Optical properties of MgCNi3MgCNi_3 in the normal state

We present the optical reflectance and conductivity spectra for non-oxide antiperovskite superconductor $MgCNi_{3}$ at different temperatures. The reflectance drops gradually over a large energy scale up to 33,000 cm$^{-1}$, with the presence of several wiggles. The reflectance has slight temperature dependence at low frequency but becomes temperature independent at high frequency. The optical conductivity shows a Drude response at low frequencies and four broad absorption features in the frequency range from 600 $cm^{-1}$ to 33,000 $cm^{-1}$. We illustrate that those features can be well understood from the intra- and interband transitions between different components of Ni 3d bands which are hybridized with C 2p bands. There is a good agreement between our experimental data and the first-principle band structure calculations.Comment: 4 pages, to be published in Phys. Rev.

The upper critical field and its anisotropy in LiFeAs

The upper critical field $\mu_0H_{c2}(T_c)$ of LiFeAs single crystals has been determined by measuring the electrical resistivity using the facilities of pulsed magnetic field at Los Alamos. We found that $\mu_0H_{c2}(T_c)$ of LiFeAs shows a moderate anisotropy among the layered iron-based superconductors; its anisotropic parameter $\gamma$ monotonically decreases with decreasing temperature and approaches $\gamma\simeq 1.5$ as $T\rightarrow 0$. The upper critical field reaches 15T ($H\parallel c$) and 24.2T ($H\parallel ab$) at $T=$1.4K, which value is much smaller than other iron-based high $T_c$ superconductors. The temperature dependence of $\mu_0H_{c2}(T_c)$ can be described by the Werthamer-Helfand-Hohenberg (WHH) method, showing orbitally and (likely) spin-paramagnetically limited upper critical field for $H\parallel c$ and $H\parallel ab$, respectively.Comment: 5 pages,5 figure

Controllable coupling between a nanomechanical resonator and a coplanar-waveguide resonator via a superconducting flux qubit

We study a tripartite quantum system consisting of a coplanar-waveguide (CPW) resonator and a nanomechanical resonator (NAMR) connected by a flux qubit, where the flux qubit has a large detuning from both resonators. By a unitray transformation and a second-order approximation, we obtain a strong and controllable (i.e., magnetic-field-dependent) effective coupling between the NAMR and the CPW resonator. Due to the strong coupling, vacuum Rabi splitting can be observed from the voltage-fluctuation spectrum of the CPW resonator. We further study the properties of single photon transport as inferred from the reflectance or equivalently the transmittance. We show that the reflectance and the corresponding phase shift spectra both exhibit doublet of narrow spectral features due to vacuum Rabi splitting. By tuning the external magnetic field, the reflectance and the phase shift can be varied from 0 to 1 and $-\pi$ to $\pi$, respectively. The results indicate that this hybrid quantum system can act as a quantum router.Comment: 8 pages, 6 figure

Field study on the influence of spatial and environmental characteristics on the evaluation of subjective loudness and acoustic comfort in underground shopping streets

A large-scale measurement and subjective survey was undertaken in five underground shopping streets to determine the influence of spatial and environmental characteristics on users’ subjective loudness and acoustic comfort. The analysis on the spatial characteristics shows that the subjective loudness is higher in “street type” than in “square type” underground shopping streets when the equivalent continuous A-weighted sound pressure level (LAeq) is relatively high (75 dBA). Acoustic comfort is higher in “square type” than in “street type” underground shopping streets where LAeq is relatively low (55 dBA). Considering spatial functions, it is found that acoustic comfort is higher in a dining area than in a shopping area. In terms of environmental characteristics where air temperature, relative humidity, luminance and visual aspect were considered, the subjective loudness is influenced by humidity and luminance, with correlation coefficients of 0.10 to 0.30. The evaluation of acoustic comfort is influenced by air temperature, humidity, and luminance, with correlation coefficients of 0.1 to 0.4. There are significant correlations between the evaluation of environmental factors and subjective loudness, as well as, acoustic comfort. The correlation coefficients are 0.1 to 0.5. Moreover, respondents’ attitude to sound environment could influence their evaluation of subjective loudness and acoustic comfort

Effects of individual sound sources on the subjective loudness and acoustic comfort in underground shopping streets

Previous studies have demonstrated that human evaluation of subjective loudness and acoustic comfort depends on a series of factors in a particular situation rather than only on sound pressure levels. In the present study, a large-scale subjective survey has been undertaken on underground shopping streets in Harbin, China, to determine how individual sound sources influence subjective loudness and acoustic comfort evaluation. Based on the analysis of case study results, it has been shown that all individual sound sources can increase subjective loudness to a certain degree. However, their levels of influence on acoustic comfort are different. Background music and the public address system can increase acoustic comfort, with a mean difference of 0.18 to 0.32 and 0.21 to 0.27, respectively, where a five-point bipolar category scale is used. Music from shops and vendor shouts can decrease acoustic comfort, with a mean difference of -0.11 to -0.38 and -0.39 to -0.62, respectively. The feasibility of improving acoustic comfort by changing certain sound sources is thus demonstrated