5,5′-(Butane-1,4-di­yl)bis­(1H-tetra­zole) dihydrate

The title compound, C6H10N8·2H2O, was prepared by the reaction of hexanedinitrile and sodium azide. The di-1H-tetra­zole mol­ecule lies on a crystallographic centre of inversion and is linked to the water mol­ecules by N—H⋯O and O—H⋯N hydrogen bonds, forming a two-dimensional supra­molecular structure in the crystal

Fuzzy Filter Spectrum of a BCK Algebra

The notion of fuzzy s-prime filters of a bounded BCK-algebra is introduced. We discuss the relation between fuzzy s-prime filters and fuzzy prime filters. By the fuzzy s-prime filters of a bounded commutative BCK-algebra X, we establish a fuzzy topological structure on X. We prove that the set of all fuzzy s-prime filters of a bounded commutative BCK-algebra forms a topological space. Moreover, we show that the set of all fuzzy s-prime filters of a bounded implicative BCK-algebra is a Hausdorff space

Long-term results of clear lens extraction combined with piggyback intraocular lens implantation to correct high hyperopia

<b>AIM:</b> To assess the refractive outcome of clear lensectomy combined with piggyback intraocular lens implantation in highly hyperopic patients.<b>METHODS:</b> This case review included 19 eyes of 10 patients with high hyperopia and axial length less than 21mm. Intraocular lens power was calculated for emmetropia using the Holladay II formula in 17 eyes, and SRK/T formula in 2 eyes following clear lens extraction and piggyback intraocular lens implantation. Patients were examined periodically over 24 months for visual acuity and spherical equivalent (SE).<b>RESULTS:</b> The mean postoperative SE at 24 months was 0.20±1.39D (range, -3.00 to 2.50D), better than preoperative 9.81±2.62D (range, +6.00 to +14.50D) (<i>P</i><0.001). Five eyes had SE within ±0.5D of emmetropia and 11 eyes within ±1.00D at postoperative 24 months. The mean postoperative uncorrected visual acuity (UCVA) at 24 months was 0.60±0.36, significantly improved compared to preoperative 1.39±0.33 (<i>P</i><0.001). The mean best-corrected visual acuity (BCVA) at 24 months was 0.49±0.35, not statistically different compared to preoperative 0.38±0.30 (<i>P</i>=0.34). Twelve eyes maintained and 1 gained 1 or more Snellen line of BCVA, 4 eyes lost 1 line, and 2 eyes lost 2 lines at 24 postoperative months. Twelve eyes best-corrected near visual acuity (BCNVA) achieved J1 at postoperative 24 months compared to preoperative 7 eyes and the other 7 eyes better than J3.<b>CONCLUSION:</b> Clear lens extraction combined piggyback intraocular lens implantation appears to be an effective procedure to correct high hyperopia but mild overcorrection and intralenticular opacification may require secondary procedure

Topological Dirac states beyond π\pi orbitals for silicene on SiC(0001) surface

The discovery of intriguing properties related to the Dirac states in graphene has spurred huge interest in exploring its two-dimensional group-IV counterparts, such as silicene, germanene, and stanene. However, these materials have to be obtained via synthesizing on substrates with strong interfacial interactions, which usually destroy their intrinsic $\pi$($p_z$)-orbital Dirac states. Here we report a theoretical study on the existence of Dirac states arising from the $p_{x,y}$ orbitals instead of $p_z$ orbitals in silicene on 4H-SiC(0001), which survive in spite of the strong interfacial interactions. We also show that the exchange field together with the spin-orbital coupling give rise to a detectable band gap of 1.3 meV. Berry curvature calculations demonstrate the nontrivial topological nature of such Dirac states with a Chern number $C = 2$, presenting the potential of realizing quantum anomalous Hall effect for silicene on SiC(0001). Finally, we construct a minimal effective model to capture the low-energy physics of this system. This finding is expected to be also applicable to germanene and stanene, and imply great application potentials in nanoelectronics.Comment: 6 Figures , Accepted by Nano Letter

Gamma rays and neutrinos from dark matter annihilation in galaxy clusters

The $\gamma$-ray and neutrino emissions from dark matter (DM) annihilation in galaxy clusters are studied. After about one year operation of Fermi-LAT, several nearby clusters are reported with stringent upper limits of GeV $\gamma$-ray emission. We use the Fermi-LAT upper limits of these clusters to constrain the DM model parameters. We find that the DM model distributed with substructures predicted in cold DM (CDM) scenario is strongly constrained by Fermi-LAT $\gamma$-ray data. Especially for the leptonic annihilation scenario which may account for the $e^{\pm}$ excesses discovered by PAMELA/Fermi-LAT/HESS, the constraint on the minimum mass of substructures is of the level $10^2-10^3$ M$_{\odot}$, which is much larger than that expected in CDM picture, but is consistent with a warm DM scenario. We further investigate the sensitivity of neutrino detections of the clusters by IceCube. It is found that neutrino detection is much more difficult than $\gamma$-rays. Only for very heavy DM ($\sim 10$ TeV) together with a considerable branching ratio to line neutrinos the neutrino sensitivity is comparable with that of $\gamma$-rays.Comment: 21 pages, 8 figures and 1 table; extended discussion about the uncertainties of concentration and subhalo models, figures replotted for better read; references updated; accepted for publication by Phys. Rev.

Green credit and PM2.5: a time-varying perspective of China

The causal link between green credit (GC) and particulate matter 2.5 (PM2.5) is discussed this paper for the case of China using the bootstrap rolling-window Granger causality test. The fresh empirical results show that GC had both positive and negative influences on PM2.5 in two separate sub-sample periods. In turn, PM2.5 positively and consistently affected GC in two sub-sample periods. In addition, time periods without causalities were also found in the sample. These inconsistent conclusions do not provide strong support for the hypothesis that GC and PM2.5 would affect each other throughout the whole sampling period. Government intervention, public environmental awareness, the domestic economic situation, and other factors were fully considered in interpreting the deviations in certain periods. Thus, the major contribution of this study is that the linear assumption of causality was relaxed, which is more in line with China’s realities. Some policies are suggested to further strengthen the construction of the GC framework and establish a multiparticipant GC system. Moreover, PM2.5 is an important reference and can be incorporated into enterprises’ green financing strategy