land.
Lebanon
Lebanon is a country in the Middle East, on the Mediterranean Sea. It has a border with Israel to the south, and Syria to the east and north. Lebanon has been independent since 1943. Its capital city is Beirut.
Lebanon has two chains of mountains. It is often called the ruby of the Middle East. It has a coastline stretching all the way up. The area of Lebanon is 10,452 square kilometres.
Over 6.8 million people live in Lebanon. The people mostly speak Arabic. About 54% of Lebanese people are Muslim and 40.5% are Christian. There are 16 million Lebanese people living in other countries. Lebanon is a very westernized country.
The national symbol in Lebanon is the Cedar tree, because many of them grow in the Lebanon Mountains.
Lebanon is divided into six governorates. These are divided into twenty-five districts. The districts are also divided into several municipalities. The governorates and their districts are listed below:
Alan Alda
Alan Alda (real name: Alfonso Joseph D'Abruzzo) (born January 28, 1936) is an American actor. His mother was of Irish ancestry; his father was of Italian ancestry.
He directed, wrote and starred in many movies. He is probably most famous for his role as "Hawkeye" Pierce, the central character on the comedy/drama TV series "M*A*S*H", as well as writing and directing several episodes of the show, and later becoming one of its producers. Alan also hosted "Scientific American Frontiers" on PBS from 1993 to 2005.
His father, Robert Alda, was an actor, and his mother, Joan, was once crowned Miss New York. Alan has been married to Arlene Weiss since 1957 and they have three daughters and a son.
In 2015, Alda was diagnosed with Parkinson's disease. That same year, he starred in Steven Spielberg's "Bridge of Spies". In 2019, he starred as lawyer Bert Spitz in "Marriage Story".
Sally Kellerman
Sally Kellerman (June 2, 1937) is an American movie actress. She was born in Long Beach, California. Her acting performances include the pilot for the original "Star Trek" television series, and the movies "MASH" (1970) and "Back to School" (1986).
Hagar the Horrible