Study of Acoustic Emisison Characteristics for Fracture Assessment

Inspection for structural integrity of the Space Shuttle Solid Rocket Boosters (SRBs) is of paramount importance to mission safety. After every shuttle launch, the booster rockets are retrieved and an extensive inspection operation performed to detect any mission-related anomaly. If damage occurs to the structure during shuttle mission, Acoustic Emission (AE) from cracks could be monitored and used as a means for initial screening to identify potential damage locations for selective postlaunch inspection

Relevance of gonadotropin-regulated testicular RNA helicase (GRTH/DDX25) in the structural integrity of the chromatoid body during spermatogenesis

AbstractGonadotropin-regulated testicular RNA helicase (GRTH/DDX25), a multifunctional protein and a component of ribonucleoprotein complexes, is essential for the completion of spermatogenesis. We investigated the nuclear/cytoplasmic shuttling of GRTH in germ cells and its impact on the chromatoid body (CB)—a perinuclear organelle viewed as a storage/processing site of mRNAs. GRTH resides in the nucleus, cytoplasm and CB of round spermatids. Treatment of these cells with inhibitors of nuclear export or RNA synthesis caused nuclear retention of GRTH and its absence in the cytoplasm and CB. The nuclear levels of GRTH bound RNA messages were significantly enhanced and major reduction was observed in the cytoplasm. This indicated GRTH main transport function of mRNAs to the cytoplasm and CB. MVH, a germ cell helicase, and MIWI, a component of the RNA-induced-silencing complex (RISC), confined to the CB/cytoplasm, were absent in the CB and accumulated in the cytoplasm upon treatment. This also occurred in spermatids of GRTH-KO mice. The CB changed from lobular-filamentous to a small condensed structure after treatment resembling the CB of GRTH-KO. No interaction of GRTH with MVH or RISC members in both protein and RNA were observed. Besides of participating in the transport of messages of relevant spermatogenic genes, GRTH was found to transport its own message to cytoplasmic sites. Our studies suggest that GRTH through its export/transport function as a component of mRNP is essential to govern the CB structure in spermatids and to maintain systems that may participate in mRNA storage and their processing during spermatogenesis

Analysis of fatigue crack propagation behavior in fillet welded T-joint

In the fatigue analysis, the crack growth behavior in a two-dimensional welded T-joint was studied both numerically and experimentally. The geometric parameters were weld size, initial crack orientation and unsupported flange length. Crack growth direction was predicted using the minimum strain energy density factor theory. The results show that even though the fillet size and initial crack orientation affected the crack growth in the early stage, the cracks tended to converge when they entered the far-field stress region. This observation shows the initial period of crack growth could be distinguished from the rest of the propagation due to its crack growth behavior. There was reasonable agreement between the predicted and the experimentally observed crack growth paths. A correlation between the crack growth rate and the driving force parameter range was obtained for a T-joint constructed from hot-rolled AISI 1035 steel. A separate study showed that grain size had an insignificant effect on fatigue strength of the edge-cracked plate model

Role of Gonadotropin Regulated Testicular RNA Helicase (GRTH/DDX25) on Polysomal Associated mRNAs in Mouse Testis

Gonadotropin Regulated Testicular RNA Helicase (GRTH/Ddx25) is a testis-specific multifunctional RNA helicase and an essential post-transcriptional regulator of spermatogenesis. GRTH transports relevant mRNAs from nucleus to cytoplasmic sites of meiotic and haploid germ cells and associates with actively translating polyribosomes. It is also a negative regulator of steroidogenesis in Leydig cells. To obtain a genome-wide perspective of GRTH regulated genes, in particularly those associated with polyribosomes, microarray differential gene expression analysis was performed using polysome-bound RNA isolated from testes of wild type (WT) and GRTH KO mice. 792 genes among the entire mouse genome were found to be polysomal GRTH-linked in WT. Among these 186 were down-regulated and 7 up-regulated genes in GRTH null mice. A similar analysis was performed using total RNA extracted from purified germ cell populations to address GRTH action in individual target cells. The down-regulation of known genes concerned with spermatogenesis at polysomal sites in GRTH KO and their association with GRTH in WT coupled with early findings of minor or unchanged total mRNAs and abolition of their protein expression in KO underscore the relevance of GRTH in translation. Ingenuity pathway analysis predicted association of GRTH bound polysome genes with the ubiquitin-proteasome-heat shock protein signaling network pathway and NFkB/TP53/TGFB1 signaling networks were derived from the differentially expressed gene analysis. This study has revealed known and unexplored factors in the genome and regulatory pathways underlying GRTH action in mal