Hyperuniformity with no fine tuning in sheared sedimenting suspensions

Particle suspensions, present in many natural and industrial settings, typically contain aggregates or other microstructures that can complicate macroscopic flow behaviors and damage processing equipment. Recent work found that applying uniform periodic shear near a critical transition can reduce fluctuations in the particle concentration across all length scales, leading to a hyperuniform state. However, this strategy for homogenization requires fine tuning of the strain amplitude. Here we show that in a model of sedimenting particles under periodic shear, there is a well-defined regime at low sedimentation speed where hyperuniform scaling automatically occurs. Our simulations and theoretical arguments show that the homogenization extends up to a finite lengthscale that diverges as the sedimentation speed approaches zero.Comment: 11 pages, 6 figure

Viscous to Inertial Crossover in Liquid Drop Coalescence

Using an electrical method and high-speed imaging we probe drop coalescence down to 10 ns after the drops touch. By varying the liquid viscosity over two decades, we conclude that at sufficiently low approach velocity where deformation is not present, the drops coalesce with an unexpectedly late crossover time between a regime dominated by viscous and one dominated by inertial effects. We argue that the late crossover, not accounted for in the theory, can be explained by an appropriate choice of length-scales present in the flow geometry.Comment: 4 pages, 4 figure

Multiple transient memories in sheared suspensions: robustness, structure, and routes to plasticity

Multiple transient memories, originally discovered in charge-density-wave conductors, are a remarkable and initially counterintuitive example of how a system can store information about its driving. In this class of memories, a system can learn multiple driving inputs, nearly all of which are eventually forgotten despite their continual input. If sufficient noise is present, the system regains plasticity so that it can continue to learn new memories indefinitely. Recently, Keim & Nagel showed how multiple transient memories could be generalized to a generic driven disordered system with noise, giving as an example simulations of a simple model of a sheared non-Brownian suspension. Here, we further explore simulation models of suspensions under cyclic shear, focussing on three main themes: robustness, structure, and overdriving. We show that multiple transient memories are a robust feature independent of many details of the model. The steady-state spatial distribution of the particles is sensitive to the driving algorithm; nonetheless, the memory formation is independent of such a change in particle correlations. Finally, we demonstrate that overdriving provides another means for controlling memory formation and retention

Multiple transient memories in experiments on sheared non-Brownian suspensions

A system with multiple transient memories can remember a set of inputs but subsequently forgets almost all of them, even as they are continually applied. If noise is added, the system can store all memories indefinitely. The phenomenon has recently been predicted for cyclically sheared non-Brownian suspensions. Here we present experiments on such suspensions, finding behavior consistent with multiple transient memories and showing how memories can be stabilized by noise.Comment: 5 pages, 4 figure

Intrinsic avalanches and collective phenomena in a Mn(II)-free radical ferrimagnetic chain

Magnetic hysteresis loops below 300 mK on single crystals of the Mn(II) - nitronyl nitroxide free radical chain (Mn(hfac)_2({\it R})-3MLNN) present abrupt reversals of the magnetization, or avalanches. We show that, below 200 mK, the avalanches occur at a constant field, independent of the sample and so propose that this avalanche field is an intrinsic property. We compare this field to the energy barrier existing in the sample and conclude that the avalanches are provoked by multiple nucleation of domain-walls along the chains. The different avalanche field observed in the zero field cooled magnetization curves suggests that the avalanche mechanisms are related to the competition between ferromagnetic and antiferromagnetic order in this compound.Comment: 9 pages, 7 fig, to be published in Phys. Rev.

PRIMARY AND SECONDARY REACTIONS OF CELLULOSE MELT PYROLYSIS

Fast pyrolysis of biomass is a next-generation biofuels production process that is capable of converting solid lignocellulosic materials (in their raw form) to a transportable liquid (bio-oil) which can be catalytically hydrogenated to fuels and chemicals. Pyrolysis reactors depolymerize solid biomass by heating the feedstock (in the absence of oxygen) up to high temperatures (400 – 600 °C) to produce a short-lived intermediate liquid phase (only a few seconds), which ultimately breaks down to form small (1-6 carbon) oxygenates. These vapor-products can then be condensed at room temperature to produce liquid bio-oil. While biomass fast pyrolysis has enormous potential to produce renewable fuels, an understanding of the fundamental chemistry and transport processes of biomass pyrolysis to produce bio-oil is not available in the literature. This work utilizes co-pyrolysis and isotopic labeling to study the liquid-phase secondary reactions of levoglucosan to form anhydrosugars, pyrans, and light oxygenates. Isotopic labeling studies also reveal that hydrogen exchange is a critical component of levoglucosan deoxygenation. Next, the effects of pyrolysis reaction temperature and sample length scale are discussed. These studies revealed that the yield of total furan rings (i.e., all products containing a five-membered furan ring) does not change significantly with increased reaction temperature compared to other pyrolysis products, such as light oxygenates and anhydrosugars. However, the functional groups bound to the furan ring (e.g., alcohols and aldehydes) are easily cleaved to produce smaller furans. This chemistry was targeted by impregnating cellulose with palladium on carbon to selectively decarbonylate oxygenated furans within liquid intermediate cellulose to form deoxygenated furans resulting in a more stable bio-oil. The last part of this thesis, a new experimental technique, Spatiotemporally-Resolved Diffuse Reflectance in situ Spectroscopy of Particles (STR-DRiSP), which is capable of measuring biomass composition during fast pyrolysis with high spatial (ten micron) and temporal (one millisecond) resolution is developed. Compositional data were compared with a comprehensive two-dimensional single particle model. The STR-DRiSP technique can be used to determine the transport-limited kinetic parameters of biomass decomposition for a wide variety of biomass feedstocks

A Journey Through Homelessness: a Photovoice Project With Youth Experiencing Homelessness in Minnesota

The purpose of this project was to conduct a photovoice project with youth experiencing homelessness who frequent a drop-in center in the Midwest. Youth experiencing homelessness are a marginalized population whose numbers continue to grow. Photovoice is a method by which marginalized populations have an opportunity to express their lived experiences through photographs and what those photographs mean to them. Four youth from the drop-in center in the Midwest participated in the photovoice project. The youths were given cameras and instructions to take photographs of three broad areas: what homelessness means to them, their dreams for their futures and how has drop-in center helped them on their journey through homelessness. Their photographs and narratives are explained in this paper. The photographs were categorized into three themes: Caring Connections, Where Will I Sleep, and Dreams for the Future. Margaret Newman’s Health as Expanding Consciousness Theory and the concepts of health, nursing, human, and environment provided a framework and guided this project. A conceptual model was developed to represent the journey of the youths’ lives. Increased authentic connections using photovoice may change policy decisions, help communities deliver equitable services, and empower the participants of the photovoice project. Increased use of photovoice for community needs assessments, evaluation of programs, and a way to inform communities about issues should be considered