Allergy is a state of hypersensitivity acquired through the exposure to a particular substance, called allergen. Spores, pollen, cat’s hair and proteins of egg, milk, and fish are some common allergens. The most common allergen is the house-dust mite.
Usually only parts of the body which are exposed to allergens show signs of allergy in the form of rashes or weals. However, if an allergen gets into the blood stream, it can cause reactions almost anywhere in the body.
Practically all allergies are caused by an over-reaction of the body’s defence mechanism when white blood cells react with allergens considering them as dangerous infectious organisms, it leads to allergy. Under normal conditions, the white blood cells (lymphocytes) on coming in contact with foreign substances like bacteria, viruses and proteinaceous matter produce what are called antibodies. The antibodies combine with the foreign substance and neutralize it. But when an antibody is formed against a harmless protein it attaches itself to mast cells which contain chemical— histamine. When the particular protein enters the body again, histamine is released. Due to the action of histamine blood capillaries are dilated, their walls become leaky and fluid from the blood comes out in the nearby tissues and they swell. The characteristic redness and itching in an allergy is due to dilation of blood capillaries.
Compact disc is a system of recording or storing of digital audio or video information using laser technology on a metal disc. The data is stored on a small aluminium disc in the form of microscopic pits etched by a laser beam. The stored information is read by using a laser beam which scans the rotating disc much like the replaying of phonograph records. The pits read as 0 and the smooth surface as 1, creating the sound digitally. As the laser beam does not wear out the surface, music replayed from an audio compact disc is without any distortion or noise and such music compact discs have virtually replaced phonograph records or turntables. The compact disc also allows recording and storage of text, pictures as well as sound simultaneously on a single disc and it has enormous capacity to store data. For example, the entire text and pictures contained in the 30-volume Encyclopedia Britannica can be stored on a single compact disc. Because of their versatility, adaptability and large storage capacity, compact discs are likely to be the choice medium for home entertainment and computer systems of the future.
Computer mouse is a device for manipulating figures on a computer screen without using a keyboard. It is an input mechanism that bears some resemblance to the animal. Computer operations often involve creating, selecting, or manipulating items on a screen. A computer mouse can perform these tasks by pointing or taking the cursor to the desired place, on the screen.
A cyclone is a low pressure area in the atmosphere in which the winds spiral inward in an anticlockwise direction. All cyclones are characterized by having an atmospheric pressure lowest at the centre and winds spiraling in towards this low pressure central zone called the ‘eye’. Cyclones are usually characterized by gusts of winds which may even go up to 250 kilometres/hour. In addition they are also accompanied by heavy rain. Along coastal areas they sometimes produce high tidal waves. In the southern hemisphere the winds blow in a clockwise direction. Cyclones are called hurricanes if they form in the West Indies and typhoons if they form in western Pacific.
Detergents are synthetic chemical salts which change the surface property of water and which are used as cleaning agents. Detergents contain one or more chemicals called surfactants, which reduce the surface tension of water by weakening the forces between water molecules. This enhances the cleaning action of water. A detergent molecule has two different parts. One part is hydrophilic (water-loving head) while the other is hydrophobic (water-hating tail). When soiled clothes are put in a detergent solution, water-loving head remains in water while the tail attaches to the grease or oil holding the dirt particles on the soiled material. Rubbing helps in breaking up the dirt. In this way the dirt particles are dislodged from the surface of the material and drawn into the wash water. After the dirt particles are suspended in water, a thin layer of surfactant remains around the particles keeping them separated. This prevents the dirt from settling on the washed material again. This is how detergents help in cleaning.
The El Nino is a narrow current of warm water that appears off the coast of Peru sometime in December-January and which lasts till March. The name literally means ‘The Child’ and refers to the Child Christ, apt because the appearance of the current coincides with Christmas. As it flows southward along the west coast of South America, it warms the cold waters of the coast of Ecuador and Peru.
Fax or facsimile is a device used for transmission of a written document, photograph, map or any other graphic material electronically. It is one of the variants of e-mail. For transmission the original document is placed in the facsimile or fax machine which scans the document and converts the written or graphic information into electronic signals and establishes a link-up with a similar receiving fax machine at the receiving end. The receiving fax reconverts the electronic signals into written or graphic form. As the sending machine scans the documents, the receiving machine reproduces the scanned image which is an exact duplicate of the originals. A typical fax machine can transmit a document of A-4 size in less than a minute over thousands of kilometres. Since fax operates through the normal telephone lines, the fax number is usually a telephone number. Also the same STD and ISD codes are used for sending a fax to another city or another country. The document is scanned page-by-page in the fax machine. Like the e-mail, fax communication eliminates the postal delay and is very convenient for communication between persons located in different time zones, but it costs more than the e-mail.
Atomic clock is a device for measuring time. It makes precise measurements of time. It makes use of the vibration of atoms or molecules, instead of quartz crystals or a coiled spring which are used in quartz and mechanical watches respectively, to measure time.
Acquired Immune Deficiency Syndrome (AIDS) is the most devastating and fatal disease of the 21st century. It is a viral disease caused by the Human Immune Deficiency Virus (HIV). What makes it different from other viruses is that, it strikes at the body’s own defence machinery (the immune system) that constantly fights the vast array of microbial enemies invading our bodies. The virus may remain dormant upto 10 years until some event activates it. On awakening, it disarms the immune system. With its main line of defence shattered, the body now falls easy prey to even the common infecting agents that it would otherwise ward off. The patient usually dies of these infections.
