Monitoring Changes On The Sheyenne National Grassland Using Multitemporal Landsat Data

Tallgrass prairies are one of the rarest ecosystems on the planet as up to 99% of their historical extent has been converted to agriculture. Once a prairie is converted there is often a loss of ecosystem services such as soil retention, carbon storage, water quality and a loss of biodiversity. It can take centuries to restore a native prairie after conversion has taken place. The Sheyenne National Grassland is managed by the U.S. Forest Service and contains the largest publicly owned tract of tallgrass prairie remaining in North America making it a highly valuable for conservation. Ordinary least squares regression was implemented to evaluate statistically significant trends at a per pixel basis in selected Vegetation Indices (VI) between the years of 1984 and 2011 on the Sheyenne National Grassland. VIs included NDVI, NDII RGR and SWIR32. Additionally, a Composite Index which sought to combine information from the original four indexes was created to evaluate the usefulness of combining indexes. A random forest regression model was also used to evaluate which independent variables were the most useful in predicting VI values through time. Between 1984 and 2011 the NDVI and NDII have increased while the RGR and SWIR32 have decreased. This indicates that greenness and wetness have increased through time while stress and non-photosynthetic vegetation have decreased. It is likely that the increase in NDVI is driven by a complex relationship between the influence of climate change and cattle grazing on the relative abundance of C3 and C4 plants. It is hypothesized that continuously stocked cattle grazing has reduced the vigor and competitive ability of native C4 grasses which competitively releases C3 grasses that are more tolerant of grazing and are primarily invasive. In addition to the competitive release of cattle grazing, C3 establishment is promoted through increased spring precipitation which has increased over the last century

Fast hierarchical low-rank view factor matrices for thermal irradiance on planetary surfaces

We present an algorithm for compressing the radiosity view factor model commonly used in radiation heat transfer and computer graphics. We use a format inspired by the hierarchical off-diagonal low rank format, where elements are recursively partitioned using a quadtree or octree and blocks are compressed using a sparse singular value decomposition -- the hierarchical matrix is assembled using dynamic programming. The motivating application is time-dependent thermal modeling on vast planetary surfaces, with a focus on permanently shadowed craters which receive energy through indirect irradiance. In this setting, shape models are comprised of a large number of triangular facets which conform to a rough surface. At each time step, a quadratic number of triangle-to-triangle scattered fluxes must be summed; that is, as the sun moves through the sky, we must solve the same view factor system of equations for a potentially unlimited number of time-varying righthand sides. We first conduct numerical experiments with a synthetic spherical cap-shaped crater, where the equilibrium temperature is analytically available. We also test our implementation with triangle meshes of planetary surfaces derived from digital elevation models recovered by orbiting spacecrafts. Our results indicate that the compressed view factor matrix can be assembled in quadratic time, which is comparable to the time it takes to assemble the full view matrix itself. Memory requirements during assembly are reduced by a large factor. Finally, for a range of compression tolerances, the size of the compressed view factor matrix and the speed of the resulting matrix vector product both scale linearly (as opposed to quadratically for the full matrix), resulting in orders of magnitude savings in processing time and memory space.Comment: 21 pages, 10 figure

Euclid preparation : II. The EUCLIDEMULATOR - a tool to compute the cosmology dependence of the nonlinear matter power spectrum

We present a new power spectrum emulator named EuclidEmulator that estimates the nonlinear correction to the linear dark matter power spectrum depending on the six cosmological parameters ωb, ωm, ns, h, w0, and σ8. It is constructed using the uncertainty quantification software UQLab using a spectral decomposition method called polynomial chaos expansion. All steps in its construction have been tested and optimized: the large highresolution N-body simulations carried out with PKDGRAV3 were validated using a simulation from the Euclid Flagship campaign and demonstrated to have converged up to wavenumbers k ≈ 5 h Mpc−1 for redshifts z ≤ 5. The emulator is based on 100 input cosmologies simulated in boxes of (1250 Mpc/h)3 using 20483 particles. We show that by creating mock emulators it is possible to successfully predict and optimize the performance of the final emulator prior to performing any N-body simulations. The absolute accuracy of the final nonlinear power spectrum is as good as one obtained with N-body simulations, conservatively, ∼1 per cent for k 1 h Mpc−1 and z 1. This enables efficient forward modelling in the nonlinear regime, allowing for estimation of cosmological parameters using Markov ChainMonteCarlo methods. EuclidEmulator has been compared to HALOFIT, CosmicEmu, and NGenHalofit, and shown to be more accurate than these other approaches. This work paves a new way for optimal construction of future emulators that also consider other cosmological observables, use higher resolution input simulations, and investigate higher dimensional cosmological parameter spaces.Peer reviewe

Corrosion of potential first stage blade materials in simulated supercritical CO2

Global power consumption is predicted to double by 2050, notably driven by the transportation and energy sectors necessitating limitations of emissions. Due to its compact turbomachinery, better thermal efficiency, and simpler layout, supercritical-CO2 cycles have received attention, with numerous variations proposed (either indirect-fired/closed cycles or direct-fired-open cycles). One technical challenge is degradation pathway quantification of turbine materials in sCO2 as selection is crucial to successfully and economically operate new plants. This requires degradation assessment in representative environments simulating the Allam cycle. Laboratory tests were conducted on a first stage turbine blade alloy, CM247, with either an environmentally resistant coating or bond coat/thermal barrier coat at one atmosphere and 800°C, with potential exposure including (O2, H2O, N2, SO2) for up to 1000 h. Weight change and metallographic measurements tracked scale development. Scanning electron microscopy/energy dispersive X-ray spectroscopy studied scales and internal precipitates. Locations of contaminant element in the CO2-rich environment were investigated

Burned area and carbon emissions across northwestern boreal North America from 2001-2019

Fire is the dominant disturbance agent in Alaskan and Canadian boreal ecosystems and releases large amounts of carbon into the atmosphere. Burned area and carbon emissions have been increasing with climate change, which have the potential to alter the carbon balance and shift the region from a historic sink to a source. It is therefore critically important to track the spatiotemporal changes in burned area and fire carbon emissions over time. Here we developed a new burned-area detection algorithm between 2001-2019 across Alaska and Canada at 500 m (meters) resolution that utilizes finer-scale 30 m Landsat imagery to account for land cover unsuitable for burning. This method strictly balances omission and commission errors at 500 m to derive accurate landscape- and regional-scale burned-area estimates. Using this new burned-area product, we developed statistical models to predict burn depth and carbon combustion for the same period within the NASA Arctic-Boreal Vulnerability Experiment (ABoVE) core and extended domain. Statistical models were constrained using a database of field observations across the domain and were related to a variety of response variables including remotely sensed indicators of fire severity, fire weather indices, local climate, soils, and topographic indicators. The burn depth and aboveground combustion models performed best, with poorer performance for belowground combustion. We estimate 2.37×106 ha (2.37 Mha) burned annually between 2001-2019 over the ABoVE domain (2.87 Mha across all of Alaska and Canada), emitting 79.3 ± 27.96 Tg (±1 standard deviation) of carbon (C) per year, with a mean combustion rate of 3.13 ± 1.17 kg C m-2. Mean combustion and burn depth displayed a general gradient of higher severity in the northwestern portion of the domain to lower severity in the south and east. We also found larger-fire years and later-season burning were generally associated with greater mean combustion. Our estimates are generally consistent with previous efforts to quantify burned area, fire carbon emissions, and their drivers in regions within boreal North America; however, we generally estimate higher burned area and carbon emissions due to our use of Landsat imagery, greater availability of field observations, and improvements in modeling. The burned area and combustion datasets described here (the ABoVE Fire Emissions Database, or ABoVE-FED) can be used for local- to continental-scale applications of boreal fire science

Catheter Ablation of Atrial Fibrillation in Patients with Previous Lobectomy or Partial Lung Resection: Long-Term Results of an International Multicenter Study.

INTRODUCTION Data regarding the efficacy of catheter ablation in patients with atrial fibrillation (AF) and patients' previous history of pulmonary lobectomy/pneumonectomy are scanty. We sought to evaluate the efficacy and long-term follow-up of catheter ablation in this highly selected group of patients. MATERIAL AND METHODS Twenty consecutive patients (8 females, 40%; median age 65.2 years old) with a history of pneumonectomy/lobectomy and paroxysmal or persistent AF, treated by means of pulmonary vein isolation (PVI) at ten participating centers were included. Procedural success, intra-procedural complications, and AF recurrences were considered. RESULTS Fifteen patients had a previous lobectomy and five patients had a complete pneumonectomy. A large proportion (65%) of PV stumps were electrically active and represented a source of firing in 20% of cases. PVI was performed by radiofrequency ablation in 13 patients (65%) and by cryoablation in the remaining 7 cases. Over a median follow up of 29.7 months, a total of 7 (33%) AF recurrences were recorded with neither a difference between patients treated with cryoablation or radiofrequency ablation or between the two genders. CONCLUSIONS Catheter ablation by radiofrequency ablation or cryoablation in patients with pulmonary stumps is feasible and safe. Long-term outcomes are favorable, and a similar efficacy of catheter ablation has been noticed in both males and females

Standalone vertex finding in the ATLAS muon spectrometer

A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at √s = 7 TeV collected with the ATLAS detector at the LHC during 2011

Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC

Measurements are presented of production properties and couplings of the recently discovered Higgs boson using the decays into boson pairs, H →γ γ, H → Z Z∗ →4l and H →W W∗ →lνlν. The results are based on the complete pp collision data sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at centre-of-mass energies of √s = 7 TeV and √s = 8 TeV, corresponding to an integrated luminosity of about 25 fb−1. Evidence for Higgs boson production through vector-boson fusion is reported. Results of combined fits probing Higgs boson couplings to fermions and bosons, as well as anomalous contributions to loop-induced production and decay modes, are presented. All measurements are consistent with expectations for the Standard Model Higgs boson

Measurement of the top quark-pair production cross section with ATLAS in pp collisions at \sqrt{s}=7\TeV

A measurement of the production cross-section for top quark pairs(\ttbar) in $pp$ collisions at \sqrt{s}=7 \TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in two different topologies: single lepton (electron $e$ or muon $\mu$) with large missing transverse energy and at least four jets, and dilepton ($ee$, $\mu\mu$ or $e\mu$) with large missing transverse energy and at least two jets. In a data sample of 2.9 pb-1, 37 candidate events are observed in the single-lepton topology and 9 events in the dilepton topology. The corresponding expected backgrounds from non-\ttbar Standard Model processes are estimated using data-driven methods and determined to be $12.2 \pm 3.9$ events and $2.5 \pm 0.6$ events, respectively. The kinematic properties of the selected events are consistent with SM \ttbar production. The inclusive top quark pair production cross-section is measured to be \sigmattbar=145 \pm 31 ^{+42}_{-27} pb where the first uncertainty is statistical and the second systematic. The measurement agrees with perturbative QCD calculations.Comment: 30 pages plus author list (50 pages total), 9 figures, 11 tables, CERN-PH number and final journal adde