环境工程微生物学教学改革探索与实践

环境工程微生物学是环境工程专业重要的专业基础课程,内容抽象、工程实践性强,重视实践创新型人才的培养。如何激发学生学习热情,夯实教学效果,培育专业的环保人才,是环保教育工作者的责任和使命。本文结合湖南农业大学环境工程微生物学的教学实践,探索教学模式、教学内容和考核模式等对教学质量的影响,以期为环境工程微生物学课程的教学改革提供参考。

基于环境工程专业课程属性的教学探索与实践

环境工程专业课程门类广、实践性强,是高校培养应用创新型人才的重大挑战。依据课程属性和培养目标,因课而异选取适宜的教学方法是保证人才培养质量的必然要求。以湖南农业大学环境工程专业教学改革的成果为基础,探讨混合式教学、项目式和案例式教学、启发式教学、"教学、科研、生产"三基地结合和校企合作办学分别在基础理论课程、设计课程、实验课程和实习环节中的适用情形。结果表明,以课程属性和人才培养目标为导向的授课方式,能更好的激发学生学习热情,提高学生的实践能力,保障学习效果,是课程改革的重要方向。

Redistribution of Trace Elements During Shock-inducd Melting and Phase Tranzition of Minerals in the Suizhou l6 Chondrite

The Suizhou meteorite is an L6 chondrite. This meteorite is consisted of olivine, low-Ca pyroxene, plagioclase, FeNi metal, troilite, whitlockite, chlorapatite, chromite and ilmenite. Olivine and pyroxene grains display shock-induced mosaic texture, and most plagioclase grains were melted and transformed to maskelynite. This meteorite contains a few very thin shock-produced melt veins ranging from 20 to 100 μm in width. They are chondritic in composition and contain abundant high-pressure minerals in two assemblages. One is the coarse-grained assemblage of ringwoodite, majorite, lingunite with minor amount of tuite, xieite, the CF-phase, akimotoite and amorphized perovskite, and the fine-grained assemblage (the melt vein matrix) composed of majorite-pyrope garnet, magnesiowüstite. FeNi metal and troilite in the Suizhou shock veins were molten and occur as small intergrowth grains or veinlets filling the interstices of garnet crystals or cracks in the vein matrix. It was revealed that olivine, pyroxene and plagioclase in the Suizhou shock veins have transformed in solid state to their high-pressure polymorphs ringwoodite, majorite, and lingunite, respectively, without change in their chemical compositions.

Transmission electron microscopic study of the fine-grained vein matrix in the Suizhou L6 meteorite

The mineralogy of shock vein matrix in the Suizhou meteorite has been investigated by optical and transmission electron microscopy. It was revealed that the vein matrix is composed of majorite-pyrope garnet, mag- aesiowtistite, and ringwoodite, with FeNi-FeS inter- growths. The observation and character of ring-like selected electron diffraction （SAED） patterns indicate that Lhe idiomorphic garnet crystals in the vein matrix have different orientations. The polycrystalline nature of magnesiowtistite is also confirmed by a ring-like SAED pattern. Both garnet and magnesiowtistite crystals showed sharp Jiffraction spots, signifying the good crystallinity of these ：wo minerals. The SAED pattern of cryptocrystalline 5ngwoodite shows only diffuse concentric diffraction tings. FeNi metal and troilite （FeS）, which were molten during the shock event, occur in the matrix as fine eutectic FeNi-FeS intergrowths filling the interstices between garaet and magnesiowiistite grains. Based on the phase dia- gram of the Allende chondrite and the results of this TEM study, it is inferred that majorite-pyrope garnet first crystallized from the Suizhou chondritic melt at 22-26 GPa, Followed by crystallization of magnesiowtistite at 20-24 GPa, and then ringwoodite at 18-20 GPa. The eutectic intergrowths of FeNi-metal and troilite are proposed to have crystallized during meteorite cooling and solidified at the last stage of vein formation.

High-pressure polymorph of TiO_2-Ⅱ from the Xiuyan crater of China

Abundant TiO2-Ⅱ,a high-pressure polymorph of titanium dioxide,was found in the gneiss fragments of impact-produced breccias from the Xiuyan crater.Rutile in the gneiss was severely fragmented and fine-grained clasts less than 2 m in size had been transformed to TiO2-II.Irregular thin layered TiO2-Ⅱ is also observed in coarse-grained rutile fragments,where the TiO2-Ⅱ layers distributes along fractures and cracks in rutile.About 30 percent of rutile in the gneiss had been transformed to TiO2-Ⅱ.Fine grains of TiO2-Ⅱ display light bluish grey to light yellow brown in plane-polarized reflected light.Crystallographic investigation shows that TiO2-Ⅱ has an orthorhombic structure with space group Pbcn.The cell parameters are a=4.543(1),b=5.491(9)and c=4.895(2).Its empirical formula calculated on the basis of two oxygen atoms can be written as(Ti0.985Fe0.008Nb0.006-Si0.003Zr0.001)1.003O2,or simply formula TiO2.According to the shock effects of quartz and feldspars,the peak shock pressure and post-shock temperature in the TiO2-Ⅱ-bearing gneiss are estimated to be between 35 and 43 GPa and 300–900°C,respectively.The finding of TiO2-Ⅱ in the shock-metamorphosed gneiss provides another mineral physics evidence for shock origin of the Xiuyan crater.

Shock-produced akimotoite in the Suizhou L6 chondrite

Shock-produced akimotoite was identified in the Suizhou chondritic meteorite, which occurs in two kinds of occurrence. The first is the irregular layers of akimotoite up to 4 ?m in thickness occurring in fractures and cracks of low-Ca pyroxene enclosed in the shock veins. The second is the zonal polycrystalline aggregates of akimotoite in shocked pyroxene grains close to the shock vein, where akimotoite occurs in a zonal area in between pyroxene and Mg Si O3-glass as irregular small clumps up to 5 ?m in size. This investigation suggests a solid-state transformation mechanism of pyroxene to akimotoite, and that akimotoite should have nucleated and grew in the area with abundant defects caused by shock deformation because the defect significantly enhances the solid-state reactivity and the kinetics of nucleation of high-pressure phase. The spatial relationship among the composed grains of pyroxene, akimotoite and Mg Si O3-glass(possibly vitrified perovskite) demonstrates a temperature gradient from the vein wall to the unmelted chondritic meteorite.

Chenguodaite (Ag_9FeTe_2S_4):a new tellurosulfide mineral from the gold district of East Shandong Peninsula,China

Chenguodaite, approved by IMA-CNMMN (2004-042a), was discovered in the Bunan quartz vein-type gold deposit in the gold district of East Shandong Peninsula. The mineral occurs in high grade Au-Ag-Cu ores, coexisting with galena, chalcopyrite, hessite, electrum, unnamed Ag6TeS2 and Ag16FeBiTe3S8, enclosed and replaced by native silver and acanthite. In the reflected light microscope, the mineral has light gray color, indistinguishable anistropism and hardness around 2―3. The color indices of chenguodaite relative to ICE C illuminator are: x=0.3027, y=0.3076, Y=25.78%, λd=474 nm, Pe=3.68%, similar to those of canfieldite. The average chemical composition from 16 microprobe analyses is Ag8.97Fe1.00Te1.99S4.04, idealized to Ag9FeTe2S4. The polycrystalline X-ray diffraction of chenguodaite by Gandolfi camera and synchrotron oscillation photography results in 67 reflections with the 12 strongest being (relative intensity in bracket): 6.742(69), 6.416(39), 5.951(33), 3.265(100), 2.981(24), 2.649(22), 2.25(24), 2.188(71), 2.142(22), 2.123(31), 2.044(23), 1.949(33), which are indexed to a primitive orthorhombic cell with a=12.769 (2) , b= 14.814(2), c= 16.233 (1) , V= 3070.63, Z = 9, Dcal.=6.85 g/cm3. The name is for the late Prof. Chen Guoda, a famous Chinese geologist and the founder of Diwa-Geodepression theory of tectonics.