How long does it take an electron to tunnel?

The combination of ab-initio numerical experiments and theory shows that optical tunnelling of an electron from an atom can occur instantaneously.

How long does it take an atom to absorb a photon and lose an electron? And what if not one but many photons are needed for ionization? How much time would absorption of many photons take? These questions lie at the core of attosecond spectroscopy, which aims to resolve electronic motion at its natural time scale.

Ionization in strong infrared fields is often viewed as electron tunnelling through a potential barrier, created by the combination of the atomic potential that binds the electron and the electric field of the laser pulse that pulls the electron away. Thus, unexpectedly, attosecond spectroscopy finds itself facing an almost age-old and controversial question: how long does it take an electron to tunnel through a barrier?

In the paper by Torlina et al (http://arxiv.org/pdf/1402.5620v2.pdf), this question is studied by using the so-called atto-clock setup. Continue reading How long does it take an electron to tunnel?

A Penny For Your Thoughts

How much is your time really worth? Student paper evaluates the economics of thought

Big thinkers may wish to re-evaluate their rates, according to a student study at the University of Leicester, which tested the popular idiom ‘A penny for your thoughts’ by working out how much of a person’s thought could theoretically be purchased with a single penny.

The study suggests that a penny could, in theory, purchase 3 hours, 7 minutes and 30 seconds of thought according to Natural Sciences student Osarenkhoe Uwuigbe from the University of Leicester’s Centre for Interdisciplinary Science.
In a paper published in the Journal of Interdisciplinary Science Topics, a peer-reviewed student journal run by the University of Leicester’s Centre for Interdisciplinary Science, the student first investigated how much power is needed to produce thought.
For simplicity, the study examined the power necessary for the brain – which consumes roughly 20 per cent of the body’s energy – to run as being the power necessary for the production of thought.
Given that the average power consumption of a typical adult is approximately 100 watts, the student calculated that the power necessary to run a human brain and produce thought is roughly 20 per cent of this – or 20 watts.
To apply monetary value to thought, the price per kilowatt hour (kWh) charged by UK energy companies was calculated, settling on 16 pence per kWh, which is within the range of prices typically charged by UK energy companies.
Assuming that it requires 20 W or 1/50 kW to produce thought, charging 16p per kWh means that one penny can purchase 1/16th of a kWh. Therefore the length of time (in hours) a penny can purchase thought for is (1/16)÷(1/50)=3.125.
Assuming that it is possible to think as fast as you can speak, the student suggests that 3 hours, 7 minutes and 30 seconds of thought and speech can be bought with a penny.
Student Osarenkhoe Uwuigbe said: “This model is likely to be an underestimate as power required for the brain to operate does not necessarily translate to power used in thought. The brain has several autonomic functions it carries out during thought processing and as a result thought processing could not take 100% of the power consumption of the brain.
“Furthermore, it is unlikely that it is possible to think as fast as you speak due to delay caused by biological constrains such as conduction velocity of nerves carrying the signal from the brain to the mouth, the release of Ca2+ ions during muscle contraction of the tongue and lips and so on.”
Dr Cheryl Hurkett from the University of Leicester’s Centre for Interdisciplinary Science said: “An important part of being a professional scientist (as well as many other professions) is the ability to make connections between the vast quantity of information students have at their command, and being able to utilise the knowledge and techniques they have previously mastered in a new or novel context.
“The Interdisciplinary Research Journal module models this process, and gives students an opportunity to practise this way of thinking. The intention of this module is to allow students to experience what it’s like to be at the cutting edge of scientific research.
“The course is engaging to students and the publishing process provides them with an invaluable insight into academic publishing. It also helps students feel more confident when submitting future papers. I find it a very rewarding module to teach and I am always pleased to see my students engaging so enthusiastically with the subject. I encourage them to be as creative as possible with their subject choices as long as they can back it up with hard scientific facts, theories and calculations!”

Read more at: phys.org – physics.le.ac.uk

Oxymoronic Black Hole Provides Clues to Growth

A Sloan Digital Sky Survey image of RGG 118, a galaxy containing the smallest supermassive black hole ever detected. The inset is a Chandra image showing hot gas around the black hole. Credits: NASA/CXC/Univ of Michigan/V.F.Baldassare, et al; Optical: SDSS

A Sloan Digital Sky Survey image of RGG 118, a galaxy containing the smallest supermassive black hole ever detected. The inset is a Chandra image showing hot gas around the black hole.
Credits: NASA/CXC/Univ of Michigan/V.F.Baldassare, et al; Optical: SDSS

Astronomers using NASA’s Chandra X-ray Observatory and the 6.5-meter Clay Telescope in Chile have identified the smallest supermassive black hole ever detected in the center of a galaxy. This oxymoronic object could provide clues to how larger black holes formed along with their host galaxies 13 billion years or more in the past.

Astronomers estimate this supermassive black hole is about 50,000 times the mass of the sun. This is less than half the mass of the previous smallest black hole at the center of a galaxy. Continue reading Oxymoronic Black Hole Provides Clues to Growth

Meals Ready to Eat: Expedition 44 Crew Members Sample Leafy Greens Grown on Space Station

Astronauts on the International Space Station are ready to sample their harvest of a crop of "Outredgeous" red romaine lettuce from the Veggie plant growth system that tests hardware for growing vegetables and other plants in space. Credits: NASA

Astronauts on the International Space Station are ready to sample their harvest of a crop of “Outredgeous” red romaine lettuce from the Veggie plant growth system that tests hardware for growing vegetables and other plants in space.
Credits: NASA

Fresh food grown in the microgravity environment of space officially is on the menu for the first time for NASA astronauts on the International Space Station. Expedition 44 crew members, including NASA’s one-year astronaut Scott Kelly, are ready to sample the fruits of their labor after harvesting a crop of “Outredgeous” red romaine lettuce Monday, Aug. 10, from the Veggie plant growth system on the nation’s orbiting laboratory.

The astronauts will clean the leafy greens with citric acid-based, food safe sanitizing wipes before consuming them. They will eat half of the space bounty, setting aside the other half to be packaged and frozen on the station until it can be returned to Earth for scientific analysis.

NASA’s plant experiment, called Veg-01, is being used to study the in-orbit function and performance of the plant growth facility and its rooting “pillows,” which contain the seeds. Continue reading Meals Ready to Eat: Expedition 44 Crew Members Sample Leafy Greens Grown on Space Station

Aside

Tracking the radiation reaction energy when charged bodies accelerate

Andrew M. Steane – scitation.aip.org
We consider radiation reaction and energy conservation in classical electromagnetism. We first treat the well-known problem of energy accounting during radiation from a uniformly accelerating particle. This gives rise to the following paradox: when the self-force vanishes, the system providing the applied force does only enough work to give the particle its kinetic energy—so where does the energy that is eventually radiated away come from? We answer this question using a modern treatment of radiation reaction and self-force, as it appears in the expression due to Eliezer and Ford and O’Connell. We clarify the influence of the Schott force, and we find that the radiated power is , which differs from Larmor’s formula. Finally, we present a simple and highly visual argument that enables one to track the radiated energy without the need to appeal to the far field in the distant future (the “wave zone”)…
Read more at http://arxiv.org/pdf/1408.1349v1.pdf