Results for "Shriram Krishnamurthi"

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Event Loops as First-Class Values: A Case Study in Pedagogic Language DesignFeb 02 2019The World model is an existing functional input-output mechanism for event-driven programming. It is used in numerous popular textbooks and curricular settings. The World model conflates two different tasks -- the definition of an event processor and ... More
Automated Fault Localization Using Potential InvariantsOct 18 2003We present a general method for fault localization based on abstracting over program traces, and a tool that implements the method using Ernst's notion of potential invariants. Our experiments so far have been unsatisfactory, suggesting that further research ... More
Putting in All the Stops: Execution Control for JavaScriptFeb 08 2018Apr 16 2018Scores of compilers produce JavaScript, enabling programmers to use many languages on the Web, reuse existing code, and even use Web IDEs. Unfortunately, most compilers inherit the browser's compromised execution model, so long-running programs freeze ... More
The Essence of JavaScriptOct 04 2015We reduce JavaScript to a core calculus structured as a small-step operational semantics. We present several peculiarities of the language and show that our calculus models them. We explicate the desugaring process that turns JavaScript programs into ... More
ADsafety: Type-Based Verification of JavaScript SandboxingJun 25 2015Web sites routinely incorporate JavaScript programs from several sources into a single page. These sources must be protected from one another, which requires robust sandboxing. The many entry-points of sandboxes and the subtleties of JavaScript demand ... More
A Random Walk with Collapsing Bonds and Its Scaling LimitNov 24 2006We introduce a new self-interacting random walk on the integers in a dynamic random environment and show that it converges to a pure diffusion in the scaling limit. We also find a lower bound on the diffusion coefficient in some special cases. With minor ... More
Compiling Stateful Network Properties for Runtime VerificationJul 12 2016Jul 15 2016Networks are difficult to configure correctly, and tricky to debug. These problems are accentuated by temporal and stateful behavior. Static verification, while useful, is ineffectual for detecting behavioral deviations induced by hardware faults, security ... More
Putting in All the Stops: Execution Control for JavaScriptFeb 08 2018Scores of compilers produce JavaScript, enabling programmers to use many languages on the Web, reuse existing code, and even use Web IDEs. Unfortunately, most compilers expose the browser's compromised execution model, so long-running programs freeze ... More
Direct in-situ observation of structural transition driven actuation in VO2 utilizing electron transparent cantileversJun 17 2013Direct imaging and quantification of actuation in nanostructures that undergo structural phase transitions could advance our understanding of collective phenomena in the solid state. Here, we demonstrate visualization of structural phase transition induced ... More
Correlated Electron Materials and Field Effect Transistors for Logic: A ReviewDec 12 2012Correlated electron systems are among the centerpieces of modern condensed matter sciences, where many interesting physical phenomena, such as metal-insulator transition and high-Tc superconductivity appear. Recent efforts have been focused on electrostatic ... More
GaN / VO2 heteroepitaxial p-n junctions: Band offset and minority carrier dynamicsJun 04 2013We report on experimental realization of p-n heterojunctions based on p-type GaN, and an n-type correlated oxide, VO2. The band offsets are evaluated by current-voltage and capacitance voltage measurements at various temperatures. A band diagram based ... More
The Similarity Boundary of a Self-Similar SetJul 16 1999We define the similarity boundary of a self-similar set and use it to analyze the properties of self-similar sets in the general setting of any complete metric space. The similarity boundary is an attempt at extending the concept of the topological boundary ... More
A Brownian dynamics algorithm for entangled wormlike threadsOct 17 2006We present a hybrid Brownian dynamics / Monte Carlo algorithm for simulating solutions of highly entangled semiflexible polymers or filaments. The algorithm combines a Brownian dynamics time-stepping approach with an efficient scheme for rejecting moves ... More
Chain motion and viscoelasticity in highly entangled solutions of semiflexible rodsFeb 06 2007Brownian dynamics simulations are used to study highly entangled solutions of semiflexible polymers. Bending fluctuations of semiflexible rods are signficantly affected by entanglement only above a concentration $c^{**}$, where $c^{**}\sim 10^{3}L^{-3}$ ... More
Human Brain Mapping based on COLD Signal Hemodynamic Response and Electrical NeuroimagingJul 16 2013To understand Working of Human Brain measurements related to the brain function are required. These measurements should be possibly non-invasive. Brain should be disturbed as less as possible during the measurement. Integration of various modalities plays ... More
Brain Connectivity Analysis Methods for Better Understanding of CouplingDec 16 2012Action, cognition, emotion and perception can be mapped in the brain by using set of techniques. Translating unimodal concepts from one modality to another is an important step towards understanding the neural mechanisms. This paper provides a comprehensive ... More
Hydrodynamics for totally asymmetric $k$-step exclusion processesNov 26 1999We describe the hydrodynamic behavior of the $k$-step exclusion process. Since the flux appearing in the hydrodynamic equation for this particle system is neither convex nor concave, the set of possible solutions include in addition to entropic shocks ... More
A Search for Radio Emission at the Bottom of the Main Sequence and BeyondJun 07 1999We have used the VLA to conduct a deep search for 3.6 cm radio emission from nearby very low mass stars and brown dwarfs. The Gudel-Benz relation is used to predict radio luminosities for some very low mass stars and candidate brown dwarfs with measured ... More
The Lithium-Rotation Correlation in the Pleiades RevisitedNov 02 1999Nov 10 1999The dispersion in lithium abundance at fixed effective temperature in young cool stars like the Pleiades has proved a difficult challenge for stellar evolution theory. We propose that Li abundances relative to a mean temperature trend, rather than the ... More
Fully Convolutional Multi-scale Residual DenseNets for Cardiac Segmentation and Automated Cardiac Diagnosis using Ensemble of ClassifiersJan 16 2018Deep fully convolutional neural network (FCN) based architectures have shown great potential in medical image segmentation. However, such architectures usually have millions of parameters and inadequate number of training samples leading to over-fitting ... More
Automatic Segmentation and Overall Survival Prediction in Gliomas using Fully Convolutional Neural Network and Texture AnalysisDec 06 2017In this paper, we use a fully convolutional neural network (FCNN) for the segmentation of gliomas from Magnetic Resonance Images (MRI). A fully automatic, voxel based classification was achieved by training a 23 layer deep FCNN on 2-D slices extracted ... More
Applications of fMRI for Brain MappingDec 27 2012Brain-mapping techniques have proven to be vital in understanding the molecular, cellular, and functional mechanisms of the brain. Normal anatomical imaging can provide structural information on certain abnormalities in the brain. However there are many ... More
Metal-insulator transition and electrically-driven memristive characteristics of SmNiO3 thin filmsJan 18 2011The correlated oxide SmNiO3 (SNO) exhibits an insulator to metal transition (MIT) at 130 {\deg}C in bulk form. We report on synthesis and electron transport in SNO films deposited on LaAlO3 (LAO) and Si single crystals. X-ray diffraction studies show ... More
Enhanced Optic Disk and Cup Segmentation with Glaucoma Screening from Fundus Images using Position encoded CNNsSep 14 2018In this manuscript, we present a robust method for glaucoma screening from fundus images using an ensemble of convolutional neural networks (CNNs). The pipeline comprises of first segmenting the optic disk and optic cup from the fundus image, then extracting ... More
The cone percolation model on Galton-Watson and on spherically symmetric treesOct 09 2015Nov 10 2016We study a rumour model from a percolation theory and branching process point of view. The existence of a giant component is related to the event where the rumour, which started from the root of a tree, spreads out through an infinite number of its vertices. ... More
Origins of bad metal conductivity and the insulator-metal transition in the rare-earth nickelatesSep 28 2013For most metals, increasing temperature (T) or disorder will quicken electron scattering. This hypothesis informs the Drude model of electronic conductivity. However, for so-called bad metals this predicts scattering times so short as to conflict with ... More
Conductivity noise study of the insulator-metal transition and phase co-existence in epitaxial samarium nickelate thin filmsAug 03 2014Interaction between the lattice and the orbital degrees of freedom not only makes rare-earth nickelates unusually "bad metal", but also introduces a temperature driven insulator-metal phase transition. Here we investigate this insulator-metal phase transition ... More
ASP: Learning to Forget with Adaptive Synaptic Plasticity in Spiking Neural NetworksMar 22 2017Jun 08 2018A fundamental feature of learning in animals is the "ability to forget" that allows an organism to perceive, model and make decisions from disparate streams of information and adapt to changing environments. Against this backdrop, we present a novel unsupervised ... More
Semi-supervised Learning using Denoising Autoencoders for Brain Lesion Detection and SegmentationNov 26 2016Nov 30 2016The work presented explores the use of denoising autoencoders (DAE) for brain lesion detection, segmentation and false positive reduction. Stacked denoising autoencoders (SDAE) were pre-trained using a large number of unlabeled patient volumes and fine ... More
The rumor percolation model and its variationsDec 12 2016The study of rumor models from a percolation theory point of view has gained a few adepts in the last few years. The persistence of a rumor, which may consistently spread out throughout a population can be associated to the existence of a giant component ... More
Three-terminal field effect devices utilizing thin film vanadium oxide as the channel layerJun 22 2010Electrostatic control of the metal-insulator transition (MIT) in an oxide semiconductor could potentially impact the emerging field of oxide electronics. Vanadium dioxide is of particular interest due to the fact that the MIT happens in the vicinity of ... More
Electrostatic gating of metallic and insulating phases in SmNiO3 ultrathin filmsMay 09 2013The correlated electron system SmNiO3 exhibits a metal-insulator phase transition at 130 {\deg}C. Using an ionic liquid as an electric double layer (EDL) gate on three-terminal ultrathin SmNiO3 devices, we investigate gate control of the channel resistance ... More
Electrical switching dynamics and broadband microwave characteristics of VO2 RF devicesJun 03 2013Vanadium dioxide is a correlated electron system that features a metal-insulator phase transition (MIT) above room temperature and is of interest in high speed switching devices. Here, we integrate VO2 into two-terminal coplanar waveguides and demonstrate ... More
Asteroseismic determination of fundamental parameters of sun-like stars using multi-layered neural networksFeb 02 2016Jul 01 2016The advent of space-based observatories such as CoRoT and Kepler has enabled the testing of our understanding of stellar evolution on thousands of stars. Evolutionary models typically require five input parameters, the mass, initial Helium abundance, ... More
A Search for Photometric Rotation Periods in Low-Mass Stars and Brown Dwarfs in the PleiadesJun 08 1999We have photometrically monitored (Cousins Ic) eight low mass stars and brown dwarfs which are probable members of the Pleiades. We derived rotation periods for two of the stars - HHJ409 and CFHT-PL8 - to be 0.258 d and 0.401 d, respectively. The masses ... More
Observations of the core of the Pleiades with the Chandra X-ray ObservatorySep 13 2000We present results from a 36-ksec observation of the core of the Pleiades open cluster using ACIS-I on the Chandra X-ray Observatory. We have detected 57 sources, most of which do not have previously known optical counterparts. Follow-up photometry indicates ... More
Measurement Bounds for Sparse Signal Ensembles via Graphical ModelsFeb 14 2011Mar 28 2013In compressive sensing, a small collection of linear projections of a sparse signal contains enough information to permit signal recovery. Distributed compressive sensing (DCS) extends this framework by defining ensemble sparsity models, allowing a correlated ... More
Vanadium dioxide as a natural disordered metamaterial: perfect thermal emission and large broadband negative differential thermal emittanceApr 30 2013We experimentally demonstrate that a thin (~150 nm) film of vanadium dioxide (VO2) deposited on sapphire has an anomalous thermal emittance profile when heated, which arises due to the optical interaction between the film and the substrate when the VO2 ... More
Hall carrier density and magnetoresistance measurements in thin film vanadium dioxide across the metal-insulator transitionJun 22 2010Temperature dependent magneto-transport measurements in magnetic fields of up to 12 Tesla were performed on thin film vanadium dioxide (VO2) across the metal-insulator transition (MIT). The Hall carrier density increases by 4 orders of magnitude at the ... More
Very Slow Cooling Dynamics of Photoexcited Carriers in Graphene Observed by Optical-Pump Terahertz-Probe SpectroscopyAug 13 2011Using optical-pump terahertz-probe spectroscopy, we study the relaxation dynamics of photoexcited carriers in graphene at different temperatures. We find that at lower temperatures the tail of the relaxation transients as measured by the differential ... More
Thickness Estimation of Epitaxial Graphene on SiC using Attenuation of Substrate Raman IntensityJul 21 2008Apr 01 2009A simple, non-invasive method using Raman spectroscopy for the estimation of the thickness of graphene layers grown epitaxially on silicon carbide (SiC) is presented, enabling simultaneous determination of thickness, grain size and disorder using the ... More
Ultrafast Optical-Pump Terahertz-Probe Spectroscopy of the Carrier Relaxation and Recombination Dynamics in Epitaxial GrapheneMay 30 2008Jul 22 2008The ultrafast relaxation and recombination dynamics of photogenerated electrons and holes in epitaxial graphene are studied using optical-pump Terahertz-probe spectroscopy. The conductivity in graphene at Terahertz frequencies depends on the carrier concentration ... More
Reconfigurable anisotropy and functional transformations with VO$_{2}$-based metamaterial electric circuitsMay 29 2014We demonstrate an innovative multifunctional artificial material that combines exotic metamaterial properties and the environmentally responsive nature of phase change media. The tunable metamaterial is designed with the aid of two interwoven coordinate-transformation ... More
Voltage-triggered Ultra-fast Metal-insulator Transition in Vanadium Dioxide SwitchesJul 14 2013Electrically driven metal-insulator transition in vanadium dioxide (VO2) is of interest in emerging memory devices, neural computation, and high speed electronics. We report on the fabrication of out-of-plane VO2 metal-insulator-metal (MIM) structures ... More
Neuromimetic Circuits with Synaptic Devices based on Strongly Correlated Electron SystemsNov 15 2014Strongly correlated electron systems such as the rare-earth nickelates (RNiO3, R = rare-earth element) can exhibit synapse-like continuous long term potentiation and depression when gated with ionic liquids; exploiting the extreme sensitivity of coupled ... More
Using atom probe tomography to understand Schottky barrier height pinning at the ZnO:Al / SiO2 / Si interfaceOct 29 2015We use electronic transport and atom probe tomography to study ZnO:Al / SiO2 / Si Schottky junctions on lightly-doped n- and p-type Si. We vary the carrier concentration in the the ZnO:Al films by two orders of magnitude but the Schottky barrier height ... More
Distributed Compressive SensingJan 22 2009Compressive sensing is a signal acquisition framework based on the revelation that a small collection of linear projections of a sparse signal contains enough information for stable recovery. In this paper we introduce a new theory for distributed compressive ... More
Measurement of Ultrafast Carrier Dynamics in Epitaxial GrapheneDec 02 2007Using ultrafast optical pump-probe spectroscopy, we have measured carrier relaxation times in epitaxial graphene layers grown on SiC wafers. We find two distinct time scales associated with the relaxation of nonequilibrium photogenerated carriers. An ... More
Rotational velocities of low-mass stars in the Pleiades and HyadesNov 30 1999We have obtained high-resolution spectra of 89 M dwarf members of the Pleiades and Hyades and have derived radial velocities, H-alpha equivalent widths, and spectroscopic rotational velocities for these stars. Typical masses of the newly-observed Pleiades ... More
Hall effect measurements on epitaxial SmNiO3 thin films and implications for antiferromagnetismJan 09 2013Mar 05 2013The rare-earth nickelates (RNiO3) exhibit interesting phenomena such as unusual antiferromagnetic order at wavevector q = (1/2, 0, 1/2) and a tunable insulator-metal transition that are subjects of active research. Here we present temperature-dependent ... More
Carrier Recombination and Generation Rates for Intravalley and Intervalley Phonon Scattering in GrapheneJan 02 2009Jan 06 2009Electron-hole generation and recombination rates for intravalley and intervalley phonon scattering in Graphene are presented. The transverse and the longitudinal optical phonon modes ($E_{2g}$-modes) near the zone center ($\Gamma$-point) contribute to ... More
Emission of Terahertz Radiation from SiCSep 04 2008May 13 2009We report the emission of strong coherent broadband terahertz radiation from 6H-Silicon-Carbide (SiC) excited with optical pulses. The measured terahertz spectral signal-to-noise ratio is better than one thousand. We determine that the terahertz radiation ... More
Measurement of the Optical Absorption Spectra of Epitaxial Graphene from Terahertz to VisibleJan 22 2008Aug 16 2008We present experimental results on the optical absorption spectra of epitaxial graphene from the visible to the terahertz (THz) frequency range. In the THz range, the absorption is dominated by intraband processes with a frequency dependence similar to ... More
Strongly correlated proton-doped perovskite nickelate memory devicesMay 01 2018We demonstrate memory devices based on proton doping and re-distribution in perovskite nickelates (RNiO3, {R=Sm,Nd}) that undergo filling-controlled Mott transition. Switching speeds as high as 30 ns in two-terminal devices patterned by electron-beam ... More
Ultrafast Relaxation Dynamics of Hot Optical Phonons in GrapheneSep 27 2009Dec 28 2009Using ultrafast optical pump-probe spectroscopy, we study the relaxation dynamics of hot optical phonons in few-layer and multi-layer graphene films grown by epitaxy on silicon carbide substrates and by chemical vapor deposition on nickel substrates. ... More
Limiting optical diodes enabled by the phase transition of vanadium dioxideJan 20 2018A limiting optical diode is an asymmetric nonlinear device that is bidirectionally transparent at low power, but becomes opaque when illuminated by sufficiently intense light incident from a particular direction. We explore the use of a phase-transition ... More
Perovskite Quantum OrganismoidsMar 03 2017A central characteristic of living beings is the ability to learn from and respond to their environment leading to habit formation and decision making1-3. This behavior, known as habituation, is universal among forms of life with a central nervous system, ... More
Two-phonon coupling to the antiferromagnetic phase transition in multiferroic BiFeO3Dec 03 2007A prominent band centered at around 1000-1300 cm-1 and associated with resonant enhancement of two-phonon Raman scattering is reported in multiferroic BiFeO3 thin films and single crystals. A strong anomaly in this band occurs at the antiferromagnetic ... More
Temperature-independent thermal radiationFeb 01 2019Thermal emission is the process by which all objects at non-zero temperatures emit light, and is well-described by the classic Planck, Kirchhoff, and Stefan-Boltzmann laws. For most solids, the thermally emitted power increases monotonically with temperature ... More
Optical properties of thin-film vanadium dioxide from the visible to the far infraredJan 08 2019The insulator-to-metal transition (IMT) in vanadium dioxide (VO2) can enable a variety of optics applications, including switching and modulation, optical limiting, and tuning of optical resonators. Despite the widespread interest in optics, the optical ... More
New rotation periods in the Pleiades: Interpreting activity indicatorsNov 24 1997We present results of photometric monitoring campaigns of G, K and M dwarfs in the Pleiades carried out in 1994, 1995 and 1996. We have determined rotation periods for 18 stars in this cluster. In this paper, we examine the validity of using observables ... More
Increasing the Number of Underrepresented Minorities in Astronomy: Executive SummaryMar 26 2009Promoting racial and ethnic diversity is critically important to the future success and growth of the field of astronomy. The raw ability, drive and interest required to excel in the field is distributed without regard to race, gender, or socioeconomic ... More
Increasing the Number of Underrepresented Minorities in Astronomy Through K-12 Education and Public Outreach (Paper II)Mar 26 2009In order to attract, recruit and retain underrepresented minority students to pursue Astronomy and related fields, we must ensure that there continues to be a well qualified pool of graduate and undergraduate students from which to recruit. This required ... More
Increasing the Number of Underrepresented Minorities in Astronomy at the Undergraduate, Graduate, and Postdoctoral Levels (Paper I)Mar 26 2009If the ethnic makeup of the astronomy profession is to achieve parity with the general population within one generation (~30 years), the number of underrepresented minorities earning graduate degrees in astronomy and astrophysics must increase in the ... More
Identifying the Best Machine Learning Algorithms for Brain Tumor Segmentation, Progression Assessment, and Overall Survival Prediction in the BRATS ChallengeNov 05 2018Gliomas are the most common primary brain malignancies, with different degrees of aggressiveness, variable prognosis and various heterogeneous histologic sub-regions, i.e., peritumoral edematous/invaded tissue, necrotic core, active and non-enhancing ... More