Research on casing deformation prevention technology based on cementing slurry system optimization

The casing deformation prevention technology based on the optimization of cement slurry is proposed to reduce the casing deformation of shale oil and gas wells during hydraulic fracturing. In this paper, the fracture mechanism of hollow particles in cement sheath was firstly analyzed by discrete element method, and the effect of hollow particles in cement on casing deformation was investigated by laboratory experiment method. Finally, field test was carried out to verify the improvement effect of the casing deformation based on cement slurry modification. The results show that the formation displacement can be absorbed effectively by hollow particles inside the cement transferring the excessive deformation away from casing. The particles in the uncemented state provide deformation space during formation slipping. The casing with diameter of 139.7 mm could be passed through by bridge plug with the diameter of 99 mm when the mass ratio of particle/cement reaches 1:4. According to the field test feedback, the method based on optimization of cement slurry can effectively reduce the risk of casing deformation, and the recommended range of hollow microbeads content in the cement slurry is between 15% and 25%.

Neuroprotective mechanisms of DNA methyltransferase in a mouse hippocampal neuronal cell line after hypoxic preconditioning

Hypoxic preconditioning has been shown to improve hypoxic tolerance in mice,accompanied by the downregulation of DNA methyltransferases(DNMTs)in the brain.However,the roles played by DNMTs in the multiple neuroprotective mechanisms associated with hypoxic preconditioning remain poorly understood.This study aimed to establish an in vitro model of hypoxic preconditioning,using a cultured mouse hippocampal neuronal cell line(HT22 cells),to examine the effects of DNMTs on the endogenous neuroprotective mechanisms that occur during hypoxic preconditioning.HT22 cells were divided into a control group,which received no exposure to hypoxia,a hypoxia group,which was exposed to hypoxia once,and a hypoxic preconditioning group,which was exposed to four cycles of hypoxia.To test the ability of hypoxic preadaptation to induce hypoxic tolerance,cell viability was measured using the 3-(4,5-dimethylthiazol-2-yl)-5(3-carboxymethonyphenol)-2-(4-sulfophenyl)-2H-tetrazolium assay.Cell viability improved in the hypoxic preconditioning group compared with that in the hypoxia group.The effects of hypoxic preconditioning on the cell cycle and apoptosis in HT22 cells were examined by western blot assay and flow cytometry.Compared with the hypoxia group,the expression levels of caspase-3 and spectrin,which are markers of early apoptosis and S-phase arrest,respectively,noticeably reduced in the hypoxic preconditioning group.Finally,enzyme-linked immunosorbent assay,real-time polymerase chain reaction,and western blot assay were used to investigate the changes in DNMT expression and activity during hypoxic preconditioning.The results showed that compared with the control group,hypoxic preconditioning downregulated the expression levels of DNMT3A and DNMT3B mRNA and protein in HT22 cells and decreased the activities of total DNMTs and DNMT3B.In conclusion,hypoxic preconditioning may exert anti-hypoxic neuroprotective effects,maintaining HT22 cell viability and inhibiting cell apoptosis.These neuroprotective mechanisms may be associated with the inhibition of DNMT3A and DNMT3B.

Plastid genome evolution of a monophyletic group in the subtribe Lauriineae(Laureae,Lauraceae)

Litsea,a non-monophyletic group of the tribe Laureae(Lauraceae),plays important roles in the tropical and subtropical forests of Asia,Australia,Central and North America,and the islands of the Pacific.However,intergeneric relationships between Litsea and Laurus,Lindera,Parasassafras and Sinosassafras of the tribe Laureae remain unresolved.In this study,we present phylogenetic analyses of seven newly sequenced Litsea plastomes,together with 47 Laureae plastomes obtained from public databases,representing six genera of the Laureae.Our results highlight two highly supported monophyletic groups of Litsea taxa.One is composed of 16 Litsea taxa and two Lindera taxa.The 18 plastomes of these taxa were further compared for their gene structure,codon usage,contraction and expansion of inverted repeats,sequence repeats,divergence hotspots,and gene evolution.The complete plastome size of newly sequenced taxa varied between 152,377 bp(Litsea auriculata)and 154,117 bp(Litsea pierrei).Seven of the 16 Litsea plastomes have a pair of insertions in the IRa(trnL-trnH)and IRb(ycf2)regions.The 18 plastomes of Litsea and Lindera taxa exhibit similar gene features,codon usage,oligonucleotide repeats,and inverted repeat dynamics.The codons with the highest frequency among these taxa favored A/T endings and each of these plastomes had nine divergence hotspots,which are located in the same regions.We also identified six protein coding genes(accD,ndhJ,rbcL,rpoC2,ycf1 and ycf2)under positive selection in Litsea;these genes may play important roles in adaptation of Litsea species to various environments.

One hundred noteworthy boletes from China

Fungi of the family Boletaceae are of great importance in both ecology and economy.Our previous molecular phylogenetic studies have shown this family to have an extremely high species diversity in China.To further document the Chinese boletes,morphological studies and phylogenetic analyses were conducted including species of Boletaceae from China and other parts of the world.The results indicate that seven subfamily-level major clades and 62 generic clades can be retrieved,52 of which are found in China.Furthermore,100 species(comprising 32 genera)common in China are illustrated and described here in detail.Among them,four genera and 46 species are new to science,and 26 new combinations are proposed.To interpret the species concepts consistently,epitypes for five species are designated based on collections made from or near the type localities.Notes on eight extralimital species are also provided.Among the species reported here,most of the species are known only from East Asia.Only Leccinum scabrum(Bull.)Gray,Porphyrellus porphyrosporus(Fr.&Hok)E.-J.Gilbert and Tylopilus felleus(Bull.)P.Karst.are widely distributed in the Holarctic,and Buchwaldoboletus lignicola(Kallenb.)Pila´t;Strobilomyces strobilaceus(Scop.)Berk.are in Eurasia;while Aureoboletus mirabilis(Murrill)Halling,Harrya chromapes(Frost)Halling et al.,and Sutorius eximius(Peck)Halling et al.are found throughout East Asia-North America based on morphological and molecular phylogenetic evidences.