| 1. |
- Zhang, Guojie, et al.
(författare)
-
Comparative genomics reveals insights into avian genome evolution and adaptation
- 2014
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 346:6215, s. 1311-1320
-
Tidskriftsartikel (refereegranskat)abstract
- Birds are the most species-rich class of tetrapod vertebrates and have wide relevance across many research fields. We explored bird macroevolution using full genomes from 48 avian species representing all major extant clades. The avian genome is principally characterized by its constrained size, which predominantly arose because of lineage-specific erosion of repetitive elements, large segmental deletions, and gene loss. Avian genomes furthermore show a remarkably high degree of evolutionary stasis at the levels of nucleotide sequence, gene synteny, and chromosomal structure. Despite this pattern of conservation, we detected many non-neutral evolutionary changes in protein-coding genes and noncoding regions. These analyses reveal that pan-avian genomic diversity covaries with adaptations to different lifestyles and convergent evolution of traits.
|
|
| 2. |
- Liu, Jingjing, et al.
(författare)
-
Locally-Optimized Reweighted Belief Propagation for Decoding Finite-Length LDPC codes
- 2013
-
Ingår i: IEEE Wireless Communications and Networking Conference, WCNC. - 1525-3511. - 9781467359399 ; , s. 4311-4316
-
Konferensbidrag (refereegranskat)abstract
- In practice, LDPC codes are decoded using message passing methods. These methods offer good performance but tend to converge slowly and sometimes fail to converge and to decode the desired codewords correctly. Recently, tree-reweighted message passing methods have been modified to improve the convergence speed at little or no additional complexity cost. This paper extends this line of work and proposes a new class of locally optimized reweighting strategies, which are suitable for both regular and irregular LDPC codes. The proposed decoding algorithm first splits the factor graph into subgraphs and subsequently performs a local optimization of reweighting parameters. Simulations show that the proposed decoding algorithm significantly outperforms the standard message passing and existing reweighting techniques.
|
|
| 3. |
- Zou, Ji, et al.
(författare)
-
A top-down approach to densify ZrB2-SiC-BN composites with deeper homogeneity and improved reliability
- 2014
-
Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 249, s. 93-101
-
Tidskriftsartikel (refereegranskat)abstract
- A novel top down approach was developed to fabricate dense ZrB2-SiC-BN (ZSN) composites with a fine-grained (<1 mu m) microstructure using coarse-grained (similar to 10 mu m) ZrN and Si precursors that reacted with fine (similar to 0.5 mu m) B4C powders at 1850 degrees C. The results show that the reaction and densification mechanisms acting during sintering could be separated or happen simultaneously by changing the pressure loading strategy. Loading cycles not only have a substantial influence on the microstructure homogeneity and the strength reliability of as sintered composites, but might alter the electric current path during the Spark Plasma Sintering process as well. A residual compressive stress of 361 MPa, generated upon the SiC grains in the ZSN composites, was measured by Raman spectroscopy. The fine SiC grains tended to form larger clusters in the dense microstructure if the loading cycle is inappropriate, which was further employed to interpret the observed scattering of strength values in one batch of ZSN. The 48ZrB(2)-24SiC-28BN (number in vol%) composite has an average strength of 473 MPa, which was 94% of that of in situ densified ZrB2-SiC ceramics (ZS). Considering the corresponding Youngs modulus was only half of that for ZS, the in situ ZSN composite owns a better mechanical strain tolerance.
|
|
| 4. |
- Zou, Ji, et al.
(författare)
-
Hexagonal BN-encapsulated ZrB2 particle by nitride boronizing
- 2014
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 72, s. 167-177
-
Tidskriftsartikel (refereegranskat)abstract
- A facile method based on an in situ reaction, called nitride boronizing, was first developed to directly coat ZrB2 particles with a nano-scale hexagonal boron nitride (h-BN) film. The crystallinity of the BN coating and the diameters of the ZrB2 particles could be tailored by changing the reaction conditions. A mechanism was proposed from thermodynamic calculations to clarify the formation of a core-shell nanostructure, i.e. the shock heat generated by the exothermal reaction. The core-shell ZrB2 powders showed excellent sinterability and the advantage in producing dense h-BN texture-free composites. Even when sintered at 2000 degrees C for 20 min and under a uniaxial pressure of 60 MPa, no texture created by h-BN was observed. The isotropic bending strength (similar to 300 MPa) of ZrB2-37 vol.% BN ceramics from core-shell precursor powders were investigated and compared with ceramics of the same nominal composition, but densified from commercial powders containing highly aligned h-BN grains. The nitride boronizing approach could be explored to synthesize other h-BN-coated IVB group transition metal borides.
|
|
