Rodents

December 15, 2011 by · Leave a Comment 

tufailA rodent is a member of the mammalian order Rodentia, characterized by front teeth adapted for gnawing and cheek teeth adapted for chewing. The Rodentia is by far the largest mammalian order; nearly half of all mammal species are rodents. They are worldwide in distribution and are found in almost every terrestrial and freshwater habitat, from the shores of the Arctic Ocean to the hottest deserts. They are variously adapted for running, jumping, climbing, burrowing, swimming, and gliding. Many of them have dexterous forepaws, which they use as hands while sitting on their haunches in a position characteristic of many rodents. The great majority are under a few inches in length; the largest, the capybara, is about 4 ft (120 cm) long and 20 in. (50 cm) high at the shoulder.

Rodents have enlarged, chisel-shaped upper and lower front incisors that grow throughout their lives. These have hard enamel on the front surface and soft dentine on the back surface, so that unequal wear keeps the chisel edge sharp. There is a gap between the front teeth and the cheek teeth. When the lower jaw is in a forward position, for gnawing, the upper and lower incisors are in contact but the upper and lower cheek teeth are not; thus, wear on the cheek teeth is avoided. The cheeks are drawn in behind the incisors when the animal is gnawing, so that bits of hard material cannot be swallowed. When the lower jaw is pulled back into the chewing position, only the cheek teeth make contact.

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Static Electricity

February 11, 2010 by · Leave a Comment 

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Static electricity refers to the build up of electric charge on the surface of objects. The static charges remain on an object until they either bleed off to ground or are quickly neutralized by a discharge. Although charge exchange can happen whenever any two surfaces come into contact and separate, a static charge will only remain when at least one of the surfaces has a high resistance to electrical flow (an electrical insulator). The effects of static electricity are familiar to most people because we can see, feel and even hear the spark as the excess charge is neutralized when brought close to a large electrical conductor (for example a path to ground), or a region with an excess charge of the opposite polarity (positive or negative). The familiar phenomenon of a static ‘shock’ is caused by the neutralization of charge.

The materials we observe and interact with from day to day are formed from atoms and molecules that are electrically neutral, having an equal number of positive charges (protons, in the nucleus) and negative charges (electrons, in shells surrounding the nucleus). The phenomenon of static electricity requires a separation of positive and negative charges.

Removing or preventing a buildup of static charge can be as simple as opening a window or using a humidifier to increase the moisture content of the air, making the atmosphere more conductive. Air ionizers can perform the same task.

Items that are particularly sensitive to static discharge may be treated with the application of an antistatic agent, which adds a conducting surface layer that ensures any excess charge is evenly distributed. Fabric softeners and dryer sheets used in washing machines and clothes dryers are an example of an antistatic agent used to prevent and remove static cling.

Many semiconductor devices used in electronics are particularly sensitive to static discharge. Conductive antistatic bags are commonly used to protect such components, while people working on circuits containing them will often ground themselves using a conductive antistatic strap.

In the industrial settings such as paint or flour plants as well as in hospitals, antistatic safety boots are sometimes used to prevent a buildup of static charge due to contact with the floor. These shoes have soles with good conductivity. Anti-static shoes should not be confused with insulating shoes, which provide exactly the opposite benefit — some protection against serious electric shocks from the mains voltage.

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