Lasers in metrology

Lasers are widely used in metrology due to its unique high degree of monochromaticity. High monochromaticity yields clear interference fringes.  Low power He-Ne laser is preferred in metrological applications. In metrology, lasers are used in interferometry, holography and in scanning. Interferometry is a method used for the determination of distance by the proper measurement of wavelengths. Lasers are also used for machine tool calibration and alignment testing.  This method yields high accuracy and greater speeds. In a laser scanner, the object is mounted in a space between the laser source and a receiver. The receiver which contains a photo diode and a microprocessor computes dimension based on the shadow. Holography is a method based on interference and requires highly monochromatic light sources. Lasers are the automatic choice here. Holographic technique is widely used by automotive industry for the study of noise and vibration.

Cauvery river water dispute

Cauvery river water dispute is a main cause for tension in south India nowadays. Cauvery river is known as Ganga of the south. Harangi, Hemavathi, Kabani, Bhavani and Suvanavathi are the principal tributaries of Cauvery river. Cauvery river rises in western ghats near Talakaveri in Karnataka state. It merges into Bay of Bengal after flowing more than 800 kms through Karnataka and Tamilnadu states. The various projects executed and completed using Cauvery water are Krishnarajasagar, near Mysore in Karnataka, Mettur dam in Tamilnadu, Lower Bhavani in Tamilnadu and Cauvery delta system in Tamilnadu. Some of the important ongoing projects are Hemavathi, Harangi, Varuna and Kabini canals. In 1995, Supreme Court of India asked Cauvery water tribunal to take an appropriate decision on releasing water to Tamilnadu by Karnataka state. Tribunal ordered for release of 11 TMC water to Tamilnadu. A.B.Vajpayee during his primeministership conducted meeting of both Karnataka and Tamilnadu state political leaders and amicably settled the issue. Around 15 years after that there was no issues related to this. But now in the year 2012 again clashes between two states for Cauvery water restarted.

Radio wave propagation

Radio waves are used in long distance communication as carrier waves. Radio waves are mixed with the signal which is to be transmitted. This process is known as modulation. Radio waves are electromagnetic radiations. Radio waves always travel in straight paths in free space. Radio waves require very small time to travel and gets reflected if there is any object in their path. If there is any density change in the medium of travelling, radio waves undergo refraction. Radio waves can be produced by passing high frequency alternating current through an antenna. There exist three methods by which radio waves propagates through space. They are ground wave propagation (or surface wave propagation), sky wave propagation and space wave propagation. In ground wave propagation, transmitting and receiving antennas of radio waves are located very close to the surface of the earth. Ground wave propagation is used for medium-wave radio broadcasting. When radio waves travel in ionosphere, it is known as sky wave propagation. Space wave propagation or line-of-sight communication is used for VHF and UHF bands. This method is used in TV transmissions. 

Stroboscopic holography

Holography is the method of producing 3-dimensional image of an object by employing interference phenomenon. Idea of holography was first developed by Dennis Gabor in the year 1948. But since interference phenomenon badly required high quality coherent sources, this idea did not find any momentous applications.  After the invention of laser, holography attracted many researchers. The main limitation of holography is time averaging. To overcome this, stroboscopic holography technique can be used. Stroboscopic holography involves production of equal intensity fringes whose fringe width is proportional to amplitude. Measurement of relative phases of different points is also possible in this technique. The first step in stroboscopic holography is the recording of the hologram of a stationary object. Here exposure time is adjusted to get half of the final density. Now the object is vibrated and the light source chopped in synchronism. This illuminates the object and hologram stroboscopically. A synchronous motor can also be used to get synchronized stroboscopic illumination.

Control schemes and speed control

The three types of control schemes for an electric drive are manual control, semiautomatic control and fully automatic control. In a fan, manual control is employed where a starter and resistance is used for setting required speed. In semi-automatic control, some commands are manually controlled and some commands automatically. Automatic control electric drive consists of a control gear.

Electric drives are divided into four categories based on speed control. They are first group, second group, third group and fourth group. The first group drives provide uncontrolled constant speed of rotation during normal operating conditions.  The electric drives used in pumps, compressors and ventilators are first group drives. The second group electric drives provide step changes in speed during normal operating conditions. In each step, constant speed is maintained here. This type of drive is used in machine tools. The third group electric drive is used in electric locomotive where smooth speed control of the fraction motor is required. The third group provides smooth, narrow step speed control within certain ranges. Lifting devices use fourth group electric drives where drives are capable of providing speed control for fixed positions of the load.

Liquid limit and plastic limit of soil

Soil is an essential ingredient in agriculture and building construction. Soil has to be tested properly before using it. Liquid limit and plastic limit are two important parameters of soil. Liquid limit which is expressed in % is the water content at which the soil transforms from zero strength state to infinitesimal strength state. It is very difficult to determine accurately the actual liquid limit value. Plastic limit which is also expressed in % is the moisture content at which the soil has the smallest plasticity. Beyond plastic limit, soil behaves like a semi solid. The difference in moisture content between the liquid and plastic limit is termed as the plasticity index. Plasticity chart is a chart between liquid limit and plasticity index of soil materials. Liquid limit and plastic limit values are used for the classification of fine-grained soils. For the determination of plastic limit and liquid limit, we require a casagrande liquid limit device, a glass plate, a rod, a grooving tool, a spatula, some water containers, a wash bottle, a mixing bowl, a sensitive balance and a drying oven.

Science of vibration

Vibration science is a subject which deals with oscillatory motion of dynamic systems and various forces associated with them. Vibration is a virtue in some areas while it is a cause of concern in some other areas. In machines and structures, vibration causes undesirable effects. But in some machines, presence of vibration is essential. Examples are washing machines, mechanical shakers, sorting devices, conveyors and compactors, musical instruments, some medical equipment and some stress relieving instruments. Some main causes of vibration are unbalance, misalignment, looseness, dry friction between two rubbing surfaces, wind induced vibration, oil whirl and external excitation. The four important vibration characteristics are vibration displacement, vibration velocity, vibration acceleration and phase. Vibration displacement is the total distance travelled by the vibrating part from one extreme limit of travel to the other extreme limit of travel. Vibration velocity and vibration acceleration changes with position of vibrating part. Velocity is maximum at neutral position and minimum at the extreme position. Acceleration is zero at neutral position and maximum at the extreme position. Phase is defined as the position of a vibrating part with respect to a fixed point or another vibrating part at the given instant.