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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2022

A Network of Field-Calibrated Low-Cost Sensor Measurements of PM2.5 in Lomé, Togo, Over One to Two Years

Air pollution is a leading cause of global premature mortality and is especially prevalent in many low- and middle-income countries (LMICs). In sub-Saharan Africa, preliminary monitoring networks, satellite retrievals of air-quality-relevant species, and air quality models show ambient fine particulate matter (PM 2.5 ) concentrations that far exceed the World Health Organization guidelines, yet many areas remain largely unmonitored and understudied. Deploying a network of five low-cost PurpleAir PM 2.5 monitors over 2 years (2019–2021), we present the first multiyear ambient air pollution monitoring data results from Lomé, Togo, a major West African coastal city with a population of about 1.4 million people. The full-study time period network-wide mean measured daily PM 2.5 concentration is 23.5 μ g m –3 m –3 . The strong regional influence of the dry and dusty Harmattan wind increases the local average PM 2.5 concentration by up to 58% during December through February, but the diurnal and weekly trends in PM 2.5 are largely controlled by local influences. At all sites, more than 87% of measured days exceeded the new WHO Daily PM 2.5 guidelines; these first measurements highlight the need for air quality improvement in a rapidly growing urban metropolis.

air pollution↗
NASA NTRS1994

Teacher Enhancement Institute

During the 1980's, a period of intense concern over educational quality in the United States, few indicators of U.S. student achievement garnered the interest of policy makers and pundits as successfully as the results of international testing in mathematics and science. This concern was so great that as a part of the Goals 2000 initiative, President George Bush indicated that 'By the year 2000, U.S. students should be first in the world in mathematics and science.' The Clinton Administration is placing a major emphasis, not only on rigorous academic standards and creating a new system for assessing students' progress, but also including professional development as a major focus. The argument being that teachers need more sustained, intensive training to prepare them to teach to higher standards. Executive order 12821 mandates that national laboratories 'assist in the mathematics and science education of our Nation's students, teachers, parents and the public by establishing programs at their agency to provide for training elementary and secondary school teachers to improve their knowledge of mathematics and science'. These and other issues led to the development of ideas for a project that addresses the need for excellence in mathematics, science and technology instruction. In response to these initiatives the NASA/LaRC Teacher Enhancement Institute was proposed. The TEI incorporated systemic reform perspectives, enhanced content knowledge for teachers, and teacher preparation. Emphasis was also placed on recruiting those educators who teach in impoverished urban school districts with at-risk student populations who have been traditionally under represented in science, mathematics, technology and engineering. Participants in the Teacher Enhancement Institute were 37 teachers from grades K-8, teaching in Region 2 in the state of Virginia, as well as 2 preservice teachers from Norfolk State University and one teacher from Dublin, Virginia, where a Science/Mathematics model school has been established. Teachers selected for this project represented school systems where income levels are extremely low, and students served tend not to receive innovative instruction in mathematics and science and their use of technology is limited. The Teacher Enhancement Institute contained several features, that when combined, allowed for a unique experience. Some of these features included local teachers, administrators and school board members as presenters, instruction and use of technology every day, tours of select features of the research facility, briefings by NASA/LaRC scientists, engineers and researchers as well as individuals from the Continuous Electron Beam Accelerator Facility (CEBAF). Another unique feature of this program is to have participants convene on three separate occasions throughout the academic year to discuss strategies for information dissemination and implementation results. Teachers' attitudes towards the use of technology, their ability to develop lessons using technology and their ability to develop lessons using information obtained through TEI were assessed using instruments developed by TEI summer faculty members. Data from these instruments were analyzed and reported in a final report submitted to the director of the Office of Education.

Marshall-Bradley, Tina↗
NASA NTRS2002

Transient Voltage Recorder

A voltage transient recorder can detect lightning induced transient voltages. The recorder detects a lightning induced transient voltage and adjusts input amplifiers to accurately record transient voltage magnitudes. The recorder stores voltage data from numerous monitored channels, or devices. The data is time stamped and can be output in real time, or stored for later retrieval. The transient recorder, in one embodiment, includes an analog-to-digital converter and a voltage threshold detector. When an input voltage exceeds a pre-determined voltage threshold, the recorder stores the incoming voltage magnitude and time of arrival. The recorder also determines if its input amplifier circuits clip the incoming signal or if the incoming signal is too low. If the input data is clipped or too low, the recorder adjusts the gain of the amplifier circuits to accurately acquire subsequent components of the lightning induced transients.

Pedro J Medelius↗
NASA NTRS2006

Algorithm for Aligning an Array of Receiving Radio Antennas

A digital-signal-processing algorithm (somewhat arbitrarily) called SUMPLE has been devised as a means of aligning the outputs of multiple receiving radio antennas in a large array for the purpose of receiving a weak signal transmitted by a single distant source. As used here, aligning signifies adjusting the delays and phases of the outputs from the various antennas so that their relatively weak replicas of the desired signal can be added coherently to increase the signal-to-noise ratio (SNR) for improved reception, as though one had a single larger antenna. The method was devised to enhance spacecraft-tracking and telemetry operations in NASA's Deep Space Network (DSN); the method could also be useful in such other applications as both satellite and terrestrial radio communications and radio astronomy. Heretofore, most commonly, alignment has been effected by a process that involves correlation of signals in pairs. This approach necessitates the use of a large amount of hardware most notably, the N(N - 1)/2 correlators needed to process signals from all possible pairs of N antennas. Moreover, because the incoming signals typically have low SNRs, the delay and phase adjustments are poorly determined from the pairwise correlations. SUMPLE also involves correlations, but the correlations are not performed in pairs. Instead, in a partly iterative process, each signal is appropriately weighted and then correlated with a composite signal equal to the sum of the other signals (see Figure 1). One benefit of this approach is that only N correlators are needed; in an array of N much greater than 1 antennas, this results in a significant reduction of the amount of hardware. Another benefit is that once the array achieves coherence, the correlation SNR is N - 1 times that of a pair of antennas.

Rogstad, David↗
NASA NTRSDate not supplied

The Potential of Medical Drones: An Analysis of Current and Future Use Cases

Modern Application of Medical-Based Drone Delivery Drones have been used advantageously by militaries for nearly a century, but their uses in civilian life are still mostly cutting-edge, if not theoretical. After a decade of bold proclamations, Amazon’s “PrimeAir” drone delivery system is still in the stage of “preparing” for deliveries, while the public awaits for start ups like SkyDrop (formerly Flirtey) to follow through on impressive promises. Despite the well-publicized disappointment so far in commercial drone delivery, medical drone delivery has already proven itself practical and cheap in several countries, and it promises to expand in the coming years. Drones are uniquely suited to make valuable and urgent deliveries to remote areas, quickly transporting medical supplies where road transportation is prohibitively slow or not available at all. Drones have been used notably to deliver AEDs for out-of-hospital cardiac arrest, frequently beating first-responders to the scene; to deliver blood when there is none on hand at hospitals; to deliver vaccines to an island nation with little transportation infrastructure; and to respond flexibly to medical emergencies in a war zone. Economics make the delivery of food and other cheap goods by drone unattractive in the near-term, but the value and time-sensitivity of medical deliveries mean that drones are already saving lives in healthcare. “We believe the value of new technology is most valuable where it is clearly needed...that’s why we wanted to focus on drones delivering medicine and not delivering pizzas, ”said one executive of a drone system manufacturer. The immediate prospects for the expansion of medical drone use are many; however, they do not exist without their own drawbacks and challenges. Most obvious is the limited range of current commercially-available drones, most of which are isolated to a perimeter of roughly 18 miles. Technological know-how presents another barrier to integration of medical drones on a larger scale. Reports from the United Nations frequently cite a“skill deficit”—a prohibitively low number of qualified drone operators in low-and moderate-income countries (LMICs). Another perhaps more discreet speed bump in global drone development and usage are the various regulations on drone usage. Drone technology has developed so quickly that many states, out of an excess of caution, have nearly snuffed out the fledgling industry with regulation. There also exist significant concerns over the security of private citizens, the efficacy of medical deliveries, and the costs of drone operation. It is these last three barriers which this study will seek to overcome. Put simply, the prospect for human development in LMICs from drone-based medical delivery is far too great to disregard. As of 2020, 3.4 billion people live in rural communities, containing fewer than 5,000 people/km^2. Often lacking infrastructure, these communities are largely isolated from their more populated, urban counterparts. In drones lies the potential to reshape the geographic and developmental distinctions that divide the global population. This development must, therefore, begin first and foremost with advancement in regional well-being and life expectancy. Life expectancy makes up a key facet of human development. The United Nations relies on it as a key indicator of a state’s health. Lars Kunze of the Dortmund University Department of Economic sex plains this as a matter of physical capital accumulation. The longer people live, the more they save as opposed to spend. The more they save, the more which eventually gets invested in themselves and the community as a whole. In providing medical products via drone, it is the intention of this study to enable communities with the means and incentives for long-run savings and investment for future economic development. Through a close analysis of Vanuatu, Rwanda, Tanzania, and Ukraine—four states where drones are currently used to deliver medical supplies—this study develops a framework that LMICs in general and Mexico and particular can adopt and to use medical drones in difficult-to-reach communities for the sake of long-run human developmental initiatives.

Ryan Teoh↗
NASA NTRS1991

Numerical study of juncture flows

The present paper describes a computational study of laminar/turbulent and subsonic/supersonic horseshoe vortex systems generated by a cylindrical protuberance mounted on a flat plate. Various vortex structures are predicted and discussed. Low-speed laminar juncture flows are computed to determine the Reynolds number effect with the same incoming boundary-layer thickness. For a low subsonic laminar flow, the number of vortex arrays increases with the Reynolds number, in agreement with both experimental and numerical observations. Qualitative comparisons are made along with the computations, experimental observations, and analytical work. For incompressible flow, the relationships among pressure extrema, vorticity, and singular points in flow structure are discussed. A parametric study of the effect of the free-stream Mach number on the flow structure for laminar flow is conducted. The juncture flow when the incoming flow is turbulent and supersonic is computed.

Chen, Chung-Lung↗
NASA NTRS2020

Fusion Approach for Remotely-Sensed Mapping of Agriculture (FARMA): A Scalable Open Source Method for Land Cover Monitoring Using Data Fusion

The increasing availability of very-high resolution (VHR; <2 m) imagery has the potential to enable agricultural monitoring at increased resolution and cadence, particularly when used in combination with widely available moderate-resolution imagery. However, scaling limitations exist at the regional level due to big data volumes and processing constraints. Here, we demonstrate the Fusion Approach for Remotely-Sensed Mapping of Agriculture (FARMA), using a suite of open source software capable of efficiently characterizing time-series field-scale statistics across large geographical areas at VHR resolution. We provide distinct implementation examples in Vietnam and Senegal to demonstrate the approach using WorldView VHR optical, Sentinel-1 Synthetic Aperture Radar, and Sentinel-2 and Sentinel-3 optical imagery. This distributed software is open source and entirely scalable, enabling large area mapping even with modest computing power. FARMA provides the ability to extract and monitor sub-hectare fields with multisensor raster signals, which previously could only be achieved at scale with large computational resources. Implementing FARMA could enhance predictive yield models by delineating boundaries and tracking productivity of smallholder fields, enabling more precise food security observations in low and lower-middle income countries.

fusion↗
NASA NTRSDate not supplied

Fabrication and Performance Characterization of Electrospun Nanofibers for Terrestrial and Space Applications

Passive thermal control is vital in space, especially for extended missions involving cryogen storage needing protection from sunlight. This presentation covers the development of a thermal coating with wavelength-selective characteristics using polymeric materials that scatter sunlight with minimal absorption, resulting in high solar reflectance. Furthermore, these coatings allow emission in infrared wavelengths, making them suitable for deep-space missions requiring extended storage. The study chose polymer and surface morphology suitable as solar reflectors that are lightweight, compact, and easily manufacturable, focusing on different multilayered nanofibers made using polytetrafluoroethylene and polyethylene-oxide (PTFE-PEO), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and silica (SiO2). To understand how these materials interact with sunlight, we analyze light propagation through several layers of electrospun nanofibers to determine spectral reflectance, absorptance, and transmittance by solving the Maxwell equations. The model is also compared with measurements of spectral reflectance and transmittance of the various electrospun nanofibers using spectrophotometers interfaced with integrating spheres in the ultraviolet, visible, near-infrared, and mid-infrared wavelengths. The presentation will also describe the design and analysis, fabrication of the nanofibers using electrospinning, and several experimental characterization techniques to determine suitability for space applications. The nanofibers are tested using various tools to determine their suitability for cryogenic applications in space. Lastly, the samples were tested under low vacuum conditions and exposing them to sunlight inside a vacuum chamber maintained at 300 K. Relative to the incoming solar flux (1000 W/m2), only 1% of the energy was absorbed under these operating conditions. With further optimization and testing under high vacuum cryogenic environments, the samples could demonstrate much lower absorption or higher reflection of incoming solar radiation, which can translate to low temperatures suitable for cryogen storage.

Chieloka Ibekwe↗
NASA NTRS1991

Low-Noise Charge-Coupled Device

Same quantity measured many times to reduce uncertainty. "Skipper" charge-coupled device (CCD) underlines development of new class of imaging detectors exhibiting exceptionally low readout noise. Operates on nondestructive-readout scheme combined with other advances in CCD technology to reduce average readout noise to less than 1 electron rms. Concept has potential for improving video images made at ultra-low light levels, involving only few incoming photons per picture element (pixel).

Janesick, James R.↗
NASA NTRS1999

Condensation of Forced Convection Two-Phase Flow in a Miniature Tube

A physical/mathematical model of annular film condensation at the inlet of a miniature tube has been developed. In the model, the liquid flow is coupled with the vapor flow along the liquid-vapor interface through the interfacial temperature, heat flux, shear stress, and pressure jump conditions due to surface tension effects. The model predicts the shape of the liquid-vapor interface along the condenser and leads to the conclusion that there is complete condensation at a certain distance from the condenser inlet. The numerical results show that complete condensation of the incoming vapor is possible at comparatively low heat loads and that this is a special case of a more general condensation regime with two-phase bubbly flow downstream of the initial annular film condensation region. Observations from the flow visualization experiment confirm the existence and qualitative features of annular film condensation leading to the complete condensation phenomenon in a small diameter (3.25 mm) circular tube condenser.

Begg, E.↗
NASA NTRS1992

Phase-locked loop FM demodulator

A conventional phase-locked loop is improved by replacing its phase detector with one comprising a linear ramp generator and a sample-and-hold circuit, thus eliminating the need for a lowpass loop filter, although the output of the sample-and-hold circuit may be filtered in the case of a very low level modulating signal on the incoming FM signal, but then filtering is not a difficult problem as in a conventional phase-locked loop. The result is FM demodulation by zero-order estimation. For FM demodulation by first-order estimation, the arithmetic difference between adjacent samples is formed, and using a second sample-and-hold circuit an arithmetic difference signal is produced as an input to a second ramp generator that is reset after each sampling cycle to generate a ramp the slope of which is a function of the arithmetic difference signal stored in the second sample-and-hold circuit. The ramp thus generated by the second ramp generator is arithmetically summed with the zero-estimation signal from the first sample-and-hold circuit to form a first-order estimation signal. Filtering such a first-order estimation signal is less of a problem than filtering a zero-order estimation signal.

Kirkham, Harold↗
NASA NTRS2001

Reaction Kernel Structure of a Slot Jet Diffusion Flame in Microgravity

Diffusion flame stabilization in normal earth gravity (1 g) has long been a fundamental research subject in combustion. Local flame-flow phenomena, including heat and species transport and chemical reactions, around the flame base in the vicinity of condensed surfaces control flame stabilization and fire spreading processes. Therefore, gravity plays an important role in the subject topic because buoyancy induces flow in the flame zone, thus increasing the convective (and diffusive) oxygen transport into the flame zone and, in turn, reaction rates. Recent computations show that a peak reactivity (heat-release or oxygen-consumption rate) spot, or reaction kernel, is formed in the flame base by back-diffusion and reactions of radical species in the incoming oxygen-abundant flow at relatively low temperatures (about 1550 K). Quasi-linear correlations were found between the peak heat-release or oxygen-consumption rate and the velocity at the reaction kernel for cases including both jet and flat-plate diffusion flames in airflow. The reaction kernel provides a stationary ignition source to incoming reactants, sustains combustion, and thus stabilizes the trailing diffusion flame. In a quiescent microgravity environment, no buoyancy-induced flow exits and thus purely diffusive transport controls the reaction rates. Flame stabilization mechanisms in such purely diffusion-controlled regime remain largely unstudied. Therefore, it will be a rigorous test for the reaction kernel correlation if it can be extended toward zero velocity conditions in the purely diffusion-controlled regime. The objectives of this study are to reveal the structure of the flame-stabilizing region of a two-dimensional (2D) laminar jet diffusion flame in microgravity and develop a unified diffusion flame stabilization mechanism. This paper reports the recent progress in the computation and experiment performed in microgravity.

Takahashi, F.↗
NASA NTRS2004

First Astronomical Use of Multiplexed Transition Edge Sensor Bolometers

We present performance results based on the first astronomical use of multiplexed superconducting bolometers. The Fabry-Perot Interferometer Bolometer Research Experiment (FIBRE) is a broadband submillimeter spectrometer that achieved first light in June 2001 at the Caltech Submillimeter Observatory (CSO). FIBRE's detectors are superconducting transition edge sensor (TES) bolometers read out by a SQUID multiplexer. The Fabry-Perot uses a low resolution grating to order sort the incoming light. A linear bolometer array consisting of 16 elements detects this dispersed light, capturing 5 orders simultaneously from one position on the sky. With tuning of the Fabry-Perot over one free spectral range, a spectrum covering Delta lambda/lambda = 1/7 at a resolution of delta lambda/lambda approx. 1/1200 can be acquired. This spectral resolution is sufficient to resolve Doppler-broadened line emission from external galaxies. FIBRE operates in the 350 m and 450 m bands. These bands cover line emission from the important star formation tracers neutral carbon (CI) and carbon monoxide (CO). We have verified that the multiplexed bolometers are photon noise limited even with the low power present in moderate resolution spectrometry.

Staguhn, J. G.↗
NASA NTRS2001

First Astronomical Use Of Multiplexed Transition Edge Bolometers

We present performance results based on the first astronomical use of multiplexed superconducting bolometers. The Fabry-Perot Interferometer Bolometer Research Experiment (FIBRE) is a broadband submillimeter spectrometer that achieved first light in June 2001 at the Caltech Submillimeter Observatory (CSO). FIBRE's detectors are superconducting transition edge sensor (TES) bolometers read out by a SQUID multiplexer. The Fabry-Perot uses a low resolution grating to order sort the incoming light. A linear bolometer array consisting of 16 elements detects this dispersed light, capturing five orders simultaneously from one position on the sky. With tuning of the Fabry-Perot over one free spectral range, a spectrum covering delta-lamda/lamda = 1/7 at a resolution of delta-lamda/lamda = 1/1200 can be acquired. This spectral resolution is sufficient to resolve doppler broadened line emission from external galaxies. FIBRE operates in the 350 micrometer and 450 micrometer bands. These bands cover line emission from the important PDR tracers neutral carbon [CI] and carbon monoxide (CO). We have verified that the multiplexed bolometers are photon noise limited even with the low power present in moderate resolution spectrometry.

Benford, D. J.↗
NASA NTRS2004

Glow Discharge Plasma Demonstrated for Separation Control in the Low-Pressure Turbine

Flow separation in the low-pressure turbine (LPT) is a major barrier that limits further improvements of aerodynamic designs of turbine airfoils. The separation is responsible for performance degradation, and it prevents the design of highly loaded airfoils. The separation can be delayed, reduced, or eliminated completely if flow control techniques are used. Successful flow control technology will enable breakthrough improvements in gas turbine performance and design. The focus of this research project was the development and experimental demonstration of active separation control using glow discharge plasma (GDP) actuators in flow conditions simulating the LPT. The separation delay was shown to be successful, laying the foundation for further development of the technologies to practical application in the LPT. In a fluid mechanics context, the term "flow control" means a technology by which a very small input results in a very large effect on the flow. In this project, the interest is to eliminate or delay flow separation on LPT airfoils by using an active flow control approach, in which disturbances are dynamically inserted into the flow, they interact with the flow, and they delay separation. The disturbances can be inserted using a localized, externally powered, actuating device, examples are acoustic, pneumatic, or mechanical devices that generate vibrations, flow oscillations, or pulses. A variety of flow control devices have been demonstrated in recent years in the context of the external aerodynamics of aircraft wings and airframes, where the incoming flow is quiescent or of a very low turbulence level. However, the flow conditions in the LPT are significantly different because there are high levels of disturbances in the incoming flow that are characterized by high free-stream turbulence intensity. In addition, the Reynolds number, which characterizes the viscous forces in the flow and is related to the flow speed, is very low in the LPT passages.

Ashpis, David e.↗
NASA NTRS2002

Broadband Direct Detection Submillimeter Spectrometer with Multiplexed Superconducting Transition Edge Thermometer Bolometers

We present performance results based on the first astronomical use of multiplexed superconducting bolometers as direct detectors (i.e., with cold electrons) for spectroscopy. The Fabry-Perot Interferometer Bolometer Research Experiment (FIBRE) is a broadband submillimeter spectrometer for the Caltech Submillimeter Observatory (CSO). FIBRE's detectors are superconducting transition edge sensor (TES) bolometers read out by a SQUID multiplexer. The Fabry-Perot uses a low resolution grating to order sort the incoming light. A linear bolometer array consisting of 16 elements detects this dispersed light, capturing 5 orders simultaneously from one position on the sky. With tuning of the Fabry-Perot over one free spectral range, a spectrum covering Delta lambda/lambda = 1/7 at a resolution of delta lambda/lambda = 1/1200 can be acquired. This spectral resolution is sufficient to resolve Doppler-broadened line emission from external galaxies. FIBRE has been operated in the 350 Am (850 GHz) band. These bands cover line emission from the important star formation tracers neutral carbon [CI] and carbon monoxide (CO).

Benford, D. J.↗
NASA NTRS1973

Mechanisms for Mars dust storms.

Characteristics of the Mars global dust storm are reviewed. At the Mariner 9 encounter, the dust consisted of highly absorbing particles distributed rather uniformly up to great height (about 50 km). These observations together with temperature distributions inferred from the Mariner 9 IRIS by Hanel et al. (1972) are used to estimate global wind systems during the dust storm. The global distribution and direction of light surface streaks indicate that the axisymmetric circulation was a dominant part of flow during the dust storm. The axisymmetric winds may become strong enough to raise dust over wide areas of Mars' tropics under unusual conditions: the incoming solar radiation must be near its seasonal maximum, the static stability must be low, and the atmosphere must be able to absorb and re-emit a sizeable fraction of the incoming radiation. Strong winds around the periphery of the retreating south polar cap would be driven by the temperature gradient at the cap edge and by the mass outflow due to subliming CO2. These polar winds could generate local dust storms, raising the general level of dustiness, and providing the conditions necessary for onset of a global dust storm.

Leovy, C. B.↗
NASA NTRS1990

Computational analysis of the flowfield of a two-dimensional ejector nozzle

A time-iterative full Navier-Stokes code, PARC, is used to analyze the flowfield of a two-dimensional ejector nozzle system. A parametric study was performed for two controlling parameters, duct to nozzle area ratio and nozzle pressure ratio. Results show that there is an optimum area ratio for the efficient pumping of secondary flow. At high area ratios, a freestream flow passes directly through the mixing duct without giving adequate pumping. At low area ratios, the jet boundary blocks the incoming flow. The nozzle pressure ratio variation shows that the pumping rate increases as the pressure ratio increases, provided there is no interaction between the shroud wall and the shock cell structure.

Choi, Y. H.↗