☛ Creating “Linked-List” type posts

One of my long-time to-do’s for this blog was to be able to create “linked-list” type posts, where the main heading points, not to a single webpage for the dedicated blog post, but to an external website of interest. (This type of post has been made famous by John Gruber, who is, incidentally, also the creator of the Markdown syntax.)

Well, now I know how to do this (evidence—this post! Ta-da! The title for this post points to The Candler Blog). It turns out it’s not too difficult, but even so, I had help all the way, from The Candler Blog. He has this same implementation, and it turns out, he also has a blog post dedicated to discussing how he did it!

Okay, so, “Daring Fireball-style Linked List posts,” for the uninitiated, refers to the publishing style of John Gruber’s Daring Fireball. For the most thorough explanation of how this works, see Shawn Blanc’s excellent 2009 article, “The Link Post” […]

But how is it done in Octopress? It’s actually very simple. I got a great deal of help, when I was first setting up the site, from Connor Montgomery, who posted his own link post tutorial a few weeks ago. I have since refined the code on my site beyond what we worked out together.

(The Candler Blog website seems otherwise very interesting as well. Go check it out!)


Of Cricket, Mankad-ing, and the Spirit of the Game

The Under-19 cricket world cup is on, and there has been a lot of controversy about a West Indies bowler running a Zimbabwean batsman out as he came in to bowl. Colloquially, this is called ‘Mankad’-ing, and some people view this form of dismissal as “not quite done”. As it happens every time, lots of people are talking about “spirit of the game” and “no warnings issued to the batsman”.

I think those people are in the wrong.

(Here’s the video.)

What would these same people say when a bowler gets a wicket, but his heel is found to be where the bat is spotted in our case? “Spirit of the game”, and give the batsman out? “Give a warning to the bowler”, and give the batsman out? No, of course not, because the rulebook says some part of the bowler’s foot must stay behind the line. The bowler made a mistake, and is penalized for it.

Well, guess what the rulebook says in this case.

Also, to be clear, backing up itself is not illegal; backing up too early is. ICC playing conditions says that the bowler may attempt this dismissal only if he has not completed his delivery swing. So, in effect, once the bowler is in the middle of rolling his bowling arm over to bowl, the bowler can no longer run the batsman out, and the batsman is free to start backing up.

In my opinion, “spirit of the game” issues should only come up when a) the fielding side resorts to subterfuge, or b) it is “obvious” that the batsman is not attempting to take an advantage, and is behaving as if the play is dead. For examples of this second case, see:

  • http://youtu.be/6zgvjC9WUCs (bad spirit of the game),
  • https://youtu.be/AsznuSW-1Ug (good spirit of the game) and
  • http://youtu.be/9vYPWYAoJhM (good spirit of the game, even though it was a close rescue).

In our present case, the batsman was definitely attempting to take advantage, and his opponent ran him out perfectly legally. The batsman made a mistake, and was penalized for it. What’s wrong with that, and what’s all this about giving the batsman a second chance?!

Play on, I say! (Or in this case, game over!)


On Failure in Metallic Materials

As a continuation of my series on composite materials and health monitoring, I wanted to talk about failure in composites. In writing it, I decided that first I needed to talk about failure in metallic materials. In writing that, it turned out that it was long enough to be a separate post by itself. So here it is, a small primer on failure, especially in metallic materials.

We’ll talk about composites next time.

What exactly is "failure"?

A component is said to have failed when it can no longer perform the task that it was designed for. Failure does not necessarily mean breaking, although sometimes it might. Failure in an engineering sense has as much to do with “what the designer intended” as with “the physical structure itself”.

For example, a bridge may be getting old and developing some cracks here and there. At what point do you say that the bridge is “unsafe for use”? The design and engineering teams set up some criteria to evaluate the structure. For example, they might say that “any cracks detected must not be greater than so-and-so length”. This does not mean that the bridge is going to break apart when a crack of that so-and-so length appears. It just means that the engineers are no longer satisfied with how the bridge may hold up in the future. Hence, the bridge component that developed the big-enough crack will be said to have failed.

Tacoma Narrows Bridge

Tacoma Narrows Bridge. (Source)

If the above paragraph seems to convey unnecessary caution on the part of the engineer (why call the bridge unsafe if it isn’t breaking up?), consider that a bunch of reasons go into making such decisions. As an example, the engineers may consider their ability to detect every crack. The engineering team may consider the possibility that they could not detect some defects. What is the probability of a serious defect not being detected?

And there’s good reason to be cautious – if they get it wrong, bridges do collapse.

How do metallic materials fail?

In the previous section, we have been talking about cracks. Here’s why they form in the first place. Cracks form when the load on a given region of a component (i.e. stress, = force per unit area) becomes higher than what the material can handle. This may be because an unexpected amount of load was put on the structure that it was never designed for. It may also be that the capacity of the structure to withstand stresses has diminished over time as the component has aged. In any case, when the stress is too much for the component to bear, the component fractures and develops a crack. The particular mechanics of the fracture itself is a vast area of study in itself, and is way beyond the scope of this piece. Suffice to say, that crack formation weakens the component, and the larger the crack gets, the worse in condition the component becomes. Ultimately, the crack will grow large enough that the component will break into two, and will be unable to take any load at all.

Crack propagation under fatigue loading

Crack propagation under certain conditions. (Source)

For metallic components, since the material itself is nominally homogenous (nominally, because nothing can be perfectly homogenous, but for all intents homogeneity may be assumed), the crack that ultimately causes the material to fail usually occurs where the stress happens to be the greatest. Further, as I mentioned above, the formation of a crack weakens the material, and so once a crack does form, any further worsening in that region accumulates around the same crack (weak zone) instead of creating new cracks all the time. “Where the stress is greatest” usually depends on the geometry of the component, on how the loads are distributed, and, indeed, on tiny variations in the homogeneity of the material itself.

Crack propagation in glass shot at extremely high frame rate. (Source)

For metals, therefore, the mantra for evaluating the component may be condensed as: “follow the cracks”. Wherever a crack seems to be worsening, is where final failure will most likely occur.

That’s it for today’s discussion on crack propagation; next time we’ll get to what I had actually set out to discuss – failure in composites.


On India’s World Cup performance (they lost today)

It’s always gutting to see your team lose, isn’t it. Gutting, and infuriating. “They should have won! If only they’d played better!”

Let’s think back though, to the beginning of the World Cup, before a ball had been bowled. Remember those days, just after the triseries with Australia and England? What if someone had said then that India would reach the semifinal? We’d have smirked. “With this team? This bowling attack?” Winning 7 games on the trot? Smirk. 70 wickets in 7 games? Best economy rate as a bowling unit? Cohesive batting performance from the entire unit? Fast bowlers bowling with pace and discipline? Smirk; smirk; smirk.

India have done well to reach the semifinals. They’ve been an excellent team. Their flaw today was that they were not a great team. But that’s okay, being excellent isn’t half bad.

Yes, they had a collective off-day. The bowlers sprayed it around a bit, uncharacteristically. The batters got out in inopportune moments, uncharacteristically. Dhawan usually scores big once he gets a start (and gets a catch dropped). Kohli usually gets himself in and ups his scoring rate, and doesn’t get out at all. There’s usually always Rahane, and even Raina has scored a hundred this world cup. Usually; just not today.

They came across a genuinely better team today, and lost. No shame in that; that takes nothing away from their excellence. Then too, they actually brought Australia back from what looked to be a certain 360+ score. That’s something in itself, no?

Also, a thought: how many teams have defended their world cup titles successfully? West Indies in the 1970s, and Australia in the 1990s and 2000s. It needs a great team, not merely an excellent one, to be able to defend trophies across four year periods and in different conditions. Would we call this Indian team “great”, comparable to the West Indian and Australian teams of before? Definitely not, right? Not yet. Maybe with time and more experience, and maybe a couple of different players, but certainly not yet.

So they came across a better team. They lost. So what? They played well until they lost; they played with pride and with skill and with passion and with excellence.

They kept the Tricolor flying high. Let’s be proud of that.


☛ So-called “Scientist” bets against science; loses

This is from the BBC:

A German biologist who offered €100,000 (£71,350; $106,300) to anyone who could prove that measles is a virus has been ordered by a court to pay up.

Stefan Lanka, who believes the illness is psychosomatic, made the pledge four years ago on his website.

The reward was later claimed by German doctor David Barden, who gathered evidence from various medical studies. Mr Lanka dismissed the findings.

The guy is a biologist? I can understand a non-scientist being deeply skeptical of journal articles and medical findings… but a biologist?

The institution that gave him his degree(s) should consider rescinding whatever degree(s) he has, because:

(a) he clearly cannot review scientific literature and gain an understanding of a subject by himself.

(b) he clearly cannot follow a trail of logic and scientific understanding through published medical research even when it is presented to him by someone else.

Here’s how human society works — we all have our own specializations, and it’s part of our responsibility as specialists to help out others who aren’t knowledgeable in, and cannot tell good from bad, or even have an understanding of, our area of expertise. This isn’t just for “scientists”, of course, but for everyone.

Imagine how little we in general know about the inner workings of our automobiles compared to the expert (mechanic) who’s in charge of fixing them. Now imagine a person who calls himself a mechanic, but (a) doesn’t understand how a certain system in the car works, and (b) cannot follow the logic, and doesn’t believe it when another mechanic shows it to him! Would you ever go solicit this person’s expertise again?

This ‘biologist’ is like our hypothetical mechanic.