230 research outputs found
A Compiler and Runtime Infrastructure for Automatic Program Distribution
This paper presents the design and the implementation of a compiler and runtime infrastructure for automatic program distribution. We are building a research infrastructure that enables experimentation with various program partitioning and mapping strategies and the study of automatic distribution's effect on resource consumption (e.g., CPU, memory, communication). Since many optimization techniques are faced with conflicting optimization targets (e.g., memory and communication), we believe that it is important to be able to study their interaction.
We present a set of techniques that enable flexible resource modeling and program distribution. These are: dependence analysis, weighted graph partitioning, code and communication generation, and profiling. We have developed these ideas in the context of the Java language. We present in detail the design and implementation of each of the techniques as part of our compiler and runtime infrastructure. Then, we evaluate our design and present preliminary experimental data for each component, as well as for the entire system
Quality Assurance of Software Applications Using the In Vivo Testing Approach
Software products released into the field typically have some number of residual defects that either were not detected or could not have been detected during testing. This may be the result of flaws in the test cases themselves, incorrect assumptions made during the creation of test cases, or the infeasibility of testing the sheer number of possible configurations for a complex system; these defects may also be due to application states that were not considered during lab testing, or corrupted states that could arise due to a security violation. One approach to this problem is to continue to test these applications even after deployment, in hopes of finding any remaining flaws. In this paper, we present a testing methodology we call in vivo testing, in which tests are continuously executed in the deployment environment. We also describe a type of test we call in vivo tests that are specifically designed for use with such an approach: these tests execute within the current state of the program (rather than by creating a clean slate) without affecting or altering that state from the perspective of the end-user. We discuss the approach and the prototype testing framework for Java applications called Invite. We also provide the results of case studies that demonstrate Invite's effectiveness and efficiency
A Constrained Sequential-Lamination Algorithm for the Simulation of Sub-Grid Microstructure in Martensitic Materials
We present a practical algorithm for partially relaxing multiwell energy
densities such as pertain to materials undergoing martensitic phase
transitions. The algorithm is based on sequential lamination, but the evolution
of the microstructure during a deformation process is required to satisfy a
continuity constraint, in the sense that the new microstructure should be
reachable from the preceding one by a combination of branching and pruning
operations. All microstructures generated by the algorithm are in static and
configurational equilibrium. Owing to the continuity constrained imposed upon
the microstructural evolution, the predicted material behavior may be
path-dependent and exhibit hysteresis. In cases in which there is a strict
separation of micro and macrostructural lengthscales, the proposed relaxation
algorithm may effectively be integrated into macroscopic finite-element
calculations at the subgrid level. We demonstrate this aspect of the algorithm
by means of a numerical example concerned with the indentation of an Cu-Al-Ni
shape memory alloy by a spherical indenter.Comment: 27 pages with 9 figures. To appear in: Computer Methods in Applied
Mechanics and Engineering. New version incorporates minor revisions from
revie
Spectral variability in Cygnus X-3
We model the broad-band X-ray spectrum of Cyg X-3 in all states displayed by
this source as observed by the Rossi X-ray Timing Explorer. From our models, we
derive for the first time unabsorbed spectral shapes and luminosities for the
full range of spectral states. We interpret the unabsorbed spectra in terms of
Comptonization by a hybrid electron distribution and strong Compton reflection.
We study the spectral evolution and compare with other black hole as well as
neutron star sources. We show that a neutron star accretor is not consistent
with the spectral evolution as a function of Ledd and especially not with the
transition to a hard state. Our results point to the compact object in Cyg X-3
being a massive, ~30 Msun black hole.Comment: 14 pages, 9 figures, accepted for publication in MNRA
Photodissociation in proto-planetary nebulae. Hydrodynamical simulations and solutions for low-velocity multi-lobes
We explore the effects of photodissociation at the stages of post-asymptotic
giant branch stars to find a mechanism able to produce multi-polar shapes. We
perform two-dimensional gasdynamical simulations to model the effects of
photodissociation in proto-planetary nebulae. We find that post-asymptotic
giant branch stars with 7,000 K or hotter are able to photodissociate a large
amount of the circumstellar gas. We compute several solutions for nebulae with
low-velocity multi-lobes. We find that the early expansion of a dissociation
front is crucial to understand the number of lobes in proto-planetary nebulae.
A dynamical instability appears when cooling is included in the swept-up
molecular shell. This instability is similar to the one found in
photoionization fronts, and it is associated with the thin-shell Vishniac
instability. The dissociation front exacerbates the growth of the thin-shell
instability, creating a fast fragmentation in shells expanding into media with
power-law density distributions such as r^-2.Comment: 4 pages, 2 figures, acepted by A&A Letter
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Network Analysis: Applications for the Developing Brain
Development of the human brain follows a complex trajectory of age-specific anatomical and physiological changes. The application of network analysis provides an illuminating perspective on the dynamic interregional and global properties of this intricate and complex system. Here, we provide a critical synopsis of methods of network analysis with a focus on developing brain networks. After discussing basic concepts and approaches to network analysis, we explore the primary events of anatomical cortical development from gestation through adolescence. Upon this framework, we describe early work revealing the evolution of age-specific functional brain networks in normal neurodevelopment. Finally, we review how these relationships can be altered in disease and perhaps even rectified with treatment. While this method of description and inquiry remains in early form, there is already substantial evidence that the application of network models and analysis to understanding normal and abnormal human neural development holds tremendous promise for future discovery
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