The Internet is the largest computer network in the world. It links millions of smaller networks which are connected to each other by phone lines, cables, or wireless connections.

If your computer is connected to the Internet, it can help you to get information from other computers, send messages to a friend who lives far away, or do lots of other amazing things like hear a song, or watch a famous movie.

This is possible because when you log on to the Internet, you are given access to the other computers that are also connected.

Today, people rarely write letters- they send e-mails instead. Electronic mail or e-mail, is a method of using your computer to send messages to other people who are connected to the Internet via their computers. Your message is first delivered to a computer called the mail server.

From there, it is transferred through the net, until it reaches its destination Just as you need to know a person’s address to send a letter, you have to know a person’s e-mail address to send an e-mail.



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Fire is a chemical reaction that occurs very quickly, and in the process, gives off heat and light.

Three things are necessary for this reaction to occur- fuel, oxygen, and heat.

Fuel whether it is paper or wood-by itself will not catch fire. It is only when the fuel is heated, and becomes hot enough, that the oxygen in the air combines freely with it to burst into flames.

The reason, fire is hot is because it releases a lot of energy that has been stored in fuel. For example, energy from sunlight is stored in the wood that is used as fuel.

When energy is released very quickly, heat and light are produced.

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In 1917 Radon develop the basic mathematical equation.

In 1920 develop the method to image the specific section of the body known as body section radiograph.

In 1935 Grossman define the technique and labelled it as tomography.

In 1937 Watson develop another tomography technique this is known as transverse axial tomography.

In 1940 frank and Takahashi published the basic principle of axial ct.

In 1956 Cormark developed the theory of image reconstruction.

In 1967 Hounsfield develop the clinical useful CT scanner.

In 1972 first clinical brain scanner.

In 1975 dynamic spatial reconstructor was installed a biodynamic unit
at the myoclinic.

1980 a high speed CT scanner introduced that is used electron beam technique was used to image the cardiovascular system to overcome motion artefact this is known as EBCT.

In 1992 the dual slice spiral CT scanner was introduced.

1998 MSCT was introduced at the radiological society of
north America in Chicago.

In 2000 , 16 & 32 slice CT scanner was introduced.

In 2004 , 64 slice Ct scanner was introduced.

In 2006 dual source CT scanner was introduced Two x-ray tube coupled two detector array.

In 2006, 256 slice was introduced.

In 2007, 320 slice was introduced




  • Piezoelectric effect
  • Pulse echo principle

Piezoelectric effect

  • An electric current passes through a cable to the transducer and is applied to the crystals, causing them to deform and vibrate. This vibration produces the ultrasound beam.

pulse-echo principle, 

  • Explains how the image is generated.
  • Ultrasound waves are produced in pulses, not continuously, because the same crystals are used to generate and receive sound waves, and they cannot do both at the same time.
  •  In the time between the pulses, the ultrasound beam enters the patient and is bounced or reflected back to the transducer.
  • These reflected sound waves, or echoes, cause the crystals in the transducer to deform again and produce an electrical signal that is then converted into an image displayed on the monitor.
  • The transducer generally emits ultrasound only 1% of the time; the rest of the time is spent receiving the returning echoes.

Interaction of ultrasound with matter

  1. Reflection – occur at tissue boundary and it create ultrasound image
  2. Refraction – change in direction of the transmitted ultrasound energy.
  3. Scattering – occur by both reflection and refraction
  4. Attenuation/Absorption – conversion of acoustic energy into thermal energy in the medium.

R = [(Z2 – Z1) ÷ (Z2 + Z1)]2 

Z= acoustic impedance is a physical property of tissue. It is describe how much resistance an ultrasound beam encounters as it passes through a tissue

R = resistance coefficient


  • 2D
  • 3D


  • two-dimensional scans are then combined by specialized computer software to form 3D images
  • Early detection of cancerous and benign tumors
  • examining the prostate gland for early detection of tumors
  • looking for masses in the colon and rectum
  • detecting breast lesions for possible biopsies
  • Visualizing a fetus to assess its development, especially for observing abnormal development of the face and limbs

Doppler ultrasound

  • the object reflecting the ultrasound waves is moving, it changes the frequency of the echoes,
  • creating a higher frequency if it is moving toward the probe
  • lower frequency if it is moving away from the probe.
  • A Doppler ultrasound is a noninvasive test that can be used to estimate the blood flow through your blood vessels by bouncing high-frequency sound waves (ultrasound) off circulating red blood cells.


  • ultrasound examination can be displayed in a variety of ways, called modes.
  • three types of USG mode
  • A-mode – AMPLITUDE OF THE REPLICATED WAVE – about the depth of structure and the amplitude of the returning echo
  • B-mode – BRIGHTNESS MODE – 2d information about the cross section.
  • M-mode – MOTION MODE – evaluate motion and timing, and can document tissue movement in a still image when the recording of a clip is not feasible.


  • To detect and measure distance of the object.
  • Helps in non-invasive painless treatment.
  • Preferred method to diagnose complications of unborn babies.
  • Ultrasound frequencies are unaffected by direct sunlight, fluorescent tubes and other sources of light.
  • Useful to acquire 3d image.


  • Ultrasound has limited use in the head and neck region because sound waves are absorbed by bone. Its use is therefore restricted to the superficial structure.
  • Lower resolution
  • Equipment expense
  • Less effective due to obesity ( subcutaneous fat ), gas ( gastric or intestinal),
  • Can’t penetrate bones and gas.
  • Do not provide direction and velocity of flow.





  • A type of imaging test to examine the internal organs using very high frequency sound waves.
  • Ultrasound or ultrasonography is a medical imaging technique that uses high frequency sound waves and their echoes. The technique is similar to the echolocation used by bats, whales and dolphins, as well as SONAR used by submarines.: sound navigation and ranging


 Sound is a mechanical form of energy

Sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid.


20Hz – 20000Hz human hearing sound

Lower 20Hz- infrasound

Higher 20000Hz – ultrasound


DIAGNOSTIC ULTRASOUND – Diagnostic ultrasound uses 1-20MHz frequency.

Wavelength is the distance between successive wave crest.

AMPLITUDE – distance between peak and midpoint of the wave or highest point of the wave

Period is the time taken for one complete cycle and is equal to 1/f. – 1 PERIOD

Frequency is the number of occurrences of a repeating event per unit of time. – DAY

ECHO – The reflection from tissue is called echo, which form the image.

Velocity is inversely proportional to compressibility and it depend on temperature of the medium. Inversely Proportional : when one value decreases at the same rate that the other increases.

  • Velocity higher in bone and lower in gas
  • Frequency do not change, but change of velocity may occur due to change of wavelength.

SPECKLE – Interference of scattered echoes from different site is called speckle.

In abdomen imaging, strong echoes arise from gas bubbles. Kidney, pancreas, spleen, and liver constitutes complex tissues containing scattering sites, gives rise to speckled texture. Bladder, blood vessels and cysts (fluids) have no internal structure, hence no echoes and appear as black.

Higher the frequency, greater the attenuation

A velocity of 1540m/sec is used as an average for body tissues.

Higher frequencies are more attenuated than low frequencies, resulting in increased SPL. This will degrade image resolution.


1794 – lazzaro spallanzani discovered non-audible sound. Echolocation in bat

1877 – pierre curie discovered piezoelectric effect

1917 – langevin produced ultrasound device using piezoelectric.

1942 – karl dussik investigates ultrasound transmission of the brain.

1958 – Dr. ian Donald obs/gyn.

1980 – real time ultrasound possible

1986 – first 3d image of foetus.

1990 – 3D and 4D ultrasound emerge.


  • The ultrasound machine transmits high-frequency sound pulses into your body using a probe.
  • The sound waves travel into your body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue and bone).
  • Some of the sound waves get reflected back to the probe, while some travel on further until they reach another boundary and get reflected.
  • The reflected waves are picked up by the probe and relayed to the machine.
  • The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue (1,540 m/s) and the time of the each echo’s return (usually on the order of millionths of a second).
  • The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image.

PRINCIPLE OF ULTRASOUND/ physics of ultrasound in short

  • USE high frequency sound waves and their echoes.
  • transmits high-frequency (1 to 5 megahertz) sound pulses into your body using a probe.
  • Some of the sound waves get reflected back to the probe, while some travel on further until they reach another boundary and get reflected.



WHAT IS LIVING ? part- 1

this is very normal question and very important question specially for biology student.

so here I uploaded part -1 and part -2 is uploaded tomorrow so read it and understand it

to be continue in part -2

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Earth – the blue planet

Earth is a Germanic word, and it means “the ground“, and it is at least 1000 years old . but all of the planets were named on greek and roman god and goddess (except earth).

Earth is about 4.5 billion years old and third planet from sun.

you could be spinning through space at just over 1,000 miles per hour.

Earth have different seasons because  Earth is tilted 23.4 degrees on its ‘axis.

The Earth’s diameter is about 12,800km.

Earth’s Core Is as Hot as the Sun’s Surface.

We live on the earth ,not in the earth.

About 70% of the Earth’s Surface is Covered in Water. Earth have only 3% fresh water and other 97% of it is salted.

About 100 lightning bolts strike earth every second.

About 5000 people dies due to drinking polluted water and about 100 million mammals dies by pollutionon earth.

Currently earth has about 3 trillion trees.

The earth’s population is about 7.6 to 7.8 billion.

many claims states that Nicolaus Copernicus was the man who discovered earth.




A Belgian priest named George Lemaitre firstly suggested the idea of big bang theory in age 1920s.
The actual beginning of everything may not be explain by Big Bang Theory.

13.8 billion years ago, an explosion occurs because of every speck of energy dense into a very tiny point called singularity. This explosion was beyond the imagination.
After this explosion, all the matter spread in all over surrounding directions with very high speed approximate speed of light. The temperature at that time was 1000 trillion degree Celsius.

Events after big bang-

After Big Bang, in initial three lakh years, all the matter was in plasma state. After this, the protons and neutrons combine together and form nuclei and then a complete atom.

The first atom formed after Big Bang was Hydrogen atom and then Helium by hydrogen’s fusion, then higher atoms.

The atoms combine and form small terrestrial bodies then stars, planets, galaxies and our universe.

The estimated numbers of atoms in the present universe are approximately 10⁷⁸ – 10⁸².

Expansion of universe

The expansion of universe is the main evidence for the existance of big bang. According to some theories, the universe is still expanding after big bang. It is predicted by the light coming from other galaxies that the galaxies are moving far away from our galaxy (milky way).

According to planck’s observations the rate of expansion of universe is 67km/sec/megaparsec. But according to present understandings of universe it is 9% faster rate then planck’s prediction.

During big bang, the infrared light form. But now we observe these rays as cosmic microwaves.

According to some theories there are other universe like our universe called multiverse.

Our universe form after big bang and expanding, but after some billion years it would be contracted and again a big bang occurs. This cycle would be happen continually, called oscillating universe.

If we see the stars in space, it means we see the past of stars because light can take thousand years reach to earth from these stars.

Experiment related to big bang

Physicists create conditions of big bang by a gigantic machine called Large Hadron Collider (LHC). The LHC is an 27km long underground tunnel in ring shape.

It comprises superconducting magnets to accelerate the particle (protons and heavy ions) inside the tunnel.

In LHC, two particles accelerated close to the speed of light. The accelerated particles collide and produce extreme energy. By these conditions, physicists understand that how big bang creates the universe.