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1. chinaXiv:201703.01046 [pdf]

Thermal Analysis of Void Cavity for Heat Pipe Receiver under Microgravity

GUI Xiaohong; SONG Xiange; NIE Baisheng
Subjects: Dynamic and Electric Engineering >> Engineering Thermophysics

Based on theoretical analysis of PCM (Phase Change Material) solidification process, the model of improved void cavity distribution tending to high temperature region is established. Numerical results are compared with NASA (National Aeronautics and Space Administration) results. Analysis results show that the outer wall temperature, the melting ratio of PCM and the temperature gradient of PCM canister, have great difference in different void cavity distribution. The form of void distribution has a great effect on the process of phase change. Based on si- mulation results under the model of improved void cavity distribution, phase change heat transfer process in thermal storage container is analyzed. The main goal of the improved designing for PCM canister is to take measures in reducing the concentration distribution of void cavity by adding some foam metal into phase change material.

submitted time 2017-03-31 Cooperative journals:《Advances in Atmospheric Sciences》 Hits1384Downloads672 Comment 0

2. chinaXiv:201609.01035 [pdf]

Next-to-next-to-leading-order QCD corrections to $\chi_c0,2\rightarrow \gamma\gamma$

Wen-Long Sang; Feng Feng; Yu Jia; Shuang-Ran Liang
Subjects: Physics >> Nuclear Physics

We calculate the next-to-next-to-leading-order (NNLO) perturbative corrections to?P-wave quarkonia annihilation decay to two photons, in the framework of nonrelativistic QCD (NRQCD) factorization. The order-α2s?short-distance coefficients associated with each helicity amplitude are presented in a semi-analytic form, including the "light-by-light" contributions. With substantial NNLO corrections, we find disquieting discrepancy when confronting our state-of-the-art predictions with the latest \textsf{BESIII} measurements, especially fail to account for the measured?χc2→γγwidth. Incorporating the effects of spin-dependent forces would even exacerbate the situation, since it lifts the degeneracy between the nonperturbative NRQCD matrix elements of?χc0?and?χc2?toward the wrong direction. We also present the order-α2s?predictions to?χb0,2→γγ, which await the future experimental test.

submitted time 2016-09-14 Hits1781Downloads993 Comment 0

3. chinaXiv:201609.00930 [pdf]

Can NRQCD Explain the $\gamma\gamma^* \to \eta_c$ Transition Form Factor Data?

Feng Feng; Yu Jia; Wen-Long Sang
Subjects: Physics >> Nuclear Physics

Unlike the bewildering situation in the?γγ?→π?form factor, a widespread view is that perturbative QCD can decently account for the recent \textsc{BaBar} measurement of?γγ?→ηc?transition form factor. The next-to-next-to-leading order (NNLO) perturbative correction to the?γγ?→ηc,b?form factor, is investigated in the NRQCD factorization framework for the first time. As a byproduct, we obtain by far the most precise order-α2s?NRQCD matching coefficient for the?ηc,b→γγ?process. After including the substantial negative order-α2s?correction, the good agreement between NRQCD prediction and the measured?γγ?→ηc?form factor is completely ruined over a wide range of momentum transfer squared. This eminent discrepancy casts some doubts on the applicability of NRQCD approach to hard exclusive reactions involving charmonium.

submitted time 2016-09-13 Hits1697Downloads996 Comment 0

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