2,158 research outputs found
New fire diurnal cycle characterizations to improve fire radiative energy assessments made from low-Earth orbit satellites sampling
Accurate near real time fire emissions estimates are required for
air quality forecasts. To date, most approaches are based on
satellite-derived estimates of fire radiative power (FRP), which can
be converted to fire radiative energy (FRE) which is directly
related to fire emissions. Uncertainties in these FRE estimations
are often substantial. This is for a large part because the most
often used low-Earth orbit satellite-based instruments like the
MODerate-resolution Imaging Spectroradiometer (MODIS) have
a relatively poor sampling of the usually pronounced fire diurnal
cycle. In this paper we explore the spatial variation of this fire
diurnal cycle and its drivers. Specifically, we assess how
representing the fire diurnal cycle affects FRP and FRE estimations
when using data collected at MODIS overpasses. Using data
assimilation we explored three different methods to estimate hourly
FRE, based on an incremental sophistication of parameterizing the
fire diurnal cycle. We sampled data from the geostationary Meteosat
Spinning Enhanced Visible and Infrared Imager (SEVIRI) at MODIS
detection opportunities to drive the three approaches. The full
SEVIRI time-series, providing full coverage of the diurnal cycle,
were used to evaluate the results. Our study period comprised three
years (2010–2012), and we focussed on Africa and the Mediterranean
basin to avoid the use of potentially lower quality SEVIRI data
obtained at very far off-nadir view angles. We found that the fire
diurnal cycle varies substantially over the study region, and
depends on both fuel and weather conditions. For example, more
"intense" fires characterized by a fire diurnal cycle with high
peak fire activity, long duration over the day, and with nighttime
fire activity are most common in areas of large fire size (i.e.,
large burned area per fire event). These areas are most prevalent in
relatively arid regions. Ignoring the fire diurnal cycle as done
currently in some approaches caused structural errors, while
generally overestimating FRE. Including information on the
climatology of the fire diurnal cycle provided the most promising avenue
to improve FRE estimations. This approach also improved the
performance on relatively high spatiotemporal resolutions, although
only when aggregating model results to coarser spatial and/or
temporal scale good correlation was found with the full SEVIRI
hourly reference dataset. In general model performance was best in
areas of frequent fire and low errors of omission. We recommend the use
of regionally varying fire diurnal cycle information within the
Global Fire Assimilation System (GFAS) used in the Copernicus
Atmosphere Monitoring Services, which will improve FRE estimates and
may allow for further reconciliation of biomass burning emission
estimates from different inventories
Virtual reality and collaborative learning: a systematic literature review
Computer Systems, Imagery and Medi
Reduced neural connectivity but increased task-related activity during working memory in de novo Parkinson patients
Objective: Patients with Parkinson's disease (PD) often suffer from impairments in executive functions, such as working memory deficits. It is widely held that dopamine depletion in the striatum contributes to these impairments through decreased activity and connectivity between task-related brain networks. We investigated this hypothesis by studying task-related network activity and connectivity within a sample of de novo patients with PD, versus healthy controls, during a visuospatial working memory task. Methods: Sixteen de novo PD patients and 35 matched healthy controls performed a visuospatial n-back task while we measured their behavioral performance and neural activity using functional magnetic resonance imaging. We constructed regions-of-interest in the bilateral inferior parietal cortex (IPC), bilateral dorsolateral prefrontal cortex (DLPFC), and bilateral caudate nucleus to investigate group differences in task-related activity. We studied network connectivity by assessing the functional connectivity of the bilateral DLPFC and by assessing effective connectivity within the frontoparietal and the frontostriatal networks. Results: PD patients, compared with controls, showed trend-significantly decreased task accuracy, significantly increased task-related activity in the left DLPFC and a trend-significant increase in activity of the right DLPFC, left caudate nucleus, and left IPC. Furthermore, we found reduced functional connectivity of the DLPFC with other task-related regions, such as the inferior and superior frontal gyri, in the PD group, and group differences in effective connectivity within the frontoparietal network. Interpretation: These findings suggest that the increase in working memory-related brain activity in PD patients is compensatory to maintain behavioral performance in the presence of network deficits. Hum Brain Mapp 36:1554-1566, 2015. (c) 2015 Wiley Periodicals, Inc
Exploring the molecular chemistry and excitation in obscured luminous infrared galaxies: An ALMA mm-wave spectral scan of NGC 4418
We obtained an ALMA Cycle 0 spectral scan of the dusty LIRG NGC 4418,
spanning a total of 70.7 GHz in bands 3, 6, and 7. We use a combined local
thermal equilibrium (LTE) and non-LTE (NLTE) fit of the spectrum in order to
identify the molecular species and derive column densities and excitation
temperatures. We derive molecular abundances and compare them with other
Galactic and extragalactic sources by means of a principal component analysis.
We detect 317 emission lines from a total of 45 molecular species, including 15
isotopic substitutions and six vibrationally excited variants. Our LTE/NLTE fit
find kinetic temperatures from 20 to 350 K, and densities between 10 and
10 cm. The spectrum is dominated by vibrationally excited HCN,
HCN, and HNC, with vibrational temperatures from 300 to 450 K. We find high
abundances of HCN, SiO, HS, and c-HCCCH and a low CHOH abundance. A
principal component analysis shows that NGC 4418 and Arp 220 share very similar
molecular abundances and excitation, which clearly set them apart from other
Galactic and extragalactic environments. The similar molecular abundances
observed towards NCG 4418 and Arp 220 are consistent with a hot gas-phase
chemistry, with the relative abundances of SiO and CHOH being regulated by
shocks and X-ray driven dissociation. The bright emission from vibrationally
excited species confirms the presence of a compact IR source, with an effective
diameter 350 K. The molecular abundances
and the vibrationally excited spectrum are consistent with a young
AGN/starburst system. We suggest that NGC 4418 may be a template for a new kind
of chemistry and excitation, typical of compact obscured nuclei (CON). Because
of the narrow line widths and bright molecular emission, NGC 4418 is the ideal
target for further studies of the chemistry in CONs.Comment: accepted by A&A on 29/06/201
Impaired planning in Parkinson's disease is reflected by reduced brain activation and connectivity
Contains fulltext :
159315.pdf (publisher's version ) (Open Access)13 p
- …