Tag Archives: physics

What does current look like on a quantum level?

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To understand how current flows in a material you first have to understand electrons behave in a material. The key feature of solid state physics is that many materials are crystals. This means that the atoms are spaced periodically. As you mention, band structures are the way that we summarize the effect of this periodic potential. Basically, a band structure just relates an electrons momentum p=mv=hbar k to its energy. The momentum can be positive or negative, the sign only denotes direction. In free space this is very boring, Energy=m v2 /2 = p2 /2m=hbar k2 /2m. When you throw in a periodic potential, this becomes modified and results in bands. Actually calculating band structures is quite difficult. The key idea is that there are ranges of energy where the electron can live and ranges of energy where the electron cannot live.

via What does current look like on a quantum level? : askscience.

Matchstick-sized sensor can record your private chats

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Conventional microphones work when sound waves make a diaphragm move, creating an electrical signal. Microflown’s sensor has no moving parts. It consists of two parallel platinum strips, each just 200 nanometres deep, that are heated to 200 °C. Air molecules flowing across the strips cause temperature differences between the pair. Microflown’s software counts the air molecules that pass through the gap between the strips to gauge sound intensity: the more air molecules in a sound wave, the louder the sound. At the same time, it analyses the temperature change in the strips to work out the movement of the air and calculate the coordinates of whatever generated the sound.

via Matchstick-sized sensor can record your private chats – 26 September 2013 – New Scientist.

Acoustic Vector Sensors

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In acoustics this movement of air is called particle velocity. The Microflown sensor is based upon MEMS technology, and uses the temperature difference in the corss section of two extremely sensitivy platinum wires that are heated up to 200°C in order to determine Acoustic Particle Velocity. When air flows across the wires, the first wire cools down a little and due to heat transfer the air picks up some heat. Hence, the second wire is cooled down with the heated air and cools down less than the first wire. A temperature difference occurs in the wires, which alters their electrical resistance. This generates a voltage difference that is proportional to the Particle velocity and the effect is directional: when the direction of the airflow reverses, the temperature difference will reverse too.

via Overview – Acoustic Vector Sensors – Microflown AVISA.

“Synthetic Tracking” Set to Revolutionise Near-Earth Asteroid Discovery

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By contrast, they say that with a 5 metres telescope, synthetic tracking should spot about 80 of these objects each night. That’s “almost 1000 times higher than the discovery rate of these small objects over the last 5 years,” they say.

via “Synthetic Tracking” Set to Revolutionise Near-Earth Asteroid Discovery  — The Physics arXiv Blog — Medium.

But there are other uses for this data. NASA is hoping to send a crewed mission to a near Earth asteroid in the not-too-distant future and has started a program called the Asteroid Grand Challenge to identify potential targets.

Paper on this subject here.

The Feynman Lectures on Physics

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Caltech and The Feynman Lectures Website are pleased to present this online edition of The Feynman Lectures on Physics. Now, anyone with internet access and a web browser can enjoy reading a high-quality up-to-date copy of Feynman’s legendary lectures. This edition has been designed for ease of reading on devices of any size or shape; text, figures and equations can all be zoomed without degradation.1

via The Feynman Lectures on Physics.

European scientists propose world’s largest quantum network, between Earth and the ISS

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In recent years, quantum physicists have successfully teleported entangled photons over a free-space distance of 143 kilometers (89 miles) using lasers, and 250 kilometers (155 miles) over optical fiber in the lab. In the past year we have also seen the first ground-to-air network, between a base station and an airplane flying 20 kilometers (12 miles) above. These were impressive feats, but to prove the possibility of a worldwide, satellite-based quantum network, larger distances are needed — something like the 400 kilometers (248 miles) to the ISS.

via European scientists propose world’s largest quantum network, between Earth and the ISS | ExtremeTech.

What the Dalai Lama can teach us about temperatures below absolute zero

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Here’s the new definition that they came up with. Temperature measures the willingness of an object to give up energy. Actually, I lied. This isn’t how they really define temperature, because physicists speak math, not english. They define it as \frac{1}{T} = \frac{dS}{dE} which says, in words, that the temperature is inversely proportional to the slope of the entropy vs. energy curve.

via What the Dalai Lama can teach us about temperatures below absolute zero | Empirical Zeal.

Highly charged – the US Navy’s electromagnetic railgun programme

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Railguns consist of two parallel metal rails, between which a projectile held in an armature is loaded, completing a circuit between them. A massive electrical current of the order of one million amperes is applied, creating an electromagnetic field, which in turn produces a force that accelerates the projectile along the rails.

via Highly charged – the US Navy’s electromagnetic railgun programme – Naval Technology.

Railgun projectiles are generally non-explosive, relying on their enormous speed to destroy the target and thus reducing the risk of a fire on board a ship, and comparatively small and lightweight, so they can be more readily transported and stored. The kinetic energy they deliver could do as much damage as a Tomahawk missile, enabling them to travel clean through a ship.

Kinetic Energy = 1/2 * mass * velocity squared.   KE=1/2mv^2

How NASA’s GRAIL Probes Will Map the Moon’s Gravity

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How NASA’s GRAIL Probes Will Map the Moon’s Gravity Infographic | Moon Gravity, Phases & Facts | Moon Exploration & NASA Moon Missions, GRAIL Spacecraft | Space.com.

NASA’s twin Grail probes are designed to map the moon’s gravity field like no other spacecraft before. The $496 million mission will use the ultra-precise moon gravity maps to help scientists better understand the moon’s composition and structure, as well as how the moon evolved during its formation. Learn how the Grail mission works in the SPACE.com infographic above.