农村小水电发电机干燥技术探讨

对农村小水电站高低压机组抢修中的干燥方法和技术作了较全面的分析和归纳,尤其对高等级绝缘发电机的干燥技术作了较详细的说明,可作为农村新建、老电站灾后(或受潮后)机组抢修时参考。     

Comparison of the desiccation effects of marine and freshwater diatomaceous earths on insects

The desiccating effects of two different types of diatomaceous earths (DEs), of freshwater and marine origin, applied by two different methods, were compared on four species of insects, Cryptolestes ferrugineus, Rhyzopertha dominica, Sitophilus oryzae and Sitophilus granarius. The purpose was to investigate the performance of DEs, including their abrasive and absorptive effects through the accumulation of silica dusts on the insect cuticle, resulting in death of the insects by desiccation. The data obtained showed that similar insects treated with the same type of diatom, but applied either by spraying or dusting, did not have the same initial mortality rate.

After examining and comparing the data obtained, it appeared that weight loss at death of insects subjected to the action of sprayed DEs was slightly less than for insects subjected to dust application, while mortality was slightly more rapid during the observation period. The extra weight of dusted insects was ascribed to greater adherence of dust particles to the treated insects.     

Influence of silica fume on the desiccation cracks of compacted clayey soils

Clayey soils containing smectites are widely used for construction of liner and cover systems to reduce the hydraulic conductivity in geotechnical applications because of their low permeability and high cation exchange capacity. However, the compacted clayey soils crack on drying because of their high swelling potential, and their hydraulic conductivities increase. To solve this problem, it is essential to stabilize the clayey soils using additive materials. The aim of this study is to examine the suitability of silica fume as a stabilization material to reduce the development of desiccation cracks in compacted clayey liner and cover systems. Natural clayey soil and clayey soil–silica fume mixtures were compacted at the optimum moisture content and subjected to laboratory tests. The results show that silica fume decreases the development of desiccation cracks on the surface of compacted samples. We concluded that silica fume waste material can be successfully used to reduce the development of desiccation cracks in compacted clayey liner and cover systems.     

考虑基底起伏的土体失水开裂动态过程试验研究

土体失水开裂会导致大量的工程和环境问题。利用失水收缩性强的膨润土,进行了土体失水开裂特征试验。研究表明土体失水开裂过程可划分为开裂前Ⅰ、快速开裂Ⅱ、开裂趋于停滞Ⅲ 3个阶段,裂缝发育演化中受到了模型边界和基底起伏的显著影响。在快速开裂阶段Ⅱ前期裂缝主要发育在模型的角部,后期裂缝主要在基底起伏影响范围内发育。在Ⅲ阶段,尽管表面开裂仍在发生,裂缝发育的整体格局已经不再发生显著变化。从裂缝形态看,后期裂缝与前期裂缝主要呈现为垂直相交,特别是在起伏区范围内。     

Effect of prehydration,permeant, and desiccation on GCL/Geomembrane interface transmissivity

A laboratory investigation was conducted on two different conventional GCLs (one with fine granular and another one with powdered bentonite) to explore the effect of prehydration and permeant fluid; GCL desiccation on the interface transmissivity, θ, between the interfaces of a 1.5 mm-thick high-density polyethylene (HDPE) geomembrane (GMB) and a GCL. The study also aimed to assess the self-healing capacity of desiccated GCLs for three different permeant solutions under a range of applied stresses (10–150 kPa). It was found that at stresses less than 70 kPa, θ was dominated by variability in the initial contact condition between the GMB-GCL interfaces. The effect of other factors was largely masked by the contact variability. At 100–150 kPa, the effects of initial variability were largely eliminated, but there was no notable effect of other factors on θ in the absence of desiccation. GCL desiccation increased θ by up to three orders of magnitude than an intact specimen at 10–100 kPa. Even at 150 kPa, desiccated specimens had a θ ≤ 8.0 × 10⁻⁹ m²/s for all specimens tested. The chemical composition of the permeant solutions, crack width, and nature of bentonite could play an important role in healing the cracks of desiccated GCLs.     

关于引黄南干1￣#洞混凝土裂缝的分析

山西省万家寨引黄工程南干１＃隧洞在贯通后仅１４ｄ就出现了裂缝。这对于绝大多数处于地下的引黄工程来说虽然是个特例，但随着今后地面工程的依次展开，混凝土早期表面保护问题应当引起重视。本文以实测资料为依据，对导致温度裂缝发生的各个方面原因作了分析。为此，期待围绕这一问题的种种歧见得以廓清。     

微波对物料微结构的影响

本文介绍了微波加热在陶瓷烧结、木材干燥、食品膨化、超细粉体干燥等过程中对物料微结构的影响。指出，微波加热具有抑制微结构垮塌、膨化食品微结构、抑制纳米粒子团聚等作用。认为微波加热可为纳米粉体干燥和纳米材料制备提供一种潜在处理方法。应当充分研究微细粒子传热传质特性和物料微细粒子介电行为，从而深入认识微波加热对物料微结构的影响。     

Changes in culturability and virulence of Salmonella typhimurium during long-term starvation under desiccating conditions

The survival of Salmonella typhimurium under desiccation and starvation conditions commonly associated with farm buildings was investigated in a desiccation model system: filtration onto polycarbonate membranes placed in a sealed desiccator with 0.0067 g/m³ absolute humidity. Heterogeneities within bacterial populations in relation to time of desiccation were investigated on a single-cell basis by epifluorescence microscopy coupled with an image analysis system in conjunction with fluorescent dyes Chemchrome V6 and DAPI. Changes in cellular states were compared to the results of plate counts (colony forming units, CFU) on selective (modified semi-solid Rappaport Vassiliadis (MSRV)) and non-selective (nutrient agar (NA) and R2A agar) media, and to the measurements of infectivity and virulence using two animal models (chicks and mice). During 9 weeks of experimental desiccation, total cell counts (DAPI) of starved S. typhimurium remained stable, as did esterase activity (Chemchrome V6), but DAPI fluorescence intensity decreased slowly. Bacterial cells entered gradually into non-culturable states (decrease of CFU counts on MSRV, NA and R2A agar media) and the total loss of culturability on NA (defined as probability of presence of 1 CFU on the membrane inferior to 10⁻⁶) was obtained after 9 weeks. Loss of chick infectivity and mice virulence in animal models occurred more rapidly, within three weeks of experimental desiccation.     

Measuring desiccation-induced tensile stress during cracking process

The desiccation cracking of soil occurs when shrinkage is restricted during the drying process and the induced tensile stress equals the tensile strength. Thus far, experimental estimations of the tensile stress of soil have not been realized, although such estimates are important for predicting crack initiation. This study presents the development of a laboratory-based desiccation stress test to measure the tensile stress generated during the drying process until crack initiation. In this proposed desiccation stress test, the tensile stress is induced during the drying process in the longitudinal direction of bar-shaped specimens with fixed ends. Desiccation stress tests were performed on sandy soil with a rich fine fraction, and the results were verified through photographic observations of crack initiation and comparisons with the results of direct tension tests. The results show that the desiccation stress test yields reliable tensile stress until cracking. The application of the desiccation test results is illustrated via the verification of an existing model of crack initiation by desiccation. The results of the desiccation stress tests are useful for determining the model parameters that significantly influence the development of tensile stress and enable its accurate prediction until crack initiation.     

Temporal Characteristics of Desiccation Cracking and Resistivity of Lateritic Soil in Drying Process

To describe and measure the initiation and development of desiccation cracks in lateritic soil and to discuss the relationship between crack ratio and resistivity, three parallel specimens are prepared and dried under different temperatures and humidity. The geoelectrical resistivity technique combined with image processing method is applied. Water content, surface crack ratio, and electrical resistivity are monitored during the drying path. Results indicate that the calculated surface crack ratios can be identified on the basis of five distinct stages. The occurrence of the first crack in three specimens indicates that the first cracking time occurs earlier with increasing temperature and decreasing relative humidity. The time that crack ratios stabilize indicates that environmental parameters significantly influence crack evolution. The temporal characteristics of resistivity can also be identified on the basis of five distinct stages. The resistivity and crack ratio can be effectively described by a mathematical equation, which is considered as the basis for the use of the geoelectrical technique for the assessment of the temporal variability of soil desiccation cracking.