Search NASA⌕ Search

SEARCH · Search NASA

Results for “Population dynamics”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

High-Resolution Near-Infrared Spectroscopy of an Equivalent Width-Selected Sample of Starbursting Dwarf Galaxies

Spectroscopic observations from the Large Binocular Telescope and the Very Large Telescope reveal kinematically narrow lines (approx. 50 km/s) for a sample of 14 Extreme Emission Line Galaxies (EELGs) at redshifts 1.4 < zeta < 2.3. These measurements imply that the total dynamical masses of these systems are low ( 3 × 10(exp 9) M). Their large [O III]5007 equivalent widths (500 − 1100 A) and faint blue continuum emission imply young ages of 10−100 Myr and stellar masses of 10(exp 8)−10(exp 9) M, confirming the presence of a violent starburst. The stellar mass formed in this vigorous starburst phase thus represents a large fraction of the total (dynamical) mass, without a significantly massive underlying population of older stars. The occurrence of such intense events in shallow potentials strongly suggests that supernova-driven winds must be of critical importance in the subsequent evolution of these systems.

Spectroscopy↗
NASA NTRS2017

Temporal Consistency Between Gross Primary Production and Solar-Induced Chlorophyll Fluorescence in the Ten Most Populous Megacity Areas over Years

The gross primary production (GPP) of vegetation in urban areas plays an important role in the study of urban ecology. It is difficult however, to accurately estimate GPP in urban areas, mostly due to the complexity of impervious land surfaces, buildings, vegetation, and management. Recently, we used the Vegetation Photosynthesis Model (VPM), climate data, and satellite images to estimate the GPP of terrestrial ecosystems including urban areas. Here, we report VPM-based GPP (GPPvpm) estimates for the world's ten most populous megacities during 2000-2014. The seasonal dynamics of GPPvpm during 2007-2014 in the ten megacities track well that of the solar-induced chlorophyll fluorescence (SIF) data from GOME-2 at 0.5deg x 0.5deg resolution. Annual GPPvpm during 2000-2014 also shows substantial variation among the ten megacities, and year-to-year trends show increases, no change, and decreases. Urban expansion and vegetation collectively impact GPP variations in these megacities. The results of this study demonstrate the potential of a satellite-based vegetation photosynthesis model for diagnostic studies of GPP and the terrestrial carbon cycle in urban areas.

urban↗
NASA NTRS1993

Radio morphology and parent population of X-ray selected BL Lacertae objects

High-dynamic range (typically 1700:1) radio maps of 15 X-ray BL Lac (XBL) objects from the HEAO-1 Large Area Sky Survey are presented. Morphological characteristics of these sources are compared with Fanaroff-Riley (FR) class I radio galaxies in the context of unified schemes, with reference to one-sided kiloparsec-scale emission. Evidence that cluster membership of XBLs is significantly higher than previously thought is also presented. It is shown that the extended radio powers, X-ray emission, core-to-lobe ratios, and linear sizes of the radio selected BL Lac (RBL) and XBL populations are consistent with an FR I radio galaxy parent population. A source list and VLA observing log and map parameters are provided.

Laurent-Muehleisen, S. A.↗
NASA NTRS1991

Dynamic (computer) modelling of the particulate environment: Transformations from the LDEF reference frame to decode geocentric and interplanetary populations

The Long Duration Exposure Facility's impact signature record and the size frequency distribution of craters and perforations offers a unique record of environmental data referenced conveniently to the geocentric reference frame. Chemical analysis of residues can offer only limited assistance. Hence, flux modelling has been developed to transform from both geocentric orbital distributions and geocentrically unbounded interplanetary source distributions. This is applied to the foil and crater penetration records in the Ram (E), Trailing (W), and Space Pointing directions to offer the means of decoding the records. It shows that the mix of the components is size dependent. Parametric forms of the modelling transformations are presented for the orbital and unbound populations.

Mcdonnell, J. A. M.↗
NASA NTRS1992

Dynamic (computer) modelling of the particulate environment: Transformations from the LDEF reference frame to decode geocentric and interplanetary populations

The Long Duration Exposure Facility (LDEF) impact signature record and the size frequency distribution of craters and perforations offers a unique record of environmental data referenced conveniently to the geocentric reference frame. Chemical analysis of residues can offer only limited assistance. Hence, flux modeling has been developed to transform both geocentric orbital distributions and geocentrically unbounded interplanetary source distributions. This is applied to the foil and crater penetration records in the Ram (E), Trailing (W), and Space Pointing directions to offer the means of decoding the records. It shows that the mix of the components is size dependent. Parametric forms of the modeling transformations are presented for the orbital and unbounded populations.

Mcdonnell, J. A. M.↗
NASA NTRS1986

The Oort cloud and the Galaxy - Dynamical interactions

The results of recent dynamical studies of the Oort cloud and its interaction with the Galaxy are discussed. Various studies which used Monte Carlo simulations to investigate the evolution of comets in the Oort cloud and the manner in which they are injected into the planetary region are reviewed. Work done on perturbation of cometary orbits by stars, interstellar clouds, and the Galaxy is examined. The growing consensus that there is a massive inner Oort cloud with a population up to 100 times that of the dynamically active outer cloud is addressed. Variations on the Oort hypothesis are discussed. It is argued that speculations about the existence of a small unseen solar companion star or a tenth planet causing periodic comet showers from the inner Oort cloud are not supported by dynamical studies or analyses of the terrestrial and lunar cratering record. Evidence for Oort clouds around other stars is summarized.

Weissman, Paul R.↗
NASA NTRS1982

Dynamical history of the Oort Cloud

Oort's hypothesis for the origin of long-period comets is reviewed, along with evidence for the existence of the Oort Cloud and recent research in stellar perturbations of cometary orbits. A Monte Carlo model is used to analyze the dynamics of comets in the Oort Cloud, to estimate the present and original populations of the cloud, and to examine implications for various theories of the origin of comets. The problem of interstellar comets is briefly considered. It is concluded that: (1) the weight of evidence favors Oort's hypothesis of a cloud of a trillion comets surrounding the solar system and extending out to about 100,000 AU; (2) the dynamical evolution of the cloud is consistent with observational data on long-period comets; and (3) estimates of the population necessary to produce the observed flux of dynamically new comets lead to physically reasonable values for the current and initial cloud masses.

Weissman, P. R.↗
NASA NTRS2010

Implementing and Simulating Dynamic Traffic Assignment with Intelligent Transportation Systems in Cube Avenue

As urban populations and traffic congestion levels increase, effective use of information and communication tools and intelligent transportation systems as becoming increasingly important in order to maximize the efficiency of transportation networks. The appropriate placement and employment of these tools within a network is critical to their effectiveness. This presentation proposes and demonstrates the use of a commercial transportation simulation tool to simulate dynamic traffic assignment and rerouting to model route modifications as a result of traffic information.

Foytik, Peter↗
NASA NTRS2019

Architecture and Dynamics of Kepler's Multi-Transiting Planet Systems.III. Comprehensive Investigation Using All Four Years of Kepler Mission Data

We study the orbital architectures of planetary systems orbiting within ∼1 AU of their stars by analyzing the ensemble of Kepler systems having two or more planet candidates. We use data from the entire Kepler mission, and in many cases we apply improved analysis techniques (e.g., replacing histograms by top-hat Kernel Density Estimators that avoid the loss of information resulting from choosing a particular phase for the bin boundaries) to extend and enhance the studies of Lissauer et al. (2011, ApJS 197, 8) and Fabrycky et al. (2014, ApJ 790, 146).These data show ~ 1700 transiting planet candidates in > 600 multiple-planet systems, far more than were available for our previous two studies. The increased numbers and better information about planetary radii and the properties of stellar hosts made possible by Gaia DR2 allow more statistically-robust analyses of the entire ensemble of Kepler multis as well as independent analyses of subsets of the population. We are thus able to contrast the dynamical configurations of small and large planets, short-period and longer-period planets, and planets orbiting various types of host stars. We reinforce our previous findings that most pairs of planets within the same system are neither in nor near low-order mean motion resonances and that there is a substantial excess of planets having period ratios slightly larger than those of first-order mean-motion resonances. However, neglecting three systems whose planets are locked in 3- body resonances and summing over all first-order mean motion resonances, the deficit of planet pairs with period ratios just narrow of resonance is as large as the excess of planets wide of resonance (within statistical uncertainties), suggesting that overall there is no overall excess of planet pairs in the vicinity of resonance. Other aspects of our study, including estimates of the typical relative inclinations of planetary orbits and their variations as functions of orbital period, planet sizes and stellar properties, are in progress, with results expected to be available for presentation by the time of the conference.

Lissauer, Jack↗
NASA NTRS1992

The first identification of a mainbelt asteroid source for a meteorite Class E-type Apollo asteroid (3103) 1982BB: A link between the Hungaria asteroid zone and the Aubrite meteorites

One of the major goals of asteroid investigators has been to determine the source bodies of the meteorites, and, thus, to provide the needed spatial context. However, despite careful investigation of many of these asteroids, no specific mainbelt asteroidal parent bodies for particular meteorites have yet been identified. Results are reported that represent the first direct link of a set of meteorites (the aubrites or enstatite achondrites) back to a particular source region in the asteroid belt (the Hungaria zone of the innermost belt located at a heliocentric distance of about 1.9 AU (1.9 times the Earth's distance from the Sun)). Since most asteroids in the belt are still located near their original heliocentric formation distances, this link allows the composition and temperature of the solar nebula to be determined at a specific distance from the Sun during the time of planetesimal formation. Orbital considerations suggest that 3103 could be derived from the Hungaria zone. However, the spectral gype of 3103 makes such a source probable. The Hungaria zone is the only region of the asteroid belt where E-type asteroids are common. E-type objects constitute about 55 percent of the classified Hungaria population. Although a more detailed investigation of the dynamical evolution of this object is needed, it appears highly probable that 3103 1982BB was derived from the Hungaria region of the innermost asteroid belt, that it is a fragment of the collisional breakup of an E-object near 1.9 AU, and escaped the mainbelt via the nu sup 16 resonance.

Gaffey, M. J.↗
NASA NTRS1992

The Galileo Energetic Particles Detector

Amongst its complement of particles and fields instruments, the Galileo spacecraft carries an Energetic Particles Detector (EPD) designed to measure the characteristics of particle populations important in determining the size, shape, and dynamics of the Jovian magnetosphere. To do this the EPD provides 4pi angular coverage and spectral measurements for Z greater than or equal to 1 ions from 20 keV to 55 MeV, for electrons from 15 keV to greater than 11 MeV, and for the elemental species helium through iron from approximately 10 keV/nucl to 15 MeV/nucl. Two bidirectional telescopes, mounted on a stepping platform, employ magnetic deflection, energy loss versus energy, and time-of-flight techniques to provide 64 rate channels and pulse height analysis of priority selected events. The EPD data system provides a large number of possible operational modes from which a small number will be selected to optimize data collection during the many encounter and cruise phases of the mission. The EPD employs a number of safeing algorithms that are to be used in the event that its self-checking procedures indicate a problem. The instrument and its operation are described.

Williams, D. J.↗
NASA NTRS1995

The striking near-infrared morphology of the inner region in M100

New optical and near-infrared (NIR) K-band images of the inner 3 kpc region of the nearby Virgo spiral M100 (NGC 4321) display remarkable morphological changes with wavelength. While in the optical the light is dominated by circumnuclear zone of enhanced star formation, the morphological features in the 2.2 micrometer image correspond to a newly discovered kiloparsec-size stellar bar and a pair of leading arms situated inside an ovally shaped region. Analysis of the K image confirms its symmetry: only a very small percentage of the flux, some 5%, is emitted in antisymmetric structures. This indicates that the overall morphology observed in the NIR is dominated by a global density wave. Making a first-order correction for the presence of localized dust extinction in the K light using the I-K image, we find that the observed leading arm morphology is not caused or enhanced but in fact slightly hidden by dust. Possible mechanisms responsible for the optical and NIR morphology are discussed, and tests are proposed to discriminate between them. Our dynamical conclusions are supported with an evolutionary stellar population model reproducing the observed optical and NIR colors in a number of star-forming zones. We argue that the observed morphology is compatible with the presence of a pair of inner Lindblad resonances in the region and show this explicitly in an accompanying paper by detailed numerical modeling. The phenomena observed in NGC 4321 may provide insight into physical process leading to central activity in galaxies.

Knapen, J. H.↗
NASA NTRS1987

Evolution of planetesimal velocities

A self-consistent set of equations for the velocity evolution of a general planetesimal population is presented. The equations are given in a form convenient for calculations of the early stages of planetary accumulation when it is necessary to model the planetesimal swarm by methods of gas dynamics, rather than follow the orbital evolution of individual bodies. Steady state velocities of a simple planetesimal population consisting of two different sizes of bodies are calculated. Dynamical friction is found to be an important mechanism for transferring kinetic energy from the larger planetesimals to the smaller ones. When the small planetesimals are relatively abundant, gas drag and inelastic collisions among the smaller bodies are of comparable importance for dissipating energy from the population.

Stewart, Glen R.↗
NASA NTRS1975

Physical and dynamical studies of meteors. Meteor-fragmentation and stream-distribution studies

Population parameters of 275 streams including 20 additional streams in the synoptic-year sample were found by a computer technique. Some 16 percent of the sample is in these streams. Four meteor streams that have close orbital resemblance to Adonis cannot be positively identified as meteors ejected by Adonis within the last 12000 years. Ceplecha's discrete levels of meteor height are not evident in radar meteors. The spread of meteoroid fragments along their common trajectory was computed for most of the observed radar meteors. There is an unexpected relationship between spread and velocity that perhaps conceals relationships between fragmentation and orbits; a theoretical treatment will be necessary to resolve these relationships. Revised unbiased statistics of synoptic-year orbits are presented, together with parallel statistics for the 1961 to 1965 radar meteor orbits.

Sekanina, Z.↗
NASA NTRS1997

Comparison of Dawn and Dusk Precipitating Electron Energy Populations Shortly After the Initial Shock for the January 10th, 1997 Magnetic Cloud

The observed precipitating electron energy between 0130 UT and 0400 UT of January 10 th, 1997, indicates that there is a more energetic precipitating electron population that appears in the auroral oval at 1800-2200 UT at 030) UT. This increase in energy occurs after the initial shock of the magnetic cloud reaches the Earth (0114 UT) and after faint but dynamic polar cap precipitation has been cleared out. The more energetic population is observed to remain rather constant in MLT through the onset of auroral activity (0330 UT) and to the end of the Polar spacecraft apogee pass. Data from the Ultraviolet Imager LBH long and LBH short images are used to quantify the average energy of the precipitating auroral electrons. The Wind spacecraft located about 100 RE upstream monitored the IMF and plasma parameters during the passing of the cloud. The affects of oblique angle viewing are included in the analysis. Suggestions as to the source of this hot electron population will be presented.

Spann, J.↗
NASA NTRS1981

The Retarding Ion Mass Spectrometer on Dynamics Explorer-A

The thermal component of the magnetospheric plasma plays a key role in magnetosphere-ionosphere coupling processes, acting as a strong influence on ionospheric structure at low altitudes and as a source and modifier of the hotter plasma population at high altitudes. The Retarding Ion Mass Spectrometer (RIMS) instrument on Dynamics Explorer-A is designed to measure this important thermal plasma component. Using a combination of retarding potential analysis and magnetic ion mass spectrometer techniques, the RIMS instrument will measure the bulk plasma parameters of ion density (0.1 to 1,000,000 ions/cu cm), temperature (0-45 eV), and bulk flow (greater than 0.5 km/sec) in the inner plasmasphere and ionosphere, and the specific ion pitch angle and energy spectral characteristics in the outer plasmasphere and plasma trough for a mass range of 1-32 amu. The energy and mass spectral step sequences, as well as the multiplexing of the resultant data, can be tailored to accomplish a variety of thermal ion measurements throughout the inner magnetosphere.

Chappell, C. R.↗
NASA NTRS2016

Assessing Woody Vegetation Trends in Sahelian Drylands Using MODIS Based Seasonal Metrics

Woody plants play a major role for the resilience of drylands and in peoples' livelihoods. However, due to their scattered distribution, quantifying and monitoring woody cover over space and time is challenging. We develop a phenology driven model and train/validate MODIS (MCD43A4, 500m) derived metrics with 178 ground observations from Niger, Senegal and Mali to estimate woody cover trends from 2000 to 2014 over the entire Sahel. The annual woody cover estimation at 500 m scale is fairly accurate with an RMSE of 4.3 (woody cover %) and r(exp 2) = 0.74. Over the 15 year period we observed an average increase of 1.7 (+/- 5.0) woody cover (%) with large spatial differences: No clear change can be observed in densely populated areas (0.2 +/- 4.2), whereas a positive change is seen in sparsely populated areas (2.1 +/- 5.2). Woody cover is generally stable in cropland areas (0.9 +/- 4.6), reflecting the protective management of parkland trees by the farmers. Positive changes are observed in savannas (2.5 +/- 5.4) and woodland areas (3.9 +/- 7.3). The major pattern of woody cover change reveals strong increases in the sparsely populated Sahel zones of eastern Senegal, western Mali and central Chad, but a decreasing trend is observed in the densely populated western parts of Senegal, northern Nigeria, Sudan and southwestern Niger. This decrease is often local and limited to woodlands, being an indication of ongoing expansion of cultivated areas and selective logging.We show that an overall positive trend is found in areas of low anthropogenic pressure demonstrating the potential of these ecosystems to provide services such as carbon storage, if not over-utilized. Taken together, our results provide an unprecedented synthesis of woody cover dynamics in theSahel, and point to land use and human population density as important drivers, however only partially and locally offsetting a general post-drought increase.

Brandt, Martin↗
NASA NTRS1982

LIDAR and acoustics applications to ocean productivity

The requirements for the submersible, the instrumentation necessary to perform these measurements, and the optical and acoustical technology required to develop the ocean color scanner instrumentation are described. The development of a second generation ocean color scanner produced the need for coincident in situ scientific measurements which examine the primary productivity of the upper ocean on time and space scales which are large compared to the environmental scales. The vertical and horizontal variability of the biota, including the relationship between chlorophyll and primary productivity, the productivity of zooplankton, and the dynamic interaction between phytoplankton and zooplankton, and between these populations and the physical environment are investigated. A towed submersible will be constructed which accommodates both an underwater LIDAR instrument and a multifrequency sonar.

Collins, D. J.↗