DSpace@RPI (Rensselaer Polytechnic Institute)
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Plant and control optimization in the context of chaotic dynamical systems
No full textMay 2022School of EngineeringThe combined plant and control design (co-design) of complex systems governed by chaotic dynamics presents many unique and interesting challenges associated with the multidisciplinary nature of the design problem and the chaotic behavior of the system dynamics. The challenges investigated in this work are 1) the relationship between design space complexity and system multidisciplinary optimality; 2) the failure of conventional sensitivity analysis methods to produce usable derivatives; and 3) the optimality and stability guarantees for the final design. Typically, co-design problems are dealt with in a sequential (segregated fashion), where the control is designed after all operational and optimality conditions for the plant design have been achieved. Furthermore, there is no existing literature where optimal co-design is applied to problems where chaotic dynamics dominates, such as active control of chaotic flows. This thesis aims for the development of a co-design methodology capable of handling nonlinear dynamical systems that exhibit chaotic behavior. The purpose of such a methodology is to assist engineers in the initial stages of a product development cycle in order to help improve the overall efficiency of the final design. More narrowly, the goal of this research is to help further the development of active flow control design methodologies which in turn can be used to improve overall efficiency and/or mission capability of future aircraft designs. Towards that goal, firstly, a gradient-based algorithm capable of handling chaotic dynamics and simple bound constraints is developed for (generic) chaotic co-design problems. Secondly, two co-design approaches are investigated and their results analyzed. Finally, optimal active-flow control is explored as a means to improve aerodynamic performance of aeronautical systems; more specifically, a methodology for optimization of closed-loop active-flow control systems that avoids the shortcomings of the previously discussed methods, and that guarantees, at every optimization iteration, a form of nonlinear stability and robustness. This thesis proposes and studies solutions to address all main 3 challenges, previously mentioned, associated with co-design and active flow control.Ph
Identity centered design : the liberating of the post-discretionary user
No full textAugust 2022School of Humanities, Arts, and Social SciencesThe intersection of critical creative practices and HCI was explored in an effort to create a design framework for developing material speculations in the form of communication tools that evoke critical reflection. In an effort to resurrect the individual within option-oriented technologies, Identity Centered Design was created. Identity Centered Design is an alternative conceptual framework for approaching HCI design that emphasizes communication, interaction, and physicality in an effort to diversify ‘users,’ giving emphasis to the ‘individual-as-user.’ The application of an Identity Centered Design methodology to the creation of material speculations leverages social disfluency in the form of creative tools to reintroduce discretionary use and individuality within digital-communication systems. This was demonstrated within a case study that featured the creation of a situated artifact in the form of a chat-based application entitled Digital Penmanship. Digital Penmanship relies on the use of disfluency through the encoded presence of the individual-as-user as a way to induce critical reflection on the limitations of modern-day communication systems. The Digital Penmanship application features the visual encoding of an individual’s biometric data, specifically their keystrokes, to the non-verbal elements of type design.Ph
Soluble klotho and heparin modulate the pathologic cardiac actions of FGF23 in chronic kidney disease
No full textKidney International, in pressNote : if this item contains full text it may be a preprint, author manuscript, or a Gold OA copy that permits redistribution with a license such as CC BY. The final version is available through the publisher’s platform.Fibroblast growth factor (FGF) 23 is a phosphate-regulating hormone that is elevated in patients with chronic kidney disease and associated with cardiovascular mortality. Experimental studies showed that elevated FGF23 levels induce cardiac hypertrophy by targeting cardiac myocytes via FGF receptor isoform 4 (FGFR4). A recent structural analysis revealed that the complex of FGF23 and FGFR1, the physiologic FGF23 receptor in the kidney, includes soluble α-klotho (klotho) and heparin, which both act as co-factors for FGF23/FGFR1 signaling. Here, we investigated whether soluble klotho, a circulating protein with cardio-protective properties, and heparin, a factor that is routinely infused into patients with kidney failure during the hemodialysis procedure, regulate FGF23/FGFR4 signaling and effects in cardiac myocytes. We developed a plate-based binding assay to quantify affinities of specific FGF23/FGFR interactions and found that soluble klotho and heparin mediate FGF23 binding to distinct FGFR isoforms. Heparin specifically mediated FGF23 binding to FGFR4 and increased FGF23 stimulatory effects on hypertrophic growth and contractility in isolated cardiac myocytes. When repetitively injected into two different mouse models with elevated serum FGF23 levels, heparin aggravated cardiac hypertrophy. We also developed a novel procedure for the synthesis and purification of recombinant soluble klotho, which showed anti-hypertrophic effects in FGF23-treated cardiac myocytes. Thus, soluble klotho and heparin act as independent FGF23 co-receptors with opposite effects on the pathologic actions of FGF23, with soluble klotho reducing and heparin increasing FGF23-induced cardiac hypertrophy. Hence, whether heparin injections during hemodialysis in patients with extremely high serum FGF23 levels contribute to their high rates of cardiovascular events and mortality remains to be studied
Multi-scale computational modeling of interplay of fibers, reinforcement and cementitious matrix for ultra-high performance concrete in fluid and solid states
No full textDecember 2021School of EngineeringUltra-High-Performance Concrete (UHPC) is a special class of concrete with superior mechanical and rheological properties. Optimal gradation with only very fine aggregate (typically less than 1 mm) and the presence of discrete smeared fiber reinforcements holds the key behind its special features. UHPC has significantly higher compressive strength ( 150 MPa) and much lower permeability compared to regular concrete which makes it much more durable. The presence of fibers enables UHPC to sustain large tensile stresses for much larger strains compared to regular concrete too. Thus, the contribution from tension zones in UHPC beams due to fiber crack bridging is not negligible as it was in regular concrete. These additional features come at a price. From a mechanical behavior complexity point of view, previous research works have shown that the key failure modes of reinforced-UHPC (R-UHPC) beams are governed by the relative proportion of continuous and discrete reinforcements which originates from the mechanics of interplay. However, not only the interplay is a complex phenomenon, but also, the tensile capacity of UHPC is not an isotropic property. This is because of the highly flowable nature of UHPC that creates flow-induced fiber orientation based on the casting geometry as well as rheological properties of UHPC at fresh state. This phenomenon makes UHPC behavior anisotropic. Therefore, the macroscopic tensile strength (and to some extent its shear strength) of UHPC becomes an extrinsic property and hence increases the uncertainty during the structural design process. Additionally, the quantification of these complex interactions is challenging even with the most rigorous experimental tools given the challenges of measuring individual fiber contributions and their orientations. Therefore, this presented research aims to address these issues with a comprehensive multi-state multi-scale computational framework that links fresh state to hardened state of UHPC and mesoscale description to structural length scale via multi-scaling modeling. The numerical framework can be broadly divided into three projects. In the first project, a state-of-the-art discrete numerical model, the Lattice Discrete Particle Model with Fibers (LDPM-F) is used to probe into shear and flexural failure mechanisms of R-UHPC beams. In this work, a UHPC material model was calibrated and validated based on lab-scale companion specimen tests. The calibrated model was then used to simulate R-UHPC beams with different fiber and rebar reinforcement contents followed by sectional analysis to quantitatively evaluate the different contributions of UHPC matrix, rebar, and fiber in load-carrying capacity. The detailed probing of failure mechanisms was able to furnish a fundamental understanding of stress redistribution for different failure modes. Next, the second project was focused on enabling the computationally cost-effective simulation of R-UHPC structural beams while keeping as much rich physics of their constituents interactions. This was done by extending an energy-based coarse-graining model for plain concrete to account for discrete fibers explicit contribution. To study the applicability of the model and the ranges of its scaling factor, a parametric study was designed for different coarse realizations to show that the length scale of the fiber dictates the limit of the coarse realization to reliably preserve the complex energy dissipation mechanisms of the fine-scale. The results showed the capabilities of the new coarse-graining model in achieving very large computational cost reductions with high accuracy in predicting the same failure mode and load-displacement response for a large number of lab-scale and full structural scale experiments. Finally, the third project intends to link the flow-induced fiber orientation during casting to the hardened mechanical behavior of UHPC. An orientation tensor-based approach was used to predict the evolution of fiber orientation in a semi-explicit manner where instead of tracking each fiber due to hydrodynamic interaction, a fiber orientation state is predicted in a statistical sense. This model successfully predicted the fiber orientation state which was subsequently validated by simulating the hardened behavior of UHPC in presence of a preferential fiber alignment. Collectively, the presented research provides a virtual numerical framework of R-UHPC structural elements that allow for investigating and evaluating complex failure mechanisms as functions of reinforcement ratio, fiber content, and flow-induced fiber orientation. At the same time, this framework is capable of simulating large-scale elements thanks to its cost-effective multi-scale modeling capability. Collectively, the presented research serves as a digital twin for R-UHPC beams that can be used to understand and link the Processing-Structure-Properties-Performance relationships of this complex and advanced class of reinforced cementitious composites.Ph
Multigrid for high-order accurate difference equations on overset grids
No full textAugust 2021School of ScienceMultigrid algorithms of solving elliptic or hyperbolic partial differential equations and boundary value problems to high-order accuracy on overset grids are developed and studied in this thesis. The thesis consists of three main parts. In the first part, we consider several nonstandard coarsening strategies for geometric multigrid, including lower-order accurate coarse-level operators, red-black coarsening, and general factor-r coarsening. In the second part, the fourth-order accurate multigrid algorithm on overset grids is described, for solving elliptic problems with general geometry in two and three dimensions. The algorithm is implemented in the Ogmg solver in the Overture framework. Theoretical results based on local Fourier analysis and model problems are effectively applied on overset grids, to optimize multigrid convergence. In the third part, we examine the the application of multigrid solvers to high-order accurate implicit schemes for the wave equation.Ph
Automatic vectorization for multi-party computation
No full textAugust 2022School of ScienceWe introduce a new compiler for multi-party computation (MPC) which performs backend-independent optimizations over the MPC Source intermediate representation and outputs C++ code using the MOTION framework for MPC. We showcase a specific optimization: novel automatic vectorization over MPC Source. This optimization is shown to provide significant performance improvement in most benchmarks, and mitigations are suggested to detect and prevent cases where this optimization leads to a performance regression. Both circuit generation and evaluation time improves, and there is a consistent reduction in communication size and amount. We additionally compare results to hand-optimized MOTION code and find that there are only minor differences which can easily be overcome in future work.M
Dynamics of individual learning
No full textAugust 2022School of Humanities, Arts, and Social SciencesThis work focuses on understanding how individuals learn complex tasks. Most real-world tasks that we learn and need help with, are complex. Yet most of our knowledge about human learning is based on simple tasks. We think the main reason is the lack of appropriate tools of analysis, as learning curves in complex tasks must be studied from an individual-specific perspective due to large individual differences of methods. Therefore, as our first step, we developed a novel, uncertainty-based tool -- the SpotLight -- to model changes in uncertainty of individual performance and highlight the plateaus, dips, and leaps at different levels of complex task performance. We applied the SpotLight to investigate the changes of individuals' methods while learning the complex game of Space Fortress (SF). Our results indicate that, underneath a sea of individual differences of methods, individuals applied a common, simple heuristic to recurrently update methods. While our SpotLight analysis helped us identify similarities across individuals, it also revealed scopes of improving measures of complex task performance to prevent false negatives of training benefits. Application of heuristics to update methods, as observed for our SF players, indicates at boundedly rational behavior to deal with the computational complexity of finding appropriate methods for complex tasks. Therefore, in our final study, we investigated how an individual searches for better methods while learning the complex game of Ms. Pacman. Our results indicate an efficient approach by the individual to search for better methods, by developing and refining a set of elementary, heuristic-based methods. Finally, we tie together the four studies and discuss how we may progress towards a boundedly rational theory of learning complex tasks.Ph
Homogalacturonan from squash: Characterization and tau-binding pattern of a sulfated derivative
No full textCarbohydrate Polymers, 285, 119250Note : if this item contains full text it may be a preprint, author manuscript, or a Gold OA copy that permits redistribution with a license such as CC BY. The final version is available through the publisher’s platform.A pectic polysaccharide (WAP) was isolated from squash and identified as a homogalacturonan with a molecular mass of 83.2 kDa by GPC, monosaccharide composition analysis, FT-IR and NMR spectra. Sulfation modification of WAP was carried out and a sulfated derivative (SWAP) was obtained with a substitution degree of 1.81. The NMR spectrum indicated that the sulfation modification mainly occurred at the C-2 and C-3 positions of galacturonan residues. The binding pattern of SWAP to tau K18 protein was observed in 2D 1Hsingle bond15N HSQC spectra of tau, which resembled the tau-heparin interaction, with R2 domain as the major binding region. These results suggest that SWAP has the potential to act as a heparin mimic to inhibit the transcellular spread of tau; thus natural polysaccharide from squash may be developed into therapies for AD and related tauopathies.National Institutes of Healthhttps://login.libproxy.rpi.edu/login?url=https://doi.org/10.1016/j.carbpol.2022.11925
Gaze, steering, and active vision during skilled quadcopter flight
No full textAugust 2022School of Humanities, Arts, and Social SciencesPrevious accounts of how humans locomote have focused on movements and perceptualjudgments along the 2D ground plane, such as when driving automobiles or walking over various
types of terrain. Humans, however, can also locomote in very different conditions as evidenced by
the flight of experienced quadcopter pilots as they fly through cluttered three-dimensional
environments. In this thesis, I investigated how quadcopter pilots coordinate gaze with steering in
a variety of environmental conditions. Chapter 1 reviews previous accounts of visually guided
locomotion in humans and discusses whether such accounts may be able to explain the gaze and
steering behavior of quadcopter pilots. The second chapter outlines a novel experimental paradigm
designed to investigate how quadcopter pilots coordinate gaze with steering in a virtual reality
(VR) environment. Chapters 3 and 4 detail the results from two experiments. There are three main
takeaways from the present set of experiments. First, coordination of gaze and steering during
quadcopter flight share some similarities with gaze during other forms of locomotion. During a
purely path following task, participants spent a large portion of time orienting gaze towards the
ground over which they would soon pass. However, in Experiment 1, the presence of hoops
resulted in gaze predominantly being oriented through the center of those hoops. Second, pilots
adapt their current trajectory in accordance with upcoming environmental conditions, suggesting
anticipatory steering through the nearest hoop to align themselves with the subsequent. Lastly,
Experiment 2 showed that even when obstacles lie directly on or close to the path participant gaze
was still oriented towards the path outline or the terrain near the path. The findings from both
studies provide evidence in support of a predominant gaze strategy where participants look towards
their desired direction of steering, with little time spent orienting gaze towards obstacles or other
objects. The last chapter is a general discussion, outlining the limitations and future directions of
the current study.Ph
Using diffusion equation model to analyze advanced sound energy decay in reverberation chamber
No full textAugust 2022School of ArchitectureIn the room acoustics measurement process, a non-diffused sound field is neglected in conventional chamber-based studies of absorbing materials, which reduces accuracy and can even produce inconsistent results. An additional discrepancy about the definition of a complete diffuse sound field around the border of the target absorption material under test is revealed by an analysis of the energy flow in the reverberation room[Schroeder \& Manfred R., JASA, Vol 31, pp. 1407-1414 (1959)]. Currently, one can easily create a model simulating the sound energy flow inside the reverberation chamber with the help of a diffusion equation model, especially for measurements of random incidence absorption coefficients. This model also offers a lighter computational load at roughly the same level of precision as wave-based methods. In order to acquire the energy flow of the chamber more effectively than wave-based simulation models, a technique for applying the diffusion equation model to the modeling of reverberation chambers is presented in this study. For highly absorbent materials, further investigation reveals that one-twelfth of mean free route length is the meshing condition that is deemed realistically correct for getting random incidence absorption coefficient. With Jing's boundary condition and the simulated energy flow, an inverted computation of a high absorption coefficient is made achievable. Due to the accuracy and greater order of energy decay simulation, it is now possible to determine absorption coefficients without the interference of an incomplete diffuse sound field by comparing the results of simulations with measurement data.M