736 research outputs found
Climatic versus biotic constraints on carbon and water fluxes in seasonally drought-affected ponderosa pine ecosystems
We investigated the relative importance of climatic versus biotic controls on gross primary production (GPP) and water vapor fluxes in seasonally drought-affected ponderosa pine forests. The study was conducted in young (YS), mature (MS), and old stands (OS) over 4 years at the AmeriFlux Metolius sites. Model simulations showed that interannual variation of GPP did not follow the same trends as precipitation, and effects of climatic variation were smallest at the OS (50%), and intermediate at the YS (<20%). In the young, developing stand, interannual variation in leaf area has larger effects on fluxes than climate, although leaf area is a function of climate in that climate can interact with age-related shifts in carbon allocation and affect whole-tree hydraulic conductance. Older forests, with well-established root systems, appear to be better buffered from effects of seasonal drought and interannual climatic variation. Interannual variation of net ecosystem exchange (NEE) was also lowest at the OS, where NEE is controlled more by interannual variation of ecosystem respiration, 70% of which is from soil, than by the variation of GPP, whereas variation in GPP is the primary reason for interannual changes in NEE at the YS and MS. Across spatially heterogeneous landscapes with high frequency of younger stands resulting from natural and anthropogenic disturbances, interannual climatic variation and change in leaf area are likely to result in large interannual variation in GPP and NEE
Young GI angle: Choosing a mentor/mentee
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/166219/1/ueg2bf01002.pd
The kinematics of ionized gas in lyman-break analogs at z ~ 0.2
We present results for 19 âLyman-break analogsâ observed with Keck/OSIRIS with an adaptive-optics-assisted
spatial resolution of less than 200 pc. We detect satellites/companions, diffuse emission, and velocity shear, all
with high signal-to-noise ratios. These galaxies present remarkably high velocity dispersion along the line of sight
(~70 km s^(â1)), much higher than standard star-forming spirals in the low-redshift universe. We artificially redshift
our data to z ~ 2.2 to allow for a direct comparison with observations of high-z Lyman-break galaxies and find
striking similarities between both samples. This suggests that either similar physical processes are responsible
for their observed properties, or, alternatively, that it is very difficult to distinguish between different mechanisms
operating in the low- versus high-redshift starburst galaxies based on the available data. The comparison between
morphologies in the UV/optical continuum and our kinemetry analysis often shows that neither is by itself sufficient
to confirm or completely rule out the contribution from recent merger events. We find a correlation between the
kinematic properties and stellar mass, in that more massive galaxies show stronger evidence for a disk-like structure.
This suggests a co-evolutionary process between the stellar mass buildup and the formation of morphological and
dynamical substructure within the galaxy
No Radio Bursts Detected from FIRST J141918.9+394036 in Green Bank Telescope Observations
Precise localization of the first-known repeating fast radio burst source, FRB 121102 (Spitler et al. 2016; Chatterjee et al. 2017), led to its association with a star-forming region inside a low-metallicity dwarf host galaxy (Tendulkar et al. 2017). This host environment is similar to that typically associated with long gamma-ray bursts (GRB) and superluminous supernovae, potentially linking these astrophysical phenomena (Metzger et al. 2017). In addition, the bursting source is found to be spatially coincident with a compact (< 0.7 pc; Marcote et al. 2017), persistent radio source (Chatterjee et al. 2017). Ofek (2017) identified similar radio sources in the Very Large Array FIRST survey (Becker et al. 1995). One of these sources, FIRST J141918.9+394036 (hereafter FIRST J1419+3940), was identified as a radio transient decaying in brightness by a factor of ~50 over several decades (Law et al. 2018). Very-long-baseline radio interferometric observations support the theory that FIRST J1419+3940 is the afterglow of a long GRB, based on the inferred physical size of the emission region (1.6 ± 0.3 pc; Marcote et al. 2019)
No Radio Bursts Detected from FIRST J141918.9+394036 in Green Bank Telescope Observations
Precise localization of the first-known repeating fast radio burst source, FRB 121102 (Spitler et al. 2016; Chatterjee et al. 2017), led to its association with a star-forming region inside a low-metallicity dwarf host galaxy (Tendulkar et al. 2017). This host environment is similar to that typically associated with long gamma-ray bursts (GRB) and superluminous supernovae, potentially linking these astrophysical phenomena (Metzger et al. 2017). In addition, the bursting source is found to be spatially coincident with a compact (< 0.7 pc; Marcote et al. 2017), persistent radio source (Chatterjee et al. 2017). Ofek (2017) identified similar radio sources in the Very Large Array FIRST survey (Becker et al. 1995). One of these sources, FIRST J141918.9+394036 (hereafter FIRST J1419+3940), was identified as a radio transient decaying in brightness by a factor of ~50 over several decades (Law et al. 2018). Very-long-baseline radio interferometric observations support the theory that FIRST J1419+3940 is the afterglow of a long GRB, based on the inferred physical size of the emission region (1.6 ± 0.3 pc; Marcote et al. 2019)
Tectonic Transport Directions, Shear Senses and Deformation Temperatures Indicated by Quartz câAxis Fabrics and Microstructures in a NWâSE Transect across the Moine and Sgurr Beag Thrust Sheets, Caledonian Orogen of Northern Scotland
Moine metasedimentary rocks of northern Scotland are characterized by arcuate map patterns of mineral lineations that swing progressively clockwise from orogenâperpendicular Eâtrend-ing lineations in greenschist facies mylonites above the Moine thrust on the foreland edge of the Caledonian Orogen, to Sâtrending lineations at higher structural levels and metamorphic grades in the hinterland. Quartz câaxis fabrics measured on a west to east coast transect demonstrate that the lineations developed parallel to the maximum principal extension direction and therefore track the local tectonic transport direction. Microstructures and câaxis fabrics document a progressive change from top to the N shearing in the hinterland to top to the W shearing on the foreland edge. Field relationships indicate that the domain of top to the N shearing was at least 55 km wide before later horizontal shortening on kmâscale Wâvergent folds that detach on the underlying Moine thrust. Previously published data from the Moine thrust mylonites demonstrate that top to the W shearing had largely ceased by 430 Ma, while preliminary isotopic age data suggest top to the N shearing occurred at ~470â450 Ma. In addition, data from the east coast end of our transect indicate normal-sense top downâSE shearing at close to peak temperatures at ~420 Ma that may be related to the closing stages of Scandian deformation, metamorphism and cooling/exhumation
MASSIV: Mass Assembly Survey with SINFONI in VVDS. V. The major merger rate of star-forming galaxies at 0.9 < z < 1.8 from IFS-based close pairs
We aim to measure the major merger rate of star-forming galaxies at 0.9 < z
<1.8, using close pairs identified from integral field spectroscopy (IFS). We
use the velocity field maps obtained with SINFONI/VLT on the MASSIV sample,
selected from the star-forming population in the VVDS. We identify physical
pairs of galaxies from the measurement of the relative velocity and the
projected separation (r_p) of the galaxies in the pair. Using the well
constrained selection function of the MASSIV sample we derive the gas-rich
major merger fraction (luminosity ratio mu = L_2/L_1 >= 1/4), and, using merger
time scales from cosmological simulations, the gas-rich major merger rate at a
mean redshift up to z = 1.54. We find a high gas-rich major merger fraction of
20.8+15.2-6.8 %, 20.1+8.0-5.1 % and 22.0+13.7-7.3 % for close pairs with r_p <=
20h^-1 kpc in redshift ranges z = [0.94, 1.06], [1.2, 1.5) and [1.5, 1.8),
respectively. This translates into a gas-rich major merger rate of
0.116+0.084-0.038 Gyr^-1, 0.147+0.058-0.037 Gyr^-1 and 0.127+0.079-0.042 Gyr^-1
at z = 1.03, 1.32 and 1.54, respectively. Combining our results with previous
studies at z < 1, the gas-rich major merger rate evolves as (1+z)^n, with n =
3.95 +- 0.12, up to z = 1.5. From these results we infer that ~35% of the
star-forming galaxies with stellar masses M = 10^10 - 10^10.5 M_Sun have
undergone a major merger since z ~ 1.5. We develop a simple model which shows
that, assuming that all gas-rich major mergers lead to early-type galaxies, the
combined effect of gas-rich and dry mergers is able to explain most of the
evolution in the number density of massive early-type galaxies since z ~ 1.5,
with our measured gas-rich merger rate accounting for about two-thirds of this
evolution.Comment: Published in Astronomy and Astrophysics, 24 pages, 30 figures, 2
tables. Appendix with the residual images from GALFIT added. Minor changes
with respect to the initial versio
Valuing innovative endoscopic techniques: prophylactic clip closure after endoscopic resection of large colon polyps
Background and Aims
Clip closure of the mucosal defect after resecting large (â„20 mm) nonpedunculated colorectal polyps reduces postprocedure bleeding and is cost saving for payers. Clip costs are not reimbursed by payers, posing a major barrier to adoption of this technique in the community. We aimed to determine appropriate clip costs to support broader use of this procedure in practice.
Methods
We performed budget impact analysis using our recent decision analytic model, comparing prophylactic clip closure with no clip closure on national cost and outcomes data, to determine the maximum feasible clip price while maintaining cost savings in practice. Sensitivity analyses were performed on important clinical factors.
Results
In the original model, the baseline postprocedure bleeding risk was 6.8%, increasing cost of care by 100 or less. Comparatively, prophylactic clip closure of large left-sided polyps had no clinical benefit and was not cost saving. Clip closure strategies focused only on extra-large polyps (â„40 mm), or patients taking antithrombotics regardless of polyp characteristics, were only minimally cost saving. Cost savings and maximum tolerated clip prices depended on medical comorbidity, which directly influences the costs of care to manage postprocedure bleeding.
Conclusions
Prophylactic clip closure after endoscopic resection of large colon polyps, particularly those in the right colon segment, is cost saving but requires clip costs less than $100. Translating these findings into practice requires gastroenterology practices to obtain reimbursement from payers for improved clinical outcomes and to align commercial clip prices with this clinical indication
- âŠ