Tuesday, June 12, 2012

Wireless and Mobile Networks




Wireless and Mobile Networks


Click here to start



Table of Contents




http://www.cse.wustl.edu/~jain//cse473-09/ftp/i_6wmn/index.htm
Thanks to :
Author: Raj Jain
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Tuesday, June 5, 2012

How Soap is made ?



Soap is a combination of animal fat or plant oil and caustic soda. When dissolved in water, it breaks dirt away from surfaces. Through the ages soap has been used to cleanse, to cure skin sores, to dye hair, and as a salve or skin ointment. But today we generally use soap as a cleanser orperfume.
The exact origins of soap are unknown, though Roman sources claim it dates back to at least 600 B.C. , when Phoenicians prepared it from goat's tallow and wood ash. Soap was also made by the Celts, ancient inhabitants of Britain. Soap was used widely throughout the Roman empire, primarily as a medicine. Mention of soap as a cleanser does not appear until the second century A.D. By the eighth century, soap was common in France, Italy, and Spain, but it was rarely used in the rest of Europe until as late as the 17th century.
Manufacture of soap began in England around the end of the 12th century. Soap-makers had to pay a heavy tax on all the soap they produced. The tax collector locked the lids on soap boiling pans every night to prevent illegal soap manufacture after hours. Because of the high tax, soap was a luxury item, and it did not come into common use in England until after the tax was repealed in 1853. In the 19th century, soap was affordable and popular throughout Europe.
Early soap manufacturers simply boiled a solution of wood ash and animal fat. A foam substance formed at the top of the pot. When cooled, it hardened into soap. Around 1790, French soapmaker Nicolas Leblanc developed a method of extracting caustic soda (sodium hydroxide) from common table salt (sodium chloride), replacing the wood ash element of soap. The French chemist Eugene-Michel Chevreul put the soap-forming process (called in English saponification) into concrete chemical terms in 1823. In saponification, the animal fat, which is chemically neutral, splits into fatty acids, which react with alkali carbonates to form soap, leaving glycerin as a byproduct. Soap was made with industrial processes by the end of the 19th century, though people in rural areas, such as the pioneers in the western United States, continued to make soap at home.

Raw Materials

Soap requires two major raw materials: fat and alkali. The alkali most commonly used today is sodium hydroxide. Potassium hydroxide can also be used. Potassium-based soap creates a more water-soluble product than sodium-based soap, and so it is called "soft soap." Soft soap, alone or in combination with sodium-based soap, is commonly used in shaving products.
Animal fat in the past was obtained directly from a slaughterhouse. Modern soapmakers use fat that has been processed into fatty acids. This eliminates many impurities, and it produces as a byproduct water instead of glycerin. Many vegetable fats, including olive oil, palm kernel oil, and coconut oil, are also used in soap making.
Additives are used to enhance the color, texture, and scent of soap. Fragrances and perfumes are added to the soap mixture to
The above illustrations show the kettle process of making soap.
The above illustrations show the kettle process of making soap.
cover the odor of dirt and to leave behind a fresh-smelling scent. Abrasives to enhance the texture of soap include talc, silica, and marble pumice (volcanic ash). Soap made without dye is a dull grey or brown color, but modern manufacturers color soap to make it more enticing to the consumer.

The Manufacturing
Process

The kettle method of making soap is still used today by small soap manufacturing companies. This process takes from four to eleven days to complete, and the quality of each batch is inconsistent due to the variety of oils used. Around 1940, engineers and scientists developed a more efficient manufacturing process, called the continuous process. This procedure is employed by large soap manufacturing companies all around the world today. Exactly as the name states, in the continuous process soap is produced continuously, rather than one batch at a time. Technicians have more control of the production in the continuous process, and the steps are much quicker than in the kettle method—it takes only about six hours to complete a batch of soap.

The Kettle Process

Boiling

  • 1 Fats and alkali are melted in a kettle, which is a steel tank that can stand three stories high and hold several thousand pounds of material. Steam coils within the kettle heat the batch and bring it to a boil. After boiling, the mass thickens as the fat reacts with the alkali, producing soap and glycerin.

Salting

  • 2 The soap and glycerin must now be separated. The mixture is treated with salt, causing the soap to rise to the top and the glycerin to settle to the bottom. The glycerin is extracted from the bottom of the kettle.

Strong change

  • 3 To remove the small amounts of fat that have not saponified, a strong caustic solution is added to the kettle. This step in the process is called "strong change." The mass is brought to a boil again, and the last of the fat turns to soap. The batch may be given another salt treatment at this time, or the manufacturer may proceed to the next step.

Pitching

  • 4 The next step is called "pitching." The soap in the kettle is boiled again with added water. The mass eventually separates into two layers. The top layer is called "neat soap," which is about 70% soap and 30% water. The lower layer, called "nigre," contains most of the impurities in the soap such as dirt and salt, as well as most of the water. The neat soap is taken off the top. The soap is then cooled. The finishing process is the
    Developed around 1940 and used by today's major soap-making companies, the above illustrations show the continuous process of making soap.
    Developed around 1940 and used by today's major soap-making companies, the above illustrations show the continuous process of making soap.
    same as for soap made by the continuous process.

The Continuous Process

Splitting

  • 1 The first step of the continuous process splits natural fat into fatty acids and glycerin. The equipment used is a vertical stainless steel column with the diameter of a barrel called a hydrolizer. It may be as tall as 80 feet (24 m). Pumps and meters attached to the column allow precise measurements and control of the process. Molten fat is pumped into one end of the column, while at the other end water at high temperature (266°F [130°C]) and pressure is introduced. This splits the fat into its two components. The fatty acid and glycerin are pumped out continuously as more fat and water enter. The fatty acids are then distilled for purification.

Mixing

  • 2 The purified fatty acids are next mixed with a precise amount of alkali to form soap. Other ingredients such as abrasives and fragrance are also mixed in. The hot liquid soap may be then whipped to incorporate air.

Cooling and finishing

  • 3 The soap may be poured into molds and allowed to harden into a large slab. It may also be cooled in a special freezer. The slab is cut into smaller pieces of bar size, which are then stamped and wrapped. The entire continuous process, from splitting to finishing, can be accomplished in several hours.

Milling

  • 4 Most toiletry soap undergoes additional processing called milling. The milled bar lathers up better and has a finer consistency than non-milled soap. The cooled soap is fed through several sets of heavy rollers (mills), which crush and knead it. Perfumes can best be incorporated at this time because their volatile oils do not evaporate in the cold mixture. After the soap emerges from the mills, it is pressed into a smooth cylinder and extruded. The extruded soap is cut into bar size, stamped and wrapped.

Byproducts

Glycerin is a very useful byproduct of soap manufacture. It is used to make hand lotion, drugs, and nitroglycerin, the main component of explosives such as dynamite.

Where To Learn More

Books

Cavitch, Susan M. The Natural Soap Book: Making Herbal and Vegetable-Based Soaps. Storey Communications, 1995.
Maine, Sandy. The Soap Book: Simple Herbal Recipes. Interweave Press, 1995.
Spitz, Luis, ed. Soap Technologies in the 1990s. American Oil Chemists Society, 1990.

Other

About Soap. Procter & Gamble, 1990. (513) 983-1100.
— Sheila Dow
Thanks to:
http://www.madehow.com/Volume-2/Soap.html#b
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Tuesday, May 15, 2012

Setting up a Linksys router with Cable Internet service



Title: Setting up a Linksys router with Cable Internet service

Article ID: 3686


This article will discuss how to manually set up a Linksys router with a Cable Internet service.  For Linksys E-Series routers and Valet Hotspots, it is recommended to use the Cisco Connect software to initially set up the router.
QUICK TIP:  If you are unsure about the type of Internet connection you have, contact your Internet Service Provider (ISP).
To set up a Linksys router with Cable connection, you need to perform four (4) steps using the computer that is registered with the ISP:
QUICK TIP:  To reconfigure a previously used router, reset the router to factory default settings before doing the following procedure.  To learn how to reset your router, clickhere.
Verifying Internet connection
Connect the computer to the Cable modem using an Ethernet cable without the router installed.  If your computer is getting Internet connection, you may proceed with the next step.  Otherwise, contact your ISP.
NOTE:  Some Cable modems have their USB ports configured by the ISP to give your computer the Internet connection.  If the physical connection is through a USB port, you will not be able to go online using an Ethernet connection.  Contact your ISP to have the Ethernet port of the modem configured.
NOTE:  The image may vary depending on the computer and modem you’re using.
Connecting devices together
NOTE:  Images may vary depending on the type of computer and router model you are using.  In this example, Linksys E4200 and a laptop computer are used.
Step 1:Connect the Cable modem to the router’s WAN or Internet port.
Step 2:Connect a computer to any of the numbered ports (1, 2, 3 or 4).  If you are using a wireless computer, you will need to connect it first with an Ethernet cable.
NOTE:  In this example, a computer is connected to port number 2.
Step 3:Connect the power adapter of your router to the power outlet.
Checking the router's LEDs
After connecting the devices together, check the lights on the front panel of the router.  Ensure that the lights corresponding to the ports where the Ethernet cords are connected to are lit.  For further instructions, click here.
Configuring a Linksys router for Cable Internet connection
Step 1:Access the router’s web-based setup page.  For instructions, click here.
NOTE:  If you are using a Mac computer to access the router’s web-based setup page, click here.
Step 2:On the Setup tab, click the MAC Address Clone sub-tab.
Step 3:Select Enabled then click on Clone My PC’s MAC.
 
Step 4:Click .
Checking Internet connection status
Once the MAC Address Clone feature is enabled, Internet status should be active.  To check the Internet Connection status, follow the procedure below.
NOTE:  Ensure that the Internet Connection Type is set to Automatic Configuration – DHCP.
Step 1:Click on the Status tab.
 
Step 2:Check the Internet IP Address.  If it has numbers, this means the router has been properly configured.
NOTE:  If the Internet IP Address values are showing up 0.0.0.0, click on Release IP Address then the Renew IP Address buttons.
 
NOTE:  For wireless-B and wireless-G routers, click on the DHCP Release and DHCP Renew buttons.
You should now be able to access the Internet.  If not, powercycle the modem, the router then the computer.  To know how, follow the steps below:
IMPORTANT:  You should do the following procedure with caution since most Cable modems run together with the phone line and Cable TV connection.  Most Cable modems also have backup batteries that may prevent it from being powered OFF even if the power adapter is detached from it.  Refer to your ISP for detailed instructions on powercycling the modem. 
To perform the powercycle process:
Step 1: Power OFF the modem.
Step 2: While the modem is powered OFF, unplug the power adapter from the router and shutdown your computer.
Step 3: Power ON the modem and wait for its lights to go steady.
Step 4: Power ON the router, wait for its lights to go steady, then turn ON the computer.
Your Internet connection should now be active.  If you’re still unable to go online, contact your ISP to reconfigure the modem.
NOTE:  Most Cable Internet Service Providers (ISP) use Media Access Control (MAC) Address authentication to establish Internet connection to Internet subscribers.  A MAC address is a unique identifier pre-assigned to the network adapter/s of the computer.  When you connect a computer directly to the Cable modem, the Internet Service Provider (ISP) verifies if the MAC address is allowed to obtain Internet access.  All routers also have a unique MAC address.
If this MAC address is not recognized by the Cable Internet Service Provider, you will not be able to share Internet connection using a router.  To set up your Linksys router to work with a Cable ISP, you have to enable the MAC Address Clone feature using the router’s web-based setup page.  This feature will allow your ISP to recognize the router as the computer with the registered MAC address.

  
Related Articles:

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Wednesday, April 25, 2012

CSMA/CA


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Technical Enhancements of 802.11n


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Power Save Mechanisms Supported in IEEE 802.11 Protocol


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Sunday, April 15, 2012

How to Compile a C Program Using the GNU Compiler (GCC)




  1. In order to see if you have the GNU C/C++ compiler installed on your system
    • Type/Copy/Paste: gcc --version
    • If the command is not found, it is likely that gcc/g++ isn't installed.
  2. 3
    Install gcc/g++ on your system, consult your Unix or GNU/Linux distribution documentation for the appropriate installation method. If you are using Microsoft Windows, please see the following installation method used to install MinGW GNU C/C++ compiler for Microsoft Windows How to install MinGW( Minimalist GNU C/C++ Compiler) on Microsoft Windows
  3. 4
    First, create a working directory using the following command:
    • Type/Copy/Paste: mkdir CCPP
  4. 5
    Second, change into the directory
    • Type/Copy/Paste: cd CCPP
  5. 6
    Third, use a text editor such as nano, gedit, vi, notepad,(on Microsoft Windows ) for example,
  6. 7
    Unix/GNU/Linux Instructions:
    • Type/Copy/Paste: nano main.c
    • Type/Copy/Paste: gedit main.c
    • Type/Copy/Paste: vi main.c
  7. 8
    Windows Instructions:
    • Type/Copy/Paste: notepad main.c
    • You can use notepad as a text editor on Microsoft Windows
  8. 9
    Enter the following source code below:
  9. 10
    Type/Copy/Paste:
    • #include
    • #include
    • int main()
    • {
    • printf("Hello World\n");
    • return(0);
    • }
  10. 11
    Once this task is complete save the source code as a text file in your editor asmain.c
  11. 12
    Fourth, compile the file by issuing the following command
    • Type/Copy/Paste:
    • gcc main.c -o HelloWorld
  12. 13
    Fifth, run the command by issuing the following command
  13. 14
    Unix/GNU/Linux instructions:
    • Type/Copy/Paste: ./HelloWorld
  14. 15
    Microsoft Windows Instructions:
    • Type/Copy/Paste: HelloWorld.exe
    • On Windows when the HelloWorld.c file is compiled it will usually have an .exe extention.
  15. 16
    To compile multiple files:
    • Type/Copy/Paste:
    • gcc -o outputfile file1.c file2.c file3.c
  16. 17
    To compile with more error checking using the -Wall tag:
    • Type/Copy/Paste:
    • gcc -Wall -o outputfile file1.c
  17. 18
    To compile files without linking them:
    • Type/Copy/Paste:
    • gcc -c file1.c file2.c file3.c
    • After the last step, if you want to link them, type: gcc -o outputfile file1.o file2.o file3.o


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Sunday, April 8, 2012

How will determine if a station is connected to an Access point in HT20 or HT40 ( in a linux based Systems)



Getting link status



To determine if you are connected to an AP or not and if you are the last TX rate used you can use the command below.
Example output when associated to a legacy (non-802.11n) AP:
iw dev wlan0 link
Connected to 04:21:b0:e8:c8:8b (on wlan0)
        SSID: attwifi
        freq: 2437
        RX: 2272 bytes (18 packets)
        TX: 232 bytes (3 packets)
        signal: -57 dBm
        tx bitrate: 36.0 MBit/s
Example output when associated to an 802.11n AP:
iw dev wlan0 link
Connected to 68:7f:74:3b:b0:01 (on wlan0)
        SSID: tesla-5g-bcm
        freq: 5745
        RX: 30206 bytes (201 packets)
        TX: 4084 bytes (23 packets)
        signal: -31 dBm
        tx bitrate: 300.0 MBit/s MCS 15 40Mhz short GI
Example output when not connected to an AP:
iw dev wlan0 link
Not connected.
This would happen if you are not connected to an AP. To connect to an AP you can use iw connect if the connection requires:
  • No encryption
  • Uses WEP for encryption
If you need to connect to an AP with WPA or WPA2 encryption requirements then you must usewpa_supplicant.

Thanks to : 
http://wireless.kernel.org/en/users/Documentation/iw
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