Fatigue Characteristics of 7050-T7451 Aluminum Alloy Friction Stir Welding Joints and the Stress Ratio Effect

The fatigue crack initiation and growth characteristics in 7050-T7451 aluminum alloy butt joints subjected to different stress ratios and owing to friction stir welding (FSW) were investigated using fatigue tests for stress ratios of 0.1, 0.3, and 0.5. The difference between the fatigue crack initiation in the base material (BM) and FSW joints, related to coarse secondary phases, was explored using scanning electron microscopy (SEM). Accordingly, Al23CuFe4, Al7Cu2Fe, and Al2Mg3Zn3 were the preferred joint crack initiation locations, whereas Mg2Si was the major fracture initiation point of the parent material, and cracks tended to propagate along dense, coarse secondary phases, becoming more pronounced for larger cracks. In addition, as the stress ratio increased, non-Mg2Si phase fracture initiation points appeared in the BM. Meanwhile, the quantity of non-Mg2Si phases in the joints continued to increase, and the crack initiation sites became increasingly concentrated in the TMAZ-HAZ region

Experimental investigation of out-of-plane constraint effect on fracture toughness of the SE(T) specimens

In the study, the experiments are performed to determine thickness effect on critical crack tip opening displacement (δ_IC) of the single-edge tension (SE(T)) specimen with side-groove. The applicability and thickness sensitivity of several fracture toughness estimation procedures are also investigated by the experimental data. Referring to the results by the double clip gauge method, it is found that the critical crack initiation toughness decreases significantly as specimen thickness increases until the thickness-to-width ratio equal to 4, beyond which thickness effect becomes relatively weak. Accordingly, a dimension size is recommended for the fracture toughness testing to take the out-of-plane constraint into account for SE(T) specimen. The further analyses based on the plastic zone size confirm the result as well

Identification and Phylogenetic Analysis of a CC-NBS-LRR Encoding Gene Assigned on Chromosome 7B of Wheat

Hexaploid wheat displays limited genetic variation. As a direct A and B genome donor of hexaploid wheat, tetraploid wheat represents an important gene pool for cultivated bread wheat. Many disease resistant genes express conserved domains of the nucleotide-binding site and leucine-rich repeats (NBS-LRR). In this study, we isolated a CC-NBS-LRR gene locating on chromosome 7B from durum wheat variety Italy 363, and designated it TdRGA-7Ba. Its open reading frame was 4014 bp, encoding a 1337 amino acid protein with a complete NBS domain and 18 LRR repeats, sharing 44.7% identity with the PM3B protein. TdRGA-7Ba expression was continuously seen at low levels and was highest in leaves. TdRGA-7Ba has another allele TdRGA-7Bb with a 4 bp deletion at position +1892 in other cultivars of tetraploid wheat. In Ae. speltoides, as a B genome progenitor, both TdRGA-7Ba and TdRGA-7Bb were detected. In all six species of hexaploid wheats (AABBDD), only TdRGA-7Bb existed. Phylogenic analysis showed that all TdRGA-7Bb type genes were grouped in one sub-branch. We speculate that TdRGA-7Bb was derived from a TdRGA-7Ba mutation, and it happened in Ae. speltoides. Both types of TdRGA-7B participated in tetraploid wheat formation. However, only the TdRGA-7Bb was retained in hexaploid wheat

Identification and characterization of high-molecular-weight glutenin subunits from Agropyron intermedium.

High-molecular-weight glutenin subunit (HMW-GS) is a primary determinant of processing quality of wheat. Considerable progress has been made in understanding the structure, function and genetic regulation of HMW-GS in wheat and some of its related species, but less is known about their orthologs in Agropyron intermedium, a useful related species for wheat improvement. Here seven HMW-GSs in Ag. intermedium were identified using SDS-PAGE and Western blotting experiments. Subsequently, the seven genes (Glu-1Aix1 ∼ 4 and Glu-1Aiy1 ∼ 3) encoding the seven HMW-GSs were isolated using PCR technique with degenerate primers, and confirmed by bacterial expression and Western blotting. Sequence analysis indicated that the seven Ag. intermedium HMW-GSs shared high similarity in primary structure to those of wheat, but four of the seven subunits were unusually small compared to the representatives of HMW-GS from wheat and two of them possessed extra cysteine residues. The alignment and clustering analysis of deduced amino acid sequences revealed that 1Aix1 and 1Aiy1 subunits had special molecular structure, belonging to the hybrid type compounding between typical x- and y-type subunit. The xy-type subunit 1Aix1 is composed of the N-terminal of x-type and C-terminal of y-type, whereas yx-type subunit 1Aiy1 comprises the N-terminal of y-type and C-terminal of x-type. This result strongly supported the hypothesis of unequal crossover mechanism that might generate the novel coding sequence for the hybrid type of HMW-GSs. In addition to the aforementioned, the other novel characteristics of the seven subunits were also discussed. Finally, phylogenetic analysis based on HMW-GS genes was carried out and provided new insights into the evolutionary biology of Ag. intermedium

Structures of capsid and capsid-associated tegument complex inside the Epstein–Barr virus

As the first discovered human cancer virus, Epstein-Barr virus (EBV) causes Burkitt's lymphoma and nasopharyngeal carcinoma. Isolating virions for determining high-resolution structures has been hindered by latency-a hallmark of EBV infection-and atomic structures are thus available only for recombinantly expressed EBV proteins. In the present study, by symmetry relaxation and subparticle reconstruction, we have determined near-atomic-resolution structures of the EBV capsid with an asymmetrically attached DNA-translocating portal and capsid-associated tegument complexes from cryogenic electron microscopy images of just 2,048 EBV virions obtained by chemical induction. The resulting atomic models reveal structural plasticity among the 20 conformers of the major capsid protein, 2 conformers of the small capsid protein (SCP), 4 conformers of the triplex monomer proteins and 2 conformers of the triplex dimer proteins. Plasticity reaches the greatest level at the capsid-tegument interfaces involving SCP and capsid-associated tegument complexes (CATC): SCPs crown pentons/hexons and mediate tegument protein binding, and CATCs bind and rotate all five periportal triplexes, but notably only about one peri-penton triplex. These results offer insights into the EBV capsid assembly and a mechanism for recruiting cell-regulating factors into the tegument compartment as 'cargoes', and should inform future anti-EBV strategies

Properties of the primary structure of the HMW-GS from <i>Ag. intermedium</i> in comparison with those of the representatives of wheat HMW-GS.

a<p>The nucleotide number of Open Reading Frame;</p>b<p>The number of Cys.</p

MALDI-TOF-MS analysis of peptide mass fingerprint of native 1Aiy1 subunit.

<p>Peptide mass is available at <a href="http://www.expasy.org/tools/peptide-mass.html" target="_blank">http://www.expasy.org/tools/peptide-mass.html</a>.</p

SDS-PAGE (A) and Western blotting (B) analysis of HMW-GSs of <i>Ag. intermedium</i>.

<p>Lane 1 shows the named HMW-GSs from common wheat variety Chinese Spring as a control. Lanes 2∼7 show the HMW-GSs from six representative seeds of the <i>Ag. intermedium</i> line used in this study. The seven expressed HMW-GSs with distinct electrophoretic mobility comparing with Chinese Spring were detected by SDS-PAGE (A) and were confirmed using Western blotting experiment with polyclonal antibody specific for HMW-GSs (B). Among the seven HMW-GSs from <i>Ag. intermedium</i>, three subunits (marked with solid triangles in lane 2 of B) share comparable electrophoretic mobility with Chinese Spring, the other four subunits (marked with hollow triangles in lane 2 of B) moved faster than those HMW-GSs from Chinese Spring.</p

Illustration for the developmental mechanism of two hybrid HMW-GSs based on unequal double crossover hypothesis.

<p>The broken line box indicates the double crossover region. The xy and yx represent the hybrid subunit with 5′region of x-type and 3′region of y-type and the hybrid subunit with 5′region of y-type and 3′region of x-type, respectively.</p