Solar pond

Solar pond is an artificial pond which is constructed in such a way that temperature rise at lower regions are facilitated by preventing convection. Dissolving salt in the water is the best method to prevent convection which also maintains a good concentration gradient. Such ponds are known as salt gradient solar pond. Some other commonly constructed solar ponds are gel solar pond and equilibrium solar pond. The experiment with solar pond was first initiated by Tabor in Israel about 50 years ago. India’s largest solar pond is situated at Bhuj, Gujarat. A thick durable plastic liner is laid at the bottom of the pond to facilitate long term storage. Low density polyethylene, high density polyethylene, woven polyester yarn and hypalon reinforced with nylon mesh are used for this. Commonly used salts are magnesium chloride, sodium chloride and sodium nitrate. Concentration should be 30% at the bottom and zero at the top to obtain a good concentration gradient in the pond. During extraction of energy, hot water is removed continuously from the bottom. Solar pond is normally characterized by three zones- surface convective zone (SCZ), non-convective zone (NCZ) and lower convective zone (LCZ).

Asynchronous transfer mode (ATM)

Asynchronous transfer mode is a connection-oriented network. Here transmission is not synchronous. This was designed and introduced in the year 1990. ATM is effective in merging voice, data, cable television, telex, telegraph etc. and thus forming a single integrated system. ATM is widely used in the telephone system for moving IP packets. ATM networks support permanent virtual circuits which are permanent connections between two hosts. ATM transmits information in the form of small packets called cells. These cells are 53 bytes long. Here 5 bytes are header and remaining 48 bytes are payload. Part of the header is the connection identifier which allows each router to identify incoming cell. ATM hardware is capable of setting up one incoming cell to multiple output lines. This allows broadcasting of television program to multiple viewers. Since small cells do not block any line, quality of the service is guaranteed. ATM reference model is different from OSI model and TCP/IP model and consists of three layers. The ATM layer deals with cells and transportation of cells. ATM adaptation layer divides the packets and transmits the cells. The physical layer deals with voltages and bit timing. The ATM adaptation layer is further divided into segmentation and reassembly sublayer and convergence sublayer.

Ion selective electrodes

Ion selective electrodes are electrodes which respond to a wide range of selected ions. Glass electrode which measures hydrogen ion activity is an example. pH meters are used here to determine water purity. According to the ion species to be determined, glass membrane composition has to be changed. By this method, we can measure sodium, silver, potassium, ammonia and other univalent cations. The membrane is either a single crystal or a compacted disc in solid state electrodes. This membrane effectively isolates the reference solution from the solution under measurement. In fluoride ion measurement, lanthanum fluoride is used as membrane of solid state electrodes. In sulphide ion measurement, silver sulphide membrane is employed. There exists one more category of electrodes- heterogeneous membrane electrodes. These electrodes are similar to the solid state electrodes differing in one aspect-active material being dispersed in an inert matrix. In the latest version- liquid-ion exchange electrode, reference solution and the solution to be measured are separated by a porous layer containing an organic liquid of low water solubility.