Rebecca J. Christianson

• Commonwealth Fusion Systems

Breakthrough cell therapies for the treatment of cancers require the separation of specific cells, such as T cells, from the patient's blood. Current cell therapy processes rely on magnetic separation, which adds clinical risk and requires elevated manufacturing controls due to the added foreign material that constitutes the magnetic beads. Acousto...

Solid-state batteries offer the potential to improve safety, cyclability, and energy density of Li-ion batteries. However, their conductivity, stability, and processing limit their use. To this end, the effects of solid electrolyte microstructure on overall battery performance are determined. The conductivities of Al-doped Li7La3Zr2O12 (Al-LLZO), w...

Autologous cellular therapies based on modifying T cells to express chimeric antigen receptor genes have been highly successful in treating hematological cancers. Deployment of these therapies is limited by the complexity and costs associated with their manufacturing. Transitioning these processes from virus-based methods for gene delivery to a non...

In response to the well documented lack of highly qualified STEM educators in the United States, this work seeks to understand how to increase interest in K-12 STEM teaching among engineering students. This paper presents a preliminary framework and findings exploring factors that motivate the choice of a teaching career among the alumni of a small...

We examined biofilms formed by the metabolically versatile bacterium Rhodopseudomonas palustris grown via different metabolic modes. R. palustris was grown in flow cell chambers with identical medium conditions either in the presence or absence of light and oxygen. In the absence of oxygen and the presence of light, R. palustris grew and formed bio...

Chemical signaling has been found in the past to play a central role in bacterial biofilm formation, and may be important for the cyanobacterium Synechocystis sp. Strain PCC 6803. We investigate the cell‐cell communication system of this species and whether it involves acyl homoserine lactone (AHL) signaling molecules. We use the biosensor, Chromob...

Biofilms are how bacteria naturally exist‐enclosed in an extracellular matrix of proteins, nucleic acids, and polysaccharides. This state protects bacteria against environmental stresses, such as antibiotics and biocides. Two strains of Synechocystis sp. Strain 6803, a wildtype strain and an extremely motile mutant strain, were grown in flow cells...

Bacterial aggregates on submerged substrates can produce complex biofilm morphologies that are subject to environmental and metabolic factors. We develop a reductionistic cellular automata model of these structures with the intent of guiding experimentation and explaining prior results. We focus on reproducing the columnar and ``mushroom'' phases o...

Bacteria are the most numerous and ubiquitous organisms in nature. Recently the collective motion of bacteria has attracted considerable interest as an experimentally realizable and natural instance of active matter. In this work, I will present recent experimental results on studies of collective motion inspired by the biofilm environment, and spe...

This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, st...

The prospects for increased cooling capacity from the use of nanofluid coolants has created a tremendous amount of interest. However, in the years since the initial thermal conductivity measurements of nanoparticle suspensions were reported, there has been much inconsistency in data published in the literature. The International Nanofluids Benchmar...

This article reports viscosity data on a series of colloidal dispersions collected as part of the International Nanofluid Property Benchmark Exercise (INPBE). Data are reported for seven different fluids that include dispersions of metal-oxide nanoparticles in water, and in synthetic oil. These fluids, which are also referred to as ‘nanofluids,’ ar...

During the last ten years, the search for improved thermal transport fluids has led to the study of the thermal properties of suspensions of nanoparticles. Particularly in the literature on metallic nanoparticle suspensions, there has been a wide range of results reported, with some authors reporting enormously high enhancements to the thermal cond...

In the past fifteen years, nanofluids have been studied as heat transfer and storage fluids. The citrate reduction synthesis method, originally developed in the 1950's, produces stable aqueous solutions of gold nanoparticles for this application. A variety of particle sizes can be produced by varying the citrate concentration at reduction. In this...

This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, st...

In the search for new, more effective coolant fluids, nanoparticle suspensions have shown promise due to their enhanced thermal conductivity. However, there is a concomitant increase in the viscosity, requiring an increase in pumping power to achieve the same flow rate.Studies of flow cooling in simple geometries indicate that there is a benefit to...

It has been known since the 1800's that addition of solid phase particles to a liquid can improve the thermal conductivity of the liquid. However, the instability of such suspensions made them impractical for cooling applications. With the advent of affordable technology for synthesizing nanometer scale particles, it became possible for stable susp...

Using the transient hot wire and pulsed field gradient nuclear magnetic resonance methods we determined the thermal conductivity and the solvent self-diffusion coefficient (SDC) in aqueous suspensions of quasi-monodisperse spherical silica nanoparticles. The thermal conductivity was found to increase at higher volume fraction of nanoparticles in ac...

We study phase separation in a deeply quenched colloid-polymer mixture in microgravity on the International Space Station using small-angle light scattering and direct imaging. We observe a clear crossover from early-stage spinodal decomposition to late-stage, interfacial-tension-driven coarsening. Data acquired over 5 orders of magnitude in time s...

This thesis presents results of two scattering studies of low dimensional magnetic materials. The first is a neutron scattering study of Rb2MnF4, a nearly ideal two-dimensional square lattice Heisenberg antiferromagnet with S = 5/2. When this material is placed in a magnetic field on an extrapolation of the spin-flop phase boundary into the paramag...

Colloidal silica gels are shown to stiffen with time, as demonstrated by both dynamic light scattering and bulk rheological measurements. Their elastic moduli increase as a power law with time, independent of particle volume fraction; however, static light scattering indicates that there are no large-scale structural changes. We propose that increa...

The low-temperature magnetic excitations of the two-dimensional spin-$\frac{5}{2}$ square-lattice Heisenberg antiferromagnet ${\mathrm{Rb}}_{2}\mathrm{Mn}{\mathrm{F}}_{4}$ have been probed using pulsed inelastic neutron scattering. In addition to dominant sharp peaks identified with one-magnon excitations, a relatively weak continuum scattering is...

We show that the dynamics of large fractal colloid aggregates are well described by a combination of translational and rotational diffusion and internal elastic fluctuations, allowing both the aggregate size and internal elasticity to be determined by dynamic light scattering. The comparison of results obtained in microgravity and on Earth demonstr...

We report comprehensive synchrotron x-ray scattering and magnetic susceptibility studies of the doped spin-Peierls materials Cu1-xZnxGeO3 and CuGe1-ySiyO3. Temperature versus dopant concentration phase diagrams are mapped out for both Zn and Si dopants. The phase diagrams of both Cu1-xZnxGeO3 and CuGe1-ySiyO3 closely resemble that of Cu1-xMgxGeO3,...

The Physics of Colloids in Space (PCS) experiment was accommodated within International Space Station (ISS) EXpedite the PRocessing of Experiments to Space Station (EXPRESS) Rack 2 and was remotely operated from early June 2001 until February 2002 from NASA Glenn Research Center's Telescience Support Center (TSC) in Cleveland, Ohio, and from the re...

The Physics of Colloids in Space is an experiment which flew in the ISS. Data on several different samples of colloidal particles were obtained. They provided unexpected information about the behavior of the samples in microgravity. The data are currently being analyzed. The most recent findings will be discussed in this talk.

We present results of a systematic x-ray scattering study of the effects of Mg doping on the high-field incommensurate phase of CuGeO3. Lorentzian-squared line shapes, the changing of the first-order transition to second order, and the destruction of long-range order with infinitesimal doping are observed, consistent with random-field effects in a...

We report a neutron-scattering study of the dynamic spin correlations in Rb2MnF4, a two-dimensional spin-5/2 antiferromagnet. By tuning an external magnetic field to the value for the spin-flop line, we reduce the effective spin anisotropy to essentially zero, thereby obtaining a nearly ideal two-dimensional isotropic antiferromagnet. From the shap...

We report a neutron-scattering study of the dynamic spin correlations in Rb2MnF4, a two-dimensional spin-5/2 antiferromagnet. By tuning an external magnetic field to the value for the spin-flop line, we reduce the effective spin anisotropy to essentially zero, thereby obtaining a nearly ideal two-dimensional isotropic antiferromagnet. From the shap...

The critical fluctuations of CuGeO$_3$ have been measured by synchrotron x-ray scattering, and two length scales are clearly observed. The ratio between the two length scales is found to be significantly different along the $a$ axis, with the $a$ axis along the surface normal direction. We believe that such a directional preference is a clear sign...

We report a neutron scattering study of the dynamic spin correlations of Rb_2MnF_4, a two dimensional spin 5/2 antiferromagnet. Using an external magnetic field, we tuned the effective spin anisotropy to zero, obtaining a nearly perfect Heisenberg antiferromagnet. Measuring the shape in energy of the quasielastic peak as a function of temperature a...

We report a neutron scattering study of the spin correlations for the spin- 5/2 two-dimensional antiferromagnet Rb 2MnF 4 in an external magnetic field. Choosing fields near the system's bicritical point, we tune the effective anisotropy in the spin interaction to zero, constructing an ideal S = 5/2 Heisenberg system. The correlation length and str...

We report a neutron scattering study of the spin correlations for the spin- 5/2 two-dimensional antiferromagnet Rb 2MnF 4 in an external magnetic field. Choosing fields near the system's bicritical point, we tune the effective anisotropy in the spin interaction to zero, constructing an ideal S = 5/2 Heisenberg system. The correlation length and str...

Measurements are reported of the time dependence of the current during electrochemical oxidation and reduction at a fixed voltage of single crystals and ceramic samples of La2CuO4+δ. Staging peaks in neutron measurements of the single crystals together with the electrochemical measurements and magnetization measurements confirm that stage n=6 corre...

Neutron scattering experiments have revealed a fascinating interplay between the hole doping, the spin fluctuations, and the superconductivity of the cuprate superconductors. Recently, electrochemical techniques have been used to produce large single crystals of La2CuO4+ y, which has mobile oxygen dopants. Staging behavior of the excess oxygen has...

Over the past decade, we have studied in detail the low-energy spin fluctuations in :a2−xSrxCuO4 for x between 0 and 0.18. Our experiments, as well as those by others, have revealed a fascinating interplay between the hole doping, the static and dynamic spin fluctuations and superconductivity. Recently, using electrochemical techniques, we have lea...

We review structural and magnetic neutron scattering studies performed on single crystals of La2CuO4+y containing excess oxygen in interstitial sites. Several structural transitions occur in this material. For low oxygen contents, macroscopic phase separation takes place below room temperature in which the material phase separates into an oxygen-ri...

Monodisperse hard-sphere colloids have long been studied as a model crystallizing system and for potential photonic applications. Adding a second component of spheres which differ in size from the first component increases the number of possible crystalline structures, and changes the fundamental kinetics of crystallization due to the necessity of...