Friday, June 30, 2017

Data Communication

Data Communication(DC)

Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable, wireless or optical fiber etc. For data communications to occur, the communication devices must be part of a communication system to made up of a combination of hardware (physical equipment) and software (programs).

Characteristics of data communication 

  1. Delivery: Must deliver data to the correct destination
  2. Accuracy: Must deliver the data accurately
  3. Timeliness: Must deliver data in a timely manner. (For video and audio, timely deliver means delivering data as they are produced, in the same order as they produced and without significant delay. This kind of delivery is called real-time transmission. 
  4. Jitter: Jitter refers to the variation in the packet arrival time. (Example: video packets are sent every 30-ms if some of the packets arrive with 30-ms delay and others with 40-ms delay, an uneven quality in the video is the result.) 


There are five components of data communications.

  1. Message: text, numbers, pictures, audio, and video. 
  2. Sender: person, computer, telephone, video camera etc. 
  3. Receiver: same as sender and television. etc. 
  4. Transmission medium: cable (twisted-pair, coaxial), radio waves, optical fiber. 
  5. Protocol: Protocol is a set of rules that govern the data communications. Actually, it represents an agreement between the communicating devices (sender and receiver).

Fig: 5 components of data communication 

Data Representation


Texts are represented as a bit pattern, a sequence of bits (0s or 1s). Different sets of bit patterns have been designed to represent text symbols. Each set is called code and the process of representing symbols is called coding. Today, the prevalent coding system is called Unicode, which uses 32-bits to represent a symbol or character used in any language in the world. 

Numbers are also represented by bit patterns. The number directly converted to a binary number to simplify mathematical operations. 

Images are also represented by bit patterns. First, an image divided into pixels then each pixel is assigned a bit pattern

Audio is by nature different from text, numbers, or images. It is continuous, not discrete. 

Video can either be produced as a continuous entity (TV camera), or it can be a combination of images, each a discrete entity, arranged to convey the idea of motion.

Data Flow 

Communication between two devices can be simplex, half-duplex, or full-duplex. 

Simplex Mode 
In simplex mode, the communication is unidirectional (one-way street). Only one of the two devices on a link can transmit and the other can only receive.
Fig: Simplex
Half-Duplex Mode
In half-duplex mode, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa.
Fig: Half-duplex

In full-duplex mode, both stations can transmit and receive simultaneously.
Fig: Full-duplex

Wednesday, June 14, 2017

The Terrifying True Scale of Nuclear Weapons (video)

Nuclear weapons have come a long way and come in all types of different sizes. Some are relatively small while others are enormous, so big they boggle the mind at what they can be capable of. This video analyzes the sizes and impacts of various different nuclear devices, the history of nuclear weapons and what countries in the world are in possession of such devices.


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Saturday, June 10, 2017

The Biggest Rocket ever Designed (video)

That one rocket, which is still the Tallest, heaviest and most powerful ever built, was the Saturn V, which was designed to take men to the moon and later launched the first American Space station, Skylab. 

But if things had been a little different back in the 60’s we might have had a different rocket to hang on the bedroom walls of the space fans of the 70’s and 80’s.

In the early 1960’s, a rocket was designed which made the Saturn V look small comparison.
This was the Sea Dragon, a super heavy lift rocket that would have been 10 times more powerful with 80 Million lb’s of thrust compared to the Saturn’s 7.8 million and that was from just one massive engine. 

It was designed to lift a payload of 1,100,000 lbs into orbit, compared to the 310,000 lbs of the Saturn V. This meant it could have lifted an entire space station into Low Earth Orbit in one mission.

The rocket bell of this single engine would be so large at 75 feet in diameter, that you could fit the entire first stage of a Saturn V with all 5 of its F1 engines inside with room to spare.
So what happened to the Sea Dragon and why didn’t it get built ?. 

At the time of the design in 1962, it was thought that by the 1970’s, 80’s and beyond, thousands of people would be working in space and on the moon, even on Mars and as such, rockets with huge lifting capabilities would have been in great demand as they would dramatically lower the cost of getting materials into space.

The sea dragon was designed by Robert Truax, a US navy Captain and Rocket engineer. He was one of the pioneers of American rocketry and worked on the Thor and Polaris missiles amongst others. His team debriefed the German Rocket engineers at the end of World War 2 including Werner Von Braun who went on to design the Saturn V.

Traux believed it was complexity that drove up the cost of rockets and not their size. His designs for the Sea Dragon were very simple but very big. The sea dragon would have been 75 ft in diameter and 500ft tall, half the Hight of Chrysler building. 

This type of low-cost super heavy rocket is now known as a “big dumb booster” due to its simplistic design.
Instead of having very complicated turbopump driven engine like the Saturn’s, his were the simplest possible design for a rocket engine. 

In place of having powerful fuel pumps to push the huge amounts of rocket fuel and oxidizer in the engine, he proposed a pressure fed system with a separate liquid nitrogen tank to pressurise the fuel tanks, this would push the fuel into the massive combustion chamber.

His engines were literally not much more than the valves to turn on the fuel and the huge engine bell, this would make them not only much cheaper to manufacture but much easier to refurbish and reuse, unlike the F1 engines of the Saturn which were left crash in the sea and be discarded.

The rocket would be a two-stage design, the first stage would lift it to a height of 130,000 ft before it separated and fell back into the sea, using drag bags to slow it impacts with the water, where it would be recovered for reuse.

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Friday, June 9, 2017

What Happened on the Moon Before Apollo? (video)

The Apollo landings from 1969 to 1972 marked a high point in lunar exploration but Apollo didn’t just rock up on to the moon out of the blue, it took many, many missions by probes and landers over the preceding years to establish if we could send men to the moon and get them back

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Wednesday, June 7, 2017

How Far have we gone into the Universe? (video)

Humanity is a fledgling space-faring species, with only a tiny percentage of people who have traveled into space. Most people throughout history have lived their whole life on our tiny rock, but how far have those select few explorers gone? How far into the void of space have we extended our reach? 


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How big is the Universe? (video)

The universe is about 13.8 billion years old, so any light we see has to have been travelling for 13.8 billion years or less – we call this the 'observable universe'. However, the distance to the edge of the observable universe is about 46 billion light years because the universe is expanding all of the time.


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Crashing Into Saturn: Cassini's last Mission (video)

NASA's Cassini spacecraft begin the last chapter of its 20-year mission to Saturn. Diving deeper into Saturn's rings than ever before, scientists hope that the data from Cassini's final orbits will help to improve our understanding of the giant ringed planet. The probe's last act will be to plunge itself into the planet's atmosphere, where it will burn up and become part of the planet itself.


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Tuesday, June 6, 2017

Friday, June 2, 2017

Real-time Face Recognition (Video Demonstration)

Our developed model was a real-time system for recognizing faces (PCA algorithm) in a video stream provided by a webcam camera was implemented, having real-time face detection (Viola-Jones algorithm) & also real-time face tracking (KLT algorithm).

In this video demonstration first 3 persons are known objects and the last persons is unknown object.

Accuracy rate is 88.8%.


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