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At least 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

The Analysis of the Patterns of Radiation-Induced DNA Damage Foci by a Stochastic Monte Carlo Model of DNA Double Strand Breaks Induction by Heavy Ions and Image Segmentation Software

To create a generalized mechanistic model of DNA damage in human cells that will generate analytical and image data corresponding to experimentally observed DNA damage foci and will help to improve the experimental foci yields by simulating spatial foci patterns and resolving problems with quantitative image analysis. Material and Methods: The analysis of patterns of RIFs (radiation-induced foci) produced by low- and high-LET (linear energy transfer) radiation was conducted by using a Monte Carlo model that combines the heavy ion track structure with characteristics of the human genome on the level of chromosomes. The foci patterns were also simulated in the maximum projection plane for flat nuclei. Some data analysis was done with the help of image segmentation software that identifies individual classes of RIFs and colocolized RIFs, which is of importance to some experimental assays that assign DNA damage a dual phosphorescent signal. Results: The model predicts the spatial and genomic distributions of DNA DSBs (double strand breaks) and associated RIFs in a human cell nucleus for a particular dose of either low- or high-LET radiation. We used the model to do analyses for different irradiation scenarios. In the beam-parallel-to-the-disk-of-a-flattened-nucleus scenario we found that the foci appeared to be merged due to their high density, while, in the perpendicular-beam scenario, the foci appeared as one bright spot per hit. The statistics and spatial distribution of regions of densely arranged foci, termed DNA foci chains, were predicted numerically using this model. Another analysis was done to evaluate the number of ion hits per nucleus, which were visible from streaks of closely located foci. In another analysis, our image segmentaiton software determined foci yields directly from images with single-class or colocolized foci. Conclusions: We showed that DSB clustering needs to be taken into account to determine the true DNA damage foci yield, which helps to determine the DSB yield. Using the model analysis, a researcher can refine the DSB yield per nucleus per particle. We showed that purely geometric artifacts, present in the experimental images, can be analytically resolved with the model, and that the quantization of track hits and DSB yields can be provided to the experimentalists who use enumeration of radiation-induced foci in immunofluorescence experiments using proteins that detect DNA damage. An automated image segmentaiton software can prove useful in a faster and more precise object counting for colocolized foci images.

Ponomarev, Artem↗
NASA NTRS1925

Pressure distribution on the nose of an airship in circling flight

In recent tests on the pressures occurring on the envelope and control surfaces of the naval airship C-7, it was noted that the pressures on the nose of the airship, while flying in level circling flight, were symmetrically distributed. Such a condition can only occur when the nose of the airship is pointed directly into the wind, and to accomplish this in circling flight, the axis of the airship must then be parallel to the direction of the motion of the nose. The question was raised as to whether the same conditions occur generally on all airships in circling flight. It appears that airships flying in a constant, level, circling flight path will generally head very closely into the wind, and any deviation will be so slight that the distribution of pressure over the nose will be but slightly, if at all, changed from a symmetrical distribution.

Fairbanks, Karl J↗
NASA NTRS1997

By Hand or Not By-Hand: A Case Study of Alternative Approaches to Parallelize CFD Applications

While parallel processing promises to speed up applications by several orders of magnitude, the performance achieved still depends upon several factors, including the multiprocessor architecture, system software, data distribution and alignment, as well as the methods used for partitioning the application and mapping its components onto the architecture. The existence of the Gorden Bell Prize given out at Supercomputing every year suggests that while good performance can be attained for real applications on general purpose multiprocessors, the large investment in man-power and time still has to be repeated for each application-machine combination. As applications and machine architectures become more complex, the cost and time-delays for obtaining performance by hand will become prohibitive. Computer users today can turn to three possible avenues for help: parallel libraries, parallel languages and compilers, interactive parallelization tools. The success of these methodologies, in turn, depends on proper application of data dependency analysis, program structure recognition and transformation, performance prediction as well as exploitation of user supplied knowledge. NASA has been developing multidisciplinary applications on highly parallel architectures under the High Performance Computing and Communications Program. Over the past six years, the transition of underlying hardware and system software have forced the scientists to spend a large effort to migrate and recede their applications. Various attempts to exploit software tools to automate the parallelization process have not produced favorable results. In this paper, we report our most recent experience with CAPTOOL, a package developed at Greenwich University. We have chosen CAPTOOL for three reasons: 1. CAPTOOL accepts a FORTRAN 77 program as input. This suggests its potential applicability to a large collection of legacy codes currently in use. 2. CAPTOOL employs domain decomposition to obtain parallelism. Although the fact that not all kinds of parallelism are handled may seem unappealing, many NASA applications in computational aerosciences as well as earth and space sciences are amenable to domain decomposition. 3. CAPTOOL generates code for a large variety of environments employed across NASA centers: MPI/PVM on network of workstations to the IBS/SP2 and CRAY/T3D.

Yan, Jerry C.↗
NASA NTRS2010

Unveiling the Galaxy Population at 1.3 < z < 4: the HUDF05 NICMOS Parallel Fields

Using the Hubble Ultra Deep Field Near Infrared Camera and Multi-Object Spectrometer (HUDF-NICMOS) UDF05 parallel fields, we cross-matched 301 out of 630 galaxies with the ACS filters V606 and z850, NICMOS filters J110 and H160, and Spitzer IRAC filters at 3.6, 4.5, 5.8 , and 8.0 (mu)m. We modeled the spectral energy distributions (SEDs) to estimate: photometric redshifts, dust extinction, stellar mass, bolometric luminosity, starburst age and metallicity. To validate the photometric redshifts, comparisons with 16 spectroscopic redshifts give 75% within Delta < 0.2, which agrees with the sensitivities expected from the Balmer-break in our dataset. Five parallel fields observed by NICMOS have sensitivities in the H160-band of 80% at mAB = 25.4 and 50% at mAB = 26.7. Because the sample is H160-band selected, it is sensitive to stellar mass rather than UV luminosities. We also use Monte Carlo simulations to determine that the parameters from the best-fit SEDs are robust for the redshift ranges z > or approx. 1.3. Based on the robustness of the photometric redshifts, we analyze a subsample of the 301 galaxies at 1.3 < or = z < or = 2 (35 objects) and 3 < or = z < or = 4 (31 objects) and determine that L(BoI) and the star formation rate increase significantly from z approx. 1.5 to 4. The Balmer decrement is indicative of more evolved galaxies, and at high redshifts, they serve as records of some of the first galaxies. Therefore, the galaxies in this sample are great candidates for future surveys with the James Webb Space Telescope and Atacama Large Millimeter Array.

Petty, Sara M.↗
NASA NTRS2001

A Parallel Cartesian Approach for External Aerodynamics of Vehicles with Complex Geometry

This workshop paper presents the current status in the development of a new approach for the solution of the Euler equations on Cartesian meshes with embedded boundaries in three dimensions on distributed and shared memory architectures. The approach uses adaptively refined Cartesian hexahedra to fill the computational domain. Where these cells intersect the geometry, they are cut by the boundary into arbitrarily shaped polyhedra which receive special treatment by the solver. The presentation documents a newly developed multilevel upwind solver based on a flexible domain-decomposition strategy. One novel aspect of the work is its use of space-filling curves (SFC) for memory efficient on-the-fly parallelization, dynamic re-partitioning and automatic coarse mesh generation. Within each subdomain the approach employs a variety reordering techniques so that relevant data are on the same page in memory permitting high-performance on cache-based processors. Details of the on-the-fly SFC based partitioning are presented as are construction rules for the automatic coarse mesh generation. After describing the approach, the paper uses model problems and 3- D configurations to both verify and validate the solver. The model problems demonstrate that second-order accuracy is maintained despite the presence of the irregular cut-cells in the mesh. In addition, it examines both parallel efficiency and convergence behavior. These investigations demonstrate a parallel speed-up in excess of 28 on 32 processors of an SGI Origin 2000 system and confirm that mesh partitioning has no effect on convergence behavior.

Aftosmis, M. J.↗
NASA NTRS1991

Mapping implicit spectral methods to distributed memory architectures

Spectral methods were proven invaluable in numerical simulation of PDEs (Partial Differential Equations), but the frequent global communication required raises a fundamental barrier to their use on highly parallel architectures. To explore this issue, a 3-D implicit spectral method was implemented on an Intel hypercube. Utilization of about 50 percent was achieved on a 32 node iPSC/860 hypercube, for a 64 x 64 x 64 Fourier-spectral grid; finer grids yield higher utilizations. Chebyshev-spectral grids are more problematic, since plane-relaxation based multigrid is required. However, by using a semicoarsening multigrid algorithm, and by relaxing all multigrid levels concurrently, relatively high utilizations were also achieved in this harder case.

Overman, Andrea L.↗
NASA NTRS2010

Whistler Waves Driven by Anisotropic Strahl Velocity Distributions: Cluster Observations

Observed properties of the strahl using high resolution 3D electron velocity distribution data obtained from the Cluster/PEACE experiment are used to investigate its linear stability. An automated method to isolate the strahl is used to allow its moments to be computed independent of the solar wind core+halo. Results show that the strahl can have a high temperature anisotropy (T(perpindicular)/T(parallell) approximately > 2). This anisotropy is shown to be an important free energy source for the excitation of high frequency whistler waves. The analysis suggests that the resultant whistler waves are strong enough to regulate the electron velocity distributions in the solar wind through pitch-angle scattering

Vinas, A.F.↗
NASA NTRS1992

A new tool for analyzing microinstabilities in space plasmas modeled by a generalized Lorentzian (kappa) distribution

The modified plasma dispersion function Z* sub kappa (xi) based on the generalized Lorentzian distribution, which was introduced by Summers and Thorne (1991), is used to analyze three classical problems of plasma physics. These include the Landau damping of Langmuir waves, the ion acoustic instability in a current-carrying plasma, and the cyclotron resonant instability of electromagnetic R mode waves propagating parallel to an ambient magnetic field. It was found that, in each case, the results for a generalized Lorentzian plasma can differ significantly from those for a Maxwellian plasma. It is suggested that previous calculations based on a Maxwellian plasma distribution function Z(xi) have to be reexamined.

Summers, Danny↗
NASA NTRS1997

Determination of Stress Intensity Factor Distributions for "Interface" Cracks in Incompressible, Dissimilar Materials

The present study was undertaken in order to develop test methods and procedures for measuring the variation of the stress intensity factor through the thickness in bimaterial specimens containing cracks within and parallel to the bond line using the frozen stress photoelastic method. Since stress freezing materials are incompressible above critical temperature, and since thick plates are to be employed which tend to produce a state of plane strain near the crack tip, the interface near tip fracture equations reduce to the classic form for homogeneous materials. Moreover, zero thickness interfaces do not exist when materials are bonded together. It was decided early on that it would be important to insure a uniform straight and accurate crack tip region through the thickness of the body to reduce scatter in the SIF distribution through the thickness. It was also observed that rubberlike materials which were desired to be modeled exhibited significant tip blunting prior to crack extension and that some blunting of the tip would provide a more realistic model. It should be noted that, in normal stress freezing photoelastic work, it is considered good practice to avoid utilizing data near bond lines in photoelastic models due to the bond line stresses which inevitably develop when two parts are bonded together. Thus, the present study involves certain exploratory aspects in deviating from standard practice in stress freezing work. With the above ideas in mind, several different test methods were investigated and are described in the following sections and appendices. The geometry selected for the program was a thick, edge cracked specimen containing a bond line.

Smith, C. W.↗
NASA NTRS2006

Implementing Distributed Operations: A Comparison of Two Deep Space Missions

Two very different deep space exploration missions--Mars Exploration Rover and Cassini--have made use of distributed operations for their science teams. In the case of MER, the distributed operations capability was implemented only after the prime mission was completed, as the rovers continued to operate well in excess of their expected mission lifetimes; Cassini, designed for a mission of more than ten years, had planned for distributed operations from its inception. The rapid command turnaround timeline of MER, as well as many of the operations features implemented to support it, have proven to be conducive to distributed operations. These features include: a single science team leader during the tactical operations timeline, highly integrated science and engineering teams, processes and file structures designed to permit multiple team members to work in parallel to deliver sequencing products, web-based spacecraft status and planning reports for team-wide access, and near-elimination of paper products from the operations process. Additionally, MER has benefited from the initial co-location of its entire operations team, and from having a single Principal Investigator, while Cassini operations have had to reconcile multiple science teams distributed from before launch. Cassini has faced greater challenges in implementing effective distributed operations. Because extensive early planning is required to capture science opportunities on its tour and because sequence development takes significantly longer than sequence execution, multiple teams are contributing to multiple sequences concurrently. The complexity of integrating inputs from multiple teams is exacerbated by spacecraft operability issues and resource contention among the teams, each of which has their own Principal Investigator. Finally, much of the technology that MER has exploited to facilitate distributed operations was not available when the Cassini ground system was designed, although later adoption of web-based and telecommunication tools has been critical to the success of Cassini operations.

Cassini Mission↗
NASA NTRS2002

Software Engineering Support of the Third Round of Scientific Grand Challenge Investigations: An Earth Modeling System Software Framework Strawman Design that Integrates Cactus and UCLA/UCB Distributed Data Broker

One of the most significant challenges in large-scale climate modeling, as well as in high-performance computing in other scientific fields, is that of effectively integrating many software models from multiple contributors. A software framework facilitates the integration task. both in the development and runtime stages of the simulation. Effective software frameworks reduce the programming burden for the investigators, freeing them to focus more on the science and less on the parallel communication implementation, while maintaining high performance across numerous supercomputer and workstation architectures. This document proposes a strawman framework design for the climate community based on the integration of Cactus, from the relativistic physics community, and UCLA/UCB Distributed Data Broker (DDB) from the climate community. This design is the result of an extensive survey of climate models and frameworks in the climate community as well as frameworks from many other scientific communities. The design addresses fundamental development and runtime needs using Cactus, a framework with interfaces for FORTRAN and C-based languages, and high-performance model communication needs using DDB. This document also specifically explores object-oriented design issues in the context of climate modeling as well as climate modeling issues in terms of object-oriented design.

Talbot, Bryan↗
NASA NTRS1994

(abstract) Neptune: CO and HCN Distributions from Observations at the CSO

We used the Caltech Submillimeter Observatory (CSO ) to make spatially unresolved observations of the 230.538 GHz 2-1 transition of CO and the 265.886 GHz 3-2 transition of HCN at Neptune. All observations used the 10.4 meter antenna with a double sideband SIS junction heterodyne receiver. Spectra were observed with parallel acousto-optic spectrometers simultaneously providing 580 MHz bandwidth at 0.57 MHz resolution and 50 MHz bandwidth at 0.049 MHz resolution. Observed line shapes agree with prior observations by Rosenqvist et al and Marten et al. Analysis of the line shapes and intensities will yield information about the distributions of CO and HCN in the stratosphere of Neptune, and these results will be compared with previous results. The data imply that the mixing ratios of CO and HCN must decrease with altitude somewhere within the pressure range from 1 to 0.001 mbar. HCN data will also address the sharp saturation-induced decrease in the HCN mixing ratio at the lower levels in the stratosphere.

Caltech Submillimeter Observatory SRO CO carbon mo↗
DOE OSTI2025

A scoping study of far-SOL main-wall protection limiters for steady-state operation of compact pilot plant tokamaks

We present a novel method for handling steady-state heat fluxes incident on the main wall of pilot plant-scale magnetic fusion devices, based on the utilization of protection limiters in the far scrape-off layer (SOL). This method helps avoid large plasma-wall gaps, without excessively compromising blanket performance. We present an optimization algorithm for determining the appropriate size and scale of these protection limiters given (1) probability distributions of SOL plasma parameters and (2) assumed risk tolerance. As part of this optimization, we have developed an analytic description of parallel heat fluxes across limiter shadows, and an objective cost function (the ‘Far-SOL Marginal Cost’) to quantify the impact that different main-wall thermal management design choices have on reactor capital cost. Applying the model to a midscale fusion pilot plant concept shows that making use of far-SOL protection limiters can reduce capital costs on the order of $500 M, relative to naively increasing the plasma-wall gap. Our analysis demonstrates that the far-SOL power decay length is the highest-leverage plasma assumption for thermal loading of the first wall, and the primary cost driver for main wall thermal management. The relative cost efficiency of protection limiters increases as assumptions on the far-SOL heat flux become more pessimistic. The concepts described in this paper motivate the further development of far-SOL protection limiters as part of larger efforts to design economical core-edge-wall compatible solutions for a fusion pilot plant.

Design under uncertainty↗
DOE OSTI2024

Approach for energy efficient building design during early phase of design process

Energy consumption in the building sector is about 40% of total energy consumed globally and is trending upwards, along with its contribution to greenhouse gas (GHG) emissions. Given the adverse impacts of GHG emissions, it is crucial to integrate energy efficiency into building designs. The most significant opportunities for enhancing energy performance are present during the initial phases of building design, when there is less impact of other design constraints. Various tools exist for simulating different design options and providing feedback in terms of energy consumption and comfort parameters. These simulation outputs must then be analyzed to derive design solutions. This paper presents an innovative approach that utilizes user input parameters, processes them through cloud computing, and outputs easily understandable strategies for energy-efficient building design. The methodology employs Asynchronous Distributed Task Queues (DTQ) - a more scalable and reliable alternative to conventional speedup techniques-for conducting parametric energy simulations in the cloud. The goal of this approach is to assist design teams in identifying, visualizing, and prioritizing energy-saving design strategies from a range of possible solutions for each project. Furthermore, a tool ‘eDOT’ has been developed utilizing the discussed methodology. Unlike existing tools, eDOT leverages artificial intelligence to dynamically generate and provide design strategies during the early phases of design process. By simplifying the simulation process, eDOT enables design teams to make informed, data-driven decisions without needing to interpret complex simulation outputs. A case study simulated for two locations is provided in this paper to demonstrate the effectiveness of eDOT, further underscoring its practical impact on energy-efficient building design.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2020

The Kokkos Ecosystem [Brief]

In 2016/2017, the field of High-Performance Computing (HPC) entered a new era driven by fundamental physics challenges to produce ever more energy and cost-efficient processors. Since the convergence on the Message-Passing Interface (MPI) standard in the mid-1990s, application developers enjoyed a seemingly static view of the underlying machine — that of a distributed collection of homogeneous nodes executing in collaboration. However, after almost two decades of dominance, the sole use of MPI to derive parallelism acted as a limiter to improved future performance. While MPI is widely expected to continue to function as the basic mechanism for communication between compute nodes for the immediate future, additional parallelism is required on the computing node itself if high performance and efficiency goals are to be realized. When reviewing the architectures of the top HPC systems today, the change in paradigm is clear: the compute nodes of the leading machines in the world are either powered by many-core chips with a few dozen cores each, or use heterogeneous designs, where traditional CPUs marshal work to massively parallel compute accelerators which has as many as 200,000 processing threads in flight simultaneously. Complicating matters further for application developers, each processor vendor has its own preferred way of writing code for their architecture.The Kokkos EcoSystem was released by Sandia in 2017 to address this new era in HPC system design by providing a vendor independent performance portable programming system for scientific, engineering, and mathematical software applications written in the C++ programming language. Using Kokkos, application developers can be more productive because they will not have to create and maintain separate versions of their software for each architecture, nor will they have to be experts in each architecture's peculiar requirements. Instead, they will have a single method of programming for the diverse set of modern HPC architectures. While Kokkos started in 2011 as a programming model only, it soon became clear that complex applications needed more. It is also critical to have a portable mathematical functions and developers need tools to debug their applications, gain insight into the performance characteristics of their codes and tune algorithm performance parameters through automated processes. The Kokkos EcoSystem addresses those needs through its three main components: the Kokkos Core programming model, the Kokkos Kernels math library, and the Kokkos Tools project.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2021

TAO Users Manual (Rev. 3.15)

The Toolkit for Advanced Optimization (TAO) focuses on the development of algorithms and software for the solution of large-scale optimization problems on high-performance architectures. Areas of interest include unconstrained and bound-constrained optimization, nonlinear least squares problems, optimization problems with partial differential equation constraints, and variational inequalities and complementarity constraints. The development of TAO was motivated by the scattered support for parallel computations and the lack of reuse of external toolkits in current optimization software. Our aim is to produce high-quality optimization software for computing environments ranging from workstations and laptops to massively parallel high-performance architectures. Our design decisions are strongly motivated by the challenges inherent in the use of large-scale distributed memory architectures and the reality of working with large, often poorly structured legacy codes for specific applications.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

An Observed Transition of Galaxy Spins on Void Surfaces

In linear theory, the galaxy angular momentum vectors that originate from initial tidal interactions with surrounding matter distribution intrinsically develop perpendicular alignments with the directions of maximum matter compression, regardless of galaxy mass. In simulations, however, galaxy spins exhibit parallel alignments in the mass range lower than a certain threshold, which depends on redshift, web type, and background cosmology. We show that the observed three-dimensional spins of the spiral galaxies located on the void surfaces from the Sloan Digital Sky Survey indeed transit from perpendicular to parallel alignments with the directions toward the nearest void centers at the threshold zone, 9.51 $\leqslant$ log[M th,$\star$ /(h -1 M ⊙ )] $\leqslant$ 10.03. This study presents the first direct observational evidence for the occurrence of mass-dependent spin transition of real galaxies with respect to non-filamentary structures of the cosmic web, opening a way to constrain the initial conditions of the early universe by measuring the spin transition threshold.

79 ASTRONOMY AND ASTROPHYSICS↗