Elemental Sulfur Oxidation by Thiobacillus spp. and Aerobic Heterotrophic Sulfur-Oxidizing Bacteria

The prediction of the oxidation rate of elemental sulfur （S^0） is a critical step in sulfur （S） fertilizer strategy to supply plant-available sulfur. An incubation experiment was conducted to determine the rate and amount of S^0 oxidation in relation to the contribution of Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria. After 84 days, 16.3% and 22.4% of the total S^0 applied to the soil were oxidized at 20 and 30 ℃, respectively. The oxidation of So proved to be a two-step process with a rapid oxidation during the first 28 days and a slow oxidation from then on. The highest oxidation rate of 12.8 μg S cm ^-2 d^-1 was measured during the first two weeks at 30 ℃. At 20 ℃ the highest oxidation rate of 10.2 μg S cm^-2 d^-1 was obtained from two to four weeks after start of the experiment. On an average the soil pH declined by 3.6 and 4.0 units after two weeks of experiment. At the same time the electric conductivity increased nine times. With the oxidation of S^0 the population of Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria increased. The corresponding values for Thiobacillus spp. and aerobic heterotrophic S-oxidizing bacteria increased from 2.9 × 10^5 and 1.4 × 10^5 g^-1 soil at the start of the experiment to 4 × 10^8 and 5.6 × 10^8 g^-1 soil 14 days after S^0 application, respectively. No Thiobacillus spp. was present eight weeks after S^0 application. The results suggested that oxidation of residual S^0 completely relied oll aerobic heterotrophic S-oxidizing bacteria.

Uptake, Subcellular Distribution, and Chemical Forms of Cadmium in Wild-Type and Mutant Rice

Wild-type （Zhonghua 11） and mutant rice （Oryza sativa L.） plants were used to investigate the effect of cadmium （Cd） application on biomass production, to characterize the influx of Cd from roots to shoots, and to determine the form, content, and subcellular distribution of Cd in the roots, leaf sheaths, and leaves of the rice plants. Seedlings were cultivated in a nutrient solution and were treated with 0.5 mmol L^-1 of Cd^2＋ for 14 d. The sensitivity of rice plants to Cd toxicity was tested by studying the changes in biomass production and by observing the onset of toxicity symptoms in the plants. Both the wild-type and mutant rice plants developed symptoms of Cd stress. In addition, Cd application significantly （P ≤ 0.01） decreased dry matter production of roots, leaf sheaths, and leaves of both types, especially the mutant. The Cd content in roots of the mutant was significantly （P ≤0.05） higher than that of the wild-type rice. However, there was no significant difference in the Cd content of roots, leaf sheaths, and leaves between the wild-type and mutant rice. Most of the Cd was bound to the cell wall of the roots, leaf sheaths, and leaves, and the mutant had greater Cd content in cell organelles than the wild type. The uneven subcellular distribution could be responsible for the Cd sensitivity of the mutant rice. Furthermore, different chemical forms of Cd were found to occur in the roots, leaf sheaths, and leaves of both types of rice plants. Ethanol-, water-, and NaCl-extractable Cd had greater toxicity than the other forms of Cd and induced stunted growth and chlorosis in the plants. The high Cd content of the toxic forms of Cd in the cell organelles could seriously damage the cells and the metabolic processes in mutant rice plants.

Occurrence of cGMP/nitric oxide-sensitive store-operated calcium entry in fibroblasts and its effect on matrix metalloproteinase secretion

AIM： To examine the existence of Nitric oxide/ cGMP sensitive store-operated Ca^2＋ entry in mouse fibroblast NIH/3T3 cells and its influence on matrix metalloproteinase （MMP） production and adhesion ability of fibroblasts. METHODS： NIH/3T3 cells were cultured. Confocal laser scanning microscopy was used to examine the existence of thapsigargin-induced store-operated Ca^2＋ entry in fibroblasts. Gelatin zymography and semiquantitative reverse transcriptase-polymerase chain reaction （RTPCR） were employed to detect the involvement of [Ca^2＋]i and NO/cGMP in MMP secretion. The involvement of NO/ cGMP-sensitive Ca^2＋ entry in adhesion was determined using matrigel-coated culture plates. RESULTS： 8-bromo-cGMP inhibited the thapsigargin-induced Ca^2＋ entry in 3T3 cells. The cGMP-induced inhibition was abolished by an inhibitor of protein kinase G, KT5823 （1μmol/L）. A similar effect on the Ca^2＋ entry was observed in 3T3 cells in response to a NO donor, （±）-S-nitroso-N-acetylpenicillamine （SNAP）. The inhibitory effect of SNAP on the thapsigargin-induced Ca^2＋ entry was also observed, indicating NO/cGMP-regulated Ca^2＋ entry in 3T3 cells. Results of gelatin zymography assay showed that addition of extracellular Ca^2＋ concentration induced MMP release and activation in a dose-dependent manner. RT-PCR also showed that cGMP and SNAP reduced the production of MMP mRNA in 3T3 cells. Experiments investigating adhesion potentials demonstrated that cGMP and SNAP could upgrade 3T3 cell attachment rate to the matrigel-coated culture plates.CONCLUSION： NO/cGMP sensitive store-operated Ca^2＋ entry occurs in fibroblasts, and attenuates their adhesion potentials through its influence on MMP secretion.

Effect of Nd addition on microstructure and tensile properties of laser additive manufactured TC11 titanium alloy

Single-layer and multilayer laser additive manufacturing(LAM)for TC11 alloy with different Nd additions was conducted and the effect of Nd addition on microstructure and properties was studied.With the addition of Nd,the aspect ratio of melting pools of single-layer specimens increases and the columnar-to-equiaxed transition occurs.The originalβgrain size andαplate width of TC11−1.0Nd are significantly reduced compared with those of pure TC11 specimens.It is proposed that the evenly distributed fine Nd_(2)O_(3) precipitates of about 1.51μm are formed preferentially during rapid solidification of melting pool,and they serve as heterogeneous nucleation particles to refine the microstructure in the subsequent solidification and solid-state phase transformation.Due to the multiple effects of Nd on the microstructure,the ultimate tensile strength of TC11−1.0Nd increases,while the yield strength,ductility and microhardness decrease compared with those of pure TC11.

Direct-chilling casting of Mg alloy under electromagnetic and ultrasonic combined field

The effects of low frequency electromagnetic (LFEC) field and ultrasonic (US) field on the microstructures, macrosegregation of alloying elements and the mechanical properties of DC cast AZ80 alloy were studied. The results show that both LFEC and US fields can refine the grains of the billets, which results in the increase in mechanical properties and uniformity of alloying element distribution. The effective refinement takes place on the edge of ingots when LFEC field is applied, while in the center of billets when field US is adopted. Combined the characteristics of LFEC and US fields, a new process for direct-chilling (DC) casting of Mg-electromagnetic-ultrasonic (ECUS) casting is developed, by which the grains are refined significantly and are more uniform in the whole ingots, and the mechanical properties of the ingots are improved.

Influence of minor Sc additions on grain refinement and microstructure characteristics of a high Zn-containing Al-Zn-Mg-Cu-Zr alloy

In the present work, scandium elements with a series of contents(0.06 wt.%, 0.10 wt.%, 0.14 wt.%,0.17 wt.%, 0.20 wt.% and 0.25 wt.%) were added in a high Zn-containing Al-Zn-Mg-Cu-Zr alloy and the corresponding as-cast microstructure characteristics including grains and phases were thoroughly investigated. The results indicated that fine grain boundaries existed in these alloys and fine MgZn2phases discontinuously distributed on them. Besides,AlZnMgCu eutectic phases and Sc, Zr-containing phases with flocculent morphology were observed. As scandium contents vary from 0.06 wt.% to 0.17 wt.%, the average grain size continuously decreased and its equiaxial characteristics were strengthened. Meanwhile, the content of AlZnMgCu eutectic phase showed a decrease trend. When scandium contents were 0.20 wt.% and 0.25 wt.%, no further enhancement on grain refinement was observed, so as to the reduction of AlZnMgCu eutectic phase content. Besides, Sc, Zr-containing phases with blocky morphology were observed and the alloy with a scandium content of 0.25 wt.% possessed a larger amount of blocky Sc, Zr-containing phase than the alloy with a scandium content of 0.20 wt.%. Grain refinement and reduction of AlZnMgCu eutectic phase content associated with scandium addition were discussed.

理工科课程思政建设的范式探索

立德树人是教育的根本目标。立德旨在价值塑造,树人则包括育人和育才,育人旨在知识传授,育才旨在能力养成。价值塑造、知识传授和能力培养三位一体,课程思政是核心要素。在遵循课程教育教学规律的前提下,思政元素挖掘和融入具有一定的范式可循。从课程的定位、目录的编排、知识的内涵、实践的隐育四个角度出发,赋予课程思政元素泛化、体化、细化和感化四个属性。泛化侧重新时代新思想,体化要义核心价值观,细化涵盖优秀文化,感化强调职业伦理。思政元素融入则分为知识点分割和切入点设计两个重要环节。本文以笔者所带课程思政建设为例,详细说明了范式探索的方案。The fundamental goal of education is to cultivate virtue and nurture people. Moral education aims to shape values, while nurturing people includes educating and nurturing talents. Educating people aims to impart knowledge, while nurturing talents aims to develop abilities. The trinity of value shaping, knowledge imparting, and ability cultivation, with ideological and political education in the curriculum as the core element. On the premise of following the laws of curriculum education and teaching, there is a certain paradigm for exploring and integrating ideological and political elements. From the perspectives of course positioning, directory arrangement, knowledge connotation, and practical cultivation, endow the ideological and political elements of the course with four attributes: generalization, embodiment, refinement, and influence. Generalization of new ideas for the new era, embodiment of core values, refinement of excellent culture, and emphasis on professional ethics. The integration of ideological and political elements can be divided into two important stages: knowledge point segmentation and entry point design. This article takes the ideological and political construction course taught by the author as an example to explain in detail the paradigm exploration plan.