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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,639 records · Page 91
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

SU-E-J-121: Measuring Prompt Gamma Emission Profiles with a Multi-Stage Compton Camera During Proton Beam Irradiation: Initial Studies

Purpose: Recent studies have suggested that the characteristics of prompt gammas (PG) emitted during proton beam irradiation are advantageous for determining beam range during treatment delivery. The purpose of this work was to determine the feasibility of determining the proton beam range from PG data measured with a prototype Compton camera (CC) during proton beam irradiation. Methods: Using a prototype multi-stage CC the PG emission from a water phantom was measured during irradiation with clinical proton therapy beams. The measured PG emission data was used to reconstruct an image of the PG emission using a backprojection reconstruction algorithm. One dimensional (1D) profiles extracted from the PG images were compared to: 1) PG emission data measured at fixed depths using collimated high purity Germanium and Lanthanum Bromide detectors, and 2) the measured depth dose profiles of the proton beams. Results: Comparisons showed that the PG emission profiles reconstructed from CC measurements agreed very well with the measurements of PG emission as a function of depth made with the collimated detectors. The distal falloff of the measured PG profile was between 1 mm to 4 mm proximal to the distal edge of the Bragg peak for proton beam ranges from 4 cm to 16 cm in water. Doses of at least 5 Gy were needed for the CC to measure sufficient data to image the PG profile and localize the distal PG falloff. Conclusion: Initial tests of a prototype CC for imaging PG emission during proton beam irradiation indicated that measurement and reconstruction of the PG profile was possible. However, due to limitations of the operational parameters (energy range and count rate) of the current CC prototype, doses of greater than a typical treatment dose (∼2 Gy) were needed to measure adequate PG signal to reconstruct viable images. Funding support for this project provided by a grant from DoD.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Long-Term Outcomes of Early-Stage Nasopharyngeal Carcinoma Patients Treated With Intensity-Modulated Radiotherapy Alone

Purpose: Reports of intensity-modulated radiotherapy (IMRT) for early-stage nasopharyngeal carcinoma (NPC) have been limited. The present study evaluated the long-term survival outcomes and toxicity of early-stage NPC patients treated with IMRT alone. Methods and Materials: Between February 2001 and January 2008, 198 early-stage (T1-T2bN0-N1M0) NPC patients had undergone IMRT alone. The data from these patients were retrospectively analyzed. The patients were treated to 68 Gy at 2.27 Gy/fraction prescribed to the planning target volume of the primary nasopharygeal gross tumor volume. The Radiation Therapy Oncology Group scoring system was used to assess the toxicity. Results: At a median follow-up of 50.9 months (range, 12-104), the 5-year estimated disease-specific survival, local recurrence-free survival, and distant metastasis-free survival rate was 97.3%, 97.7%, and 97.8%, respectively. The 5-year local recurrence-free survival rate was 100% for those with Stage T1 and T2a and 94.2% for those with Stage T2b lesions (p = 0.252). The 5-year distant metastasis-free survival rate for Stage T1N0, T2N0, T1N1, and T2N1 patients was 100%, 98.8%, 100%, and 93.8%, respectively (p = .073). All local recurrence occurred in patients with T2b lesions. Five patients developed distant metastasis. Of these 5 patients, 4 had had Stage T2bN1 disease and 1 had had Stage T2bN0 disease with retropharyngeal lymph node involvement. The most common acute toxicities were mainly Grade 1 or 2. At 24 months after IMRT, no Grade 3 or 4 xerostomia had developed, and 62 (96.9%) of 64 evaluated patients were free of trismus; only 2 patients (3.1%) had Grade 1 trismus. Radiation encephalopathy and cranial nerve injury were not observed. Conclusions: IMRT alone for Stage T1N0, T2N0, T1N1, and T2N1 yielded satisfactory survival outcomes with acceptable toxicity, and no differences were found in survival outcomes among these four subgroups. Patients with Stage T2b lesions might have relatively greater risk of local recurrence and those with T2bN1 disease mighth have a greater risk of distant metastasis.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Atomistic Scale Analysis of the Carbonization Process for C/H/O/N-Based Polymers with the ReaxFF Reactive Force Field

During the carbonization process of raw polymer precursors, graphitic structures can evolve. The presence of these graphitic structures affects mechanical properties of the carbonized carbon fibers. To gain a better understanding of the chemistry behind the evolution of these structures, we performed atomistic-scale simulations using the ReaxFF reactive force field. Three different polymers were considered as a precursor: idealized ladder PAN (polyacrylonitrile), a proposed oxidized PAN, and poly(p-phenylene- 2,6-benzobisoxazole). We determined the underlying molecular details of polymer conversion into a carbon fiber structure. Because these are C/H/O/ N-based polymers, we first developed an improved force field for C/H/O/N chemistry based on the density functional theory data with a particular focus on N2 formation kinetics and its interactions with polymer-associated radicals formed during the carbonization process. Then, using this improved force field, we performed atomistic-scale simulations of the initial stage of the carbonization process for the considered polymers. On the basis of our simulation data, the molecular pathways for the formation of low-molecular-weight gas species and all-carbon ring formation were determined. We also examined the possible alignment of the developed all-carbon 6-membered ring clusters, which is crucial for the further graphitic structure evolution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Assessing direct and indirect emissions of greenhouse gases in road transportation, taking into account the role of uncertainty in the emissions inventory

Highlights: • The use-chain model implemented in this paper is effective in minimizing uncertainty. • Data integration is important to reduce uncertainty. • An innovative metric, Emission Value at Risk, was used to adjust uncertainty values. • Indirect impacts of economic activities change the estimate of GHG emissions. - Abstract: Greenhouse gas (GHG) concentration in the atmosphere has increased since the beginning of the industrial era, with dramatic effects on climate change. Transportation is one of the main sources of GHGs, with more than two-thirds of transport-related GHG emissions attributable to road vehicles. Any policy that aims to reduce GHG emissions needs robust measuring methods that guarantee the quality and reliability of primary data and estimates. However, these estimates are subject to uncertainty, both at the stage of compiling accounting tables and at the stage of using this information to formulate a specific policy question. This paper considers how to reduce uncertainty in estimating GHG emissions from road transportation, with specific reference to a regional emissions inventory in Italy. We propose the application of a use-chain model that can tackle uncertainty in measuring GHG emissions by enhancing the quality of the emissions data registry in the inventory. This new metric, which we call emission value at risk (VaR), draws from methodologies and concepts employed in the insurance and financial sectors. Moreover, additional assessments are performed, integrating the inventory data with those available in the regional energy balance and disaggregated sectoral economic dataset. The results show that a sound accounting method enables uncertainty in emission data to be taken into account, thus improving the design of appropriate strategies to reduce GHG emissions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Transfer learning-based soybean LAI estimations by integrating PROSAIL, UAV, and PlanetScope imagery

Accurate Leaf Area Index (LAI) estimations at the soybean plot scale is achievable using high-resolution Unmanned Aerial Vehicle (UAV) imagery and field measurement samples. However, the limited coverage of UAV flights restricts large-scale remote sensing monitoring in expansive soybean fields. This study leverages the broad coverage and 3-m resolution of PlanetScope satellite imagery to extend LAI prediction from UAV to satellite scales through transfer learning, using UAV-scale LAI estimates as a benchmark to validate cross-scale consistency. To address this challenge, this study proposed the LAI-TransNet, a two-stage transfer learning framework designed for precise and scalable soybean LAI prediction across large areas, demonstrating its effectiveness in cross-scale monitoring. In Stage 1, a UAV-scale benchmark is established using PROSAIL-simulated UAV reflectance data (UAV-Sim) and field-measured soybean LAI. Traditional machine learning, deep learning, and transfer learning models are trained on a hybrid UAV-Sim and field-measured dataset (UAV-Sim_Measured), with the transfer learning model CNN-TL, fine-tuned using pre-trained weights derived from UAV-Sim, achieving the highest accuracy (R 2 = 0.81, RMSE = 0.64 m 2 /m 2 , rRMSE = 11.5 %). In Stage 2, LAI-TransNet is developed by fine-tuning the CNN-TL model on PlanetScope simulated data (PS-Sim), preprocessed via cross-domain mapping to align UAV and satellite spectral features. Real PlanetScope imagery is corrected for reflectance consistency with reference to UAV imagery spectral profiles. LAI-TransNet outperforms other deep learning models trained directly on PS-Sim (R 2 = 0.69 vs. 0.60–0.63), ensuring robust cross-scale consistency. In conclusion, by bridging UAV and satellite scales, LAI-TransNet enables large-scale soybean LAI monitoring, enhancing precision agriculture management through improved monitoring with the PlanetScope imagery.

Leaf area index (LAI)↗
NASA NTRS1991

Three-dimensional flow calculations inside SSME GGGT first stage blade rows

A numerical analysis of the first stage of the Space Shuttle Main Engine (SSME) GGGT was conducted using a 3-D Reynolds averaged Navier-Stokes flow solver. This turbine stage was designed to improve both aerodynamic efficiency and durability. The blade has an unconventional shape with a large blade thickness. No experimental data is available to verify the computational results. The objective of the current study is to analyze this turbine blade stage with a well established Navier-Stokes computational method in order to determine if the turbine is operating in the subsonic flow regime and if these are any significant separated flow regions. The stage was analyzed in a steady state flow condition. The inlet vane was analyzed with the flow conditions from the axisymmetric entire stage solution. The viscous flow solution of the first vane is used as the inlet flow condition for the rotor.

Hah, Chunill↗
DOE OSTI2012

Randomized Control Trial: Evaluating Aluminum-Based Antiperspirant Use, Axilla Skin Toxicity, and Reported Quality of Life in Women Receiving External Beam Radiotherapy for Treatment of Stage 0, I, and II Breast Cancer

Purpose: Standard skin care instructions regarding the use of antiperspirants during radiotherapy to the breast varies across North America. Women have articulated that when instructed to not use antiperspirant, the potential for body odor is distressing. Historical practices and individual opinions have often guided practice in this field. The present study had 2 purposes. To evaluate whether the use of aluminum-based antiperspirant while receiving external beam radiotherapy for stage 0, I, or II breast cancer will increase axilla skin toxicity and to evaluate whether the use of antiperspirant during external beam radiotherapy improves quality of life. Methods: A total of 198 participants were randomized to either the experimental group (antiperspirant) or control group (standard care-wash only). The skin reactions in both groups were measured weekly and 2 weeks after treatment using the National Cancer Institute Common Toxicity Criteria Adverse Events, version 3, toxicity grading criteria. Both groups completed the Functional Assessment for Chronic Illness Therapy's questionnaire for the breast population quality of life assessment tool, with additional questions evaluating the effect of underarm antiperspirant use on quality of life before treatment, immediately after treatment, and 2 weeks after treatment during the study. Results: The skin reaction data were analyzed using the generalized estimating equation. No statistically significant difference was seen in the skin reaction between the 2 groups over time. The quality of life data also revealed no statistically significant difference between the 2 groups over time. Conclusions: Data analysis indicates that using antiperspirant routinely during external beam radiotherapy for Stage 0, I, or II breast cancer does not affect the intensity of the skin reaction or the self-reported quality of life. This evidence supports that in this particular population, there is no purpose to restrict these women from using antiperspirants during their treatment, and the decision to use an antiperspirant or not in this setting should be left to the discretion of the patient.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2020

Synergistic ground and orbital observations of iron oxides on Mt. Sharp and Vera Rubin ridge

Visible/short-wave infrared spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) show absorptions attributed to hematite at Vera Rubin ridge (VRR), a topographic feature on northwest Mt. Sharp. The goals of this study are to determine why absorptions caused by ferric iron are strongly visible from orbit at VRR, and to improve interpretation of CRISM data throughout lower Mt. Sharp. These goals are achieved by analyzing coordinated CRISM and in situ spectral data along the Curiosity Mars rover’s traverse. VRR bedrock within areas that have the deepest ferric absorptions in CRISM data also have the deepest ferric absorptions measured in situ. This suggests strong ferric absorptions are visible from orbit at VRR because of the unique spectral properties of VRR bedrock. Dust and mixing with basaltic sand additionally inhibit the ability to measure ferric absorptions in bedrock stratigraphically below VRR from orbit. There are two implications of these findings: (1) Ferric absorptions in CRISM data initially dismissed as noise could be real, and ferric phases are more widespread in lower Mt. Sharp than previously reported, (2) Patches with the deepest ferric absorptions in CRISM data are, like VRR, reflective of deeper absorptions in the bedrock. One model to explain this spectral variability is late-stage diagenetic fluids that changed the grain size of ferric phases, deepening absorptions. Curiosity’s experience highlights the strengths of using CRISM data for spectral absorptions and associated mineral detections, and the caveats in using these data for geologic interpretations and strategic path planning tools.

58 GEOSCIENCES↗
DOE OSTI2018

Automatic identification and classification of Palomar Transient Factory astrophysical objects in GLADE

Palomar Transient Factory (PTF) is a comprehensive detection system for the identification and classification of transient astrophysical objects. In this paper, we make two significant contributions to the PTF pipeline. First, we present an experimental study that evaluates a novel implementation of the real-time classifier in GLADE - a parallel data processing system that combines the efficiency of a database with the extensibility of map-reduce. We show how each stage in the classifier maps optimally into GLADE tasks by taking advantage of the unique features of the system - range-based data partitioning, columnar storage, multi-query execution, and in-database support for complex aggregate computation. Second, we introduce a novel parallel similarity join algorithm for advanced transient classification. In conclusion, we implement this algorithm in GLADE and execute it on a massive supercomputer with more than 3,000 threads, achieving more than three orders of magnitude improvement over the PostgreSQL solution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Dataset of ultralow temperature refrigeration for COVID 19 vaccine distribution solution

Abstract Most COVID-19 vaccines require temperature control for transportation and storage. Two types of vaccine have been developed by manufacturers (Pfizer and Moderna). Both vaccines are based on mRNA and lipid nanoparticles requiring low temperature storage. The Pfizer vaccine requires ultra-low temperature storage (−80 °C to −60 °C), while the Moderna vaccine requires −30 °C storage. However, the last stage of distribution is quite challenging, especially for rural or suburban areas, where local towns, pharmacy chains and hospitals may not have the infrastructure required to store the vaccine at the required temperature. In addition, there is limited data available to address ancillary challenges of the distribution framework for both transportation and storage stages, including safety concerns due to human exposure to large amounts of CO 2 from dry-ice sublimation, issues due to the pressure increase caused by dry-ice sublimation, and the potential issue caused by non-uniform cryogenic temperatures. As such, there is a need for test dataset to assist the development of a quick, effective, secure, and safe solution to mitigate the challenges faced by vaccine distribution logistics.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

A Two-Stage Kalman Filter Approach for Robust and Real-Time Power System State Estimation

As electricity demand continues to grow and renewable energy increases its penetration in the power grid, realtime state estimation becomes essential for system monitoring and control. Recent development in phasor technology makes it possible with high-speed time-synchronized data provided by Phasor Measurement Units (PMU). In this paper we present a two-stage Kalman filter approach to estimate the static state of voltage magnitudes and phase angles, as well as the dynamic state of generator rotor angles and speeds. Kalman filters achieve optimal performance only when the system noise characteristics have known statistical properties (zero-mean, Gaussian, and spectrally white). However in practice the process and measurement noise models are usually difficult to obtain. Thus we have developed the Adaptive Kalman Filter with Inflatable Noise Variances (AKF with InNoVa), an algorithm that can efficiently identify and reduce the impact of incorrect system modeling and/or erroneous measurements. In stage one, we estimate the static state from raw PMU measurements using the AKF with InNoVa; then in stage two, the estimated static state is fed into an extended Kalman filter to estimate the dynamic state. Simulations demonstrate its robustness to sudden changes of system dynamics and erroneous measurements.

Zhang, Jinghe↗
DOE OSTI2012

Regulation of ITAM adaptor molecules and their receptors by inhibition of calcineurin-NFAT signalling during late stage osteoclast differentiation

Highlights: Black-Right-Pointing-Pointer Calcineurin/NFAT inhibitors FK506 and VIVIT treated human PBMC derived osteoclasts in vitro. Black-Right-Pointing-Pointer Differential regulation of ITAM receptors and adaptor molecules by calcineurin/NFAT inhibitors. Black-Right-Pointing-Pointer FK506 and VIVIT suppress ITAM factors during late phase osteoclast differentiation. -- Abstract: Osteoclasts are specialised bone resorptive cells responsible for both physiological and pathological bone loss. Osteoclast differentiation and activity is dependent upon receptor activator NF-kappa-B ligand (RANKL) interacting with its receptor RANK to induce the transcription factor, nuclear factor of activated T-cells, cytoplasmic, calcineurin-dependent 1 (NFATc1). The immunoreceptor tyrosine-based activation motif (ITAM)-dependent pathway has been identified as a co-stimulatory pathway in osteoclasts. Osteoclast-associated receptor (OSCAR) and triggering receptor expressed in myeloid cells (TREM2) are essential receptors that pair with adaptor molecules Fc receptor common gamma chain (FcR{gamma}) and DNAX-activating protein 12 kDa (DAP12) respectively to induce calcium signalling. Treatment with calcineurin-NFAT inhibitors, Tacrolimus (FK506) and the 11R-VIVIT (VIVIT) peptide, reduces NFATc1 expression consistent with a reduction in osteoclast differentiation and activity. This study aimed to investigate the effects of inhibiting calcineurin-NFAT signalling on the expression of ITAM factors and late stage osteoclast genes including cathepsin K (CathK), Beta 3 integrin ({beta}3) and Annexin VIII (AnnVIII). Human peripheral blood mononuclear cells (PBMCs) were differentiated with RANKL and macrophage-colony stimulating factor (M-CSF) over 10 days in the presence or absence of FK506 or VIVIT. Osteoclast formation (as assessed by tartrate resistant acid phosphatase (TRAP)) and activity (assessed by dentine pit resorption) were significantly reduced with treatment. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis demonstrated that FK506 treatment significantly (p < 0.05) reduced the expression of NFATc1, CathK, OSCAR, FcR{gamma}, TREM2 and DAP12 during the terminal stage of osteoclast formation. VIVIT treatment significantly (p < 0.05) decreased CathK, OSCAR, FcR{gamma}, and AnnVIII, gene expression. This data suggest FK506 and VIVIT act differently in targeting the calcineurin-NFAT signalling cascade to suppress key mediators of the ITAM pathway during late stage osteoclast differentiation and this is associated with a reduction in both osteoclast differentiation and activity.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1995

A seismic data compression system using subband coding

This article presents a study of seismic data compression techniques and a compression algorithm based on subband coding. The algorithm includes three stages: a decorrelation stage, a quantization stage that introduces a controlled amount of distortion to allow for high compression ratios, and a lossless entropy coding stage based on a simple but efficient arithmetic coding method. Subband coding methods are particularly suited to the decorrelation of nonstationary processes such as seismic events. Adaptivity to the nonstationary behavior of the waveform is achieved by dividing the data into separate blocks that are encoded separately with an adaptive arithmetic encoder. This is done with high efficiency due to the low overhead introduced by the arithmetic encoder in specifying its parameters. The technique could be used as a progressive transmission system, where successive refinements of the data can be requested by the user. This allows seismologists to first examine a coarse version of waveforms with minimal usage of the channel and then decide where refinements are required. Rate-distortion performance results are presented and comparisons are made with two block transform methods.

Kiely, A. B.↗
DOE OSTI2017

The JCMT Transient Survey: Data Reduction and Calibration Methods

Though there has been a significant amount of work investigating the early stages of low-mass star formation in recent years, the evolution of the mass assembly rate onto the central protostar remains largely unconstrained. Examining in depth the variation in this rate is critical to understanding the physics of star formation. Instabilities in the outer and inner circumstellar disk can lead to episodic outbursts. Observing these brightness variations at infrared or submillimeter wavelengths constrains the current accretion models. The JCMT Transient Survey is a three-year project dedicated to studying the continuum variability of deeply embedded protostars in eight nearby star-forming regions at a one-month cadence. We use the SCUBA-2 instrument to simultaneously observe these regions at wavelengths of 450 and 850 μ m. In this paper, we present the data reduction techniques, image alignment procedures, and relative flux calibration methods for 850 μ m data. We compare the properties and locations of bright, compact emission sources fitted with Gaussians over time. Doing so, we achieve a spatial alignment of better than 1″ between the repeated observations and an uncertainty of 2%–3% in the relative peak brightness of significant, localized emission. This combination of imaging performance is unprecedented in ground-based, single-dish submillimeter observations. Finally, we identify a few sources that show possible and confirmed brightness variations. These sources will be closely monitored and presented in further detail in additional studies throughout the duration of the survey.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRSDate not supplied

NASA’s Moon to Mars (M2M) Transit Habitat (TH) Refinement Point of Departure (PoD) Design

As NASA prepares for the next human footsteps on the lunar surface, the Agency is already looking ahead to systems that will enable a sustained human presence on the lunar surface and mission to Mars, including a lunar Surface Habitat and Mars Transit Habitat (TH). This paper describes the latest NASA government reference design for the TH and how it will support NASA's Moon to Mars human exploration architecture. First, it will serve as a test and demonstration platform in lunar orbit, demonstrating capabilities required for long-duration microgravity human spaceflight as part of the lunar-Mars analog missions. Then, the TH will also serve as a major Mars habitation exploration element to support the crew during their transit from the lunar orbit to Mars and returning them safely to lunar orbit. This paper will cover several considerations contributing to the latest habitat design refinement, including data on the TH's concept of operations, system functional definition, subsystem assumptions, notional interior layouts, a detailed mass and volume breakdown, and trade studies and analyses required to close identified technology/ development/architecture gaps. In addition to a technical description of the TH, this paper describes how the current TH government reference design will achieve many of the current lunar and Mars mission goals. Additionally, there are many assumed technological advances needed to support the prescribed mission phases leading up to the crewed mission to Mars in the late 2030s. The paper will describe many of the TH systems requiring further technology development and identify architectural solutions to achieve these mass, reliability, autonomy, and crew health targets. As a whole, the data in the paper shows that a TH meeting the 43 metric tons launch mass/trans-Mars injection burn limits specified by the Evolvable Mars Campaign is achievable near the desired timeframe with moderate strategic investments including maintainable life support systems, re-purposable structures and packaging, and lightweight exercise modalities. It also identifies operational and technological options to reduce this mass to less than 41 metric tons, including staging of launch structure/packaging and alternate structural materials. The resulting design detail and data contained in this paper are intended to help teams across NASA and potential commercial, academic, or international partners understand the current performance targets of the Transit Habitat and vehicle interface considerations imposed by the latest Moon to Mars mission scope.

Habitation Systems↗
NASA NTRS1994

Comparison of predicted and actual orbital lifetimes for the SEDS-2 mission

This paper documents a series of estimates of the orbital lifetime of the SEDS-2 flight configuration made prior to the mission. These estimates were made with program LTIME, which has been in use at MSFC for a number of years. Because of the unusual configuration of upper-stage/tether/endmass flown on this mission, and the type of assumptions and inputs used in LTIME, the effective area used in the drag calculation had to be estimated in an unusual way. The final pre-flight predicted lifetime was 28.35 days. In the actual flight, the tether was cut approximately 5 days into the mission. The instrumented endmass plus about 12 km of tether rapidly reentered the atmosphere, and the Delta II Second Stage plus the remaining 8 km of tether reentered on mission day 60. Tracking data was used to reconstruct reentry sequences for the two parts of the configuration after the cut. The predicted lifetimes for the endmass plus tether-fragment were in the range of 0.2 to 2.8 days, depending on the perigee altitudes assumed. The predicted lifetime of the upper-stage plus tether was 56.4 days, which corresponds to reentry on mission day 61, in good agreement with the actual reentry on day 60.

Evans, Steven W.↗
DOE OSTI2023

Validation of semi-analytical, semi-empirical covariance matrices for two-point correlation function for early DESI data

ABSTRACT We present an extended validation of semi-analytical, semi-empirical covariance matrices for the two-point correlation function (2PCF) on simulated catalogs representative of luminous red galaxies (LRGs) data collected during the initial 2 months of operations of the Stage-IV ground-based Dark Energy Spectroscopic Instrument (DESI). We run the pipeline on multiple effective Zel’dovich (EZ) mock galaxy catalogs with the corresponding cuts applied and compare the results with the mock sample covariance to assess the accuracy and its fluctuations. We propose an extension of the previously developed formalism for catalogs processed with standard reconstruction algorithms. We consider methods for comparing covariance matrices in detail, highlighting their interpretation and statistical properties caused by sample variance, in particular, non-trivial expectation values of certain metrics even when the external covariance estimate is perfect. With improved mocks and validation techniques, we confirm a good agreement between our predictions and sample covariance. This allows one to generate covariance matrices for comparable data sets without the need to create numerous mock galaxy catalogs with matching clustering, only requiring 2PCF measurements from the data itself. The code used in this paper is publicly available at https://github.com/oliverphilcox/RascalC.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Efficient Lossy Compression for Scientific Data Based on Pointwise Relative Error Bound

An effective data compressor is becoming increasingly critical to today's scientific research, and many lossy compressors are developed in the context of absolute error bounds. Based on physical/chemical definitions of simulation fields or multiresolution demand, however, many scientific applications need to compress the data with a pointwise relative error bound (i.e., the smaller the data value, the smaller the compression error to tolerate). To this end, we propose two optimized lossy compression strategies under a state-of-the-art three-staged compression framework (prediction + quantization + entropy-encoding). The first strategy (called block-based strategy) splits the data set into many small blocks and computes an absolute error bound for each block, so it is particularly suitable for the data with relatively high consecutiveness in space. The second strategy (called multi-threshold-based strategy) splits the whole value range into multiple groups with exponentially increasing thresholds and performs the compression in each group separately, which is particularly suitable for the data with a relatively large value range and spiky value changes. We implement the two strategies rigorously and evaluate them comprehensively by using two scientific applications which both require lossy compression with point-wise relative error bound. Experiments show that the two strategies exhibit the best compression qualities on different types of data sets respectively. In conclusion, the compression ratio of our lossy compressor is higher than that of other state-of-the-art compressors by 17.2-618 percent on the climate simulation data and 30-210 percent on the N-body simulation data, with the same relative error bound and without degradation of the overall visualization effect of the entire data.

97 MATHEMATICS AND COMPUTING↗