Radon is radioactive, meaning that it can give off harmful rays. Some people have high levels of radon in their houses, and this can be very dangerous. A lot of radon can get stuck in the basement of old houses, and so people end up breathing it in. It gets stuck in the lungs and has been known to cause cancer. There are groups that try to make sure there is no dangerous radon in houses.
FTP
FTP, also known as File Transfer Protocol, is a communication protocol for the rapid, simple transmission of files across a network supporting the TCP/IP. This network is generally the Internet, or a local network. FTP is a way of accessing files on another computer. FTP uses the Client-Server architecture, meaning that there is a server, that holds the files, and does the authentication, and a client, or the end-user, who is accessing the files. The server listens on the network for connection requests from other computers. The client can make a connection to the FTP server by using FTP client software. Once connected and authenticated (via rsh or SFTP) the client can do things such as uploading files to the server, downloading files (taking the server's files and putting them on his own computer) from the server, and renaming, deleting files on the server, changing file permissions, etc.
Most modern operating systems support FTP. This implies that any computer connected to a TCP/IP based network can manipulate files on another computer on that network regardless of which operating systems are involved, provided that they are open to FTP connections. There are many existing FTP client and server programs, many of these are available free, or open source.
FTP connection is also seen in cellular phones when trying to transfer or receive data from a computer nearby.
FTP server return codes show their status by the digits within them. A short explanation of various digits' meanings are given below:
FTP may run in "active" or "passive" mode, which determines how the data connection is established. In both cases, the client creates a TCP control connection from a random, usually an unprivileged, port N to the FTP server command port 21.
Some popular open source FTP server implementations are:
Hypertext Transfer Protocol
Hypertext Transfer Protocol (often abbreviated to HTTP) is a communications protocol. It is used to send and receive webpages and files on the internet. It was developed by Tim Berners-Lee and is now coordinated by the W3C. HTTP version 1.1 is the most common used version today. It is defined in RFC 2616.
HTTP works by using a user agent to connect to a server. The user agent could be a web browser or spider. The server must be located using a URL or URI. This always contains http:// at the start. It normally connects to port 80 on a computer.
A more secure version of HTTP is called HTTPS (Hypertext Transfer Protocol Secure). This contains https:// at the beginning of the URL. It encrypts all the information that is sent and received. This can stop malicious users such as hackers from stealing the information and is often used on payment websites. HTTPS uses port 443 for communication instead of port 80.
The request message contains the following:
The request line and headers must all end with two characters: a carriage return followed by a line feed, often written <CR><LF>. The empty line must consist of only <CR><LF> and no other whitespace. In the HTTP/1.1 protocol, all headers except Host are optional.
A request line containing only the path name is accepted by servers to maintain compatibility with HTTP clients before the HTTP/1.0 standard.
Ethernet
Ethernet is a way of connecting computers together in a local area network or LAN. It has been the most widely used method of linking computers together in LANs since the 1990s. The basic idea of its design is that multiple computers have access to it and can send data at any time. This is comparatively easy to engineer.
If two computers send data at the same time, a collision will occur. When this happens, the data sent is not usable. In general, both computers will stop sending, and wait a random amount of time, before they try again. A special protocol was developed to deal with such problems. It is called Carrier sense multiple access with collision detection or CSMA/CD.
There are different Ethernet standards. Today, Ethernet cables look like thick telephone cables. They connect to boxes called hubs or switches. Each cable runs from a computer's network interface card (NIC) to such a box. This cable is called 10BaseT or 100BaseT, or 1000BaseT Cable.
All cable types:
Today, the cables for 10BaseT, 100BaseT, and 1000BaseT are the same. Their transmission medium is unshielded twisted pair for Category 5 (UTP-Cat5) or 5e. Shielded cable (STP-Cat5 or Cat5e) can be used when there is a lot of electrical noise, and Category 6 (UTP-Cat6 or STP-Cat6) works better with faster signals such as 1GBit or 10GBit.
Other devices, such as video game consoles, can also be connected using the same kind of cabling. Certain computer peripherals, for example printers and certain hard disks can be directly connected to the network with such cables.
Ethernet can go at different speeds. In the beginning, Ethernet was at 10 MBits per second. The Ethernet most often used today is at 100 MBits per second. Most new computers now have the NIC built in, and can go at 1GBit per second. There are also standards for 1GBit per second and 10 GBit per second. 100 MBit can usually talk to 10 MBit, and 1 GBit can talk to 100 MBit and usually to 10 MBit (both full and half duplex).
Obesity
Obesity is the condition of being much too heavy for one's height so that one's health is affected. In other words, it means to be too overweight. Also known as being fat. It is considered a disease and has been described as an epidemic.
To know if a person is overweight, the body mass index (BMI) is calculated, by dividing the person's weight (in kilograms), by their height (in metres) squared (multiplied by itself). (This is only meaningful for adults who are fully grown, and should not be used for children. Growth charts can be used to measure obesity in children.)
A BMI between 18.5 and 25 is considered "normal". People with a BMI of 25 or more are said to be overweight; with 30 and above, they are considered obese, and with 35 and above, they are considered "severely obese" (this used to be called "morbidly obese"). In general, the BMI number is a good quantifiable measurement of a person's obesity. However, it is a poor predictor in people who are very athletic, because a person with a higher than average amount of muscle tissue will weigh more than an average person, thus resulting in a BMI that is higher than normal, even if that person is very large.
The most common cause for obesity is getting more calories than are used by the body. Other factors that often contribute to obesity are:
Genetics are known to contribute to obesity. Leptin is a hormone that is linked to obesity.
Many health problems are associated with obesity. An example is Type 2 diabetes. A woman with a BMI higher than 35 is 93 times more likely to develop diabetes. A 2009 review found that people with a BMI between 40 and 50 were 22.5 times more likely to die from diabetes than people with BMIs between 22.5 and 25.
An obese woman is more likely to have an unhealthy baby.
Risk is associated with where the excess fat is stored on the body. Abdominal obesity is particularly dangerous.
Some people think that the idea that obesity causes bad health is not completely true and has been exaggerated. An example is J. Eric Oliver. He wrote a book called "Fat Politics: The Real Story Behind America's Obesity Epidemic". There is evidence for this belief.