In clinical settings, dynamic foot function is commonly inferred from static and passive foot measurements; however, there is little evidence that static foot structure can predict dynamic foot function during walking gait. Previous research seeking to find correlations between the two have focused primarily on sagittal plane midfoot angles even though the midfoot has triplanar motion, which misses potentially important information. Additionally, the focus on kinematics alone may miss the contributions that forces play in midfoot mechanics. To address the angle limitations, a novel Signed Helical Angle (SHA) was developed to capture the triplanar motion of the midfoot from a multi-segment foot model. This was combined with foot segmental force measurements and inverse dynamics to capture dynamic midfoot stiffness. The SHA method and static-dynamic analysis were evaluated on 40 healthy subjects walking at a controlled speed. Subjects were divided into three structural groups based on static arch height (high, normal, low) and stiffness (stiff, normal, flexible). One-way ANOVA was used to evaluate differences among groups in dynamic motion and stiffness and a multiple regression was employed to evaluate relationships across the sample. Calculating the SHA resulted in a greater range of motion (ROM) compared to the sagittal Euler angle commonly used, showing that the motion in the other planes are captured in the SHA. The Finite Helical Axis (FHAx) associated with the SHA also showed that on average the population had a clear distinction between pronation and supination during the stance phase, although individual subjects exhibited substantial variability. While there were visual distinctions in the SHA and the midfoot stiffness among the three stiffness groups and the three arch height groups, the differences were not statistically significant. The only measurement achieving statistical significance was the mean of the sagittal plane midfoot Euler angles among the three AHI groups (p = 0.015); however, this is a postural measure which simply confirms that a high arch will remain high and a low arch will remain low throughout the gait cycle. The lack of any relationships between static foot structure and dynamic foot function, despite advanced modeling and measurements, further confirms that other factors play a large role in foot mechanics. Future studies should focus on evaluating the role of the intrinsic foot musculature (e.g., muscle strength, activation, and redundancy) during gait, and replacing traditional shoe and orthotic recommendations.

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<p> The phonon dispersion relation in the principal symmetry directions of a crystal of Cu-Ni-Zn was measured at 298°K by means of inelastic scattering of thermal neutrons. The specimen had an electronic concentration per atom very close to that of pure copper and it came as no surprise that no significant shift in the phonon spectrum relative to that of pure copper could be observed. </p> <p> The particular specimen used had a poor mosaic distribution; this contribution was taken into account in the calculation of the line shape and it was found that the widths of the neutron groups could be well accounted for in this way. </p> <p> The appendix is divided into six parts, four of which contain a description of projects of secondary importance that were realized. </p> / Thesis / Master of Science (MSc)

Sequential single-axis vibration testing strategies often produce over-testing when qualifying system hardware. Multi-axis excitation techniques can simulate realistic service environments, but the hardware and testing strategies needed to do so tend to be costly and complex. Test engineers instead must execute sequential tests on single-axis shaker tables to excite each degree of freedom, which the previous two decades of vibration testing literature have shown to cause extensive over-testing when considering cross-axis responses in assessing the severity of the applied test environments. Traditional assessments assume that the test article responds only in the axis of excitation, but often significant response occurs in the off-axes as well. This paper proposes a method to address the over-testing problem by approximating a simultaneous multi-axis test using readily-available, single-axis shaker tables. By optimizing the angle of excitation and the boundary condition through dynamic test fixture design, the test article can be tested using a Single-Input, Multiple-Output (SIMO) test in a way that approximates a Multiple-Input, Multiple-Output (MIMO) test. This paper shows the proposed method in simulation with a 2D finite element box assembly with removable component (BARC) model attached to springs with variable stiffness. The results include quantified test quality assessment metrics with comparison to standard sequential testing. The proposed method enables access to rapid, approximate, multi-axis testing using existing hardware, thereby reducing the over-conservatism of sequential single-axis tests and requisite over-design of systems.

Microbiota-released extracellular vesicles (MEVs) have emerged as key players in intercellular signaling in host-microbiome communications. However, their role in gut-brain axis signaling has been poorly investigated. Here, we performed deep multi-omics profiling of MEVs generated ex-vivo and from stool samples to gain insight into their role in gut-brain-axis signaling. Metabolomics unveiled a wide array of metabolites embedded in MEVs, including many neurotransmitter-related compounds such as arachidonyl-dopamine (NADA), gabapentin, glutamate, and N-acylethanolamines. To test the biodistribution of MEVs from the gut to other parts of the body, Caco-2, RIN-14B, and hCMEC/D3 cells showed the capacity to internalize labeled MEVs through an endocytic mechanism. Additionally, MEVs exhibited dose-dependent paracellular transport through Caco-2 intestinal cells and hCMEC/D3 brain endothelial cells. Overall, our results revealed the capabilities of MEVs to cross the intestinal and blood-brain barriers to delivering their cargo to distant parts of the body.

Master of Science / Material extrusion is a common form of 3D printing that has historically been limited to producing prototypes, models, and low load-bearing parts. This is primarily because parts are manufactured layer-by-layer, resulting in poor adhesion along the build direction, and machines struggle to print with high-strength polymers, which tend to shrink significantly as they cool. However, one way to address these limitations is to use fiber-reinforced materials in combination with multi-axis deposition strategies. In material extrusion, embedded fibers will align themselves along the deposition path, providing structural, thermal, and chemical improvements. Multi-axis toolpathing can enable the deposition of this fiber-filled material in full 3D along a part's expected stress paths. This is possible using a complex kinematic system like an industrial robot arm that can rotate the angle of the tool relative to the part as it is printing. The objective of this work was to develop and test a tool capable of multi-axis continuous carbon fiber reinforcement, which required a dedicated cutting mechanism to shear the fiber at the end of each deposition path, control over the amount of fiber used, and a slender tool profile to avoid collisions during multi-axis printing. The findings of this work revealed that while the use of continuous carbon fiber further reduced the adhesion between deposition paths, it substantially improved the strength of the part along them. To validate the multi-axis capability of the system, a toolpath was generated for a curved tensile bar. The results showed that the continuous carbon fiber multi-axis toolpath resisted a load 820.57% higher than an XY-planar sliced part printed with traditional filament, confirming the effectiveness of the presented approach. Multi-axis motion can also be used for avoiding support material requirements. In traditional 3-axis material extrusion, steep overhanging features often require additional, sacrificial material to be printed underneath. This leads to longer print times, more material waste, and a poor surface finish left behind on the final part. To minimize the amount of support material required, various techniques have been explored, including changing the toolpath, part geometry, or material processing parameters. However, none of these techniques have been successful in eliminating the need for supports entirely. A promising approach to address this issue is multi-axis material extrusion, where the angle of the printing tool and the direction of the layers can be precisely controlled during the printing process. This technique can be used to ensure that the tool is always extruding material onto a well-supported surface, rather than over thin air. However, research to date has not yet fully explored how the range of achievable overhang features changes as the tool is rotated. To address this knowledge gap, this work used an industrial robot arm equipped for material extrusion to investigate the relationship between tool angle, build direction, and achievable overhang threshold. The results showed that the same overhang limitations that exist in the XY plane will rotate with the tool and are unaffected by gravitational forces. These findings provide valuable insights for advancing the use of multi-axis material extrusion in the production of complex and intricate 3D objects without the need of supports.

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