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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Comparative Study of Additively Manufactured Inconel 625 In the As-Built and Heat-Treated Condition

This study was conducted to characterize the microstructure and mechanical properties of Inconel 625 manufactured with laser powder bed fusion (L-PBF), electron beam melting (EBM), wire arc additive manufacturing (WAAM), electron beam directed energy deposition (EB-DED), laser powder directed energy deposition (LP-DED), and laser wire directed energy deposition (LW-DED) in both the as built and heat-treated condition. The heat treatment in this study included stress relieving, hot isostatic pressure (HIP), and solution treatment. The effects of the heat treatment on the grain widths and hardness of the alloy will be observed across the technologies before and after heat-treatment. At the end of this study there will be a comparative analysis of the alloy Inconel 625 across the six technologies.

V Luna↗
NASA NTRS2005

Chemical colloids versus biological colloids: a comparative study for the elucidation of the mechanism of protein fiber formation

Fiber formation from murine serum amyloid A1 (SAA) was compared to the linear aggregation and fiber formation of colloidal gold particles. Here we report the similarities of these processes. Upon incubation with acetic acid, SAA misfolds and adopts a new conformation, which we termed saa. saa apparently is less soluble than SAA in aqueous solution; it aggregates and forms nucleation units and then fibers. The fibers appear as a string of the nucleation units. Additionally, an external electric field promotes saa fiber formation. These properties of saa are reminiscent of colloidal gold formation from gold ions and one-dimensional aggregation of the gold colloids. Colloidal gold particles were also found to be capable of aggregating one-dimensionally under an electric field or in the presence of polylysine. These gold fibers resembled in structure that of saa fibers. In summary, protein aggregation and formation of fibers appear to follow the generalized principles derived in colloidal science for the aggregation of atoms and molecules, including polymers such as polypeptides. The analysis of colloidal gold formation and of one-dimensional aggregation provides a simple model system for the elucidation of some aspects of protein fiber formation.

Colloids↗
DOE OSTI2022

First-principles comparative study of Cr migration in O3 and O/P hybrid-phased NaCrO 2

In layered Na transition-metal (TM) oxides, TM migration usually occurs at highly charged states and severely deteriorates the capacity and reversibility. Meanwhile, the formation of hybrid phases with the intergrowth of octahedral (O-type) and prismatic (P-type) Na layers also takes place at highly charged states. These hybrid phases are often more stable than simple O3 or P3 stackings. However, little is known about the mechanism and impact of TM migration in these hybrid phases. In this work, a comparative first-principles study is performed to understand the connections between structural changes and Cr migration in layered O3 and hybrid-phased NaCrO 2 . After Cr migration, the hybrid-phased NaCrO 2 suffers from greater layer shrinkage than the O3 phase. Three factors affect the Cr migration energy E mig : the Na concentration, local 3D configurations, and 2D in-plane geometries. Low Na concentrations and certain local 3D configurations facilitate the Cr migration. The Cr migration barriers in both O3 and hybrid-phased NaCrO 2 are positively correlated with the Cr E mig . The Cr migration in 17 doped O3 and hybrid-phased NaCrO 2 is surveyed. In these doped NaCrO 2 , a more uniform distribution of the Cr–O bond lengths usually suggests suppressed Cr migration. Optimal dopants for suppressing Cr migration are identified by considering E mig for both Cr and the dopant. Finally, our comparative study on Cr migration in O3 and hybrid-phased NaCrO 2 reveals the significant role of hybrid-phased structures in the development of layered cathode materials.

36 MATERIALS SCIENCE↗
NASA NTRS1971

Globular-cluster stars - Results of theoretical evolution and pulsation studies compared with the observations.

Survey of recently published studies on globular clusters, and comparison of stellar evolution and pulsation theory with reported observations. The theory of stellar evolution is shown to be capable of describing, in principle, the behavior of a star through all quasi-static stages. Yet, as might be expected, estimates of bulk properties obtained by comparing observations with results of pulsation and stellar atmosphere theory differ somewhat from estimates of these same properties obtained by comparing observations with results of evolution theory. A description is given of how such estimates are obtained, and suggestions are offered as to where the weak points in each theory may lie.

Iben, I., Jr.↗
DOE OSTI2023

Do people spend travel time the way they think they would? a comparative study of generic and trip-specific travel time allocation using hybrid multiple discrete continuous (MDC) framework

Unlike driving alone, public transportation allows one to engage in extraneous activities while traveling – often referred to as travel-based multitasking. Research involving travel-based multitasking often relies on either generic (i.e. not related to an actual trip) or revealed (i.e. related to an executed trip) data. The data collected for this study provided a unique opportunity to compare the generic and trip-specific preferences while traveling on public transportation. To this end, the study develops two integrated choice and latent variable models with multiple discrete-continuous (MDC) kernels to simultaneously model the activity selection and the time allocation for generic and trip-specific data, respectively. According to the results the trip-specific data could identify more nuances in the travel-based multitasking behavior than the generic data. Finally, the heterogeneity identified by the developed models will be helpful for the transit operators in providing appropriate facilities (e.g. internet access, reading lights) along various transit corridors.

99 GENERAL AND MISCELLANEOUS↗
NASA NTRS1982

The lunar regolith - Comparative studies of the Apollo and Luna sites. Chemistry of soils from Apollo 17, Luna 16, 20, and 24

The present investigation represents an extension of a comparative regolith study reported by Labotka et al. (1980) to the Apollo 17 site and to the east limb of the moon (Luna 16, 20, and 24 sites). Chemical systematics are considered, taking into account major and minor element characteristics, and large ion-lithophile patterns (K, REE, and Th). Attention is also given to chemical mixing calculations and the significance of the fine fraction. It is found that the chemistries of 1000-90, 90-20, and 20-10 micrometer size fractions are very similar to each other but quite different from the 'less than 10 micrometer' fine fractions. The 'less than 10 micrometer' fine fractions, which comprise about 5 to 20% of the bulk soils, are consistently more feldspathic and enriched in LIL-rich material relative to the coarse fractions in all soils. The KREEP type is different at each site and is largely derived locally.

Laul, J. C.↗
NASA NTRS2000

A Simulation Study Comparing Incineration and Composting in a Mars-Based Advanced Life Support System

The objective of this study is to compare incineration and composting in a Mars-based advanced life support (ALS) system. The variables explored include waste pre-processing requirements, reactor sizing and buffer capacities. The study incorporates detailed mathematical models of biomass production and waste processing into an existing dynamic ALS system model. The ALS system and incineration models (written in MATLAB/SIMULINK(c)) were developed at the NASA Ames Research Center. The composting process is modeled using first order kinetics, with different degradation rates for individual waste components (carbohydrates, proteins, fats, cellulose and lignin). The biomass waste streams are generated using modified "Eneray Cascade" crop models, which use light- and dark-cycle temperatures, irradiance, photoperiod, [CO2], planting density, and relative humidity as model inputs. The study also includes an evaluation of equivalent system mass (ESM).

Hogan, John↗
DOE OSTI2025

Solving disorder in (3D) real space: a comparative study of the three-dimensional difference pair distribution function and atomic resolution holography reconstructions

The quantitative analysis of local ordering principles in disordered crystalline systems has gained much attention over the past few years, as it is often considered crucial for optimizing material functionality. This development has been driven by significant advancements in computational and experimental methods, which have led to the establishment and widespread use of various analytical techniques. In this study, we perform model calculations to compare the effectiveness of atomic resolution holography and three-dimensional difference pair distribution function analysis (3D-ΔPDF). Using Cu 3 Au as a model system, we demonstrate an approach to derive local order parameters quantitatively and show that both techniques are well suited to quantifying chemical short-range order correlations and local bond-distance variations. By evaluating the strengths and limitations of both techniques, we advocate for their combined use to solve complex short-range order problems accurately.

3D-ΔPDF↗
NASA NTRS2002

Near-infrared diode laser based spectroscopic detection of ammonia: a comparative study of photoacoustic and direct optical absorption methods

A photoacoustic spectroscopic (PAS) and a direct optical absorption spectroscopic (OAS) gas sensor, both using continuous-wave room-temperature diode lasers operating at 1531.8 nm, were compared on the basis of ammonia detection. Excellent linear correlation between the detector signals of the two systems was found. Although the physical properties and the mode of operation of both sensors were significantly different, their performances were found to be remarkably similar, with a sub-ppm level minimum detectable concentration of ammonia and a fast response time in the range of a few minutes.

NASA Discipline Life Sciences Technologies↗
NASA NTRS1982

A comparative study of atmospheric density models in the context of definitive and predictive earth satellite orbit determination

The results of a comparative orbit determination study of four global atmospheric density models (modified Harris-Priester, Jacchia-Roberts, Mass Spectrometer/Incoherent Scatter (MSIS), and Simple Exponential Model (SEM)) are presented. Utilizing these models, definitive orbit determination consistency and accuracy are evaluated using the maximum position differences that occur during 6-hour overlap periods between ephemerides generated from 30-hour data arcs. Propagated ephemerides are compared with definitive orbit solutions to evaluate predictive accuracy. The results indicate that, for satellites above 300 kilometers, all four atmospheric density models produce comparable orbit determination accuracies when an atmospheric drag scaling factor and the satellite state vector are estimated in the orbit determination process.

Shanklin, R. E., Jr.↗
DOE OSTI2017

Why do general circulation models overestimate the aerosol cloud lifetime effect? A case study comparing CAM5 and a CRM

Abstract. Observation-based studies have shown that the aerosol cloud lifetime effect or the increase of cloud liquid water path (LWP) with increased aerosol loading may have been overestimated in climate models. Here, we simulate shallow warm clouds on 27 May 2011 at the southern Great Plains (SGP) measurement site established by the Department of Energy's (DOE) Atmospheric Radiation Measurement (ARM) program using a single-column version of a global climate model (Community Atmosphere Model or CAM) and a cloud resolving model (CRM). The LWP simulated by CAM increases substantially with aerosol loading while that in the CRM does not. The increase of LWP in CAM is caused by a large decrease of the autoconversion rate when cloud droplet number increases. In the CRM, the autoconversion rate is also reduced, but this is offset or even outweighed by the increased evaporation of cloud droplets near the cloud top, resulting in an overall decrease in LWP. Our results suggest that climate models need to include the dependence of cloud top growth and the evaporation/condensation process on cloud droplet number concentrations.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1972

A comparative study of stability methods for flexible satellites.

This paper compares three approaches to the stability of hybrid dynamical systems, all three methods being based on the Liapunov direct method. The first method uses testing density functions, whereas the second involves defining certain integral coordinates. Both the method using testing density functions and the method of integral coordinates lead to closed-form stability criteria in terms of the system parameters. Criteria obtained using the method of integral coordinates are in general less restrictive than those derived by the method using testing density functions. On the other hand, the latter method is easier to apply and requires less work than the former. The third method is the standard modal analysis. The modal analysis generally yields more involved criteria, depending on the number of modes used to represent the elastic displacements. As an application, the attitude stability of an earth-pointing satellite with multi-elastic domains is investigated.

Meirovitch, L.↗
DOE OSTI2019

SOI-MEMS Bulk Piezoresistive Displacement Sensor: A Comparative Study of Readout Circuits

Performance of several readout circuits, when applied to a MEMS-based bulk piezoresistive displacement sensor is compared in this study. The sensor comprises a pair of tilted clamped-guided silicon beams whose bulk piezoresistivity is used for displacement sensing. Wheatstone half-bridge, constant-voltage, and constant-current circuits are implemented to measure resistance changes of this sensor. We report full characterization of the sensor with these circuits and explore the sensor’s important characteristics such as linearity, bandwidth, and noise. The results reveal that the constant-current circuit provides the highest sensitivity at equal-power bias condition. Here, we find that the resolution of the sensor is degraded from 1.6 nm with the Wheatstone half-bridge and constant-voltage circuits to about 4.2 nm with the constant-current configuration. In the frequency domain, the sensor captures the full dynamics of the MEMS nanopositioner up to 20 kHz with all readout circuits.

42 ENGINEERING↗
DOE OSTI2015

SU-C-207-05: A Comparative Study of Noise-Reduction Algorithms for Low-Dose Cone-Beam Computed Tomography

Purpose: To study different noise-reduction algorithms and to improve the image quality of low dose cone beam CT for patient positioning in radiation therapy. Methods: In low-dose cone-beam CT, the reconstructed image is contaminated with excessive quantum noise. In this study, three well-developed noise reduction algorithms namely, a) penalized weighted least square (PWLS) method, b) split-Bregman total variation (TV) method, and c) compressed sensing (CS) method were studied and applied to the images of a computer–simulated “Shepp-Logan” phantom and a physical CATPHAN phantom. Up to 20% additive Gaussian noise was added to the Shepp-Logan phantom. The CATPHAN phantom was scanned by a Varian OBI system with 100 kVp, 4 ms and 20 mA. For comparing the performance of these algorithms, peak signal-to-noise ratio (PSNR) of the denoised images was computed. Results: The algorithms were shown to have the potential in reducing the noise level for low-dose CBCT images. For Shepp-Logan phantom, an improvement of PSNR of 2 dB, 3.1 dB and 4 dB was observed using PWLS, TV and CS respectively, while for CATPHAN, the improvement was 1.2 dB, 1.8 dB and 2.1 dB, respectively. Conclusion: Penalized weighted least square, total variation and compressed sensing methods were studied and compared for reducing the noise on a simulated phantom and a physical phantom scanned by low-dose CBCT. The techniques have shown promising results for noise reduction in terms of PSNR improvement. However, reducing the noise without compromising the smoothness and resolution of the image needs more extensive research.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Comparing identified and statistically significant lipids and polar metabolites in 15-year old serum and dried blood spot samples for longitudinal studies: Comparing lipids and metabolites in serum and DBS samples

The use of dried blood spots (DBS) has many advantages over traditional plasma and serum samples such as smaller blood volume required, storage at room temperature, and ability for sampling in remote locations. However, understanding the robustness of different analytes in DBS samples is essential, especially in older samples collected for longitudinal studies. Here we analyzed DBS samples collected in 2000-2001 and stored at room temperature and compared them to matched serum samples stored at -80°C to determine if they could be effectively used as specific time points in a longitudinal study following metabolic disease. Four hundred small molecules were identified in both the serum and DBS samples using gas chromatograph-mass spectrometry (GC-MS), liquid chromatography-MS (LC-MS) and LC-ion mobility spectrometry-MS (LC-IMS-MS). The identified polar metabolites overlapped well between the sample types, though only one statistically significant polar metabolite in a case-control study was conserved, indicating degradation occurs in the DBS samples affecting quantitation. Differences in the lipid identifications indicated that some oxidation occurs in the DBS samples. However, thirty-six statistically significant lipids correlated in both sample types indicating that lipid quantitation was more stable across the sample types.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

National Population-Based Study Comparing Treatment-Related Toxicity in Men Who Received Intensity Modulated Versus 3-Dimensional Conformal Radical Radiation Therapy for Prostate Cancer

To compare, in a national population-based study, severe genitourinary (GU) and gastrointestinal (GI) toxicity in patients with prostate cancer who were treated with radical intensity modulated radiation therapy (IMRT) or 3-dimensional conformal radiation therapy (3D-CRT).

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

A Comparative Study of Single-pulse and Double-pulse Laser-Induced Breakdown Spectroscopy with Uranium-containing Samples

Laser-induced breakdown spectroscopy (LIBS) holds potential advantages in special nuclear material (SNM) sensing and nuclear forensics which require rapid analysis, minimal sample preparation and stand-off distance capability. SNM, such as U, however, result in crowded emission spectra with LIBS, and characteristic emission lines are challenging to discern. It is well-known that double-pulse LIBS (DPLIBS) improves the signal intensity for analytes over conventional single-pulse LIBS (SPLIBS). This study investigates U signal in a glass matrix using DPLIBS and compares to signal features obtained using SPLIBS. DPLIBS involves sequential firing of 1.06 µm Nd:YAG pre-pulse and 10.6 µm TEA CO2 heating pulse in near collinear geometry. Optimization of experimental parameters including inter-pulse delay and energy follows identification of characteristic lines and signals for bulk analyte Ca and minor constituent analyte U for both DPLIBS and SPLIBS. Spatial and temporal coupling of the two pulses in the proposed DPLIBS technique yields improvements in analytical merits with negligible further damage to the sample compared to SPLIBS. Subsequently, the study discusses optimum plasma emission conditions of U lines and relative figures of merit in both SPLIBS and DPLIBS. Investigation into plasma characteristics also addresses plausible mechanisms related to observed U analyte signal variation between SPLIBS and DPLIBS.

Skrodzki, P. J.↗