Results for “sampling methods” — Page 42

NASA NTRS2016

The Effects of Experimental Conditions on the Refractive Index and Density of Low-Temperature Ices: Solid Carbon Dioxide

We present the first study on the effects of the deposition technique on the measurements of the visible refractive index and the density of a low-temperature ice using solid carbon dioxide (CO2) at 14-70 K as an example. While our measurements generally agree with previous studies that show a dependence of index and density on temperature below 50 K, we also find that the measured values depend on the method used to create each sample. Below 50 K, we find that the refractive index varied by as much as 4% and the density by as much as 16% at a single temperature depending on the deposition method. We also show that the Lorentz-Lorenz approximation is valid for solid CO2 across the full 14-70 K temperature range, regardless of the deposition method used. Since the refractive index and density are important in calculations of optical constants and infrared (IR) band strengths of materials, our results suggest that the deposition method must be considered in cases where nvis and ρ are not measured in the same experimental setup where the IR spectral measurements are made.

planetary nebulae↗

NASA NTRSDate not supplied

Reduced-order Modeling for Spacecraft Thermal-structural Applications

Leveraging the speed of reduced-order models (ROMs), thermal analysis teams have previously had access to rapid optimization, sensitivity studies, rapid model correlation, and uncertainty quantification, to name a few. An advantage of the developed approach is its relative robustness, which enabled expansion to include structural models in addition to thermal models leading to both rapid thermal-structural and rapid structural-only analyses. This method was tested for a sample thermal-structural application and showed good performance. It was then applied to a complex NASA mission and showed how ROMs could be used to quickly evaluate system uncertainties. Finally, these methods were applied to a structural-only application and used to better optimize and understand the structural design.

Derek Hengeveld↗

NASA NTRS2009

Modulation Based on Probability Density Functions

A proposed method of modulating a sinusoidal carrier signal to convey digital information involves the use of histograms representing probability density functions (PDFs) that characterize samples of the signal waveform. The method is based partly on the observation that when a waveform is sampled (whether by analog or digital means) over a time interval at least as long as one half cycle of the waveform, the samples can be sorted by frequency of occurrence, thereby constructing a histogram representing a PDF of the waveform during that time interval.

Williams, Glenn L.↗

NASA NTRS1974

Trace-element analysis of 1000 environmental samples per year using instrumental neutron activation analysis

The technology and methods developed at the Plum Brook Reactor to analyze 1000 samples per year and report data on as many as 56 elements are described. The manpower for the complete analysis of 20 to 24 samples per week required only 3 to 3.5 hours per sample. The solutions to problems encountered in sample preparation, irradiation, and counting are discussed. The automation of data reduction is described. Typical data on various sample matrices are presented.

Sheibley, D. W.↗

NASA NTRS1972

The organic analysis and carbon chemistry of lunar samples: Their significance for exobiology; Proceedings of the Conference, University of Maryland, College Park, Md., October 26-28, 1971.

Various methods used in the organic analysis of lunar samples are reviewed. The scope, advantages, and limitations of these methods are discussed, with particular emphasis on possible sources of contamination and experimental artifacts inherent in their use. A broad survey of the organogenic elements and compounds found in lunar samples covers the search for biogenic structures and viable organisms; the abundance and isotopic composition of various elements and compounds; the search for porphyrins, amino acids, or amino acid precursors; and the presence of heterocylics, aromatic hydrocarbons, and other organic compounds. The sources of the organogenic elements and compounds detected in lunar samples are discussed. The significance of the lunar organic analysis for exobiology is discussed in terms of its relevance to and implications for the studies of chemical evolution and terrestrial organic geochemistry. Individual items are announced in this issue.

Source record↗

NASA NTRS2005

Simultaneous quantification of poly-dispersed anionic, amphoteric and nonionic surfactants in simulated wastewater samples using C18 high-performance liquid chromatography-quadrupole ion-trap mass spectrometry

This paper describes the development of a guantitative method for direct and simultaneous determination of three frequently encountered surfactants, amphoteric (cocoamphoacetate, CAA), anionic (sodium laureth sulfate, SLES), and nonionic (alcohol ethoxylate, AE) using a reversed-phase C18 HPLC coupled with an ESI ion-trap mass spectrometer (MS). Chemical composition, ionization characteristics and fragmentation pathways of the surfactants are presented. Positive ESI was effective for all three surfactants in agueous methanol buffered with ammonium acetate. The method enables rapid determinations in small sample volumes containing inorganic salts (up to 3.5 g L(-1)) and multiple classes of surfactants with high specificity by applying surfactant specific tandem mass spectrometric strategies. It has dynamic linear ranges of 2-60, 1.5-40, 0.8-56 mg L(-1) with R2 egual or greater than 0.999, 0.98 and 0.999 (10 microL injection) for CAA, SLES, and AE, respectively.

Chromatography, High Pressure Liquid/methods↗

NASA NTRS1983

On a finite-difference method for solving transient viscous flow problems

A method has been developed to solve the unsteady, compressible Navier-Stokes equation with the property of consistency and the ability of minimizing the equation stiffness. It relies on innovative extensions of the state-of-the-art finite-difference techniques and is composed of: (1) the upwind scheme for split-flux and the central scheme for conventional flux terms in the inviscid and viscous regions, respectively; (2) the characteristic treatment of both inviscid and viscous boundaries; (3) an ADI procedure compatible with interior and boundary points; and (4) a scalar matrix coefficient including viscous terms. The performance of this method is assessed with four sample problems; namely, a standing shock in the Laval duct, a shock reflected from the wall, the shock-induced boundary-layer separation, and a transient internal nozzle flow. The results from the present method, an existing hybrid block method, and a well-known two-step explicit method are compared and discussed. It is concluded that this method has an optimal trade-off between the solution accuracy and computational economy, and other desirable properties for analyzing transient viscous flow problems.

Li, C. P.↗

NASA NTRS2020

Air Quality Monitoring Case Study Using Mobile Low-cost Sensors Mounted on Trash-Trucks: Methods Development and Lessons Learned

Air quality monitoring (AQM) is crucial for cities to develop management plans supporting population health. However, there is a dearth of measurements due to the high cost of standard reference instruments. Mobile AQM using low-cost sensors deployed on routine fleets of vehicles can enable the continuous detection of fine-scale pollutant variations in cities at a lower cost. New methods need to be developed to interpret these measurements. This paper presents three such methods. First, we propose a technique to identify aerosol hotspots. Second, we employ techniques published previously to assess the generalizable map of fine and coarse particle number concentrations, to understand qualitatively the contribution of local and regional sources across the region sampled. By using the raw number concentration of differently sized particles from the Optical Particle Counters (OPCs) instead of the noisier mass concentrations, we obtain more robust results. Third, in order to evaluate source signatures in cities, we propose another technique, in which we cluster the entire range of aerosol size-distribution measurements acquired. The properties of each cluster provide insight into the aerosol source characteristics in the sampling environment. We test these methods using a dataset we collected by mounting OPCs on two trash-trucks in Cambridge, Massachusetts.

Drive-by sensing↗

NASA NTRS2020

Air Quality Monitoring Case Study Using Mobile Low-cost Sensors mounted on Trash-Trucks: Methods Development and Lessons Learned

Air quality monitoring (AQM) is crucial for cities to develop management plans supporting population health. However, there is a dearth of measurements due to the high cost of standard reference instruments. Mobile AQM using low-cost sensors deployed on routine fleets of vehicles can enable the continuous detection of fine-scale pollutant variations in cities at a lower cost. New methods need to be developed to interpret these measurements. This paper presents three such methods. First, we propose a technique to identify aerosol hotspots. Second, we employ techniques published previously to assess the generalizable map of fine and coarse particle number concentrations, to understand qualitatively the contribution of local and regional sources across the region sampled. By using the raw number concentration of differently sized particles from the Optical Particle Counters (OPCs) instead of the noisier mass concentrations, we obtain more robust results. Third, in order to evaluate source signatures in cities, we propose another technique, in which we cluster the entire range of aerosol size-distribution measurements acquired. The properties of each cluster provide insight into the aerosol source characteristics in the sampling environment. We test these methods using a dataset we collected by mounting OPCs on two trash-trucks in Cambridge, Massachusetts.

Drive-by sensing↗

NASA NTRS2024

Mechanical Testing of Soils from the South Range of the Utah Test and Training Range: Derivation of Soil Properties to Support the Earth Entry System Landing for Mars Sample Return

This report summarizes results from laboratory tests conducted by Applied Research Associates, Inc. (ARA) on soil samples collected from multiple sites within the South Range of the U.S. Air Force Utah Test and Training Range (UTTR). The goal of the laboratory tests was to establish soil constitutive properties and develop computational soil models enabling NASA to simulate impact landings of the Earth Entry System (EES) for the Mars Sample Return (MSR) mission. Test methods and results are presented describing the strength, compressibility, and stiffness of soils in the UTTR South Range including methods to incorporate the measured properties into Ansys LS-DYNAÒ constitutive material models for EES landing simulations.

Soil↗

NASA NTRS2005

Method for Determination of Less Than 5 ppm Oxygen in Sodium Samples

Alkali metals used in pumped loops or heat pipes must be sufficiently free of nonmetallic impurities to ensure long heat rejection system life. Life issues are well established for alkali metal systems. Impurities can form ternary compounds between the container and working fluid, leading to corrosion. This Technical Memorandum discusses the consequences of impurities and candidate measurement techniques to determine whether impurities have been reduced to suf.ciently low levels within a single-phase liquid metal loop or a closed two-phase heat transfer system, such as a heat pipe. These techniques include the vanadium wire equilibration, neutron activation analysis, plug traps, distillation, and chemical analysis. Conceptual procedures for performing vanadium wire equilibration purity measurements on sodium contained in a heat pipe are discussed in detail.

Reid, R. S.↗

NASA NTRS1991

Digital phase-lock loop

An improved digital phase lock loop incorporates several distinctive features that attain better performance at high loop gain and better phase accuracy. These features include: phase feedback to a number-controlled oscillator in addition to phase rate; analytical tracking of phase (both integer and fractional cycles); an amplitude-insensitive phase extractor; a more accurate method for extracting measured phase; a method for changing loop gain during a track without loss of lock; and a method for avoiding loss of sampled data during computation delay, while maintaining excellent tracking performance. The advantages of using phase and phase-rate feedback are demonstrated by comparing performance with that of rate-only feedback. Extraction of phase by the method of modeling provides accurate phase measurements even when the number-controlled oscillator phase is discontinuously updated.

Thomas, Jr., Jess B.↗

NASA NTRS2018

Intercomparison of Field Methods for Acquiring Ground Reflectance at Railroad Valley Playa for Spectral Calibration of Satellite Data

Ground reflectance was acquired at the Railroad Valley Playa calibration site in Nevada USA using different methods of collection. The data was collected near the time and date of Landsat 8 OLI and Sentinel-2 satellite overpasses so an inter-comparison could be made with the reflectance products to determine which method was more suitable for vicarious calibration. The field spectrometers and reference panels were characterized before the field campaign. A continuous acquisition method was compared to stop and measure collections. Both acquisition methods were collected along an 80 m east-west transect as well as for a series of north-south transects over an 80 x 320 m area, with the stop and measure method being performed at random sampling locations. The measurements were performed using two field spectrometers by three teams of two people to compare the repeatability. The aim of the field campaign was to determine the variability due to the operator and the method of collection.

Lau, Ian C.↗

NASA NTRS2018

Intercomparison of Field Methods for Acquiring Ground Reflectance at Railroad Valley Playa for Spectral Calibration of Satellite Data

Ground reflectance was acquired at the Railroad Valley Playa calibration site in Nevada USA using different methods of collection. The data was collected near the time and date of Landsat 8 OLI and Sentinel-2 satellite overpasses so an inter-comparison could be made with the reflectance products to determine which method was more suitable for vicarious calibration. The field spectrometers and reference panels were characterized before the field campaign. A continuous acquisition method was compared to stop and measure collections. Both acquisition methods were collected along an 80 m east-west transect as well as for a series of north-south transects over an 80 x 320 m area, with the stop and measure method being performed at random sampling locations. The measurements were performed using two field spectrometers by three teams of two people to compare the repeatability. The aim of the field campaign was to determine the variability due to the operator and the method of collection.

Lau, Ian C.↗

NASA NTRS2012

In-situ Measurements of the Radiolytic Destruction of Glycine in Ices: Applications to the Martian Subsurface

Amino acids and other organic molecules are thought to be easily destroyed on the surface of Mars by the high flux of incident ultraviolet rays or by chemical interactions with oxidizing substances in the soil. However, organic molecules may survive in the subsurface, where chemical processes are driven by penetrating galactic cosmic rays such as MeV protons. Models of the radiation dose as a function of depth on Mars have shown that the contribution of galactic cosmic rays dominates from about one centimeter to a few meters [1 J. Theoretical models have also been published to aid in understanding molecular destruction at these depths, but these usually are based on room-temperature laboratory data, studies of single-component samples, and ex-situ methods of chemical analysis. Recent studies of amino-acid survivability include those involving UV photolysis [2, 3J and gamma radiolysis [4], but nearly all chemical and kinetic analyses from such experiments involved room-temperature measurements on samples irradiated and then removed from sealed containers. We report new laboratory studies of the radiation-induced destruction of glycine-containing ices. In-situ infrared spectroscopy was used to study decay rates as a function of temperature and initial glycine concentrations. Our results indicate that glycine's destruction rate depends on temperature, the presence of H20-ice, and the initial relative abundance of glycine. These trends are not obvious in previous work, suggesting that room-temperature measurements on pure glycine's radiation stability are not directly applicable to Mars and other environments.

Gerakines, Perry A.↗

NASA NTRS1990

Digital carrier demodulator employing components working beyond normal limits

In a digital device, having an input comprised of a digital sample stream at a frequency F, a method is disclosed for employing a component designed to work at a frequency less than F. The method, in general, is comprised of the following steps: dividing the digital sample stream into odd and even digital samples streams each at a frequency of F/2; passing one of the digital sample streams through the component designed to work at a frequency less than F where the component responds only to the odd or even digital samples in one of the digital sample streams; delaying the other digital sample streams for the time it takes the digital sample stream to pass through the component; and adding the one digital sample stream after passing through the component with the other delayed digital sample streams. In the specific example, the component is a finite impulse response filter of the order ((N + 1)/2) and the delaying step comprised passing the other digital sample streams through a shift register for a time (in sampling periods) of ((N + 1)/2) + r, where r is a pipline delay through the finite impulse response filter.

Hurd, William J.↗

NASA NTRSDate not supplied

Infrared Reflection Removal in Wind Tunnels using Polarization Theory

Infrared radiometry with infrared cameras allows for high spatial resolution, noncontact measurements in wind tunnel experiments and has been increasingly used to visualize flow features. Reflections from test section walls present a major challenge in collecting these measurements as it is difficult or impossible to separate them from the true model emission signal. This paper implements a method to quantitatively separate the reflections from the emission using polarization theory. Samples with a range of emissivities were tested, and in all samples the reflections were significantly reduced. This method will lead to more accurate radiometric and thermographic measurements in wind tunnel experiments.

Infrared↗

NASA NTRSDate not supplied

Infrared Reflection Removal in Wind Tunnels using Polarization Theory

Infrared radiometry with infrared cameras allows for high spatial resolution, noncontact measurements in wind tunnel experiments and has been increasingly used to visualize flow features. Reflections from test section walls present a major challenge in collecting these measurements as it is difficult or impossible to separate them from the true model emission signal. This paper implements a method to quantitatively separate the reflections from the emission using polarization theory. Samples with a range of emissivities were tested, and in all samples the reflections were significantly reduced. This method will lead to more accurate radiometric and thermographic measurements in wind tunnel experiments.

Infrared↗