Tag: Structure characterization

Publications

Local number fluctuations in water

michaelandreasklatt

Using our recently developed platform for local number fluctuations with a special focus on the higher-order moments, we analyzed density fluctuations in ordered and disordered phases of water across temperatures.

Michael A. Klatt, Jaeuk Kim, Thomas E. Gartner III, and Salvatore Torquato, Local number fluctuations in ordered and disordered phases of water across temperatures: Higher-order moments and degrees of tetrahedrality, The Journal of Chemical Physics 160, 204502 (2024).

Some anomalies of water are well-know, for example, that ice floats on
water because the crystalline ice is less dense than the disordered
liquid. These commonly known anomalies are only part of a large set
of interrelated anomalies of water in its dynamic, structural, and
thermodynamic properties.

In this work we find another anomaly in the density fluctuations of
water. Therefore, we use a recently developed platform to systematically
study local fluctuations in the number of molecules with a focus on the
higher-order moments of the distribution of these fluctuations. We apply
it to a rich variety of simulated states of water, crystalline and
disordered, in equilibrium and quenched, and for a broad range of
temperatures (from 80 K to 1600 K). What we find is yet another type of
anomaly: simply speaking, an approximation of the distribution by a
(standard) Gaussian distribution works best close to ambient conditions.
This local optimum around room temperature is probably due to a
balancing of thermal fluctuations and the tretrahedrality of water since
we observe clear signatures of tetrahedrality in the higher-order
moments. This new type of anomaly can help further studies to reveal new
links between the already known structural, dynamic, and thermodynamic
anomalies.

Publications

Predicting flow through porous media via pore-space descriptors

michaelandreasklatt

Together with Robert Ziff and Salvatore Torquato, I determined the void percolation thresholds around hard and overlapping sphere models, including MRJ sphere packings and our amorphous inherent structures of the quantizer energy. The latter have a remarkably low critical porosity.

M. A. Klatt, R. M. Ziff, S. Torquato. Critical pore radius and transport properties of disordered hard- and overlapping-sphere models. Phys. Rev. E 104:014127-1–10 (2021).

Fluid flow through porous media plays a crucial role in many applications, from groundwater hydrology to industrial filtration. Our aim is to find convenient yet reliable estimates of the fluid permeability based on the structural and topological characteristics of the complex tortuous pore space. Such predictions can facilitate the design of porous media with desirable transport properties. For porous media with a well-connected pore space, a recent study suggested the second moment of the pore-size distribution as a convenient alternative to the often-used critical pore radius, which requires a sophisticated percolation analysis. We determine both descriptors for disordered and ordered model microstructures, including maximally random jammed (MRJ) spheres, overlapping spheres, equilibrium hard spheres, quantizer configurations, and lattice packings. Interestingly. we find that the second moment of the pore-size distribution is — to a good approximation — proportional to the critical pore radius. In fact, in contrast to the latter, the former predicts the correct ranking of the permeability for our models. Moreover, we find that the hyperuniform structures, which are characterized by an anomalous suppression of volume-fraction fluctuations, tend to have lower values of the permeability, including MRJ sphere packings, quantizer configurations, and BCC sphere packings.

Publications

Characterization of maximally random jammed sphere packings. III. Transport and electromagnetic properties via correlation functions

michaelandreasklatt

In this paper, we study the physical properties of the hyperuniform maximally random jammed sphere packings.

dissipationless-sphere-packing
Visualization of electromagnetic waves propagating through an MRJ sphere packing

M. A. Klatt and S. Torquato. Characterization of maximally random jammed sphere packings. III. Transport and Electromagnetic Properties Via Correlation Functions. Phys. Rev. E, 97:012118-1–17 (2018)

How do unique geometrical features of heterogeneous materials bring forth unique physical properties? Here, we study the link between the structure of sphere packings and a variety of physical properties using analytic approximations and rigorous bounds. In particular, we are interested in the most disordered among all mechanically stable packings of hard spheres (that are monodisperse and frictionless).

This maximally random jammed (MRJ) state exhibits an anomalous suppression of large-scale density fluctuations, known as hyperuniformity. Although the system is isotropic and locally disordered, it appears uniform on large scales. We compare the diffusion in the pore-space of the MRJ spheres to that of an equilibrium hard-sphere liquid or non-interacting spheres. Moreover, we study flow properties and effective conductivity; the latter also for anisotropic packings of spheroids. Therefore, we provide a comprehensive overview of rigorous bounds that connect these seemingly unrelated physical properties.

The most surprising result is found for electromagnetic waves that propagate through the MRJ sphere packings, where the wavelengths are much larger than the radii of the spheres. Usually disorder causes dissipation, but because of the unique property of hyperuniformity, the MRJ state forms, to a very good approximation, a dissipationless isotropic heterogeneous medium. This is demonstrated using an analytic strong-contrast expansion. It holds for any phase dielectric contrast ratio. The anomalous suppression of density fluctuations also suppresses the scattering of the electromagnetic waves.

This attribute could be useful for the design of photonic materials with novel structural color characteristics or color-sensing capabilities. Additive manufacturing fabrication techniques offer a simple production of samples for experiments with microwaves. So, our analytic results call for an experimental testing of these predicted qualitative trends in the physical properties associated with the MRJ structure.

Link: https://link.aps.org/doi/10.1103/PhysRevE.97.012118

Publications

Characterization of Jammed Packings with Maximal Disorder

michaelandreasklatt

In this paper, we characterize the global structure of MRJ sphere packings:

MRJ-II
Three disordered 3D sphere configurations representing a “gas”, a “fluid”, and a “glass”

M. A. Klatt, S. Torquato. Characterization of maximally random jammed sphere packings. II. Correlation functions and density fluctuations. Phys. Rev. E, 94:022152-1–22 (2016)

Packings of hard, impenetrable spheres are useful models of granular media, low-temperature states of matter, suspensions and biological systems. What is the structure of the most disordered among all mechanical stable packings?

A unique property of this maximally random jammed (MRJ) state is that despite the local disorder, similar to a liquid, there is a hidden long-range order that anomalously suppresses density fluctuations on large length scales, more like in a crystalline solid. In a series of papers, we describe both the local and global structure of such disordered sphere packings using a variety of different structural characteristics.

In this second article, we derive explicit formulas but also apply Monte Carlo methods. By comparing the structure of MRJ packings to common models of disordered materials, our shape analysis helps to distinguish, despite seemingly similar features in all of those systems, their distinctly different structure.

Moreover, these structural characteristics are related to a host of different effective physical behavior, for example, flow or diffusion in these systems as well as their elastic moduli or electromagnetic properties. Our analysis thus links problems from material science, chemistry, physics, mathematics and biology.

Link: https://journals.aps.org/pre/abstract/10.1103/PhysRevE.94.022152

 

Publications

Characterization of maximally random jammed sphere packings. I. Voronoi correlation functions

michaelandreasklatt

In this paper, we characterize the local and global structure of maximally random jammed sphere packings.

MRJ-sphere-packing-v3
MRJ sphere packing: (left) only the spheres, (right) spheres and Voronoi cells

M. A. Klatt and S. Torquato. Characterization of Maximally Random Jammed Sphere Packings: Voronoi Correlation Functions. Phys. Rev. E, 90:052120-1–12 (2014)

We characterize the structure of the maximally disordered packing among the set of all packings of monodisperse frictionless hard spheres, the so-called maximally random jammed (MRJ) sphere packing. Therefore, we compute the Minkowski functionals of the associated Voronoi cells and compare the structure to that of the Poisson point process (ideal gas) and of an equilibrium hard-sphere liquid.

In particular, we consider correlation functions or probability density functions of these Voronoi characteristics. Here we introduce and compute correlation functions and probability density functions of Minkowski functionals to quantify the global structure of the Voronoi diagram.

The local analysis using the distribution of the Voronoi volumes finds no qualitative difference for the structure of liquid or random jammed hard-sphere packings. In contrast to this, the higher-order statistical descriptors introduced here qualitatively distinguish the Voronoi structure of the MRJ sphere packings (prototypical glasses) from that of a hard-sphere liquid. We find strong anti-correlations in the MRJ sphere packings that arise because the MRJ state is “hyperuniform”.

Link: http://link.aps.org/doi/10.1103/PhysRevE.94.022152

Publications

Morphometric analysis in gamma-ray astronomy using Minkowski functionals. I. Source detection via structure quantification

michaelandreasklatt

In this paper, we introduce a morphometric data analysis of gamma-ray sky maps.

computation_Minkowski_sky_map
How to compute a Minkowski sky map

D. Göring, M. A. Klatt, C. Stegmann, and K. Mecke. Morphometric Analysis in Gamma-Ray Astronomy using Minkowski Functionals. Astron. Astrophys., 555:A38-1–7 (2013)

We introduce a novel approach to source detection via structural deviations from typical features of a random homogeneous background. Minkowski functionals are powerful tools from integral geometry; in 2D, they are the area, the perimeter and the Euler characteristics (a topological quantity, which is given by the sum of all components minus the sum of all holes).

Via a combination of these different geometric measures that quantify the shape of level sets of a counts map, more information can be taken out of the same data without the need to assume prior knowledge about potential sources.

We introduce Minkowski sky maps that quantify local structural deviations. Moreover, they localize and visualize potential sources.