DSpace@RPI (Rensselaer Polytechnic Institute)
Not a member yet
6809 research outputs found
Sort by
Effect of displacement-dependent stiffness on performance of seismically-isolated bridges: an investigation using design optimization
No full textAugust 2021School of EngineeringSeismic isolation systems have been employed in bridge structures to increase their lateral flexibility, and consequently their natural period, and thereby improve their seismic performance by reflecting seismic energy away from the structure. In recent years, stiffness devices that could passively-generate both positive and negative tangential stiffness that continuously varies with displacement were introduced within bridge isolation systems in an attempt to further improve seismic performance by reducing their lateral stiffness to near-zero values and thus increasing the natural period to near infinity. Previous investigations on such displacement-dependent stiffness devices have focused on their effect on the seismic response of existing bridges, where design parameters that characterize the behavior of stiffness devices often had nominal values from preliminary designs or, at best, values obtained from sensitivity studies. A potentially different level of performance could be realized in new bridge designs if isolation system components (bearings, supplemental dampers and displacement-dependent stiffness devices) were designed simultaneously through optimization. This study concentrates on an evaluation of the effectiveness of displacement-dependent stiffness devices in improving the response of a highway bridge structure with a well-designed (optimized) seismic isolation system. A holistic design framework is developed that optimizes configurations of the isolation system with respect to multiple objectives. The identified optimized performance of the bridge structure using various combinations of the isolation system components is evaluated against criteria that quantify their relative performance and which determine how the performance is affected by the inclusion of the displacement-dependent stiffness devices within the isolation system.Ph
Spacial sound reproduction through crosstalk cancellation and head tracking
No full textAugust 2015School of ArchitectureReal time systems for the reproduction of binaural signals over loudspeakers require crosstalk cancellation (CTC) that necessitates accurate positioning of the listener in a 'sweet spot.' This thesis presents a binaural reproduction system that uses head tracking to update the position information in the CTC filter calculation, moving the sweet spot in concert with the listener.M
The interiorization of reality: subjective turn, therapeutic governance, and the case of internet addiction in china
No full textMay 2023School of Humanities, Arts, and Social SciencesThis dissertation explores the trend of internalization across historical, artistic, and sociopolitical dimensions. In the historical dimension, this research reviews the emergence of the subjective turn during the nineteenth century, where the body became a site for the production and management of reality. A contradictory process, it involved simultaneously a shift in people's attention from external realities towards interiorized experiences, and the opening up of the internal experience for external measurements and control. In the artistic dimension, this research examines artworks from the twentieth centuries, ranging from memoirs, documentaries, and science fiction from China and abroad that engage with themes of internalization and subjective perception. In the sociopolitical dimension, this research fosters understanding of therapeutic governance and internalization as a form of social control by exploring China's internet addiction phenomenon.Ph
A clinically relevant wireless pressure sensor for acute compartment syndrome
No full textDecember 2022School of EngineeringAcute compartment syndrome (ACS) is a surgical emergency requiring rapid diagnosis and intervention. ACS occurs after traumatic injury when edema causes the pressure within a myofascial compartment to rise above capillary perfusion pressure. Circulation in the compartment is compromised, leading to cellular anoxia, muscle ischemia, tissue death, and limb loss. To aid in the diagnosis of ACS we have developed a small, simple, inexpensive, wireless, implantable sensor technology for monitoring intracompartmental pressure. When placed under hydrostatic load, the resonant frequency of the sensor changes proportional to the change in pressure. An analytical model was created and validated to predict the electrical characteristics of the novel coil geometries which comprise our sensors. Using this model, we designed sensors of clinically relevant size and frequency. Sensors were then tested under physiologically relevant pressure changes, and finally they were validated in an in-situ simulation of ACS. Results showed that the analytical model predicts coil properties and sensor performance to within a 10% error in almost all cases. Under physiologic conditions, sensors were sensitive to pressure changes to within 11% error. Performance of sensors in situ correlated well to benchtop testing. During simulated ACS in a fresh cadaver, sensors were sufficiently sensitive to monitor intracompartmental pressures. From this work, we developed and validated an analytical model of the electrical characteristics of a planar, stadium-geometry Archimedean spiral, both as a single coil, and in an anti-aligned inductive pair. We identified a dielectric material with unique properties favorable to hydrostatic compression and refined a clinically relevant configuration appropriately sized for clinical use. Each of these components was tested and validated comprehensively for use in a clinical setting. This work has provided several of the elements needed for a functional, clinically relevant, pressure sensor and a validated model of the electrical characteristics for novel stadium geometry Archimedean spirals for use in implantable sensors.Ph
Generating natural language summaries from temporal personal health data
No full textDecember 2022School of ScienceWithin the personal health domain, there is a vast amount of temporal knowledge that can be collected about an individual (e.g., their time-stamped heart rate and step count data) due to the recent surge in the production of health and fitness tracking devices (i.e., smart, wearable technologies such as smart watches). Although everyday individuals have access to their own data via their personal mobile devices, they typically lack the knowledge or tools required to access the underlying patterns hidden within. Without these patterns, there is a sea of information unavailable to them that could potentially aid them in better comprehending their data and utilizing this knowledge to improve their daily routines. The work within this dissertation focuses on closing this gap between the non-expert individual and the meaningful patterns within their temporal personal health data. The basis of this work revolves around the incorporation of automated explainability in the form of natural language summary generation to highlight the behaviors exhibited by an individual and to evaluate them against their defined health goals. In particular, this work showcases the contributions of our time-series summarization framework within the personal health domain, automating this approach via deep learning, and future plans to include unsupervised rule generation.Ph
A continuous approximation model for the design of park-and-ride systems
No full textAugust 2023School of EngineeringPark-and-Ride (P&R) systems have emerged as a popular traffic management solution in response to the need for sustainable transportation options to combat the climate crisis and improve traffic flow. The goal of this research is to foster the use of public transportation by facilitating the design of P&R through sketch planning tools. This research aims to (1) formulate mathematical models to optimize the selection of P&R design variables, (2) analyze the effects of local conditions of land use and traffic on design variables of P&R, (3) analyze the influence of key features (location, transit service level, fares, etc.) on the expected demand and benefits. The models consider a continuous metropolitan area with population distribution defined by density functions. The number of P&R users are estimated through an analytical formulation of the catchment area of a P&R site and mode choice functions that take into the generalized travel costs of using P&R or driving-only. The mathematical models maximize expected user benefit and can be used to select P&R location and design the public transportation servicing the site. Numerical experiments are conducted to provide valuable insights into the implementation of P&R systems and offer guidelines for future design and planning efforts.Ph
High-order accurate finite-difference methods for partial differential equations on complex geometry
No full textMay 2023School of ScienceWe devise two high-order accurate finite-difference methods to solve scalar partial differential equations (PDEs), in second-order form, on curvilinear and overset grids. The first method addresses high-order accurate boundary closures. The second method develops high-order accurate fast algorithms for the wave equation on complex geometry. A high-order accurate boundary treatment through centered differences requires solution values on ghost cells, added beyond the bounds of the physical domain. To approximate the solution at such ghost values, traditional centered approaches utilize direct discretization of compatibility boundary conditions (CBCs)— generated from the expression of the boundary conditions and the PDE. Centered approaches rival one-sided approximations due to attractive stability and accuracy properties. Nevertheless, as the order of accuracy increases, some PDE problems exhibit involved algebra limiting the automation to high-orders of accuracy. Furthermore, discrete equation systems to evaluate the solution at the ghost points often couple tangentially impacting the efficiency of explicit time-dependent schemes, or schemes that employ iterative methods. To assuage such challenges at the boundary, we introduce the local compatibility boundary conditions (LCBC) method. The LCBC method computes solution values at ghost cells through a local interpolating polynomial. Interior values, boundary values, and compatibility boundary conditions determine the coefficients of the polynomial. The LCBC method reduces down to a formula describing solution approximations at ghost points in terms of interior and data values on a compact stencil, equal in width to that of the interior scheme. We give algorithms itemizing the LCBC procedure to an arbitrary order of accuracy. The local nature of the procedure avoids the algebraic difficulty and tangential coupling that occurs from the direct discretization of CBCs. We prove odd/even symmetry of the LCBC procedure for the unforced wave, heat and Laplace equations, with homogenous Dirichlet/Neumann BCs on Cartesian grids. Using symmetry, we demonstrate stability of the LCBC method with the high-order accurate Modified Equation scheme for the wave equation under a time-step restriction independent of the order of accuracy. A variety of numerical results on 2D Cartesian and curvilinear grids demonstrate accuracy up to order 6. On curvilinear and overset grids, algebraic complexity limits the usage of the high- order accurate Modified Equation (ME) scheme for the wave equation. While the ME scheme achieves high-order accuracy in both time and space in a single step, it involves taking repeated powers of the variable-coefficient spatial operator of the PDE. Traditional approaches expand such powers and discretize them using centered differences. As the order of accuracy increases, the operation count magnifies and impacts efficiency. We thus introduce the fast, high-order accurate factored modified equation (FAME) schemes. The FAME algorithms involve stages where second-order accurate differences of even derivatives of the solution are prepared to assemble high-order accurate differences in the final stage. This hierarchical procedure avoids the direct expansion of powers of the PDE spatial operator, and subsequent high-order accurate discretization. We demonstrate the superiority of the FAME schemes in terms of flop count, storage requirements and computational performance by comparing them to traditional ME algorithms. A variety of numerical examples employs the FAME schemes, along with the LCBC method, to demonstrate accuracy up to order 8 on 2D and 3D curvilinear and overset grids.Ph
Facilitating Reuse of Mental Health Questionnaires via Knowledge Graphs
No full textQuestionnaires are one of the most common instrument types for screening patients for mental disorders. They are composed of items whose answers are typically scored to determine the elevation on a specified dimension, and hence the statistical probabilities associated with the corresponding disorder or diagnosis. The Patient Health Questionnaire (PHQ-9) and the Generalized Anxiety Disorder (GAD-7) questionnaire, for instance, measure levels of depression and anxiety respectively, and can be used to support diagnosis of depression and generalized anxiety disorder. Some questionnaires are multidimensional, such as the Revised Children's Anxiety and Depression Scale (RCADS), and can thereby estimate elevations on multiple dimensions that underlie a variety of disorders. Mental health screening questionnaires are designed so that each item assesses specific symptoms whose pattern of co-occurence (often organized in a subscale) allows estimation of how likely such symptoms would occur in the absence of the disorder whose symptoms the items represent. Questionnaire users typically estimate how likely a set of co-occuring symptoms would be (i.e., a score) in the general population as a strategy to estimate the likelihood that the respondent has a disorder warranting mental health services. The RCADS is a 47-item, youth self-report questionnaire with subscales (separation anxiety disorder, social phobia, generalized anxiety disorder, panic disorder, obsessive compulsive disorder, and major depressive disorder). It also yields a Total Anxiety Scale (sum of the 5 anxiety subscales) and a Total Internalizing Scale (sum of all 6
Investigation of climate-adaptive opaque building components: toward an ectothermic approach to heating and cooling in buildings
No full textAugust 2023School of ArchitectureWhile the predominant practice for low-energy buildings aims to achieve highly insulating building envelopes, there is a growing interest in exploring climate-adaptive building envelopes as an alternative. However, most climate-adaptive technologies for opaque building envelopes have been proposed as supplementary systems to traditional heating and cooling methods and have exhibited limited climate adaptability. To drive a radical paradigm shift in heating and cooling forbuildings, this thesis proposes a novel approach to building envelopes, referred to as an ectothermic heating and cooling approach, aiming to maximize interactions with climates by directly utilizing ambient low-grade energy sources for building thermoregulation. The thesis provides a comprehensive review on the development of climate-adaptive building envelopes,
covering both design and technical perspectives. Additionally, the thesis introduces an ectothermic approach-based integrated heating and cooling structural building module, called HydroSIP. HydroSIP consists of a unique double-sided hydronic heating and cooling layer embedded in a composite structural insulated panel. This module exhibits various dynamic thermal behaviors, allowing it to maximize thermal resistance in isolating modes or minimize thermal resistance in
heat exchange modes to directly harness ambient thermal energy sources. The thesis focuses on the design and evaluation of HydroSIP, along with the following key areas of investigation: 1) Identification of module design and configuration; 2) Development of a simulation model using Modelica to address challenges encountered in modern standalone building energy modeling tools; 3) Investigation of thermal performance of HydroSIP over a static wall; 4) Exploration of the feasibility and energy-saving potential of HydroSIP in comparison to a conventional heating and
cooling system; and 5) Design and system development for multiple envelope applications. Various envelope application cases were investigated across eight U.S. climate regions. The findings revealed that, without the integration of renewable energy systems, annual heating energy savings of up to 38% and cooling energy savings of up to 52% when compared to a standard heating and cooling system in U.S. climate zones 4 to 8. By incorporating the HydroSIP system with a
geothermal loop system, the annual cooling energy was significantly reduced by 85% compared to a standard system. Additionally, as a supplementary system to existing heating and cooling systems, HydroSIP enhanced the rated COP of a standard system from 2.5 to a range of 4.8 to 5.2.Ph
The impact of microstructured morphology on macroscale properties of anion exchange membranes
No full textMay 2021School of EngineeringThis research seeks to explore the relationship between polymer morphology and ion transport to contribute to the development of inexpensive and high-performance ion exchange membranes. The goal of the projects described herein, and from future work, is to work towards a structure-property understanding that will enable the design of ionomers that self-assemble efficient hydrated ion-conducting channels. The materials must also have good mechanical integrity: having properties that prevent the excess swelling / water uptake that is known to lead to the failure of membrane materials. This will enable electrochemical energy devices, such as fuel cells and electrolyzers, that employ ion-transporting membranes to become more economically viable solutions to the cleaner and more sustainable production of energy. In this thesis, novel polymer backbones were designed, synthesized by anionic polymerization, functionalized by the post-polymerization addition of alkyl side chains with terminal ionic groups, and fully characterized as anion exchange membranes. Characterization techniques included differential scanning calorimetry (DSC), x-ray scattering, laser scanning confocal microscopy, ion conductivity, water uptake, and tensile stress-strain measurements. In the first project, the backbone employed was the semi-crystalline triblock copolymer poly(ethylene-b-styrene-b-ethylene) (ESE). The ESE triblock copolymer was functionalized via an acid-catalyzed Friedel-Crafts reaction to attach alkyl side chains containing bromofunctional groups for subsequent quaternization, but the high-temperature condition increased the polydispersity of the functionalized ESE copolymers and we found that the resulting ionomer membranes formed different microstructures (either long-range ordered lamellar or disordered) depending on the polydispersity. We found that the long-range ordered lamellar microstructures caused adverse morphological effects that negatively impacted the ion transport and mechanical properties of the ionomer membranes, leading to the conclusion that long-range ordered structures in block copolymers are not necessarily beneficial to the performance of block copolymer membranes. In the second project, the two backbones investigated were higher glass transition temperature polystyrene-analogs: poly(1,1-diphenylethylene-alt-styrene) (DPE/S) and poly(1,1-diphenylethylene-alt-4-tert-butylstyrene) (DPE/tBS), with glass transition temperatures of 173 °C and 194 °C, respectively. The DPE monomer cannot self-polymerize, which lends it to the synthesis of precisely tailored alternating copolymer backbones. This work demonstrated the benefits of employing a polymer backbone with a glass transition temperature > 120 °C on the overall mechanical stability and ion conductivity of AEMs operating in hydrated conditions. In addition, evidence for the benefits of having a precisely-tailored backbone where the ion functional groups are regularly spaced along the polymer backbone chain with a minimum distance of four methylene groups is presented. Finally, the feasibility of depolymerizing DPE/S and DPE/tBS styrene-analog polymers is demonstrated at room temperature using triflic acid as the catalyst, unlocking potentials for these polymers to be recycled unlike polystyrene.Ph