Category Science

GPS is a system which shows the exact position on the earth, anytime in any weather and anywhere. There are 24 GPS satellites orbiting at 11,000 nautical miles above the earth. They are continuously monitored by ground station located worldwide. The satellites transmit signal that can be detected by anyone with a GPS receiver. Using the receiver one can determine the exact position namely longitude, latitude, altitude and the time, with greater precision. GPS has 3 parts: the space segment, user segment and the central segment.  Space segments consists of 24 satellites as stated above. User segment consists of receivers which we can hold in hand or mount in a car and this gives the exact location on the earth. The control segment consists of ground stations that make sure that the satellites are working properly.

The satellites are equipped with precise clocks that keep accurate time to within 3 nano seconds (3×10-9 secs). The time signals are transmitted along with their orbital parameters. The receiver detects the time signal and calculates the distance of the satellite. By getting the signals from three different satellites and by doing mathematical calculations, the receiver is able to give the exact position where the receiver’s located. By getting the information from fourth satellite, it is able to give the time also.

Thus four satellites are required to compute the four dimensions of x, y, z (position) and time. At any time and at any location always a minimum of four satellites will be visible for the receiver.

Global Positioning System (GPS) works on set of navigational satellites (18 to 21 nos) around the earth in orbit and their signals to a receiver on earth. The signal from each satellite provides the position of the satellite at a specific time.

The receiver software analyses the signals and displays the position of the receiver with reference to a specific spherical coordinates, which has, its centre of earth as its origin.  The navigational satellites are so orbiting that at any given time and spaces on the earth, a minimum of three are visible to the receiver. 

 The accuracy of the position increases with the number of satellites the positional accuracy is around 200 NV, with a different correction (a method of using two or more receiver) the accuracy can be increased to centimetres. Ifs are has been increasing since Iraq war, especially in all modes transportation.  

The Global Positioning System is a satellite based Radio Navigation System developed by the United States Department of Defence. It provides continuous, all weather worldwide navigation capability for sea, land and air applications.

The user can easily determine his position, i.e. latitude, longitude and altitude using the GPS receiver which receives signals from various satellites orbiting the earth. ‘Tie complete GPS constellation consists of 21 operational satellites and 3 spares, orbiting the earth about once every 12 hours at a distance of roughly 10,900 nautical miles.

 Unlike ground based navigational system signal generators the satellites are able to cover a very large area of the earth because of their altitude and the fact that their signals are free of interference from local geography. The error in GPS at times may come up to 30 to 100 Mts.

An advanced system known as GDPs or differential Global Positioning System evaluates this error with an accuracy of within 5 Mts.

The basic difference between a sound wave and a light wave is that the former is a mechanical wave while light is an electromagnetic (EM) wave. Mechanical propagate by the actual displacement of physical particles. Each particle oscillates about its mean position in a synchronized manner to cause energy propagation in a mechanical wave pattern. In case of EM waves, electric and magnetic fields ‘oscillate’ about their mean zero in mutually perpendicular planes and cause wave motion. Mechanical waves require particles to oscillate and enable it to move on. Hence, they require some medium (to provide these particles) for travel. EM waves consist of only change in electric and magnetic fields. So, they do not need any medium for propagation.

The most likely explanation for this phenomenon is that warm, damp air at ground level was sitting below a layer of drier, hotter air above. This results in refraction of the sound back down towards the ground and also the unusually high propagation distances – you hear sound which, under normal circumstances would pass over your head.

Also another explanation could be that sound travel better at night, but the reduction of daytime noise means that continual sounds become more apparent. In the evening it is usual for the temperature near the ground to fall more quickly than that higher up, causing a temperature inversion. It is not uncommon for there to be a change in the air’s moisture content at the top of this inversion layer.

The change in temperature and moisture lead to a density discontinuity which refracts sound waves much as the refraction of light causes a mirage. Sounds are trapped near the ground rather than dispersed. The wind speed in this low-level inversion layer is also normally lighter and this adds to the effect.

Sleep does not reflect an inactive brain and so we do hear sound while sleeping.  It is a recurrent healthy state of inertia and reduced responsiveness found among higher vertebrates. It is controlled by the brain and is associated with characteristic electrical rhythms in the brain. Sleep is induced when the central core of the brainstem situated below the cerebral hemisphere is stimulated. Stimulation of the reticular formation (portion of the central nervous system which consists of small islands of gray matter separated by fine bundles of nerve fibres running in every direction) by natural sensory input, by messages from the cerebral cortex can awaken sleeping persons.

 Neurons (nerve cells) in REM sleep are as active as they are in wakefulness. Mental capacity also does not decrease. Incoming sounds are subjected to ceaseless scrutiny. Unimportant sounds are ignored but important ones even if feeble cause arousal. Arousal thresholds are variable and they are a function of the meaningfulness of the stimulus.

 With a stimulus having no significance, to the sleeper, thresholds can be rather high. So irrelevant stimuli are actively shut out during REM. Behaviourally, it has been established that motor responses can be evolved in all stages of sleep, but it is difficult to demonstrate that new responses can be acquired during sleep. But, in meditation man achieves a state of rest deeper than sleep indicated by slower heartbeat and breathing and so we do not hear sound. 

 

When the pen is full of ink, there is very little space for air inside the pen. So while writing the ink gradually oozes out through the cut in the nib. This leads to a very weak vacuum inside the pen. So the outside air tries to enter the pen and holds the ink from flowing out freely. This ensures a smooth flow of ink.

As the ink runs out and when there are only a few drops of ink the air column inside the pen is no longer isolated from outside the air. Hence the outside air can enter the pen freely and there is no difference in air pressure. Thus the force acting on the ink will be only the gravitational pull and so the ink begins to drain out. 

Dolby mentioned in tape recorders and other sound system actually refers to a noise reduction circuit used in them. Over the past 30 years, sound recording has been revolutionized by technical developments by Dolby labs founded by Ray. M. Dolby, a sound engineer. His first invention was a circuit that eliminates the noise, usually heard as a hiss, inherent in most tape recordings. Unlike the earlier antihiss technologies which distorted the quality of sound, Dolby’s method involved separating the acoustic components of a given sound into different electronic channels based on their frequency and amplitude, eliminating those signals that contributed most to noise and then recombining the other components.