Response of carbon isotopic compositions of Early-Middle Permian coals in North China to palaeo-climate change

To investigate the magnitude to which the carbon isotopic ratio (delta C-13) varies in coals in response to their contemporary terrestrial environment, the Early-Middle Permian Huainan coals (including coals from the Shanxi Formation, Lower Shihezi Formation and Upper Shihezi Formation) in North China were systematically sampled. A 2.5 parts per thousand variation range of delta C-13 values (-25.15%o to -22.65%o) was observed in Huainan coals, with an average value of -24.06 parts per thousand. As coal diagenesis exerts little influence on carbon isotope fractionation, delta C-13 values in coals were mainly imparted by those of coal -forming flora assemblages which were linked to the contemporary climate. The delta C-13 values in coals from the Shanxi and Lower Shihezi Formations are variable, reflecting unstable climatic oscillations. Heavy carbon isotope is enriched in coals of the Capitanian Upper Shihezi Formation, implying a shift to high positive delta C-13 values of coeval atmospheric CO2. Notably, our study provides evidence of the Kamura event in the terrestrial environment for the first time

Performance Evaluation of Cluster Validity Indices (CVIs) on Multi/Hyperspectral Remote Sensing Datasets

The number of clusters (i.e., the number of classes) for unsupervised classification has been recognized as an important part of remote sensing image clustering analysis. The number of classes is usually determined by cluster validity indices (CVIs). Although many CVIs have been proposed, few studies have compared and evaluated their effectiveness on remote sensing datasets. In this paper, the performance of 16 representative and commonly-used CVIs was comprehensively tested by applying the fuzzy c-means (FCM) algorithm to cluster nine types of remote sensing datasets, including multispectral (QuickBird, Landsat TM, Landsat ETM+, FLC1, and GaoFen-1) and hyperspectral datasets (Hyperion, HYDICE, ROSIS, and AVIRIS). The preliminary experimental results showed that most CVIs, including the commonly used DBI (Davies-Bouldin index) and XBI (Xie-Beni index), were not suitable for remote sensing images (especially for hyperspectral images) due to significant between-cluster overlaps; the only effective index for both multispectral and hyperspectral data sets was the WSJ index (WSJI). Such important conclusions can serve as a guideline for future remote sensing image clustering applications

Constraining C iii] Emission in a Sample of Five Luminous z = 5.7 Galaxies

Recent observations have suggested that the CIII]$\lambda1907/1909$ emission lines could be alternative diagnostic lines for galaxies in the reionization epoch. We use the F128N narrowband filter on the Hubble Space Telescope's ($\it{HST}$) Wide Field Camera 3 (WFC3) to search for CIII] emission in a sample of five galaxies at z = 5.7 in the Subaru Deep Field and the Subaru/XMM-Newton Deep Field. Using the F128N narrowband imaging, together with the broadband imaging, we do not detect CIII] emission for the five galaxies with $J_{\rm{AB}}$ ranging from 24.10 -- 27.00 in our sample. For the brightest galaxy J132416.13+274411.6 in our sample (z = 5.70, $J_{\rm{AB}} = 24.10$), which has a significantly higher signal to noise, we report a CIII] flux of $3.34\pm1.81 \times 10^{-18}$ $\mathrm{erg\ s^{-1}\ cm^{-2}}$, which places a stringent 3-$\rm\sigma$ upper limit of $5.43\times 10^{-18}$ $\mathrm{erg\ s^{-1}\ cm^{-2}}$on CIII] flux and 6.57 \AA\ on the CIII] equivalent width. Using the stacked image, we put a 3-$\rm\sigma$upper limit on the mean CIII] flux of$\mathrm{2.55\times10^{-18}\ erg\ s^{-1}\ cm^{-2}}$, and a 3-$\rm\sigma$upper limit on the mean CIII] equivalent width of 4.20 {\AA} for this sample of galaxies at z = 5.70. Combined with strong CIII] detection reported among high-z galaxies in the literature, our observations suggest that the equivalent widths of CIII] from galaxies at z$>$ 5.70 exhibit a wide range of distribution. Our strong limits on CIII] emission could be used as a guide for future observations in the reionization epoch