Information filtering based on transferring similarity

In this Brief Report, we propose a new index of user similarity, namely the transferring similarity, which involves all high-order similarities between users. Accordingly, we design a modified collaborative filtering algorithm, which provides remarkably higher accurate predictions than the standard collaborative filtering. More interestingly, we find that the algorithmic performance will approach its optimal value when the parameter, contained in the definition of transferring similarity, gets close to its critical value, before which the series expansion of transferring similarity is convergent and after which it is divergent. Our study is complementary to the one reported in [E. A. Leicht, P. Holme, and M. E. J. Newman, Phys. Rev. E {\bf 73} 026120 (2006)], and is relevant to the missing link prediction problem.Comment: 4 pages, 4 figure

Electronic structure and Fermi surface character of LaONiP from first principles

Based on First-principles calculation, we have investigated electronic structure of a ZrCuSiAs structured superconductor LaNiPO. The density of states, band structures and Fermi surfaces have been given in detail. Our results indicate that the bonding of the La-O and Ni-P is strongly covalent whereas binding property between the LaO and NiP blocks is mostly ionic. It's also found that four bands are across the Fermi level and the corresponding Fermi surfaces all have a two-dimensional character. In addition, we also give the band decomposed charge density, which suggests that orbital components of Fermi surfaces are more complicated than cuprate superconductors.Comment: Submitted to Phys.Rev.

Development of Ultra-High Sensivity Silicon Carbide Detectors

A variety of silicon carbide (SiC) detectors have been developed to study the sensitivity of SiC ultraviolet (UV) detectors, including Schottky photodiodes, p-i-n photodiodes, avalanche photodiodes (APDs), and single photon-counting APDs. Due to the very wide bandgap and thus extremely low leakage current, Sic photo-detectors showed excellent sensitivity. The specific detectivity, D*, of SiC photodiodes are orders of magnitude higher than that of their competitors, such as Si photodiodes, and comparable to the D* of photomultiplier tubes (PMTs). To pursue the ultimate detection sensitivity, SiC APDs and single photon-counting avalanche diodes (SPADs) have also been fabricated. By operating the SiC APDs at a linear mode gain over 10(exp 6), SPADs in UV have been demonstrated. SiC UV detectors have great potential for use in solar blind UV detection and biosensing. Moreover, SiC detectors have excellent radiation hardness and high temperature tolerance which makes them ideal for extreme environment applications such as in space or on the surface of the Moon or Mars

Thermal rectification effect of an interacting quantum dot

We investigate nonlinear thermal transport properties of a single interacting quantum dot with two energy levels tunnel-coupled to two electrodes using nonequilibrium Green function method and Hartree-Fock decoupling approximation. In the case of asymmetric tunnel-couplings to two electrodes, for example, when the upper level of the quantum dot is open for transport, whereas the lower level is blocked, our calculations predict a strong asymmetry for the heat (energy) current, which shows that, the quantum dot system may act as a thermal rectifier in this specific situation.Comment: 5 pages, 5 figure

Effects of ac-field amplitude on the dielectric susceptibility of relaxors

The thermally activated flips of the local spontaneous polarization in relaxors were simulated to investigate the effects of the applied-ac-field amplitude on the dielectric susceptibility. It was observed that the susceptibility increases with increasing the amplitude at low temperatures. At high temperatures, the susceptibility experiences a plateau and then drops. The maximum in the temperature dependence of susceptibility shifts to lower temperatures when the amplitude increases. A similarity was found between the effects of the amplitude and frequency on the susceptibility.Comment: 8 pages, 7 figures, Phys. Rev. B (in July 1st

Optical study of Dirac fermions and related phonon anomalies in the antiferromagnetic compound CaFeAsF

We performed optical studies on CaFeAsF single crystals, a parent compound of the 1111-type iron-based superconductors that undergoes a structural phase transition from tetragonal to orthorhombic at Ts=121 K and a magnetic one to a spin density wave (SDW) state at TN=110 K. In the low-temperature optical conductivity spectrum, after the subtraction of a narrow Drude peak, we observe a pronounced singularity around 300cm−1 that separates two regions of quasilinear conductivity. We outline that these characteristic absorption features are signatures of Dirac fermions, similar to what was previously reported for the BaFe2As2 system [Z.-G. Chen et al., Phys. Rev. Lett. 119, 096401 (2017)]. In support of this interpretation, we show that for the latter system this singular feature disappears rapidly upon electron and hole doping, as expected if it arises from a van Hove singularity in between two Dirac cones. Finally, we show that one of the infrared-active phonon modes (the Fe-As mode at 250cm−1) develops a strongly asymmetric line shape in the SDW state and note that this behavior can be explained in terms of a strong coupling with the Dirac fermions

Asymmetry of Strange Sea in Nucleons

Based on the finite-temperature field theory, we evaluate the medium effects in nucleon which can induce an asymmetry between quarks and antiquarks of the strange sea. The short-distance effects determined by the weak interaction can give rise to $\delta m\equiv \Delta m_s-\Delta m_{\bar s}$ where $\Delta m_{s(\bar s)}$ is the medium-induced mass of strange quark by a few KeV at most, but the long-distance effects by strong interaction are sizable. Our numerical results show that there exists an obvious mass difference between strange and anti-strange quarks, as large as 10-100 MeV.Comment: 15 latex pages, 3 figures, to appear in PR

Dielectric nonlinearity of relaxor ferroelectric ceramics at low ac drives

Dielectric nonlinear response of (PbMg$_{1/3}$Nb$_{2/3}$O$_3$)$_{0.9}$(PbTiO$_3$)$_{0.1}$ (0.9PMN-0.1PT) relaxor ceramics was investigated under different ac drive voltages. It was observed that: (i) the dielectric permittivity is independent on ac field amplitude at high temperatures; (ii) with increasing ac drive, the permittivity maximum increases, and the temperature of the maximum shifts to lower temperature; (iii) the nonlinear effect is weakened when the measurement frequency increases. The influences of increasing ac drive were found to be similar to that of decreasing frequency. It is believed that the dielectric nonlinearities of relaxors at low drives can be explained by the phase transition theory of ergodic space shrinking in succession. A Monte Carlo simulation was performed on the flips of micro polarizations at low ac drives to verify the theory.Comment: Submitted to J. Phys.: Cond. Matte

Estimating Mass of Sigma-Meson and Study on Application of the Linear Sigma-Model

Whether the $\sigma-meson$ ($f_0(600)$) exists as a real particle is a long-standing problem in both particle physics and nuclear physics. In this work, we analyze the deuteron binding energy in the linear $\sigma$ model and by fitting the data, we are able to determine the range of $m_{\sigma}$ and also investigate applicability of the linear $\sigma$ model for the interaction between hadrons in the energy region of MeV's. Our result shows that the best fit to the data of the deuteron binding energy and other experimental data about deuteron advocates a narrow range for the $\sigma-$meson mass as $520\leq m_{\sigma}\leq 580$ MeV and the concrete values depend on the input parameters such as the couplings. Inversely fitting the experimental data, our results set constraints on the couplings. The other relevant phenomenological parameters in the model are simultaneously obtained.Comment: 12 page

Galaxy Bulges As Tests of CDM vs MOND in Strong Gravity

The tight correlation between galaxy bulges and their central black hole masses likely emerges in a phase of rapid collapse and starburst at high redshift, due to the balance of gravity on gas with the feedback force from starbursts and the wind from the black hole; the average gravity on per unit mass of gas is ~ 2 x 10^-10 m/sec^2 during the star burst phase. This level of gravity could come from the real r^{-1} cusps of Cold Dark Matter (CDM) halos, but the predicted gravity would have a large scatter due to dependence on cosmological parameters and formation histories. Better agreement is found with the gravity from the scalar field in some co-variant versions of MOND, which can create the mirage of a Newtonian effective dark halo of density Pi r^{-1} near the center, where the characteristic surface density Pi=130alpha^{-1} Msun pc^{-2} and alpha is a fundamental constant of order unity fixed by the Lagrangian of the co-variant theory if neglecting environmental effects. We show with a toy analytical model and a hydrodynamical simulation that a constant background gravity due to MOND/TeVeS scalar field implies a critical pressure synchronizing starbursts and the formation of galaxy bulges and ellipticals. A universal threshold for the formation of the brightest regions of galaxies in a MONDian universe suggests that the central BHs, bulges and ellipticals would respect tight correlations like the M_{bulge}-M_{BH}-sigma relations. In general MOND tends to produce tight correlations in galaxy properties because its effective halo has less freedom and scatter than CDM halos.Comment: 30p, 6 figs, expanded. Accpeted for Ap