Significance of Specific Force Models in Two Applications: Solar Sails to Sun-Earth L4/L5 and GRAIL Data Analysis Suggesting Lava Tubes and Buried Craters on the Moon

In the trajectory design process, gravitational interaction between the bodies of interest plays a key role in developing the over-arching force model. However, non-gravitational forces, such as solar radiation pressure (SRP), can significantly influence the motion of a spacecraft. Incorporating SRP within the dynamical model can assist in estimating the trajectory of a spacecraft with greater precision, in particular, for a spacecraft with a large area-to-mass ratio, i.e., solar sails. Subsequently, in the trajectory design process, solar radiation pressure can be leveraged to maneuver the sail-based spacecraft. First, to construct low energy transfers, the invariant manifolds are explored that form an important tool in the computation and design of complex trajectories. The focus is the investigation of trajectory design options, incorporating solar sail dynamics, from the Earth parking orbit to the vicinity of triangular Lagrange points. Thereafter, an optimization scheme assisted in investigating the ΔV requirement to depart from the Earth parking orbit. Harnessing the solar radiation pressure, the spacecraft is delivered to the vicinity of the displaced Lagrange point and maintains a trajectory close to the artificial libration point with the help of the solar sail. However, these trajectories are converged in a model formulated as a three-body problem with additional acceleration from solar radiation pressure. Thus, the trajectories are transitioned to higher fidelity ephemeris model to account for additional perturbing accelerations that may dominate the sail-craft dynamics and improve upon the trajectory design process

Global wealth disparities drive adherence to COVID-safe pathways in head and neck cancer surgery

Peer reviewe

Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection

The Science Case for Io Exploration

Io is a priority destination for solar system exploration, as it is the best natural laboratory to study the intertwined processes of tidal heating, extreme volcanism, and atmosphere-magnetosphere interactions. Io exploration is relevant to understanding terrestrial worlds (including the early Earth), ocean worlds, and exoplanets across the cosmos

Recommendations for Addressing Priority Io Science in the Next Decade

Io is a priority destination for solar system exploration. The scope and importance of science questions at Io necessitates a broad portfolio of research and analysis, telescopic observations, and planetary missions - including a dedicated New Frontiers class Io mission

Algorithms and data structures for automated teaching workload allocation

Fair allocation of teaching workload to academic staff is one of the most important administrative duties of an educational institution. However, it is often managed manually with limited data and, often with an arbitrary set of constraints due its complexity, thereby resulting in sub optimal allocations. The objective of this research is to develop efficient methods to automatic the realization of a fair and transparent workload allocation system. A detailed exploration of past attempts, aimed at improving the workload allocation at tertiary institutions, was undertaken to gain a deeper understanding of the various approaches and challenges associated with the process. In particular, it was observed that various approaches were adopted to quantify a variety of components of the workload during the allocation process covering teaching, research and administrative duties. This motivated the development of an efficient time-based workload model called the Workload Unit (WLU) Model as the quantitative framework for measuring and comparing different faculty workloads. This involved the utilization of a combination of weightages corresponding to nature of teaching duties, the number and appointment of faculty as well as their availability for undertaking teaching duties, and attributes (such as class size, level of course, preparation requirements, etc.) of the courses to be offered. In addition, the proposed workload model takes into account the research activeness and administrative duties carried out by each faculty. The resulting workload is separated into two components, namely formal and informal teaching for the purpose of systematic workload allocation. Next, an efficient workload allocation method for formal teaching comprising of lectures, tutorials and labs was proposed by taking into consideration of faculty preference and performance, School policies and priorities and availability of teaching expertise. A novel combined cost function was proposed to determine the feasibility of individual allocations called the Feasibility Index (FI). A greedy approach, with activity-type and course-priority heuristics, is implemented to optimize the quality of the allocations. The proposed approach was validated against the workload allocations made at one of the schools of a University consisting of 100 teaching faculty, 120 courses and 1500 students. The resulting allocations improved workload distribution and quality of assignments over existing manual processes, improving preferences and performance indices by as much as 18% and 7% respectively, while reducing workload variations by 21%. Methods for the automatic translation of the resulting workload allocations into faculty and student centric timetable were proposed. This was achieved using an iterated greedy approach, with an objective to reasonably spread the allocated workload across the week for both faculty as well as students while making efficient use of teaching venues. The proposed approach has been shown to improve the spread of time table allocations across the week by 20% for both students and faculty. Moreover, it has also improved the utilization of the teaching venues by 30%. Realizing Final Year Projects (FYP) allocation is the most challenging part of the informal teaching allocation process, methods for its automation have been proposed by taking into consideration other informal teaching duties such as M.Sc. and Ph.D. supervisions. The proposed methods ensure that the student preference are taken into consideration while adhering to informal workload limits for each faculty. An iterative implementation of the optimal Hungarian algorithm which works on a student-project cost matrix with the preference ranks as the cost of assignment was introduced and multiple iterations were invoked to adjust the cost matrix based on workload constraints to achieve desired results. The resulting solutions comprehensively bettered those achieved by a competing existing system used at a reputable school – improving average student preference for assignments by 10% and workload deviations for faculty by 15%. The above methods were integrated and validated in a real-world scenario. Overview of the technology and platforms used to implement the above solutions have been presented together with screen captures of the platform that is being deployed in the School for past 5 consecutive semesters. This has unreservedly demonstrated the feasibility for automating an inclusive workload allocation process to realize an efficient and fair workload distribution, which is critical to any educational institution. Finally, avenues for future research and improvements are also stated.Master of Engineering (SCE

Solar sail applications for mission design in sun-planet systems from the perspective of the circular restricted three-body problem

As a consequence of the successful harnessing of solar radiation pressure demonstrated by JAXA\u27s IKAROS mission, the interest and developments in the field of solar sails has gained a significant momentum. Sail-based spacecraft potentially offer indefinite maneuvering capability by exploiting photons from the Sun as a means of propulsion. Incorporating a solar sail model within the context of the circular restricted three-body problem extends trajectory design options. In the last few decades, the Lagrangian points, L i, as defined in the restricted problem, have increasingly become a focus for scientific spacecraft mission applications. In this investigation, a hybrid model that incorporates a solar sail force into the circular restricted three-body problem (SS-CR3BP) is developed. As a result of the additional force, the displaced locations of artificial collinear Lagrangian points are determined and exploited for trajectory design. In fact, various trajectories are constructed that employ only sail orientation angles to move through this dynamical regime. In particular, periodic orbits are computed in the vicinity of the displaced artificial L1 equilibrium point, located between the Sun and the Earth in this Sun-planet system. A sample offset periodic orbit is demonstrated that hovers over the displaced L1 point. Trajectory modifications are performed in the vicinity of the L1 equilibrium point using solar sail angles. Three-dimensional transfers between halos at three different sizes is also constructed to exhibit the capabilities of solar sails based on specific mission objectives. Thus, in this investigation, solar sail capabilities that widen the design space for mission design in the restricted three-body problem are explored

SmallSat Swarm Gravimetry: Revealing the Interior Structure of Asteroids and Comets

A growing database of interesting small bodies motivates research into rapid characterization methods for economic or scientific objectives. The computational tools developed in this work enable reconstruction of internal structure for irregularly shaped celestial bodies, thus aiding target selection and exploration. Simulations of on-orbit data are used to recover the density map of a multi layered polyhedron, and reconstruction accuracies are investigated across multiple scenarios. The presented results and analysis demonstrate successful density recovery of a fully heterogeneous, multilayered asteroid with on-orbit measurements

SmallSat Swarm Gravimetry: Revealing the Interior Structure of Asteroids and Comets

A growing database of interesting small bodies motivates research into rapid characterization methods for economic or scientific objectives. The computational tools developed in this work enable reconstruction of internal structure for irregularly shaped celestial bodies, thus aiding target selection and exploration. Simulations of on-orbit data are used to recover the density map of a multi layered polyhedron, and reconstruction accuracies are investigated across multiple scenarios. The presented results and analysis demonstrate successful density recovery of a fully heterogeneous, multilayered asteroid with on-orbit measurements