[Structure Characteristics and Driving Variables of Epilithic Algae Community in Lhasa River Basin of Qinghai-Tibet Plateau]

In order to explore the characteristics and driving factors of the epilithic algae community in the middle and lower reaches of the Lhasa River, epilithic algae was collected and identified in September 2019, the species composition and spatial distribution were analyzed, and the key environmental factors affecting the epilithic algae community were identified through redundancy analysis. The results indicated that 31 genera of epilithic algae belonging to six phyla were identified, and the average cell density of the epilithic algae was 1.92×10⁶ cells·m^-2. The number of species and cell density of the diatom phylum were the largest at each sampling point. The species number and cell density of the epilithic algae were significantly different between the main stream and tributaries. The main stream and tributaries contained relatively small differences in the dominant algae genera, which were Gomphonema, Fragilaria, Cymbella, and Planktolyngbya in the main stream and Gomphonema, Fragilaria, Cymbella, and Oscillatoria in the tributaries. The redundancy analysis revealed that temperature, pH, and dissolved oxygen were the main driving factors affecting the community structure of the dominant genus in the main stream, while HCO₃^- and flow velocity controlled the community structure of the dominant genus in the tributaries. This study provides basic data and the theoretical basis for the conservation of aquatic ecosystems and water quality management in the middle and lower reaches of the Lhasa River.

[Influence Factors of Potential Nitrification Rates and Functional Genes Abundance in the Jinshui River and the Qihe River of the Hanjiang River Basin]

In the context of increasing nitrogen loading in river systems worldwide, it is critically important to understand nitrification to maintain river ecosystem health. This comparative study was conducted to explore the relationships among the intensity of human disturbance, environmental factors, potential nitrification rate, and functional gene abundance in the Jinshui River (slightly disturbed basin) and the Qihe River (intensely disturbed basin). The results showed that AOA-amoA gene abundance was higher than that of AOB-amoA. The potential nitrification rate in the Qihe River was higher than that in the Jinshui River. There was no significant difference in AOA-amoA gene abundance between the two rivers; however, the AOB-amoA gene abundance in the Qihe River was significantly higher than that in the Jinshui River in the low flow season. The abundance of nitrification functional genes was significantly correlated with water temperature, pH, NO₃^-, NH₄⁺, and organic carbon. The potential nitrification rate was positively correlated with water temperature, pH, and NO₃^-, and negatively correlated with AOB-amoA gene abundance. These results showed that the intensely disturbed sites had higher potential nitrification rates and nitrification functional genes abundances, and potential nitrification rates and abundances of nitrification function genes were significantly related to physical and chemical water and sediment factors. This study will be important for nitrogen pollution control in the river systems.

Flexible endoscope visualization to assist in the removal of a string of 10 schwannomas at the cauda equina: technical case report

Bead-like schwannomas at the cauda equina are rare but benign intraspinal tumors. They can involve multiple nerve roots and spread within the spinal canal, and open resection would cause significant trauma. The authors have successfully applied a novel minimally invasive technique for the total removal of such schwannomas. A 68-year-old woman presented with a 1-month history of left waist and leg pain. MRI demonstrated multiple intraspinal lesions located from L1 to S1. The diagnosis was bead-like schwannomas at the cauda equina. Two incisions were made at the T12 and L5 levels. A flexible endoscope was introduced into the spinal canal following hemisemilaminectomy under a microscope to identify the relationship between the tumors and the carrying nerves. After dissecting both cranial and caudal ends of the carrying nerve, the string of bead-like tumors was gently pulled out from the caudal end as a whole. The endoscope was reintroduced into the spinal canal to ensure complete tumor removal. The patient recovered quickly, and no tumor residual was found at postoperative MRI. Flexible endoscope-assisted visualization plus microscopic hemisemilaminectomy via 2 incisions is a feasible minimally invasive approach for selected patients with bead-like schwannomas at the cauda equina.

[Biomechanical study of different kinds of internal fixation for the typeⅠ Hangman fracture, type Ⅱ odontoid fracture and the C(2/3) disc injury: a finite-element analysis]

Objectives: To analyze the biomechanical stability of four kinds of internal fixation for the type Ⅰ Hangman fracture, type Ⅱ odontoid fracture and the C(2/3) disc injury by finite element (FE) analysis. Methods: Thin-section spiral computed tomography (0.5 mm) was performed on C(1) to C(3) region of cervical vertebra in healthy male volunteers.A three-dimensional hexahedral FE model of upper cervical spine was established by software (Mimics, GEOMAGICS, Pro/E and Ansys). Then the weakening of the strength of grid was performed to simulate the FE model of the type Ⅰ Hangman fracture, type Ⅱ odontoid fracture and the C(2/3) disc injury (FE/Fracture), the four internal fixation models: anterior cervical plate+ odontoid screw+ cage (FE/ACP+ OS+ cage), affixing rods from pedicle screws in C(2) to lateral mass screws in C(3)+ odontoid screw + cage (FE/C(2)PS+ C(3)LMS+ OS+ cage), affixing rods from pedicle screws in C(1) to pedicle screws in C(2) and lateral mass screws in C(3) (FE/C(1)PS+ C(2)PS+ C(3)LMS), anterior odontoid screw plate fixation system (FE/AOSP) were simulated on the FE/Fracture model.Flexion, extension, lateral bending and axial rotation were imposed on the FE/Intact, FE/Fracture and the four fixation models respectively. Results: The intact model of upper cervical spine (C(1)-C(3)) was established successfully, consisting of 259 641 nodes and 403 674 units.There was no significant difference among the FE/ACP+ OS+ cage, the FE/ C(2)PS+ C(3)LMS+ OS+ cage and the FE/AOSP of ROMC(1/2).During flexion, extension, left axial rotation and right axial rotation of ROMC(2)-C(3), the FE/AOSP decreased 70.7%, 74.4%, 38.9%, 41.1% respectively compared with the FE/C(1)PS+ C(2)PS+ C(3)LMS.The ROMC(2)-C(3) during flexion, extension, left lateral bending, right lateral bending, left axial rotation and right axial rotation in the FE/AOSP decreased for 82.2%, 82.8%, 73.2%, 64.8%, 72.2%, 81.5% respectively when compared with those in FE/ACP+ OS+ cage.The ROMC(2)-C(3) during flexion, extension, left lateral bending, right lateral bending, left axial rotation and right axial rotation in the FE/AOSP decreased 88.2%, 81.2%, 47.6%, 41.2%, 38.9%, 39.0% respectively when compared with those in FE/C(2)PS+ C(3)LMS+ OS+ cage.The stress concentrated on the connection between plate and screw in the FE/ACP+ OS+ cage, the FE/C(2)PS+ C(3)LMS+ OS+ cage and the FE/C(1)PS+ C(2)PS+ C(3)LMS, while it distributed evenly in the FE/AOSP. Conclusion: Anterior odontoid screw plate fixation system can be used to treat the type Ⅰ Hangman fracture, type Ⅱ odontoid fracture, and the C(2/3) disc injury and can reserve the function of atlanto-axial joint.

[Evaluation of biocompatibility of Ti-6Al-4V scaffolds fabricated by electron beam melting]

Objective: To investigate the biocompatibility of Ti-6Al-4V scaffolds fabricated by electron beam melting(EBM). Methods: Bone marrow mesenchymal stem cells(BMSC) co-cultured with Ti-6Al-4V specimens fabricated with EBM was prepared as experimental group and the regular cells culture was employed as control. The biocompatibility was detected using CCK-8 and cytoskeleton staining. The osteogenic differentiation ability was assessed using mineralization nodule formation. A 24 mm defect was created on the right mandibular body in 12 beagles. The mandibular defects were repaired with Ti-6Al-4V scaffolds mesh fabricated by EBM. General observation, CT and histology examination was carried out to evaluated the biocompatibility of Ti-6Al-4V scaffolds in vivo. Results: CCK-8 result showed the A values of the two groups had no significant difference(P >0.05). There was no significant difference between the two groups (P>0.05). Cytoskeletal staining showed that cells were fully stretched out and grew well on T-i6Al-4V specimen. The actin fibers were arranged in parallel and stained uniformly with fluorescent. After osteogenic culture, the quantity of the nodule formation of the experimental group and control group were 5.7±0.7 and 5.1 ± 0.6, respectively(P>0.05). All animals had tolerated the surgery and healed well. CT examination showed that Ti-6Al-4V scaffolds mesh had good retention with surrounding bone and the continuity of mandible was restored. Histological examination showed that no inflammation reaction or toxity was caused in the soft tissue surrounding the scaffolds and in the liver and kidney after implantation. Ti-6Al-4V scaffolds had good retention with surrounding bone. Conclusions: Ti-6Al-4V fabricated with electron beam melting has good biocompatibility.

[Comparison of surface characteristics and cytocompatibility of Ti-6Al-4V alloy fabricated with select laser melting and electron beam melting]

Objective: To evaluate the surface characteristics and cytocompatibility of Ti-6Al-4V alloy fabricated using select laser melting (SLM) and electron beam melting (EBM) technique. Methods: Ti-6Al-4V alloy specimens were fabricated with SLM and EBM. A wrought form of Ti-6Al-4V alloy was used as a control. Its properties were evaluated using component analysis, contact angle test, surface roughness, surface topography, cell ultrastructure, cell attachment and proliferation observation, metal ion precipitation examination. Results: The roughness of SLM and EBM specimens was suitable for cell attachment but not the best. The character of SLM and EBM specimens was hydrophobic (>65°). The surface topography of EBM and SLM specimens were similar, but were not the best type for cell attachment. The components of Ti-alloy oxide film were detected in all the specimens. The content of Ti, Al, V ions of EBM, SLM and wrought specimens were very low and did not affect the cell attachment and proliferation. The ultrastructure of cell was normal, and the cytomembrane was intact. The number of cells was similar to each other among the three kinds of specimens and increased obviously with the culture time. Conclusions: The results of the study suggested that EBM and SLM Ti-6Al-4V specimens possessed good surface characteristics. However, the surface modification are needed further.

An old but simple and efficient method to elucidate the oxidation mechanism of NAD(P)H model 1-Aryl-1,4-dihydronicotinamides by cations 2-methyl-5-nitroisoquinolium, tropylium, and xanthylium in aqueous solution

Cations 2-methyl-5-nitroisoquinolinium (IQ+), tropylium (T+), and xanthylium (Xn+) were treated by an NAD(P)H model 1-(p-substituted phenyl)-1.4-dihydronicotinamide series (1) in buffered aqueous solution to give the corresponding reduced products by accepting hydride. Effects of the 4-substituents of 1 on the reaction rates were investigated. Hammett's linear free energy relationship analysis on the three reactions of 1 provides the reaction constants of -0.48, -2.2, and -1.4 with IQ+, T+, and Xn+ as the hydride acceptors, respectively. Comparison of the present reactions with the reaction examples whose mechanisms are well-known, such as the reaction of 1 with a one-electron oxidant Fe(CN)6(-3), shows that the active site of 1 in the oxidation with IQ+ is at the 4-position on the dihydropyridine ring but that the active site of 1 in the oxidations with T+ and Xn+ is at the 1-position, which is in agreement with the results from the Brønsted-type linear analysis and the relation studies of the logarithm of the second-order rate constants with the oxidation potentials of the hydride donors. According to the dependence of the reaction mechanism on the active site of 1, a conclusion can be made that the reaction of 1 with IQ+ proceeds by direct one-step hydride transfer mechanism, but the reactions of 1 with T+ and Xn+ would take place via multistep hydride transfer mechanism initiated by one-electron transfer.

Mechanisms of the oxidations of NAD(P)H model Hantzsch 1,4-dihydropyridines by nitric oxide and its donor N-methyl-N-nitrosotoluene-p-sulfonamide

4-Substituted derivatives of Hantzsch 1,4-dihydropyridine were treated by nitric oxide (NO) or its donor N-methyl-N-nitrosotoluene-p-sulfonamide (MNTS) to give the corresponding pyridine derivatives. When the 4-substituted group was methyl, ethyl, n-propyl, and aryl groups, it was preserved, but when the group was isopropyl or benzyl one, it was lost. 2,3-Dichloro-5, 6-dicyano-1,4-benzoquinone (DDQ) was used in place of NO and MNTS to react with the 4-substituted Hantzsch 1,4-dihydropyridines, no the corresponding 4-dealkyl Hantzsch pyridines were obtained from all the reactions. 1-Benzyl-1,4-dihydronicotinamide (BNAH), a close analogue of Hantzsch 1,4-dihydropyridine (HEH), was used instead of HEH to react with either of NO and MNTS, no reactions were observed for 3 days. Replacement of HEH by N-d-HEH and HEH-4,4-d(2) to react with NO, MNTS and DDQ gave the observed kinetic isotope effects of 3.1 and 1.4 for NO, 1.1 and 1.3 for MNTS, and 1.1 and 2.1 for DDQ, respectively. When p-dinitrobenzene, an electron-transfer inhibitor, was added into the title reaction systems, no remarkable inhibitory effect was observed. These results indicated that the oxidation of HEH by NO was initiated by hydrogen transfer from the N(1)-position to give the corresponding aminyl radical, which then underwent homolytic cleavage to become the final aromatized product (A). But the reaction of HEH with MNTS was initiated by nitrosation to give the corresponding N-nitroso compound, which was subsequently subjected to two steps of homolytic cleavage to afford the aromatized Hantzsch pyridine A.