铝粉对AAC发气孔结构及其强度的影响研究

为了积极响应国家节能减排、环境保护的政策,全国各地加强了新型环保建材的推广和应用,蒸压加气混凝土材料作为新型环保建材得到了较快的发展。AAC(蒸压加气混凝土)具有轻质性、抗压性、保温性、隔音性及抗渗水性的特点,这与其是一种多孔结构材料有关,大量独立、均匀的气孔决定了材料的孔结构,直接影响AAC的特性,而发气孔是对AAC性能影响最大的特征孔,铝粉作为发气剂直接影响了AAC的发气孔结构。简述了AAC目前发展现状和未来发展趋势,综述了铝粉在AAC生产过程的发气原理以及发气孔的形成过程。重点阐述了实验探究不同粒径的铝粉的发气速率,以及通过车间生产线实验探究了不同粒径的铝粉在AAC生产过程中的实际发气速率对发气孔孔径和强度的影响。

水料比对粉煤灰加气混凝土性能的影响

通过加气混凝土小模实验,研究不同水料比对加气混凝土性能的影响。结果表明:随着水料比的增加,试样的容重和强度均随之降低。分析了水料比对加气混凝土发气孔形态和分布的影响,当铝粉发气孔水料比小时,发气孔孔径较小,孔隙均匀;水料比增加,孔隙均匀度降低,孔径增大。

Developmental Mechanism and Distribution Pattern of Stomatal Clusters in Begonia peltatifolia

The function of stomata in plants is controlling gas exchange and modulating water balance. The distribution pattern of stomata in most vascular plants follows a certain regulation with at least one normal epidermal cell between two stomata. However, some plants restricted in several genera of vascular plants have stomatal clusters in which more than one stoma is adjacently arranged with no epidermal cells among them. The developmental process of stomatal clusters in plants, especially in non-mutant (wild type) vascular plants, has rarely been documented, and very few studies concerning the distribution pattern of stomatal clusters on leaf epidermis have been carried out. We reported the developmental mechanism and distribution pattern of stomatal clusters in Begonia peltatifolia Li native to China. The results indicated that the clustered arrangement of meristemoids at the juvenile stage of the leaf development contributed greatly to the pattern of stomatal clusters. Additionally, satellite meristemoids derived from subsidiary cells around the mature stomata also had an impact on the development as well as the pattern of stomatal clusters. Regarding stomatal cluster and singly occurring stoma both as a stomatal unit, we found that the stomatal unit density (i.e., number of stomatal unit per area) increased gradually from the middle part to the edge and the apex of the leaf, while stomatal unit size (i.e., number of stomata per stomatal unit) decreased. The possible reason of this pattern was discussed.

Dysplasia in perforated intestinal pneumatosis complicating a previous jejuno-ileal bypass:A cautionary note

We present the case of an elderly woman who developed a bowel perforation related to pneumatosis intestinalis, 33 years after a jejuno-ileal bypass for severe obesity. Final histological examination revealed the presence of dysplasia in the resected specimen. On the basis of our case and a review of the literature, we discuss the etiopathogenesis, the clinical aspects and the treatment of this rare condition.

Response of coal reservoir porosity to magma intrusion in the Shandong Qiwu Mine,China

The Qiwu Mine is located in the Ten Xian coal field of Shandong province.It experienced repeated volcanic activity,after the coal beds formed,where magma intrusion was significant The effect of coal reservoir porosity after magma intrusion was studied by analysis of regional and mine structure and magmatic activity.Experimental methods including maceral measurement under the microscope and mercury porosimetry were used for testing the pore structure.The authors believe that magma intrusion into low-rank bituminous coal causes reservoir porosity to gradually increase：the closer to the magmatic rock a sample is,the less the porosity.The pore size distribution also changes.In the natural coal bed the pore size is mainly in the transitive and middle pore range.However,the coal changes to anthracite next to the magmatic rock and larger pores dominate.Regional magma thermal evolution caused coal close to magmatic rock to be roasted,which reduced the volatile matter,developed larger holes,and destroyed plant tissue holes.The primary reason for a porosity decrease in the vicinity of magmatic rock is that Bituminite resulting from the roasting fills the holes that were present initially.

Air-entrained Concrete： Relationship between Thermal Conductivity and Pore Distribution Analyzed by X-Ray Tomography

The thermal conductivity values of ordinary concrete can be adjusted to those prescribed in constructions by entraining air bubbles to reduce the density of concrete in order to achieve good thermal insulation. This paper concerns the analysis of air bubble distribution in concrete obtained by micro X-ray μCT （computed tomography） and correlates it with its thermal conductivity （k）. The samples were prepared of ordinary concrete varying the density by air-entraining additives, ranging between 2,277 kg/m3 and 1,779 kg/m3, aiming to correlate the mechanical properties and k with the characteristics of the bubble distribution. The results show that air-entrainment leads to viable use of this material as sealer to achieve good thermal insulation, and it can be adjusted, but there seems to be a limit to air entraining. By analysis of the μCT images, it was possible to correlate the more quantity of bubbles of smaller diameter with the minor k, in dry or wet state, and to prove that there is a limit in the entrapped air content, and if it is exceeded, the coalescence occurs.

Plant ontogenetic changes in vein and stomatal traits and their relationship with economic traits in leaves of three Mediterranean oaks

Aims We compared vein and stomatal traits of seedlings and adults of three Mediterranean Quercus species.Previous work suggests that gas-exchange rates tend to be higher at the seedling stage than in adults.Our objective was to determine whether vein and stomatal traits vary throughout whole-plant ontogeny in parallel with the changes in gas-exchange rates.We addressed the following alternative hypotheses:hypothesis 1—seedlings show higher vein and stomatal densities than adults;and hypothesis 2—seedlings have lower investments in vascular tissues to reduce construction costs.Methods Ten specimens from each growth stage were randomly sampled for each species in a location in central-western Spain.We measured mean stomatal and vein traits(size and number of stomata per unit of leaf area,vein density,vein volume,vein to epidermis distance),leaf mass per area and lamina thickness.Important Findings Minor vein density and vein volume per area increased with tree age,which seems inconsistent with the ontogenetic trends in gas-exchange rates.This discrepancy is in support of our hypothesis 2,and it suggests that,at the seedling stage,reducing investments in vascular tissues in benefit of maximizing growth rates is a priority.Larger interveinal distances in seedlings were compensated by smaller vein to epidermis distances.The thin leaves of the seedlings may thus constitute as a necessary trait for achieving shorter path length distances for the transport of water to evaporation sites without the need for a strong investment in costly vascular tissues.