43,444 research outputs found
Contributions of natural and human factors to increases in vegetation productivity in China
Increasing trends in vegetation productivity have been identified for the last three decades for many regions in the northern hemisphere including China. Multiple natural and human factors are possibly responsible for the increases in vegetation productivity, while their relative contributions remain unclear. Here we analyzed the long-term trends in vegetation productivity in China using the satellite-derived normalized difference vegetation index (NDVI) and assessed the relationships of NDVI with a suite of natural (air temperature, precipitation, photosynthetically active radiation (PAR), atmospheric carbon dioxide (CO2) concentrations, and nitrogen (N) deposition) and human (afforestation and improved agricultural management practices) factors. Overall, China exhibited an increasing trend in vegetation productivity with an increase of 2.7%. At the provincial scale, eleven provinces exhibited significant increases in vegetation productivity, and the majority of these provinces are located within the northern half of the country. At the national scale, annual air temperature was most closely related to NDVI and explained 36.8% of the variance in NDVI, followed by afforestation (25.5%) and crop yield (15.8%). Altogether, temperature, total forest plantation area, and crop yield explained 78.1% of the variance in vegetation productivity at the national scale, while precipitation, PAR, atmospheric CO2 concentrations, and N deposition made no significant contribution to the increases in vegetation productivity. At the provincial scale, each factor explained a part of the variance in NDVI for some provinces, and the increases in NDVI for many provinces could be attributed to the combined effects of multiple factors. Crop yield and PAR were correlated with NDVI for more provinces than were other factors, indicating that both elevated crop yield resulting from improved agricultural management practices and increasing diffuse radiation were more important than other factors in increasing vegetation productivity at the provincial scale. The relative effects of the natural and human factors on vegetation productivity varied with spatial scale. The true contributions of multiple factors can be obscured by the correlation among these variables, and it is essential to examine the contribution of each factor while controlling for other factors. Future changes in climate and human activities will likely have larger influences on vegetation productivity in China
More hidden heavy quarkonium molecules and their discovery decay modes
To validate the molecular description of the observed
and , it is valuable to investigate their counterparts,
denoted as in this work, and the corresponding decay modes.
In this work, we present an analysis of the using flavor
symmetry. We also use the effective Lagrangian based on the heavy quark
symmetry to explore the rescattering mechanism and calculate the partial widths
for the isospin conserved channels . The
predicted partial widths are of an order of MeV for ,
which correspond to branching ratios of the order of . For
, the partial widths are a few hundreds of keV and
the branching ratios are about . Future experimental measurements can
test our predictions on the partial widths and thus examine the molecule
description of heavy quarkoniumlike exotic states.Comment: 11 pages, 2 figures; accepted by Phys. Rev.
Branching ratios, asymmetries and polarizations of decays
We analyzed the nonleptonic decays with by employing the perturbative QCD (PQCD) factorization
approach. Here the branching ratios, the asymmetries and the complete set
of polarization observables are investigated systematically. Besides the
traditional contributions from the factorizable and nonfactorizable diagrams at
the leading order, the next-to-leading order (NLO) vertex corrections could
also provide considerable contributions. The PQCD predictions for the branching
ratios of the decays are consistent
with the measured values within errors. As for decays, the branching ratios can reach the order of and could
be measured in the LHCb and Belle-II experiments. The numerical results show
that the direct asymmetries of the considered decays are very small. Thus
the observation of any large direct asymmetry for these decays will be a
signal for new physics. The mixing induced asymmetries in the neutral
modes are very close to , which suggests that these channels
can give a cross-check on the measurement of the Cabbibo-Kobayashi-Maskawa
(CKM) angle and . We found that the longitudinal polarization
fractions are suppressed to due to the large nonfactorizable
contributions. The magnitudes and phases of the two transverse amplitudes
and are roughly equal, which
is an indication for the approximate light quark helicity conservation in these
decays. The overall polarization observables of and
channels are also in good agreement with the
experimental measurements as reported by LHCb and BaBar. Other results can also
be tested by the LHCb and Belle-II experiments.Comment: 14 pages, 1 figure, 6 table
Semileptonic decays of meson to S-wave charmonium states in the perturbative QCD approach
Inspired by the recent measurement of the ratio of branching fractions
to and final states at the LHCb
detector, we study the semileptonic decays of meson to the S-wave ground
and radially excited 2S and 3S charmonium states with the perturbative QCD
approach. After evaluating the form factors for the transitions , where and denote pseudoscalar and vector S-wave charmonia,
respectively, we calculate the branching ratios for all these semileptonic
decays. The theoretical uncertainty of hadronic input parameters are reduced by
utilizing the light-cone wave function for meson. It is found that the
predicted branching ratios range from up to and could be
measured by the future LHCb experiment. Our prediction for the ratio of
branching fractions is in good
agreement with the data. For decays, the relative
contributions of the longitudinal and transverse polarization are discussed in
different momentum transfer squared regions. These predictions will be tested
on the ongoing and forthcoming experiments.Comment: 12 pages, 3 figures, 5 table
- …