- Technical University of DenmarkPost doc, 2011 - present
- National Institute of Information and Communications Technology, TokyoPost doc, 2008 - 2011
- Niels Bohr Institute, University of CopenhagenPhD student, 2005 - 2008
- University of Copenhagen Faculty of SciencePhysics, 1999 - 2005
- Frederiksværk Gymnasium1996 - 1999
Thermal machines - such as the refrigerator which keeps your beer cold and makes ice for your caipirinha, or a steam turbine generating electricity from heat in a power plant - have been studied for a long time. The desire to improve early steam engines led to the development of thermodynamics which is now a very broad physical theory dealing with any process where heat is exchanged or converted into other forms of energy. Thermodynamics now allows us to understand well what goes on in thermal machines.
Quantum mechanics is another very successful theory, which gives us a good description of things on very small scales - the interaction of a few atoms with each other, or of an atom with light and so on. As you may know, on these scales the physics is different from everyday experience, and weird things start to happen. Quantum systems can be in superpositions - the famous Schrödinger's cat which is neither dead nor alive - and can show correlations that are stronger than in any classical system (as I have written about before, for example here: https://plus.google.com/u/0/+JonatanBohrBrask/posts/QbF1cy8mQ91).
Usually, when we think about thermal processes, such as cooling a beer, large systems with many particles are involved (the beer and the refrigerator consist of zillions of atoms). It is natural to ask though, what happens when we make things so small that quantum effects begin to matter? Can we understand thermodynamics at the quantum level? Can we still define quantities such as heat and work? What happens to important concepts in thermodynamics such as the Carnot efficiency or the second law?
There is a lot of work going on at present trying to answer these questions. One approach is to go back to the beginnings of thermodynamics - steam engines and other thermal machines - and make the machines as small as possible. Such quantum thermal machines are a good testing ground where ideas from thermodynamics and quantum mechanics can be combined. Our work follows this approach. We look at a small absorption refrigerator consisting of just three two-level systems (think of three atoms) coupled to thermal baths at different temperatures.
This quantum fridge has already been used to find several interesting results, for example that quantum entanglement can improve cooling, and that quantum machines can reach Carnot efficiency. These results were obtained by looking at the fridge in the 'steady state' - i.e. after a long time, when the 'beer' in the fridge is already cold. In this paper, we take a look at the 'transient regime' of the fridge - i.e. what happens in the time between putting a warm beer in the fridge and taking out a cold one. Our contribution is a bit technical. We map out some details of this process and find the time scales for the 'beer' to loose it's quantum character or approach the steady state. Among other things, we find that the 'beer' can sometimes get colder at an intermediate time than in the steady state - i.e. if you want the beer cold you shouldn't leave in the fridge too long. This is a purely quantum effect and that happens to single-atom beers but definitely not to that tasty IPA you were saving for later!
When I was interviewed for a position by Hewlett-Packard in the late 1970s they were still a major scientific instruments company with a tagline of if it produces a signal, we can measure it! They had manufacturing facilities in Scotland, or "just down the road" according to Kim, my American interlocutor, a couple of field offices and they were hiring for an R&D facility they were planning in Pinewood, Wokingham.
They had very view dedicated conference rooms in the Winnersh, Wokingham field office and so I was interviewed in their Fourier Analyzer room. I sat alongside a six foot tall, imposing rack machine that included a real-time computer, a Digital to Analog convertor, an Analog to Digital convertor and a lovely HP Oscilloscope. This was an HP digital Fourier Analyzer and it was the first one I had seen.
The purpose of the digital Fourier Analyzer was to take in a complicated continuous signal from the real world, something that was hard to work with like a vibration signal, and break it down into a finite number of manageable sine and cosine functions with their magnitude and phase relationships. This work was based on the development by Jean-Baptiste Fourier, more than a hundred years ago, of his eponymous infinite series. The amazing feat performed by this machine was, however, made possible even with a fast computer in a reasonable amount of time, only by the development of the cunning Cooley-Tukey FFT Algorithm in 1965.
The interactive codepen below gives us an idea of the way that a simple periodic function, like a square wave, or a sawtooth curve, can actually be simulated to a reasonable degree of accuracy with only a limited number of terms.
Interactive Codepen: http://goo.gl/qURwrA
Before digital computers, there were analog devices for Fourier Analysis. If you have a bit more time and you haven't seen them yet, you might enjoy these videos (and the e/book) by +Bill Hammack. He and team restored one such machine. This analog computer was originally developed by Albert Michelson (of Michelson-Morley fame). It uses gears, springs and levers to add sines and cosines.
(1/4) Intro/History: Introducing a 100-year-old mechanical computer: https://goo.gl/YFowTo
(2/4) Synthesis: A machine that uses gears, springs and levers to add sines and cosines: https://goo.gl/y4ZXdH
(3/4) Analysis: Explaining Fourier analysis with a machine: https://goo.gl/O6xIGl
(4/4) Operation: The details of setting up the Harmonic Analyzer: https://goo.gl/fJxIPc
Book (free pdf or buy printed): http://goo.gl/9oy9yS
HP Journal 1970/06: https://goo.gl/W0F0Sw
30 Years of FFT: https://goo.gl/qkPUm0
Fourier Series (Wikip): https://goo.gl/bEfHiI
Fourier Transform (Wikip): https://goo.gl/osR3Cf
Fast Fourier Transform: https://goo.gl/t9ezSe
Fourier Analysis (Wikip): https://goo.gl/B8zC1w
Harmonic Analysis: (Wikip): https://goo.gl/p2U1ur
Image courtesy of Computer History Museum: http://goo.gl/OaoDqy
I guess I should be happy enough with what we have now - 20-30 years from now I'll probably look back at it with the same nostalgia :)
Thank you, for this imaginative piece of popsci and for the link and the background story!
A few years ago, most physicists thought there would be no way of distinguishing different interpretations based on observation, but now there are several theoretical and experimental results which at least indicate that certain interpretations must be ruled out.
You can follow the launch live via NASA TV:
More info about AAUSAT5 can be found in this article:
Also: I so want to mod myself with LEGO right now!
When I don't want to take a bath, don't be mad and don't embarrass me. Remember when I had to run after you making excuses and trying to get you to take a shower when you were just a girl?
When you see how ignorant I am when it comes to new technology, give me the time to learn and don't look at me that way ... remember, honey, I patiently taught you how to do many things like eating appropriately, getting dressed, combing your hair and dealing with life's issues every day... the day you see I'm getting old, I ask you to please be patient, but most of all, try to understand what I'm going through.
If I occasionally lose track of what we're talking about, give me the time to remember, and if I can't, don't be nervous, impatient or arrogant. Just know in your heart that the most important thing for me is to be with you.
And when my old, tired legs don't let me move as quickly as before, give me your hand the same way that I offered mine to you when you first walked. When those days come, don't feel sad... just be with me, and understand me while I get to the end of my life with love. I'll cherish and thank you for the gift of time and joy we shared. With a big smile and the huge love I've always had for you, I just want to say, I love you ... my darling daughter.
Original text in Spanish and photo by Guillermo Peña.
Translation to English by Sergio Cadena
Fun fact: Ozzy has only 3 times as many Twitter followers as Funassyi.
Funassyi, an unofficial mascot of Funabashi city, is a superstar in Japan:
There is more magic coming from SIGGRAPH this year (2105) with the help of Google researchers and the University of Washington.
It is now possible to have a system look at millions of photographs, sort for common landmarks and scenes, time sequence pictures in each, computationally adjust the images for viewpoint, and tweak lighting to produce viable flicker-free time-lapse movies.
We introduce an approach for synthesizing time-lapse videos of popular landmarks from large community photo collections. The approach is completely automated and leverages the vast quantity of photos available online. First, we cluster 86 million photos into landmarks and popular viewpoints. Then, we sort the photos by date and warp each photo onto a common viewpoint. Finally, we stabilize the appearance of the sequence to compensate for lighting effects and minimize flicker. Our resulting time-lapses show diverse changes in the world's most popular sites, like glaciers shrinking, skyscrapers being constructed, and waterfalls changing course.
More here: http://goo.gl/GsPxpI
Video (5:04): https://goo.gl/TmVT72
Paper (open) (pdf): http://goo.gl/URvR7i
SIGGRAPH 2015: http://goo.gl/5cyaYo
One of my continuing interests has always been what the physical objects which we create and with which we surround ourselves say about us, both as individuals and as a society.
Who does not walk into someone else's living space and eye the collection of books, or music, or video to help form some opinion of the person who lives there?
Our possessions are both archival (what we treasure about our pasts) and aspirational (what we hope to accomplish in our future). When we feel overwhelmed by our possessions, a need to purge them, it's evidence that we need to move on from some impediment, some shackle to the past or illusory future.
People tend to foist stuff on us (think spam mail) and we find it hard to say no. Tidying up is the physical first step to regaining our sense of self, to assessing our own true needs and desires.
In writing these little meditations on "what we keep", I came across Marie Kondo and her konmari method for taking control of clutter. Her method is far closer to my own than say, the Puritan-style "Clutterers Anonymous". Cleaning isn't about focusing on what to get rid of, on shaming people to get rid of their stuff. (Apparently so they can buy new stuff and keep the consumerist economy going.) No. No. No. It's about focusing on what to keep, those things that bring us delight.
When I sit here drinking my tea, I consider my cup. And yes, it brings me delight. Because I was quite poor in my youth, I always spent a great deal of time carefully weighing the characteristics of any purchase until finding just the thing that brought that spark of delight. If I didn't find it, I didn't buy it. (For example, I didn't own a couch until my late 30s).
When I look at my tea cup, I also think of the Japanese tea ceremony, which is about truly appreciating (paying attention to) the present moment, the radiance of the ordinary. Every time I look at this cup it makes me happy. I just have to remember to look.
So ends my long introduction to the linked story which examines the KonMari Method from the perspective of an economist. I think it will be interesting to those of you who prefer a less lyrical explanation.
Generation of single photons and Schrödinger kitten states of light
Generation of single photons and Schrödinger kitten states of light
Thomas Müller not to blame for Pepe's headbutt during Germany's 4-0 win ...
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