Tag Archives: water

An introduction to the water structure problem

Although the macroscopic properties of water have been heavily studied, there are things we don’t understand about this ubiquitous substance. In this post, I will provide an introduction to the problem of describing water’s structure. At first glance, the idea of a liquid having structure seems preposterous. Indeed, liquids cannot maintain a structural arrangement of atoms like solids can. Instead, the atoms/molecules tumble past each other in constant state of motion. This allows for the defining property of the liquid state – the ability to fill a container.   Continue reading

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Our Nature Communciations paper – ice-like phonons in liquid water

Our paper, “The hydrogen-bond network of water supports propagating optical phonon-like modes” was published on January 4th in Nature Communications (full open access pdf). A press release about our work has been issued by the Stony Brook Newsroom and picked up by news aggregator Phys.org.

Our work shows that propagating vibrations or phonons can exist in water, just as in ice. The work analyzes both experimental data and the results of extensive molecular dynamics simulations performed with a rigid model (TIP4P/eps), a flexible model (TIP4P/2005f), and an ab-initio based polarizable model (TTM3F). Many of these simulations were performed on the new supercomputing cluster at Stony Brook’s Institute for Advanced Computational Science.

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Why do we see the frequencies we do?

Why can’t we see in the infrared or ultraviolet?
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Periodic Boundary Conditions

As promised , I shall now reveal why I had a bout of interest in polyhedra, as discussed in my last post.

[Sorry for those of you who were waiting on the edge of your seats for three weeks]

It all has to do with periodic boundary conditions (PBCs).

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A misconception about microwaves

Or, “how microwaves actually work”

This is a short note on a misconception which I had and which I believe is widely shared.

As you probably know, microwave ovens are named after the type of electromagnetic radiation that they produce. Most microwaves produce radiation with a frequency of 2.45 GHz.

The misconception I had is that this frequency is tuned to one of the vibrational frequencies of the water molecule.

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Does hot water freeze faster than cold? Explaining the Mpemba effect

In this article I would like to lay the following question to rest:

“Does hot water freeze faster than cold?”

The answer is:

“Yes, in some cases.”

In the rest of this article I will explain what these cases are and why the phenomena of hot water freezing faster than cold is not as mysterious as some have made it out to be.

A bit of history
I do not have room here to discuss the long history of this problem, which goes back to Aristotle, was pondered by Thomas Bacon and was more recently revived by a student in Africa named Erasto Mpemba. [For this reason, it is sometimes called the Mpemba effect, even though Mpemba was studying sugared milk during ice cream preperation and not water in his experiments.] While long discussions of the history of this subject are common (see reference 1), I feel that discussing the historical narrative is counterproductive to the point I wish to get across. The standard historical narrative on this subject gives the impression that this is a ‘great mystery’ which has stumped scientists through the ages. The truth is that this phenomena has stumped many great thinkers, but careful experiments on this phenomena have only been carried out very recently. My hope here is to convince you that this phenomena is actually not very mysterious (although it is a bit complicated), and then if interested you can read the historical narrative afterwards from that perspective.

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