中国亚热带地区造林对土壤碳周转的影响

Afforestation in China's subtropics plays an important role in sequestering CO2 from the atmosphere and in storage of soil carbon (C). Compared with natural forests, plantation forests have lower soil organic carbon (SOC) content and great potential to store more C. To better evaluate the effects of afforestation on soil C turnover, we investigated SOC and its stable C isotope (δ13C) composition in three planted forests at Qianyanzhou Ecological Experimental Station in southern China. Litter and soil samples were collected and analyzed for total organic C, δ13C and total nitrogen. Similarly to the vertical distribution of SOC in natural forests, SOC concentrations decrease exponentially with depth. The land cover type (grassland) before plantation had a significant influence on the vertical distribution of SOC. The SOC δ13C composition of the upper soil layer of two plantation forests has been mainly affected by the grass biomass 13C composition. Soil profiles with a change in photosynthetic pathway had a more complex 13C isotope composition distribution. During the 20 years after plantation establishment, the soil organic matter sources influenced both the δ13C distribution with depth, and C replacement. The upper soil layer SOC turnover in masson pine (a mean 34% of replacement in the 10 cm after 20 years) was more than twice as fast as that of slash pine (16% of replacement) under subtropical conditions. The results demonstrate that masson pine and slash pine plantations cannot rapidly sequester SOC into long-term storage pools in subtropical China.     

Sesquiterpene synthases from grand fir (Abies grandis). Comparison of constitutive and wound-induced activities, and cDNA isolation, characterization, and bacterial expression of delta-selinene synthase and gamma-humulene synthase

Grand fir (Abies grandis) has been developed as a model system for the study of oleoresin production in response to stem wounding and insect attack. The turpentine fraction of the oleoresin was shown to contain at least 38 sesquiterpenes that represent 12.5% of the turpentine, with the monoterpenes comprising the remainder. Assays of cell-free extracts from grand fir stem with farnesyl diphosphate as substrate indicated that the constitutive sesquiterpene synthases produced the same sesquiterpenes found in the oleoresin and that, in response to wounding, only two new products were synthesized, delta-cadinene and (E)-alpha-bisabolene. A similarity based cloning strategy yielded two new cDNA species from a stem cDNA library that, when expressed in Escherichia coli and the gene products subsequently assayed, yielded a remarkable number of sesquiterpene products. The encoded enzymes have been named delta-selinene synthase and gamma-humulene synthase based on the principal products formed; however, each enzyme synthesizes three major products and produces 34 and 52 total sesquiterpenes, respectively, thereby accounting for many of the sesquiterpenes of the oleoresin. The deduced amino acid sequence of the delta-selinene synthase cDNA open reading frame encodes a protein of 581 residues (at 67.6 kDa), whereas that of the gamma-humulene synthase cDNA encodes a protein of 593 residues (at 67.9 kDa). The two amino acid sequences are 83% similar and 65% identical to each other and range in similarity from 65 to 67% and in identity from 43 to 46% when compared with the known sequences of monoterpene and diterpene synthases from grand fir. Although the two sesquiterpene synthases from this gymnosperm do not very closely resemble terpene synthases from angiosperm species (52-56% similarity and 26-30% identity, there are clustered regions of significant apparent homology between the enzymes of these two plant classes. The multi-step, multi-product reactions catalyzed by the sesquiterpene synthases from grand fir are among the most complex of any terpenoid cyclase thus far described.     

护套不同破坏形式下钢绞线的腐蚀特性研究

PE护套破坏是导致斜拉索中钢绞线发生腐蚀的直接原因。为了研究护套不同破坏形式下钢绞线腐蚀形态特征及力学性能退化规律,基于钢绞线电化学加速腐蚀试验,通过静力拉伸试验测定腐蚀钢绞线力学性能参数。结果表明：PE护套在两种破坏形式下钢绞线的锈蚀形态不同。PE护套环向破坏时,腐蚀产物在损伤口两端堆积,而纵向破坏时,腐蚀产物堆积在两侧;通过钢绞线腐蚀损伤评定,发现护套环向破坏时,钢绞线的腐蚀率随着时间呈指数增长,而纵向破坏时为线性增长,说明前者的腐蚀损伤危害要大于后者;护套两种破坏形式下,腐蚀钢绞线的力学性能不同,环向破坏后腐蚀钢绞线的承载力小于纵向破坏形式;在弹性模量和抗拉强度方面,环向破坏时,钢绞线的损伤率在20%以内时快速衰减,随后衰减缓慢,而纵向破坏时,腐蚀钢绞线的弹性模量和抗拉强度随损伤率呈线性衰减。PE套管环向破坏时,腐蚀钢绞线的力学性能损耗较大,在实际工程中应当重点关注。     

减少八钢2号高炉风口损坏的实践

八钢2号高炉由于焦炭强度下滑及设备故障无计划休风,炉缸工作不活,并伴随风口频繁烧损。通过洗炉、稳定煤气流措施使风口频繁烧损现象消除。     

应力—渗流耦合作用下损伤岩石渗流特性

地下矿产资源开采过程中,频繁的应力扰动会对深部硬岩造成一定的损伤。硬岩内部孔隙和裂隙在高地应力和高渗透压的状态下迅速扩展贯通,严重威胁岩体工程的安全和稳定性。针对损伤花岗岩开展了一系列应力—渗流耦合试验,结合CT扫描,考虑渗透压、围压和损伤程度等因素的影响,综合分析了损伤岩石在应力—渗流耦合作用下的力学和渗流特性。试验结果表明：随着损伤程度的增加,岩样孔隙及裂隙体积呈现出从平缓增加、稳步增加到急剧增加的变化趋势;在围压相同的情况下,岩样的峰值强度随着渗透压的增加呈线性减小,渗透压对损伤花岗岩的强度具有明显的弱化效应,且弱化程度与围压无关;损伤程度越大,裂隙发育程度越高,渗透率越大,同时,孔隙及裂隙的发育程度可用于表征渗透率的大小。     

首钢炼铁厂减少风口损坏的实践

首钢炼铁厂高炉扩容改造后风口损坏严重，1995年全厂损坏风口400多个，损坏风口的原因是烧坏、磨坏及风口质量问题。通过逐项改进，风口损坏得到了控制，2000年风口只损坏100多个，保证了炼铁生产的稳定顺行。     

基于PnET-CN模型的亚热带人工针叶林生产力与固碳潜力模拟研究

A generalized, lumped-parameter ecological model PnET-CN was calibrated and validated for a subtropical coniferous plantation in southem China. PnET-CN model describes the biogeochemical cycles of carbon(C)and nitrogen(N)and can assist in estimating carbon sequestration potential. For validation of PnET-CN, data from coniferous forest plantations in southern China was used. Simulated daily gross primary productivity(GPP)from 2005 to 2007 agreed well with observations(R2=0.56, S.D.=0.009). Simulations of monthly soil res-piration(R3)from 2005-2007 agreed well with R8 observations(R2=0.67, S.D. =0.03). Simu-lated annual net primary productivity(NPP)from 1998-2006 was 803±33 gCm-2a-1, about 4% higher than NPP observation(752±51 gCm-2a-1). Simulations of annual NEP from 2005-2007 only overestimate 9 gCm-2a-1(4%), 4 gCm-2a-1(1%)and 34 gCm-2a-1(8%)compared to NEP observations, respectively. Simulated annual foliar N concentration(FolNCon)(1.09%)is 10% lower than observed monthly FolNCon(0.87%-1.58%). Simulated annual N leaching(0.26 gNm-2)is about 10% lower than leaching observation(0.29 gNm-2). PnET-CN model valida-tion indicates that PnET-CN is capable to simulate daily GPP, annual NPP, annual NEP, monthly R,, annual FolNCon and annual nitrate N leaching for subtropical coniferous planta-tions in southem China. The results obtained from the validation test revealed that PnET-CN model can be used to simulate carbon sequestration of planted coniferous forests in southern China to a high level of precision. Sensitivity analysis suggests that great care should be taken in developing generalizations as to how forests will respond to a changing climate. PnET-CN performed satisfactorily in comparison to other models that have already been calibrated and validated in coniferous planted subtropical forests in China. Based on PnET-CN validation and its comparison to other models, future improvement of PnET-CN should focus on seasonal foliar N dynamics and the effects of water stress on autotrophic respirations in subtropical coniferous plantations in southern China.     

钢轨轨底裂纹成因分析

在某焊轨厂对75 kg/m钢轨进行焊接前,发现多支钢轨在轨底出现裂纹和掉块伤损。经对伤损钢轨取样进行研究分析,钢轨性能、冶金质量均符合相应技术标准要求。针对钢轨裂纹特征,采用某软件对钢轨焊接前堆垛中的受力状态进行分析。结果表明,钢轨出现轨底裂纹伤损的原因是:钢轨堆垛时未按要求放平,出现倾斜,造成一侧轨底角局部受力过大,从而产生裂纹伤损。     

Damage Analysis of Hanshin Expressway Viaducts during 1995 Kobe Earthquake. II: Damage Mode of Single Reinforced Concrete Piers

The damage mode that single reinforced concrete (RC) piers of the Hanshin Expressway Kobe Route suffered during the 1995 Kobe earthquake is discussed. On the Kobe Route, many single RC piers suffered from flexural mode damage; however, some suffered from shear failure, and most shear failure occurred in piers with rectangular cross sections. The flexural and shear capacity of each pier are calculated based on the design documents, and the ratio of flexure to shear capacity, r, is calculated by taking into account the mass of the pier column. It is found that the damage mode (flexure or shear) in the severely damaged single RC piers from P1 to P350 can be explained by the value of r, either >1.0 (flexural mode) or <1.0 (shear mode).     

Damage Analysis of Hanshin Expressway Viaducts during 1995 Kobe Earthquake. I: Residual Inclination of Reinforced Concrete Piers

The damage suffered by elevated viaducts of the Hanshin Expressway Kobe Route during the 1995 Kobe earthquake is described with emphasis on reinforced concrete (RC) piers. Although many piers were severely damaged, it is also true that the damage to many piers appeared moderate or even mild. On the other hand, a number of piers suffered from large residual inclination in spite of the apparently light damage. By considering that the large residual inclination of piers included severe earthquake-induced damage, it is pointed out that almost all the RC single piers from P35 to P350 received consistently severe damage. The cause of large residual inclination, especially in apparently nondamaged piers, is studied. A dynamic analysis of a single RC pier is conducted to study the relationship between residual inclination and residual deformation of a pier. As a result, we find that the flexural residual deformation of a pier cannot explain the observed large residual inclination, but it is suggested that the pulling out of reinforcing bar from the footing can be a primary cause of the observed large residual inclination.