Picture: Colloidal quantum dots irradiated with a UV light. Different sized quantum dots emit different color light due to quantum confinement.
Quantum dots are constructed of a few hundred atoms, yet have all the quantum properties of a single atom. Some have been designed to reveal the workings of the nervous system, and others to be the detectors of breast cancer.
They’re zero dimensional, so they have less density 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.
Researchers have tested them in transistors, solar cells, LEDs, and diode lasers. They have investigated them as agents for medical imaging and hope to use them as qubits ( qubit- In a classical system, a bit would have to be in one state or the other, but quantum mechanics allows the qubit to be in a superposition of both states at the same time).
In fluorescent dye applications, higher frequencies of light emitted after excitation of the dot as the crystal size grows smaller results in a color shift from red to blue in the light emitted.
An immediate optical feature of colloidal quantum dots is their coloration. Quantum dots of the same material, but with different sizes, can emit light of different colors. This is the quantum confinement effect. The larger the dot, the redder (lower energy); Conversely, smaller dots emit bluer (higher energy) light.Quantitatively speaking, the energy (and hence color) of the fluorescent light is inversely proportional to the size of the quantum dot
Quantum dots of different sizes can be assembled into a gradient multi-layer nanofilm —- Properties of such nanostructures are finding its applications in design of solar cells and energy storage devices.
In an unconfined semiconductor, an electron-hole pair is given a characteristic length, called the exciton Bohr radius. This is estimated by replacing the positively charged atomic core with the hole in the Bohr formula. If the electron and hole are constrained further, then properties of the semiconductor change. For example, the absorption and emission wavelength of light shifts towards smaller wavelengths. This effect is a form of quantum confinement, and it is a key feature in many emerging electronic structures.
Lee et al. (2002) reported using genetically engineered M13 bacteriophage viruses to create quantum dot biocomposite structures. It is known that liquid crystalline structures of wild-type viruses (Fd, M13, and TMV) are adjustable by controlling the solution concentrations, solution ionic strength, and the external magnetic field applied to the solutions.
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Theory of Everything (intro)
A brief intro to the current theory of (almost) everything - the Standard Model of particle physics. It’s like cake, only universal.
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Minute Physics provides an energetic and entertaining view of old and new problems in physics — all in a minute!
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Time Need Not End In The Multiverse
Imaged Above: Ultimate guide to the Multiverse
Gamblers already had enough to think about without factoring the end of time into their calculations. But a year after a group of cosmologists argued that they should, another team says time need not end after all.
It all started with this thought experiment. In a back room in a Las Vegas casino, you are handed a fair coin to flip. You will not be allowed to see the outcome, and the moment the coin lands you will fall into a deep sleep. If the coin lands heads up, the dealer will wake you 1 minute later; tails, in 1 hour. Upon waking, you will have no idea how long you have just slept.
The dealer smiles: would you like to bet on heads or tails? Knowing it’s a fair coin, you assume your odds are 50/50, so you choose tails. But the house has an advantage. The dealer knows you will almost certainly lose, because she is factoring in something you haven’t: that we live in a multiverse.
The idea that our universe is just one of many crops up in a number of physicists’ best theories, including inflation. It posits that different parts of space are always ballooning into separate universes, so that our observable universe is just a tiny island in an exponentially growing multiverse.
In any infinite multiverse, everything that can happen, will happen - an infinite number of times. That has created a major headache for cosmologists, who want to use probabilities to make predictions, such as the strength of the mysterious dark energy that is accelerating the expansion of our own universe. How can we say that anything is more or less probable than anything else?
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Radioactive Particles Are Spreading Across Europe and No One Knows Why
‘Iodine-131 is a dangerous radioactive isotope. It can clog up your thyroid gland and contaminate food. It’s been a big problem in Japan (for obvious reasons), but now it’s been scarily detected throughout Europe. And nobody knows the source.’
Before everyone puts on their lead suits, it’s important to understand that the current iodine-131 levels are incredibly low and unlikely to cause harm to anyone (the estimated dose level was 1/40,000 of the radiation that a person receives during a Transatlantic flight). However, what is causing this is a complete mystery which remains to be solved.
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