Efficient de novo assembly and modification of large DNA fragments

Synthetic genomics has provided new bottom-up platforms for the functional study of viral and microbial genomes.The construction of the large,gigabase(Gb)-sized genomes of higher organisms will deepen our understanding of genetic blueprints significantly.But for the synthesis and assembly of such large-scale genomes,the development of new or expanded methods is required.In this study,we develop an efficient pipeline for the construction of large DNA fragments sized 100 kilobases(kb)or above from scratches and describe an efficient method for“scar-free”engineering of the assembled sequences.Our method,therefore,should provide a standard framework for producing long DNA molecules,which are critical materials for synthetic genomics and metabolic engineering.

Three-dimensional temperature prediction in cylindrical turning with large-chamfer insert based on a modified slip-line field approach

Chamfered inserts have found broader applications in metal cutting process especially in high-performance machining of hard-to-cut materials for their excellent edge resistance and cutting toughness.However,excessive heat generation and resulting high cutting temperature eventually cause severe tool wear and poor surface integrity,which simultaneously limits the optimal selection of machining parameters.In the present study,an analytical thermal–mechanical model is proposed for the prediction of the three-dimensional(3-D)temperature field in cylindrical turning with chamfered round insert based on a modified slip-line field approach.First,an innovative discretization method is introduced in a general 3-D coordinate system to provide a comprehensive demonstration of the irregular cutting geometry and heat generation zones.Then,a plasticity-theory-based slip-line field model is developed and employed to determine the intensities and geometries of every elementary heat sources in Primary Deformation Zones(PDZ),Secondary Deformation Zones(SDZ)and Dead Metal Zones(DMZ).At last,a 3-D analytical model is suggested to calculate the temperature increases caused by the entire heat sources and associated images.The maximum cutting temperature region predicted is found existing upon the chip-tool contact area rather than the tool edge.Moreover,the rationalities of cutting parameters employed are analyzed along with theoretical material removal rates and ensuing maximum cutting temperatures.The results indicate that the cutting conditions with large depth of cut and high cutting speed are more desirable than those with high feed rates.The proposed models are respectively verified through a series of 3-D Finite Element(FE)simulations and dry cutting experiments of Inconel 718 with chamfered round insert.Satisfactory agreement has been reached between the predictions and simulations as well as the measurements,which confirms the correctness and effectiveness of the presented analytical model.