Do you know why you can’t boil an egg on Mount Everest?

Imagine you climbed the Mount Everest! You have achieved something unbelievable and wonderful, you are unspeakably proud of yourself and you are absolutely excited and happy. But you will not be able to have one thing: a freshly boiled egg!

After you have done the unthinkable you believe anything is possible, just not boiling an egg. Why?

Well, the problem is with the height, the air pressure and the water temperature.

Air pressure and temperature – a never-ending relationship

As higher you get as lower the air pressure becomes. And air pressure is always connected with temperature. So, if the air pressure goes down the temperature goes down, logically if the air pressure goes up the temperature goes up as well. They are always in a relationship and connection.

So due to the low air pressure on a high mountain the water boils, with bubbles and steam, already at a low temperature.  We have to remember that once the water boils it will not get hotter. So if the water boils at a specific water temperature it will stay at this temperature, no matter what.

It’s about height, air pressure and water temperature!

At sea level water boils at 100 degrees Celsius (212 degrees Fahrenheit). And with every 300 m we go up the temperature at which the water boils goes down by 3 degrees Celsius.

Boiling eggs

So what’s the story with boiling eggs? Eggs have something interesting, the yolk and the egg white don’t harden at the same water temperature. The yolk needs around 65 C (149 F) to get hard and the egg white needs around 85 C (185 F) to get hard. So if we are at the Mount Everest, which we climbed up at the beginning, we are at 8 848 m (29029 feet).  There the water boils already at around 70 C (158 F). So the yolk might get hard but the white outside will stay glibber and we cannot enjoy our egg.

What about other famous mountains?

Mont Blanc at 4 810 m (15 782 feet), Mount Kilimanjaro at 5 895 m (19 341 feet) and  Mount McKinley at 6 194 m (20 237 feet) ?

Well, at Mont Blanc water boils at 84 C (183 F).  We can boil our egg there with no problem. At Mount Kilimanjaro the water boils at 80 C (176 F) and at Mount McKinley the water boils at 79 C (174 F). There we might have a problem with boiling the egg white. But maybe, if we boil the egg long enough, we will be successful there as well. But once we are above 7 000 m (22 966 feet) no eggs can be boiled anymore.

And do you know what a pressure cooker has to do with all I mentioned above? Well, in a pressure cooker you get the pressure really high which allows the temperature to be above 100 Celsius (212 Fahrenheit). This speeds up cooking.

Source:-

http://simplyilka.com/2014/05/22/know-cant-boil-egg-mount-everest/

How do Astronauts communicate in space?

How do Astronauts communicate in space?

Sound is a form of energy which require material medium to travel.

In order to hear sound it must travel through air (gas particles). Sound can only travel through a solid, liquid or gas. Space being an almost perfect vacuum does not allow sound to travel and be heard by the ears. Sound is vibrations of air particles, so any “sound” that is heard in space has to come from other means such as from the electromagnetic spectrum and these waves are not sound.

As such, astronauts communicate with each other in space when they are spacewalking through the use of radio waves. Radio wave signal are sent to their headsets which then translates the signal into the form of sound . When receiving and sending message to earth it is sent in the form of radio waves which is then translated to sound wave by a radio set.

Radio wave is a part of the light spectrum called electromagnetic spectrum and is therefore a light wave. Electromagnetic waves does not need a medium to travel.

Astronauts can however, talk to each other as if they were on Earth only when they are in their space ship. Here, there are enough air particles to vibrate and take the sound to their ear drum.

Source:-

http://tellmewhyfacts.com/2007/12/how-do-astronauts-communicate-in-space.html

Bernoulli Balls

Bernoulli Balls

A simple hair-dryer becomes a magical levitation device through an understanding of the principles of fluid flow.

Ingredients:

1. hair dryer (make sure you have an appropriate power supply available!)
2. small light balls (such as polystyrene balls available at most craft shops, or ping pong balls)

Instructions

1. Orient the hair dryer so that the outlet is pointing directly upwards. Turn it on.
Place a ball carefully in the flow from the hairdryer. It will balance in the air, appearing to levitate!
2. Gently move the hairdryer from side to side – the ball will stay in the air stream, i.e. will also move back and forth. Repeat this process moving the hairdryer up and down.
3. Carefully tilt the hairdryer – the ball will still stay in the airstream, hanging in mid-air with nothing directly underneath it.
4. Try using balls of differing sizes, and challenge your audience to see how many they can place in the airstream at once.

How Does it Work?

The upward pressure from the hairdryer balances the downward force of gravity, keeping the ball 'levitating'. The more impressive part of this trick is being able to move the ball along with the hairdryer and angle it. The stream of air sticks to the surface of the ball. This is a demonstration of the Coanda Effect, which emerges when fluids like air or water pass over curved surfaces. When the ball approaches the edge of the stream, air is curved round the ball and directed out of the stream. This has the effect of pushing the ball back into the stream. This is the process that enables the ball to balance inside the airstream and stay in the airstream as the hairdryer is moved around.

Tips for Success

Try to find a hairdryer with a 'cool' setting – it will last longer and allow you to perform the trick for much longer in one sitting, without the hairdryer overheating. Make sure that the balls aren't larger than the output of the hairdryer or it won't work. Tilting the hairdryer to too great an angle will cause the ball to fall out of the airstream – although most audiences enjoy seeing the effect!

Serving Suggestions

This is a good eye-catching demonstration that can keep audiences amused for a significant period of time – everyone wants to have a go, especially when challenged to make the largest number of balls stay within the airstream. However, it does require a power supply so is generally limited to indoor venues.

Did You Know?

The Bernoulli Effect underlies the principle of the aerofoil. By encouraging air to flow more quickly over the top surface of a wing an upward pressure is produced by the slower moving air beneath. This phenomenon can also be demonstrated by holding up two sheets of paper and blowing between them. Instead of moving apart, they are drawn together. If you thought anyone could have worked this out, remember that Daniel Bernoulli was awarded his masters degree at the ripe old age of 16.

Source:-
http://www.physics.org/interact/physics-to-go/bernoulli-balls/index.html

Balloon Kebabs

Balloon Kebabs

Density and pressure effects are explored using a simple visual demonstration.

Ingredients:

balloons
wooden kebab skewers

Instructions

1. Blow up the balloons (not full) and tie them off.
2. Challenge your audience to make a 'balloon kebab' – to insert the wooden skewer all the way through the balloon without popping it. Let a few people have a try – they will invariably try to insert the skewer fairly slowly through the side, and the balloon will pop.

Show them how physics can make the trick work:

1. Start by lining up the skewer point with the darker patch on the balloon, opposite the tie end. Gently push the skewer through. You may find that a twisting motion works best.
2. Once the skewer is through one side, push it gently through the balloon until the point of the skewer is at the opposite end – the darker area around the tie.
3. Insert the skewer tip gently through the soft part of the balloon where the tie is – again use the twisting motion if it helps. Voila! – you have made a balloon kebab!

See video at:- http://m.youtube.com/watch?v=jwE4oSv7Qds

How Does it Work?

This trick works through an understanding of surface properties. A balloon is formed by inserting air into a flexible thin rubber sheet. Most of the balloon is stretched evenly, but there are two points where the rubber is least stretched – and thus there is the lowest surface tension. These correspond to the tied section and the darker patch at the opposite side of the balloon – in fact the darker colour indicates that the balloon is less stretched over that region. Most of the balloon is under high tension, so attempting to push the skewer through just makes the balloon pop. But at the low tension sections it is possible to make a small hole without breaking the overall surface of the balloon.

Tips for Success

This trick works best with round balloons (rather than long skinny ones) – mainly so that the kebab skewers can fit! Don't blow up the balloon too much or it will pop even if you do it correctly. Make sure the skewer ends are fairly sharp – blunt skewers are more likely to pop the balloon.
You may find that your balloons sometimes burst even if you follow the instructions. The audience will enjoy the entertainment so just laugh it off and try again!

Source:- http://www.physics.org/interact/physics-to-go/balloon-kebabs/index.html

Is this anti-gravity wheel a magic trick or just cool physics?

A man effortlessly lifts a 42-pound weight at the end of a long rod over his head. It seems like it's floating! What is this sorcery? Is this guy a wizard? Perhaps he has discovered an anti-gravity device to make Back to the Future skateboards? Actually, it's just good old physics in action.

First watch the demonstration by Veritasium's Derek Muller:

http://m.youtube.com/watch?t=36&v=GeyDf4ooPdo

The phenomenon that makes this seemingly magical act possible is called torque-induced precession—also known as gyroscopic precession:

Torque-induced precession is the phenomenon in which the axis of a spinning object (e.g., a part of a gyroscope) "wobbles" when a torque is applied to it, which causes a distribution of force around the acted axis. The phenomenon is commonly seen in a spinning toy top, but all rotating objects can undergo precession. If the speed of the rotation and the magnitude of the torque are constant, the axis will describe a cone, its movement at any instant being at right angles to the direction of the torque. In the case of a toy top, its weight is acting downwards from its centre of mass and the normal force (reaction) of the ground pushing up on it at the point of contact with the support constitute two opposite and equal forces producing a torque.
The phenomenon doesn't make the weight lighter, although it will feel lighter to person lifting it.

Still not clear about how it works?

Here's the video that explains it all in detail:

http://m.youtube.com/watch?v=NeXIV-wMVUk&t=12

Source:-
http://sploid.gizmodo.com/is-this-anti-gravity-wheel-a-magic-trick-or-just-cool-p-1546185172

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Newtons Experiments - rolling cone and catenoid

Newtons Experiments - rolling cone and catenoid

Here we have a simple triangular ramp made out of two pieces of long straight metal with adjustable screws at the three ends. The screws can be adjusted so that ramp slopes. We have three things to put on the ramp: a cylindrical rod, a double cone and a shape called a catenoid. The cylinder is simply a piece of painted broom pole which is uniform along its length. The double cone (or spindle) is made out of two wooden christmas cone decorations glued back-to-back at the wide ends to make something that is thicker in the middle than it is at the ends. This was smoothed and painted. Finally the catenoid, believe it or not, is the body of a loo brush holder. It has the 'opposite sort' of shape to the double cone in that the metal body is wider at the ends and tappers in smaller at the middle.

Experiment 1 - cylinder
First we set up the screws so that the ramp just slopes. That is we adjust the two screws at the ends of the metal bars to be slightly higher than the screw located at the meeting point of the two metal bars. What will happen if we put the cylindrical rod onto the middle of the ramp? Well no prizes for guessing that it will roll down hill - correct!

Experiment 2 - double cone

However if we put the double cone in the middle what will happen? - it apparently defies gravity and rolls up hill! What's going on?? The explanation is something like this. As the double cone rolls along the sloping ramp it only ever makes contact at two points. Because of the ramp shape these points of contact change (move out from near the center of the double cone) as it moves along. At first the ramp may contact the double cone near to the center where it is quite thick and so the center point of the double cone is quite high above the ramp. As it rolls up the ramp the point of contact changes and this center points drops down toward the level of the ramp. Now as long as this drop is greater than the apparent rise up the sloping ramp, the center of mass of the double cone is always falling even if it looks like its actually going up hill ! The crucial point here is that the center of mass is actually always falling down hill as it apparently looks like its going uphill - its a sort of optical illusion (also see the diagram below). If the ramp gets too steep the center of mass of the double cone will not be able to move downhill enough to compensate for the rise and the illusion will not work.

Experiment 3 - catenoid

If the ramp is now turned over (so that it slopes the other way) its now at the correct angle for the catanoid to apparently roll up-hill. Newton didnt have such high tech loo-brush holders, although he would have probably known of the shape - the catenoid !

There is no magic here (apart from the magic of physics) its just depends on the relationship between the ramp slope angle (A), the angle / width of the ramp
(B) and the way the double cone or catanode shapes change over its length
(C) that makes for this very interesting illusion of apparently defying gravity - see the diagram below.

Source:-http://www.creative-science.org.uk/rolling_cone.html

WATERPROOF HANKY

A great excuse to threaten to pour water over your audience – but with a surprise twist thanks to physics.

Ingredients:

large glass
ashtray or similar
water
handkerchief

Instructions

Push the centre of the handkerchief into the glass, so that the edges are hanging over the outside of the rim of the glass.
Pour water into the glass, through the loose handkerchief. Make sure that your audience can see the water easily passing through the handkerchief into the glass. Keep pouring the water until the glass is roughly half full.
Pull the corners of the handkerchief so that the material is taut over the top of the glass. Hold the glass and handkerchief so that the material stays tightly stretched over the opening. For younger audiences you may like to say some 'magic words' that make the hanky waterproof.
Place the ashtray on the top of the glass and tip it all upside down, being careful to keep the handkerchief pulled tight.
Choose a likely suspect from your audience to threaten with a drenching! Hold the upside-down glass and ashtray above their head, making sure that the glass is vertical and the handkerchief is tight. Remove the ashtray and voila! – nothing happens! The water stays inside the glass.
How Does it Work?

This demonstration is based on surface tension and air pressure. When the handkerchief is loose, the water can pour through the gaps in the fabric. However, when the handkerchief is pulled tight, the water molecules can form a single surface or membrane across the handkerchief due to a property called surface tension. The air surrounding us is exerting a force in all directions - air pressure. When the membrane is formed on the surface of the handkerchief, it provides a uniform surface for the air pressure to act upon. The force of the surrounding air acting upon this membrane is sufficient to overcome gravity, and so the water stays in the glass.

Tips for Success

Don't try to substitute a paper tissue for the handkerchief as it won't work! If the glass isn't held vertically, some water may dribble out where the membrane attaches to the edge of the glass.
Serving Suggestions

This trick will work in almost any environment and with any age group.

Did You Know?

Galileo was among the earliest to demonstrate the existence of surface tension on water by showing that an iron needle can be floated lengthways on water, but not on its point.

Source and See video at:- http://www.physics.org/interact/physics-to-go/waterproof-hanky/index.html

New technology can expand LED lighting, cutting energy use and greenhouse gas emissions

• New technology can expand LED lighting, cutting energy use and greenhouse gas emissions

An LED coated with a yellow "phosphor" is shown turned off (left) and then turned on (right). This "green" LED is inexpensive and provides warm white light. Credit: Zhichao Hu, Ph.D.

Highly efficient, light-emitting diodes (LEDs) could slash the world's electricity consumption. They are already sold in stores, but more widespread adoption of the technology has been hindered by high costs due to limited availability of raw materials and difficulties in achieving acceptable light quality. But researchers will report today that they have overcome these obstacles and have developed a less expensive, more sustainable white LED.

The scientists will discuss their research at the 250th National Meeting & Exposition of the American Chemical Society (ACS).

"If more people in the U.S. used LEDs in their homes and businesses, the country's electricity consumption could be cut in half," says Zhichao Hu, Ph.D., a member of the Rutgers University team that performed the research under the direction of Jing Li, Ph.D. At that time, he was a graduate student. He is now a postdoc at Rutgers and is studying the recovery of rare-earth elements there. Zhichao adds that studies show substituting one LED light for a common incandescent light bulb in every American household could save the nation $700 million annually in energy costs.

To achieve the common, soft white light that consumers expect, current LED technologies typically use a single semiconductor chip to produce light, usually blue, and then rely on a yellow-emitting "phosphor" coating to shift the color to white. That's because LEDs do not emit a white light. The phosphor is made from materials, such as cerium-doped yttrium aluminum garnet, that are composed of rare-earth elements. These elements are expensive and in limited supply, since they are primarily available only from mining operations outside the U.S. Additionally, the light output of these phosphors tends to be harsh, "cold" colors.

Li's team is developing hybrid phosphor-based technologies that are much more sustainable, efficient and low-cost. They combine common, earth-abundant metals with organic luminescent molecules to produce phosphors that emit a controllable white light from LEDs. By varying the metal and organic components, the researchers can systematically tune the color of the phosphors to regions of the visible light spectrum that are most acceptable to the human eye, Hu and Li note. The team is continuing to experiment and develop other rare-earth-free LED phosphors based on different metals and organic compounds.

Many material combinations are possible, so they use a computational approach to initially sort through the possibilities and to predict what color of light the various metals and organics combinations will emit. They then test the best combinations experimentally.

Their approach allows a systematic fine tuning of band gaps and optical emissions that cover the entire visible range, including yellow and white colors. As a result, their LEDs can be fine-tuned to create a warmer white light, similar to cheaper but inefficient incandescent lights. Their approach shows significant promise for use in general lighting applications.

"One of challenges we had to overcome was to figure out the right conditions to synthesize the compound," Hu notes. "Like cooking, the synthesis requires a 'recipe.' It's often not the case that one can simply mix the starting materials together and get the desired product. We optimized the reaction conditions—temperature and the addition of a solvent—and developed an easy procedure to make the compound with high yield."

Experiments with some materials have shown that the team's technology can cut LED costs by as much as 90 percent from current methods that rely on rare-earth elements. They have several granted and pending U.S. patents and are exploring manufacturing possibilities.


Source:-http://m.phys.org/news/2015-08-technology-energy-greenhouse-gas-emissions.html

Superconductivity record sparks wave of follow-up physics

Superconductivity record sparks wave of follow-up physics

Hydrogen sulfide — the compound responsible for the smell of rotten eggs — conducts electricity with zero resistance at a record high temperature of 203 kelvin (–70 °C), reports a paper published today in Nature1.

Low temperature superconductivity can be used to levitate objects but researchers dream of room-temperature versions of today's devices.

The first results of the work, which represents a historic step towards finding a room-temperature superconductor, were released on the arXiv preprint server in December2 and followed up by more in June3. They have already sparked a wave of excitement within the research community.


A superconductor that works at room-temperature would make everyday electricity generation and transmission vastly more efficient, as well as giving a massive boost to current uses of superconductivity such as the enormous magnets used in medical imaging machines.

Hydrogen sulfide — the compound responsible for the smell of rotten eggs — conducts electricity with zero resistance at a record high temperature of 203 kelvin (–70 °C), reports a paper published today in Nature1.

The first results of the work, which represents a historic step towards finding a room-temperature superconductor, were released on the arXiv preprint server in December2 and followed up by more in June3. They have already sparked a wave of excitement within the research community.

A superconductor that works at room-temperature would make everyday electricity generation and transmission vastly more efficient, as well as giving a massive boost to current uses of superconductivity such as the enormous magnets used in medical imaging machines.

Not exotic

According to Christoph Heil of the Graz University of Technology in Austria, other scientists are intensely interested in the result because it was achieved without using exotic materials such as the copper-containing compounds called 'cuprates' which until now have held the record for the highest superconducting temperature (133 K (–140 °C) at ambient pressure and 164 K (–109 °C) at high pressure). He says that the pressurized hydrogen sulfide seems to be a 'conventional' superconductor in which vibrations within the material's crystal lattice drive electrons to form ‘Cooper pairs’ that can flow through the crystal without resistance.

In calculations reported in April5, Matteo Calandra of the Pierre and Marie Curie University in Paris and his colleagues found that the Mainz hydrogen sulfide results could be explained using a modified version of the conventional theory of low-temperature superconductivity based on lattice vibrations. That is surprising because many scientists assumed that superconductivity at temperatures of more than a few tens of Kelvin required exotic materials that do not exhibit conventional superconductivity.

For others, such theoretical analyses are superfluous until the result by Eremets and co-workers is confirmed experimentally by independent teams. Several are working towards that goal, including Katsuya Shimizu of Osaka University in Japan and colleagues, who have seen the loss of resistance in pressurized hydrogen sulfide, but have yet to observe the Meissner effect. Meanwhile, four other groups contacted by Nature's news team — three in China and one in the United States — have yet to confirm either the electrical or magnetic effects.

If Eremets and colleagues are right, then other hydrogen compounds may be good candidates for high-temperature superconductivity too. For instance, other researchers have published theory papers on arXiv suggesting compounds that pair hydrogen with platinum, potassium, selenium or tellurium, instead of sulfur.

Taking a slightly different tack, Zhang in Dallas and Yugui Yao of the Beijing Institute of Technology in China predict that substituting 7.5% of the sulfur atoms in hydrogen sulfide with phosphorus and upping the pressure to 2.5 million atmospheres (250 GPa) could raise the superconducting transition temperature all the way to 280 K6, which is above water's freezing point.


Source:-http://www.nature.com/news/superconductivity-record-sparks-wave-of-follow-up-physics-1.18191

CORAL REEF

What is a coral reef?

A coral reef is a community of living organisms. It is made up of plants, fish, and many other creatures. Coral reefs are some of the most diverse ecosystems in the world. They are home to about 25% of all marine life!

There are sponges, sea slugs, oysters, clams, crabs, shrimp, sea worms, starfish and sea urchins, jellyfish and sea anemones; various types of fungi, sea turtles, and many species of fish. Think of them as the “rainforests of the oceans.”

Coral reefs have been around for millions of years. Less than 0.1% of the world’s ocean floor is covered by coral reefs. The reefs grow best in warm, shallow, clear, sunny and moving water. However, they grow very slowly—anywhere from 0.3 cm to 10 cm per year. The reefs we see today have been growing over the past 5 000 to 10 000 years.

Coral reefs are made of tiny animals called “polyps” that stay fixed in one place and are the main structure of a reef. Polyps have a hard outer skeleton made of calcium (similar to a snail’s shell).

Each polyp is connected by living tissue to form a community. Only the top layer of a coral reef contains living polyps. As new layers of the coral reef are built, the polyps leave the lower layers.

Each polyp has a ring of tentacles shaped like a cup around a central opening. The tentacles are like long arms with tips that can sting. They are used either for defense or to capture zooplankton (small animal life) for food.

The Great Barrier Reef is the largest coral reef. It is made up of over 2 900 individual reefs and 900 islands stretching for over 2 600 kilometers off the northeast coast of Australia.

Why are they important?

Coral reefs do a number of amazing things! Reefs

1. Protect shorelines from big waves by absorbing wave energy
2. Provide a safe place for fish to spawn (release eggs into the water)
3. Provide habitats for a large variety of organisms
4. Provide food (fish and shellfish) for many people living along coastlines
5. Are a source of medication—some anti-cancer drugs and painkillers come from reefs
6. Help in the carbon cycle
Are a good sign of ocean water quality: Healthy reefs = Healthy water.

Coral Reefs at Risk

Coral reefs are fragile ecosystems. They are very sensitive to any changes. Worldwide, coral reefs are disappearing for a number of reasons.

Bladeless Fans

This is an amazing technology for fan. Let's see how it works:-

Why rain clouds are dark grey?

It's pretty well-known that most clouds are white, while rain clouds are usually a darker shade of gray. But why are rain clouds so dark?

Let's start by discussing how clouds form.

The air around you is full of water in its gaseous form, called water vapor. When the air near the ground warms, it starts to rise, taking the water vapor along with it.
The air starts to cool as it rises higher into the sky, causing the water vapor to condense onto atmospheric dust from volcanoes, car exhaust and other sources. The resulting water droplets and ice crystals coalesce, or join together, to form clouds.
Unlike atmospheric particles that scatter more blue light than other colors (making the sky blue), the tiny cloud particles equally scatter all colors of light, which together make up white light.
However, rain clouds are gray instead of white because of their thickness, or height.
That is, a cloud gets thicker and denser as it gathers more water droplets and ice crystals — the thicker it gets, the more light it scatters, resulting in less light penetrating all the way through it.

The particles on the underside of the rain cloud don't have a lot of light to scatter to your eyes, so the base appears gray as you look on from the ground below.
This effect becomes more pronounced the larger the water droplets get — such as right before they're large enough to fall from the sky as rain or snow — because they become more efficient at absorbing light, rather than scattering it.

Angioplasty-What are stents?

What are Stents?

A stent is a tube-shaped device that can be inserted into a narrowed passageway or vessel to hold it open. A stent therefore acts as a scaffold that holds bodily tubes open.

The coronary stent is one of the most commonly used types of stent. Coronary artery disease causes a narrowing of the coronary arteries that normally supply blood to the heart muscles. Narrowing of these arteries leads to restricted blood flow to a region of the heart, which can lead to a heart attack or myocardial infarction.

The part of the heart muscle deprived of blood becomes necrotic or dies and so cannot function. The narrowing of the coronary blood vessel is usually caused by atherosclerosis or the build up of fatty deposits that eventually form a plaque. As blood flow becomes reduced, angina or chest pain may occur. Stents are placed within the narrowed arteries to hold them open and restore blood flow.

Implanting a stent

A stent is implanted using a procedure called percutaneous coronary intervention (PCI) or coronary angioplasty. For this procedure, a long, thin tube called a catheter with an inflatable balloon at the tip is inserted into an artery (usually a large artery in the patient's groin) and is threaded through to the heart under the guidance of X-ray imaging.

Once the tip of the catheter reaches the narrowed part of the artery, the tip is inflated to push the artery walls open. Once the artery is widened, the balloon is deflated and removed, while the stent is locked in place, holding open the vessel even after the balloon is deflated.

Around one third of patients who have had their coronary blood vessels dilated with a balloon but have not had stents inserted, have found the vessel narrows again after a few months of balloon angioplasty. This re-narrowing is called restenosis. Stenting helps prevent restenosis.

Nowadays, a more recent type of stent called the drug-eluting stent is available. These stents are embedded with drugs that slowly elute into the coronary artery to prevent the closing of the vessel on a long-term basis. Stents that do not contain drugs are called bare metal stents.

After a stenting procedure, antiplatelet and anticoagulant drugs such as aspirin and clopidogrel can be used to prevent clot formation around the stent and restenosis.

NASA Spent Millions to Develop a Pen that Would Write in Space, whereas the Soviet Cosmonauts Used a Pencil

NASA Spent Millions to Develop a Pen that Would Write in Space, whereas the Soviet Cosmonauts Used a Pencil.

An AG-7 Astronaut Space Pen in presentation case.

1960s, legend has it, NASA scientists realized that pens could not function in space. They needed to figure out another way for the astronauts to write things down. So they spent years and millions of taxpayer dollars to develop a pen that could put ink to paper without gravity. But their crafty Soviet counterparts, so the story goes, simply handed their cosmonauts pencils.

Originally, NASA astronauts, like the Soviet cosmonauts, used pencils, according to NASA historians. In fact, NASA ordered 34 mechanical pencils from Houston's Tycam Engineering Manufacturing, Inc., in 1965. They paid $4,382.50 or $128.89 per pencil. When these prices became public, there was an outcry and NASA scrambled to find something cheaper for the astronauts to use.

Pencils may not have been the best choice anyway. The tips flaked and broke off, drifting in microgravity where they could potentially harm an astronaut or equipment. And pencils are flammable--a quality NASA wanted to avoid in onboard objects after the Apollo 1 fire.

Paul C. Fisher and his company, the Fisher Pen Company, reportedly invested $1 million to create what is now commonly known as the space pen.

In 1965 Fisher patented a pen that could write upside-down, in frigid or roasting conditions (down to minus 50 degrees Fahrenheit or up to 400 degrees F), and even underwater or in other liquids. If too hot, though, the ink turned green instead of its normal blue.

That same year, Fisher offered the AG-7 "Anti-Gravity" Space Pen to NASA. Because of the earlier mechanical pencil fiasco, NASA was hesitant. But, after testing the space pen intensively, the agency decided to use it on spaceflights beginning in 1967.

Unlike most ballpoint pens, Fisher's pen does not rely on gravity to get the ink flowing. The cartridge is instead pressurized with nitrogen at 35 pounds per square inch. This pressure pushes the ink toward the tungsten carbide ball at the pen's tip.

The ink, too, differs from that of other pens. Fisher used ink that stays a gellike solid until the movement of the ballpoint turns it into a fluid. The pressurized nitrogen also prevents air from mixing with the ink so it cannot evaporate or oxidize.

How space pen was made?

The ballpoint is made from tungsten carbide and is precisely fitted in order to avoid leaks. A sliding float separates the ink from the pressurized gas. The thixotropic ink in the hermetically sealed and pressurized reservoir is able to write for three times longer than a standard ballpoint pen. The pen can write at altitudes up to 12,500 feet (3800 m). 

The ink is forced out by compressed nitrogen at a pressure of nearly 35 psi (240 kPa). Operating temperatures range from −30 to 250 °F (−35 to 120 °C). The pen has an estimated shelf life of 100 years.

Source:- http://www.scientificamerican.com/article/fact-or-fiction-nasa-spen/

And

Wikipedia

Amazing Facts

1. An asteroid once destroyed a massive forest in Siberia without ever hitting the ground.

The event is known as the "Tunguska Impact." It occurred in 1908 in Siberia when an asteroid entered Earth's atmosphere traveling around 33,500 miles per hour and exploded at a height of about 28,000 feet. The resulting fireball released about 185 Hiroshima bombs' worth of energy, destroying around 800 square miles of Siberian forest. Even though it is classified as an impact, the asteroid itself never made it to the ground. It was probably pretty freaking terrifying

2. There is a lake in Venezuela that experiences almost constant lightning.

This weird but totally badass phenomenon occurs at the mouth of the Catatumbo River, where it empties into Lake Maracaibo in Venezuela. This flashy place actually has the most lightning in the world. Its origins are mysterious, but scientists think that it most likely has to do with the local topography and wind patterns of the region.

Aurora -A natural light display in the sky.

An aurora is a natural light display in the sky, predominantly seen in the high latitude (Arctic and Antarctic) regions.

If you're camping near the United States/Canada border or points farther north, you might see an eerie glow in the night sky. Sometimes it can look like twilight. At other times it can look like a glowing, dancing ribbon of light. The light may be green, red, blue or a combination of these colors. What you are seeing is called the aurora borealis, or simply an aurora.

Because auroras are caused by the interaction of solar winds with the Earth's magnetic field, you can see them most often near the poles, both north and south. In the north, they're called aurora borealis, or Northern Lights. Aurora is the name of the Roman goddess of the dawn, and "boreal" means "north" in Latin. In the southern hemisphere, auroras are called aurora australis (Latin for "south").

What causes auroras?

Auroras are indicators of the connection between the Earth and the sun. The frequency of auroras correlates to the frequency of solar activity and the sun's 11-year cycle of activity.

As the process of fusion occurs inside the sun, it spews high-energy particles (ions, electrons, protons, neutrinos) and radiation in the solar wind. When the sun's activity is high, you'll also see large eruptions called solar flares and coronal mass ejections. These high-energy particles and radiations get released into space and travel throughout the solar system. When they hit the Earth, they encounter its magnetic field.

The poles of the Earth's magnetic field lie near, but not exactly on, its geographic poles (where the planet spins on its axis). Scientists believe that the Earth's liquid iron outer core spins and makes the magnetic field. The field is distorted by the solar wind, getting compressed on the side facing the sun (bow shock) and drawn out on the opposite side (magnetotail). The solar winds create an opening in the magnetic field at the polar cusps. Polar cusps are found on the solar side of the magnetosphere (the area around the Earth that's influenced by the magnetic field).

Let's look at how this leads to an aurora.

1) As the charged particles of solar winds and flares hit the Earth's magnetic field, they travel along the field lines.
2) Some particles get deflected around the Earth, while others interact with the magnetic field lines, causing currents of charged particles within the magnetic fields to travel toward both poles -- this is why there are simultaneous auroras in both hemispheres. These currents are called Birkeland currents after Kristian Birkeland, the Norwegian physicist who discovered them.
3) When an electric charge cuts across a magnetic field it generates an electric current. As these currents descend into the atmosphere along the field lines, they pick up more energy.
4) When they hit the ionosphere region of the Earth's upper atmosphere, they collide with ions of oxygen and nitrogen.
The particles impact the oxygen and nitrogen ions and transfer their energy to these ions.
5) The absorption of energy by oxygen and nitrogen ions causes electrons within them to become "excited" and move from low-energy to high-energy orbitals.
6) When the excited ions relax, the electrons in the oxygen and nitrogen atoms return to their original orbitals. In the process, they re-radiate the energy in the form of light. This light makes up the aurora, and the different colors come from light radiated from different ions.

As we mentioned, auroras take on different appearances. They can look like an orange or red glow on the horizon -- like a sunrise or sunset. Sometimes they may be mistaken for fires in the distance, like the American Indians thought. They can look like curtains or ribbons and move and undulate during the night.

Auroras can be green, red or blue. Often they will be a combination of colors, with each color visible at a different altitude in the atmosphere.

Note: The particles that interact with the oxygen and nitrogen ions in the atmosphere don't come from the sun, but rather were already trapped by the Earth's magnetic field. The solar winds and flares perturb the magnetic field and set these particles within the magnetosphere in motion.

How do we know what causes auroras?

In 1895, a Norwegian physicist named Kristian Birkeland addressed the queston of what causes auroras. Birkeland believed that auroras were caused by electrons from the sun that interacted with the Earth's magnetic field. To test this, he placed a spherical magnet called a terrella inside a vacuum chamber. He also had an electron gun inside the chamber. When he turned on the gun, electrons interacted with the magnet's field and produced an artificial aurora, supporting his hypothesis.

Birkeland's artificial aurora didn't show the characteristic oval ring. The auroral ring was actually predicted by a Japanese graduate student named Shun-ichi Akasofu in 1964. He examined photographs of auroras and concluded that auroras were rings. So, why weren't Birkeland's auroras oval? Birkeland thought the electrons that excited the oxygen and nitrogen ions came directly from the sun. Only when satellites began to study auroras and measure the magnetosphere did scientists figure out that the electrons came from the magnetosphere itself. When this idea was placed in mathematical models, auroral rings could be explained.

Do auroras occur only on Earth?

Because auroras are caused by the interactions of solar winds and solar flares with the magnetic fields of a planet, you'd think they'd happen on other planets as well. What you need is:
Solar flares and winds that provide the charged particles and energy to interact with a planet’s magnetic field
A planetary magnetic field (probably of some strength) that traps electrons from space
A planetary atmosphere that contains ionic gases that interact with energetic electrons from the magnetic field and produce light through excitation and relaxation of their electrons
So, with these conditions, we have observed auroras on Jupiter and Saturn. Both planets have powerful magnetic fields and atmospheres with ionized gases, mainly hydrogen and helium.

The Hubble Space Telescope caught images of auroras on Jupiter, and the Cassini probe orbiting Saturn has photographed auroras there. ­

Source:-

http://science.howstuffworks.com/nature/climate-weather/atmospheric/aurora2.htm

How pressure cooker works?

What is a pressure cooker, and what does it do?
A pressure cooker works on a simple principle: Steam pressure. A sealed pot, with a lot of steam inside, builds up high pressure, which helps food cook faster.

When was the pressure cooker invented?
It was invented in the 1600s by a Frenchman by Denis Papin, who wanted to translate new discoveries in physics about pressure and steam into cooking. He called his pot the "Digester" but it took quite a while before better manufacturing standards and technology could make these high pressure pots safe.

How does a pressure cooker work?
A pressure cooker is a sealed pot with a valve that controls the steam pressure inside. As the pot heats up, the liquid inside forms steam, which raises the pressure in the pot. This high pressure steam has two major effects:

Raises the boiling point of the water in the pot. When cooking something wet, like a stew or steamed vegetables, the heat of your cooking is limited to the boiling point of water (100°C). But with the steam's pressure now the boiling point can get as high as 138°C. This higher heat helps the food to cook faster.
Raises the pressure, forcing liquid into the food. The high pressure also helps force liquid and moisture into the food quickly, which helps it cook faster and also helps certain foods, like tough meat, get very tender very quickly.

The extra-high heat of the pressure cooker also promotes caramelization and browning in a surprising way — we're not used to food caramelizing when it is cooking in liquid. But the flavors created in a pressure cooker can be really deep and complex — unlike regular steamed foods.

What can you cook in the pressure cooker?
Almost anything! It cooks rice in just a few minutes, and it cooks tougher things like beans and chickpeas in much less than an hour. It is very good for foods that need to be tenderized like braised meats and roasts. But people have cooked all kinds of other things in it too. Laura at Hip Pressure Cooking even made hard-boiled eggs (apparently the shells pop right off). But it is used most frequently around the world for beans and pulses, stews, and vegetables.

This is a link to see the working of pressure cooker at youtube.

http://m.youtube.com/watch?v=TWV3FbgPPXo

How the Human Eye Works?

The human eye has been called the most complex organ in our body. It's amazing that something so small can have so many working parts.

Parts of the Eye

Aqueous Humour
The aqueous humour is a jelly-like substance located in the anterior chamber of the eye.

Choroid
The choroid layer is located behind the retina and absorbs unused radiation.

Ciliary Muscle
The ciliary muscle is a ring-shaped muscle attached to the iris. It is important because contraction and relaxation of the ciliary muscle controls the shape of the lens.

Cornea
The cornea is a strong clear bulge located at the front of the eye (where it replaces the sclera - that forms the outside surface of the rest of the eye). The front surface of the adult cornea has a radius of approximately 8mm. The cornea contributes to the image-forming process by refracting light entering the eye.

Fovea
The fovea is a small depression (approx. 1.5 mm in diameter) in the retina. This is the part of the retina in which high-resolution vision of fine detail is possible.

Hyaloid
The hyaloid diaphragm divides the aqueous humour from the vitreous humour.

Iris
The iris is a diaphragm of variable size whose function is to adjust the size of the pupil to regulate the amount of light admitted into the eye. The iris is the coloured part of the eye (illustrated in blue above but in nature may be any of many shades of blue, green, brown, hazel, or grey).

Lens
The lens of the eye is a flexible unit that consists of layers of tissue enclosed in a tough capsule. It is suspended from the ciliary muscles by the zonule fibers.

Optic Nerve
The optic nerve is the second cranial nerve and is responsible for vision. Each nerve contains approx. one million fibres transmitting information from the rod and cone cells of the retina.

Papilla
The papilla is also known as the "blind spot" and is located at the position from which the optic nerve leaves the retina.

Pupil
The pupil is the aperture through which light - and hence the images we "see" and "perceive" - enters the eye. This is formed by the iris. As the size of the iris increases (or decreases) the size of the pupil decreases (or increases) correspondingly.

Retina
The retina may be described as the "screen" on which an image is formed by light that has passed into the eye via the cornea, aqueous humour, pupil, lens, then the hyaloid and finally the vitreous humour before reaching the retina.
The retina contains photosensitive elements (called rods and cones) that convert the light they detect into nerve impulses that are then sent onto the brain along the optic nerve.

Sclera
The sclera is a tough white sheath around the outside of the eye-ball.
This is the part of the eye that is referred to by the colloquial terms "white of the eye".

Visual Axis
A simple definition of the "visual axis" is "a straight line that passes through both the centre of the pupil and the centre of the fovea". However, there is also a stricter definition (in terms of nodal points) which is important for specialists in optics and related subjects.

Vitreous Humour
The vitreous humour (also known as the "vitreous body") is a jelly-like substance.

Zonules
The zonules (or "zonule fibers") attach the lens to the ciliary muscles.

How the Human Eye Works
In a number of ways, the human eye works much like a digital camera:

Light is focused primarily by the cornea — the clear front surface of the eye, which acts like a camera lens.

The iris of the eye functions like the diaphragm of a camera, controlling the amount of light reaching the back of the eye by automatically adjusting the size of the pupil (aperture).

The eye's crystalline lens is located directly behind the pupil and further focuses light. Through a process called accommodation, this lens helps the eye automatically focus on near and approaching objects, like an autofocus camera lens.

Light focused by the cornea and crystalline lens (and limited by the iris and pupil) then reaches the retina — the light-sensitive inner lining of the back of the eye. The retina acts like an electronic image sensor of a digital camera, converting optical images into electronic signals. The optic nerve then transmits these signals to the visual cortex — the part of the brain that controls our sense of sight.

GPS - How it works?

GPS, or Global Positioning System, is also sometimes called NavStar. GPS is a satellite based global navigation satellite system, GNSS that is used to provide accurate location and time information anywhere on or near the Earth.

GPS is run and maintained by the US government, although access to it has been opened up so that it is freely available worldwide when used with suitable GPS receivers.

Typically GPS is able to provide position information to within a few metres, allowing accurate positioning to be made. It is also possible to extract timing information that enables frequencies and time to be very accurately maintained. Frequency stability performance figures of systems using GPS timing are far in better than crystal or many other accurate frequency sources.

The performance and ease of use of GPS has meant that it is now an integral part of everyday life, with many portable or car-based "satnav" systems being used, as well as many mobile phones incorporating them to enable them to provide location information superimposed on the maps from the phone or satnav.

GPS basics

The basic concept behind GPS is that signals are transmitted from the satellites in space and these are received by the receivers on or near to the surface of the earth. Using timing it is possible to determine the distance from each satellite and thereby using a process of triangulation and a knowledge of the satellite positions the position on Earth can be determined.

The satellites all send timing information so the receiver knows when the message was sent. As radio signals travel at the speed of light they take a very short but finite time to travel the distance from the satellite to the receiver. The satellites also transmit information about their positions. In this way the receiver is able to calculate the distance from the satellite to the receiver. To obtain a full fix of latitude, longitude and altitude, four or more satellites are required, and when the receiver is in the clear, more than four satellites are in view all the time. A fix of just latitude and longitude can be obtained from three satellites.

The fully operational GPS satellite system consists of a constellation of 24 operational satellites with a few more in orbit as spares in case of the failure of one. The GPS satellites are in one of six orbits. These are in planes that are inclined at approximately 55° to the equatorial plane and there are four satellites in each orbit. This arrangement provides the earth user with a view of between five and eight satellites at any time from any point on the Earth.

Using economic ground based receivers GPS is able to provide position information to within a number of metres. The economic costs have also meant that it is now fitted to many motor vehicles, while separate GPS receivers can be bought for a few hundred pounds or dollars. As a result it is widely used by private individuals, as well as many commercial and professional users. In fact the primary use for GPS is as a military navigation system. The fact that it is used so widely is a by-product of its success.

GPS satellites

The satellites are orbiting above the Earth. Their orbits are tightly controlled because errors in their orbit will translate to errors in the final positions. The time signals are also tightly controlled. The satellites contain an atomic clock so that the time signals they transmit are very accurate. Even so these clocks will drift slightly and to overcome this, signals from Earth stations are used to correct this.

The GPS satellites themselves have a design life of ten years, but to ensure that there are no holes in service in the case of unexpected failures, spares are held in orbit and these can be brought into service at short notice.

The satellites are provide their own power through their solar panels. These extend to about 17 feet, and provide the 700 watts needed to power the satellite and its batteries when it is in sunlight. Naturally the satellite needs to remain operation when it is on the dark side of the Earth when the solar panels do not provide any power. This means that when in sunlight the solar panels need to provide additional power to charge batteries, beyond just powering the basic satellite circuitry.

GPS receivers

A large number of GPS receivers are available today. They make widespread use of digital signalling processing techniques. The transmissions from the satellites use spread spectrum technology, and the signal processors correlate the signals received to recover the data. As the signals are very weak it takes some time after the receiver is turned on to gain the first fix. This Time To First Fix (TTFF) is of importance, and in early receivers it could be as long as twelve minutes, although modern receivers use many more correlators are able to shorten this considerably.

When using a GPS receiver the receiver must be in the open. Buildings, or any structure will mask the signals and it may mean that few satellites can be seen. Thus the receivers will not operate inside buildings, and urban areas may often cause problems.

GPS Applications

The primary use for GPS is as a military navigational aid. Run by the American Department of Defense its primary role is to provide American forces with an accurate means of navigation anywhere on the globe. However its use has been opened up so that commercial and private users have access to the signals and can use the system. Accordingly it is very widely used for many commercial applications from aircraft navigation, ship navigation to surveying, and anywhere where location information is required. For private users very cost effective receivers are available these days and may be used for applications including sailing. Even many motor vehicles have them fitted now to provide SatNav systems enabling them to navigate easily without the need for additional maps.

It can be said that GPS has revolutionised global navigation since it became available. Prior to this navigation systems were comparatively localised, and did not offer anything like the same degrees of accuracy

Source:-

http://www.radio-electronics.com/info/satellite/gps/gps-technology-basics-tutorial.php

Part 3. Nanorobot Locomotion and tools.

Nanorobot Locomotion

Assuming the nanorobot isn't tethered or designed to float passively through the bloodstream, it will need a means of propulsion to get around the body. Because it may have to travel against the flow of blood, the propulsion system has to be relatively strong for its size. Another important consideration is the safety of the patient -- the system must be able to move the nanorobot around without causing damage to the host.

Some scientists are looking at the world of microscopic organisms for inspiration. Paramecium move through their environment using tiny tail-like limbs called cilia. By vibrating the cilia, the paramecium can swim in any direction. Similar to cilia are flagella, which are longer tail structures. Organisms whip flagella around in different ways to move around.

Scientists in Israel created microrobot, a robot only a few millimeters in length, which uses small appendages to grip and crawl through blood vessels. The scientists manipulate the arms by creating magnetic fields outside the patient's body. The magnetic fields cause the robot's arms to vibrate, pushing it further through the blood vessels. The scientists point out that because all of the energy for the nanorobot comes from an external source, there's no need for an internal power source. They hope the relatively simple design will make it easy to build even smaller robots.
Other devices sound even more exotic. One would use capacitors to generate magnetic fields that would pull conductive fluids through one end of an electromagnetic pump and shoot it out the back end. The nanorobot would move around like a jet airplane. Miniaturized jet pumps could even use blood plasma to push the nanorobot forward, though, unlike the electromagnetic pump, there would need to be moving parts.

Another potential way nanorobots could move around is by using a vibrating membrane. By alternately tightening and relaxing tension on a membrane, a nanorobot could generate small amounts of thrust. On the nanoscale, this thrust could be significant enough to act as a viable source of motion.

Nanorobot tools

Current microrobots are only a few millimeters long and about a millimeter in diameter. Compared to the nanoscale, that's enormous -- a nanometer is only one-billionth of a meter, while a millimeter is one-thousandth of a meter. Future nanorobots will be so small, you'll only be able to see them with the help of a microscope. Nanorobot tools will need to be even smaller. Here are a few of the items you might find in a nanorobot's toolkit:

Medicine cavity -- a hollow section inside the nanorobot might hold small doses of medicine or chemicals. The robot could release medication directly to the site of injury or infection. Nanorobots could also carry the chemicals used in chemotherapy to treat cancer directly at the site. Although the amount of medication is relatively miniscule, applying it directly to the cancerous tissue may be more effective than traditional chemotherapy, which relies on the body's circulatory system to carry the chemicals throughout the patient's body.

Probes, knives and chisels -- to remove blockages and plaque, a nanorobot will need something to grab and break down material. They might also need a device to crush clots into very small pieces. If a partial clot breaks free and enters the bloodstream, it may cause more problems further down the circulatory system.

Microwave emitters and ultrasonic signal generators -- to destroy cancerous cells, doctors need methods that will kill a cell without rupturing it. A ruptured cancer cell might release chemicals that could cause the cancer to spread further. By using fine-tuned microwaves or ultrasonic signals, a nanorobot could break the chemical bonds in the cancerous cell, killing it without breaking the cell wall. Alternatively, the robot could emit microwaves or ultrasonic signals in order to heat the cancerous cell enough to destroy it.

Electrodes -- two electrodes protruding from the nanorobot could kill cancer cells by generating an electric current, heating the cell up until it dies.

Lasers -- tiny, powerful lasers could burn away harmful material like arterial plaque, cancerous cells or blood clots. The lasers would literally vaporize the tissue.

The two biggest challenges and concerns scientists have regarding these small tools are making them effective and making them safe. For instance, creating a small laser powerful enough to vaporize cancerous cells is a big challenge, but designing it so that the nanorobot doesn't harm surrounding healthy tissue makes the task even more difficult. While many scientific teams have developed nanorobots small enough to enter the bloodstream, that's only the first step to making nanorobots a real medical application.

Nanorobots: Today and Tomorrow

Teams around the world are working on creating the first practical medical nanorobot. Robots ranging from a millimeter in diameter to a relatively hefty two centimeters long already exist, though they are all still in the testing phase of development and haven't been used on people. We're probably several years away from seeing nanorobots enter the medical market. Today's microrobots are just prototypes that lack the ability to perform medical tasks.

Source:-

http://electronics.howstuffworks.com/nanorobot.htm

Part 2. Nanorobots navigation and power source

Nanorobot Navigation

There are three main considerations scientists need to focus on when looking at nanorobots moving through the body -- navigation, power and how the nanorobot will move through blood vessels. Nanotechnologists are looking at different options for each of these considerations, each of which has positive and negative aspects. Most options can be divided into one of two categories: external systems and onboard systems.

External navigation systems might use a variety of different methods to pilot the nanorobot to the right location. One of these methods is to use ultrasonic signals to detect the nanorobot's location and direct it to the right destination. Doctors would beam ultrasonic signals into the patient's body. The signals would either pass through the body, reflect back to the source of the signals, or both. The nanorobot could emit pulses of ultrasonic signals, which doctors could detect using special equipment with ultrasonic sensors. Doctors could keep track of the nanorobot's location and maneuver it to the right part of the patient's body.

Using a Magnetic Resonance Imaging (MRI) device, doctors could locate and track a nanorobot by detecting its magnetic field. Doctors and engineers at the Ecole Polytechnique de Montreal demonstrated how they could detect, track, control and even propel a nanorobot using MRI. They tested their findings by maneuvering a small magnetic particle through a pig's arteries using specialized software on an MRI machine. Because many hospitals have MRI machines, this might become the industry standard -- hospitals won't have to invest in expensive, unproven technologies.

Doctors might also track nanorobots by injecting a radioactive dye into the patient's bloodstream. They would then use a fluoroscope or similar device to detect the radioactive dye as it moves through the circulatory system. Complex three-dimensional images would indicate where the nanorobot is located. Alternatively, the nanorobot could emit the radioactive dye, creating a pathway behind it as it moves through the body.

Other methods of detecting the nanorobot include using X-rays, radio waves, microwaves or heat. Right now, our technology using these methods on nano-sized objects is limited, so it's much more likely that future systems will rely more on other methods.

Onboard systems, or internal sensors, might also play a large role in navigation. A nanorobot with chemical sensors could detect and follow the trail of specific chemicals to reach the right location. A spectroscopic sensor would allow the nanorobot to take samples of surrounding tissue, analyze them and follow a path of the right combination of chemicals.

Hard as it may be to imagine, nanorobots might include a miniature television camera. An operator at a console will be able to steer the device while watching a live video feed, navigating it through the body manually. Camera systems are fairly complex, so it might be a few years before nanotechnologists can create a reliable system that can fit inside a tiny robot.

Powering the Nanorobot

Just like the navigation systems, nanotechnologists are considering both external and internal power sources. Some designs rely on the nanorobot using the patient's own body as a way of generating power. Other designs include a small power source on board the robot itself. Finally, some designs use forces outside the patient's body to power the robot.

Nanorobots could get power directly from the bloodstream. A nanorobot with mounted electrodes could form a battery using the electrolytes found in blood. Another option is to create chemical reactions with blood to burn it for energy. The nanorobot would hold a small supply of chemicals that would become a fuel source when combined with blood.

A nanorobot could use the patient's body heat to create power, but there would need to be a gradient of temperatures to manage it. Power generation would be a result of the Seebeck effect. The Seebeck effect occurs when two conductors made of different metals are joined at two points that are kept at two different temperatures. The metal conductors become a thermocouple, meaning that they generate voltage when the junctures are at different temperatures. Since it's difficult to rely on temperature gradients within the body, it's unlikely we'll see many nanorobots use body heat for power.

While it might be possible to create batteries small enough to fit inside a nanorobot, they aren't generally seen as a viable power source. The problem is that batteries supply a relatively small amount of power related to their size and weight, so a very small battery would only provide a fraction of the power a nanorobot would need. A more likely candidate is a capacitor, which has a slightly better power-to-weight ratio.

Another possibility for nanorobot power is to use a nuclear power source. The thought of a tiny robot powered by nuclear energy gives some people the willies, but keep in mind the amount of material is small and, according to some experts, easy to shield. Still, public opinions regarding nuclear power make this possibility unlikely at best.
External power sources include systems where the nanorobot is either tethered to the outside world or is controlled without a physical tether. Tethered systems would need a wire between the nanorobot and the power source. The wire would need to be strong, but it would also need to move effortlessly through the human body without causing damage. A physical tether could supply power either by electricity or optically. Optical systems use light through fiber optics, which would then need to be converted into electricity on board the robot.

The Piezoelectric Effect
Some crystals gain an electrical charge if you apply force to them. Conversely, if you apply an electric charge to one of these crystals, it will vibrate as a result, giving off ultrasonic signals. Quartz is probably the most familiar crystal with piezoelectric effects.
External systems that don't use tethers could rely on microwaves, ultrasonic signals or magnetic fields. Microwaves are the least likely, since beaming them into a patient would result in damaged tissue, since the patient's body would absorb most of the microwaves and heat up as a result. A nanorobot with a piezoelectric membrane could pick up ultrasonic signals and convert them into electricity. Systems using magnetic fields, like the one doctors are experimenting with in Montreal, can either manipulate the nanorobot directly or induce an electrical current in a closed conducting loop in the robot.

Source:-

http://electronics.howstuffworks.com/nanorobot.htm