3,300 research outputs found
Simulations of Adaptive Optics with a Laser Guide Star for SINFONI
The SINFONI instrument for ESO's VLT combines integral field spectroscopy and
adaptive optics (AO). We discuss detailed simulations of the adaptive optics
module. These simulations are aimed at assessing the AO module performance,
specifically for operations with extended sources and a laser guide star.
Simulated point spread function (PSF) images will be used to support scientific
preparations and the development of an exposure time calculator, while
simulated wavefront sensor measurements will be used to study PSF
reconstruction methods. We explain how the adaptive optics simulations work,
focusing on the realistic modelling of the laser guide star for a curvature
wavefront sensor. The predicted performance of the AO module is discussed,
resulting in recommendations for the operation of the SINFONI AO module at the
telescope.Comment: 12 pages, 6 figures, to appear in SPIE conference proceedings vol
5490, "Advancements in Adaptive Optics", eds. D. Bonaccini, B.L. Ellerbroek,
R. Ragazonni, Glasgow UK, 21-25 June 200
First CO J=6-5, 4-3 detections in local ULIRGs: the dense gas in Mrk231, and its colling budget
We report on detections of the high-excitation CO J=6-5, J=4-3 lines in
Mrk231, a prototypical Ultra Luminous Infrared Galaxy (ULIRG) and Seyfert 1
QSO. These observations are combined with CO J=3-2, HCN J=4-3 (this work), and
CO J=2-1, J=1-0, 13CO J=2-1, HCN J=1-0 measurements taken from the literature
to provide better constraints on the properties of the molecular gas in an
extreme starburst/QSO in the local Universe. We find that the CO J=4-3 and
J=6-5 transitions trace a different gas phase from that dominating the lower
three CO transitions, with n(H_2) ~ (1-3)x10^4 cm-3 and Tk ~ (40-70) K. This
phase is responsible for the luminous HCN emission, and contains most of the H2
gas mass of this galaxy. The total CO line cooling emanating from this dense
phase is found similar to that of the [CII] line at 158 micron, suggesting a
very different thermal balance to that seen in lower IR-luminosity galaxies,
and one likely dominated by dense photon-dominated regions. Our dense
"sampling" of the CO rotational ladder and the HCN lines enables us to produce
well-constrained Spectral Line Energy Distributions (SLEDs) for the dense
molecular gas in Mrk231 and compare them to those of high redshift starbursts,
many of which have SLEDs that may be affected by strong lensing. Finally, we
use our local molecular line excitation template to assess the capabilities of
future cm and mm/sub-mm arrays in detecting CO and HCN transitions in similar
systems throughout the local and distant universe.Comment: accepted for publication in The Astrophysical Journal; 37 pages,
preprint format; 5 figures (2 in color
Ruimte voor akkers en tuinen, bomen en bollen : verkenning naar ontwikkelingen in de akkerbouw en opengrondstuinbouw en effecten hiervan op natuur en landschap
Invloed van landbouwkundig grondgebruik op natuur en alndschap: een inventaristatie door Natuurplanburea
Fire in the Heart: A Characterization of the High Kinetic Temperatures and Heating Sources in the Nucleus of NGC253
The nuclear starburst within the central (
pc; pc) of NGC253 has been extensively studied as
a prototype for the starburst phase in galactic evolution. Atacama Large
Millimeter/submillimeter Array (ALMA) imaging within receiver Bands 6 and 7
have been used to investigate the dense gas structure, kinetic temperature, and
heating processes which drive the NGC253 starburst. Twenty-nine transitions
from fifteen molecular species/isotopologues have been identified and imaged at
to resolution, allowing for the
identification of five of the previously-studied giant molecular clouds (GMCs)
within the central molecular zone (CMZ) of NGC253. Ten transitions from the
formaldehyde (HCO) molecule have been used to derive the kinetic
temperature within the to
dense-gas structures imaged. On scales we measure K, while on size scales we measure K. These kinetic temperature measurements further delineate the
association between potential sources of dense gas heating. We have
investigated potential heating sources by comparing our measurements to models
which predict the physical conditions associated with dense molecular clouds
that possess a variety of heating mechanisms. This comparison has been
supplemented with tracers of recently-formed massive stars (Br) and
shocks ([FeII]). Derived molecular column densities point to a
radially-decreasing abundance of molecules with sensitivity to cosmic ray and
mechanical heating within the NGC253 CMZ. These measurements are consistent
with radio spectral index calculations which suggest a higher concentration of
cosmic ray producing supernova remnants within the central 10 pc of NGC253.Comment: 60 pages, 25 figures (whew!), Accepted for publication in ApJ, Latest
version includes minor corrections following proof submissio
Te hooi en te gras. Verkenning naar ontwikkeling in de grondgebonden veehouderij en gevolgen hiervan voor natuur en landschap
Onderzoek naar de relatie tuusen landbouwkundig grondgebruik en natuur; analyse ten behoeve van het Natuurplanburea
Precipitation–fire linkages in Indonesia (1997–2015)
Over the past decades, fires have burned annually in Indonesia,
yet the strength of the fire season is for a large part modulated by the El
Niño Southern Oscillation (ENSO). The two most recent very strong El
Niño years were 2015 and 1997. Both years involved high incidences of
fire in Indonesia. At present, there is no consistent satellite data stream
spanning the full 19-year record, thereby complicating a comparison between
these two fire seasons. We have investigated how various fire and
precipitation datasets can be merged to better compare the fire dynamics in
1997 and 2015 as well as in intermediary years. We combined nighttime active
fire detections from the Along Track Scanning Radiometer (ATSR) World Fire
Atlas (WFA) available from 1997 until 2012 and the nighttime subset of the
Moderate-Resolution Imaging Spectroradiometer (MODIS) sensor from 2001 until
now. For the overlapping period, MODIS detected about 4Â times more fires than
ATSR, but this ratio varied spatially. Although the reasons behind this
spatial variability remain unclear, the coefficient of determination for the
overlapping period was high (R2 = 0. 97, based on monthly data) and allowed
for a consistent time series. We then constructed a rainfall time series
based on the Global Precipitation Climatology Project (GPCP, 1997–2015) and
the Tropical Rainfall Measurement Mission Project (TRMM, 1998–2015).
Relations between antecedent rainfall and fire activity were not uniform in
Indonesia. In southern Sumatra and Kalimantan, we found that 120Â days of
rainfall accumulation had the highest coefficient of determination with
annual fire intensity. In northern Sumatra, this period was only 30Â days.
Thresholds of 200 and 305 mm average rainfall accumulation before each
active fire were identified to generate a high-incidence fire year in southern Sumatra
and southern Kalimantan, respectively. The number of active fires detected in
1997 was 2.2Â times higher than in 2015. Assuming the ratio between nighttime
and total active fires did not change, the 1997 season was thus about twice
as severe as the one in 2015. Although large, the difference is smaller than
found in fire emission estimates from the Global Fire Emissions Database
(GFED). Besides different rainfall amounts and patterns, the two-fold
difference between 1997 and 2015 may be attributed to a weaker El Niño
and neutral Indian Ocean Dipole (IOD) conditions in the later year. The
fraction of fires burning in peatlands was higher in 2015 compared to 1997
(61 and 45 %, respectively). Finally, we found that the non-linearity
between rainfall and fire in Indonesia stems from longer periods without rain
in extremely dry years
Fire-Related Carbon Emissions from Land Use Transitions in Southern Amazonia
Various land-use transitions in the tropics contribute to atmospheric carbon emissions, including forest conversion for small-scale farming, cattle ranching, and production of commodities such as soya and palm oil. These transitions involve fire as an effective and inexpensive means for clearing. We applied the DECAF (DEforestation CArbon Fluxes) model to Mato Grosso, Brazil to estimate fire emissions from various land-use transitions during 2001-2005. Fires associated with deforestation contributed 67 Tg C/yr (17 and 50 Tg C/yr from conversion to cropland and pasture, respectively), while conversion of savannas and existing cattle pasture to cropland contributed 17 Tg C/yr and pasture maintenance fires 6 Tg C/yr. Large clearings (>100 ha/yr) contributed 67% of emissions but comprised only 10% of deforestation events. From a policy perspective, results imply that intensification of agricultural production on already-cleared land and policies to discourage large clearings would reduce the major sources of emissions from fires in this region. Copyright 2008 by the American Geophysical Union
Generation of a Vero-Based Packaging Cell Line to Produce SV40 Gene Delivery Vectors for Use in Clinical Gene Therapy Studies
Replication-defective (RD) recombinant simian virus 40 (SV40)-based gene delivery vectors hold a great potential for clinical applications because of their presumed non-immunogenicity and capacity to induce immune tolerance to the transgene products in humans. However, the clinical use of SV40 vectors has been hampered by the lack of a packaging cell line that produces replication-competent (RC) free SV40 particles in the vector production process. To solve this problem, we have adapted the current SV40 vector genome used for the production of vector particles and generated a novel Vero-based packaging cell line named SuperVero that exclusively expresses the SV40 large T antigen. SuperVero cells produce similar numbers of SV40 vector particles compared to the currently used packaging cell lines, albeit in the absence of contaminating RC SV40 particles. Our unique SV40 vector platform named SVac paves the way to clinically test a whole new generation of SV40-based therapeutics for a broad range of important diseases
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