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At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Monte Carlo mesh tallies based on a Kernel Density Estimator approach using integrated particle tracks

A new Monte Carlo mesh tally based on a Kernel Density Estimator (KDE) approach using integrated particle tracks is presented. We first derive the KDE integral-track estimator and present a brief overview of its implementation as an alternative to the MCNP fmesh tally. To facilitate a valid quantitative comparison between these two tallies for verification purposes, there are two key issues that must be addressed. The first of these issues involves selecting a good data transfer method to convert the nodal-based KDE results into their cell-averaged equivalents (or vice versa with the cell-averaged MCNP results). The second involves choosing an appropriate resolution of the mesh, since if it is too coarse this can introduce significant errors into the reference MCNP solution. After discussing both of these issues in some detail, we present the results of a convergence analysis that shows the KDE integral-track and MCNP fmesh tallies are indeed capable of producing equivalent results for some simple 3D transport problems. In all cases considered, there was clear convergence from the KDE results to the reference MCNP results as the number of particle histories was increased. (authors)

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

An analysis of the operational GFS simplified Arakawa Schubert parameterization within a WRF framework: A Hurricane Sandy (2012) long‐term track forecast perspective

Abstract Hurricane Sandy (2012) is known as an incredibly destructive storm and one defined meteorologically by its large size, and its significant forecast track spreads among various operational models roughly 1 week before landfall. While the operational European Centre for Medium‐Range Weather Forecasts model accurately depicted a northeastern United States landfall, the Global Forecasting System (GFS) model consistently forecast a track toward the North Atlantic Ocean. Using a Weather Research and Forecasting (WRF) model framework, Bassill ( ) suggested that these differences were primarily a function of differences between the two models' cumulus parameterization (CP). This study also uses a WRF model framework to examine the simplified Arakawa Schubert CP used in the GFS model. It is found that increasing the deep convective entrainment coefficient produces more realistic forecast tracks for forecasts initialized roughly 1 week before landfall. This occurs through a reorientation of the precipitation (and associated latent heating) around Sandy during a critical time period in which it was interacting with a series of upper troughs to its west and northwest. Reorienting the latent heating reshapes the upper tropospheric steering pattern toward the one that is more negatively tilted and consistent with observations.

Bassill, Nick P.↗
DOE OSTI2019

Spatially tracking carbon through the root-rhizosphere-soil system using laser ablation-IRMS

The intimate relationships between plant roots, rhizosphere, and soil are fostered by the release of organic compounds from the plant into soil through various forms of rhizodeposition and the simultaneous harvestingof inorganic nutrients from the soil to the plant. Here we present a method to spatially track and map the migration of plant-derived carbon (C) through roots into the rhizosphere and surrounding soil using laser ablation-isotope ratio mass spectrometry (LA-IRMS). Weused switchgrass microcosms containing soil from field plots at the Kellogg Biological Station (Hickory Corners, Michigan, USA), which have been cropped with switchgrass since 2008. We used a 13 CO 2 tracerto isotopically label switchgrass plants for two diel cycles and tracked subsequent movement of labeled C using the spatially specific (<100 µm resolution) δ 13 C analysis enabled by LA-IRMS.This approach permitted assessment of variable C flow through different roots and enabled mapping of spatial variability of C allocation to the rhizosphere. Highly 13 C-enriched C (consistent with production during the 13 CO 2 application period) extended ~0.5 – 1 mm from the root into the soil, suggesting that the majority of recent plant-derived C was within this distance of the root after 48 hours. Tracking the physical extent of root exudation into the rhizosphere can help evaluate the localization of plant-microbe interactions in highly variable subsurface environments,and the use of the isotopic label can differentiate freshly fixed C (presumably from root exudates) from other types of subsurface C (e.g., plant necromass and microbial turnover). The LA-IRMS technique mayalso serve as a valuable screening technique to identify areas of high activity for additional microbial or geochemicalassays.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Search for long-lived charginos based on a disappearing-track signature in pp collisions at $ \sqrt{s}=13 $ TeV with the ATLAS detector

Here, this paper presents a search for direct electroweak gaugino or gluino pair production with a chargino nearly mass-degenerate with a stable neutralino. It is based on an integrated luminosity of 36.1 fb –1 of pp collisions at √s = 13 TeV collected by the ATLAS experiment at the LHC. The final state of interest is a disappearing track accompanied by at least one jet with high transverse momentum from initial-state radiation or by four jets from the gluino decay chain. The use of short track segments reconstructed from the innermost tracking layers significantly improves the sensitivity to short chargino lifetimes. The results are found to be consistent with Standard Model predictions. Exclusion limits are set at 95% confidence level on the mass of charginos and gluinos for different chargino lifetimes. For a pure wino with a lifetime of about 0.2 ns, chargino masses up to 460 GeV are excluded. For the strong production channel, gluino masses up to 1.65 TeV are excluded assuming a chargino mass of 460 GeV and lifetime of 0.2 ns.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

A new inventory tracking method for Mark-V electrorefiner

Here, we discuss the current practice of assessing the Mark-V electrorefiner inventory and a proposed new way of tracking this inventory. The presented approach only involves the total mass measurement of the transferred materials and the consideration of metallic uranium phase in the inventory while the current practice involves the estimation/calculation of the salt phase mass in the transferred material mass and the calculation of the holdup. Without estimating the involved salt inventory in the incoming and outgoing material streams, the proposed method yields the salt inventory agreeing with the current mass tracking practice. The estimated holdup in the current mass tracking practice is entirely explained with the introduced metallic uranium phase in the proposed model. The current practice of closing out the special nuclear material inventory is revisited with the insight gained from the proposed model. Suggestions are given to achieve the bounded uncertainty of the inventory estimates with the emerging in-situ measurement technique on the molten salt density.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

A novel mouse model for tracking the fate of CXCR5-expressing T cells

Highlights: • Tfh cell fate-mapping mouse was developed. • Tfh cells could be tracked from the effector phase to the memory phase. • Tfh-derived memory cells were localized in the T-B border area and T cell zone. The germinal center (GC) reaction, a critical process in the humoral immune response, requires follicular helper T (Tfh) cells. Tfh cells express the master transcription factor Bcl6 and chemokine receptor CXCR5, which enable them to migrate from the T cell zone to B cell follicles and interact with GC B cells. However, CXCR5 is downregulated when Tfh cells become memory cells. Therefore, it is difficult to track Tfh cells continuously in vivo. In this study, we generated a mouse strain, Cxcr5{sup CreERT2}R26{sup Tomato}, in which the fluorescent protein tdTomato is inducibly expressed in CXCR5{sup +} cells by tamoxifen administration. After the oral administration of tamoxifen, most Tfh cells in Peyer's patches (PP) from Cxcr5{sup CreERT2}R26{sup Tomato} mice were tdTomato{sup +}. To track antigen-specific Tfh cells in vivo, OVA-specific OT-II T cells derived from Cxcr5{sup CreERT2}R26{sup Tomato} mice were transferred to wild-type mice, and the recipient mice were immunized with OVA followed by tamoxifen administration. CXCR5{sup +} T cells became tdTomato{sup +} and were mainly located in B cell follicles and GC areas 8 days after immunization. Four weeks after immunization, tdTomato{sup +} OT-II T cells migrated from B cell follicles to the T-B border area and T cell zone after CXCR5 downregulation and CCR7 upregulation. These results indicate that Cxcr5{sup CreERT2}R26{sup Tomato} mice are a useful tool for studying the cell fate of differentiated Tfh cells in vivo and therefore have implications for the development of therapeutic strategies for infectious and autoimmune diseases.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

A comparative study of shear band tracking strategies in three-dimensional finite elements with embedded weak discontinuities

We present a computational framework for the treatment of shear localization in metallic materials under dynamic loading, based on the integration of a shear band tracking strategy into an explicit 3D finite element formulation with embedded weak discontinuities. Within this computational framework, an embedded shear band’s mid-surface is represented by an iso-surface of a level set function, which is obtained by solving a heatconduction type boundary value problem (BVP). The solution of this BVP is carried out either globally over the entire problem domain, or locally at the level of individual elements in the mesh. In this paper, we present a detailed comparison of these global and local algorithmic implementations of the shear band tracking strategy. Numerical results obtained using these two implementations, and using a simplified formulation without shear band tracking, are presented and compared. Moreover, we compare the computational efficiency and parallel scaling performance of the local and global implementations. This comparative study shows that both implementations can simulate the initiation of two independent shear bands and their propagation past each other without merging, whereas only the global implementation can successfully simulate the merging of two branches of a single shear band. This study also confirms that the global implementation is more computationally intensive, since it requires a global system of linear equations associated with the level set BVP to be solved at each time step. Both implementations exhibit very good scalability in domain decomposition-based parallel simulations.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Accelerating Dynamic Magnetic Resonance Imaging (MRI) for Lung Tumor Tracking Based on Low-Rank Decomposition in the Spatial–Temporal Domain: A Feasibility Study Based on Simulation and Preliminary Prospective Undersampled MRI

Purpose: To evaluate a low-rank decomposition method to reconstruct down-sampled k-space data for the purpose of tumor tracking. Methods and Materials: Seven retrospective lung cancer patients were included in the simulation study. The fully-sampled k-space data were first generated from existing 2-dimensional dynamic MR images and then down-sampled by 5 × -20 × before reconstruction using a Cartesian undersampling mask. Two methods, a low-rank decomposition method using combined dynamic MR images (k-t SLR based on sparsity and low-rank penalties) and a total variation (TV) method using individual dynamic MR frames, were used to reconstruct images. The tumor trajectories were derived on the basis of autosegmentation of the resultant images. To further test its feasibility, k-t SLR was used to reconstruct prospective data of a healthy subject. An undersampled balanced steady-state free precession sequence with the same undersampling mask was used to acquire the imaging data. Results: In the simulation study, higher imaging fidelity and low noise levels were achieved with the k-t SLR compared with TV. At 10 × undersampling, the k-t SLR method resulted in an average normalized mean square error <0.05, as opposed to 0.23 by using the TV reconstruction on individual frames. Less than 6% showed tracking errors >1 mm with 10 × down-sampling using k-t SLR, as opposed to 17% using TV. In the prospective study, k-t SLR substantially reduced reconstruction artifacts and retained anatomic details. Conclusions: Magnetic resonance reconstruction using k-t SLR on highly undersampled dynamic MR imaging data results in high image quality useful for tumor tracking. The k-t SLR was superior to TV by better exploiting the intrinsic anatomic coherence of the same patient. The feasibility of k-t SLR was demonstrated by prospective imaging acquisition and reconstruction.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Cone-Beam Computed Tomography Internal Motion Tracking Should Be Used to Validate 4-Dimensional Computed Tomography for Abdominal Radiation Therapy Patients

Purpose: To demonstrate that fiducial tracking during pretreatment Cone-Beam CT (CBCT) can accurately measure tumor motion and that this method should be used to validate 4-dimensional CT (4DCT) margins before each treatment fraction. Methods and Materials: For 31 patients with abdominal tumors and implanted fiducial markers, tumor motion was measured daily with CBCT and fluoroscopy for 202 treatment fractions. Fiducial tracking and maximum-likelihood algorithms extracted 3-dimensional fiducial trajectories from CBCT projections. The daily internal margin (IM) (ie, range of fiducial motion) was calculated for CBCT and fluoroscopy as the 5th-95th percentiles of displacement in each cardinal direction. The planning IM from simulation 4DCT (IM{sub 4DCT}) was considered adequate when within ±1.2 mm (anterior–posterior, left–right) and ±3 mm (superior–inferior) of the daily measured IM. We validated CBCT fiducial tracking as an accurate predictive measure of intrafraction motion by comparing the daily measured IM{sub CBCT} with the daily IM measured by pretreatment fluoroscopy (IM{sub pre-fluoro}); these were compared with pre- and posttreatment fluoroscopy (IM{sub fluoro}) to identify those patients who could benefit from imaging during treatment. Results: Four-dimensional CT could not accurately predict intrafractional tumor motion for ≥80% of fractions in 94% (IM{sub CBCT}), 97% (IM{sub pre-fluoro}), and 100% (IM{sub fluoro}) of patients. The IM{sub CBCT} was significantly closer to IM{sub pre-fluoro} than IM{sub 4DCT} (P<.01). For patients with median treatment time t < 7.5 minutes, IM{sub CBCT} was in agreement with IM{sub fluoro} for 93% of fractions (superior–inferior), compared with 63% for the t > 7.5 minutes group, demonstrating the need for patient-specific intratreatment imaging. Conclusions: Tumor motion determined from 4DCT simulation does not accurately predict the daily motion observed on CBCT or fluoroscopy. Cone-beam CT could replace fluoroscopy for pretreatment verification of simulation IM{sub 4DCT}, reducing patient setup time and imaging dose. Patients with treatment time t > 7.5 minutes could benefit from the addition of intratreatment imaging.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Prospective Clinical Implementation of a Novel Magnetic Resonance Tracking Device for Real-Time Brachytherapy Catheter Positioning

Purpose: We designed and built dedicated active magnetic resonance (MR)-tracked (MRTR) stylets. We explored the role of MRTR in a prospective clinical trial. Methods and Materials: Eleven gynecologic cancer patients underwent MRTR to rapidly optimize interstitial catheter placement. MRTR catheter tip location and orientation were computed and overlaid on images displayed on in-room monitors at rates of 6 to 16 frames per second. Three modes of actively tracked navigation were analyzed: coarse navigation to the approximate region around the tumor; fine-tuning, bringing the stylets to the desired location; and pullback, with MRTR stylets rapidly withdrawn from within the catheters, providing catheter trajectories for radiation treatment planning (RTP). Catheters with conventional stylets were inserted, forming baseline locations. MRTR stylets were substituted, and catheter navigation was performed by a clinician working inside the MRI bore, using monitor feedback. Results: Coarse navigation allowed repositioning of the MRTR catheters tips by 16 mm (mean), relative to baseline, in 14 ± 5 s/catheter (mean ± standard deviation [SD]). The fine-tuning mode repositioned the catheter tips by a further 12 mm, in 24 ± 17 s/catheter. Pullback mode provided catheter trajectories with RTP point resolution of ∼1.5 mm, in 1 to 9 s/catheter. Conclusions: MRTR-based navigation resulted in rapid and optimal placement of interstitial brachytherapy catheters. Catheters were repositioned compared with the initial insertion without tracking. In pullback mode, catheter trajectories matched computed tomographic precision, enabling their use for RTP.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

The pixel tracking telescope at the Fermilab Test Beam Facility

An all silicon pixel telescope has been assembled and used at the Fermilab Test Beam Facility (FTBF) since 2009 to provide precise tracking information for different test beam experiments with a wide range of Detectors Under Test (DUTs) requiring high resolution measurement of the track impact point. The telescope is based on CMS pixel modules left over from the CMS forward pixel production. Eight planes are arranged to achieve a resolution of less than 8 μm on the 120 GeV proton beam transverse coordinate at the DUT position. In order to achieve such resolution with 100 × 150 μm 2 pixel cells, the planes were tilted to 25 degrees to maximize charge sharing between pixels. Crucial for obtaining this performance is the alignment software, called Monicelli, specifically designed and optimized for this system. This paper will describe the telescope hardware, the data acquisition system and the alignment software constituting this particle tracking system for test beam users.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Extending particle tracking capability with Delaunay triangulation

Here, particle tracking, the analysis of individual moving elements in time series of microscopic images, enables burgeoning new applications, but there is need to better resolve conformation and dynamics. Here we describe the advantages of Delaunay triangulation to extend the capabilities of particle tracking in three areas: (1) discriminating irregularly shaped objects, which allows one to track items other than point features; (2) combining time and space to better connect missing frames in trajectories; and (3) identifying shape backbone. To demonstrate the method, specific examples are given, involving analyzing the time-dependent molecular conformations of actin filaments and λ-DNA. The main limitation of this method, shared by all other clustering techniques, is the difficulty to separate objects when they are very close. This can be mitigated by inspecting locally to remove edges that are longer than their neighbors and also edges that link two objects, using methods described here, so that the combination of Delaunay triangulation with edge removal can be robustly applied to processing large data sets. As common software packages, both commercial and open source, can construct Delaunay triangulation on command, the methods described in this paper are both computationally efficient and easy to implement.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Shape of Atlantic Tropical Cyclone Tracks and the Indian Monsoon

Changes in the flow around the North Atlantic subtropical High (NASH) have important implications on the steering of Atlantic tropical cyclones (TCs). We find a significant enhancement of the NASH on interannual timescales (1970-2016) linked to an anomalously strong Indian monsoon in September. Consistent with a stronger NASH, enhanced anticyclonic flow and subtropical easterlies in the eastern Atlantic basin are found during strong monsoon years. Observational regression analysis combined with a statistical track model are used to assess the influence of these monsoon-linked wind variations on Atlantic TC tracks originating in the main development region (MDR). Even when controlling for the effects of El Niño Southern Oscillation (ENSO), a westward shift of TC tracks is shown to be robustly correlated to internal monsoon variability in September. This work highlights variability of the Indian monsoon as an additional constraint on Atlantic TCs, with potential implications for landfall probability.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Upper-Tropospheric Troughs and North American Monsoon Rainfall in a Long-Term Track Dataset

The North American monsoon is frequently affected by transient, propagating upper tropospheric vorticity anomalies. Sometimes called Tropical Upper-Tropospheric Troughs (TUTTs), these features have been claimed to episodically enhance monsoon rainfall. Here, we track long-lived TUTTs in 40 years of reanalysis data, producing composites and case studies from 340 TUTTs which last, on average, 7 days as they move westward across the North American monsoon region. TUTTs are thought to form from midlatitude Rossby wave breaking; case studies from our dataset support this theory. TUTTs move westward within the easterly upper-level flow in which they are embedded. In vortex-centered composites along the full tracks of long-lived TUTTs, here, we find no detectable increase in rainfall within the main TUTT circulation. Instead, negative precipitation anomalies lie within about 500 km of the TUTT center. Quasi-geostrophic ascent occurs in the southeast quadrant of TUTTs but is confined to the upper troposphere and does not appear to interact with precipitation. Positive anomalies of ascent and rainfall occur south and southeast of TUTTs but lie outside the main TUTT vortex, perhaps indicating concurrent variations in nearby climatological precipitation maxima. In contrast with previous case studies and subjective analyses that showed TUTTs enhance precipitation in parts of northwestern Mexico, our composites along the tracks of long-lived TUTTs portray these systems, to first order, as strong vorticity anomalies trapped in the upper troposphere that interact only weakly and indirectly with precipitation.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Accelerating the Lagrangian Particle Tracking in Hydrologic Modeling to Continental-Scale

Unprecedented climate change and anthropogenic activities have induced increasing ecohydrological problems, which have motivated the development of large-scale modeling for solutions. Water age/quality is as important as water quantity for understanding the water cycle. However, current scientific progress in tracking water parcels at large-scale with high spatiotemporal resolutions is far behind that in water balance/quantity owing to the lack of powerful tools. EcoSLIM is a particle tracking model that works with the hydrologic model ParFlow-CLM, which couples surface-subsurface hydrology with land surface processes. Here, we demonstrate a parallel framework to accelerate EcoSLIM to continental-scale on a distributed, multi-GPU platform with CUDA-Aware MPI. In tests from catchment-, to regional-, and then to continental-scale using 25-million to 1.6-billion particles, EcoSLIM shows significant speedup and excellent parallel performance. The parallel framework is portable to atmospheric and oceanic particle tracking models, where parallelization is inadequate and a standard parallel framework is absent. Parallelized EcoSLIM is a promising tool to accelerate our understanding of the terrestrial water cycle and the upscaling of subsurface hydrology to Earth system models.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

The Effects of African Easterly Wave Suppression by Wave Track on Atlantic Tropical Cyclones

Abstract It is well established that African easterly waves (AEWs) can serve as seedling disturbances for Atlantic tropical cyclones (TCs). However, research has shown that AEWs are not necessary to maintain specifically basin‐wide TC frequency. Here, we for the first time investigate the effects of AEW suppression by wave track on Atlantic TC activity. Regional model simulations were performed, where AEWs were either prescribed or suppressed from the eastern lateral boundary condition. We found that without AEWs, there was an increase in TC frequency and strength, with the most pronounced increases occurring when the waves were suppressed in the south track. These changes coincided with more favorable environmental conditions and disturbances associated with increased convective activity over the Atlantic. Our results indicate that AEWs are not a limiting factor for TCs, and that AEW suppression, specifically in the south track, can affect the large‐scale environment to enhance favorability for TC genesis.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Hillslope-Channel Transitions and the Role of Water Tracks in a Changing Permafrost Landscape

The Arctic is experiencing rapid climate change, and the effect on hydrologic processes and resulting geomorphic changes to hillslopes and channels is unclear because we lack quantitative models and theory for rapid changes resulting from thawing permafrost. Here, the presence of permafrost modulates water flow and the stability of soil-mantled slopes, implying that there should be a signature of permafrost processes, including warming-driven disturbance, in channel network extent. To inform understanding of hillslope-channel dynamics under changing climates, we examined soil-mantled hillslopes within a ~300 km 2 area of the Seward Peninsula, western Alaska, where discontinuous permafrost is particularly susceptible to thaw and rapid landscape change. In this study, we pair high-resolution topographic and satellite data to multi-annual observations of InSAR-derived surface displacement over a 5-year period to quantify spatial variations in topographic change across an upland landscape. We find that neither the basin slope nor the presence of knickzones controls the magnitude of recent surface displacements within the study basin, as may be expected under conceptual models of temperate hillslope evolution. Rather, the highest displacement magnitudes tended to occur at the broad hillslope-channel transition zone. In this study area, this zone is occupied by water tracks, which are zero-order ecogeomorphic features that concentrate surface and subsurface flow paths. Our results suggest that water tracks, which appear to occupy hillslope positions between saturation and incision thresholds, are vulnerable to warming-induced subsidence and incision. We hypothesize that gullying within water tracks will outpace infilling by hillslope processes, resulting in the growth of the channel network under future warming.

58 GEOSCIENCES↗