At over 40years, the Landsat satellites provide the longest temporal record of space-based land surface observations, and the successful 2013 launch of the Landsat-8 is continuing this legacy. ...Ideally, the Landsat data record should be consistent over the Landsat sensor series. The Landsat-8 Operational Land Imager (OLI) has improved calibration, signal to noise characteristics, higher 12-bit radiometric resolution, and spectrally narrower wavebands than the previous Landsat-7 Enhanced Thematic Mapper (ETM+). Reflective wavelength differences between the two Landsat sensors depend also on the surface reflectance and atmospheric state which are difficult to model comprehensively. The orbit and sensing geometries of the Landsat-8 OLI and Landsat-7 ETM+ provide swath edge overlapping paths sensed only one day apart. The overlap regions are sensed in alternating backscatter and forward scattering orientations so Landsat bi-directional reflectance effects are evident but approximately balanced between the two sensors when large amounts of time series data are considered. Taking advantage of this configuration a total of 59 million 30m corresponding sensor observations extracted from 6317 Landsat-7 ETM+ and Landsat-8 OLI images acquired over three winter and three summer months for all the conterminous United States (CONUS) are compared. Results considering different stages of cloud and saturation filtering, and filtering to reduce one day surface state differences, demonstrate the importance of appropriate per-pixel data screening. Top of atmosphere (TOA) and atmospherically corrected surface reflectance for the spectrally corresponding visible, near infrared and shortwave infrared bands, and derived normalized difference vegetation index (NDVI), are compared and their differences quantified. On average the OLI TOA reflectance is greater than the ETM+ TOA reflectance for all bands, with greatest differences in the near-infrared (NIR) and the shortwave infrared bands due to the quite different spectral response functions between the sensors. The atmospheric correction reduces the mean difference in the NIR and shortwave infrared but increases the mean difference in the visible bands. Regardless of whether TOA or surface reflectance are used to generate NDVI, on average, for vegetated soil and vegetation surfaces (0≤NDVI≤1), the OLI NDVI is greater than the ETM+ NDVI. Statistical functions to transform between the comparable sensor bands and sensor NDVI values are presented so that the user community may apply them in their own research to improve temporal continuity between the Landsat-7 ETM+ and Landsat-8 OLI sensor data. The transformation functions were developed using ordinary least squares (OLS) regression and were fit quite reliably (r2 values>0.7 for the reflectance data and >0.9 for the NDVI data, p-values<0.0001).
•National-scale 30m Landsat 7 ETM+ Landsat 8 OLI data comparison•Characterization of sensor reflectance and NDVI differences•Statistical functions to transform between comparable sensor bands and NDVI
Quantification of global forest change has been lacking despite the recognized importance of forest ecosystem services. In this study, Earth observation satellite data were used to map global forest ...loss (2.3 million square kilometers) and gain (0.8 million square kilometers) from 2000 to 2012 at a spatial resolution of 30 meters. The tropics were the only climate domain to exhibit a trend, with forest loss increasing by 2101 square kilometers per year. Brazil's well-documented reduction in deforestation was offset by increasing forest loss in Indonesia, Malaysia, Paraguay, Bolivia, Zambia, Angola, and elsewhere. Intensive forestry practiced within subtropical forests resulted in the highest rates of forest change globally. Boreal forest loss due largely to fire and forestry was second to that in the tropics in absolute and proportional terms. These results depict a globally consistent and locally relevant record of forest change.
A Density Functional Theory is employed to study depletion interactions between nanoparticles mediated by semiflexible polymers. The four key parameters are the chain contour length and the ...persistence length of the polymeric depletant, its radius of gyration, and the nanoparticle radius. In the Density Functional Theory calculation of the depletion interaction between the nanoparticles mediated by semiflexible polymers, the polymer gyration radius is kept constant by varying the contour length and the persistence length simultaneously. This makes it possible to study the effect of the chain stiffness on the depletion potential of mean force between the nanoparticles for a given depletant size. It is found that the depletion attraction becomes stronger for stiffer polymer chains and larger colloids. The depletion potential of mean force is used as input to compute the phase diagram for an effective one-component colloidal system.
Abstract
The article provides a comparative analysis of the efficiency of off-peak electricity conversion at nuclear power plants (NPP) using reversible fuel cells (RFC). The RFC can ensure the NPP ...the baseline electrical load through hydrogen production by electrolysis of water, as well as an increase in its maneuverability due to generation of peak electricity. The calculations have shown that at the current stage of technological advancements, the use of RFCs in terms of achievable efficiency of off-peak electricity conversion has advantages over the hydrogen power complex which utilizes an additional steam turbine to generate peak electricity. The achievable advantage equals 2.84-4.25% and 7.72-11.58% at the RFC efficiency in the mode of peak power generation of 50% and 60%, respectively, which is 5.1-7.66 MW and 13.9-20.85 MW more than the generated peak electricity. It should be noted that an increase in the electrolysis mode efficiency facilitates the RFC advantages – from 24.44 to 36.65% and from 29.32 to 43.98% respectively. The use of the "cold" combustion technology for hydrogen fuel ensures not only high efficiency, but also reliability and safety of the hydrogen power complex operation
In this Letter we report on the colossal spin splitting (on the order of several electronvolts) in the collinear antiferromagnetic (AFM) MnF2 (110) monolayer, which we obtained from first-principles ...calculations and explain in terms of group-theoretical analysis. This Pekar–Rashba AFM-induced spin splitting with a magnetic mechanism does not require the presence of spin–orbit coupling such as with a traditional Rashba–Dresselhaus electric mechanism. Furthermore, it was observed for all wave vectors, including high-symmetry points of the two-dimensional (2D) Brillouin zone. This is in contrast to recently reported AFM-induced spin splitting in the bulk structure of MnF2, which was both smaller by at least an order of magnitude and required to vanish by symmetry at several high-symmetry points and directions of the three-dimensional Brillouin zone. The crucial part of our group-theoretical analysis is the determination of the magnetic layer group for the monolayer structure for which we propose a simple and generic procedure.
The cross sections and their ratios for dijet production versus the rapidity separation between the jets in the dijet in proton–proton collisions at the energy of
TeV are presented according to the ...most recent measurements performed with the CMS detector at the Large Hadron Collider. The measured observables are sensitive to high-energy effects of Balitsky–Fadin–Kuraev–Lipatov (BFKL) evolution. The results are compared with the predictions of various Monte Carlo generators based both on high-energy BFKL evolution and on Dokshitzer–Gribov–Lipatov–Altarelli–Parisi evolution for hard processes.
The paper deals with the computation of delay Lyapunov matrices for linear exponentially stable time-invariant systems with several pointwise delays. It is shown that the matrices depend continuously ...on the system delays. Based on this theoretical result, an algorithm of approximation of the delay Lyapunov matrices with a prescribed accuracy is presented. The result is illustrated by an example.
Density Functional Theory is employed to study structural properties and interactions between solvent-free polymer-grafted nanoparticles. Both monodisperse and bidisperse polymer brushes with ...variable chain stiffness are considered. The three major control parameters are the grafting density, the grafted chain length, and its stiffness. The effect of these parameters on the brush-brush overlap and attractive interaction strength is analyzed. The Density Functional Theory results are compared with the available simulation data, and good quantitative agreement is found.
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