2,563 research outputs found
Evaluation of high-latitude boreal forest growth using satellite-derived vegetation indices
Vegetation in northern high-latitudes plays an important role in energy exchange and carbon dynamics, thereby influencing regional and global climate. Vegetation indices derived from the space-borne Advanced Very High Resolution Radiometers (AVHRR) have suggested decreased photosynthetic activity during recent decades within some continental regions of the pan-arctic boreal forests. The purpose of this research was to determine associations between the normalized difference vegetation index (NDVI), as derived by both AVHRR and Moderate Resolution Imaging Spectroradiometers (MODIS), and inter-annual variations in radial stem growth in high-latitude coniferous forests. During 2008 and 2009, tree core samples were collected at 12 sites in northeast Russia and at 10 sites in northwest Canada. Ring-width indices (RWI; n = 27) were generated for larch, spruce, and pine genera and these were correlated with summer NDVI derived from the AVHRR sensors over the 1982 to 2008 period. The correlations between NDVI and RWI were then examined between 2000 and 2008 using both MODIS and AVHRR. The sensors showed similar abilities to proxy radial growth and NDVI-RWI correlations appeared mostly insensitive to changes in MODIS grain sizes between 250 m and 24 km. Over the 27 year period RWI and NDVI showed positive, though variable, correlations (r = 0.43 Ā± 0.19, n = 27). For pine and spruce, both evergreen conifers, the annual rate of radial growth was significantly correlated with growth during previous years, as was canopy development, as proxied by NDVI. Larch, however, did not show year to year persistence in either radial growth or canopy development, a finding that points to differences in growth patterns between functionally-distinct tree genera. These findings suggest that negative trends in NDVI may reflect decreased radial growth at some locations and that attempts to model tree growth and carbon uptake using NDVI need to take into account multi-year persistence in tree growth. Additionally, the work shows similarities between AVHRR and MODIS, suggesting potential to bridge the historical AVHRR record with the newer and finer resolution MODIS record
Climate simulation of the latest Permian: Implications for mass extinction
This report presents the results of climate modeling research which indicates that elevated levels of carbon dioxide in the atmosphere at the end of the Permian period led to climatic conditions inhospitable to both marine and terrestrial life. The Permian-Triassic boundary (about 251 million years ago) was the time of the largest known mass extinction in Earth's history, when greater than ninety percent of all marine species, and approximately seventy percent of all terrestrial species, died out. The model, which used paleogeography and paleotopography correct for the time period, indicated that warm high-latitude surface air temperatures and elevated carbon dioxide levels may have resulted in slowed circulation and stagnant, anoxic conditions in Earth's oceans. The report also suggests that the excess carbon dioxide (and sulfur dioxide) may have originated from volcanic activity associated with eruption of the Siberian Trap flood basalts, which took place at the same time. Educational levels: Undergraduate lower division, Undergraduate upper division, Graduate or professional
PSY33 Total costs of care in the 90 days following emergency department visits for patients taking exclusively class-II or class-III short-acting opioids
Periglacial vegetation dynamics in Arctic Russia:decadal analysis of tundra regeneration on landslides with time series satellite imagery
Climate change and health effects in Northwest Alaska
This article provides examples of adverse health effects, including weather-related injury, food insecurity, mental health issues, and water infrastructure damage, and the responses to these effects that are currently being applied in two Northwest Alaska communities
āLandsatTS': an R package to facilitate retrieval, cleaning, crossācalibration, and phenological modeling of Landsat time series data
The Landsat satellites provide decades of nearāglobal surface reflectance measurements that are increasingly used to assess interannual changes in terrestrial ecosystem function. These assessments often rely on spectral indices related to vegetation greenness and productivity (e.g. Normalized Difference Vegetation Index, NDVI). Nevertheless, multiple factors impede multiādecadal assessments of spectral indices using Landsat satellite data, including ease of data access and cleaning, as well as lingering issues with crossāsensor calibration and challenges with irregular timing of cloudāfree acquisitions. To help address these problems, we developed the āLandsatTS' package for R. This software package facilitates sampleābased time series analysis of surface reflectance and spectral indices derived from Landsat sensors. The package includes functions that enable the extraction of the full Landsat 5, 7, and 8 records from Collection 2 for point sample locations or small study regions using Google Earth Engine accessed directly from R. Moreover, the package includes functions for 1) rigorous data cleaning, 2) crossāsensor calibration, 3) phenological modeling, and 4) time series analysis. For an example application, we show how āLandsatTS' can be used to assess changes in annual maximum vegetation greenness from 2000 to 2022 across the Noatak National Preserve in northern Alaska, USA. Overall, this software provides a suite of functions to enable broader use of Landsat satellite data for assessing and monitoring terrestrial ecosystem function during recent decades across local to global geographic extents
Direct k-space mapping of the electronic structure in an oxide-oxide interface
The interface between LaAlO3 and SrTiO3 hosts a two-dimensional electron
system of itinerant carriers, although both oxides are band insulators.
Interface ferromagnetism coexisting with superconductivity has been found and
attributed to local moments. Experimentally, it has been established that Ti 3d
electrons are confined to the interface. Using soft x-ray angle-resolved
resonant photoelectron spectroscopy we have directly mapped the interface
states in k-space. Our data demonstrate a charge dichotomy. A mobile fraction
contributes to Fermi surface sheets, whereas a localized portion at higher
binding energies is tentatively attributed to electrons trapped by O-vacancies
in the SrTiO3. While photovoltage effects in the polar LaAlO3 layers cannot be
excluded, the apparent absence of surface-related Fermi surface sheets could
also be fully reconciled in a recently proposed electronic reconstruction
picture where the built-in potential in the LaAlO3 is compensated by surface
O-vacancies serving also as charge reservoir.Comment: 8 pages, 6 figures, incl. Supplemental Informatio
The measurement of primary productivity in a high-rate oxidation pond (HROP)
A high-rate oxidation pond is studied as a model system for comparing 14C and oxygen evolution methods as tools for measuring primary productivity in hypertrophic aquatic systems. Our results indicate that at very dense algal populations (up to 5 mg chl. a lā1) and high photosynthetic rates, 14C based results may severely underestimate primary productivity, unless a way is found to keep incubation times very short. Results obtained with our oxygen electrode were almost an order of magnitude higher than those obtained by all 14C procedures. These higher values correspond fairly well with a field-tested computer-simulation model, as well as with direct harvest data obtained at the same pond when operated under similar conditions. The examination of the size-fractionation of the photosynthetic activity underscored the important contribution of nannoplanktonic algae to the total production of the syste
Impaired belief updating and devaluation in adult women with bulimia nervosa
Recent models of bulimia nervosa (BN) propose that binge-purge episodes ultimately become automatic in response to cues and insensitive to negative outcomes. Here, we examined whether women with BN show alterations in instrumental learning and devaluation sensitivity using traditional and computational modeling analyses of behavioral data. Adult women with BN (nā=ā30) and group-matched healthy controls (nā=ā31) completed a task in which they first learned stimulus-response-outcome associations. Then, participants were required to repeatedly adjust their responses in a ābaseline testā, when different sets of stimuli were explicitly devalued, and in a āslips-of-action testā, when outcomes instead of stimuli were devalued. The BN group showed intact behavioral sensitivity to outcome devaluation during the slips-of-action test, but showed difficulty overriding previously learned stimulus-response associations on the baseline test. Results from a Bayesian learner model indicated that this impaired performance could be accounted for by a slower pace of belief updating when a new set of previously learned responses had to be inhibited (pā=ā0.036). Worse performance and a slower belief update in the baseline test were each associated with more frequent binge eating (pā=ā0.012) and purging (pā=ā0.002). Our findings suggest that BN diagnosis and severity are associated with deficits in flexibly updating beliefs to withhold previously learned responses to cues. Additional research is needed to determine whether this impaired ability to adjust behavior is responsible for maintaining automatic and persistent binge eating and purging in response to internal and environmental cues
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