College of Engineering (COE)
http://hdl.handle.net/10919/5539
2017-09-20T05:04:13ZIntroduction to Linear, Time-Invariant, Dynamic Systems for Students of Engineering
http://hdl.handle.net/10919/78864
Hallauer, William L. Jr.
2016-06-02T00:00:00ZThis is a complete college textbook, including a detailed Table of Contents, seventeen Chapters (each with a set of relevant homework problems), a list of References, two Appendices, and a detailed Index. The book is intended to enable students to:
-Solve first-, second-, and higher-order, linear, time-invariant (LTI) ordinary differential equations (ODEs) with initial conditions and excitation, using both time-domain and Laplace-transform methods;
-Solve for the frequency response of an LTI system to periodic sinusoidal excitation and plot this response in standard form;
-Explain the role of the time constant in the response of a first-order LTI system, and the roles of natural frequency, damping ratio, and resonance in the response of a second-order LTI system;
-Derive and analyze mathematical models (ODEs) of low-order mechanical systems, both translational and rotational, that are composed of inertial elements, spring elements, and damping devices;
-Derive and analyze mathematical models (ODEs) of low-order electrical circuits composed of resistors, capacitors, inductors, and operational amplifiers;
-Derive (from ODEs) and manipulate Laplace transfer functions and block diagrams representing output-to-input relationships of discrete elements and of systems;
-Define and evaluate stability for an LTI system;
-Explain proportional, integral, and derivative types of feedback control for single-input, single-output (SISO), LTI systems;
-Sketch the locus of characteristic values, as a control parameter varies, for a feedback-controlled SISO, LTI system;
-Use MATLAB as a tool to study the time and frequency responses of LTI systems.
The book’s general organization is:
-Chapters 1-10 deal primarily with the ODEs and behaviors of first-order and second-order dynamic systems;
-Chapters 11 and 12 discuss the ODEs and behaviors of mechanical systems having two degrees of freedom, i.e., fourth-order systems;
-Chapters 13 and 14 introduce classical feedback control;
-Chapter 15 presents the basic features of proportional, integral, and derivative types of classical control;
-Chapters 16 and 17 discuss methods for analyzing the stability of classical control systems.
The general minimum prerequisite for understanding this book is the intellectual maturity of a junior-level (third-year) college student in an accredited four-year engineering curriculum. A mathematical second-order system is represented in this book primarily by a single second-order ODE, not in the state-space form by a pair of coupled first-order ODEs. Similarly, a two-degrees-of-freedom (fourth-order) system is represented by two coupled second-order ODEs, not in the state-space form by four coupled first-order ODEs. The book does not use bond graph modeling, the general and powerful, but complicated, modern tool for analysis of complex, multidisciplinary dynamic systems. The homework problems at the ends of chapters are very important to the learning objectives, so the author attempted to compose problems of practical interest and to make the problem statements as clear, correct, and unambiguous as possible. A major focus of the book is computer calculation of system characteristics and responses and graphical display of results, with use of basic (not advanced) MATLAB commands and programs. The book includes many examples and homework problems relevant to aerospace engineering, among which are rolling dynamics of flight vehicles, spacecraft actuators, aerospace motion sensors, and aeroelasticity. There are also several examples and homework problems illustrating and validating theory by using measured data to identify first- and second-order system dynamic characteristics based on mathematical models (e.g., time constants and natural frequencies), and system basic properties (e.g., mass, stiffness, and damping). Applications of real and simulated experimental data appear in many homework problems. The book contains somewhat more material than can be covered during a single standard college semester, so an instructor who wishes to use this as a one-semester course textbook should not attempt to cover the entire book, but instead should cover only those parts that are most relevant to the course objectives.
William L. Hallauer, Jr. is an Adjunct Professor in the Department of Aerospace and Ocean Engineering at Virginia Tech.
Education:
B.S. in Mechanical Engineering, Stanford University, 1961-65;
S.M. in Aeronautics and Astronautics, Massachusetts Institute of Technology, 1965-66;
Ph.D. in Aeronautics and Astronautics, Stanford University, 1969-74.
Employment in Higher Education:
-Virginia Polytechnic Institute and State University (Aerospace and Ocean Engineering, Mechanical Engineering), 1974-87, 1989-91, 2000-05;
-United States Air Force Academy (Engineering Mechanics), 1987-89, 1994-99.
Employment in Industry:
-Boeing Company (Commercial Airplane Group), 1966-69;
-Lockheed Missiles and Space Company, 1973-74;
-Dynacs Engineering Company, Inc. (contractor for the U.S. Air Force), 1992-94.
Primary Technical Areas of Learning, Teaching, and Research:
-Structures, structural dynamics, and fluid-structure interaction (theory and computation);
-Experimental analysis of structural dynamics, including electrical and electromechanical systems used in experiments;
-Active control of vibration in highly flexible structures;
-Composition of research articles and instructional material.SOLR supported search on an OpenStack metadata service
http://hdl.handle.net/10919/78741
Komawar, Nikhil
2017-08-26T00:00:00ZIn cloud computing, the use of databases, particularly the MySQL database system, is a common practice. While the MySQL database system has advantages such as consistency and transaction support, some software architects believe that use of indexed search systems such as SOLR gives better read performance as compared to the traditionally deployed database servers. We propose an architecture that allows us to leverage the advantages of both systems. To study the same, we created a test bed with behavior similar to a real world scenario of a cloud metadata service, and compared the results of searching the metadata using a MySQL database with that of searching the same data using SOLR. We found that indexing the data using SOLR, although expensive in terms of disk space, gives us read performance orders of magnitude better than the MySQL database. These results may encourage cloud operators to try using SOLR for serving the users’ search requests, thereby avoiding API timeouts and slowness.CommAnalyzer: Automated Estimation of Communication Cost on HPC Clusters Using Sequential Code
http://hdl.handle.net/10919/78701
Helal, Ahmed E.; Jung, Changhee; Feng, Wu-chun; Hanafy, Yasser Y.
2017-08-14T00:00:00ZMPI+X is the de facto standard for programming applications on HPC clusters. The performance and scalability on such systems is limited by the communication cost on different number of processes and compute nodes. Therefore, the current communication analysis tools play a critical role in the design and development of HPC applications. However, these tools require the availability of the MPI implementation, which might not exist in the early stage of the development process due to the parallel programming effort and time. This paper presents CommAnalyzer, an automated tool for communication model generation from a sequential code. CommAnalyzer uses novel compiler analysis techniques and graph algorithms to capture the inherent communication characteristics of sequential applications, and to estimate their communication cost on HPC systems. The experiments with real-world, regular and irregular scientific applications demonstrate the utility of CommAnalyzer in estimating the communication cost on HPC clusters with more than 95% accuracy on average.Personal Reflections on 50 Years of Scientific Computing: 1967–2017
http://hdl.handle.net/10919/78691
Watson, Layne T.
2017-08-10T00:00:00ZComputer hardware, software, numerical algorithms, and science and engineering applications are traced for a half century from the author's perspective.Understanding Recurring Software Quality Problems of Novice Programmers
http://hdl.handle.net/10919/78337
Techapalokul, Peeratham; Tilevich, Eli
2017-07-12T00:00:00ZIt remains unclear when is the right time to introduce software quality into the computing curriculum. Introductory students often cannot afford to also worry about software quality, while
advanced students may have been groomed into undisciplined development practices already. To be able to answer these questions, educators need strong quantitative evidence about the persistence of software quality problems in programs written by novice programmers.
This technical report presents a comprehensive study of software quality in programs written by novice programmers. By leveraging the patterns of recurring quality problems, known as code smells,
we analyze a longitudinal dataset of more than 100 novice Scratch programmers and close to 3,000 of their programs. Even after gaining proficiency, students continue to introduce certain quality problems into their programs, suggesting the need for educational interventions. Given the importance of software quality for modern society, computing educators should teach quality-promoting practices alongside the core computing
concepts.Thermal stability and electrical conductivity of carbon-enriched silicon oxycarbide
http://hdl.handle.net/10919/77560
Lu, Kathy; Erb, Donald; Liu, Mengying
2016-01-28T00:00:00ZSilicon oxycarbide (SiOC) is an interesting polymer-derived system that can be tailored to embody many different properties such as lightweight, electrochemical activity, and high temperature stability. One intriguing property that has not been fully explored is the electrical conductivity for the carbon-rich SiOC compositions. In this study, a carbon-rich SiOC system is created based on the crosslinking and pyrolysis of polyhydromethylsiloxane (PHMS) and divinylbenzene (DVB) mixed precursors. The carbon-rich nature can effectively delay SiOC phase separation and crystallization into SiO2 and SiC during pyrolysis. In an oxidizing air atmosphere, the SiOC materials are stable up to 1000 °C with <0.5 wt% weight loss. Before the onset of electrical conductivity drop at ∼400 °C, the material has electrical conductivity as high as 4.28 S cm−1. In an inert argon atmosphere, the conductivity is as high as 4.64 S cm−1. This new semi-conducting behavior with high thermal stability presents promising application potential for high temperature MEMS devices, protective coatings, and bulk semi-conducting components that must endure high temperature conditions.Bacterial chemotaxis-enabled autonomous sorting of nanoparticles of comparable sizes
http://hdl.handle.net/10919/77561
Suh, SeungBeum; Traore, Mahama A.; Behkam, Bahareh
2016-02-18T00:00:00ZHigh throughput sorting of micro/nanoparticles of similar sizes is of significant interest in many biological and chemical applications. In this work, we report a simple and cost-effective sorting technique for separation of similarly-sized particles of dissimilar surface properties within a diffusion-based microfluidic platform using chemotaxis in Escherichia coli bacteria. Differences in surface chemistry of two groups of similarly-sized nanoparticles in a mixture were exploited to selectively assemble one particle group onto motile E. coli, through either specific or non-specific adhesion, and separate them from the remaining particle group via chemotaxis of the attached bacteria. To enable optimal operation of the sorting platform, the chemotaxis behavior of E. coli bacteria in response to casamino acids, the chemoeffector of choice was first characterized. The chemical concentration gradient range within which the bacteria exhibit a positive chemotactic response was found to be within 0.25 × 10−7–1.0 × 10−3 g ml−1 mm−1. We demonstrate that at the optimum concentration gradient of 5.0 × 10−4 g ml−1 mm−1, a sorting efficiency of up to 81% at a throughput of 2.4 × 105 particles per min can be achieved. Sensitivity of the sorting efficiency to the adhesion mechanism and particle size in the range of 320–1040 nm was investigated.Investigation of helium at a Y2Ti2O7 nanocluster embedded in a BCC Fe matrix
http://hdl.handle.net/10919/77566
Danielson, Thomas; Tea, Eric; Hin, Celine
2016-10-18T00:00:00ZNanostructured ferritic alloys (NFAs) are prime candidates for structural and first wall components of fission and fusion reactors. The main reason for this is their ability to effectively withstand high concentrations of the transmutation product helium. A high number density of oxide nanoclusters dispersed throughout a BCC Fe matrix act as trapping sites for helium and prevent its eventual delivery to high risk nucleation sites. The current study uses density functional theory to investigate the helium trapping mechanisms at the boundary between BCC iron and Y2Ti2O7, a common stoichiometry of the oxide nanoclusters in NFAs. The investigation is carried out on a structure matched oxide nanocluster that is embedded within a BCC Fe supercell. Investigation of the electronic structure and a mapping of the potential energy landscape reveals that the localized iono-covalent bonds present within the oxides create a potential energy-well within the metallically bonded BCC Fe matrix, so that trapping of helium at the oxide nanocluster is thermodynamically and kinetically favorable.Charge carrier transport and lifetimes in n-type and p-type phosphorene as 2D device active materials: an ab initio study
http://hdl.handle.net/10919/77565
Tea, Eric; Hin, Celine
2016-07-25T00:00:00ZIn this work, we provide a detailed analysis of phosphorene’s performance as an n-type and p-type active material. This study is based on first principles calculations of the phosphorene electronic structure, and the resulting electron and hole scattering rates and lifetimes. Emphasis is put on extreme regimes commonly found in semiconductor devices, i.e. high electric fields and heavy doping, where impact ionization and Auger recombination can occur. We found that electron-initiated impact ionization is weaker than the hole-initiated process, when compared to carrier–phonon interaction rates, suggesting resilience to impact ionization initiated breakdown. Moreover, calculated minority electron lifetimes are limited by radiative recombination only, not by Auger processes, suggesting that phosphorene could achieve good quantum efficiencies in optoelectronic devices. The provided scattering rates and lifetimes are critical input data for the modeling and understanding of phosphorene-based device physics.Spun-wrapped aligned nanofiber (SWAN) lithography for fabrication of micro/nano-structures on 3D objects
http://hdl.handle.net/10919/77564
Ye, Zhou; Nain, Amrinder S.; Behkam, Bahareh
2016-06-01T00:00:00ZFabrication of micro/nano-structures on irregularly shaped substrates and three-dimensional (3D) objects is of significant interest in diverse technological fields. However, it remains a formidable challenge thwarted by limited adaptability of the state-of-the-art nanolithography techniques for nanofabrication on non-planar surfaces. In this work, we introduce Spun-Wrapped Aligned Nanofiber (SWAN) lithography, a versatile, scalable, and cost-effective technique for fabrication of multiscale (nano to microscale) structures on 3D objects without restriction on substrate material and geometry. SWAN lithography combines precise deposition of polymeric nanofiber masks, in aligned single or multilayer configurations, with well-controlled solvent vapor treatment and etching processes to enable high throughput (>10−7 m2 s−1) and large-area fabrication of sub-50 nm to several micron features with high pattern fidelity. Using this technique, we demonstrate whole-surface nanopatterning of bulk and thin film surfaces of cubes, cylinders, and hyperbola-shaped objects that would be difficult, if not impossible to achieve with existing methods. We demonstrate that the fabricated feature size (b) scales with the fiber mask diameter (D) as b1.5 ∝ D. This scaling law is in excellent agreement with theoretical predictions using the Johnson, Kendall, and Roberts (JKR) contact theory, thus providing a rational design framework for fabrication of systems and devices that require precisely designed multiscale features.