Symmetry-protected topological invariant and Majorana impurity states in time-reversal-invariant superconductors

We address the question of whether individual nonmagnetic impurities can induce zero-energy states in time-reversal-invariant topological superconductors, and define a class of symmetries which guarantee the existence of such states for a specific value of the impurity strength. These symmetries allow the definition of a position-space topological Z_2 invariant, which is related to the standard bulk topological Z_2 invariant. Our general results are applied to the time-reversal-invariant p-wave phase of the doped Kitaev-Heisenberg model, where we demonstrate how a lattice of impurities can drive a topologically trivial system into the nontrivial phase.Comment: published versio

Understanding Gendered Risks for Severe COVID-19 Through Surveying the Gender Diverse Community

Early on in the pandemic, the medical community began noticing that men were more likely to be hospitalized, require admission to the ICU, and die of COVID-19 than women but few studies of COVID-19 make mention of gender diverse people, an often-overlooked population who may have vastly different experiences than non-gender diverse men or women. Their variations in gender and sex characteristics may also help provide further insight into which traits are protective or risk factors for this disease. This project used Poisson regression in order to analyze self-reported survey data. The major associations of interest will be between disease severity and an individual\u27s hormone profile, primarily measured by whether they are on hormone replacement, and if applicable what kind; measures of minority stress such as closetedness; and other sex traits such as presence of gonads

Bound states and resistive edge transport in two-dimensional topological phases

The subject of the present thesis are some aspects of impurities affecting mesoscopic systems with regard to their topological properties and related effects like Majorana fermions and quantized conductance. A focus is on two-dimensional systems including both topological insulators and superconductors. First, the question of whether individual nonmagnetic impurities can induce zero-energy states in time-reversal invariant superconductors from Altland-Zirnbauer (AZ) symmetry class DIII is addressed, and a class of symmetries which guarantee the existence of such states for a specific value of the impurity strength is defined. These general results are applied to the time-reversal invariant p-wave phase of the doped Kitaev-Heisenberg model, where it is also demonstrated how a lattice of impurities can drive a topologically trivial system into the nontrivial phase. Second, the result about the existence of zero-energy impurity states is generalized to all AZ symmetry classes. This is achieved by considering, for general Hamiltonians H from the respective symmetry classes, the “generalized roots of det H”, which subsequently are used to further explore the opportunities that lattices of nonmagnetic impurities provide for the realization of topologically nontrivial phases. The 1d Kitaev chain model, the 2d px + ipy superconductor, and the 2d Chern insulator are considered to show that impurity lattices generically enable topological phase transitions and, in the case of the 2d models, even provide access to a number of phases with large Chern numbers. Third, elastic backscattering in helical edge modes caused by a magnetic impurity with spin S and random Rashba spin-orbit coupling is investigated. In a finite bias steady state, the impurity induced resistance is found to slightly increase with decreasing temperature for S > 1/2. Since the underlying backscattering mechanism is elastic, interference between different scatterers can explain reproducible conductance fluctuations. Thus, the model is in agreement with central experimental results on edge transport in 2d topological insulators

Perils and Promise of Basing Welfare Through the Tax System: An Analysis of Tax Filing and Credits

Using Survey of Income and Program Participant (SIPP) Census Data, this paper employs a regression discontinuity and panel data analysis to determine the impact of the tax filing cutoff on an individual’s decision to file and whether a person’s decision to file is impacted by the value of the tax credit available to them. The Biden administration’s expansion of the Child Tax Credit (CTC) changed the CTC from a tax deduction to a cash transfer program as the credit became available to everyone, even if they did not pay taxes. Importantly, to receive the tax credit from the Internal Revenue Service (IRS), individuals and families had to have filed their taxes or needed to fill out a simplified tax form to claim the CTC. The IRS is not a welfare distribution service and this paper studies whether it can effectively distribute programs such as the CTC and reach those who would benefit from the tax credit most. The paper shows mixed findings, suggesting that people with children under 18 file at higher rates and are more likely to receive tax credits. However, there is also a large correlation between filing and education, with people who have more education being more likely to file. The regression results suggest support for the effective distribution of welfare through the IRS but also a need for more tax filing help and outreach to less educated communities

Leveraging the Methodological Affordances of Facebook: A Model of Social Networking Strategy in Longitudinal Writing Research

While composition studies researchers have examined the ways social media are impacting our lives inside and outside of the classroom, less attention has been given to the ways in which social media—specifically Social Network Sites (SNSs)—may enhance our own research methods and methodologies by helping to combat research participant attrition and build a community around a research project. In this article, we share some of the successes and shortfalls of using SNSs for research purposes, based on our own experiences using Facebook in the context of our writing program’s Longitudinal Study of Student Writers. Specifically, we present five considerations related to the integration of Facebook for research—Building a Community, Sharing Study Data, Constructing Identity, Understanding Analytics, and Conducting Usability Testing—and we discuss how these methods can be extended to other SNSs

Vorbruchverhalten von Gesteinen in gebirgsschlaggefährdeten Gebieten: Laboruntersuchungen von mikroakustischen Emissionen

Rockbursts are mainly induced by mining activity and result in the emission of seismic signals transmitted through the rock. Up to now, the monitoring of mining regions to detect stress changes and stress accumulations in rock uses incidences of occurrence and intensities of seismic events that occur due to mining activity. Within this research work, the occurring frequencies of microacoustic events are determined and analysed to find indicators for the approaching macroscopic failure of rock. The first part of this work treats extensively the basics of rockbursts, fracture mechanisms and acoustic emissions. It becomes obvious that measuring techniques can already give information about stress changes and stress accumulations in rock with the help of incidences of occurrence and intensities of microacoustic events. A prediction of the time of approaching rockbursts is yet not possible. The main focus of this research work is, therefore, the complement investigations of the frequency behaviour of microacoustic events of rock. To investigate the stress changes inside the material, uniaxial compression tests are carried out and the microacoustic events that are generated by the load application are especially analysed in the phase of prefailure in which already existing microcracks inside the specimen grow, interact and coalesce until the specimen fails macroscopically. The carried out laboratory tests are mainly investigated by analysing the frequency behaviour of the microacoustic events. It is presented that the frequencies change during load application. Hence, recorded signals and their spectra can be assigned to their state of fracture and their state of loading by investigating the frequencies of signal spectra of the microacoustic events. With these first investigations of their kind, specific indicators are found to identify the present state of fracture and loading.Gebirgsschläge sind durch den Berg- oder Tunnelbau induzierte seismische Ereignisse, die Bruchereignisse im Untergrund darstellen. Mithilfe messtechnischer Überwachung in Bergbaugebieten können Aussagen über Häufigkeiten und Intensitäten auftretender mikroakustischer Ereignisse gemacht werden. Allerdings ist eine Vorhersage zum Zeitpunkt des Versagens nicht möglich. In der vorliegenden Arbeit werden im Speziellen die auftretenden Frequenzen der emittierenden Wellen bestimmt und analysiert, um Indikatoren für die Vorhersage des makroskopischen Bruchs zu ermitteln. Der erste Teil der Arbeit befasst sich umfassend mit den Grundlagen von Gebirgsschlägen, Bruchmechanismen im Gestein und mikroakustischen Emissionen. Vorhersagen über bevorstehende Gebirgsschläge sind noch nicht möglich, da sich die Untersuchung der mikroakustischen Ereignisse auf deren Häufigkeiten und Intensitäten beschränkt. Die ergänzende Bestimmung und Auswertung der auftretenden Frequenzen mikroakustischer Ereignisse wird daher als Kernpunkt dieser Arbeit hergeleitet. Im zweiten Teil der Arbeit werden die durchgeführten Laborversuche ausführlich beschrieben und dargestellt. Es werden einaxiale Druckversuche durchgeführt, die mit mikroakustischer Überwachung speziell das Vorbruch-verhalten eines Kalksandsteines analysieren. Die durchgeführten Laborversuche werden auf Häufigkeiten, Intensitäten und im Besonderen auf die auftretenden Frequenzen der mikroakustischen Ereignisse untersucht und analysiert. Es wird gezeigt, dass sich die Frequenzen der mikroakustischen Ereignisse während des Versuchsverlaufes ändern. Daher ist eine Zuordnung der mikroakustischen Ereignisse anhand ihrer Frequenzgehalte zur jeweiligen Belastungsphase bzw. zum Bruchzustand möglich. Diese Arbeit liefert die ersten Erkenntnisse dieser Art zum Frequenzverhalten mikroakustischer Ereignisse aufgrund einer einaxialen Belastung im Gestein

Investigation of the lineâ pair pattern method for evaluating mammographic focal spot performance

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135107/1/mp7921.pd

Gender stratified adjustment of the DAS28-CRP improves inter-score agreement with the DAS28-ESR in rheumatoid arthritis

Objectives: To evaluate determinants of discordance between DAS28-ESR and DAS28-CRP and resulting impact on disease activity stratification in rheumatoid arthritis (RA)Methods: Paired DAS28-ESR and DAS28-CRP readings (n=31,074) were obtained from the British Society for Rheumatology Biologics Register for Rheumatoid Arthritis (BSRBR-RA). Factors influencing discordance between DAS28-ESR and DAS28-CRP were evaluated alongside the resulting effect on disease activity stratification. The impact of gender adjustment to the DAS28-CRP was evaluated. Results: DAS28-CRP scores were ~0.3 lower than DAS28-ESR overall, with greatest differences for women (-0.35) and patients over 50 years old (-0.34). Mean male DAS28-CRP scores were 0.15 less than corresponding DAS28-ESR scores. Discordance between DAS28-ESR and DAS28-CRP significantly impacted disease activity stratification at low disease activity (LDA) and remission thresholds (32.0% and 66.6% concordance respectively). Adjusting DAS28-CRP scores by gender significantly (p <0.001) improved agreement with the DAS28-ESR. Conclusion: Discordance between DAS28-ESR and DAS28-CRP is greatest for women and patients over 50 years of age, and influences disease activity stratification. The proposed gender adjusted DAS28-CRP improves inter-score agreement with DAS28-ESR, supporting more reliable disease activity stratification in treat-to-target approaches for RA

Student perceptions of laboratory classroom activities and experimental physics practice

We report results from a study designed to identify links between undergraduate students' views about experimental physics and their engagement in multiweek projects in lab courses. Using surveys and interviews, we explored whether students perceived particular classroom activities to be features of experimental physics practice. We focused on 18 activities, including maintaining lab notebooks, fabricating parts, and asking others for help. Interviewees identified activities related to project execution as intrinsic to experimental physics practice based on high prevalence of those activities in interviewees' own projects. Fabrication-oriented activities were identified as conditional features of experimentation based on differences between projects, which interviewees attributed to variations in project resources. Interpersonal activities were also viewed as conditional features of experimentation, dependent upon one's status as novice or expert. Our findings suggest that students' views about experimental physics are shaped by firsthand experiences of their own projects and secondhand experiences of those of others.Comment: 6 pages, 1 table, accepted for publication in 2020 Physics Education Research Conference Proceeding