80 research outputs found
Analysis of Vegetation Vulnerability Dynamics and Driving Forces to Multiple Drought Stresses in a Changing Environment
Quantifying changes in the vulnerability of vegetation to various drought stresses in
different seasons is important for rational and effective ecological conservation and restoration.
However, the vulnerability of vegetation and its dynamics in a changing environment are still
unknown, and quantitative attribution analysis of vulnerability changes has been rarely studied. To
this end, this study explored the changes of vegetation vulnerability characteristics under various
drought stresses in Xinjiang and conducted quantitative attribution analysis using the random
forest method. In addition, the effects of ecological water transport and increased irrigation areas
on vegetation vulnerability dynamics were examined. The standardized precipitation index (SPI),
standardized precipitation-evapotranspiration index (SPEI), and standardized soil moisture index
(SSMI) represent atmospheric water supply stress, water and heat supply stress, and soil water supply
stress, respectively. The results showed that: (1) different vegetation types responded differently to
water stress, with grasslands being more sensitive than forests and croplands in summer; (2) increased
vegetation vulnerability under drought stresses dominated in Xinjiang after 2003, with vegetation
growth and near-surface temperature being the main drivers, while increased soil moisture in the
root zone was the main driver of decreased vegetation vulnerability; (3) vulnerability of cropland
to SPI/SPEI/SSMI-related water stress increased due to the rapid expansion of irrigation areas,
which led to increasing water demand in autumn that was difficult to meet; and (4) after ecological
water transport of the Tarim River Basin, the vulnerability of its downstream vegetation to drought
was reduced
Model-Free Large-Scale Cloth Spreading With Mobile Manipulation: Initial Feasibility Study
Cloth manipulation is common in domestic and service tasks, and most studies
use fixed-base manipulators to manipulate objects whose sizes are relatively
small with respect to the manipulators' workspace, such as towels, shirts, and
rags. In contrast, manipulation of large-scale cloth, such as bed making and
tablecloth spreading, poses additional challenges of reachability and
manipulation control. To address them, this paper presents a novel framework to
spread large-scale cloth, with a single-arm mobile manipulator that can solve
the reachability issue, for an initial feasibility study. On the manipulation
control side, without modeling highly deformable cloth, a vision-based
manipulation control scheme is applied and based on an online-update Jacobian
matrix mapping from selected feature points to the end-effector motion. To
coordinate the control of the manipulator and mobile platform, Behavior Trees
(BTs) are used because of their modularity. Finally, experiments are conducted,
including validation of the model-free manipulation control for cloth spreading
in different conditions and the large-scale cloth spreading framework. The
experimental results demonstrate the large-scale cloth spreading task
feasibility with a single-arm mobile manipulator and the model-free deformation
controller.Comment: 6 pages, 6 figures, submit to CASE202
GRACE-Based Terrestrial Water Storage in Northwest China: Changes and Causes
Monitoring variations in terrestrial water storage (TWS) is of great significance for the management of water resources. However, it remains a challenge to continuously monitor TWS variations using in situ observations and hydrological models because of a limited number of gauge stations and the complicated spatial distribution characteristics of TWS. In contrast, the Gravity Recovery and Climate Experiment (GRACE) could overcome the aforementioned restrictions, providing a new reliable means of observing TWS variation. Thus, GRACE was employed to investigate TWS variations in Northwest China (NWC) between April 2002 and March 2016. Unlike previous studies, we focused on the interactions of multiple climatic and vegetational factors, and their combined effects on TWS variation. In addition, we also analyzed the relationship between TWS variations and socioeconomic water consumption. The results indicated that (i) TWS had obvious seasonal variations in NWC, and showed significant decreasing trends in most parts of NWC at the 95% confidence level;(ii) decreasing sunshine duration and wind speed resulted in an increase in TWS in Qinghai province, whereas the increasing air temperature, ameliorative vegetational coverage, and excessive groundwater withdrawal jointly led to a decrease in TWS in the other provinces of NWC;(iii) TWS variations in NWC had a good correlation with water storage variations in cascade reservoirs of the upper Yellow River;and (iv) the overall interactions between multiple climatic and vegetational factors were obvious, and the strong effects of some climatic and vegetational factors could mask the weak influences of other factors in TWS variations in NWC. Hence, it is necessary to focus on the interactions of multiple factors and their combined effects on TWS variations when exploring the causes of TWS variations
Electronic and magnetic phase diagrams of Kitaev quantum spin liquid candidate NaCoTeO
The 3 Co-based insulating magnet \NCTO{} has recently been
reported to have strong Kitaev interactions on a honeycomb lattice, and is thus
being considered as a Kitaev quantum spin liquid candidate. However, due to the
existence of other types of interactions, a spontaneous long-range magnetic
order occurs. This order is suppressed by applied magnetic fields leading to a
succession of phases and ultimately saturation of the magnetic moments. The
precise phase diagram, the nature of the phases, and the possibility that one
of the field-induced phases is a Kitaev quantum spin liquid phase are still a
matter of debate. Here we measured an extensive set of physical properties to
build the complete temperature-field phase diagrams to magnetic saturation at
10 T for magnetic fields along the - and -axes, and a partial phase
diagram up to 60 T along . We probe the phases using magnetization, specific
heat, magnetocaloric effect, magnetostriction, dielectric constant, and
electric polarization, which is a symmetry-sensitive probe. With these
measurements we identify all the previously incomplete phase boundaries and
find new high-field phase boundaries. We find strong magnetoelectric coupling
in the dielectric constant and moderate magnetostrictive coupling at several
phase boundaries. Furthermore, we detect the symmetry of the magnetic order
using electrical polarization measurements under magnetic fields. Based on our
analysis, the absence of electric polarization under zero or finite magnetic
field in any of the phases or after...Comment: LA-UR-22-3257
Continuous spin excitations in the three-dimensional frustrated magnet K2Ni2(SO4)3
Continuous spin excitations are widely recognized as one of the hallmarks of
novel spin states in quantum magnets, such as quantum spin liquids (QSLs).
Here, we report the observation of such kind of excitations in K2Ni2(SO4)3,
which consists of two sets of intersected spin-1 Ni2+ trillium lattices. Our
inelastic neutron scattering measurement on single crystals clearly shows a
dominant excitation continuum, which exhibits a distinct temperature-dependent
behavior from that of spin waves, and is rooted in strong quantum spin
fluctuations. Further using the self-consistent-gaussian-approximation method,
we determined the fourth- and fifth-nearest neighbor exchange interactions are
dominant. These two bonds together form a unique three-dimensional network of
corner-sharing tetrahedra, which we name as ''hyper-trillium'' lattice. Our
results provide direct evidence for the existence of QSL features in
K2Ni2(SO4)3 and highlight the potential for the hyper-trillium lattice to host
frustrated quantum magnetism.Comment: 6 pages and 5 figures, plus several pages of supplemental material,
comments are welcom
Metagenomic Analysis of Bacteria, Fungi, Bacteriophages, and Helminths in the Gut of Giant Pandas
To obtain full details of gut microbiota, including bacteria, fungi, bacteriophages, and helminths, in giant pandas (GPs), we created a comprehensive microbial genome database and used metagenomic sequences to align against the database. We delineated a detailed and different gut microbiota structures of GPs. A total of 680 species of bacteria, 198 fungi, 185 bacteriophages, and 45 helminths were found. Compared with 16S rRNA sequencing, the dominant bacterium phyla not only included Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria but also Cyanobacteria and other eight phyla. Aside from Ascomycota, Basidiomycota, and Glomeromycota, Mucoromycota, and Microsporidia were the dominant fungi phyla. The bacteriophages were predominantly dsDNA Myoviridae, Siphoviridae, Podoviridae, ssDNA Inoviridae, and Microviridae. For helminths, phylum Nematoda was the dominant. In addition to previously described parasites, another 44 species of helminths were found in GPs. Also, differences in abundance of microbiota were found between the captive, semiwild, and wild GPs. A total of 1,739 genes encoding cellulase, β-glucosidase, and cellulose β-1,4-cellobiosidase were responsible for the metabolism of cellulose, and 128,707 putative glycoside hydrolase genes were found in bacteria/fungi. Taken together, the results indicated not only bacteria but also fungi, bacteriophages, and helminths were diverse in gut of giant pandas, which provided basis for the further identification of role of gut microbiota. Besides, metagenomics revealed that the bacteria/fungi in gut of GPs harbor the ability of cellulose and hemicellulose degradation
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