On the Ricci dark energy model

We study the Ricci dark energy model (RDE) which was introduced as an alternative to the holographic dark energy model. We point out that an accelerating phase of the RDE is that of a constant dark energy model. This implies that the RDE may not be a new model of explaining the present accelerating universe.Comment: 8 page

Characterization of type 1 interferon production during persistent lymphocytic choriomeningitis virus (LCMV) infection.

Type 1 interferons (B5N-a/ps), are innate cytokines possessing important immunomodulatory and effector roles in the innate and adaptive response. They are transiently induced to very high levels during the initial stages of many viral infections. However, regulation of EFN-a/p production during persistent viral infections is not well understood. This project aimed to address these issues using the murine lymphocytic choriomeningitis virus (LCMV) infection model. Initial objectives were to develop assays that would allow characterisation of the EFN-a/p response during chronic LCMV infection in vivo and in vitro. Cell-based reporter gene assays were developed to measure IFN-a/p activity, along with a series of real-time quantitative reverse-transcriptase polymerase chain reaction assays to detect mRNA transcripts of IFN-a/p, and their utility was evaluated. Analysis of IFN-a/p production during acute and chronic LCMV infection indicated that there was an early burst of IFN production following infection, but only a low level of IFN-a/p production could be detected during the chronic phase of LCMV infection despite ongoing viral replication. Persistently-infected mice exhibited reduced numbers of splenic CD1 lc+ plasmacytoid dendritic cells (DC). These animals were able to produce IFN-a/p in response toll-like-receptor (TLR) stimuli. Inoculation of influenza virus elicited less IFN-a/p production than was observed in uninfected mice, but this may have been due to impairment of influenza virus replication in persistently-infected mice. In vitro LCMV infection of DC and fibroblast cell lines induced very little IFN-a/p production. Persistently-infected animals made normal IFN-a/p responses to TLR ligands but produced lower levels of IFN-a/p upon infection with Sendai virus than uninfected cells. There are several pathways by which IFN-a/p can be induced. These results suggest that the intracellular response to RNA viruses may be impaired in LCMV-infected cells, although persistently-infected cells still retain some capacity to respond to external TLR stimuli

How Many Topics? Stability Analysis for Topic Models

Topic modeling refers to the task of discovering the underlying thematic structure in a text corpus, where the output is commonly presented as a report of the top terms appearing in each topic. Despite the diversity of topic modeling algorithms that have been proposed, a common challenge in successfully applying these techniques is the selection of an appropriate number of topics for a given corpus. Choosing too few topics will produce results that are overly broad, while choosing too many will result in the "over-clustering" of a corpus into many small, highly-similar topics. In this paper, we propose a term-centric stability analysis strategy to address this issue, the idea being that a model with an appropriate number of topics will be more robust to perturbations in the data. Using a topic modeling approach based on matrix factorization, evaluations performed on a range of corpora show that this strategy can successfully guide the model selection process.Comment: Improve readability of plots. Add minor clarification

Dynamic structure selection and instabilities of driven Josephson lattice in high-temperature superconductors

We investigate the dynamics of the Josephson vortex lattice in layered high-T$_{c}$ superconductors at high magnetic fields. Starting from coupled equations for superconducting phases and magnetic field we derive equations for the relative displacements [phase shifts] between the planar Josephson arrays in the layers. These equations reveal two families of steady-state solutions: lattices with constant phase shifts between neighboring layers, starting from zero for a rectangular configuration to $\pi$ for a triangular configuration, and double-periodic lattices. We find that the excess Josephson current is resonantly enhanced when the Josephson frequency matches the frequency of the plasma mode at the wave vector selected by the lattice structure. The regular lattices exhibit several kinds of instabilities. We find stability regions of the moving lattice in the plane lattice structure - Josephson frequency. A specific lattice structure at given velocity is selected uniquely by boundary conditions, which are determined by the reflection properties of electromagnetic waves generated by the moving lattice. With increase of velocity the moving configuration experiences several qualitative transformations. At small velocities the regular lattice is stable and the phase shift between neighboring layers smoothly decreases with increase of velocity, starting from $\pi$ for a static lattice. At the critical velocity the lattice becomes unstable. At even higher velocity a regular lattice is restored again with the phase shift smaller than $\pi/2$. With increase of velocity, the structure evolves towards a rectangular configuration.Comment: 28 pages, 12 figures, submitted to Phys. Rev.

Photoresponsive and Ultraviolet to Visible-Light Range Photocatalytic Properties of ZnO:Sb Nanowires

100學年度研究獎補助論文[[abstract]]Zinc oxide (ZnO) doped antimony (Sb) nanowires have been synthesized for improving ultraviolet sensing and photocatalytic properties. Upon illumination by UV light (365nm , 2.33mWcm−2 ), the photoelectric current of the ZnO:Sb nanowires exhibited a rapid photoresponse as compared to that of the ZnO nanowires. A highest ratio of photocurrent to dark current of around 48.8-fold was achieved in the as-synthesized ZnO:Sb nanowires. A UV-visible spectrophotometer was used to investigate the absorbance spectrum of the ZnO:Sb nanowires, which exhibited a high absorbance ratio with redshift effect in contrast to that of the ZnO nanowires. Visible-light photocatalysis and UV photoresponsive properties of the ZnO:Sb nanowires are superior to those of the ZnO nanowires.[[notice]]補正完畢[[incitationindex]]SCI[[booktype]]電子

Nonuniqueness and derivative discontinuities in density-functional theories for current-carrying and superconducting systems

Current-carrying and superconducting systems can be treated within density-functional theory if suitable additional density variables (the current density and the superconducting order parameter, respectively) are included in the density-functional formalism. Here we show that the corresponding conjugate potentials (vector and pair potentials, respectively) are {\it not} uniquely determined by the densities. The Hohenberg-Kohn theorem of these generalized density-functional theories is thus weaker than the original one. We give explicit examples and explore some consequences.Comment: revised version (typos corrected, some discussion added) to appear in Phys. Rev.

Quantum Interference of Coulomb Interaction and Disorder: Phase Shift of Friedel Oscillations and an Instability of the Fermi Sea

We investigate the influence of interference between Coulomb interaction and impurity scattering on the static electronic response $\chi (0,q)$ in disordered metals to leading order in the effective Coulomb interaction. When the transport relaxation time $\tau _{tr}$ is much shorter than the quasiparticle life time, we find a \mbox{sgn}(2p_F-q)/\sqrt{|2p_F-q|} divergence of the polarization function at the Fermi surface ($q=2p_F$). It causes a phase shift of the Friedel oscillations as well as an enhancement of their amplitude. Our results are consistent with experiments and may be relevant for understanding the stability of the amorphous state of certain alloys against crystallization.Comment: 11 pages, 4 PostScript figures appended as a self-extracting tar archive; includes output instruction

Density-functional calculation of ionization energies of current-carrying atomic states

Current-density-functional theory is used to calculate ionization energies of current-carrying atomic states. A perturbative approximation to full current-density-functional theory is implemented for the first time, and found to be numerically feasible. Different parametrizations for the current-dependence of the density functional are critically compared. Orbital currents in open-shell atoms turn out to produce a small shift in the ionization energies. We find that modern density functionals have reached an accuracy at which small current-related terms appearing in open-shell configurations are not negligible anymore compared to the remaining difference to experiment.Comment: 7 pages, 2 tables, accepted by Phys. Rev.

Exact Calculation of the Vortex-Antivortex Interaction Energy in the Anisotropic 3D XY-model

We have developed an exact method to calculate the vortex-antivortex interaction energy in the anisotropic 3D-XY model. For this calculation, dual transformation which is already known for the 2D XY-model was extended. We found an explicit form of this interaction energy as a function of the anisotropic ratio and the separation $r$ between the vortex and antivortex located on the same layer. The form of interaction energy is $\ln r$ at the small $r$ limi t but is proportional to $r$ at the opposite limit. This form of interaction energ y is consistent with the upper bound calculation using the variational method by Cataudella and Minnhagen.Comment: REVTeX 12 pages, In print for publication in Phys. Rev.