Teunissen van Manen J.L.,University of Tennessee at Knoxville |
Muller L.I.,University of Tennessee at Knoxville |
Li Z.-H.,University of Tennessee at Knoxville |
Li Z.-H.,Center for Space Plasma and Aeronomic Research |
And 2 more authors.
Isotopes in Environmental and Health Studies | Year: 2014
We measured stable carbon and nitrogen isotope ratios in 117 hair samples from American black bears (Ursus americanus) in Great Smoky Mountains National Park, Tennessee, during 1980-2001 from live-trapped bears. We also collected hair from bears with known diets to compare with the wild bears. We hypothesized that biological factors (age, mass, and sex), food availability (hard mast and wild hogs (Sus scrofa)), and nuisance status would influence food selection by black bears and changes in their feeding history would be measureable using stable isotopes. We developed a set of a priori models using nine variables to examine changes in black bear stable isotope values. We found no support for changes in δ13C values associated with any of the nine variables we analyzed. Bears had enriched 15N in years with low white oak mast production and depleted 15N when white oak mast was abundant. Subadults had enriched 15N compared with adults and older adults. Variation in δ15N increased from 1980-1991 to 1992-2000 when hard mast production had greater fluctuations. Bears in a better physical condition appeared more likely to access foods with higher protein content. In years of low white oak acorn production, larger bears and subadults likely turned to alternative food sources. The long-term variation detected in this study was important in identifying which bears were potentially more susceptible to changes in availability of hard mast. © 2014 © 2014 Taylor & Francis.
Winebarger A.R.,NASA |
Warren H.P.,U.S. Navy |
Schmelz J.T.,University of Memphis |
Cirtain J.,NASA |
And 3 more authors.
Astrophysical Journal Letters | Year: 2012
Observing high-temperature, low emission measure plasma is key to unlocking the coronal heating problem. With current instrumentation, a combination of EUV spectral data from Hinode Extreme-ultraviolet Imaging Spectrometer (EIS; sensitive to temperatures up to 4MK) and broadband filter data from Hinode X-ray Telescope (XRT; sensitive to higher temperatures) is typically used to diagnose the temperature structure of the observed plasma. In this Letter, we demonstrate that a "blind spot" exists in temperature-emission measure space for combined Hinode EIS and XRT observations. For a typical active region core with significant emission at 3-4MK, Hinode EIS and XRT are insensitive to plasma with temperatures greater than ∼6 MK and emission measures less than ∼1027 cm-5. We then demonstrate that the temperature and emission measure limits of this blind spot depend upon the temperature distribution of the plasma along the line of sight by considering a hypothetical emission measure distribution sharply peaked at 1MK. For this emission measure distribution, we find that EIS and XRT are insensitive to plasma with emission measures less than ∼1026 cm-5. We suggest that a spatially and spectrally resolved 6-24 Å spectrum would improve the sensitivity to these high-temperature, low emission measure plasma. © 2012 The American Astronomical Society. All rights reserved.
Li Z.-H.,NASA |
Li Z.-H.,Center for Space Plasma and Aeronomic Research |
Driese S.G.,Baylor University |
Cheng H.,Xi'an Jiaotong University |
Cheng H.,University of Minnesota
Sedimentology | Year: 2014
The suitability of speleothems for interpreting palaeoclimate is typically determined by using either the Hendy Test, overlapping analysis or long-term cave environment monitoring. However, in many cases, these methods are not applicable, because a speleothem lacks clearly traceable layers for the Hendy Test, it is difficult to obtain an overlapping speleothem nearby, or long-term cave monitoring is impractical. The authors propose a multiple cave deposit approach to assess the suitability of speleothems for palaeoclimate study. Speleothems collected from two sites within Raccoon Mountain Cave, Tennessee (USA) exhibit remarkable spatial variation (δ13C: -10·3‰ to -2·2‰) over a relatively short distance (ca 260 m). Drip water δ18O values exhibit a seasonal precipitation signal at Site 1 and an annual signal at Site 2. Combining field observations, water isotope analysis and trace-element data, the authors propose that the speleothem formation at Site 1 and Site 2 tapped distinct sources of CO2: (i) CO2 derived from overlying soils for Site 1; and (ii) limestone dissolved inorganic carbon induced by ground water dissolution for Site 2. Using fresh cave deposits (modern speleothem) δ13C (100% C3 vegetation) as an analogue, a simple model was developed to estimate land surface vegetation for speleothems. The speleothem formation temperature estimated using fresh cave deposit δ18O values generally reflects the mean annual temperature in this region. This study indicates that spatial variations in carbon isotopes could be caused by different carbon sources dominating in different parts of the cave, which should be taken into consideration by researchers when using speleothem δ13C values to reconstruct temporal palaeo-vegetation changes. This study demonstrates a practical sampling strategy for verifying suitability of speleothems for palaeo-vegetation and palaeo-temperature reconstructions by analysing multiple cave deposits, especially for cases in which the Hendy Test, parallel sampling and long-term monitoring of cave environment are not feasible. © 2013 International Association of Sedimentologists.
News Article | November 30, 2016
The Fast Neutron Spectrometer (FNS) is now aboard the International Space Station. Neutrons contribute to crew radiation exposure and must be measured to assess exposure levels. The FNS, developed by NASA's Marshall Space Flight Center (MSFC) and Johnson Space Center (JSC), uses a new instrument design that can significantly improve the reliability of identifying neutrons in the mixed radiation field found in deep space. The MSFC principle investigator and team lead is Mark Christl. The NASA JSC project manager is Catherine Mcleod and the technical lead is Eddie Semones at NASA JSC. "Our technique improves upon the well-establish 'capture-gated' method that uses boron-10 loaded plastic scintillators to measure the energy of fast neutrons," says Evgeny Kuznetsov, a research engineer at UAH's Center for Space Plasma and Aeronomic Research (CSPAR), who with CSPAR research scientist John Watts worked on the device. "The central element of FNS is a custom composite scintillator combined with specialized electronics that work together to separate clearly the signals due to neutrons from the signals due to other forms of radiation." The FNS is deployed on the ISS for six months to conduct a technology demonstration to evaluate its performance in a space environment. It will then remain indefinitely to fulfill secondary objectives. "The FNS central detector was manufactured in the lab at NSSTC and comprises a structure of 5,000 regularly spaced neutron sensitive Li6-doped scintillating glass fibers cast in a one-liter plastic scintillator," says Kuznetsov. In combination with specially adjusted parameters of readout electronics, the design allows the detector to measure the neutron spectrum in a mixed radiation environment. "The scintillation light produced in these two scintillators is distinct, and we exploit this difference to better understand the signals generated in response to neutrons," says Watts. "The plastic scintillator responds to the neutron losing all of its energy, and the glass fibers provide positive identification that a neutron was captured. This sequence of signals produces a trigger in the electronics, and the data is recorded for analysis." At UAH, Watts did simulations of the detector performance and simulations of gamma rejection efficiency. Kuznetsov designed front-end electronics boards, which acquire signals from photomultiplier tubes attached at the opposite sides of the central detector. These electronics boards amplify and condition acquired signals to achieve optimal neutron detection efficiency and measurement of the energy of the registered neutrons. Kuznetsov also participated in the manufacturing of the central detector. Data acquired during FNS' flight on the ISS will be used to evaluate the performance of the neutron measurement technique as well as the capability of FNS to operate in the space environment. "This validation is critical to insure FNS can meet the radiation monitoring requirements for the deep space environment during manned exploration missions," says Kuznetsov. "The data collected by FNS will be analyzed and compared to measurements made by other techniques and with calculations of the neutron flux predicted by models of the ISS in the low Earth orbit environment."
Panesar N.K.,Center for Space Plasma and Aeronomic Research |
Sterling A.C.,Marshall Space Flight Center |
Innes D.E.,Max Planck Institute for Solar System Research |
Moore R.L.,Center for Space Plasma and Aeronomic Research |
Moore R.L.,Marshall Space Flight Center
Astrophysical Journal | Year: 2015
Homologous flares are flares that occur repetitively in the same active region, with similar structure and morphology. A series of at least eight homologous flares occurred in active region NOAA 11237 over 2011 June 16-17. A nearby prominence/filament was rooted in the active region, and situated near the bottom of a coronal cavity. The active region was on the southeast solar limb as seen from the Solar Dynamics Observatory/Atmospheric Imaging Assembly, and on the disk as viewed from the Solar TErrestrial RElations Observatory/EUVI-B. The dual perspective allows us to study in detail behavior of the prominence/filament material entrained in the magnetic field of the repeatedly erupting system. Each of the eruptions were mainly confined, but expelled hot material into the prominence/filament cavity system (PFCS). The field carrying and containing the ejected hot material interacted with the PFCS and caused it to inflate, resulting in a step-wise rise of the PFCS approximately in step with the homologous eruptions. The eighth eruption triggered the PFCS to move outward slowly, accompanied by a weak coronal dimming. As this slow PFCS eruption was underway, a final "ejective" flare occurred in the core of the active region, resulting in strong dimming in the EUVI-B images and expulsion of a coronal mass ejection (CME). A plausible scenario is that the repeated homologous flares could have gradually destabilized the PFCS, and its subsequent eruption removed field above the acitive region and in turn led to the ejective flare, strong dimming, and CME. © 2015. The American Astronomical Society. All rights reserved..
Panesar N.K.,Marshall Space Flight Center |
Panesar N.K.,Center for Space Plasma and Aeronomic Research |
Sterling A.C.,Marshall Space Flight Center |
Moore R.L.,Marshall Space Flight Center |
Moore R.L.,Center for Space Plasma and Aeronomic Research
Astrophysical Journal Letters | Year: 2016
We report observations of homologous coronal jets and their coronal mass ejections (CMEs) observed by instruments onboard the Solar Dynamics Observatory (SDO) and the Solar and Heliospheric Observatory (SOHO) spacecraft. The homologous jets originated from a location with emerging and canceling magnetic field at the southeastern edge of the giant active region (AR) of 2014 October, NOAA 12192. This AR produced in its interior many non-jet major flare eruptions (X- and M- class) that made no CME. During October 20 to 27, in contrast to the major flare eruptions in the interior, six of the homologous jets from the edge resulted in CMEs. Each jet-driven CME (∼200-300 km s-1) was slower-moving than most CMEs, with angular widths (20°-50°) comparable to that of the base of a coronal streamer straddling the AR and were of the "streamer-puff" variety, whereby the preexisting streamer was transiently inflated but not destroyed by the passage of the CME. Much of the transition-region-temperature plasma in the CME-producing jets escaped from the Sun, whereas relatively more of the transition-region plasma in non-CME-producing jets fell back to the solar surface. Also, the CME-producing jets tended to be faster and longer-lasting than the non-CME-producing jets. Our observations imply that each jet and CME resulted from reconnection opening of twisted field that erupted from the jet base and that the erupting field did not become a plasmoid as previously envisioned for streamer-puff CMEs, but instead the jet-guiding streamer-base loop was blown out by the loop's twist from the reconnection. © 2016. The American Astronomical Society. All rights reserved.
Regnier S.,University of Central Lancashire |
Alexander C.E.,University of Central Lancashire |
Walsh R.W.,University of Central Lancashire |
Winebarger A.R.,NASA |
And 11 more authors.
Astrophysical Journal | Year: 2014
Observing the Sun at high time and spatial scales is a step toward understanding the finest and fundamental scales of heating events in the solar corona. The high-resolution coronal (Hi-C) instrument has provided the highest spatial and temporal resolution images of the solar corona in the EUV wavelength range to date. Hi-C observed an active region on 2012 July 11 that exhibits several interesting features in the EUV line at 193 Å. One of them is the existence of short, small brightenings "sparkling" at the edge of the active region; we call these EUV bright dots (EBDs). Individual EBDs have a characteristic duration of 25 s with a characteristic length of 680 km. These brightenings are not fully resolved by the SDO/AIA instrument at the same wavelength; however, they can be identified with respect to the Hi-C location of the EBDs. In addition, EBDs are seen in other chromospheric/coronal channels of SDO/AIA, which suggests a temperature between 0.5 and 1.5 MK. Based on their frequency in the Hi-C time series, we define four different categories of EBDs: single peak, double peak, long duration, and bursty. Based on a potential field extrapolation from an SDO/HMI magnetogram, the EBDs appear at the footpoints of large-scale, trans-equatorial coronal loops. The Hi-C observations provide the first evidence of small-scale EUV heating events at the base of these coronal loops, which have a free magnetic energy of the order of 1026 erg. © 2014. The American Astronomical Society. All rights reserved.
Arthur A.D.,University of Alabama in Huntsville |
Arthur A.D.,Center for Space Plasma and Aeronomic Research |
Le Roux J.A.,University of Alabama in Huntsville |
Le Roux J.A.,Center for Space Plasma and Aeronomic Research
Astrophysical Journal Letters | Year: 2013
Observations by the plasma and magnetic field instruments on board the Voyager 2 spacecraft suggest that the termination shock is weak with a compression ratio of 2. However, this is contrary to the observations of accelerated particle spectra at the termination shock, where standard diffusive shock acceleration theory predicts a compression ratio closer to 2.9. Using our focused transport model, we investigate pickup proton acceleration at a stationary spherical termination shock with a moderately strong compression ratio of 2.8 to include both the subshock and precursor. We show that for the particle energies observed by the Voyager 2 Low Energy Charged Particle (LECP) instrument, pickup protons will have effective length scales of diffusion that are larger than the combined subshock and precursor termination shock structure observed. As a result, the particles will experience a total effective termination shock compression ratio that is larger than values inferred by the plasma and magnetic field instruments for the subshock and similar to the value predicted by diffusive shock acceleration theory. Furthermore, using a stochastically varying magnetic field angle, we are able to qualitatively reproduce the multiple power-law structure observed for the LECP spectra downstream of the termination shock. © 2013. The American Astronomical Society. All rights reserved..
Adams J.,Center for Space Plasma and Aeronomic Research |
Falconer D.,Center for Space Plasma and Aeronomic Research |
AIP Conference Proceedings | Year: 2012
The ionizing radiation environment in space poses a hazard for spacecraft and space crews. The hazardous components of this environment are reviewed and those which contribute to radiation hazards and effects identified. Avoiding the adverse effects of space radiation requires design, planning, monitoring and management. Radiation effects on spacecraft are avoided largely though spacecraft design. Managing radiation exposures of space crews involves not only protective spacecraft design and careful mission planning. Exposures must be managed in real time. The now-casting and forecasting needed to effectively manage crew exposures is presented. The techniques used and the space environment modeling needed to implement these techniques are discussed. © 2012 American Institute of Physics.
Choi J.,University of Alabama in Huntsville |
Hu Q.,Center for Space Plasma and Aeronomic Research
Proceedings of the International Astronautical Congress, IAC | Year: 2012
Our Sun, as a variable star, plays a dominant role in controlling the Solar-Terrestrial environment. It is constantly emitting highly ionized material (plasma) mostly composed of protons and electrons (so-called "solar wind"), carrying along solar magnetic field. Transient structures, often originating from explosive events on the Sun, propagate in the solar wind and impact on near-Earth space environment, generating various adverse effects. These effects include spacecraft malfunction, disruption of communication and navigation systems, radiation hazard to astronauts and passengers on polar flights, and power outage on the ground. One particular type of such structures, the interplanetary shock waves, driven by masses ejected from the Sun, is well observed and studied. We report our analysis of the set of interplanetary shock waves observed by the spacecraft Advanced Composition Explorer (ACE) between the year 1998 and 2004. We report on their properties characterizing their geometries and strengths etc. In particular, we examine the properties of turbulence associated with interplanetary shocks that have implications for energetic particle effect. We will further relate these shocks with geomagnetic storms and develop a preliminary tool for shock identification from real-time ACE solar wind data for the purpose of Space Weather forecasting.