Nonsense‐mediated decay targets have multiple sequence‐related features that can inhibit translation

Nonsense-mediated mRNA decay (NMD) is a surveillance system that eliminates transcripts with premature termination codons. In this study, we show that mRNAs targeted by NMD are also suppressed at the translational level. The low translational efficiency (TE) is a consequence of multiple features acting in concert, including low translation initiation rate, mediated by 5′ secondary structure and by use of weak initiation sites, and low translation elongation speed, mediated by low codon usage bias. Despite low elongation rates, NMD transcripts show low ribosome density in the coding sequence, probably owing to low initiation rates, high abortion rates or rapid transit of the ribosome following initiation failure. The low TE is observed in the absence of NMD and is not explained by low transcript abundance. Translational inefficiency is flexible, such that NMD targets have increased TE upon starvation. We propose that the low TE predisposes to NMD and/or that it is part of a mechanism for regulation of NMD transcripts

An ultrasound transient elastography system with coded excitation

Abstract Background Ultrasound transient elastography technology has found its place in elastography because it is safe and easy to operate. However, it’s application in deep tissue is limited. The aim of this study is to design an ultrasound transient elastography system with coded excitation to obtain greater detection depth. Methods The ultrasound transient elastography system requires tissue vibration to be strictly synchronous with ultrasound detection. Therefore, an ultrasound transient elastography system with coded excitation was designed. A central component of this transient elastography system was an arbitrary waveform generator with multi-channel signals output function. This arbitrary waveform generator was used to produce the tissue vibration signal, the ultrasound detection signal and the synchronous triggering signal of the radio frequency data acquisition system. The arbitrary waveform generator can produce different forms of vibration waveform to induce different shear wave propagation in the tissue. Moreover, it can achieve either traditional pulse-echo detection or a phase-modulated or a frequency-modulated coded excitation. A 7-chip Barker code and traditional pulse-echo detection were programmed on the designed ultrasound transient elastography system to detect the shear wave in the phantom excited by the mechanical vibrator. Then an elasticity QA phantom and sixteen in vitro rat livers were used for performance evaluation of the two detection pulses. Results The elasticity QA phantom’s results show that our system is effective, and the rat liver results show the detection depth can be increased more than 1 cm. In addition, the SNR (signal-to-noise ratio) is increased by 15 dB using the 7–chip Barker coded excitation. Conclusions Applying 7-chip Barker coded excitation technique to the ultrasound transient elastography can increase the detection depth and SNR. Using coded excitation technology to assess the human liver, especially in obese patients, may be a good choice

Growth of inter-metallic compound layers on CLAM steel by HDA and preparation of permeation barrier by oxidation

Hot-dip aluminizing (HDA) on China Low Activation Martensitic (CLAM) steel and followed by oxidation to obtain an Al2O3/FexAly layer covering was considered to be a promising method to resist the harsh environments in fusion reactors. In the present study, CLAM steel was coated in molten pure Al and Al-0.3Ce (wt.%) melt. The growth behavior of the inter-metallic compound (IMC) layers after different immersion time and temperature was investigated and described. The IMC layer mainly consists of Fe2Al5 and FeAl3 after hot-dipping. And the addition of Ce in the molten pure Al could promote the growth of IMC layers, which provided the idea of obtaining a certain thickness of the IMC layer at a lower temperature. After two independent oxidation processes (normalized heat-treatment and 760 °C for 15 h) in air, the Fe2Al5 and FeAl3 of IMC layers had been transformed into ductile phases (FeAl2 and FeAl), and Al2O3 layers were detected on the coating surface. The oxidation of 760 °C for 15 h was considered to form a denser Al2O3 film. However, cracks and pores were observed in the IMC layer after oxidation due to the heat-treatment and cooling methods

Effect of post weld heat treatment on the microstructure and properties of Laser-TIG hybrid welded joints for CLAM steel

In this paper, the Laser-TIG hybrid weld joints of China low activation martensite (CLAM) steel were produced, and then experienced different post weld heat treatment (PWHT) to achieve a good combination of strength and toughness. The microstructure and mechanical properties of the joints were investigated. Meanwhile, the performance of weld joints before and after PWHT subjected to transient heat loads were studied by using a laser beam thermal load test to simulate the transient events in the future fusion reactors. The results indicate that the microstructure of the as-deposited weld metal (WM) was composed of coarse lath martensite and a small amount of hard delta-ferrite, leading to relatively high tensile strength, but low impact toughness (only 16.5% of parent metal). After PWHT, M23C6 type carbides were precipitated along lath martensite and prior austenite grain boundaries. With the prolonging of PWHT, the amount and size of precipitates were increased. After PWHT at 760 °C for 2 h, the precipitates were aggregated. The strength of the weld joints was slightly weakened but acceptable, while the toughness of the weld joints significantly increased, with evidence of many dimples in the ductile fracture surface. After transient heat loads with laser power densities up to 205.7 MW/m2, surface damage such as cracks, pits, re-solidified metal and oxidation were observed, the WM subjected to PWHT at 760 °C for 0.5 h appeared better performance of resistance to oxidation. Hence, PWHT at 760 °C for 0.5 h was suggested for the Laser-TIG hybrid weld joints of CLAM steel, which gave rise to sufficient strength, high toughness and excellent resistance to oxidation

Microstructure and mechanical properties of diffusion bonded W/MA956 steel joints with a titanium interlayer by SPS

Diffusion bonding is an effective technique for joining dissimilar metals. In this paper, tungsten and MA956 steel were diffusion-bonded by Spark Plasma Sintering (SPS) technique with titanium (Ti) foil as an interlayer. The bonded joints were evaluated by metallographic analysis and mechanical tests, and the results reveal that all W/Ti/MA956 joints were well bonded by efficient SPS technique. Microstructure analysis showed that W-Ti solid solution formed at W/Ti interface; reaction phases at Ti/MA956 steel interface varied with the joining temperature, e.g. intermetallics phases FeTi for 850 °C, FeTi, Fe2Ti and Cr2Ti for 900 °C and 950 °C joining temperature. The peak value of microhardness occurred at the interfaces of Ti/MA956 steel owing to the formation of intermetallic compound. All specimens of shear testing fractured at the Ti/MA956 steel interface close to MA956, and the average shear strength of joints was 182 MPa, 228 MPa and 164 MPa bonded at 850 °C, 900 °C and 950 °C respectively.Accepted versionThis work was supported by National Magnetic Confinement Fusion Program [2014GB121001 and 2014GB121001B]

Effect of Cu interlayer on the microstructure and strength for brazing of Tungsten/316L steel

Brazing is an effective technique for joining tungsten and steel. However, the high residual stresses are produced due to the different coefficients of thermal expansions between tungsten and steel. Compared with the direct brazing with BNi-2 foil filler, BNi-2/Cu/ BNi-2 multiple interlayer was used as filler to minimize the residual stresses between tungsten and 316L steel. The brazing experiments were conducted at 1050 °C for 25 min using Cu foils with different thickness. The results show that tungsten and 316L steel have been successfully joined by brazing. The intermetallic compound of NiW formed at the W/BNi-2 interface, which was detrimental to the strength of the joint. The microhardness of different diffusion zones is higher than that of the substrates owing to the formation of intermetallic compound and solid solution. All specimens of shear testing fractured at the W/BNi-2 interface close to W substrate, and the average strength of joints was 197, 275 and 268 MPa with multiple interlayer thickness of 0.2 , 0.1 and 0.05 mm copper foil, respectively, while the average strength of joints was 143 MPa with BNi-2 foil filler. The significant increase in the joint shear strength can be ascribed to the Cu foil in the multiple interlayer because of with excellent plasticity and toughness.Accepted versionThis work is supported by National Magnetic Confinement Fusion Program (Grant Nos. 2014GB121001 and 2014GB121001B) and The Foundation of Laboratory of Nonferrous Metal material and Processing Engineering of Anhui Province (15CZS08031)

Microstructure and properties of the laser cladding ODS layers on CLAM steel

In this study, oxide dispersion strengthened (ODS) layers with different Y2O3 addition were cladded on China Low Activation Martensitic (CLAM) steel to improve its mechanical strength, micro-hardness and high-temperature behavior. The results show that fine surface morphologies can be observed in cladding zones. In cladding layers, the Fe, Cr, W, Y, Ti elements was discriminated by the scanning electron microscope (SEM) with energy-dispersive spectrometer (EDS) and the most stable Y-Ti oxide complexes Y2Ti2O7 phase were analyzed by X-ray diffraction (XRD). The micro-hardness of ODS layers are higher than that of CLAM steel. The CLAM steel with 2 wt% Y2O3 addition ODS layer possesses an average tensile strength of 840 MPa which is 166 MPa higher than that of CLAM steel. It is suggested that the dispersion strengthening of oxide particles in ODS layer contributed to the increased strength.Accepted versionThis work is supported by China National Magnetic Confinement Fusion Program (Grant No. 2014GB121001 and 2014GB121001B) and The Foundation of Laboratory of Nonferrous Metal Material and Processing Engineering of Anhui Province (15CZS08031)