1,095 research outputs found
Recommended from our members
Multi-Diffusion Domain Modeling of Meteorite 40Ar/39Ar Data
The majority of 40Ar/39Ar analyses involving extraterrestrial samples were collected from bulk rock samples due to fine grain sizes. This present challenges in modeling the diffusion kinetics and thermal histories of these samples because of the presence of multiple-diffusion domains. Since Lovera et al. (1989) developed the multi-diffusion domain (MDD) method of modeling, many attempts have been made to automate the modeling process. However, existing software to model diffusion parameters and thermal histories falls short in that it is either restricted in availability, restricted in flexibility, or is cumbersome to use. I have created a new program, OPTIMuM (Optimize Parameters To Interpret Multiple Minerals), that models bulk samlpe diffusion kinetics and thermal histories through a simple graphical user interface (GUI). In this paper, I present the theory behind OPTIMuM as well as modeling results of samples from three extraterrestrial bodies. These results have important implications for the impact history and the dynamical evolution of the early solar system.</p
Recommended from our members
Improving Low-Degree Gravity Estimates through New Laser Ranging Satellites, Ground Stations, and Combination Solutions
Earth's mass is constantly redistributing due to climatic and geophysical dynamics. Although changes in the deep solid Earth tend to occur over geologic timescales, near-surface processes take place over hours to years. These mass changes, which include earthquakes as well as movement of the atmosphere, hydrosphere, and ice sheets, constitute Earth's time-variable gravity (TVG) field. The observation of TVG is critical to understanding sea-level rise, terrestrial water storage, ice sheet melting, and other climatic processes. Of particular importance are certain components of low-degree, large-scale TVG signals to which dedicated gravity missions, such as the Gravity Recovery and Climate Experiment (GRACE), lack sensitivity. Alternative methods are therefore favored for estimating these parameters. Satellite Laser Ranging (SLR) is a proven technique with applications to many areas of fundamental geodesy. Through a constellation of passive satellites and network of ground tracking stations, SLR delivers more accurate estimates of low-degree gravity coefficients, which allows for validation and enhancement of the GRACE data.
This work uses high-fidelity numerical simulations to investigate potential improvements to SLR-derived gravity estimates. First, existing simulation techniques are further developed for application to SLR. A combination of real data and geophysical models ensures realistic tracking statistics in the simulation. Potential new SLR satellites are investigated at various altitudes and inclinations, with a particular focus on the inclination after it is determined to be more impactful. It is found that the addition of a low-inclination satellite significantly improves the SLR gravity solution by introducing a unique sensitivity to the gravity field that decorrelates key coefficients. Several cases involving the addition of new ground stations are then investigated. In general, the filling of geographic gaps at the poles and in the Southern hemisphere reduces errors in the recovered gravity field by improving the observing geometry. However, a hypothetical case involving a uniformly distributed ground network reveals that stations lack the ability to systematically improve SLR gravity estimates in the way that a new satellite can. Finally, the simulated SLR data are combined with simulated GRACE data to investigate a jointly inverted solution. The results show that this method fully leverages the information in the SLR data, which enhances the GRACE data more than a simple substitution of coefficients. The simulation environment provides a novel way to quantify the improvements from these rigorous combination solutions. A variety of global and regional techniques are applied to analyze these solutions.</p
Beetle Diversity in an Eastern Cottonwood (Populus deltoides Bartr.) Plantation and Adjacent Bottomland Hardwood Forest in Southeastern Arkansas
Within the Lower Mississippi Alluvial Valley (LMAV),some lands cleared of bottomland hardwood forests have the potential to return to forest as a result of private sector and government interests in Populus cultivation. Specifically, monoculture plantings of eastern cottonwood (Populus deltoides Bartr.) represent an important component of many recent afforestation efforts in the region. The impact establishment of such monocultures will have on native insect communities in the LMAV is relatively unknown. To evaluate this, beetle (Coleoptera) diversity, abundance, and functional distribution were examined within an intensively managed eastern cottonwood plantation and nearby bottomland hardwood forest in southeastern Arkansas. Beetles were sampled in both settings over the summer of 2000 using Malaise traps. When compared to the heterogeneous bottomland hardwood forest, the beetle morphospecies assemblage collected from the plantation was one characterized by lower species diversity and a depauperate xylophagous and fungivorous beetle fauna. Over half of all beetles trapped in the eastern cottonwood plantation were species considered to be economic pests of Populus
Magellan/M2FS Spectroscopy of Galaxy Clusters: Stellar Population Model and Application to Abell 267
We report the results of a pilot program to use the Magellan/M2FS
spectrograph to survey the galactic populations and internal kinematics of
galaxy clusters. For this initial study, we present spectroscopic measurements
for quiescent galaxies observed along the line of sight to the galaxy
cluster Abell 267 (). We develop a Bayesian method for modeling the
integrated light from each galaxy as a simple stellar population, with free
parameters that specify redshift () and characteristic age,
metallicity (), alpha-abundance (), and
internal velocity dispersion () for individual galaxies.
Parameter estimates derived from our 1.5-hour observation of A267 have median
random errors of ,
, $\sigma_{\mathrm{[Fe/H]}}=0.11\
\mathrm{dex}\sigma_{[\alpha/\mathrm{Fe}]}=0.07\ \mathrm{dex}\sigma_{\sigma_\mathrm{int}}=20\ \mathrm{km\ s^{-1}}$. In a companion paper,
we use these results to model the structure and internal kinematics of A267.Comment: 16 pages, 11 figures, accepted for publication in The Astronomical
Journa
Transcranial Electrical Stimulation targeting limbic cortex increases the duration of human deep sleep
Background: Researchers have proposed that impaired sleep may be a causal link in the progression from Mild Cognitive Impairment (MCI) to Alzheimer's Disease (AD). Several recent findings suggest that enhancing deep sleep (N3) may improve neurological health in persons with MCI, and buffer the risk for AD. Specifically, Transcranial Electrical Stimulation (TES) of frontal brain areas, the inferred source of the Slow Oscillations (SOs) of N3 sleep, can extend N3 sleep duration and improve declarative memory for recently learned information. Recent work in our laboratory using dense array Electroencephalography (dEEG) localized the sources of SOs to anterior limbic sites – suggesting that targeting these sites with TES may be more effective for enhancing N3. Methods: For the present study, we recruited 13 healthy adults (M = 42 years) to participate in three all-night sleep EEG recordings where they received low level (0.5 mA) TES designed to target anterior limbic areas and a sham stimulation (placebo). We used a convolutional neural network, trained and tested on professionally scored EEG sleep staging, to predict sleep stages for each recording. Results: When compared to the sham session, limbic-targeted TES significantly increased the duration of N3 sleep. TES also significantly increased spectral power in the 0.5–1 Hz frequency band (relative to pre-TES epochs) in left temporoparietal and left occipital scalp regions compared to sham. Conclusion: These results suggest that even low-level TES, when specifically targeting anterior limbic sites, can increase deep (N3) sleep and thereby contribute to healthy sleep quality.Fil: Hathaway, Evan. Brain Electrophysiology Laboratory Company; Estados UnidosFil: Morgan, Kyle. Brain Electrophysiology Laboratory Company; Estados UnidosFil: Carson, Megan. Brain Electrophysiology Laboratory Company; Estados UnidosFil: Shusterman, Roma. Brain Electrophysiology Laboratory Company; Estados UnidosFil: Fernandez Corazza, Mariano. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señales. Universidad Nacional de La Plata. Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señales; ArgentinaFil: Luu, Phan. University of Oregon; Estados UnidosFil: Tucker, Don M.. University of Oregon; Estados Unido
Antioxidant Potential of Juglans Nigra, Black Walnut, Husks Extracted Using Supercritical Carbon Dioxide with an Ethanol Modifier
The black walnut, Junglas nigra, is indigenous to eastern North America, and abscission of its fruit occurs around October. The fruit consists of a husk, a hard shell, and kernel. The husk is commonly discarded in processing, though it contains phenolic compounds that exhibit antioxidant and antimicrobial properties. For this study, black walnut husks were extracted using supercritical carbon dioxide with an ethanol modifier. The effects of temperature, ethanol concentration, and drying of walnut husks prior to extraction upon antioxidant potential were evaluated using a factorial design of experiments. The solvent density was held constant at 0.75 g/mL. The optimal extraction conditions were found to be 68°C and 20 wt-% ethanol in supercritical carbon dioxide. At these conditions, the antioxidant potential as measured by the ferric reducing ability of plasma (FRAP) assay was 0.027 mmol trolox equivalent/g (mmol TE/g) for dried walnut husk and 0.054 mmol TE/g for walnut husks that were not dried. Antioxidant potential was also evaluated using the total phenolic content (TPC) and 1,1-diphenyl-2-picryl-hydrazyl (DPPH) assays and the FRAP assay was found to linearly correlate to the TPC assa
Focal limbic sources create the large slow oscillations of the EEG in human deep sleep
Background: Initial observations with the human electroencephalogram (EEG) have interpreted slow oscillations (SOs) of the EEG during deep sleep (N3) as reflecting widespread surface-negative traveling waves that originate in frontal regions and propagate across the neocortex. However, mapping SOs with a high-density array shows the simultaneous appearance of posterior positive voltage fields in the EEG at the time of the frontal-negative fields, with the typical inversion point (apparent source) around the temporal lobe. Methods: Overnight 256-channel EEG recordings were gathered from 10 healthy young adults. Individual head conductivity models were created using each participant's own structural MRI. Source localization of SOs during N3 was then performed. Results: Electrical source localization models confirmed that these large waves were created by focal discharges within the ventral limbic cortex, including medial temporal and caudal orbitofrontal cortex. Conclusions: Although the functional neurophysiology of deep sleep involves interactions between limbic and neocortical networks, the large EEG deflections of deep sleep are not created by distributed traveling waves in lateral neocortex but instead by relatively focal limbic discharges.Fil: Morgan, Kyle K.. Brain Electrophysiology Laboratory Company; Estados UnidosFil: Hathaway, Evan. Brain Electrophysiology Laboratory Company; Estados UnidosFil: Carson, Megan. Brain Electrophysiology Laboratory Company; Estados UnidosFil: Fernandez Corazza, Mariano. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señales. Universidad Nacional de La Plata. Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señales; ArgentinaFil: Shusterman, Roma. Brain Electrophysiology Laboratory Company; Estados UnidosFil: Luu, Phan. Brain Electrophysiology Laboratory Company; Estados Unidos. University of Oregon; Estados UnidosFil: Tucker, Don M.. University of Oregon; Estados Unidos. Brain Electrophysiology Laboratory Company; Estados Unido
Liger for Next Generation Keck AO: Filter Wheel and Pupil Design
Liger is a next-generation near-infrared imager and integral field
spectrograph (IFS) for the W.M. Keck Observatory designed to take advantage of
the Keck All-Sky Precision Adaptive Optics (KAPA) upgrade. Liger will operate
at spectral resolving powers between R4,000 - 10,000 over a wavelength
range of 0.8-2.4m. Liger takes advantage of a sequential imager and
spectrograph design that allows for simultaneous observations between the two
channels using the same filter wheel and cold pupil stop. We present the design
for the filter wheels and pupil mask and their location and tolerances in the
optical design. The filter mechanism is a multi-wheel design drawing from the
heritage of the current Keck/OSIRIS imager single wheel design. The Liger
multi-wheel configuration is designed to allow future upgrades to the number
and range of filters throughout the life of the instrument. The pupil mechanism
is designed to be similarly upgradeable with the option to add multiple pupil
mask options. A smaller wheel mechanism allows the user to select the desired
pupil mask with open slots being designed in for future upgrade capabilities.
An ideal pupil would match the shape of the image formed of the primary and
would track its rotation. For different pupil shapes without tracking we model
the additional exposure time needed to achieve the same signal to noise of an
ideal pupil and determine that a set of fixed masks of different shapes
provides a mechanically simpler system with little compromise in performance.Comment: 9 pages, 7 figures, 1 tabl
Liger for Next Generation Keck Adaptive Optics: Opto-Mechanical Dewar for Imaging Camera and Slicer
Liger is a next generation adaptive optics (AO) fed integral field
spectrograph (IFS) and imager for the W. M. Keck Observatory. This new
instrument is being designed to take advantage of the upgraded AO system
provided by Keck All-Sky Precision Adaptive-optics (KAPA). Liger will provide
higher spectral resolving power (R4,000-10,000), wider wavelength
coverage (0.8-2.4 m), and larger fields of view than any current
IFS. We present the design and analysis for a custom-made dewar chamber for
characterizing the Liger opto-mechanical system. This dewar chamber is designed
to test and assemble the Liger imaging camera and slicer IFS components while
being adaptable for future experiments. The vacuum chamber will operate below
Torr with a cold shield that will be kept below 90 K. The dewar test
chamber will be mounted to an optical vibration isolation platform and further
isolated from the cryogenic and vacuum systems with bellows. The cold head and
vacuums will be mounted to a custom cart that will also house the electronics
and computer that interface with the experiment. This test chamber will provide
an efficient means of calibrating and characterizing the Liger instrument and
performing future experiments.Comment: 8 pages, 6 figure
- …