Achieving intense nearly white upconversion emission from a single β-NaYF4:Yb/Er microcrystal via saturated excitation.

No abstract

By combining the multiple signal classification (MUSIC)-based algorithm, proposed by Haghighat and Soleymani, and the segmentation-based idea, a blind multiuser spreading sequences estimation algorithm for the direct-sequence code division multiple access (DS-CDMA) signals is presented in this study. The main idea of the proposed algorithm is to divide the spreading sequences into short-time segments so as to recover them in a sequential procedure. First, the received signal samples are divided into K collections of temporal windows. Each collection is corresponding to a group of short-time segments of the spreading sequences. Secondly, by performing a sub-segmentation-based estimation scheme on the first collection of temporal windows, the first short-time segments of all the users' spreading sequences are extracted. Finally, with the help of the segments acquired in advance, the remaining segments of the spreading sequences can be recovered chip-by-chip through K 2 1 subspace projection loops. This algorithm can be applied not only to the synchronous short-code (SC) DS-CDMA signals, but also to the long-code (LC) DS-CDMA signals in non-cooperative contexts, even with minus SNR. Simulations are presented to illustrate the performance of the proposed method. In addition, for the synchronous SC-DS-CDMA signals, the computational cost of the proposed algorithm is much lower than that of the MUSIC-based algorithm. Furthermore, a derivation for blind synchronisation of the synchronous SC-DS-CDMA signals is also presented.

The pore structure and porosity of a continuous fiber reinforced ceramic matrix composite has been characterized using high-resolution synchrotron X-ray computed tomography (XCT). Segmentation of the reconstructed tomograph images reveals different types of pores within the composite, the inter-fiber bundle open pores displaying a "node-bond" geometry, and the intra-fiber bundle isolated micropores showing a piping shape. The 3D morphology of the pores is resolved and each pore is labeled. The quantitative filtering of the pores measures a total porosity 8.9 % for the composite, amid which there is about 7.1~9.3 % closed micropores.

composites were successfully prepared by polymer infiltration and pyrolysis (PIP) using polycarbosilane and a liquid ZrC precursor. The densification process, mechanical properties and microstructures were studied in a view of comparison. After the same total 20 PIP cycles, the Cf/ZrC, Cf/SiC and Cf/ZrC-SiC composites had flexural strengths of 50.1¡5.3, 285.7¡22.6, 141.5¡13.1 MPa respectively; elastic moduli of 7.8¡0.9, 57.1¡3.2 and 45.1¡2.6 GPa respectively; and fracture toughness of 2.5¡0.2, 10.4¡0.9 and 10.9¡1.1 MPa m 1/2 respectively. With the introduction of high modulus SiC phase into the ZrC matrix, the densification and modulus of the matrix were improved; as a result, the Cf/ZrC-SiC composite showed higher mechanical properties compared to Cf/ZrC.