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Strength and Behavior of Advanced High Strength Steel Structural Components
No full textAdvanced High Strength Steel (AHSS) is the next generation of steel for cold-formed steel (CFS) construction. With the superior strength of AHSS, the design space of CFS structures can be greatly extended, leading to improved efficiency and less steel consumption in construction. A research project, sponsored by the National Science Foundation, has been conducted to investigate the behavior of structural components made from AHSS, including connections, beam members, and column members.
An experimental study has been conducted to investigate the strength of bolted lap shear connections made from AHSS and the corresponding ductility demands. Multiple AHSS grades with different ductility levels and multiple failure modes are considered. A correlation is found between connection strength and ductility. The strength reduction specified by the current AISI design specification is found generally applicable to AHSS. Two new linear strength reduction factor equations are also proposed.
The buckling behavior of AHSS beam members is studied both experimentally and numerically. A series of four-point bending tests on AHSS beams have been performed. The current Direct Strength Method (DSM) is found unconservative for these tests for not considering local-distortional interaction. Numerical simulations are developed for the beam tests and confirm the findings. Another set of simulations focused on CFS floor joists made from AHSS is also developed. A predictive design method is eventually proposed for the local-distortional buckling interaction.
The study of AHSS column members consists of two parts. The first part is a parametric study on braced individual AHSS wall studs. The second part is a testing program on unbraced AHSS column members. The parametric study includes finite element simulation of AHSS cee-section wall studs with sheathing and/or bridging bracing under pure compression. It is found that the DSM is accurate for the columns with regular cee sections, but unconservative for the columns with optimized cross-sections. A modified DSM distortional buckling design equation is proposed to reduce the distortional buckling strength of the column members.
In sum, the data and design recommendations resulting from the experimental and numerical research provide the first step towards adopting AHSS for CFS construction
AN EMPIRICAL ASSESSMENT OF THE FINANCIAL PERFORMANCE OF UTILITY-SCALE BATTERIES AS PEAK GENERATORS
No full textAs the share of renewable energy continues to rise in the United States and globally, energy storage technologies such as lithium-ion batteries are increasingly being deployed to alleviate some of the issues posed by the intermittency of such resources. Specifically, batteries are able to absorb energy during times of the day when solar or wind resources are plentiful, and inject that energy into the grid when the resources are no longer available and demand for electricity peaks. In this way, batteries can help maximize consumption of clean energy all the while helping maintain the stability and reliability of the electric grid. However, despite recent growth and ongoing interest, lithium-ion batteries still cost more than most other generation technologies, and studies that use empirical data to assess the financial performance of battery projects are sparse, given that most of the deployment really happened in the last 3 years. As such, this analysis develops a financial model that calculates the rates of return on investment for a sample of battery energy storage (BES) and natural gas combustion turbines (NGCT) in order to verify whether batteries are in fact competitive with NGCTs. Unsurprisingly, the study reveals that the investment tax credit (ITC) for standalone energy storage projects provided by the Inflation Reduction Act (IRA) is one of the decisive factors that tilts the balance in favor of battery projects. In other words, although the rates of return for battery projects that are currently in operation are 0.1% to 2.4% lower compared to those of NGCTs, if those same projects were to have been built today, and therefore were eligible to receive the ITC, they would be earning 2.4% to 4.5% more on average than NGCT projects. Data related to project configuration, costs, and revenue are further dissected and analyzed to yield insights about how battery projects operate and earn revenue
On the Significance of Center Manifold Reduction: Data-Driven Dynamics at a Hopf Bifurcation
No full textThe Hartman-Grobman theorem has significance in extending a local linearization to global dynamics given the existence of a hyperbolic equilibrium point. However, many real-world systems like that of predator-prey models or chemical kinetics show oscillatory behavior, suggesting nonlinearity. The theory of stable-unstable manifolds suggests that the flow of the vector field is neither converging to an attracting point, nor is it diverging from a source. Due to the existence of the so-called center manifold, one can find a means of localizing the behavior of such a complex system. In conjunction with machine learning methods, one could learn the normalized canonical forms of complex, nonlinear dynamical systems. In this thesis, I aim to take advantage of the center manifold theorem to show existence of the reduction of nonlinear systems that exhibit oscillatory behavior in the neighborhood of an equilibrium point where one would find a Hopf bifurcation. In particular, I aim to present the normal form approximation of the Brusselator system to show that the dynamics restricted to the center manifold can be computed for validation. We aim to test the theoretical aspects through a machine learning approach, specifically employing an autoencoder architecture to discover continuous and invertible maps between a dynamical system and its normal form restricted to a center manifold. In practice, this would help to improve model reduction in the realm of data-driven dynamics
Oral History of Alexander "Alex" M. Capron
No full textThis interview with Professor Alexander “Alex” M. Capron, LLB, was conducted by Suzanne Snider on February 24 and February 25, 2023 in Newmarket, New Hampshire as part of Moral Histories: Voices and Stories from the Founding Figures of Bioethics, an oral history project of the Johns Hopkins Berman Institute of Bioethics. Prof. Capron is Professor Emeritus of Law and Medicine at University of Southern California (USC); Scott H. Bice Chair Emeritus in Healthcare, Law, Policy & Ethics; and Founding Co-Director of Pacific Center for Health Policy and Ethics at USC. Prof. Capron was born in Hartford, CT in 1944. His areas of expertise include psychoanalysis, bioethics and the law, public health law, brain death, and definitions of death.On Day 1, Prof. Capron speaks of his early life in California and describes his parents as early influences. Prof. Capron describes studying abroad in Germany as a high school senior in 1961, where he found parallels between his German peers’ reticence to discuss World War II in school and the lack of concern for racial segregation among his fellow high school students in his hometown of Palo Alto, CA. He describes his involvement in the civil rights movement while enrolled at Swarthmore College, and, later, at Yale Law School. Prof. Capron identifies fairness, justice, choice, and respect as throughlines that would connect his early interests in civil rights to his later work in psychoanalysis, law, and bioethics. He describes his time as a judicial clerk in 1969-70 for Chief Judge David Bazelon of the US Court of Appeals for the District of Columbia. Prof. Capron discusses Jay Katz’s work and philosophy on experimentation on human beings, which emphasizes a systemic rather than individualized approach. Prof. Capron describes consent as a shared process, and bioethics as a necessarily interdisciplinary field where collaboration occurs to address real life problems.On Day 2, Prof. Capron traces his path to The Hastings Center as a founding Fellow in 1970. He contextualizes The Hastings Center’s orientation towards patient autonomy and anti-paternalism during its early years, noting the publication of the first article about the United States Public Health Service Syphilis Study (informally referred to as the Tuskegee experiments) in 1972, and the National Commission for the Protection of Human Subjects of Biomedical and Behavioral Research (known as the National Commission), formed in 1973. Prof. Capron talks about an influential 1972 article he published with Leon Kass that proposed a definition of the standards for determination of human death, that ultimately was incorporated into the 1981 model state statute known as the Uniform Death Determination Act. This brought public attention to the practical work coming out of The Hastings Center. Prof. Capron offers an expanded description and discussion of the criteria for so-called “brain death.” He tells a story about a research participant named “Mrs. Kim” from a USC’s Pacific Center for Health Policy and Ethics study about the sociological considerations of advance directives. Prof. Capron emphasizes the importance of a universal legal definition of death by telling the story of Jahi McMath, a child who was declared dead by neurological criteria in California in 2013 but who was transferred to New Jersey at her family’s wishes where she continued to receive care under that State’s different policy regarding the definition of death (circulatory-respiratory death).Prof. Capron discusses teaching at University of Pennsylvania Law School (Penn Law), University of Southern California Law School, and Georgetown University Law. He highlights one course he taught at Penn Law in the 1970s which brought an interdisciplinary group of students together to apply their respective disciplinary perspectives to bioethics issues. Prof. Capron recounts his role as Executive Director of the first presidential commission on bioethics, the President’s Commission for the Study of Ethical Problems in Medicine and in Biomedical and Behavioral Research, from 1980-1983. He talks about the commission’s strategic approach, assembling its members, and the difference between recommendations and reports. He discusses his international bioethics work at the World Health Organization in Geneva in the early 2000s, when he focused on organ transplantation and research ethics. He discusses some of the concerns associated with gene therapy; his role as President of the World Congress of Bioethics in 1996 in San Francisco; and finally, how he plans to spend his recent retirement.This interview may be of interest to those wishing to learn more about the field of bioethics; early history of bioethics in the US; presidential bioethics commissions; international bioethics; student civil rights activism; bioethics, law, and psychology; the Recombinant DNA Advisory Committee (RAC) and gene therapy; definitions of death; brain death; organ transplantation
Increasing Recognition of Acute Kidney Injury Among Hospitalized Pediatric Patients
No full textBackground: Acute kidney injury (AKI), defined as an abrupt decline in kidney function, is a common complication among hospitalized pediatric patients with a rising incidence. Pediatric patients who develop AKI while hospitalized have longer hospital stays and increased morbidity and mortality. Despite the known risk factors, there is currently no efficient way to identify those at risk for developing AKI. This dissertation attempts to increase early recognition of non-critically ill hospitalized pediatric patients at risk for developing AKI. A clinical prediction model at the point of admission was developed and further enhanced incorporating inpatient variables during a patients stay.
Methods: A single center retrospective study at a tertiary medical center was conducted among all non-critically ill pediatric patients hospitalized at the Johns Hopkins Children’s Center from October 2016 to December 2021. Data from the electronic health record (EHR) was extracted to identify predictors of AKI among this sample. Random effects logistic regression was used to analyze these risk factors for development of AKI upon admission to the hospital.
Results: Dissertation findings identified several risk factors and interaction terms significantly associated with development of AKI. Secondary data analysis revealed including risk factors on admission allowed for a prediction model with an area under the curve (AUC) of the main effects model of 0.89, with a sensitivity of 84.23% and a specificity of 80.45%. When interaction terms were included, the AUC improved to 0.91, sensitivity 85.27% and specificity of 81.30%. With inclusion of nephrotoxic medications during a hospitalization, the model performance increased with an AUC of 0.958 with a sensitivity of 93.18% and a specificity of 88.45%.
Conclusions: While AKI has been hard to correctly classify and identify in this patient population, we found that certain risk factors place a pediatric patient at risk for developing AKI on admission and while hospitalized. While considering admission risk factors, it is also important to consider inpatient factors as they play an important role in AKI development. Future prospective research is needed using prediction models in real time to continue to increase recognition of AKI among these vulnerable patient population
LITERACY LEARNING LOSS AND THE MITIGATING ROLE OF THE HOME LITERACY ENVIRONMENT DURING THE COVID-19 SCHOOL CLOSURES: AN UNPRECEDENTED STORY
No full textThe purpose of this study was to examine literacy achievement in an intermediate school in New York, for a third-grade cohort not meeting state benchmarks, and the potential exacerbation of this problem due to the COVID-19 school closures. Utilizing ecological systems theory as a framework, contributing factors such as the impact of a global pandemic, the home literacy environment, parental education, parent and student attitudes toward reading, teacher self-efficacy, and reading instructional approaches were examined. A mixed methods needs assessment was conducted to investigate teachers’ perceptions of literacy learning loss, student reading achievement pre-and post-school closures, as well as the home literacy environments of the sample. The quantitative data revealed that the students outperformed themselves from the year prior as well as third graders dating back to 2016. Further, students had access to strong home literacy environments during the pandemic. However, the qualitative data from third grade teacher interviews suggested a perception of literacy loss as well as an identified lack of connection with students during the closures. To address this discrepancy, an applied project was developed in the form of a children's book titled, Unprecedented. The book aims to 1) share the research outcomes of the needs assessment, 2) honor the potential mitigating role of the home literacy environment, and 3) provide a tool in which students can discuss and reflect on their own experiences of learning during the school closures
HIV PRE-EXPOSURE PROPHYLAXIS ENGAGEMENT TRAJECTORIES AMONG TRANSGENDER WOMEN IN THE UNITED STATES
No full textBackground: Transgender women shoulder the highest HIV prevalence within the United States’ epidemic with 14% of all transgender women in the US living with HIV. HIV pre-exposure prophylaxis (PrEP) has been available in the US since 2012 yet uptake has been slow and adherence challenges have emerged. A comprehensive understanding of the factors that impact PrEP engagement among transgender women is needed to optimize PrEP engagement and address inequities in HIV incidence.
Methods: This explanatory, sequential mixed-methods study utilized group-based multi-trajectory modeling to identify groups of transgender women who followed similar patterns of PrEP engagement and indication and to identify factors associated with membership in each trajectory. We then used Cox regression to estimate rates and predictors of PrEP initiation and discontinuation. Building on quantitative findings, we conducted in-depth interviews to qualitatively explore the mechanisms by which multi-level factors impacted PrEP engagement trajectories. Findings were integrated analytically to generate archetypes of PrEP discontinuation and to develop a conceptual framework of engagement in prevention-effective adherence practices among transgender women.
Results: We identified five PrEP engagement trajectories. One quarter of transgender women followed prevention-effective adherence trajectories. Those diagnosed with sexually transmitted infections and those experiencing homelessness were more likely to follow non-prevention-effective trajectories. We observed 6.5 PrEP initiations per 100 person-years (95% CI: 5.5-7.7) and 37.5 discontinuations per 100 person-years (95% CI: 31.7-44.3). Four archetypes of discontinuation emerged: 1. Seroconversion following discontinuation, 2. Ongoing HIV acquisition risk following discontinuation, 3. Reassessment of HIV/STI prevention strategy following discontinuation, and 4. Dynamic PrEP use coinciding with changes in HIV acquisition risk. Qualitatively, we found that the capacity to safely engage with the healthcare system and compatibility between PrEP and individual values and preferences were primary factors impacting engagement in prevention-effective adherence practices. Upstream factors, including stigmas, identity-based oppression and marginalization, and sociostructural context indirectly influenced engagement in prevention-effective adherence practices.
Conclusion: This dissertation provides insights into the multi-level factors impacting PrEP engagement among transgender women in the United States. Our findings underscore the importance of addressing structural vulnerabilities to optimize PrEP implementation and address HIV inequities within transgender women communities
Evaluation of CFTR mRNA stability and dosage
No full textCystic fibrosis (CF) is an autosomal recessive disorder caused by more than 2000 variants in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. CFTR modulators have completely revolutionized the treatment of CF, with over 90% of individuals with CF being eligible for treatment. However, nonsense variants in CFTR have presented a particular challenge for therapeutic treatment. Nonsense mediated mRNA decay (NMD) targets premature termination codon (PTC)-bearing transcripts to reduce the potentially damaging effects of truncated proteins. CFTR modulators specifically target CFTR to aid in protein processing and function. Since NMD results in absence of CFTR protein, this prevents modulators from restoring CFTR function. mRNA stability is a critical consideration when evaluating therapeutic strategies for CF. In Chapter 2 of my thesis work, I investigate mRNA stability for the sixth most common CF- causing mutation, W1282X. I establish that this variant generates a PTC, targeting the transcript for degradation by NMD and resulting in low levels of steady state mRNA. This finding suggests that W1282X-bearing transcripts will not generate any protein, explaining the lack of CFTR functional response to modulators. In Chapter 3, I investigated several nonsense variants within the N- terminal region of CFTR and show that downstream translation initiation at M265 allows these variants to escape NMD. Treatment of the variant L88X with readthrough compounds combined with CFTR modulators restores full-length, functional CFTR protein. This work indicates that N-terminal variants that evade NMD are ideal candidates for combination treatment of readthrough compounds and modulator therapy. In Chapter 4, I establish a cell-based model system that enables independent expression of two copies of CFTR, which will aid in assessment of rare variants that are difficult to obtain through primary cell collection. Additionally, this system enables us to assess the fitness of the predicted model that each CFTR gene contributes to total CFTR function in an additive manner
(Un)Making Citizens: Bordering Regimes, Colonialism, and Security in South Asia
No full textIn 2019, India stripped close to 2 million people of their citizenship when the National Register of Citizens—meant to identify ‘genuine Indian citizens’—was implemented in the state of Assam. Policies of denationalization—or citizenship stripping—are not new in South Asia. As millions of people confront the possibility of statelessness, I ask: How do citizens come to be legally defined as foreigners?
I employ the concept of securitized belonging to show that citizenship is increasingly withheld from or denied to those who are objects of security or seen as a threat to state stability and endurance. Securitized belonging provides a useful framework to understand why states wish to list, track, and surveil their citizens in order to ensure their ongoing loyalty while simultaneously providing a justification to deprive of citizenship those individuals or groups who are perceived as a threat to the state. Securitized belonging simultaneously makes and unmakes citizens. The dominant scholarship on citizenship and security emphasize the role of state capacity, but without a deep investigation into the historical—specifically, imperial—construction and marginalization of certain groups as criminals, minorities, or outsiders. In British India, the colonial administration made very specific efforts—from anthropological investigations into colonized societies and to laws that criminalized specific tribal groups—to order Indian society and institutionalize certain laws, practices, and ideas.
Using extensive archival evidence, my research shows that the insecurities about imperial control were central to colonial migration control and in policing or punishing crime. These insecurities created sticky notions about who could or could not be “genuinely” Indian that then became entrenched in laws, the state apparatus, and even in social attitudes that targeted them for exclusion. In doing this research, I take seriously the call to examine colonial histories of bordering, migration control, and social ordering by scholars of postcolonial citizenship. My work challenges the long-held assumptions in the literature that tend to fetishize European (or Western) ideas, designs, and institutions as original blueprints or yardsticks for liberal abstractions yet to be realised in the non-Western world
