1,720,992 research outputs found
A Quadratic Lower Bound for Algebraic Branching Programs
Full text linkWe show that any Algebraic Branching Program (ABP) computing the polynomial ∑_{i=1}^n xⁿ_i has at least Ω(n²) vertices. This improves upon the lower bound of Ω(nlog n), which follows from the classical result of Baur and Strassen [Volker Strassen, 1973; Walter Baur and Volker Strassen, 1983], and extends the results of Kumar [Mrinal Kumar, 2019], which showed a quadratic lower bound for homogeneous ABPs computing the same polynomial.
Our proof relies on a notion of depth reduction which is reminiscent of similar statements in the context of matrix rigidity, and shows that any small enough ABP computing the polynomial ∑_{i=1}^n xⁿ_i can be depth reduced to essentially a homogeneous ABP of the same size which computes the polynomial ∑_{i=1}^n xⁿ_i + ε(), for a structured "error polynomial" ε(). To complete the proof, we then observe that the lower bound in [Mrinal Kumar, 2019] is robust enough and continues to hold for all polynomials ∑_{i=1}^n xⁿ_i + ε(), where ε() has the appropriate structure
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Towards Flight Readiness In Unmanned Aerial Systems
Full text linkFlight readiness in autonomous Unmanned Aerial Systems (UAS) is key in advancing their use in aiding humans in unstructured, uncertain, and hazardous environments. The objective of this thesis is to develop a framework for path planning in Unmanned Aerial Systems (UAS) monitoring a prescribed burn. A prescribed burn is a complex, dynamic environment that contains numerous dangers to an autonomous UAS. The primary focus is on the radiative and convective heat flux from a wild-land burn, specifically, the danger that it poses to UAS operations near ground level. This danger is best described as a path-dependent resource constraint that is enforced during global planning. The Resource Constrained Shortest Path Problem (RCSPP) is solved using a novel backtracking algorithm derived from Hybrid-A* graph search. Performance gains are shown over unmodified Hybrid-A*, and a Lagrange Relaxation based method. A UAS platform is developed to meet the performance requirements necessary to operate in prescribed burn environments. Software In the Loop (SIL) driven development methods and Hardware In the Loop (HIL) testing methods are used to verify performance requirements. Field tests in a prescribed burn demonstrate the validation of algorithm design goals and performance requirements. The impact of this research is a step towards autonomous fire monitoring to accelerate the setup and execution of prescribed wildland burns.National Science Foundation award number 2132798 under the NRI 3.0: Innovations in Integration of Robotics ProgramNo embargoAcademic Major: Mechanical Engineerin
Utilization of an Adaptive Monte Carlo Framework for Benchmarking of Data-Driven Tools and Physics-Based Models
Full text linkThere is a concurrent need for physics-based models of complex systems and data-driven tools for the design, analysis, and uncertainty quantification of such systems in a variety of fields. As the fidelity of these models increase, computational cost grows in hand. A benchmarking scheme utilizing the Adaptive Monte Carlo (AMC) framework developed at The Ohio State University will allow for more effective cross model comparison. With AMC serving as a reference, the precision and accuracy of different implementations and the associated computational cost can be contrasted to inform decisions on which model will best address the needs of the target case.
A case study involving a Direct Moment Closure (DMC) implementation for the propagation of Van der Pol Oscillator moment dynamics was examined. The DMC implementation directly integrated the moment dynamics derived from the Van der Pol equations of motion using the ode45 solver function in MATLAB. AMC is a user-defined process in which accuracy is guaranteed for the selected quantities of interest. This is achieved through particle addition to the distribution to maintain results within the user-specified error bounds and is what makes AMC a capable benchmark for model comparison. With AMC the particles were propagated according to the Van der Pol dynamics and the moments of the data set were computed in post processing.
Examination of the first order moments showed divergent behavior from zero in the DMC implementation. This is due to the truncation of the stable higher order terms which must occur in the direct integration. The AMC model remained a zero mean process due to its accuracy being guaranteed. Results indicated that AMC did a better job of capturing the zero-mean process of the first order moment dynamics over time. However, the AMC simulation took far more computational power than the DMC model.
Future work involving models that are currently being used in industry can further develop this framework. This benchmarking scheme could serve as to inform industry professionals about the performance and computational cost of various models and methods when trying to predict, design, or analyze real-world applications.No embargoAcademic Major: Aerospace Engineerin
Trustworthy Analysis of Recent Debris Cloud Conjunction Events Using an Adaptive Monte Carlo Forecasting Platform
Full text linkEvery untracked, inactive, or unfamiliar object in Earth's orbit poses a risk to satellites and rockets that wish to safely navigate through space. Objects of this nature, known as "space debris," will remain in orbit without deliberate intervention. The purpose of this project is to perform a highly accurate retrospective analysis of a certain outstanding close-approach event (also known as a conjunction event) that occurred in the geostationary belt. It is expected that the successful completion of this work will result in a trustworthy prognostics tool that can help minimize, or even eliminate, such risk in the future. Events related to candidate resident space objects were considered, and the 2016 Briz-M rocket body explosion was chosen as the particular event of interest. By appropriately modeling the motion of such candidates through astrodynamics analysis and adjusting the initial conditions to reflect sensor precision, a recently developed adaptive Monte Carlo method, a MATLAB-based forecasting platform, can be employed to propagate a particle cloud representing the object's orbit over time. The completion of this project will validate the methods used, while simultaneously reducing the risks of collision and damage in similar events in the future.Ohio Space Grant Consortium Scholarship ('21-'22)No embargoAcademic Major: Aerospace Engineerin
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Recursive Estimation of RSO Dynamics and States from Partial State Measurements
Full text linkThe modern world depends on space-based infrastructure for GPS, intelligence, telecommunications, weather, scientific research, and much more. And we are expanding our capabilities and usage each year, a process that is accelerated with the rise of satellite mega constellations. Accurate tracking and forecasting of resident space objects (RSO) is increasingly needed as a result to avoid collisions that can both damage key space assets and create potentially harmful debris fields. This task is not easy however due to a minimal number of measurement sources, a measurement's inability to capture full-state data, the nonlinear dynamics of orbital mechanics, and the often unknown parameters of those dynamics. Standard model identification methods struggle as a result, especially for use in long-duration propagation. We propose a recursive estimator as a solution to this problem. The idea is to adaptively estimate both the state variables and model parameters simultaneously, utilizing partial-state measurements to achieve convergence in both (states and model parameters) over time. This estimator starts off with an initial guess of model parameters to make predictions and compares those predictions to sensor measurements as they become available. Based on the perceived error between the forecast and measurement values, it executes a parameter update step, thus setting up the next cycle of forecasting. This solution was developed in MATLAB for identifying the eccentricity of an orbit, before being applied to estimation of the Earth's oblateness parameter . The results thus far have shown good convergence and an ability to handle the unknowns of the model while also making good predictions of the state variables. In the present version of the dual estimator, a simple feedback control type parameter correction step is implemented, proving to be effective under favorable conditions. Further analysis is required to understand its behavior, in particular, stability and convergence characteristics. The ultimate objective of this work is to integrate it within a larger uncertainty forecasting system with unknown parameters in a physics-based dynamic model, or, in a data-driven black box dynamic model. It could also be applied to a prognostics digital twin model where key model parameters are missing or unknown.No embargoAcademic Major: Mechanical Engineerin
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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