Effect of Grain Size on Differential Desorption of Volatile Species and on Non-ideal MHD Diffusivity

We developed a chemical network for modeling the chemistry and non-ideal MHD effects from the collapsing dense molecular clouds to protostellar disks. First, we re-formulated the cosmic-ray desorption rate by considering the variations of desorption rate over the grain size distribution. We find that the differential desorption of volatile species is amplified by the grains larger than 0.1 $\mu$m, because larger grains are heated to a lower temperature by cosmic-rays and hence more sensitive to the variations in binding energies. As a result, atomic nitrogen N is $\sim$2 orders of magnitude more abundant than CO; N$_2$H$^+$ also becomes a few times more abundant than HCO$^+$ due to the increased gas-phase N$_2$. However, the changes in ionization fraction due to freeze-out and desorption only have minor effects on the non-ideal MHD diffusivities. Our chemical network confirms that the very small grains (VSGs: below a few 100 $\AA$) weakens the efficiency of both ambipolar diffusion and Hall effect. In collapsing dense cores, a maximum ambipolar diffusion is achieved when truncating the MRN size distribution at 0.1 $\mu$m, and for a maximum Hall effect, the truncation occurs at 0.04 $\mu$m. We conclude that the grain size distribution is crucial to the differential depletion between CO and N$_2$ related molecules, as well as to the non-ideal MHD diffusivities in dense cores.Comment: 15 pages, 11 figures; Submitted to MNRA

Hybrid quantum device based on NV centers in diamond nanomechanical resonators plus superconducting waveguide cavities

We propose and analyze a hybrid device by integrating a microscale diamond beam with a single built-in nitrogen-vacancy (NV) center spin to a superconducting coplanar waveguide (CPW) cavity. We find that under an ac electric field the quantized motion of the diamond beam can strongly couple to the single cavity photons via dielectric interaction. Together with the strong spin-motion interaction via a large magnetic field gradient, it provides a hybrid quantum device where the dia- mond resonator can strongly couple both to the single microwave cavity photons and to the single NV center spin. This enables coherent information transfer and effective coupling between the NV spin and the CPW cavity via mechanically dark polaritons. This hybrid spin-electromechanical de- vice, with tunable couplings by external fields, offers a realistic platform for implementing quantum information with single NV spins, diamond mechanical resonators, and single microwave photons.Comment: Accepted by Phys. Rev. Applie

Parton distribution functions and nuclear EMC effect in a statistical model

A new and simple statistical approach is performed to calculate the parton distribution functions (PDFs) of the nucleon in terms of light-front kinematic variables. Analytic expressions of x-dependent PDFs are obtained in the whole x region. And thereafter, we treat the temperature T as a parameter of the atomic number A to explain the nuclear EMC effect in the region $x \in [0.2, 0.7]$. We give the predictions of PDF ratios, and they are very different from those by other models, thus experiments aiming at measuring PDF ratios are suggested to provide a discrimination of different models.Comment: 4 pages, no figure; talk given at the 5th International Conference On Quarks and Nuclear Physics (QNP09), Sep 2009, Beijing Chin

Blow up solutions to a viscoelastic fluid system and a coupled Navier-Stokes/Phase-Field system in R^2

We find explicit solutions to both the Oldroyd-B model with infinite Weissenberg number and the coupled Navier-Stokes/Phase-Field system. The solutions blow up in finite time.Comment: 5 page