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Dan Piponi
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Attended King's College London
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Well it's a complicated way to listen to This American Life but it works. Software defined radio (SDR) [1,2,5] on a raspberry pi. I have to ssh in to change channel but it should be easy to add an analogue to digital converter and then a tuning dial.

If it was just an FM radio it wouldn't be all that interesting. But right now it's tracking aircraft flying overhead using "Mode S" and displaying the map by wifi on my phone [3.4].

In recent years, with technology become ever more digital, it's been tricky for kids to figure out how devices work. SDR turns that back around again. If you want to understand how an FM radio works, now you can just read the source [6].

[1] http://sdr.osmocom.org/trac/wiki/rtl-sdr
[2] http://www.amazon.com/RTL-SDR-RTL2832U-Popular-Software-Packages/dp/B00C37AZXK/ref=sr_1_1?ie=UTF8&qid=1397935088&sr=8-1&keywords=rtlsdr
[3] http://en.wikipedia.org/wiki/Air_traffic_control_radar_beacon_system#Mode_S
[4] https://github.com/antirez/dump1090
[5] http://en.wikipedia.org/wiki/Software-defined_radio
[6] https://github.com/keenerd/rtl-sdr/blob/master/src/rtl_fm.c
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William Casarin's profile photoDan Piponi's profile photo
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+William Casarin Using square waves to transmit goes back to the days when Hertz, I think, used on/off with spark gaps to transmit.

Anyway, I got a little HD44780 LCD display to work so now my radio can at least tell you what frequency you've tuned to.
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This is a really amazing paper:

http://arxiv.org/pdf/1311.2899v1.pdf

<copenhagen interpretation>
In the EPR experiment, if you observe one half of the EPR pair, causing it to collapse, you cause the other half to collapse as well. You can think of observing one half as having an instantaneous "backreaction" on the other. 

The idea in this new experiment is that you have a nuclear spin, say A. You can arrange for it to become weakly entangled to spin B. Now you observe spin B. In this new experiment, observing B has a weak backreaction on A. By choosing what to observe about B you can iterate this backreaction to steer A to a desired state. It's borderline magic. You're manipulating A by looking at spin B which shares a history with A.
</copenhagen interpretation>

See also http://www.readcube.com/articles/10.1038/nphys2908
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Andrei Lopatenko's profile photoDan Piponi's profile photowoun zoo's profile photoJoe Philip Ninan's profile photo
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+Benjamin Russell  That's exactly what I said to the author of the second paper I linked to.
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Monads in everyday life #2

Some workplace conversations:

Conversation #1:

A: Can you make me a dongle?
B: OK, come back later and I'll give you a dongle.

Conversation #2:
A: Can you make me a dongle?
B. What the hell do you want with a dongle?
A: Well I have this dongle-to-widget converter so if you give me a dongle I can make the widget I need.
B: Come back later and I'll give you a widget.

Generally I've found approach #2 to be helpful. People often micromanage and it's good to understand what the bigger picture was before someone diced it up into what they thought were the subtasks. In conversation #2, B might have a different way to make widgets that doesn't involve dongles. Or might have a stash of widgets already under the table. Or might even use the dongle-to-widget converter many times over with different dongles so as to find the best widget possible.

But I'm not here to give life advice. Conversation #2 illustrates continuation passing style http://en.wikipedia.org/wiki/Continuation-passing_style

Challenge #1: Write a script for a conversation illustrating why continuations are functorial. (http://en.wikibooks.org/wiki/Haskell/Continuation_passing_style)

Challenge #2: Write a script illustrating why continuations are monadic.
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Michel Plungjan's profile photoBartosz Milewski's profile photoPaul Brauner's profile photoDan Piponi's profile photo
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A. I need a gadget that would take a dongle-to-widget converter and give me a widget.
B. All I have a gadget that takes a bongle and creates a gadget that fits your description. But I don't have a bongle.
C. I don't have a bongle either, but if you give me a bongle-to-widget converter, I'll give you a widget.
A. Wait, If we rig together B's gadget with my dongle-to-widget converter, we'll get a bongle-to-widget converter.
C. That's all I need.
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Dan Piponi

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Venetian Snares is possibly my favourite composer of electronic tunes, but he has a disturbing tendency to use his talents for evil. I'm glad to see that he's now decided to take the first step towards redemption and collaborate on an album with songs about good and wholesome subjects, like the ancient pony that once saved children in distress. I think on one song he even sampled a choir of real angels. Best album of the year so far.
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In many animal species an organism is usually female if it inherits an X chromosome from both parents. But within each cell, only one of those chromosomes is active. The other is disabled. As the two X chromosomes are generally different, that means neighbouring cells that seem otherwise identical may be expressing quite different genes.

Researchers at Johns Hopkins came up with an amazing way to colour a cell red or green according to whether or not its active X chromosome came from the mother or father. For example the picture here is a slice of mouse brain coloured in this way.

http://www.nytimes.com/2014/01/21/science/seeing-x-chromosomes-in-a-new-light.html
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Dan Piponi's profile photoKetil Malde's profile photoRobert Byrne's profile photoRodrigo González del Cueto's profile photo
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+Daniel Martin eh...the reason they kill them is that they want the eggs - or?  But we also would like sex markers for fish in aquaculture, e.g. halibut females grow much larger (and maybe faster) than males - and for marine fish (as opposed to anadromous ones, like salmon), it's advantageous to have single-sex stocks to avoid spawning.
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General relativity is often explained in pop science books by making reference to balls rolling about under the influence of gravity on a stretched rubber sheet. In my opinion it's a useless way to explain general relativity. After a few seconds a reader who is awake will notice that it's an analogy that replaces something difficult with an unmotivated approximate version of a system more complex than the original one.

Nonetheless, a ball rolling about on a stretchy surface is itself an interesting physical system that can be studied.

http://arxiv.org/pdf/1312.3893v1.pdf

It turns out that with a central mass the circular orbits satisfy a version of Kepler's third law with the squaring and cubing operations swapped.

Modulo the swapping of the powers, the mass of the fabric ends up playing a role a bit like a negative cosmological constant resulting in an attractive force.

So with a bit of a stretch maybe it could be said that there is something about general relativity we can learn from this system after all.
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Vijay Sharma's profile photoDan Hulme's profile photoJorge Devoto's profile photo
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“with a bit of a stretch” Ow!
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One of our balloons has had quite a journey over the past few weeks. It did a lap around the world in 22 days, and has just clocked the project’s 500,000th kilometer as it begins its second lap. It enjoyed a few loop-de-loops over the Pacific ocean before heading east on the winds toward Chile and Argentina, and then made its way back around near Australia and New Zealand. Along the way, it caught a ride on the Roaring Forties — strong west-to-east winds in the southern hemisphere that act like an autobahn in the sky, where our balloons can quickly zoom over oceans to get to where people actually need them.

Traversing the stratosphere is particularly challenging this time of year because the winds actually change direction as the southern hemisphere moves from warmer to colder weather, resulting in divergent wind paths that are hard to predict. Since last June, we’ve been using the wind data we’ve collected during flights to refine our prediction models and are now able to forecast balloon trajectories twice as far in advance. In addition, the pump that moves air in or out of the balloon has become three times more efficient, making it possible to change altitudes more rapidly to quickly catch winds going in different directions. There were times, for example, when this balloon could have been pulled into the polar vortex – large, powerful wind currents that whip around in a circle near the stratosphere in the polar region – but these improvements enabled us to maneuver around it and stay on course. We can spend hours and hours running computer simulations, but nothing teaches us as much as actually sending the balloons up into the stratosphere during all four seasons of the year.

Take a look through our photo album to see some of the specific improvements that have been made to the balloon technology, thanks to the lessons we’ve learned in flight.
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I was scratching my head trying to make sense of what engineers call "cascaded integrator comb" (CIC) filters, as described here: http://www.embedded.com/design/configurable-systems/4006446/Understanding-cascaded-integrator-comb-filters , until it suddenly clicked that they were completely familiar.

Graphics people and engineers speak such a different language it's hard to spot when they're saying the same thing. CIC filters are a great example. A classic paper by Heckbert on filtering images by using repeated integration is this: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.72.4795&rep=rep1&type=pdf In graphics language you construct summed area tables to compute box filters and then repeat that process to construct higher order b-spline filters. CIC filters are the same thing except they take advantage of the fact that you can reorder convolutions. So instead of repeatedly alternating integration (ie. forming the summed area table) and differentiation (doing lookups in the summed area table) you do all the integrations together in one block and all the differentiations together in another.
 
The graphics paper claims: "The original idea of filtering by repeated integration is due to Ken Perlin." But for many years the graphics world was busy inventing the same wheels as electronic engineers. The engineering account also studies the frequency response of the filtering process, something graphics people tend not to care about. But the graphics version also gives some insights that the engineers don't seem to mention.
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Why we need type systems
 
This made the day.
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Benjamin Russell's profile photoSergey Ten's profile photoMike Stay's profile photoPhilip Craig's profile photo
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+Alok Tiwari
> And they misspelled Arabic.

They also conflated "No" and "Smoking" into "NOSMOKING," which doesn't exist as a word in English.
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Marco Devillers's profile photoLarry Gritz's profile photoDan Piponi's profile photoManuel Chakravarty's profile photo
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Looking good fellas.
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Homo Sapiens, Hominini, Hominidae, Primates, Mammalia, Chordata, Animalia
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Blog: A Neighborhood of Infinity
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    Mathematics
  • Trinity College, Cambridge
    Mathematics
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