High thermal conductivity SiC/SiC composites for fusion applications
SiC/SiC composites offer excellent potential for fusion energy as well as numerous commercial applications. High manufacturing cost and very low through-the-thickness (transverse) thermal conductivity (below 15 W/m K) hinders wider applications of SiC/SiC composites. To overcome these obstacles, a low cost chemical vapor reaction (CVR) process was developed to fabricate crystalline, high-purity SiC fibers. Several variations of the CVR process were used to fabricate SiC/SiC composites. An unirradiated, 4-mm thick SiC/SiC composite was completely CVR-converted from a converted SiC fiber preform with a pitch graphite matrix, and exhibited a bulk density of 2.65 g/cc, 10% open porosity, room temperature (RT) and 1000°C thermal conductivity values of 70 and 35 W/m K, respectively, and an RT bend strength of 200 MPa.
SiCf/SiC Composite: Attainment Methods, Properties and Characterization
Silicon carbide exists in several polymorphic forms (over 150) and in each case, the bond between the Si and C is always tetrahedral. The simplest form is silicon carbide (SiC) in a cubic zinc blend structure, also called 3C-SiC or -SiC. The other polymorphs are a hexagonal network and are known as 2H-SiC, 4H-SiC, 6H-SiC shown in Figure 1, and all are listed as -SiC (Ching et al., 2006; Camassel, 2000).
Gut immunity in Lepidopteran insects.
Lepidopteran insects constitute one of the largest fractions of animals on earth, but are considered pests in their relationship with man. Key to the success of this order of insects is its ability to digest food and absorb nutrition, which takes place in the midgut. Because environmental microorganisms can easily enter Lepidopteran guts during feeding, the innate immune response guards against pathogenic bacteria, virus and microsporidia that can be devoured with food. Gut immune responses are complicated by both resident gut microbiota and the surrounding peritrophic membrane and are distinct from immune responses in the body cavity, which depend on the function of the fat body and hemocytes. Due to their relevance to agricultural production, studies of Lepidopteran insect midgut and immunity are receiving more attention, and here we summarize gut structures and functions, and discuss how these confer immunity against different microorganisms. It is expected that increased knowledge of Lepidopteran gut immunity may be utilized for pest biological control in the future.