339 research outputs found
Climate Dynamics: A Network-Based Approach for the Analysis of Global Precipitation
Precipitation is one of the most important meteorological variables for defining the climate dynamics, but the spatial patterns of precipitation have not been fully investigated yet. The complex network theory, which provides a robust tool to investigate the statistical interdependence of many interacting elements, is used here to analyze the spatial dynamics of annual precipitation over seventy years (1941-2010). The precipitation network is built associating a node to a geographical region, which has a temporal distribution of precipitation, and identifying possible links among nodes through the correlation function. The precipitation network reveals significant spatial variability with barely connected regions, as Eastern China and Japan, and highly connected regions, such as the African Sahel, Eastern Australia and, to a lesser extent, Northern Europe. Sahel and Eastern Australia are remarkably dry regions, where low amounts of rainfall are uniformly distributed on continental scales and small-scale extreme events are rare. As a consequence, the precipitation gradient is low, making these regions well connected on a large spatial scale. On the contrary, the Asiatic South-East is often reached by extreme events such as monsoons, tropical cyclones and heat waves, which can all contribute to reduce the correlation to the short-range scale only. Some patterns emerging between mid-latitude and tropical regions suggest a possible impact of the propagation of planetary waves on precipitation at a global scale. Other links can be qualitatively associated to the atmospheric and oceanic circulation. To analyze the sensitivity of the network to the physical closeness of the nodes, short-term connections are broken. The African Sahel, Eastern Australia and Northern Europe regions again appear as the supernodes of the network, confirming furthermore their long-range connection structure. Almost all North-American and Asian nodes vanish, revealing that extreme events can enhance high precipitation gradients, leading to a systematic absence of long-range patterns
Control-Value Appraisals, Enjoyment, and Boredom in Mathematics:A Longitudinal Latent Interaction Analysis
Based on the control-value theory of achievement emotions, this longitudinal study examined students' control-value appraisals as antecedents of their enjoyment and boredom in mathematics. Self-report data for appraisals and emotions were collected from 579 students in their final year of primary schooling over three waves. Data were analyzed using latent interaction structural equation modeling. Control-value appraisals predicted emotions interactively depending on which specific subjective value was paired with perceived control. Achievement value amplified the positive relation between perceived control and enjoyment, and intrinsic value reduced the negative relation between perceived control and boredom. These longitudinal findings demonstrate that control and value appraisals, and their interaction, are critically important for the development of students' enjoyment and boredom over time
Study of and
The decays and have been
investigated with a sample of 225.2 million events collected with the
BESIII detector at the BEPCII collider. The branching fractions are
determined to be and . Distributions of the angle
between the proton or anti-neutron and the beam direction are well
described by the form , and we find
for and
for . Our branching-fraction
results suggest a large phase angle between the strong and electromagnetic
amplitudes describing the decay.Comment: 16 pages, 13 figures, the 2nd version, submitted to PR
Search for the Lepton Flavor Violation Process at BESIII
We search for the lepton-flavor-violating decay of the into an
electron and a muon using events
collected with the BESIII detector at the BEPCII collider. Four candidate
events are found in the signal region, consistent with background expectations.
An upper limit on the branching fraction of (90% C.L.) is obtained
Search for Baryonic Decays of \psi(3770) and \psi(4040)
By analyzing data samples of 2.9 fb^{-1} collected at \sqrt s=3.773 GeV, 482
pb^{-1} collected at \sqrt s=4.009 GeV and 67 pb^{-1} collected at \sqrt
s=3.542, 3.554, 3.561, 3.600 and 3.650 GeV with the BESIII detector at the
BEPCII storage ring, we search for \psi(3770) and \psi(4040) decay to baryonic
final states, including \Lambda\bar\Lambda\pi^+\pi^-, \Lambda \bar\Lambda\pi^0,
\Lambda\bar\Lambda\eta, \Sigma^+ \bar\Sigma^-, \Sigma^0 \bar\Sigma^0,
\Xi^-\bar\Xi^+ and \Xi^0\bar\Xi^0 decays. None are observed, and upper limits
are set at the 90% confidence level.Comment: 9 pages, 3 figure
First observation of the M1 transition
Using a sample of 106 million \psi(3686) events collected with the BESIII
detector at the BEPCII storage ring, we have made the first measurement of the
M1 transition between the radially excited charmonium S-wave spin-triplet and
the radially excited S-wave spin-singlet states: \psi(3686)\to\gamma\eta_c(2S).
Analyses of the processes \psi(2S)\to \gamma\eta_c(2S) with \eta_c(2S)\to
\K_S^0 K\pi and K^+K^-\pi^0 gave an \eta_c(2S) signal with a statistical
significance of greater than 10 standard deviations under a wide range of
assumptions about the signal and background properties. The data are used to
obtain measurements of the \eta_c(2S) mass (M(\eta_c(2S))=3637.6\pm
2.9_\mathrm{stat}\pm 1.6_\mathrm{sys} MeV/c^2), width
(\Gamma(\eta_c(2S))=16.9\pm 6.4_\mathrm{stat}\pm 4.8_\mathrm{sys} MeV), and the
product branching fraction (\BR(\psi(3686)\to \gamma\eta_c(2S))\times
\BR(\eta_c(2S)\to K\bar K\pi) = (1.30\pm 0.20_\mathrm{stat}\pm
0.30_\mathrm{sys})\times 10^{-5}). Combining our result with a BaBar
measurement of \BR(\eta_c(2S)\to K\bar K \pi), we find the branching fraction
of the M1 transition to be \BR(\psi(3686)\to\gamma\eta_c(2S)) = (6.8\pm
1.1_\mathrm{stat}\pm 4.5_\mathrm{sys})\times 10^{-4}.Comment: 7 pages, 1 figure, 1 tabl
Two-photon widths of the states and helicity analysis for \chi_{c2}\ar\gamma\gamma}
Based on a data sample of 106 M events collected with the
BESIII detector, the decays \psi^{\prime}\ar\gamma\chi_{c0, 2},\chi_{c0,
2}\ar\gamma\gamma are studied to determine the two-photon widths of the
states. The two-photon decay branching fractions are determined
to be {\cal B}(\chi_{c0}\ar\gamma\gamma) = (2.24\pm 0.19\pm 0.12\pm
0.08)\times 10^{-4} and {\cal B}(\chi_{c2}\ar\gamma\gamma) = (3.21\pm 0.18\pm
0.17\pm 0.13)\times 10^{-4}. From these, the two-photon widths are determined
to be keV,
keV, and
, where the uncertainties
are statistical, systematic, and those from the PDG {\cal
B}(\psi^{\prime}\ar\gamma\chi_{c0,2}) and errors,
respectively. The ratio of the two-photon widths for helicity and
helicity components in the decay \chi_{c2}\ar\gamma\gamma is
measured for the first time to be .Comment: 10 pages, 4 figure
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