Saturday, 28 January 2012

Plasmonic cloak makes objects invisble, but only in the microwave region of the spectrum

Researchers have "cloaked" a three-dimensional object, making it invisible from all angles, for the first time.

Source: Engadget - USS Defiant
However, the demonstration works only for waves in the microwave region of the electromagnetic spectrum.

It uses a shell of what are known as plasmonic materials; they present a "photo negative" of the object being cloaked, effectively cancelling it out. The idea, outlined in New Journal of Physics, could find first application in high-resolution microscopes.

Most of the high-profile invisibility cloaking efforts have focused on the engineering of "metamaterials" - modifying materials to have properties that cannot be found in nature. The modifications allow metamaterials to guide and channel light in unusual ways - specifically, to make the light rays arrive as if they had not passed over or been reflected by a cloaked object.

Previous efforts that have made 3-D objects disappear have relied upon a "carpet cloak" idea, in which the object to be cloaked is overlaid with a "carpet" of metamaterial that bends light so as to make the object invisible. 

Now, Andrea Alu and colleagues at the University of Texas at Austin have pulled off the trick in "free space", making an 18cm-long cylinder invisible to incoming microwave light.

Friday, 27 January 2012

2012 BX34 - Asteroid Close Approach

Today, January 27, 2012 at about 15:25 UT, the asteroid designated 2012 BX34 will pass only 59,044 km (36,750 miles) or about ~0.2 lunar distance (or 0.0004 AU) above the Earth's surface. The asteroid was discovered by Catalina Sky Survey with a 0.68-m Schmidt + CCD on January 25, 2012 at magnitude ~20. According to its absolute magnitude (H=27.6) this asteroid has an estimated diameter of roughly 8-18 meters, so it is very small. We have been able to follow-up this object few hours ago remotely from the GRAS Observatory (near Mayhill, NM) through a 0.10-m f/5 reflector + CCD.  At the moment of our images from New Mexico on January 27, 11:04UT, "2012 BX34" was moving at about ~318.86 "/min and its magnitude was ~15. At the moment of its close approach around 15UT of today, 2012 BX34 will be bright as magnitude ~13.8 and moving at ~1810 "/min. Below you can see a single 120-seconds exposure showing the object as a ~11-arcminutes trail (due to its fast speed). Click on the thumbnail to see a bigger version:

Sources: Remanzacco

While there is no cause for concern, this is one of the closest approaches recorded. The table below shows the top 20 closest approaches by NEOs (Near-Earth Objects) sorted by nominal distance.

Source: remenzacco

Thursday, 26 January 2012

What are Quantum Dots?

Quantum dots are tiny particles, or “nanoparticles”, of a semiconductor material, traditionally chalcogenides (selenides or sulfides) of metals like cadmium or zinc (CdSe or ZnS, for example), which range from 2 to 10 nanometers in diameter (about the width of 50 atoms).

Source: Physorg
Because of their small size, quantum dots display unique optical and electrical properties that are different in character to those of the corresponding bulk material. The most immediately apparent of these is the emission of photons under excitation, which are visible to the human eye as light. Moreover, the wavelength of these photon emissions depends not on the material from which the quantum dot is made, but its size.

The ability to precisely control the size of a quantum dot enables the manufacturer to determine the wavelength of the emission, which in turn determines the colour of light the human eye perceives. Quantum dots can therefore be “tuned” during production to emit any colour of light desired. The ability to control, or “tune” the emission from the quantum dot by changing its core size is called the “size quantisation effect”.

The smaller the dot, the closer it is to the blue end of the spectrum, and the larger the dot, the closer to the red end. Dots can even be tuned beyond visible light, into the infra-red or into the ultra-violet.
At the end of the production process, quantum dots appear physically either as a powder or in a solution. Because of their tiny size, the ability to produce even a relatively “small” volume of quantum dots (e.g. one kilo) will yield enough actual quantum dots for industrial scale applications. Nanoco Technologies has patented a molecular seeding process which enables such “large scale” production to occur.

Now, the ability to mass-produce consistently high quality quantum dots enables product designers to envisage their use in consumer products and a wide range of other applications for the first time, and then bring these superior, next-generation products to market.

Quantum dots are particularly significant for optical applications due to their high extinction co-efficient. In electronic applications they have been proven to operate like a single electron transistor and show the Coulomb blockade effect. Quantum dots have also been suggested as implementations of qubits for quantum information processing.

The ability to tune the size of quantum dots is advantageous for many applications. For instance, larger quantum dots have a greater spectrum-shift towards red compared to smaller dots, and exhibit less pronounced quantum properties. Conversely, the smaller particles allow one to take advantage of more subtle quantum effects.

Being zero dimensional, quantum dots have a sharper density of states than higher-dimensional structures. As a result, they have superior transport and optical properties, and are being researched for use in diode lasers, amplifiers, and biological sensors. Quantum dots may be excited within a locally enhanced electromagnetic field produced by gold nanoparticles, which can then be observed from the surface Plasmon resonance in the photo luminescent excitation spectrum of (CdSe)ZnS nanocrystals. High-quality quantum dots are well suited for optical encoding and multiplexing applications due to their broad excitation profiles and narrow/symmetric emission spectra. The new generations of quantum dots have far-reaching potential for the study of intracellular processes at the single-molecule level, high-resolution cellular imaging, long-term in vivo observation of cell trafficking, tumour targeting, and diagnostics.

Wednesday, 25 January 2012

How do lasers work?

Laser is an acronym for Light Amplification by Stimulated Emission of Radiation. The next thing to consider is why laser light is different than other light. You know that laser light travels in straight lines and stays in a small beam instead of spreading out like regular light, right? The trick there is that laser light is only one color. You've seen rainbows I am sure. What we call white light (like sunlight) is actually a mixture of a whole range of colors from blue to red. All of those colors travel together all mixed up. When the colors hit something that makes them bend, like raindrops, prisms or almost anything for that matter, those colors separate.
Imagine a race track jammed full of cars all going different speeds. They travel in a bunch until they come to a curve. The cars going faster cannot turn sharply so they go to the outside of the track. The slower cars can turn sharply so they move to the inside of the track. When the cars come out of the curve the cars are arranged from fastest to slowest. The same thing happens with light although it's the lights energy level or color that separates them. Now imagine that every single car is going exactly the same speed. The cars go into the curve in a line, go through the curve and come out of the curve still in a straight line. That's how laser light works. It does bend when it hits something, but all the light gets bent the same amount, so the light does not spread out.

So again, a laser generates a light that is rigorously one color. How that is done is both extremely simple and very complex at the same time. A property of electrons is that, after being excited or energized to a higher than normal state, they will eventually fall back to their original state. The energy that they had at that higher level leaks away as light of a specific color. If we excite a lot of electrons they leak off a lot of light all of one color. We do this a number of ways. A very simple way is to take material that has the right electrons and flash a strong light on it. The electrons in that material will absorb the energy and spit it back out as a single color light. We use devices like mirrors and lenses to get all of the light traveling in the same direction and off it goes in straight line. Since laser light does not scatter very much you usually cannot see it until it hits something.

Tuesday, 24 January 2012

Solar Storm

A solar flare is a sudden brightening observed over the Sun surface or the solar limb, which is interpreted as a large energy release of up to 6 × 1025 joules of energy(about a sixth of the total energy output of the Sun each second). The flare ejects clouds of electrons, ions, and atoms through the corona into space. These clouds typically reach Earth a day or two after the event. The term is also used to refer to similar phenomena in other stars, where the term stellar flare applies.

Source: Wikipedia
Solar flares affect all layers of the solar atmosphere (photosphere, chromosphere, and corona), when the medium plasma is heated to tens of millions of kelvins andelectrons, protons, and heavier ions are accelerated to near the speed of light. They produce radiation across the electromagnetic spectrum at all wavelengths, from radio waves to gamma rays, although most of the energy goes to frequencies outside the visual range and for this reason the majority of the flares are not visible to the naked eye and must be observed with special instruments. Flares occur in active regions around sunspots, where intense magnetic fields penetrate the photosphere to link the coronato the solar interior. Flares are powered by the sudden (timescales of minutes to tens of minutes) release of magnetic energy stored in the corona. The same energy releases may produce coronal mass ejections (CME), although the relation between CMEs and flares is still not well established.

A coronal mass ejection (CME) is a massive burst of solar wind, other light isotope plasma, and magnetic fields rising above the solar corona or being released into space.

Coronal mass ejections are often associated with other forms of solar activity, most notably solar flares, but a causal relationship has not been established. Most ejections originate from active regions on Sun's surface, such as groupings of sunspots associated with frequent flares. Near solar maxima the Sun produces about three CMEs every day, whereas near solar minima there is about one CME every five days.


Monday, 23 January 2012

Aurora: Northern Lights

Polar lights (aurora polaris) are a natural phenomenon found in both the northern and southern hemispheres that can be truly awe inspiring. Northern lights are also called by their scientific name,aurora borealis, and southern lights are called aurora australis.

The origin of the aurora begins on the surface of the sun when solar activity ejects a cloud of gas. Scientists call this a coronal mass ejection (CME). If one of these reaches earth, taking about 2 to 3 days, it collides with the Earth’s magnetic field. This field is invisible, and if you could see its shape, it would make Earth look like a comet with a long magnetic ‘tail’ stretching a million miles behind Earth in the opposite direction of the sun.

When a coronal mass ejection collides with the magnetic field, it causes complex changes to happen to the magnetic tail region. These changes generate currents of charged particles, which then flow along lines of magnetic force into the Polar Regions. These particles are boosted in energy in Earth’s upper atmosphere, and when they collide with oxygen and nitrogen atoms, they produce dazzling auroral light.


Waterhole (radio)

The waterhole, or water hole, refers to an especially quiet band of the electromagnetic spectrum between 1,420 and 1,666 megahertz, corresponding to wavelengths of 21 and 18 centimeters respectively. The term was coined by Bernard Oliver. The strongest hydroxyl radical spectral line radiates at 18 centimeters, and hydrogen at 21 centimeters. These two combined form water, and water is currently thought to be essential to extraterrestrial life advanced enough to generateradio signals. Bernard M. Oliver theorized that the waterhole would be a good, obvious band for communication with extraterrestrial intelligence, hence the pun, in English a watering hole is a vernacular reference to a common place to meet and talk. Several programs involved in the search for extraterrestrial intelligence, including SETI@home, search in the waterhole.

Source: DavidDarling

Radio source SHGb02+14a

Radio source SHGb02+14a is a source and a candidate in the Search for Extra-Terrestrial Intelligence (SETI), discovered in March 2003 by SETI@home and announced in New Scientist on September 1, 2004.

The source was observed three times at a frequency of about 1420 MHz, one of the frequencies in the waterhole region, which is theorized to be a good candidate for frequencies used by extraterrestrial intelligence to broadcast contact signals.

There are a number of puzzling features of this candidate, which have led to a large amount of skepticism. The source is located between the constellations Pisces and Aries, a direction in which no stars are observed within 1000 light yearsof earth.It is also a very weak signal. The frequency of the signal has a rapid drift, which would correspond to it being emitted from a planet orbiting nearly 40 times faster than the Earth around the sun. Each time the signal was detected, it was again at about 1420 MHz, the original frequency before any drift. The signal may represent a resonating pulsar across a Gaussian belt

There are also a number of potential explanations for this signal. SETI@home has denied media reports of a likely extraterrestrial intelligence signal.It could be an artifact of random chance, cosmic noise or even just a glitch in the technology.


String Theory: The Basics

Think of a guitar string that has been tuned by stretching the string under tension across the guitar. Depending on how the string is plucked and how much tension is in the string, different musical notes will be created by the string. These musical notes could be said to be excitation modes of that guitar string under tension.

Source: Scientific American, Nov 2007
In a similar manner, in string theory, the elementary particles we observe in particle accelerators could be thought of as the "musical notes" or excitation modes of elementary strings.

In string theory, as in guitar playing, the string must be stretched under tension in order to become excited. However, the strings in string theory are floating in spacetime, they aren't tied down to a guitar. Nonetheless, they have tension. The string tension in string theory is denoted by the quantity 1/(2 p a'), where a' is pronounced "alpha prime"and is equal to the square of the string length scale. 

If string theory is to be a theory of quantum gravity, then the average size of a string should be somewhere near the length scale of quantum gravity, called the Planck length, which is about 10-33centimeters, or about a millionth of a billionth of a billionth of a billionth of a centimeter. Unfortunately, this means that strings are way too small to see by current or expected particle physics technology (or financing!!) and so string theorists must devise more clever methods to test the theory than just looking for little strings in particle experiments. 

String theories are classified according to whether or not the strings are required to be closed loops, and whether or not the particle spectrum includes fermions. In order to include fermions in string theory, there must be a special kind of symmetry calledsupersymmetry, which means for every boson (particle that transmits a force) there is a corresponding fermion (particle that makes up matter). So supersymmetry relates the particles that transmit forces to the particles that make up matter. 

Supersymmetric partners to to currently known particles have not been observed in particle experiments, but theorists believe this is because supersymmetric particles are too massive to be detected at current accelerators. Particle accelerators could be on the verge of finding evidence for high energy supersymmetry in the next decade. Evidence for supersymmetry at high energy would be compelling evidence that string theory was a good mathematical model for Nature at the smallest distance scales.

There are several ways theorists can build string theories. Start with the elementary ingredient: a wiggling tiny string. Next decide: should it be an open string or a closed string? Then ask: will I settle for only bosons ( particles that transmit forces) or will I ask for fermions, too (particles that make up matter)? (Remember that in string theory, a particle is like a note played on the string.) 

If the answer to the last question is "Bosons only, please!" then one gets bosonic string theory. If the answer is "No, I demand that matter exist!" then we wind up needing supersymmetry, which means an equal matching between bosons (particles that transmit forces) and fermions (particles that make up matter). A supersymmetric string theory is called a superstring theory. There are five kinds of superstring theories, shown in the table below. 

The final question for making a string theory should be: can I doquantum mechanics sensibly? For bosonic strings, this question is only answered in the affirmative if the spacetime dimensions number26. For superstrings we can whittle it down to 10. How we get down to the four spacetime dimensions we observe in our world is another story.

Sunday, 22 January 2012

Black Holes = Scary Sh*t

Try to jump so high that you fly right off of the Earth into outer space. What happens? Why don't you get very far? The gravitational force pulls you back down again very quickly. You could jump much higher on Mars, still higher on the moon, because they're both less massive than the Earth. The strength of gravity at the surface of the moon is only 1/6 the strength of gravity at the surface of the Earth. 

You are essentially trapped on Earth, unless you can find a rocket that can travel at escape velocity away from the Earth. This is how our space program works. If you shoot something fast enough, it can escape gravity and make it to outer space.

But hold the phone -- there's supposedly a maximum speed in the Universe, the speed of light. What happens if the escape velocity of a planet were greater than the speed of light? In other words, what if gravity were strong enough to trap light itself? 

Then you'd have yourself a black hole. A black hole is a gravitating object whose gravitational field is so strong that light cannot escape. The event horizon is where light loses the ability to escape from the black hole. Nothing that goes inside the event horizon can ever get back out again, not even light. 

Black holes can be created by the gravitational collapse of large stars that are at least twice as massive as our Sun. Normally, stars balance the gravitational force with the pressure from the nuclear fusion reactions inside. When a star gets old and burns up all of its hydrogen into helium and then turns the helium into heavier elements like iron and nickel, it can have three fates. The first two fates occur for stars less than about twice the mass of our Sun (and one of them will be our Sun's eventual fate). These two fates both depend on the fermionic repulsion pressure described by quantum mechanics -- two fermions cannot be in the same quantum state at the same time. This means that the two stable destinies for a collapsing star will be:
  1. a white dwarf supported by the fermionic repulsion pressure of the electrons in the heavy atoms in the core 
  2. a neutron star supported by the fermionic repulsion pressure of the neutrons in the nuclei of the heavy atoms in the core
If the mass of the collapsing star is too large, bigger than twice the mass of our Sun, the fermionic repulsion pressure of either the electrons or the neutrons is not strong enough to prevent the ultimate gravitational collapse into a black hole. 

The estimated age of the Universe is several times the lifespan of an average star. This means there must have been a lot of stars bigger than twice the mass of our Sun that have burned their hydrogen and collapsed since the Universe began. Our Universe ought to contain many black holes, if the model that astrophysicists use to describe their formation is correct. Black holes created by the collapse of individual stars should only be about 2 to 100 times as massive as our Sun. 

Another way that black holes can be created is the gravitational collapse of the center of a large cluster of stars. These types of black holes can be very much more massive than our Sun. There may be one of them in the center of every galaxy, including our galaxy, the Milky Way. The black hole shown above sits in the middle of the galaxy called NGC 7052, surrounded by a bright cloud of dust 3,700 light-years in diameter. The mass of this black hole is 300 million times the mass of our Sun.

Reference:, check the site out, covers some very interesting topics in a variety of difficulties.

Electromagnetic spectrum

The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object.

Electromagnetic radiation (EM radiation or EMR) is a form of energy emitted and absorbed by charged particles, which exhibits wave-like behavior as it travels through space. EMR has both electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy and wave propagation. In vacuum, electromagnetic radiation propagates at a characteristic speed, the speed of light.

James Clerk Maxwell first formally postulated electromagnetic waves. These were subsequently confirmed by Heinrich Hertz. Maxwell derived a wave form of the electric and magnetic equations, thus uncovering the wave-like nature of electric and magnetic fields, and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave.

The electromagnetic spectrum extends from low frequencies used for modern radio communication to gamma radiation at the short-wavelength (high-frequency) end, thereby covering wavelengths from thousands of kilometres down to a fraction of the size of an atom. The limit for long wavelength is the size of the universe itself, while it is thought that the short wavelength limit is in the vicinity of the Planck length.

The types of electromagnetic radiation are broadly classified into the following classes:
  1. Gamma radiation
  2. X-ray radiation
  3. Ultraviolet radiation
  4. Visible radiation
  5. Infrared radiation
  6. Microwave radiation
  7. Radio waves

WOW! Signal

The Wow! signal was a strong narrowband radio signal detected by Dr. Jerry R. Ehman on August 15, 1977, while working on a SETI project at the Big Ear radio telescope of The Ohio State University. Amazed at how closely the signal matched the expected signature of an interstellar signal in the antenna used, Ehman circled the signal on the computer printout and wrote the comment "Wow!" on its side, this how the signal became to be known as the Wow signal.

The signal bore expected hallmarks of potential non-terrestrial and non-solar system origin. It lasted for the full 72-second duration that Big Ear observed it, but has not been detected again.

There are numerous theories casting speculation on the signal's true origin, mainly that if it was artificially created, it then would have been found the next 50 times they searched for the signal, but it was not.


Thursday, 19 January 2012

Arecibo message

The Arecibo message was broadcast into space a single time via frequency modulated radio waves at a ceremony to mark the remodeling of the Arecibo radio telescope on 16 November 1974. It was aimed at the globular star cluster M13 some 25,000 light years away because M13 was a large and close collection of stars that was available in the sky at the time and place of the ceremony. The message consisted of 1679 binary digits, approximately 210 bytes, transmitted at a frequency of 2380 MHz and modulated by shifting the frequency by 10 Hz, with a power of 1000 kW. The "ones" and "zeros" were transmitted by frequency shifting at the rate of 10 bits per second. The total broadcast was less than three minutes.

Source: WikiMedia
The cardinality of 1679 was chosen because it is a semiprime (the product of two prime numbers), to be arranged rectangularly as 73 rows by 23 columns. The alternative arrangement, 23 rows by 73 columns, produces jumbled nonsense.

Dr. Frank Drake, then at Cornell University and creator of the famous Drake equation, wrote the message, with help from Carl Sagan, among others. The message consists of seven parts that encode the following (from the top down):

  1. The numbers one (1) through ten (10)
  2. The atomic numbers of the elements hydrogen, carbon, nitrogen, oxygen, and phosphorus, which make up deoxyribonucleic acid (DNA)
  3. The formulas for the sugars and bases in the nucleotides of DNA
  4. The number of nucleotides in DNA, and a graphic of the double helix structure of DNA
  5. A graphic figure of a human, the dimension (physical height) of an average man, and the human population of Earth
  6. A graphic of the Solar System
  7. A graphic of the Arecibo radio telescope and the dimension (the physical diameter) of the transmitting antenna dish

Because it will take 25,000 years for the message to reach its intended destination of stars (and an additional 25,000 years for any reply), the Arecibo message was more a demonstration of human technological achievement than a real attempt to enter into a conversation with extraterrestrials. In fact, the stars of M13 that the message was aimed at will no longer be in that location when the message arrives. According to the Cornell News press release of November 12, 1999, the real purpose of the message was not to make contact, but to demonstrate the capabilities of newly installed equipment.

Tuesday, 10 January 2012

Planets! A Short history of our celestial neighbours

Photo: Corbis

The term 'Planet' comes from the Greek word for 'Wanderer', and a planet can be defined as a celestial body that orbits a star, has sufficient mass for it's gravity to overcome rigid body forces so that it assumes a round shape, has cleared the area surrounding it's orbit.

The major planets of the solar system comprise of Mercury, Venus, Earth, Mars, Jupiter and Saturn. Their distance from the sun is respective of their order. These planets are quite visible to the naked eye and because of this fact they have been known to the human race for over a 1000 years, although because they are visible it's difficult to establish the first discoverers.

The first recorded telescope was invented by Hans Lippershey in 1608, a year later Galileo made a telescope with 3x magnification, which it later improved on to develop a telescope with 30x magnification. With this device, now known as the Galilean telescope, he first discovered the moons of Jupiter in 1610.

Uranus was originally believed to be a rogue star until 1781, when the British astronomer William Herschel'scareful tracking proved that it orbited the sun, complying the planetary definition. Slight variations in Uranus's orbit hinted that is was being disturbed by another celestial body. This prediction was proved correct in 1846 by French astronomer and celestial mechanic Urbain Jean Joseph Le Verrier.

Finally in 1930, the existence of Pluto was confirmed by Clyde Tombaugh at the Lowell Observatory in the United States. Pluto orbited the Sun for another 75 years as a planet before it was dethroned in 2005 by the International Astronomical Union, being reassigned as a dwarf planet.

The same year Pluto was dethroned another celestial body was discovered, that is larger than Pluto, by Michael Brown of Caltech. Caltech named the planet Eris. The discovery created a divide in astronomical community, with those for calling Eris the 10th planet of the solar system and those who argue it isn't a true planet.

Some interesting statistics:

Celestial Body  Distance to Sun  Orbit in days Diameter
Mercury  0.39 AU  87.96 days  4,878 km
Venus  0.723 AU  224.68 days  12,104 km
Earth  1 AU  365.26 days  12,576 km
Mars  1.524 AU  686.98 days  6,787 km
Jupiter  5.203 AU  4332.7 days  142,796 km
Saturn  9.539 AU  10759.9 days  120,660 km
Uranus  19.18 AU  30707.4 days  51,117 km
Neptune  30.06 AU  164.81 years  48,600 km
Pluto  39.53 AU  247.7 years  2,274 km

AU stands for Astronomical Unit and is the average distance from the Earth to the Sun.