Daniel Duffy

(he/him)

University of Michigan

Hi! I’m a physicist at the University of Michigan, in the Pioneer Fellows program. Previously I was a research associate at NTU (Singapore) and a PhD student in Cambridge (UK). I’m looking for junior research fellowship jobs! So far my work has focused on mechanics, and I’ve been doing a mix of theory and simulation. I’m interested in most areas of Physics, but especially soft matter, shells, biophysics, and acoustics. I love it when geometry plays a key role, partly because it means the pictures are pretty, but also because geometry brings so much mathematical depth, despite being so familiar from our daily lives. My publications can be found here on this site, or on my google scholar page, or via my ORCiD . My full CV is here.

Recent Posts

Lifting, Loading, and Buckling in Conical Shells

Our paper Lifting, Loading, and Buckling in Conical Shells has been published as an “Editor’s Suggestion” in Physical Review Letters. It’s been featured in articles on Phys.org and in the Physics magazine, which we’re chuffed about.

Oct 6, 2023 1 min read

Breaking by bending

The coolest thing about slender objects is that they can undergo large shape changes at very little energy cost (and hence only small stresses and strains). As illustration, bending a plate of thickness $t$ into a cylinder of radius $R$ incurs strains only $\sim t/R \ll 1$.

Jul 26, 2023 3 min read

Why do distance functions satisfy an eikonal equation?

Every object has a scalar field associated with it called a distance function (DF), which equals the shortest distance from each point in space to the object. I think they’re quite beautiful things, and they’re extremely powerful tools in simulations (meshing, tracking interfaces) and graphics (ray marching, defining complex objects with simple expressions).

Jul 8, 2023 8 min read

Active vs passive transformations in field theories

There’s a distinction between an active transformation and a passive one. In an active transformation, the actual value of a field at a given point in space or spacetime will change in general — you actually transform the field into a different field.

Sep 10, 2022 10 min read

Consistency of Coulomb gauge

Here’s a subtlety that I only noticed embarrassingly late: Let’s say we’re doing magnetostatics, and trying to find $\mathbf B$ given a current density $\mathbf J$, with some BCs involving $\mathbf B$.

Aug 29, 2022 9 min read

Electrostatics and simply connectedness

People sometimes mention (correctly) that $\nabla \times \mathbf E = \mathbf 0$ only implies $\mathbf E = -\nabla \phi$ in a region that is simply connected. A simply connected domain is one in which any loop can be contracted to a point without any part of the loop leaving the domain.

Aug 20, 2022 3 min read

Interfacial metric mechanics: stitching patterns of shape change in active sheets

We have a new paper out :) It's about joining together patterns of complex shape change in a sheet, without the sheet trying to tear itself apart. It has lots of pretty pictures and it's open access, so anyone can read it here:https://t.

Aug 19, 2022 1 min read

Apparent overdetermination in Maxwell's equations and the weirdness of curl

Maxwell’s equations seem to have more equations than degrees of freedom (‘unknowns’) in many reasonable problems, forming an overdetermined system. Writing the equations as $$\begin{align} \nabla \cdot \mathbf {E} &= \rho/\varepsilon_0 , \label{eq:m1}\tag{1}\\ \nabla \cdot \mathbf {B} &= 0 , \label{eq:m2}\tag{2}\\ \nabla \times \mathbf{E} &= -\dot{\mathbf{B}} , \label{eq:m3}\tag{3}\\ \nabla \times \mathbf{B} &= \mu_0 \mathbf{J} + \mu_0 \varepsilon_0 \dot{\mathbf{E} } , \label{eq:m4}\tag{4} \end{align}$$ we see that we have 8 scalar equations in total, since (\ref{eq:m3}) and (\ref{eq:m4}) each have 3 components.

Jun 2, 2022 7 min read

Complex numbers and vectors

I’ve been thinking a bit about complex numbers and why we use them. Complex numbers are just arrows in the 2D plane. They are thus essentially just 2D vectors in the 2D Euclidean plane, with some extra rules operations on them defined on top of the usual ones (addition, dot product etc), which turn out to be very useful.

Apr 11, 2022 5 min read

Let’s think of integration in a Riemann-like way: We have a function $f(x)$, and you take a particular interval $[a,b]$ of the variable $x$, with $a<b$, and split that interval into $N$ subintervals labelled by $i$, each having width $\Delta x = (b-a)/N$ and (say) central $x$ value of $x_i$, and then the integral $$\int_{[a,b]} f(x) \, \mathrm{d}x = \lim_{N \to \infty} \, \sum_{i=1}^N f(x_i) \, \Delta x .

Dec 24, 2021 6 min read

Metric mechanics with non-trivial topology: actuating irises, cylinders and evertors

We have a new paper out, feat. this lil creature that fully turns itself inside out when you heat it up! This one's my fave, but we also make morphing irises, and cylinders, and other cone-adjacent things with a hole 👁️.

Dec 23, 2021 1 min read

Shape programming lines of concentrated Gaussian curvature

I gave a talk on this paper at the 2021 SIAM Mathematical Aspects of Materials Science conference, which you can find (and watch!) under the talks tab on the navigation bar (top of this page).

Jul 9, 2021 1 min read

Defective Nematogenesis

My paper with J. Biggins is up on @softmatter, and you and everyone else can read it here, open access: https://t.co/QLiaXTFPhD We calculate the Gauss curvature encoded in thin sheets by patterns of shape change with topological defects + simulate the resulting (pretty) shapes :) pic.

Nov 6, 2020 1 min read

An initial commit

Hi, I just made this website. It’s built with Wowchemy, using the Hugo academic-pages template. This is my first post, partly by way of testing, partly by way of introduction.

Nov 3, 2020 5 min read