arnabocean

— by Arnab Gupta

☞ How the smallest programming bugs can be catastrophic

December 15, 2017

From way back in 1996:

It took the European Space Agency 10 years and $7 billion to produce Ariane 5, a giant rocket capable of hurling a pair of three-ton satellites into orbit with each launch and intended to give Europe overwhelming supremacy in the commercial space business.

All it took to explode that rocket less than a minute into its maiden voyage last June, scattering fiery rubble across the mangrove swamps of French Guiana, was a small computer program trying to stuff a 64-bit number into a 16-bit space.

One bug, one crash. Of all the careless lines of code recorded in the annals of computer science, this one may stand as the most devastatingly efficient.

More links here, and the report of the inquiry into the incident is archived here.

A fascinating, and from a programmer’s perspective chilling, read. This is the stuff of nightmares — an apparently innocuous line of code causing an exception that leads to disaster!

Adios Cassini

December 12, 2017

A couple of months ago, 15 September to be precise, marked the end of an era in the human exploration of our solar system. The Cassini spacecraft was programmed to crash into Saturn’s upper atmosphere and burn up, thus ending an almost two-decade journey and exploration of Saturn and its moons. I was in middle school when this mission launched in 1997, and at that point, even reaching Saturn in 2004 seemed eons away. Twenty years later, perhaps it’s time to look back at some of the amazing insights we’ve gained.

Cassini is actually a shortened name for the Cassini-Huygens mission, and comprises the main spacecraft — Cassini — designed to travel as a satellite in the Saturn planetary system, and a small lander — Huygens — designed to actually land on Titan, Saturn’s largest moon.

Giovanni Cassini was an Italian mathematician and astronomer, and discovered four of Saturn’s moons — Iapetus, Rhea, Tethys and Dione. The Cassini spacecraft was the first to observe all four of these moons. Christiaan Huygens was, of course, a famous Dutch astronomer and scientist, and discovered — but of course — Titan, then the first known moon of Saturn. (He also invented the pendulum clock, was mentor to Gottfried Leibniz, studied optics and the wave nature of light, and derived the modern formula for centripetal force.)

Saturn by Cassini

Saturn by Cassini (via Wikipedia).

Of the many discoveries made by Cassini, I’ll focus on just two stories: those of Saturn’s largest moon Titan, and Saturn’s hexagon. Both of these fascinate me to no end, and I think reflect the best of Cassini’s contributions.

Of India’s high-speed rail ambitions, and lazy Indian journalism

September 18, 2017

India’s plans about building a high speed rail route connecting Mumbai and Ahmedabad have been in the news lately. The project is funded by a low-interest loan from Japan (covering 80% of the cost of the project), and will make use of Japanese high-speed rail technology used for the Shinkansen.

Of course, along with the project being in the news, it is also subject to critique in news articles, as any expensive government venture is bound to (and should!) be. In many of the articles, though, I found one common piece of information mentioned over and over:

According to a study conducted by IIM Ahmedabad, Ahmedabad-Mumbai bullet train will need to make 100 trips daily and carry 88,000-118,000 passengers per day to be financially viable. This figure could well be way above the total number of passengers travelling between the two cities on any given day.

In fact, searching the internet with the name of the article in question (Dedicated High Speed Railway (HSR) Networks in India: Issues in Development) provides a result that looks like this:

Google Search Result

Google Search Result. (Source)

They all mention the same report, and all mention the exact same language about “requiring 100 trips a day”. None, however, actually provide links for the curious reader, nor provide any context or analysis. Well, I was curious, so I tried to find and read the actual report.

☞ Radiolab Podcast: Using flickering lights to treat Alzheimer’s Disease

June 14, 2017

Today, a startling new discovery: prodding the brain with light, a group of scientists got an unexpected surprise – they were able to turn back on a part of the brain that had been shut down by Alzheimer’s disease. This new science is not a cure, and is far from a treatment, but it’s a finding so … simple, you won’t be able to shake it. Come join us for a lab visit, where we’ll meet some mice, stare at some light, and come face-to-face with the mystery of memory. We can promise you: by the end, you’ll never think the same way about Christmas lights again.

I’ve been meaning to post about this particular episode ever since I listened to it. This is the Nature paper about this study. They found that simply flashing light of a certain frequency at a certain interval helps with some of the brain waves that are diminished in mice with Alzheimer’s. It’s absolutely fascinating.

(I’m not going into too much technical jargon here; go listen to the episode!)

If you don’t listen to Radiolab in general, you definitely should; it’s one of the best podcasts there are.

☞ UK Election: Interesting logistics of the Queen’s speech

June 13, 2017

In light of the recent election in the UK, the Queen, of course, is supposed to make a speech regarding forming the government by the party that has won majority. Now, however, after the interesting results of the election, the Queen’s speech is delayed, and the reason for it is very interesting.

The Telegraph UK reports:

The Queen’s Speech is going to be delayed because it has to be written on goatskin paper and the ink takes days to dry.

Apparently, the British monarchy are more concerned than others would be about the archival qualities of the paper that they use.

[…] goatskin paper is not actually made from goatskin.

The material is in fact high-quality archival paper which is guaranteed to last for at least 500 years.

Well, okay, but still, why the delay?

Well, ink on this special paper takes a few days to dry. And the monarchy had “ready to go” versions of the speech for (a) a Conservative party majority, and (b) a Labour party majority. But the results of the election, that resulted in a hung parliament, has put all pre-made plans into disarray. Since the political parties themselves don’t know yet how the government will be formed, the Queen’s speech isn’t finalized yet either.

Once the details are set in stone they can be committed to the goatskin paper and sent away for binding before being presented to the Queen.

I love how even the most apparently mundane things become fascinating just by being associated with the British monarchy.

☞ Everyday bat vocalizations are rich and complex

May 29, 2017

In this study, we continuously monitored Egyptian fruit bats for months, recording audio and video around-the-clock. We analyzed almost 15,000 vocalizations, which accompanied the everyday interactions of the bats, and were all directed toward specific individuals, rather than broadcast. We found that bat vocalizations carry ample information about the identity of the emitter, the context of the call, the behavioral response to the call, and even the call’s addressee. Our results underline the importance of studying the mundane, pairwise, directed, vocal interactions of animals.

This is brilliant. They were able to correlate their data analysis of the bats’ vocalizations with the behavior and responses that they observed… so now we know more about how bats communicate! Simply by listening to the vocalization, the context, addressee, and even “the outcome of the interaction can be predicted above chance level”. Fascinating.

From the discussion:

It is important to note that we used one set of acoustic features for classification. However, many other multi-dimensional spectro-temporal representations can be tested. The bat’s brain could thus be using some other representation that encapsulates much more information regarding different social aspects. The bat may be able to classify the context of an interaction with higher confidence, based on some acoustic feature which it evolved to use and is yet to be determined. Our analysis is thus probably only a lower bound on what a bat is capable of extracting from aggressive social vocalizations. For example, we did not include any temporal information in our analysis.

In any acoustic signal, and especially where communication is involved, the time parameter is usually crucial and will add rich layers of information. For example, just imagine taking a piece of human speech, and (a) only looking at the overal speech parameters, versus (b) observing how the speech parameters change during the speech. Case (b) will provide far more information than case (a). I think we will discover over time that bats have a pretty well-evolved communication scheme.

This is fascinating stuff.

☞ How Bayesian inference works

May 28, 2017

Bayesian inference is a way to get sharper predictions from your data. It’s particularly useful when you don’t have as much data as you would like and want to juice every last bit of predictive strength from it.

Although it is sometimes described with reverence, Bayesian inference isn’t magic or mystical. And even though the math under the hood can get dense, the concepts behind it are completely accessible. In brief, Bayesian inference lets you draw stronger conclusions from your data by folding in what you already know about the answer.

An excellent, simple introduction to Bayesian inference. This uses practical examples and an abundance of visual guides: especially useful if you don’t have an extensive math background.