Now showing items 1-20 of 67

    • Reciprocity-gap misfit functional for distributed acoustic sensing, combining data from passive and active sources 

      Faucher, Florian; de Hoop, Maarten V.; Scherzer, Otmar (2021)
      Quantitative imaging of subsurface earth properties in elastic media is performed from distributed acoustic sensing data. A new misfit functional based upon the reciprocity gap is designed, taking crosscorrelations of displacement and strain, and these products further associate an observation with a simulation. In comparison with other misfit ...
    • Quantifying pulmonary perfusion from noncontrast computed tomography 

      Castillo, Edward; Nair, Girish; Turner‐Lawrence, Danielle; Myziuk, Nicholas; Emerson, Scott; (2021)
      Purpose: Computed tomography (CT)-derived ventilation methods compute respiratory induced volume changes as a surrogate for pulmonary ventilation. Currently, there are no known methods to derive perfusion information from noncontrast CT. We introduce a novel CT-Perfusion (CT-P) method for computing the magnitude mass changes apparent on dynamic ...
    • Chromatin architecture transitions from zebrafish sperm through early embryogenesis 

      Wike, Candice L.; Guo, Yixuan; Tan, Mengyao; Nakamura, Ryohei; Shaw, Dana Klatt; (2021)
      Chromatin architecture mapping in 3D formats has increased our understanding of how regulatory sequences and gene expression are connected and regulated in a genome. The 3D chromatin genome shows extensive remodeling during embryonic development, and although the cleavage-stage embryos of most species lack structure before zygotic genome activation ...
    • Functional avoidance-based intensity modulated proton therapy with 4DCT derived ventilation imaging for lung cancer 

      Dougherty, Jingjing M.; Castillo, Edward; Castillo, Richard; Faught, Austin M.; Pepin, Mark; (2021)
      The primary objective is to evaluate the potential dosimetric gains of performing functional avoidance-based proton treatment planning using 4DCT derived ventilation imaging. 4DCT data of 31 patients from a prospective functional avoidance clinical trial were evaluated with intensity modulated proton therapy (IMPT) plans and compared with clinical ...
    • Extubation Failure in Critically Ill COVID-19 Patients: Risk Factors and Impact on In-Hospital Mortality 

      Ionescu, Filip; Zimmer, Markie S.; Petrescu, Ioana; Castillo, Edward; Bozyk, Paul; (2021)
      Purpose:We sought to identify clinical factors that predict extubation failure (reintubation) and its prognostic implications in critically ill COVID-19 patients.Materials and Methods:Retrospective, multi-center cohort study of hospitalized COVID-19 patients. Multivariate competing risk models were employed to explore the rate of reintubation and its ...
    • Clustering earthquake signals and background noises in continuous seismic data with unsupervised deep learning 

      Seydoux, Léonard; Balestriero, Randall; Poli, Piero; de Hoop, Maarten; Campillo, Michel; (2020)
      The continuously growing amount of seismic data collected worldwide is outpacing our abilities for analysis, since to date, such datasets have been analyzed in a human-expert-intensive, supervised fashion. Moreover, analyses that are conducted can be strongly biased by the standard models employed by seismologists. In response to both of these ...
    • Convergence of a Class of Stationary Iterative Methods for Saddle Point Problems 

      Zhang, Yin (2019)
      A unified convergence theory is derived for a class of stationary iterative methods for solving linear equality constrained quadratic programs or saddle point problems. This class is constructed from essentially all possible splittings of the submatrix residing in the (1,1)-block of the augmented saddle point matrix that would produce non-expansive ...
    • Reduced order modeling for time-dependent optimization problems with initial value controls 

      Heinkenschloss, Matthias; Jando, Dörte (2018)
      This paper presents a new reduced order model (ROM) Hessian approximation for linear-quadratic optimal control problems where the optimal control is the initial value. Such problems arise in parameter identification and data assimilation, where the parameters to be identified appear in the initial data, and also as subproblems in multiple shooting ...
    • An accelerated Poisson solver based on multidomain spectral discretization 

      Babb, Tracy; Gillman, Adrianna; Hao, Sijia; Martinsson, Per-Gunnar (2018)
      This paper presents a numerical method for variable coefficient elliptic PDEs with mostly smooth solutions on two dimensional domains. The method works best for domains that can readily be mapped onto a rectangle, or a collection of nonoverlapping rectangles. The PDE is discretized via a multi-domain spectral collocation method of high local order ...
    • Compositional heterogeneity near the base of the mantle transition zone beneath Hawaii 

      Yu, Chunquan; Day, Elizabeth A.; de Hoop, Maarten V.; Campillo, Michel; Goes, Saskia; (2018)
      Global seismic discontinuities near 410 and 660 km depth in Earth’s mantle are expressions of solid-state phase transitions. These transitions modulate thermal and material fluxes across the mantle and variations in their depth are often attributed to temperature anomalies. Here we use novel seismic array analysis of SSwaves reflecting off ...
    • Topological Schemas of Memory Spaces 

      Babichev, Andrey; Dabaghian, Yuri A. (2018)
      Hippocampal cognitive map-a neuronal representation of the spatial environment-is widely discussed in the computational neuroscience literature for decades. However, more recent studies point out that hippocampus plays a major role in producing yet another cognitive framework-the memory space-that incorporates not only spatial, but also non-spatial ...
    • Weight‐adjusted discontinuous Galerkin methods: Matrix‐valued weights and elastic wave propagation in heterogeneous media 

      Chan, Jesse (2018)
      Weight‐adjusted inner products are easily invertible approximations to weighted L2 inner products. These approximations can be paired with a discontinuous Galerkin (DG) discretization to produce a time‐domain method for wave propagation which is low storage, energy stable, and high‐order accurate for arbitrary heterogeneous media and curvilinear ...
    • On discretely entropy conservative and entropy stable discontinuous Galerkin methods 

      Chan, Jesse (2018)
      High order methods based on diagonal-norm summation by parts operators can be shown to satisfy a discrete conservation or dissipation of entropy for nonlinear systems of hyperbolic PDEsᅠ[1],ᅠ[2]. These methods can also be interpreted as nodal discontinuous Galerkin methods with diagonal mass matricesᅠ[3],ᅠ[4],ᅠ[5],ᅠ[6]. In this work, we describe how ...
    • Multi-patch discontinuous Galerkin isogeometric analysis for wave propagation: Explicit time-stepping and efficient mass matrix inversion 

      Chan, Jesse; Evans, John A. (2018)
      We present a class of spline finite element methods for time-domain wave propagation which are particularly amenable to explicit time-stepping. The proposed methods utilize a discontinuous Galerkin discretization to enforce continuity of the solution field across geometric patches in a multi-patch setting, which yields a mass matrix with convenient ...
    • An exact redatuming procedure for the inverse boundary value problem for the wave equation 

      de Hoop, Maarten V.; Kepley, Paul; Oksanen, Lauri (2018)
      Redatuming is a data processing technique to transform measurements recorded in one acquisition geometry to an analogous data set corresponding to another acquisition geometry, for which there are no recorded measurements. We consider a redatuming problem for a wave equation on a bounded domain, or on a manifold with boundary, and model data acquisition ...
    • Shape Optimization of Shell Structure Acoustics 

      Antil, Harbir; Hardesty, Sean; Heinkenschloss, Matthias (2017)
      This paper provides a rigorous framework for the numerical solution of shape optimization problems in shell structure acoustics using a reference-domain approach. The structure is modeled with Naghdi shell equations, fully coupled to boundary integral equations on a minimally regular surface, permitting the formulation of three-dimensional radiation ...
    • Full-waveform inversion via source-receiver extension 

      Huang, Guanghui; Nammour, Rami; Symes, William (2017)
      Full-waveform inversion produces highly resolved images of the subsurface and quantitative estimation of seismic wave velocity, provided that its initial model is kinematically accurate at the longest data wavelengths. If this initialization constraint is not satisfied, iterative model updating tends to stagnate at kinematically incorrect velocity ...
    • Predicting solvation free energies and thermodynamics in polar solvents and mixtures using a solvation-layer interface condition 

      Tabrizi, Amirhossein Molavi; Goossens, Spencer; Rahimi, Ali Mehdizadeh; Knepley, Matthew; Bardhan, Jaydeep P. (2017)
      We demonstrate that with two small modifications, the popular dielectric continuum model is capable of predicting, with high accuracy, ion solvation thermodynamics (Gibbs free energies, entropies, and heat capacities) in numerous polar solvents. We are also able to predict ion solvation free energies in water–co-solvent mixtures over available ...
    • Reduced storage nodal discontinuous Galerkin methods on semi-structured prismatic meshes 

      Chan, Jesse; Wang, Zheng; Hewett, Russell J.; Warburton, T. (2017)
      We present a high order time-domain nodal discontinuous Galerkin method for wave problems on hybrid meshes consisting of both wedge and tetrahedral elements. We allow for vertically mapped wedges which can be deformed along the extruded coordinate, and present a simple method for producing quasi-uniform wedge meshes for layered domains. We show that ...
    • A Distributed-Memory Randomized Structured Multifrontal Method for Sparse Direct Solutions 

      Xin, Zixing; Xia, Jianlin; de Hoop, Maarten V.; Cauley, Stephen; Balakrishnan, Venkataramanan (2017)
      We design a distributed-memory randomized structured multifrontal solver for large sparse matrices. Two layers of hierarchical tree parallelism are used. A sequence of innovative parallel methods are developed for randomized structured frontal matrix operations, structured update matrix computation, skinny extend-add operation, selected entry extraction ...