Biophysics at CMU

The arrival of several highly effective vaccines has dramatically changed the landscape of the Covid-19 pandemic. Remarkably, though, a considerable fraction of people are hesitant to get immunized—for reasons that would be fitting material for a different blog post, but which right now I will sidestep. What interests me here, instead, is how this hesitancy affects the ongoing pandemic—especially…

by Markus Deserno One of the fundamental facts of statistical physics is that microscopic systems are subject to constant thermal fluctuations. They are fundamentally random, but still exhibit many regularities that permit us to learn a great deal about those systems. For instance, any individual quadratic degree of freedom of the form $\frac{1}{2}Kx^2$ has an expected value of the energy equal t…

by Amirali Hossein Biological lipid membranes divide eukaryotic cells into compartments with specialized functionality and play a central role in controlling the flow of matter and information between them. Their main building blocks are hundreds of different types of lipids, and the lipid composition of the two leaflets of many bilayer membranes is known to not be the same. This asymmetry is bel…

A delightful pastime in mathematics is to think about really big numbers. And unlike many other mathematical mind games, this is one that has captured the imagination of a much wider community. It is fun to think about a million, a billion, or a trillion, and then picture how big they are, and how much bigger each subsequent number is than the previous one. This game is hard to continue, though, …

Towards the end of the year, here’s one more blog post that’s a bit wonkish, but teaches an important lesson. It’s about statistics, and about one of the many ways in which it can be counterintuitive. Almost all statistics discussed in the everyday press deals with averages, and maybe fluctuations around averages. As we all know, this can already be confusing enough. But here we wish to deal with…

by Samuel Foley Lipid membranes are fundamentally important structures in all branches of life. Not only do they form the boundary of living cells, they also perform a multitude of roles within them. To deeply understand these fluid membranes and their properties is then essential for explaining the mechanics of life at these scales. An important property of biological membranes which has recentl…

The basic structural component of cellular membranes are lipid molecules, of which a typical cell contains about a thousand different types. This is an amazingly large number, considering that a single species of lipid suffices to make a perfectly nice membrane. Over the past two decades biologists and biophysicists have come to appreciate that membranes are more than just fluid elastic sheets th…

Nematic liquid crystals are soft matter systems in which elongated molecules align and form long-range oriented fields, in 2 or 3 dimensions. They have a long history, many practical applications, and are increasingly recognized for the many roles they play in biology. In a recent paper [Phys. Rev. E 102, 012607 (2020)], my former visiting student Yiheng Zhang (张一恒), his supervisor Zhanchun Tu (涂…

Gerrymandering describes the practice of engineering the boundary of political districts in such a way as to give one party (almost invariably the one that draws the districts) an advantage in elections. This has often given rise to highly convoluted district boundaries—which just visually scream that some nefarious intent was afoot. The practice received its name when it was first used in 1812 b…

When on March 13 2020 the number of Covid-19 cases and deaths in Europe exceeded the rest of the world (excluding China), the World Health Organization declared Europe as the new epicenter of a worldwide spreading disease it had only declared a pandemic two days earlier. Five days later, ...

Living cells and many of their internal organelles are bounded by a membrane composed predominantly of lipids. These are molecules with a water-soluble head region and a water-insoluble tail region. As a result, they form a bilayer structure, with the tail regions facing each other and the head regions facing the water. [...]