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All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Field and Model Data Associated with the Manuscript “Drivers of Streamflow Intermittency in Humid Regions: 1. Evaluating Above- and Below-ground Controls of Flow Persistence in a Forested Catchment”

This package contains field data, modeling files, and scripts supporting the investigation of the drivers of streamflow intermittency in a forested catchment. It includes the field data collected from electrical resistivity tomography (ERT) surveys, ground penetrating radar (GPR), continuous self-potential (SP) monitoring, electromagnetic (EM) imaging, groundwater and stilling well. In addition, it contains the data and results of the coupled water- and electrical-flow model developed using the COMSOL Multiphysics and Advanced Terrestrial Simulator (ATS), as well as software files and Jupyter notebooks used to process the data and generate figures in the manuscript submitted for peer review. The data archive is organized in the following directories: 1) Climate Includes hourly precipitation and daily evapotranspiration time series (2024 – 2025) provided as CSV files, alongside a text file detailing dataset units. 2) Coupled_model Contains two subfolders: Synthetic and Field_Application subfolder. Synthetic subfolder contains the ATS XML input script (can be opened using any code editor) for the four synthetic hydrological cases tested (Connected and gaining, Connected and losing, Disconnected and losing, and dry stream). It also includes other experimental cases to test the influence of precipitation and concentration gradient. For each synthetic case, the flow model simulation is executed using the ATS XML scripts and the included Python script (generate_data_set.py) to convert ATS output to COMSOL-ready input. COMSOL Multiphysics template (.mph can be opened with the commercial software COMSOL and requires a license) is executed using the ATS output data to simulate the potential field. It also includes the Synthetic_model_plot.ipynb (can be opened using any code editor) to visualize the SP result and generate manuscript figures. The data subfolder contains mesh files to run both the ATS (.exo and .stl files can be viewed using Paraview; .h5 files can be opened using HDFView software and h5py Python package) and COMSOL models. Field_Application subfolder contains two subfolders: ES_MDA_inversion and Final_Model. ES_MDA_inversion contains the Python script (.py can be opened using any code editor) and SP observation data used to run the Ensemble Smoother with Multiple Data Assimilation (ES-MDA) inversion sequence to get the optimal model parameters. The Final_model subfolder contains the ATS XML input scripts, data files, output data for the two SP sites. The same workflow steps outlined for the Synthetic subfolder apply here. It also contains the Jupyter notebook (Plot_final_calib.ipynb) to visualize the results of the modeled SP, stream-groundwater exchange and moisture content. 3) Discharge Includes the electrical conductivity (EC) time series (provided as CSV files) from salt slug injections. It also includes the Jupyter notebook (Discharge_process.ipynyb) used to estimate discharge. All discharge measurements collated into rating_curve_processed.csv 4) EM Contains the CSV file of the EM data from the DUALEM-42, including spatial coordinates (x, y, z), apparent conductivity, and in-phase measurements at 2 m coil separations for horizontal coplanar (HCP) and perpendicular (PRP) geometries. 5) ERT Contains raw resistivity data (provided as CSV files), spatial location of each of the electrodes (provided as CSV files), and files used for the resistivity inversion (.resipy can be opened with the open-source ResIPy software). 6) GPR Includes GPR field datasets collected at 100 MHz and 250 MHz antenna frequencies, along with the processing/interpretation project file (GPR_process.gpz can be viewed using EKKO_Project 6, a commercial software by Sensors & Software that requires a license). 7) Slug_test Includes the slug test data at all the groundwater wells provided as CSV files, as well as the Jupyter notebook (Slug_test.ipynb) for calculating hydraulic conductivity. 8) SP Contains the SP data collected in field at the two SP sites (one in the perennial reach and the other in the intermittent reach), provided as DAT files. 9) Well_data Contains two subfolders: 1) Raw, which provides unprocessed pressure, electrical conductivity and temperature timeseries downloaded from the loggers in all the groundwater and stilling wells, and 2) Processed, which contains sorted, QA/QC timeseries data for each well. The data archive also contains data_process.ipynb, a Jupyter notebook used for field data analysis and generating figures (plotting well, SP, climate, and discharge data, as well as calculating head gradient at sites with nested groundwater wells). It also includes DTW.ipynb, a Jupyter notebook containing the code for the dynamic time warping (DTW) with sliding window to evaluate SP signal synchronicity.

ATS↗
NASA NTRS1972

Holographic nondestructive testing with impact excitation.

Review of some experimental results of bond flaw detection in composite materials by holographic recording of the surface of samples subjected to mechanical impact. The resulting deformation of the samples recorded in a sequence of double exposure holograms at increasingly longer time intervals after impact renders the presence of flaws observable. A proposed deformation enhancement technique increases detection sensitivity and is helpful in visualizing smaller flaws.

Chu, W. P.↗
NASA NTRS1979

Low-cost directionally-solidified turbine blades, volume 2

An endothermically heated technology was used to manufacture low cost, directionally solidified, uncooled nickel-alloy blades for the TFE731-3 turbofan engine. The MAR-M 247 and MER-M 100+Hf blades were finish processed through heat treatment, machining, and coating operations prior to 150 hour engine tests consisting of the following sequences: (1) 50 hours of simulated cruise cycling (high fatigue evaluation); (2) 50 hours at the maximum continuous power rating (stress rupture endurance (low cycle fatigue). None of the blades visually showed any detrimental effects from the test. This was verified by post test metallurgical evaluation. The specific fuel consumption was reduced by 2.4% with the uncooled blades.

Dennis, R. E.↗
NASA NTRS1989

Robot Acting on Moving Bodies (RAMBO): Interaction with tumbling objects

Interaction with tumbling objects will become more common as human activities in space expand. Attempting to interact with a large complex object translating and rotating in space, a human operator using only his visual and mental capacities may not be able to estimate the object motion, plan actions or control those actions. A robot system (RAMBO) equipped with a camera, which, given a sequence of simple tasks, can perform these tasks on a tumbling object, is being developed. RAMBO is given a complete geometric model of the object. A low level vision module extracts and groups characteristic features in images of the object. The positions of the object are determined in a sequence of images, and a motion estimate of the object is obtained. This motion estimate is used to plan trajectories of the robot tool to relative locations rearby the object sufficient for achieving the tasks. More specifically, low level vision uses parallel algorithms for image enhancement by symmetric nearest neighbor filtering, edge detection by local gradient operators, and corner extraction by sector filtering. The object pose estimation is a Hough transform method accumulating position hypotheses obtained by matching triples of image features (corners) to triples of model features. To maximize computing speed, the estimate of the position in space of a triple of features is obtained by decomposing its perspective view into a product of rotations and a scaled orthographic projection. This allows use of 2-D lookup tables at each stage of the decomposition. The position hypotheses for each possible match of model feature triples and image feature triples are calculated in parallel. Trajectory planning combines heuristic and dynamic programming techniques. Then trajectories are created using dynamic interpolations between initial and goal trajectories. All the parallel algorithms run on a Connection Machine CM-2 with 16K processors.

Davis, Larry S.↗
NASA NTRS1992

Smoke Generator For Studies Of Vortices In Flight

Smoke-generating system used to identify vortex-core and vortex-core-breakdown locations in flights. Housed in forebody of airplane, includes multiple pyrotechnic smoke cartridges fired simultaneously or in sequence. Firing of cartridges controlled from cockpit, and smoke produced ducted to desired locations on or near surface of aircraft. Useful for other aerodynamic flight research in which necessary to visualize local flows. Nonaerospace applications include research in reduction of aerodynamic drag on vehicles and reduction of turbulence related to structures or other obstacles.

Richwine, David M.↗
NASA NTRSDate not supplied

Self-Aligned Focusing Schlieren and OH Planar Laser-Induced Fluorescence Flow Visualization in a Dual-Mode Scramjet

Ahigh-speed self-aligned focusing schlieren (SAFS) system was used to visualize density gradients in and around the cavity flameholder of the combustor section of the University of Virginia Supersonic Combustion Facility (UVASCF). Images with this system were acquired at a framing rate of 110 kHz with no fuel injection, with fuel injection but no flame, and for fuel injection with combustion corresponding to a global equivalence ratio of 𝜙 = 0.18. Images with an air throttle in operation to modify the shock train location with fuel injection and with flame were also acquired. Simultaneous OH planar laser-induced fluorescence (PLIF) images were also acquired at a framing rate of 20 Hz. Results obtained with both visualization techniques are compared to one another to highlight how SAFS can complement more advanced flow visualization techniques and resolve dynamic behavior that may not otherwise be captured. Both proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) analysis techniques are applied to the SAFS image sequences to identify coherent periodic structures for the runs with fuel injection and combustion.

Brett F Bathel↗
NASA NTRS1987

Flow visualization of CFD using graphics workstations

High performance graphics workstations are used to visualize the fluid flow dynamics obtained from supercomputer solutions of computational fluid dynamic programs. The visualizations can be done independently on the workstation or while the workstation is connected to the supercomputer in a distributed computing mode. In the distributed mode, the supercomputer interactively performs the computationally intensive graphics rendering tasks while the workstation performs the viewing tasks. A major advantage of the workstations is that the viewers can interactively change their viewing position while watching the dynamics of the flow fields. An overview of the computer hardware and software required to create these displays is presented. For complex scenes the workstation cannot create the displays fast enough for good motion analysis. For these cases, the animation sequences are recorded on video tape or 16 mm film a frame at a time and played back at the desired speed. The additional software and hardware required to create these video tapes or 16 mm movies are also described. Photographs illustrating current visualization techniques are discussed. Examples of the use of the workstations for flow visualization through animation are available on video tape.

Lasinski, Thomas↗
NASA NTRS1992

A vision architecture for the extravehicular activity retriever

The Extravehicular Activity Retriever (EVAR) is a robotic device currently being developed by the Automation and Robotics Division at the NASA Johnson Space Center to support activities in the neighborhood of the Space Shuttle or Space Station Freedom. As the name implies, the Retriever's primary function will be to provide the capability to retrieve tools, equipment or other objects which have become detached from the spacecraft, but it will also be able to rescue a crew member who may have become inadvertently de-tethered. Later goals will include cooperative operations between a crew member and the Retriever such as fetching a tool that is required for servicing or maintenance operations. This report documents a preliminary design for a Vision System Planner (VSP) for the EVAR that is capable of achieving visual objectives provided to it by a high level task planner. Typical commands which the task planner might issue to the VSP relate to object recognition, object location determination, and obstacle detection. Upon receiving a command from the task planner, the VSP then plans a sequence of actions to achieve the specified objective using a model-based reasoning approach. This sequence may involve choosing an appropriate sensor, selecting an algorithm to process the data, reorienting the sensor, adjusting the effective resolution of the image using lens zooming capability, and/or requesting the task planner to reposition the EVAR to obtain a different view of the object. An initial version of the Vision System Planner which realizes the above capabilities using simulated images has been implemented and tested. The remaining sections describe the architecture and capabilities of the VSP and its relationship to the high level task planner. In addition, typical plans that are generated to achieve visual goals for various scenarios will be discussed. Specific topics to be addressed will include object search strategies, repositioning of the EVAR to improve the quality of information obtained from the sensors, complementary usage of the sensors and redundant capabilities.

Magee, Michael↗
NASA NTRS1993

A vision system planner for increasing the autonomy of the Extravehicular Activity Helper/Retriever

The Extravehicular Activity Retriever (EVAR) is a robotic device currently being developed by the Automation and Robotics Division at the NASA Johnson Space Center to support activities in the neighborhood of the Space Shuttle or Space Station Freedom. As the name implies, the Retriever's primary function will be to provide the capability to retrieve tools and equipment or other objects which have become detached from the spacecraft, but it will also be able to rescue a crew member who may have become inadvertently de-tethered. Later goals will include cooperative operations between a crew member and the Retriever such as fetching a tool that is required for servicing or maintenance operations. This paper documents a preliminary design for a Vision System Planner (VSP) for the EVAR that is capable of achieving visual objectives provided to it by a high level task planner. Typical commands which the task planner might issue to the VSP relate to object recognition, object location determination, and obstacle detection. Upon receiving a command from the task planner, the VSP then plans a sequence of actions to achieve the specified objective using a model-based reasoning approach. This sequence may involve choosing an appropriate sensor, selecting an algorithm to process the data, reorienting the sensor, adjusting the effective resolution of the image using lens zooming capability, and/or requesting the task planner to reposition the EVAR to obtain a different view of the object. An initial version of the Vision System Planner which realizes the above capabilities using simulated images has been implemented and tested. The remaining sections describe the architecture and capabilities of the VSP and its relationship to the high level task planner. In addition, typical plans that are generated to achieve visual goals for various scenarios are discussed. Specific topics to be addressed will include object search strategies, repositioning of the EVAR to improve the quality of information obtained from the sensors, and complementary usage of the sensors and redundant capabilities.

Magee, Michael↗
NASA NTRS2021

Dual Quaternion Visual Servo Control

This paper focuses on a dual quaternion-based estimation and control approach for position-based visual servoing (PBVS). The pose estimation of the camera is achieved using a dual quaternion-based Extended Kalman Filter (EKF), which estimates the position and orientation of the camera based on feature points acquired through a sequence of camera images. Based on the estimation, a dual quaternion control law is developed to regulate the camera to the desired pose. Leveraging the local exponential stability of the EKF and the global exponential stability of the designed controller, a nonlinear separation principle is used to prove the stability of the joint estimation and control for PBVS. The method is distinguished from other PBVS methods in the sense that a compact representation of dual quaternion is used to represent the pose, and a joint stability of estimator and controller for PBVS in dual quaternion space is presented. The proposed dual quaternion PBVS method is validated using a simulation.

Quaternions↗
NASA NTRS1987

Ultraviolet and visual spectroscopy of DB white dwarfs

Visual wavelength and ultraviolet spectroscopy and model atmospheres of DB white dwarfs are reported. The results yield no evidence for lines of C or any other element besides H or He in the spectra. Upper limits for carbon are in the range C:He less than 10 to the -5th to the -7th for the ultraviolet data and C:He less than 0.01-0.001 for the visual. The upper limits are consistent with the convective dredging theory for the origin of the atmospheric carbon observed in the cooler DQ members of the helium-rich white dwarf sequence. Additional new DBA stars are reported.

Wegner, G.↗
NASA NTRS2008

NASA Tech Briefs, June 2008

Topics covered include: Charge-Control Unit for Testing Lithium-Ion Cells; Measuring Positions of Objects Using Two or More Cameras; Lidar System for Airborne Measurement of Clouds and Aerosols; Radiation-Insensitive Inverse Majority Gates; Reduced-Order Kalman Filtering for Processing Relative Measurements; Spaceborne Processor Array; Instrumentation System Diagnoses a Thermocouple; Chromatic Modulator for a High-Resolution CCD or APS; Commercial Product Activation Using RFID; Cup Cylindrical Waveguide Antenna; Aerobraking Maneuver (ABM) Report Generator; ABM Drag_Pass Report Generator; Transformation of OODT CAS to Perform Larger Tasks; Visualization Component of Vehicle Health Decision Support System; Mars Reconnaissance Orbiter Uplink Analysis Tool; Problem Reporting System; G-Guidance Interface Design for Small Body Mission Simulation; DSN Scheduling Engine; Replacement Sequence of Events Generator; Force-Control Algorithm for Surface Sampling; Tool for Merging Proposals Into DSN Schedules; Micromachined Slits for Imaging Spectrometers; Fabricating Nanodots Using Lift-Off of a Nanopore Template; Making Complex Electrically Conductive Patterns on Cloth; Special Polymer/Carbon Composite Films for Detecting SO2; Nickel-Based Superalloy Resists Embrittlement by Hydrogen; Chemical Passivation of Li+-Conducting Solid Electrolytes; Organic/Inorganic Polymeric Composites for Heat-Transfer Reduction; Composite Cathodes for Dual-Rate Li-Ion Batteries; Improved Descent-Rate Limiting Mechanism; Alignment-Insensitive Lower-Cost Telescope Architecture; Micro-Resistojet for Small Satellites; Using Piezoelectric Devices to Transmit Power through Walls; Miniature Latching Valve; Apparatus for Sampling Surface Contamination; Novel Species of Non-Spore-Forming Bacteria; Chamber for Aerosol Deposition of Bioparticles; Hyperspectral Sun Photometer for Atmospheric Characterization and Vicarious Calibrations; Dynamic Stability and Gravitational Balancing of Multiple Extended Bodies; Simulation of Stochastic Processes by Coupled ODE-PDE; Cluster Inter-Spacecraft Communications; Genetic Algorithm Optimizes Q-LAW Control Parameters; Low-Impact Mating System for Docking Spacecraft; Non-Destructive Evaluation of Materials via Ultraviolet Spectroscopy; Gold-on-Polymer-Based Sensing Films for Detection of Organic and Inorganic Analytes in the Air; and Quantum-Inspired Maximizer.

Source record↗
NASA NTRS1978

Orbit Selection for Earth Observation Missions

The orbit selection process is simplified for most earth-oriented satellite missions by a restriction to circular orbits, which reduces the primary orbit characteristics to be determined to only two: altitude and inclination. A number of important mission performance characteristics depend on these choices, however, so a major part of the orbit selection task is concerned with developing the correlating relationships in clear and convenient forms to provide a basis for rational orbit selection procedures. The present approach to that task is organized around two major areas of mission performance, orbit plane precession and coverage pattern development, whose dependence on altitude and inclination is delineated graphically in design chart form. These charts provide a visual grasp of the relationships between the quantities cited above, as well as other important mission performance parameters including viewing time of day (solar), sensor swath width (and fields of view), swath sequencing, and pattern repeat condition and repeat periods.

King, J. C.↗
NASA NTRSDate not supplied

SPACEFLIGHT ASSOCIATED NEURO-OCULAR SYNDROME (SANS): 2023 CLINICAL UPDATE

INTRODUCTION Spaceflight Associated Neuro-ocular Syndrome (SANS) is a condition unique to long-duration spaceflight, with an unclear pathogenesis and pathophysiology, and no perfect terrestrial analog. Approximately 66% of long duration spaceflight (LDSF) astronauts present with the earliest indication of SANS, which is defined as development of any of the following signs in at least one eye during or immediately following spaceflight: 1) optic disc edema (ODE; represented by an increase of ≥ 20 microns in peripapillary total retinal thickness [ΔTRT]); 2) chorioretinal folds; 3) globe flattening; and 4) excessive shift in refractive error (≥ +0.75D). Each of these signs presents potential risk to a crewmember’s vision and mission effectiveness, with ODE posing the highest risk overall. It is not yet known what severity and/or duration of these signs might lead to acute or permanent impacts to ocular anatomy or visual performance. Brain anatomical changes also occur during long-duration spaceflight and are being monitored in the astronaut population; however, these changes have not yet been associated with functional decrements or with SANS. An update will be provided on the latest SANS clinical analyses, diagnostics, and program initiatives. METHODS Data were obtained from clinical records and SANS subject matter experts (SMEs) to compile a SANS clinical update. Areas of interest include: 1) prevalence of SANS signs, 2) defining clinical thresholds for SANS, and 3) an overview of current and planned SANS clinical efforts. DISCUSSION SANS Sign Prevalence: Analysis at the time of this abstract submission indicates that the approximate prevalence of primary SANS findings in USOS LDSF crewmembers is: 64% for ODE (≥ 20-micron ΔTRT), 15% for chorioretinal folds, 26% for globe flattening, and 14% for hyperopic shifts in refractive error (≥ +0.75D). Clinical Thresholds:  The Earliest Indication of SANS was presented publicly for the first time at the 2020 NASA Human Research Program Investigators’ Workshop. See definition in Introduction section (above).  Clinically Concerning SANS – Development of any of the following signs during or immediately following spaceflight: 1) ODE (≥ 55-micron ΔTRT* and/or Frisèn grade ≥1*), 2) sharp chorioretinal folds in the vicinity of the macula, or 3) moderate globe flattening.  Pathological SANS with an Acute Functional Impact – Development of any of the following signs/symptoms during or immediately following spaceflight: 1) visual field loss (e.g., enlarged blindspot), 2) distorted centralvision, or 3) shift in refractive error beyond power of available correction (e.g., “space anticipation glasses”).  Pathological SANS affecting Long-Term Health – Development of any of the following signs/symptoms during or following spaceflight: 1) permanent visual field loss, 2) reduced retinal nerve fiber layer (RNFL) thickness, 3) permanently distorted central vision, 4) atrophy of retinal pigment epithelium (RPE) or photoreceptors, or 5) choroidal neovascularization. Current & Planned Clinical Efforts (accurate at time of abstract submission): All SANS diagnostic hardware are performing nominally onboard the International Space Station: vision screening, fundoscope, optical coherence tomography (OCT) device, ultrasound, and tonometer. The Goggle-Based Visual Field (GBVF) device is nearing completion of its clinical validation study at Ohio State University and is planned for parabolic flight testing in fiscal year 2023 (FY23); pending positive results, this sequence may pave the way towards an ISS technology demonstration in FY24.

T J Brunstetter↗
NASA NTRS1973

Effect of prolonged bedrest and plus Gz acceleration on peripheral visual response time

Peripheral visual response time changes during +G sub z acceleration following fourteen days of bedrest are considered as well as what effect prolonged bedrest has upon this response. Eighteen test lights, placed 10 deg are apart along the horizontal meridian of the subject's field of view, were presented in a random sequence. The subject was instructed to press a button as soon as a light appeared. Response time testing occurred periodically during bedrest and continuously during centrifugation testing. The results indicate that: (1) mean response time is significantly longer to stimuli imaged in the far periphery than to stimuli imaged closer to the line of sight; (2) mean response time at each stimulus position tends to be longer at plateau g than during the preacceleration baseline period; (3) mean response time tends to lengthen as the g level is increased; (4) peripheral visual response time during +G sub x acceleration at 2, 3.2, and 3.8 g was not a reliable advanced indicator that blackout was going to occur; and (5) the subject's field of view collapsed rapidly just before blackout. Bedrest data showed that the distribution of response times to stimuli imaged across the subject's horizontal retinal meridian remained remarkably constant from day to day during both the bedrest and recovery periods.

Haines, R. F.↗
NASA NTRS2014

Flow Visualization of Liquid Hydrogen Line Chilldown Tests

We present experimental measurements of wall and fluid temperature during chill-down tests of a warm cryogenic line with liquid hydrogen. Synchronized video and fluid temperature measurements are used to interpret stream temperature profiles versus time. When cold liquid hydrogen starts to flow into the warm line, a sequence of flow regimes, spanning from all-vapor at the outset to bubbly with continuum liquid at the end can be observed at a location far downstream of the cold inlet. In this paper we propose interpretations to the observed flow regimes and fluid temperature histories for two chilldown methods, viz. trickle (i.e. continuous) flow and pulse flow. Calculations of heat flux from the wall to the fluid versus wall temperature indicate the presence of the transition/nucleate boiling regimes only. The present tests, run at typical Reynolds numbers of approx O(10 (exp 5)), are in sharp contrast to similar tests conducted at lower Reynolds numbers where a well-defined film boiling region is observed.

Line chill down↗
NASA NTRS1976

A new interpretation of luminous blue stars

A major revision of current theoretical ideas about the brightest blue stars must be made if Carson's (1976) radiative opacities are adopted in stellar models. Unlike earlier opacities, these exhibit a large 'bump' due to CNO ionization, which leads to very strong central condensation, convective instability, and pulsational instability in hot diffuse stellar envelopes. Despite a number of theoretical uncertainties, the new picture of the structure of very luminous stars is reasonably successful in accounting for a variety of previously unexplained observations. The stellar models for the phase of core hydrogen burning predict large radii and rather cool effective temperatures for O stars and a spreading out of the main-sequence band in the H-R diagram toward luminous cool supergiants for masses higher than about 20 solar masses. In massive X-ray binary systems, circular orbits and supergiant-like visual companions are expected to be quite common. Long-period variability is predicted to exist for massive blue supergiants of luminosity class Ia. The models for helium stars predict large radii and rather cool effective temperatures for Wolf-Rayet stars, as well as multimodal pulsational instability and, possibly, surface turbulence for these stars.

Stothers, R.↗
NASA NTRS1982

Quantification of pilot workload via instrument scan

The use of visual scanning behavior as an indicator of pilot workload is described. The relationship between level of performance on a constant piloting task under simulated IFR conditions, the skill of the pilot the level of mental workload induced by an additional verbal task imposed on the basic control task, and visual scanning behavior is investigated. An increase in fixation dwell times, especially on the primary instrument with increased mental loading is indicated. Skilled subjects 'stared' less under increased loading than did novice pilots. Sequences of instrument fixations were also examined. The percentage occurrence of the subject's most used sequences decreased with increased task difficulty for novice subjects but not for highly skilled subjects. Entropy rate (bits/sec) of the sequence of fixations was also used to quantify the scan pattern. It consistently decreased for most subjects as the four loading levels used increased.

Tole, J. R.↗