Sensitivity Enhancement of Modal Frequencies for Sensing using System Augmentation and Optimal Feedback Auxiliary Signals

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76542/1/AIAA-2008-2085-567.pd

Reduced Order Modeling for Nonlinear Vibration Analysis of Mistuned Multi-Stage Bladed Disks with a Cracked Blade

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90668/1/AIAA-2011-2065-784.pd

Imaging Cerenkov emission as a quality assurance tool in electron radiotherapy

A new potential quality assurance (QA) method is explored (including assessment of depth dose, dose linearity, dose rate linearity and beam profile) for clinical electron beams based on imaging Cerenkov light. The potential of using a standard commercial camera to image Cerenkov light generated from electrons in water for fast QA measurement of a clinical electron beam was explored and compared to ionization chamber measurements. The new method was found to be linear with dose and independent of dose rate (to within 3%). The uncorrected practical range measured in Cerenkov images was found to overestimate the actual value by 3 mm in the worst case. The field size measurements underestimated the dose at the edges by 5% without applying any correction factor. Still, the measured field size could be used to monitor relative changes in the beam profile. Finally, the beam-direction profile measurements were independent of the field size within 2%. A simulation was also performed of the deposited energy and of Cerenkov production in water using GEANT4. Monte Carlo simulation was used to predict the measured light distribution around the water phantom, to reproduce Cerenkov images and to find the relation between deposited energy and Cerenkov production. The camera was modelled as a pinhole camera in GEANT4, to attempt to reproduce Cerenkov images. Simulations of the deposited energy and the Cerenkov light production agreed with each other for a pencil beam of electrons, while for a realistic field size, Cerenkov production in the build-up region overestimated the dose by +8%

Correlated multiplexity and connectivity of multiplex random networks

Nodes in a complex networked system often engage in more than one type of interactions among them; they form a multiplex network with multiple types of links. In real-world complex systems, a node's degree for one type of links and that for the other are not randomly distributed but correlated, which we term correlated multiplexity. In this paper we study a simple model of multiplex random networks and demonstrate that the correlated multiplexity can drastically affect the properties of giant component in the network. Specifically, when the degrees of a node for different interactions in a duplex Erdos-Renyi network are maximally correlated, the network contains the giant component for any nonzero link densities. In contrast, when the degrees of a node are maximally anti-correlated, the emergence of giant component is significantly delayed, yet the entire network becomes connected into a single component at a finite link density. We also discuss the mixing patterns and the cases with imperfect correlated multiplexity.Comment: Revised version, 12 pages, 6 figure

The Kalman-Tran-D'Souza Model and the Semileptonic Decay Rates of Heavy Baryons

We present an investigation of the inclusive semileptonic decay widths of the heavy baryons Lambda_Q and Xi_Q, (Q=b,c) performed within a relativistic constituent quark model, formulated on the light-front. In a way conceptually similar to the deep-inelastic scattering case, the H_Q baryon inclusive width is expressed as the integral of the free Q-quark partial width multiplied by a bound-state factor related to the Q-quark distribution function in the H_Q. The non-perturbative meson structure is described through the quark-model wave functions, constructed via the Hamiltonian light-front formalism using as input the Kalman-Tran-D'Souza equal time wave functions. A link between spectroscopic quark models and the H_Q decay physics is obtained in this way. It is shown that the bound-state effects and the Fermi motion of the b-quark remarkably reduce the decay rate with respect to the free-quark result. Our predictions for the BR(Lambda_c ->X_s e nu_e) and BR(Lambda_b->X_c e nu_e) decays are in good agreement with existing data.Comment: 6 pages, latex, espcrc2.sty (included), 3 figures. The invited talk presented by C.S.K. at the 4-th International Conference on Hyperons, Charm and Beauty Hadrons, Valencia, June 27-30, 200

Pythia: AI-assisted Code Completion System

In this paper, we propose a novel end-to-end approach for AI-assisted code completion called Pythia. It generates ranked lists of method and API recommendations which can be used by software developers at edit time. The system is currently deployed as part of Intellicode extension in Visual Studio Code IDE. Pythia exploits state-of-the-art large-scale deep learning models trained on code contexts extracted from abstract syntax trees. It is designed to work at a high throughput predicting the best matching code completions on the order of 100 $ms$. We describe the architecture of the system, perform comparisons to frequency-based approach and invocation-based Markov Chain language model, and discuss challenges serving Pythia models on lightweight client devices. The offline evaluation results obtained on 2700 Python open source software GitHub repositories show a top-5 accuracy of 92\%, surpassing the baseline models by 20\% averaged over classes, for both intra and cross-project settings.Comment: Published in Proceedings of the 25th ACM SIGKDD International Conference on Knowledge Discovery & Data Mining (KDD '19

Atomistic investigation of cavitation and ablation in tantalum foils under irradiation with x-rays approaching 5 keV

The rapid irradiation and heating of matter can lead to material removal via a process known as ablation. While previous investigations have focused on ablation with optical and soft x-ray pulses, the process is not well understood for the high-energy x-rays delivered at current x-ray free electron laser facilities. In this paper, we use hybrid two-temperature model molecular dynamics simulations to determine the damage threshold and dynamics for tantalum foils under irradiation with x-rays in the range 1–5 keV. We report that damage occurs for foils with thickness 300 nm when heated to around 1.25 eV/atom. This damage results from the combined processes of melting and cavitation, finally resulting in the removal of material layers. The predictions of this study, in terms of the cavitation threshold and underlying dynamics, could guide interpretation of experiments as well as applications including development of beamline optics for free-electron lasers. We report consistency between cavitation and ablation behavior in isochoric heating experiments and spall processes in hydrodynamic compression and release experiments, confirming the primary modes of damage are mechanical in nature for the x-ray energies investigated

Pterodactyl: Trade Study for an Integrated Control System Design of a Mechanically Deployable Entry Vehicle

This paper presents the trade study method used to evaluate and downselect from a set of guidance and control (G&C) system designs for a mechanically Deployable Entry Vehicle (DEV). The Pterodactyl project was prompted by the challenge to develop an effective G&C system for a vehicle without a backshell, which is the case for DEVs. For the DEV, the project assumed a specific aeroshell geometry pertaining to an Adaptable, Deployable Entry and Placement Technology (ADEPT) vehicle, which was successfully developed by NASAs Space Technology Mission Directorate (STMD) prior to this study. The Pterodactyl project designed three different entry G&C systems for precision targeting. This paper details the Figures of Merit (FOMs) and metrics used during the course of the projects G&C system assessment. The relative importance of the FOMs was determined from the Analytic Hierarchy Process (AHP), which was used to develop weights that were combined with quantitative design metrics and engineering judgement to rank the G&C systems against one another. This systematic method takes into consideration the projects input while simultaneously reducing unintentional judgement bias and ultimately was used to select a single G&C design for the project to pursue in the next design phase