453 research outputs found
Effect of Grazing on Soil Carbon and Nitrogen in Alpine Madow, Eastern of Tibetan Plateau
As the grassland ecosystem in the Tibetan Plateau is very fragile, overgrazing likely leads to more serious damages to it than other ecosystems. In the past 30 years, 37% of the alpine meadows have been heavily damaged by grazing causing degradation of native vegetation, a decline in species richness and feed value, and more seriously soil erosion (Six et al. 2004). The impact of grazing on alpine grasslands appears to be hysteresis, as the soil needs more time to recover than the vegetation. So analysing the effect of grazing intensity on soil characteristics is an important way to reveal how grazing influenced grassland ecosystem. Although much research about grazing effects on nutrients, immobilization of carbon (C) and nitrogen (N) in soils and soil microbes have been done in different terrestrial environments, similar effort has rarely focused on the Tibetan Plateau. In this study, soil organic carbon (SOC) and total nitrogen (STN) in 0-30 cm soil depth were measured in the alpine meadow at the northeastern margin of the Tibetan Plateau, to determine suitable grazing intensity from the viewpoints of soil health and fertility, and providing a scientific basis for guiding the reasonable use of the alpine meadow
Chloridobis(1,10-phenanthroline-κ2 N,N′)copper(II) tetrakis(nitrato-κ2 O,O′)(1,10-phenanthroline-κ2 N,N′)terbate(III)
The title complex salt, [CuCl(C12H8N2)2][Tb(NO3)4(C12H8N2)], consists of discrete [CuCl(phen))2]+ cations and [Tb(NO3)4(phen)]− anions (phen is 1,10-phenanthroline). The [CuCl(phen))2]+ cation contains a five-coordinate Cu2+ ion, ligated by two bidentate phen ligands and one Cl− ion, exhibiting a distorted CuN4Cl trigonal–bipyramidal geometry. In the [Tb(NO3)4(phen)]− anion, the Tb3+ ion is coordinated by one chelating phen ligand and four chelating nitrates, forming a distorted TbN2O8 bicapped dodecahedral configuration. The anions and cations are assembled into a three-dimensional network by weak C—H⋯Cl and C—H⋯O hydrogen bonds. There is also a significant π–π stacking interaction, with a centroid–centroid distance of 3.635 (2) Å
Experimental Realization of Nonadiabatic Holonomic Single-Qubit Quantum Gates with Two Dark Paths in a Trapped Ion
For circuit-based quantum computation, experimental implementation of
universal set of quantum logic gates with high-fidelity and strong robustness
is essential and central. Quantum gates induced by geometric phases, which
depend only on global properties of the evolution paths, have built-in
noise-resilience features. Here, we propose and experimentally demonstrate
nonadiabatic holonomic single-qubit quantum gates on two dark paths in a
trapped ion based on four-level systems with resonant
drives. We confirm the implementation with measured gate fidelity through both
quantum process tomography and randomized benchmarking methods. Meanwhile, we
find that nontrivial holonomic two-qubit quantum gates can also be realized
within current experimental technologies. Compared with previous
implementations on three-level systems, our experiment share both the advantage
of fast nonadiabatic evolution and the merit of robustness against systematic
errors, and thus retains the main advantage of geometric phases. Therefore, our
experiment confirms a promising method for fast and robust holonomic quantum
computation.Comment: 13 pages, 5 figure
A SWAP Gate for Spin Qubits in Silicon
With one- and two-qubit gate fidelities approaching the fault-tolerance
threshold for spin qubits in silicon, how to scale up the architecture and make
large arrays of spin qubits become the more pressing challenges. In a scaled-up
structure, qubit-to-qubit connectivity has crucial impact on gate counts of
quantum error correction and general quantum algorithms. In our toolbox of
quantum gates for spin qubits, SWAP gate is quite versatile: it can help solve
the connectivity problem by realizing both short- and long-range spin state
transfer, and act as a basic two-qubit gate, which can reduce quantum circuit
depth when combined with other two-qubit gates. However, for spin qubits in
silicon quantum dots, high fidelity SWAP gates have not been demonstrated due
to the requirements of large circuit bandwidth and a highly adjustable ratio
between the strength of the exchange coupling J and the Zeeman energy
difference Delta E_z. Here we demonstrate a fast SWAP gate with a duration of
~25 ns based on quantum dots in isotopically enriched silicon, with a highly
adjustable ratio between J and Delta E_z, for over two orders of magnitude in
our device. We are also able to calibrate the single-qubit local phases during
the SWAP gate by incorporating single-qubit gates in our circuit. By
independently reading out the qubits, we probe the anti-correlations between
the two spins, estimate the operation fidelity and analyze the dominant error
sources for our SWAP gate. These results pave the way for high fidelity SWAP
gates, and processes based on them, such as quantum communication on chip and
quantum simulation by engineering the Heisenberg Hamiltonian in silicon.Comment: 25 pages, 5 figures
SDSS J013127.34032100.1: A newly discovered radio-loud quasar at with extremely high luminosity
Only very few z>5 quasars discovered to date are radio-loud, with a
radio-to-optical flux ratio (radio-loudness parameter) higher than 10. Here we
report the discovery of an optically luminous radio-loud quasar, SDSS
J013127.34-032100.1 (J0131-0321 in short), at z=5.18+-0.01 using the Lijiang
2.4m and Magellan telescopes. J0131-0321 has a spectral energy distribution
consistent with that of radio-loud quasars. With an i-band magnitude of 18.47
and radio flux density of 33 mJy, its radio-loudness parameter is ~100. The
optical and near-infrared spectra taken by Magellan enable us to estimate its
bolometric luminosity to be L_bol ~ 1.1E48 erg/s, approximately 4.5 times
greater than that of the most distant quasar known to date. The black hole mass
of J0131-0321 is estimated to be 2.7E9 solar masses, with an uncertainty up to
0.4 dex. Detailed physical properties of this high-redshift, radio-loud,
potentially super-Eddington quasar can be probed in the future with more
dedicated and intensive follow-up observations using multi-wavelength
facilities.Comment: 5 pages, 3 figures, accepted to ApJ
Histamine H2 receptor antagonist exhibited comparable all-cause mortality-decreasing effect as β-blockers in critically ill patients with heart failure: a cohort study
Background: Our previous study reported that histamine H2 receptor antagonists (H2RAs) exposure was associated with decreased mortality in critically ill patients with heart failure (HF) through the same pharmacological mechanism as β-blockers. However, population-based clinical study directly comparing the efficacy of H2RAs and β-blockers on mortality of HF patients are still lacking. This study aims to compare the association difference of H2RAs and β-blockers on mortality in critically ill patients with HF using the Medical Information Mart for Intensive Care III database (MIMIC-III).Methods: Study population was divided into 4 groups: β-blockers + H2RAs group, β-blockers group, H2RAs group, and Non-β-blockers + Non-H2RAs group. Kaplan–Meier curves and multivariable Cox regression models were employed to evaluate the differences of all-cause mortalities among the 4 groups. Propensity score matching (PSM) was used to increase comparability of four groups.Results: A total of 5593 patients were included. After PSM, multivariate analyses showed that patients in H2RAs group had close all-cause mortality with patients in β-blockers group. Furthermore, 30-day, 1-year, 5-year and 10-year all-mortality of patients in β-blockers + H2RAs group were significantly lower than those of patients in β-blockers group, respectively (HR: 0.64, 95%CI: 0.50–0.82 for 30-day; HR: 0.80, 95%CI: 0.69–0.93 for 1-year mortality; HR: 0.83, 95%CI: 0.74–0.93 for 5-year mortality; and HR: 0.85, 95%CI: 0.76–0.94 for 10-year mortality, respectively).Conclusion: H2RAs exposure exhibited comparable all-cause mortality-decreasing effect as β-blockers; and, furthermore, H2RAs and β-blockers had additive or synergistic interactions to improve survival in critically ill patients with HF
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