Archive for December, 2008

New Year Greetings!

December 31, 2008

A Happy and prosperous 2009 to you all — the readers of this blog — from New Delhi; since I do not yet have a picture of India Gate, the greetings come with this Iron Pillar picture!

The iron pillar

Some photos from the Qutb complex!

December 28, 2008

The Qutb Minar

The Qutb Minar -- a closer look!

The iron pillar

The iron pillar -- the other angle

Inscription on the iron pillar

The English translation of the inscription on the iron pillar

Photographs courtesy: M P Rukmani. More photos and information on the complex is available at this wiki page too!

Directions for future research in solidification and solid-state phase transformations

December 28, 2008

A quick link to a recent paper accepted for publication in Acta from some of the key players in the solidification area; more on the paper later, after I manage to read it — which might take a while.

Solidification microstructures and solid-state parallels: Recent developments, future directions

M Asta, C Beckermann, A Karma, W Kurz, R Napolitano, M Plapp, G Purdy, M Rappaz and R Trivedi

Abstract:

Rapid advances in atomistic and phase-field modeling techniques as well as new experiments have led to major progress in solidification science during the first years of this century. Here we review the most important findings in this technologically important area that impact our quantitative understanding of: (i) key anisotropic properties of the solid–liquid interface that govern solidification pattern evolution, including the solid–liquid interface free energy and the kinetic coefficient; (ii) dendritic solidification at small and large growth rates, with particular emphasis on orientation selection; (iii) regular and irregular eutectic and peritectic microstructures; (iv) effects of convection on microstructure formation; (v) solidification at a high volume fraction of solid and the related formation of pores and hot cracks; and (vi) solid-state transformations as far as they relate to solidification models and techniques. In light of this progress, critical issues that point to directions for future research in both solidification and solid-state transformations are identified.

Take a look!

Size dependence of interfacial energies and equilibrium shapes of crystals in 3D

December 26, 2008

Here are a couple of interesting papers accepted for publication in Scripta Materialia (Articles in Press):

[1] Size dependence of the interfacial energy in the generalized nearest-neighbor broken-bond approach

B Sonderegger and E Kozeschnik

The generalized nearest-neighbor broken-bond (NNBB) approach provides a powerful means of calculating the interfacial energies between two arbitrary multicomponent phases. Conceptually, the NNBB has been developed for planar, sharp interfaces, but this is inappropriate for small precipitates characterized by high interface curvature. In the present work, a size-correction expression is derived that takes this effect into account. Comparison with treatments based on thermodynamic considerations shows good consistency with the present approach.

[2] An analytic solution for three-dimensional axisymmetric equilibrium crystal shapes

P Du and H Wong

A surface free energy polar plot contains two possible sources of singularity: the cusps that give facets on an equilibrium crystal, and the circular arcs connecting the cusps that can lead to missing orientations. Instead of specifying surface free energy, we model the surface stiffness so that both singularities can be treated precisely. Here, we apply our model to three-dimensional axisymmetric crystals and obtain for the first time an analytic solution to the nonlinear differential equation governing the crystal shape.

Language Log uses the C word!

December 26, 2008

In a post, which also quotes a nice apologetic Christmas greeting from a humour column (which I am going to quote):

You know, very soon we will be reaching that special time of the year when people who subscribe to certain religious beliefs rather than to others will be celebrating what they regard as a very significant event. May I therefore take this opportunity to wish all such believers a very happy special time of the year…

Take a look!

Some people get lucky (I too was — once)

December 25, 2008

I can vouch for this feeling:

Every once in a while there occurs a musical high point in life when I realise that all discussions on raga, tala, srutis, notes and sahitya are mere hair-splitting exercises.

It happened to me after a concert of T V Sankaranarayan in which he sang a phenomenal Kambhoji (Thiruvadi Charanam). It had happened to Sriram after a lec demo at Music Academy by Nedanuri:

This morning’s lec dem by Nedanuri Krishnamurthy, supported by the Malladi Brothers and accompanied by VV Ravi on the violin, was one such.

As Sriram notes at the end of his piece,

It was a wonderful morning and words cannot express the musical experience. Those who attended were lucky.

I only wish I was that lucky!

Jeeves and the Ph D

December 24, 2008

This piece in E Kowalski’s blog is brilliant:

I sank therefore into an armchair.

A light cough was heard in the vicinity. Starting sharply, I saw Jeeves appearing in the frame of the door.

– Is there any problem, Sir?

I hesitated an instant. We had had some disagreements lately. However, there was no denying that he was there, and there was this je ne sais quoi in his voice which denoted a willingness to rally round the young master. I did not waver long.

– Jeeves, I said, in a hurried and distracted voice. Hear me.

– Yes, Sir. If I can be of any succor.

– Jeeves, I repeated, trying to gather my thoughts. You were right. I do not feel quite the same interest in Science suddenly. However, mark me closely, I have been informed by Mr. Walter Alaistair Appleton that by starting this Ph.D. I have contracted moral obligations equivalent to an engagement. Do you confirm this, Jeeves?

– Indeed, Sir, it has been the received opinion of the most prominent philosophers since Aristotle. The best treatment of the matter, in my opinion, is found in the treatise “Critic of Pure Reason” of the philosopher Kant. He argues…

– Let us keep this for later discussion, Jeeves. Is there no way to be honourably discharged of said obligation?

He eyed me quietly.

– Come on, Jeeves. You know what I mean. Such things have happened before, in different ways, in this place. You have never faltered. Is there hope?

– Well, Sir, it is widely considered that, should it occur that a student discovered that the results he had been working on for his Ph.D. had been anticipated by some other scholar, he could then consider himself exonerated of his responsibilities. Of course, it is usually expected that he then choose some other subject and renew his pledge, but a certain amount of leeway is definitely granted if he should feel discouraged by this stroke of bad luck.

– Agad, Jeeves, is it possible? I cried, hope filling my entire being.

But not for long. What hope was that? Before someone got interested again in this cursed subject of the early history of the kilt, long would grow the beard of the poor Bertram, and weary his eyes of decyphering old Scottish tales. I inclined the good old head a good deal.

– No hope, Jeeves, I said. No hope.

A slight cough attracted again my eyes to his person, and I saw him produce a thick and tightly bound volume which he proffered to me.

– It may interest you, Sir, to know that my disapproval of your idea of a kilt was not a mere whim but was based on previous thorough studies of the interesting story of this most particular garment?

I glanced at the title. “The early history of the kilt in the Highlands”, it read, with the precision “Presented for the title of Ph.D. at the University of Edinburgh, 1905″ with Jeeves name appended in calligraphic flourishes.

– It is somewhat more specialized in its geographical emphasis, but you will find that it contains most of your research.

Don’t miss it!

BMG matrix composites and 3D optical microscopy!

December 24, 2008

A couple of interesting papers from PNAS:

[1] Multilayer three-dimensional super resolution imaging of thick biological samples (Complete text is available via Open Access)

A Vaziri, J Tang, H Shroff, and C V Shank

Recent advances in optical microscopy have enabled biological imaging beyond the diffraction limit at nanometer resolution. A general feature of most of the techniques based on photoactivated localization microscopy (PALM) or stochastic optical reconstruction microscopy (STORM) has been the use of thin biological samples in combination with total internal reflection, thus limiting the imaging depth to a fraction of an optical wavelength. However, to study whole cells or organelles that are typically up to 15 μm deep into the cell, the extension of these methods to a three-dimensional (3D) super resolution technique is required. Here, we report an advance in optical microscopy that enables imaging of protein distributions in cells with a lateral localization precision better than 50 nm at multiple imaging planes deep in biological samples. The approach is based on combining the lateral super resolution provided by PALM with two-photon temporal focusing that provides optical sectioning. We have generated super-resolution images over an axial range of ≈10 μm in both mitochondrially labeled fixed cells, and in the membranes of living S2 Drosophila cells.

[2] Development of tough, low-density titanium-based bulk metallic glass matrix composites with tensile ductility

D C Hofmann, J-Y Suh, A Wiest, M-L Lind, M D Demetriou, and W L Johnson

The mechanical properties of bulk metallic glasses (BMGs) and their composites have been under intense investigation for many years, owing to their unique combination of high strength and elastic limit. However, because of their highly localized deformation mechanism, BMGs are typically considered to be brittle materials and are not suitable for structural applications. Recently, highly-toughened BMG composites have been created in a Zr–Ti-based system with mechanical properties comparable with high-performance crystalline alloys. In this work, we present a series of low-density, Ti-based BMG composites with combinations of high strength, tensile ductility, and excellent fracture toughness.

Have fun!

Gaming the system: leaks in a seal — Edition 2

December 24, 2008

Jeff Atwood on the gaming of the voting system at Stack Overflow:

I was pleasantly surprised to find that the vast, vast majority of Stack Overflow users do not engage in revenge downvoting. Unfortunately, for those users that do, the pattern was quite clear. As of today, we have several queries that look for unusual downvote patterns. If we discover these patterns in a given user’s voting history, we view all their downvotes for that user as suspect. They’re all silently deleted, and any lost reputation is restored to the unfortunate target of these downvotes.

While working on this code, I also realized that we should be checking for the inverse of this behavior — unusual upvote patterns. To game the reputation system, unscrupulous users might create alternate user accounts that vote up their main account. Again, this is a bit tougher on Stack Overflow than other sites, because we don’t allow any user account to upvote at all until they’ve earned 15 reputation first. And then of course there’s the aformentioned 30 vote per day limit.

I reformulated my queries, and I found that there were many, many more suspicious upvote patterns than downvote patterns. More than five times as many! I guess I shouldn’t be surprised, since the value of a single +10 upvote is fairly high. In parallel with the downvote validation, we now use several daily heuristics to detect strange user upvoting patterns; if we decide the upvotes are questionable, they will all be removed.

Anyway, if you find that your reputation has changed overnight, it might be because we now check for, and remove, any suspicious upvote or downvote patterns.

I thought about doling out reputation penalties to the users involved, but I figured it’s better to err on the side of forgiveness. I want to be clear that the “problem” voters are a very, very small part of the Stack Overflow community. Most people use the voting system the way it was intended. Our policy on this is simple: we’ll silently remove any vote fraud we detect. Please don’t do it. In the long run, it will be easier to earn reputation by posting great answers and questions than gaming the system.

Take a look!

Exams and cram schools!

December 23, 2008

Paul Graham, as usual, says it well:

Before credentials, government positions were obtained mainly by family influence, if not outright bribery. It was a great step forward to judge people by their performance on a test. But by no means a perfect solution. When you judge people that way, you tend to get cram schools—which they did in Ming China and nineteenth century England just as much as in present day South Korea.

What cram schools are, in effect, is leaks in a seal. The use of credentials was an attempt to seal off the direct transmission of power between generations, and cram schools represent that power finding holes in the seal. Cram schools turn wealth in one generation into credentials in the next.

It’s hard to beat this phenomenon, because the schools adjust to suit whatever the tests measure. When the tests are narrow and predictable, you get cram schools on the classic model, like those that prepared candidates for Sandhurst (the British West Point) or the classes American students take now to improve their SAT scores. But as the tests get broader, the schools do too. Preparing a candidate for the Chinese imperial civil service exams took years, as prep school does today. But the raison d’etre of all these institutions has been the same: to beat the system.

Take a look!