Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Plastic deformation of alumina reinforced with SiC whiskers

Addition of small amounts of stiff reinforcement (SiC whiskers) to a polycrystalline AL{sub 2}O{sub 3} matrix partially inhibits grain boundary sliding because of an increase in threshold stress. When the concentration of whiskers is high enough, a pure diffusional mechanism takes over the control of plastic deformation of the composites. For higher whisker loadings, the materials creep properties depend on a microstructural feature different from the nominal grain size. A tentative correlation of this effective microstructural parameter with the spacing between the whiskers was established through a model

Influence of fabrication on mechanical properties of SiC-whisker-reinforced alumina

Samples of SiC-whisker-reinforced Al{sub 2}O{sub 3} composites obtained from three different sources have been crept in compression at 1400{degrees}C using both constant load (CL) and constant strain rate (CSR). Macroscopic results indicate some difference in behavior due to fabrication. TEM is used to support this hypothesis. 10 refs., 3 figs

High-temperature deformation of ZrO{sub 2}-Al{sub 2}O{sub 3}/SiC whisker composites fabricated by two techniques

ZrO{sub 2} {minus} Al{sub 2}0{sub 3}/SiC whisker-reinforced composites, with whisker volume fractions of 0 to 28%, fabricated both by powder and precursor processing, have been deformed at temperatures of 1300--1500 C under constant compression rates of 1.7 {times} 10{sup {minus}5} to 6.8 {times} 10{sup {minus}5} s{sup {minus}1}. Above 1400 C, a stress at which the work-hardening rate became zero could be measured and correlated with whisker content. On the other hand, at 1300 C all samples broke within the elastic.regime. At 1350 C, increased whisker content appeared to inhibit fracture, so plastic behavior was obtained for samples containing 28% SiC. In the range of temperatures and compression rates, noted above, stress exponents were determined and tentatively correlated with microstructural features and their evolution during plastic deformation

High-temperature mechanical properties of SiC whisker reinforced Al sub 2 O sub 3 composites

High-temperature constant strain rate compressive tests have been performed on Al{sub 2}O{sub 3} reinforced with different concentrations of SiC whiskers. The samples were obtained from three sources, but contained whiskers from the same source. The temperature range was from 1300 to 1500{degree}C and experiments were conducted in air and argon. Strain rates varied from 3 {times} 10{sup {minus}8} to 5 {times} 10{sup {minus}5} s{sup {minus}1} with stresses between 3 and 500 MPa. Stress exponents were fond to vary between 1 and 5 and depended on microstructure, whisker concentration and stress, indicating a change in the mechanism controlling plastic deformation. Change from diffusional creep to a damage accumulation mechanism was supported by TEM observations on samples as-received and deformed both in the n = 1 regime and in the n = 5 regime. Degradation of SiC whiskers occurred when testing in air. 12 refs., 1 tab., 7 figs

Precursor Selection for Property Optimization in Biomorphic SiC Ceramics

Biomorphic SiC ceramics have been fabricated using different wood precursors. The evolution of volume, density and microstructure of the woods, carbon performs, and final SiC products are systematically studied in order to establish experimental guidelines that allow materials selection. The wood density is a critical characteristic, which results in a particular final SiC density, and the level of anisotropy in mechanical properties in directions parallel (axial) and perpendicular (radial) to the growth of the wood. The purpose of this work is to explore experimental laws that can help choose a type of wood as precursor for a final SiC product, with a given microstructure, density and level of anisotropy. Preliminary studies of physical properties suggest that not only mechanical properties are strongly anisotropic, but also electrical conductivity and gas permeability, which have great technological importance