1,256 research outputs found
Solitonic spin-liquid state due to the violation of the Lifshitz condition in FeTe
A combination of phenomenological analysis and M\"ossbauer spectroscopy
experiments on the tetragonal FeTe system indicates that the magnetic
ordering transition in compounds with higher Fe-excess, 0.11, is
unconventional. Experimentally, a liquid-like magnetic precursor with
quasi-static spin-order is found from significantly broadened M\"ossbauer
spectra at temperatures above the antiferromagnetic transition. The
incommensurate spin-density wave (SDW) order in FeTe is described by a
magnetic free energy that violates the weak Lifshitz condition in the Landau
theory of second-order transitions. The presence of multiple Lifshitz
invariants provides the mechanism to create multidimensional, twisted, and
modulated solitonic phases.Comment: 5 pages, 2 figure
Particulate emissions from large North American wildfires estimated using a new top-down method
Particulate matter emissions from wildfires affect climate, weather
and air quality. However, existing global and regional aerosol emission
estimates differ by a factor of up to 4 between different methods. Using
a novel approach, we estimate daily total particulate matter (TPM) emissions
from large wildfires in North American boreal and temperate regions. Moderate
Resolution Imaging Spectroradiometer (MODIS) fire location and aerosol
optical thickness (AOT) data sets are coupled with HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) atmospheric
dispersion simulations, attributing identified smoke plumes to sources.
Unlike previous approaches, the method (i)Â combines information from both
satellite and AERONET (AErosol RObotic NETwork) observations to take into account aerosol water uptake
and plume specific mass extinction efficiency when converting smoke AOT to
TPM, and (ii)Â does not depend on instantaneous emission rates observed during
individual satellite overpasses, which do not sample night-time emissions.
The method also allows multiple independent estimates for the same emission
period from imagery taken on consecutive days.
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Repeated fire-emitted AOT estimates for the same emission period over 2 to 3
days of plume evolution show increases in plume optical thickness by
approximately 10âŻ% for boreal events and by 40âŻ% for
temperate emissions. Inferred median water volume fractions for aged
boreal and temperate smoke observations are 0.15 and 0.47 respectively,
indicating that the increased AOT is partly explained by aerosol water
uptake. TPM emission estimates for boreal events, which predominantly
burn during daytime, agree closely with bottom-up Global
Fire Emission Database (GFEDv4) and Global Fire Assimilation System
(GFASv1.0) inventories, but are lower by approximately 30âŻ% compared
to Quick Fire Emission Dataset (QFEDv2) PM<sub>2.â5</sub>,
and are higher by approximately a factor of 2 compared to Fire Energetics and
Emissions Research (FEERv1) TPM estimates. The discrepancies are
larger for temperate fires, which are characterized by lower median
fire radiative power values and more significant night-time combustion. The TPM
estimates for this study for the biome are lower than QFED PM<sub>2.â5</sub> by
35âŻ%, and are larger by factors of 2.4, 3.2 and 4
compared with FEER, GFED and GFAS inventories respectively. A large
underestimation of TPM emission by bottom-up GFED and GFAS indicates
low biases in emission factors or consumed biomass estimates for temperate
fires
The Univariate Marginal Distribution Algorithm Copes Well With Deception and Epistasis
In their recent work, Lehre and Nguyen (FOGA 2019) show that the univariate
marginal distribution algorithm (UMDA) needs time exponential in the parent
populations size to optimize the DeceptiveLeadingBlocks (DLB) problem. They
conclude from this result that univariate EDAs have difficulties with deception
and epistasis.
In this work, we show that this negative finding is caused by an unfortunate
choice of the parameters of the UMDA. When the population sizes are chosen
large enough to prevent genetic drift, then the UMDA optimizes the DLB problem
with high probability with at most fitness
evaluations. Since an offspring population size of order
can prevent genetic drift, the UMDA can solve the DLB problem with fitness evaluations. In contrast, for classic evolutionary algorithms no
better run time guarantee than is known (which we prove to be tight
for the EA), so our result rather suggests that the UMDA can cope
well with deception and epistatis.
From a broader perspective, our result shows that the UMDA can cope better
with local optima than evolutionary algorithms; such a result was previously
known only for the compact genetic algorithm. Together with the lower bound of
Lehre and Nguyen, our result for the first time rigorously proves that running
EDAs in the regime with genetic drift can lead to drastic performance losses
Effect of Particle Size on Droplet Infiltration into Hydrophobic Porous Media As a Model of Water Repellent Soil
The wettability of soil is of great importance for plants and soil biota, and in determining the risk for preferential flow, surface runoff, flooding,and soil erosion. The molarity of ethanol droplet (MED) test is widely used for quantifying the severity of water repellency in soils that show reduced wettability and is assumed to be independent of soil particle size. The minimum ethanol concentration at which droplet penetration occurs within a short time (â€10 s) provides an estimate of the initial advancing contact angle at which spontaneous wetting is expected. In this study, we test the assumption of particle size independence using a simple model of soil, represented by layers of small (0.2â2 mm) diameter beads that predict the effect of changing bead radius in the top layer on capillary driven imbibition. Experimental results using a three-layer bead system show broad agreement with the model and demonstrate a dependence of the MED test on particle size. The results show that the critical initial advancing contact angle for penetration can be considerably less than 90° and varies with particle size, demonstrating that a key assumption currently used in the MED testing of soil is not necessarily valid
Forest floor chemical transformations in a boreal forest fire 2 and their correlations with temperature and heating duration 3
samples taken pre-and post-fire were characterized using elemental and ÎŽ 13 C 24 analysis, differential scanning calorimetry and 13 C nuclear magnetic resonance. 25 During this typical boreal crown fire average maximum temperature (Tmax) at the forest 26 floor was 745 ÂșC (550<Tmax<976 ÂșC) with the average heating duration (t) >300 ÂșC 37 Almost half of the initial total C stock in the forest floor (20 Mg C ha -1 ) was affected b
Mutations in the C-terminal region of the HIV-1 reverse transcriptase and their correlation with drug resistance associated mutations and antiviral treatment
<p>Abstract</p> <p>Objective</p> <p>Replication of HIV-1 after cell entry is essentially dependent on the reverse transcriptase (RT). Antiretroviral drugs impairing the function of the RT currently aim at the polymerase subunit. One reason for failure of antiretroviral treatment is the evolvement of resistance-associated mutations in the viral genome. For RT inhibitors, almost all identified mutations are located within the polymerase; therefore, general genotyping confines to investigate this subunit. Recently several studies have shown that substitutions within the RNase H and the connection domain increase antiviral drug-resistance in vitro, and some of them are present in patient isolates.</p> <p>Aim</p> <p>The aim of the present study was to investigate the prevalence of these substitutions and their association with mutations in the polymerase domain arising during antiretroviral treatment.</p> <p>Materials and methods</p> <p>We performed genotypic analyzes on seventy-four virus isolates derived from treated and untreated patients, followed at the HIV Centre of the Johann Wolfgang Goethe University Hospital (Frankfurt/Main, Germany). We subsequently analysed the different substitutions in the c-terminal region to evaluate whether there were associations with each other, n-terminal substitutions or with antiretroviral treatment.</p> <p>Results</p> <p>We identified several primer grip substitutions, but almost all of them were located in the connection domain. This is consistent with other in-vivo studies, in which especially the primer grip residues located in the RNase H were unvaried. Furthermore, we identified other substitutions in the connection domain and in the RNase H. Especially E399D seemed to be associated with an antiretroviral treatment and N-terminal resistance-delivering mutations.</p> <p>Conclusion</p> <p>Some of the identified substitutions were associated with antiviral treatment and drug resistance-associated mutations. Due to the low prevalence of C-terminal mutations and as only a few of them could be associated with antiviral treatment and N-terminal resistance-delivering mutations, we would not recommend routinely testing of the C-terminal RT region.</p
The Relevance of Pyrogenic Carbon for Carbon Budgets From Fires: Insights From the FIREX Experiment
Vegetation fires play an important role in global and regional carbon cycles. Due to climate warming and land use shifts, fire patterns are changing and fire impacts increasing in many of the world's regions. Reducing uncertainties in carbon budgeting calculations from fires is therefore fundamental to advance our current understanding and forecasting capabilities. Here we study 20 chamber burns from the FIREX FireLab experiment, which burnt a representative set of North American wildland fuels, to assess the following: (i) differences in carbon emission estimations between the commonly used âconsumed biomassâ approach and the âburnt carbonâ approach; (ii) pyrogenic carbon (PyC) production rates; and (iii) thermal and chemical recalcitrance of the PyC produced, as proxies of its biogeochemical stability. We find that the âconsumed biomassâ approach leads to overestimation of carbon emissions by 2â27% (most values between 2% and 10%). This accounting error arises largely from not considering PyC production and, even if relatively small, can therefore have important implications for mediumâ and longâterm carbon budgeting. A large fraction (34â100%) of this PyC was contained in the charred fine residue, a postfire material frequently overlooked in fire carbon research. However, the most recalcitrant PyC was in the form of woody charcoal, with estimated halfâlives for most samples exceeding 1,000 years. Combustion efficiency was relatively high in these laboratory burns compared to actual wildland fire conditions, likely leading to lower PyC production rates. We therefore argue that the PyC production values obtained here, and associated overestimation of carbon emissions, should be taken as lowâend estimates for wildland fire conditions
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