Search

Genome miniaturization drives key evolutionary innovations of adaptive traits in vertebrates, such as the flight evolution of birds. However, a similar evolutionary process remains poorly understood in invertebrates. Derived from the second-largest animal phylum, scallops are a special group of bivalve molluscs and acquire the evolutionary novelty of the swimming lifestyle, providing excellent models for investigating the coordinated genome and lifestyle evolution. Here, we show for the first time that genome sizes of scallops exhibit a generally negative correlation with locomotion activity. To elucidate the co-evolution of genome size and swimming lifestyle, we focus on the Asian moon scallop (Amusium pleuronectes) that possesses the smallest known scallop genome while being among scallops with the highest swimming activity. Whole-genome sequencing of A. pleuronectes reveals highly conserved chromosomal macrosynteny and microsynteny, suggestive of a highly contracted but not degenerated genome. Genome reduction of A. pleuronectes is facilitated by significant inactivation of transposable elements, leading to reduced gene length and elevated expression of energy-producing gene pathways and the decrease of copy number and expression level of biomineralization genes. Similar evolutionary changes of relevant pathways are also observed for bird genome reduction with flight evolution. The striking mimicry of genome miniaturization underlying the evolution of bird flight and scallop swimming unveils the potentially common, pivotal role of genome size fluctuation in the evolution of novel lifestyles in the animal kingdom.

Graphical abstract, Highlights • Genome-wide characterization of GH families is conducted for Mollusca. • GH9, GH10, GH18 and GH20 families are remarkably expanded in molluscs. • The wide adoption of CBMs likely facilitates the hydrolysis of polysaccharides. • Hepatopancreas is the main organ for the prominent expression of GH families. • Functional divergence of GH families possibly contributes to their adaptive roles., The hydrolysis of sugar-containing compounds by glycoside hydrolases (GHs) plays essential roles in many major biological processes, but to date our systematic understanding of the functional diversity and evolution of GH families remains largely limited to a few well-studied terrestrial animals. Molluscs represent the largest marine phylum in the animal kingdom, and many of them are herbivorous that utilize algae as a main nutritional source, making them good subjects for studying the functional diversity and adaptive evolution of GH families. In the present study, we conducted genome-wide identification and functional and evolutionary analysis of all GH families across major molluscan lineages. We revealed that the remarkable expansion of the GH9, GH10, GH18 and GH20 families and the wide adoption of carbohydrate-binding modules in molluscan expanded GH families likely contributed to the efficient hydrolysis of marine algal polysaccharides and were involved in the consolidation of molluscan algae-feeding habits. Gene expression and network analysis revealed the hepatopancreas as the main organ for the prominent expression of approximately half of the GH families (well corresponding to the digestive roles of the hepatopancreas) and key or hub GHs in the coexpression gene network with potentially diverse functionalities. We also revealed the evolutionary signs of differential expansion and functional divergence of the GH family, which possibly contributed to lineage-specific adaptation. Systematic analysis of GH families at both genomic and transcriptomic levels provides important clues for understanding the functional divergence and evolution of GH gene families in molluscs in relation to their algae-feeding biology.

An alternating magnetic field was designed to increase weld depth of laser-MIG hybrid welded 316 stainless steel joint. The influencing mechanism of alternating magnetic field on improving penetration ability of hybrid heat source of laser-MIG hybrid welding was revealed. The results suggested that the difference of weld depth under different magnetic flux density was attributed to the change of characteristics of arc plasma and laser-induced plasma, droplet transition and keyhole behavior. More compressed arc shape under lower magnetic flux density (LMFD) with 20 m T and 30 m T promoted laser-induced plasma to move along the channel of laser beam, leading to decrease of weld depth. However, the laser-induced plasmas could be dispersed away from the channel of laser beam under higher magnetic flux density (HMFD) of 60 m T and 90 m T, which was the main reason for the increased penetration ability of hybrid heat source. Besides, the droplet transferred to behind the keyhole instead of dropping into the keyhole and more stable keyhole was obtained under HMFD, which were also beneficial for deeper penetration depth of laser energy. Moreover, the motion behavior of charged particles of arc plasma and laser-induced plasma and forces condition of droplet transition were discussed in magnetic field assisted laser-MIG hybrid welding.

The eutectic point data of the ternary system Na+//Cl−,SO42−−H2O, the quaternary system Na+//Cl−,SO42−,NO3−−H2O, and the quinary system Na+,K+//Cl−,SO42−,NO3−−H2O were studied by cooling curves method. Based on the experimental data, the eutectic temperature-solution composition diagrams and projection diagrams were constructed. At the eutectic temperatures, these systems were found to belong to simple types without the formation of the double salts. For the ternary system Na+//Cl−,SO42−−H2O, the eutectic temperature-solution composition diagram could be plotted in the form of a trigonal prism, which exhibited the existence of three eutectic curves of single salt and ice or two salts, and one eutectic point of two salts and ice. For the quaternary homo-ion system Na+//Cl−,SO42−,NO3−−H2O, the eutectic temperature-solution composition diagram could be drawn as a trigonal prism, which showed three eutectic regions of single salt and ice, three eutectic curves of two salts and ice, and one eutectic point of three salts and ice. Furthermore, for the quinary system Na+,K+//Cl−,SO42−,NO3−−H2O saturated with NaCl·2H2O, the relationship between the eutectic temperature and the solution composition could be described based on the solvent-less and Cl-less diagram. This diagram exhibited the presence of four eutectic regions of two salts and ice, five eutectic curves of three salts and ice, and two eutectic points of four salts and ice, and the eutectic temperature was found to be −27.45, −24.75 °C, respectively. The eutectic region of ice-NaCl·2H2O-NaNO3 was the smallest; however, that of the ice-NaCl·2H2O-Na2SO4·10H2O was the largest. The results of this study can offer fundamental data to promote the research and application of crystallization processes at low temperature and further theoretical exploration.

In the present work, laser welding of 2-mm-thick 2060 Al-Li alloy was performed under different beam oscillation modes. Weld seam morphology, microstructure, mechanical properties were compared. The results indicated that joints welded by oscillated laser beam possessed improved collapse, refined grains, higher microhardness and tensile strength. In fusion zone, nondendritic equiaxed grains, parallel dendrite grains and cellular dendrite grains were formed in all welded joints. After applying laser beam oscillation, the collapse decreased from 0.54 mm to 0.1 mm. The maximum tensile strength of welded joint was obtained in the case of ‘8′ shaped laser beam oscillation reaching 338.15 MPa, which was improved by 68% compared with that of joint without oscillation (200.58 MPa). In this case, grain characters and molten pool fluid were studied to reveal the enhancement mechanism of beam oscillation. Enhanced fluid velocity produced with ‘8′ shaped laser oscillation refined grains and more high angle grain boundaries (HAGBs) were formed. The grain size was reduced from 105.27 μm to 89.67 μm in cellular dendrite zone (CDZ). The percentage of HAGBs increased from 65.2% to 75.2%. The refined grains resulted in larger and more uniform microhardness value and better mechanical behavior. Shallower, crystal-sugar shaped dimples were formed in fracture surface obtained by pure laser welding without oscillation while deeper and bigger dimple, including equiaxed dimple and conical dimple were generated in the fracture surfaces of oscillated laser welded joints.

Complex-valued signals occur in many areas of science and engineering and are thus of fundamental interest. The complex variational mode decomposition (CVMD) is proposed as a natural and a generic extension of the original VMD algorithm for the analysis of complex-valued data in this work. Moreover, the equivalent filter bank structure of the CVMD in the presence of white noise, and the effects of initialization of center frequency on the filter bank property are both investigated via numerical experiments. Benefiting from the advantages of CVMD algorithm, its bi-directional Hilbert time-frequency spectrum is developed as well, in which the positive and negative frequency components are formulated on the positive and negative frequency planes separately. Several applications in the real-world complex-valued signals support the analysis.

Hybrid Laser-arc welding (HLAW) and laser beam welding (LBW) of HG785D steel were investigated by comparing microstructure, mechanical properties and heat source melting efficiency. Same microstructure of lath martensite (LM) was observed in fusion zone (FZ) of the two welded joints. However, coarser grain size and more random crystallographic orientations of FZ in HLAW joint were investigated via electron back-scatter diffraction (EBSD) analysis. M-A constituent and equiaxed ferrite (EF) were observed in finer-grain HAZ of HLAW joint, whereas fine martensite was obtained in LBW joint. More M-A constituent and granular bainite (GB) appeared in coarse-grain HAZ of HLAW joint. Higher heat input and lower cooling rate of HLAW compared to LBW resulted in presence of different microstructure. All the tensile specimen in both cases fractured at the base metal, while distinct difference in microhardness and low-temperature impact property was observed. Lower microhardness and higher impact energy of fusion zone were obtained in HLAW joint. Moreover, heat source melting efficiency of HLAW for 6-mm-thick HG785D steel plate could be improved by 26% compared to LBW.