Crystalline topological phases as defect networks

A crystalline topological phase is a topological phase with spatial symmetries. In this work, we give a very general physical picture of such phases: a topological phase with spatial symmetry $G$ (with internal symmetry $G_{\mathrm{int}} \leq G$) is described by a *defect network*: a $G$-symmetric network of defects in a topological phase with internal symmetry $G_{\mathrm{int}}$. The defect network picture works both for symmetry-protected topological (SPT) and symmetry-enriched topological (SET) phases, in systems of either bosons or fermions. We derive this picture both by physical arguments, and by a mathematical derivation from the general framework of [Thorngren and Else, Phys. Rev. X 8, 011040 (2018)]. In the case of crystalline SPT phases, the defect network picture reduces to a previously studied dimensional reduction picture, thus establishing the equivalence of this picture with the general framework of Thorngren and Else applied to crystalline SPTs.Comment: 13 pages + 2 pages of appendices. v3 published version, with better justification of the equivalence relatio

Biological, simulation, and robotic studies to discover principles of swimming within granular media

The locomotion of organisms whether by running, flying, or swimming is the result of multiple degree-of-freedom nervous and musculoskeletal systems interacting with an environment that often flows and deforms in response to movement. A major challenge in biology is to understand the locomotion of organisms that crawl or burrow within terrestrial substrates like sand, soil, and muddy sediments that display both solid and fluid-like behavior. In such materials, validated theories such as the Navier-Stokes equations for fluids do not exist, and visualization techniques (such as particle image velocimetry in fluids) are nearly nonexistent. In this dissertation we integrated biological experiment, numerical simulation, and a physical robot model to reveal principles of undulatory locomotion in granular media. First, we used high speed x-ray imaging techniques to reveal how a desert dwelling lizard, the sandfish, swims within dry granular media without limb use by propagating a single period sinusoidal traveling wave along its body, resulting in a wave efficiency, the ratio of its average forward speed to wave speed, of approximately 0.5. The wave efficiency was independent of the media preparation (loosely and tightly packed). We compared this observation against two complementary modeling approaches: a numerical model of the sandfish coupled to a discrete particle simulation of the granular medium, and an undulatory robot which was designed to swim within granular media. We used these mechanical models to vary the ratio of undulation amplitude (A) to wavelength (λ) and demonstrated that an optimal condition for sand-swimming exists which results from competition between A and λ. The animal simulation and robot model, predicted that for a single period sinusoidal wave, maximal speed occurs for A/ λ = 0.2, the same kinematics used by the sandfish. Inspired by the tapered head shape of the sandfish lizard, we showed that the lift forces and hence vertical position of the robot as it moves forward within granular media can be varied by designing an appropriate head shape and controlling its angle of attack, in a similar way to flaps or wings moving in fluids. These results support the biological hypotheses which propose that morphological adaptations of desert dwelling organisms aid in their subsurface locomotion. This work also demonstrates that the discovery of biological principles of high performance locomotion within sand can help create the next generation of biophysically inspired robots that could explore potentially hazardous complex flowing environments.PhDCommittee Chair: Daniel I. Goldman; Committee Member: Hang Lu; Committee Member: Jeanette Yen; Committee Member: Shella Keilholz; Committee Member: Young-Hui Chan

First Detection of Mid-Infrared Variability from an Ultraluminous X-Ray Source Holmberg II X-1

We present mid-infrared (IR) light curves of the Ultraluminous X-ray Source (ULX) Holmberg II X-1 from observations taken between 2014 January 13 and 2017 January 5 with the \textit{Spitzer Space Telescope} at 3.6 and 4.5 $\mu$m in the \textit{Spitzer} Infrared Intensive Transients Survey (SPIRITS). The mid-IR light curves, which reveal the first detection of mid-IR variability from a ULX, is determined to arise primarily from dust emission rather than from a jet or an accretion disk outflow. We derived the evolution of the dust temperature ($T_\mathrm{d}\sim600 - 800$ K), IR luminosity ($L_\mathrm{IR}\sim3\times10^4$ $\mathrm{L}_\odot$), mass ($M_\mathrm{d}\sim1-3\times10^{-6}$ $\mathrm{M}_\odot$), and equilibrium temperature radius ($R_\mathrm{eq}\sim10-20$ AU). A comparison of X-1 with a sample spectroscopically identified massive stars in the Large Magellanic Cloud on a mid-IR color-magnitude diagram suggests that the mass donor in X-1 is a supergiant (sg) B[e]-star. The sgB[e]-interpretation is consistent with the derived dust properties and the presence of the [Fe II] ($\lambda=1.644$ $\mu$m) emission line revealed from previous near-IR studies of X-1. We attribute the mid-IR variability of X-1 to increased heating of dust located in a circumbinary torus. It is unclear what physical processes are responsible for the increased dust heating; however, it does not appear to be associated with the X-ray flux from the ULX given the constant X-ray luminosities provided by serendipitous, near-contemporaneous X-ray observations around the first mid-IR variability event in 2014. Our results highlight the importance of mid-IR observations of luminous X-ray sources traditionally studied at X-ray and radio wavelengths.Comment: 9 page, 4 figures, 1 table, Accepted to ApJ Letter

Lessons From Redefining Traditional Work Placements For University Students In TU Dublin

There is strong support for ensuring all university students have an option to undertake relevant work placement. Work-placements enable students to engage with enterprise and develop experiential learning while linking their academic study and theory to real industrial practice. Such placements, or internships, offer students an opportunity to build their self-confidence while refining their transversal skills such as creativity, innovation, communication, team-working and problem solving. Furthermore, placements broaden students’ knowledge base and improve their employability upon graduation. While student cohorts benefit from engaging with enterprise the enterprise also benefits, such as from the energy, new perspectives and ideas interns can bring to the workplace. Multiple models (such as professional apprentices and Earn and Learn models) highlight the importance of this symbiotic relationship. The need to support and expand work placement opportunities to benefit all graduates is also a key element of government policy. Supporting this ambition and reflecting changing student profiles, employer expectations and the nature of work, there is a need to reimagine the traditional understanding of work-placements to safeguard talent pipelines and increase graduate employability. A concise literature review of existing work placement models is presented. This is followed by a description of the approach developed by the Enterprise Academy within Technological University Dublin to help students achieve learning outcomes typically associated with work-placements in a new, innovative and sustainable way. The approach described was successfully piloted for 2 student cohorts during the Covid pandemic. It highlights the value of redefining traditional placements for students, enterprise and higher education providers

A situational analysis of the current level of lecturers’ engagement with internationalisation of the curriculum in Ireland’s first Technological University

The educational value of internationalisation in higher education is of critical importance for both domestic and international students. While national and institutional policies globally are increasingly prioritising internationalisation, the resultant consequences for the teaching and learning context are not adequately being explored. Understanding engagement with Internationalisation of the Curriculum from the lecturers’ perspective allows for a greater insight into the inherent implementation gap between the theory and practice of the process. This knowledge may then help inform strategies to address the gap. The present study details the current level of engagement between lecturers and Internationalisation of the Curriculum in Ireland’s first Technological University. A questionnaire was designed and distributed to all lecturers across the university to ascertain statistical evidence in an attempt to quantify the prevailing situation in the Irish higher education context. While there was an awareness and appreciation of the educational value of internationalisation, the findings demonstrate that those surveyed are at the early stages of the internationalisation process in their teaching and learning practice. The questionnaire findings are detailed here along with the implications of the findings for both internationalisation and educational policies and practice, which is of relevance to both national and international audiences

Communities of practice as a solution for the implementation gap in internationalisation of the curriculum.

The educational benefits of internationalisation in higher education are of paramount importance for all students. Despite an increasing presence of best practice guides and internationalisation strategies, there appears to be a significant implementation gap in terms of lecturers’ engagement with internationalisation in their teaching practice. Through an Action Research-informed Community of Practice approach, this study aims to provide new insights into lecturers’ engagement with Internationalisation of the Curriculum by examining their own perspectives, an area which has been underdeveloped to date. The Community of Practice provided an effective way of raising lecturers’ awareness of Internationalisation of the Curriculum, while simultaneously effecting change at teaching and institution-wide levels. It facilitated an environment that encouraged lecturers to both incorporate global dimensions into their teaching and collaborate with colleagues to provide integrated learning opportunities for students that reflect the multicultural world. The findings presented focus specifically on lecturers’ perspectives of Internationalisation of the Curriculum and are relevant to a large body of stakeholders, namely those involved in Internationalisation of the Curriculum specifically, as well as practitioners interested in Continuous Professional Learning and best practice teaching in general

3D Computer Modeling Analysis of the Surface Area and Thread Volume of the Common Sliding Hip Screw

Introduction: The Sliding Hip Screw (SHS) is a tried and tested method used to treat intertrochanteric hip fractures. Lag screw cut-out is a major complication of SHS fixation and accepted risk factors are often re-evaluated. We aim to demonstrate a new hypothesis of cut-out using 3D reconstructive modelling. We propose that the risk of cut-out is much greater in lag screws with a smaller thread surface area and larger thread volume. Method: The four commonly used SHS lag screw systems (Biomet, Synthes, Stryker and Smith & Nephew) were CT scanned and the images processed and turned into 3D computer models for further analysis. Results: There were significan differences between the surface area and thread volumes of the lag screws between manufacturers ranging from 67.0mm2 - 347.4 mm2 and 166.376mm3 - 225.687mm3 respectively. Discussion: Assuming the consistency of bone is equal, we propose that the risk of cut-out is much greater in lag screws with a smaller surface area to thread volume ratio (SA:TV). The reamer design of lag screws is also discussed. Conclusion: Although there are many non-modifiable risk factors that contribute to screw cut-out, selecting the right raw materials for SHS fixation will have a favorable impact on the overall risk

ISLAS DE FÁBULA Y GUERRA: CÓMO LAS MOLUCAS DEMARCARON EL NUEVO MUNDO

Este artículo explora los encuentros entre el incipiente Nuevo Mundo y el Archipiélago de las Molucas en el siglo XVI. Más allá de ser un estudio sobre expediciones, este es un examen de cómo las guerras y los proyectos de conquista de Hispanoamérica se entrelazaron en una disputa sobre las Molucas que comenzaba a mundializarse. Estas islas de leyenda, el epítome de las islas afortunadas que llenaban tantos vacíos en los mapas tardomedievales, eran el punto central de sueños y ambiciones en las fronteras transpacíficas de Hispanoamérica. A pesar de las prohibiciones oficiales de navegar a las Molucas después del tratado de Zaragoza de 1529, las islas mantuvieron su atractivo: eran un punto fijo, un destino que prometía riquezas inimaginables a quien lograra controlarlas. En contraste, el resto del vasto Océano Pacífico era pura especulación e incontables peligros. Las Molucas permeaban la geopolítica del Nuevo Mundo en dos registros. Primero, como idea, las Molucas eran un sueño primigenio que dio impulso a la América Española y que moldeó el pensamiento estratégico y geográfico de muchos conquistadores. En el Nuevo Mundo, la idea parecía alcanzable y rápidamente se materializó; movía capital y labor, y enviaba barcos al Mar del Sur. El segundo registro fue el archipiélago indígena en el Sureste Asiático, las Molucas mismas, al lado opuesto del gran océano, con su propia historia. Este artículo emplea las fuentes generadas por estos esfuerzos y expediciones, así como las etnohistorias de los pueblos indígenas de las Molucas y Mesoamérica, para examinar cómo los sueños hispanoamericanos sobre las Molucas se convirtieron en una fuerza globalizadora, y cómo las sociedades moluqueñas eventualmente delimitaron una frontera geopolítica del Nuevo Mundo. Así, lo que empezó como un horizonte soñado acabó siendo un campo de batalla que marcó el sangriento límite del Mar del Sur