2,994 research outputs found
Mapping Irrigated and Rainfed Wheat Areas Using Multi-Temporal Satellite Data
Irrigation is crucial to agriculture in arid and semi-arid areas and significantly contributes to crop development, food diversity and the sustainability of agro-ecosystems. For a specific crop, the separation of its irrigated and rainfed areas is difficult, because their phenology is similar and therefore less distinguishable, especially when there are phenology shifts due to various factors, such as elevation and latitude. In this study, we present a simple, but robust method to map irrigated and rainfed wheat areas in a semi-arid region of China. We used the Normalized Difference Vegetation Index (NDVI) at a 30 × 30 m spatial resolution derived from the Chinese HJ-1A/B (HuanJing(HJ) means environment in Chinese) satellite to create a time series spanning the whole growth period of wheat from September 2010 to July 2011. The maximum NDVI and time-integrated NDVI (TIN) that usually exhibit significant differences between irrigated and rainfed wheat were selected to establish a classification model using a support vector machine (SVM) algorithm. The overall accuracy of the Google-Earth testing samples was 96.0%, indicating that the classification results are accurate. The estimated irrigated-to-rainfed ratio was 4.4:5.6, close to the estimates provided by the agricultural sector in Shanxi Province. Our results illustrate that the SVM classification model can effectively avoid empirical thresholds in supervised classification and realistically capture the magnitude and spatial patterns of rainfed and irrigated wheat areas. The approach in this study can be applied to map irrigated/rainfed areas in other regions when field observational data are available
Incomplete Wood-Ljungdahl pathway facilitates one-carbon metabolism in organohalide-respiring Dehalococcoides mccartyi.
The acetyl-CoA "Wood-Ljungdahl" pathway couples the folate-mediated one-carbon (C1) metabolism to either CO2 reduction or acetate oxidation via acetyl-CoA. This pathway is distributed in diverse anaerobes and is used for both energy conservation and assimilation of C1 compounds. Genome annotations for all sequenced strains of Dehalococcoides mccartyi, an important bacterium involved in the bioremediation of chlorinated solvents, reveal homologous genes encoding an incomplete Wood-Ljungdahl pathway. Because this pathway lacks key enzymes for both C1 metabolism and CO2 reduction, its cellular functions remain elusive. Here we used D. mccartyi strain 195 as a model organism to investigate the metabolic function of this pathway and its impacts on the growth of strain 195. Surprisingly, this pathway cleaves acetyl-CoA to donate a methyl group for production of methyl-tetrahydrofolate (CH3-THF) for methionine biosynthesis, representing an unconventional strategy for generating CH3-THF in organisms without methylene-tetrahydrofolate reductase. Carbon monoxide (CO) was found to accumulate as an obligate by-product from the acetyl-CoA cleavage because of the lack of a CO dehydrogenase in strain 195. CO accumulation inhibits the sustainable growth and dechlorination of strain 195 maintained in pure cultures, but can be prevented by CO-metabolizing anaerobes that coexist with D. mccartyi, resulting in an unusual syntrophic association. We also found that this pathway incorporates exogenous formate to support serine biosynthesis. This study of the incomplete Wood-Ljungdahl pathway in D. mccartyi indicates a unique bacterial C1 metabolism that is critical for D. mccartyi growth and interactions in dechlorinating communities and may play a role in other anaerobic communities
Mitigating Memorization of Noisy Labels by Clipping the Model Prediction
In the presence of noisy labels, designing robust loss functions is critical
for securing the generalization performance of deep neural networks. Cross
Entropy (CE) loss has been shown to be not robust to noisy labels due to its
unboundedness. To alleviate this issue, existing works typically design
specialized robust losses with the symmetric condition, which usually lead to
the underfitting issue. In this paper, our key idea is to induce a loss bound
at the logit level, thus universally enhancing the noise robustness of existing
losses. Specifically, we propose logit clipping (LogitClip), which clamps the
norm of the logit vector to ensure that it is upper bounded by a constant. In
this manner, CE loss equipped with our LogitClip method is effectively bounded,
mitigating the overfitting to examples with noisy labels. Moreover, we present
theoretical analyses to certify the noise-tolerant ability of LogitClip.
Extensive experiments show that LogitClip not only significantly improves the
noise robustness of CE loss, but also broadly enhances the generalization
performance of popular robust losses.Comment: Accepted by ICML 202
Quantumness and quantum to classical transition in the generalized Rabi model
The quantum to classical transition (QCT) is one of the central mysteries in
quantum physics. This process is generally interpreted as state collapse from
measurement or decoherence from interacting with the environment. Here we
define the quantumness of a Hamiltonian by the free energy difference between
its quantum and classical descriptions, which vanishes during QCT. We apply
this criterion to the many-body Rabi model and study its scaling law across the
phase transition, finding that not only the temperature and Planck constant,
but also all the model parameters are important for this transition. We show
that the Jaynes-Cummings and anti Jaynes-Cummings models exhibit greater
quantumness than the Rabi model. Moreover, we show that the rotating wave and
anti-rotating wave terms in this model have opposite quantumness in QCT. We
demonstrate that the quantumness may be enhanced or suppressed at the critical
point. Finally, we estimate the quantumness of the Rabi model in current
trapped ion experiments. The quantumness provides an important tool to
characterize the QCT in a vast number of many-body models.Comment: 6 pages, 5 figure
Information scrambling and entanglement in quantum approximate optimization algorithm circuits
Variational quantum algorithms, which consist of optimal parameterized
quantum circuits, are promising for demonstrating quantum advantages in the
noisy intermediate-scale quantum (NISQ) era. Apart from classical computational
resources, different kinds of quantum resources have their contributions in the
process of computing, such as information scrambling and entanglement.
Characterizing the relation between complexity of specific problems and quantum
resources consumed by solving these problems is helpful for us to understand
the structure of VQAs in the context of quantum information processing. In this
work, we focus on the quantum approximate optimization algorithm (QAOA), which
aims to solve combinatorial optimization problems. We study information
scrambling and entanglement in QAOA circuits respectively, and discover that
for a harder problem, more quantum resource is required for the QAOA circuit to
obtain the solution. We note that in the future, our results can be used to
benchmark complexity of quantum many-body problems by information scrambling or
entanglement accumulation in the computing process.Comment: 11 pages, 9 figures, Some minor correction
BMP4 Activation and Secretion Are Negatively Regulated by an Intracellular Gremlin-BMP4 Interaction
Bone morphogenetic protein 4 (BMP4) is a potent growth factor that is involved in many important biological processes. Regulation of the level of secreted mature BMP4 determines the biological effects of BMP4 on cells in the local microenvironment. Previous studies suggested that Gremlin, a member of DAN family proteins, antagonizes BMP4 activity by sequestering extracellular BMP4. Herein, we report a novel intracellular regulatory mechanism by which Gremlin interacts with BMP4 precursor, prevents secretion of mature BMP4, and therefore inhibits BMP4 activity more efficiently. Furthermore, we also defined a 30-amino acid peptide sequence within the Gremlin DAN domain that is essential for BMP4 interaction. This novel Gremlin-mediated BMP4 posttranslational regulatory mechanism implies that the level of BMP4 mRNA expression does not truly reflect BMP4 activity when Gremlin and BMP4 are coexpressed within the same cell. Similar regulatory mechanisms may be utilized by other DAN family proteins
Bose-Einstein condensate in Bloch bands with off-diagonal periodic potential
We report the Bose-Einstein condensate (BEC) in the Bloch bands with
off-diagonal periodic potential (ODPP), which simultaneously plays the role of
spin-orbit coupling (SOC) and Zeeman field. This model can be realized using
two independent Raman couplings in the same three level system, in which the
time-reversal symmetry ensures the energy degeneracy between the two states
with opposite momenta. We find that these two Raman couplings can be used to
tune the spin polarization in momentum space, thus greatly modifies the
effective scatterings over the Bloch bands. We observe a transition from the
Bloch plane wave phase with condensate at one wave vector to the Bloch stripe
phase with condensates at the two Bloch states with opposite wave vectors.
These two phases will exhibit totally different spin textures and density
modulations in real space, which are totally different from that in free space.
In momentum space multiple peaks differ by some reciprocal lattice vectors can
be observed, reflecting the periodic structure of the ODPP. A three-band
effective model is proposed to understand these observations. This system can
provide a new platform in investigating of various physics, such as collective
excitations, polaron and topological superlfuids, over the Bloch bands.Comment: 6 pages, 5 figure
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