Kevin Tew

Bézier projection: A unified approach for local projection and quadrature-free refinement and coarsening of NURBS and T-splines with particular application to isogeometric design and analysis

Abstract We introduce Bezier projection as an element-based local projection methodology for B-splines, NURBS, and T-splines. This new approach relies on the concept of Bezier extraction and an associated operation introduced here, spline reconstruction, enabling the use of Bezier projection in standard finite element codes. Bezier projection exhibits provably optimal convergence and yields projections that are virtually indistinguishable from global L 2 projection. Bezier projection is used to develop a unified framework for spline operations including cell subdivision and merging, degree elevation and reduction, basis roughening and smoothing, and spline reparameterization. In fact, Bezier projection provides a quadrature-free approach to refinement and coarsening of splines. In this sense, Bezier projection provides the fundamental building block for h p k r -adaptivity in isogeometric analysis.

Using reputation to augment explicit authorization

Online social networks are formed when web applications allow users to contribute to an online community. The explosive growth of these social networks taxes the management capacity of human administrators. The continued health of an online social network depends upon the identification and utilization of users who make positive contributions to the community, but finding these individuals can be difficult. In addition, these contributing users must be explicitly granted authority to help maintain and grow these networks. Automated reputation calculations based on user contributions and behavior can be used as an effective substitute for explicit authorization, giving online social networks greater flexibility and scalability. In this paper, we examine the underlying principles of online reputation, introduce Pythia, a flexible reputation system framework, and demonstrate the use of reputation calculations to augment explicit authorization in a web application.

An enterprise-based grid resource management system

As the Internet began its exponential growth into a global information environment, software was often unreliable, slow and had difficulty in interoperating with other systems. Supercomputing node counts also continue to follow high growth trends. Supercomputer and grid resource management software must mature into a reliable computational platform in much the same way that web services matured for the Internet. DOGMA The Next Generation (DOGMA-NG) improves on current resource management approaches by using tested off-the-shelf enterprise technologies to build a robust, scalable, and extensible resource management platform. Distributed web service technologies constitute the core of DOGMA-NGs design and provide fault tolerance and scalability. DOGMA-NGs use of open standard web technologies and efficient management algorithms promises to reduce management time and accommodate the growing size of future supercomputers. The use of web technologies also provides the opportunity for anew parallel programming paradigm, enterprise web services parallel programming, that also gains benefit from the scalable, robust component architecture.

Model Consistency and Conflict Resolution With Data Preservation in Multi-User Computer Aided Design

Simultaneous multi-user computer aided design (CAD) allows multiple designers to contribute to the same model at the same time. The resulting parallel design workflow shortens product development cycles. In a replicated, simultaneous multi-user CAD system, modeling data must be kept consistent between clients. This paper presents a method that keeps independent copies of the models in sync between distributed CAD clients. This is accomplished by enforcing modeling operations to occur in the same order on all the clients. In case of conflict, a resolution method preserves conflicting operations locally for later reuse or resolution by the user. These methods are implemented in a commercial CAD system which has been enhanced to enable simultaneous multi-user. Validation tests are run to demonstrate that the methods implemented ensure model consistency and resolve conflicts while preserving conflicting operation data.

Automated Conflict Avoidance in Multi-user CAD

The NSF Center for e-Design, Brigham Young University (BYU) site has re-architected Computer Aided Design (CAD) tools enabling multiple users to concurrently create, modify and view the same CAD part or assembly. This technology allows engineers, designers and manufacturing personnel to simultaneously contribute to the design of a part or assembly in real time, enabling parallel work environments within the CAD system. Such systems are only as robust as their methods for managing conflicts (i.e. simultaneous edits of the same feature by multiple users). A heavy-handed conflict prevention would limit collaborative freedom. This paper discusses an automated feature reservation method which prevents multiple users from simultaneously editing the same feature. The method is implemented in a commercial CAD system. Results show that this methodology prevents data inconsistency that results from feature/self conflicts. This system prevents CAD modeling conflicts, while providing an agile user experience within the collaborative environment.

Back to the futures: incremental parallelization of existing sequential runtime systems

Many language implementations, particularly for high-level and scripting languages, are based on carefully honed runtime systems that have an internally sequential execution model. Adding support for parallelism in the usual form -- as threads that run arbitrary code in parallel -- would require a major revision or even a rewrite to add safe and efficient locking and communication. We describe an alternative approach to incremental parallelization of runtime systems. This approach can be applied inexpensively to many sequential runtime systems, and we demonstrate its effectiveness in the Racket runtime system and Parrot virtual machine. Our evaluation assesses both the performance benefits and the developer effort needed to implement our approach. We find that incremental parallelization can provide useful, scalable parallelism on commodity multicore processors at a fraction of the effort required to implement conventional parallel threads.

Tissue-scale, personalized modeling and simulation of prostate cancer growth

Significance We perform a tissue-scale, personalized computer simulation of prostate cancer (PCa) growth in a patient, based on prostatic anatomy extracted from medical images. To do so, we propose a mathematical model for the growth of PCa. The model includes an equation for the reference biomarker of PCa: the prostate-specific antigen (PSA). Hence, we can link the results of our model to data that urologists can easily interpret. Our model reproduces features of prostatic tumor growth observed in experiments and clinical practice. It also captures a known shift in the growth pattern of PCa, from spheroidal to fingered geometry. Our results indicate that this shape instability is a tumor response to escape starvation, hypoxia, and, eventually, necrosis. Recently, mathematical modeling and simulation of diseases and their treatments have enabled the prediction of clinical outcomes and the design of optimal therapies on a personalized (i.e., patient-specific) basis. This new trend in medical research has been termed “predictive medicine.” Prostate cancer (PCa) is a major health problem and an ideal candidate to explore tissue-scale, personalized modeling of cancer growth for two main reasons: First, it is a small organ, and, second, tumor growth can be estimated by measuring serum prostate-specific antigen (PSA, a PCa biomarker in blood), which may enable in vivo validation. In this paper, we present a simple continuous model that reproduces the growth patterns of PCa. We use the phase-field method to account for the transformation of healthy cells to cancer cells and use diffusion−reaction equations to compute nutrient consumption and PSA production. To accurately and efficiently compute tumor growth, our simulations leverage isogeometric analysis (IGA). Our model is shown to reproduce a known shape instability from a spheroidal pattern to fingered growth. Results of our computations indicate that such shift is a tumor response to escape starvation, hypoxia, and, eventually, necrosis. Thus, branching enables the tumor to minimize the distance from inner cells to external nutrients, contributing to cancer survival and further development. We have also used our model to perform tissue-scale, personalized simulation of a PCa patient, based on prostatic anatomy extracted from computed tomography images. This simulation shows tumor progression similar to that seen in clinical practice.

Places: adding message-passing parallelism to racket

Places bring new support for message-passing parallelism to Racket. This paper gives an overview of the programming model and how we had to modify our existing, sequential runtime-system to support places. We show that the freedom to design the programming model helped us to make the implementation tractable; specifically, we avoided the conventional pain of adding just the right amount of locking to a big, legacy runtime system. The paper presents an evaluation of the design that includes both a real-world application and standard parallel benchmarks.

Robust Poisson Surface Reconstruction

We propose a method to reconstruct surfaces from oriented point clouds with non-uniform sampling and noise by formulating the problem as a convex minimization that reconstructs the indicator function of the surface’s interior. Compared to previous models, our reconstruction is robust to noise and outliers because it substitutes the least-squares fidelity term by a robust Huber penalty; this allows to recover sharp corners and avoids the shrinking bias of least squares. We choose an implicit parametrization to reconstruct surfaces of unknown topology and close large gaps in the point cloud. For an efficient representation, we approximate the implicit function by a hierarchy of locally supported basis elements adapted to the geometry of the surface. Unlike ad-hoc bases over an octree, our hierarchical B-splines from isogeometric analysis locally adapt the mesh and degree of the splines during reconstruction. The hierarchical structure of the basis speeds-up the minimization and efficiently represents clustered data. We also advocate for convex optimization, instead isogeometric finite-element techniques, to efficiently solve the minimization and allow for non-differentiable functionals. Experiments show state-of-the-art performance within a more flexible framework.

Enhancements for Improved Topological Entity Identification Performance in Multi-user CAD

ABSTRACTMulti-user CAD allows designers to simultaneously work on a model, allowing designs to be realized at a much faster rate than ever before. In a replicated, simultaneous multi-user CAD system, it is critical that models be consistent between clients. A major component of model consistency is ensuring references to topological objects be the same on all clients in the same part. Previous methods are inefficient for models with a large number of faces and edges. This paper presents enhancements over previous methods which more efficiently identify faces and edges through lazy naming as well as caching and normalizing topological entity data. The implementation and results of these enhancements show significant time savings compared to an eager naming method.