Optical disk

Optical disk is a secondary storage unit which can store extremely large amount of data in a limited space. It is a random access system which consists of a rotating disk which is coated with a highly reflective material. For recording and retrieving data, laser beam technology is employed.  For this reason, optical disks are also known as laser disks. Optical disk has one long spiral track which starts at outer edge and spirals inward to the center. This is a main difference between this disk and magnetic disk where several concentric tracks exist. The optical disk track is split into various sectors.  Optical disks are very economical and with very small sizes ranging from 5 inches to 12 inches in diameter. The factors which influence storage capacity of an optical disk are number of sectors and number of bytes per sector. An optical disk has to be mounted on an optical disk drive before it can be used for reading and writing of information. This disk drive has provision to include all the mechanical, electrical and electronic components which facilitates reading and writing tasks. The different categories of optical disks are compact disk read only memory (CD-ROM), compact disk recordable (WORM-CD-R), compact disk rewritable (CD-RW) and digital video disk with read only memory (DVD-ROM). Since there is no mechanical heads in optical disks, damage due to crash is forbidden. The cost per bit of storage is very low and storage life is more than 30 years. Optical disks are ideal for storing and reading musical data. Optical disks are easy to handle, store and is portable. The main limitation of optical disk is its low data access speed. Optical disk drive mechanism is complicated and the option of reusability is forbidden in it.

Soil dynamics and earthquake engineering

The term soil has originated from the latin word solum which has different meanings. Soil dynamics deals with the study of material properties of soil under dynamic stress. Knowledge of classical dynamics of elastic continuum and dynamics of vibrations are required for the effective soil dynamics study. Since soils and rocks are naturally occurring materials, it is always preferred to have test on theses before use. Relying fully on structural handbook is not advisable. Earth quake motion dynamics is usually expressed in terms of acceleration – time trace, velocity-time trace and displacement-time trace. There exist two methods for the evaluation of soils- deterministic and non-deterministic. Since the soil dynamics and earth quake engineering are very much inter related, it lead to the emergence of new branch of engineering- geotechnical earthquake engineering. In majority of the cases, motion of the soil causes earthquakes. The motion of the soil is transmitted to the structure leading to damages. In seismic zone, study of the motion of soil or soil dynamics is very significant and for any earthquake resistant design of structures, seismic data plays a major role.

Different hydro power plants

Run-of-river plants: Here stream should be perennial with minimum flow which is adequate to generate sufficient power. Thus power generation is achieved with the utilization of minimum flow.

Storage plants: Here reservoir water storage is achieved by constructing a dam across a river. Storage is done during high rainfall season.

Cascade plant: Here available water is used more than once in a series of hydel power plants constructed to utilize the available drop in the head.

Pumped storage plant: Here power generation is carried out using the water stored in the upper reservoir during the period of low rainfall.

Tidal power: Water can be stored in a basin during high tide which can be made to fall into sea during low tide through some turbines to produce water.

Electronic mail protocols

Two types of protocols are used for the transmission of electronic mail. They are SMTP and MIME. SMTP supports only text messages while MIME supports both text message transmission and multimedia information transmission. SNMP is simple network management protocol which is designed to operate in both the TCP/IP and OSI environments. Simple mail transfer protocol (SMTP) which is defined in RFC 821 is the standard protocol for the transfer of mail between hosts in the TCP/IP environment. Here user creates mail which is comprised of a header that includes recipient’s e-mail address and other information and a body containing the message to be sent. These messages act as input to SMTP sender program. This program is usually an always-present server program on the host. Multipurpose internet mail extensions (MIME) which is an extension to the RFC 822 framework support multimedia information transfer. In MIME, five new message header fields are defined. It also defines a number of content formats and transfer encodings. The five header fields defined in MIME are MIME version, content type, content-transfer encoding, content-ID and content-description. Different MIME content type formats are test type, multipart type, message type, image type, video type, audio type and application type. MIME transfer encodings provides reliable delivery across the largest range of environments. The different MIME transfer encodings are 7-bit, 8-bit, binary, quoted-printable, base 64 (radix-64) and x-token.

Computer networks

Computer networks are now common in educational institutions, offices and even in homes. Companies which have large number of computers prefer a network between these computers to access data from one another. By the effective resource sharing, management can reduce the manpower as well as time. This also reduces the peripherals such as printer. Thus in an office a high volume networked printer can perform the work of many individual printers. This reduces cost as well as maintenance complexity. Servers are used in big offices which can store enormous amount of data. Thus client-server model is used for large network-huge data systems. World Wide Web uses this model. Electronic mail or e-mail is used for communication. Videoconferencing is a latest tool by which employees at different locations can interact with each other just like in a meeting. For doing business including buy and sell, electronic commerce is used. Internet is a network now used by individuals sitting at home. Mobile phones and laptops opened the door for accessing internet while travelling too.

History of LASER

LASER is the short form of light amplification by stimulated emission of radiation. LASER is a highly coherent, highly monochromatic, high intensity unidirectional source of light. Ruby laser was the first fabricated laser. Maiman operated it for the first time. Later Sorokin and Stevenson fabricated Uranium-calcium fluoride laser. In 1961, Neodymium: glass laser was fabricated by Snitzer and Neodymium: CaWO4 laser by Johnson. After 4 years, Johnson and team succeeded in the fabrication of Neodymium:YAG laser and Holmium: YAG laser. The working of Holmium laser is based on the cascade energy transfer phenomena. This enhances lasing efficiency. Later GaAs lasers were fabricated which are quite economical, efficient, compact and portable. Now many types of laser exist in the market that cover a wide range of wavelength from ultraviolet to infrared and with wide variety of output power. The main components of a laser system are active medium, pumping unit, cavity resonator and a cooling system.

Street lighting

Street lighting is an important thing to be implemented with utmost care and vision since this affects both motorists and pedestrians. The main reason for accident during night is poor street lighting. The major varieties of street lamps used are tungsten filament lamps, tubular fluorescent lamps, sodium vapour discharge lamps and mercury high pressure discharge lamps. Tungsten filament lamps are suitable for minor residential streets and pedestrian walk-ways. Tubular fluorescent lamps are best for shopping streets. Sodium vapour discharge lamps and mercury vapour discharge lamps are widely used nowadays in the streets of India. These lamps are highly efficient and have longer life span. Different treatments and skilled method has to be employed while designing lighting at bends or curves, bridges and tunnels.