Category Archives: General Mathematics

Graph theorist given "genius award"

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Maria Chudnovsky awarded a “genius award” under the MacArthur Fellows Program this year.

She mathematician who investigates the fundamental principles of graph theory. Her contributions to graph theory include a proof of the strong perfect graph theorem characterizing perfect graphs as being exactly the graphs with no odd induced cycles or their complements.

Although her research is highly abstract, she is laying the conceptual foundations for deepening the connections between graph theory and other major branches of mathematics, such as linear programming, geometry, and complexity theory.

The MacArthur Foundation announcement

She is currently an associate professor in the Department of Industrial Engineering and Operations Research, Columbia University.

Links

McArthur Foundation

Chudnovsky’s homepage at Columbia University

Artificial snow flakes

David Griffeath (University of Wisconsin-Madison) and Janko Gravner (University of California, Davis) have a computer model based on diffusion-limited aggregation that can simulate snowflakes. Their images look very real and demonstrate the wide variety of snowflakes found in nature.

Below are some of their snowflakes:

model1

model2

model6

model13

A PDF slideshow of 40 such snowflakes can be found here.

Links

Gravner-Griffeath Snowfakes

AMS Mathematical Imagery

Ig Nobel prize for physics

ponytail

Joseph Keller (US), Raymond Goldstein (US/UK), Patrick Warren and Robin Ball (UK) have been awarded the 2012 Ig Nobel prize for physics for calculating the balance of forces that shape and move the hair in a human ponytail [1,2].

The winners were announced and awarded on Thursday 20th September.

Anyone interested should examine the Ponytail Equation.

References

[1] Raymond E. Goldstein, Patrick B. Warren, and Robin C. Ball, “Shape of a Ponytail and the Statistical Physics of Hair Fiber Bundles.” Physical Review Letters, vol. 198, no. 7, 2012.

[2] Joseph B. Keller, “Ponytail Motion,”, Journal of Applied Mathematics, vol. 70, no. 7, 2010, pp. 2667–72.

Links

Ig Nobel prizes

A quote by Einstein

The mere formulation of a problem is far more essential than its solution, which may be merely a matter of mathematical or experimental skills. To raise new questions, new possibilities, to regard old problems from a new angle requires creative imagination and marks real advances in science.

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I strongly agree with this. Quite often a problem is not important in itself, but rather the tools developed in its solution are pivotal to science.

Mathematics

Great mathematical examples here are lemmas that go on to be more important than their original application.

One great example that springs to mind is the Poincaré lemma: “All closed differential k-forms (k > 0) are locally exact”.

Plenty of other examples exist. The point is, although initially the lemmas seem very technical and narrow, they turn out to be of independent interest and very powerful in unexpected ways.

Particle physics and space science

Possibly a better example is that of spin-off technologies from particle physics and space exploration. For example experimental particle physics has brought us, sterilisation methods, non-destructive testing, cancer treatments, medical imaging techniques and so on.

Wider society and culture

Something that should not be overlooked is the impact of science and mathematics on culture. Advances in mathematics and science can change our outlook on the Universe and shape what we are. To quote Robert R. Wilson, who was the first director of Fermilab, when asked to justify the cost of the experiments to the Congressional Joint Committee on Atomic Energy, said

It has only to do with the respect with which we regard one another, the dignity of men, our love of culture. It has to do with: Are we good painters, good sculptors, great poets? I mean all the things we really venerate in our country and are patriotic about. It has nothing to do directly with defending our country except to make it worth defending.

Witten on supermanifolds and integration on them

Edward Witten placed some notes on the arXiv on 11th September entitled “Notes On Supermanifolds and Integration” [1]. In the notes he outlines the the theory of supermanifolds and integration on them. His motivation is to present what is needed for the RNS formalism in string theory.

Witten

Edward Witten

As ever Witten has produced very readable and concise notes without over complicating things. I recommend that anyone interested in how to integrate objects on supermanifolds start here.

References

[1] Edward Witten. Notes On Supermanifolds and Integration. arXiv:1209.2199 [hep-th]

Fractal from Binomial Coefficients

Binomial

Above is a discrete fractal generated by creating a table of zeros and ones by deciding if the binomial coefficients are even or odd. The “key” here is paint black if odd, otherwise leave light blue.

The pattern is closely related to Pascal’s triangle.

The pattern clearly shows self-similarity as all fractals do.

As far as I know, this pattern was first noticed in [1]. Also note that we have a structure very similar to the Sierpinski Sieve. In the limit of infinite rows we recover the Sierpinski Sieve, up to a shift in the positions of the zeros and ones.

A slight variant

Binomial2

Just for fun I used the same algorithm to study the pattern associated with modified binomial coefficients of the form

\(\left( \begin{array}{c} (-1)^{k}n\\ k \end{array} \right)\)

Again the pattern shows lots of self-similarity.

References

[1] S. Wolfram: American Mathematical Monthly, 91 (November 1984) 566-571

A Random Walk

Random

Random walks can be found throughout nature in many different contexts. For example they been used in ecology, economics, psychology, computer science, physics, chemistry, and biology. Above is an example of a (simple) random walk I created. There is 8 directions to this walk and 1000000 points.

The random walk above is an example of a Markov process, that means that the next step only depends on the present step. Such processes have “no memory”.

Random walks are closely related to Brownian motion, which is the physical phenomenon of minute particles diffusing in a fluid.

Random walks are examples of discrete fractals. They show self-similarity on large scales (such as in the picture above), but on the smaller scales the discrete nature of the grid becomes apparent. See the picture below.

random2

Here we have another random walk generated in exactly the same way as the previous one, but not just 1000 points. One can consider this as a “zoom in” on the random walk with a million points. The finite step size is apparent and the resemblance to genuine fractals is far less clear.

Links

Wikipedia

MathWorld