Analytical evaluation of steady-state solute distribution in through- diffusion and membrane behavior test under non-perfectly flushing boundary conditions

The through-diffusion and membrane behavior testing procedure using a closed-system apparatus has been widely used for concurrent measurement of diffusion and membrane efficiency coefficients of low-permeability clay-based barrier materials.However,the common assumption of perfectly flushing conditions at the specimen boundaries could induce errors in analyses of the diffusion coefficients and membrane efficiencies.In this study,an innovative pseudo three-dimensional(3D)analytical method was proposed to evaluate solute distribution along the boundary surfaces of the soil-porous disks system,considering the non-perfectly flushing conditions.The results were consistent with numerical models under two scenarios considering different inflow/outflow positions.The proposed model has been demonstrated to be an accurate and reliable method to estimate solute distributions along the bound-aries.The calculated membrane efficiency coefficient and diffusion coefficient based on the proposed analytical method are more accurate,resulting in up to 50%less relative error than the traditional approach that adopts the arithmetic mean value of the influent and effluent concentrations.The retar-dation factor of the clay specimen also can be calculated with a revised cumulative mass approach.Finally,the simulated transient solute transport matched with experimental data from a multi-stage through-diffusion and membrane behavior test,validating the accuracy of the proposed method.

Numerical simulation based on two-directional freeze and thaw algorithm for thermal diffusion model

Freeze-thaw processes significantly modulate hydraulic and thermal char- acteristics of soil. The changes in the frost and thaw fronts （FTFs） affect the water and energy cycles between the land surface and the atmosphere. Thus, the frozen soil com- prising permafrost and seasonally frozen soil has important effects on the land surface hydrology in cold regions. In this study, a two-directional freeze and thaw algorithm is incorporated into a thermal diffusion equation for simulating FTFs. A local adaptive variable-grid method is used to discretize the model. Sensitivity tests demonstrate that the method is stable and FTFs can be tracked continuously. The FTFs and soil tempera- ture at the Qinghai-Tibet Plateau D66 site are simulated hourly from September 1, 1997 to September 22, 1998. The results show that the incorporated model performs much better in the soil temperature simulation than the original thermal diffusion equation, showing potential applications of the method in land-surface process modeling.

Durability problems of lining structures for Xiamen Xiang'an subsea tunnel in China

Durability problem of reinforced concrete for underground structures is a hot issue in the field of structural engineering. For underground structures, the prediction of structural service life and methodology for durability design are needed to estimate structural durability. Taking the case of Xiamen Xiang＇an subsea tunnel as background, which is designed to meet the requirement of lO0-year service life, the influential factors on tunnel lining durability are analyzed. Under the criteria of crack controlling and bearing capacity of linin~ structures, the theoretical service life of Xiamen Xiang＇an subsea tunnel lining is studied. The regulations, which are needed for the diffusion capability of chloride ions in concrete by the relevant diffusion tests, are proposed. After a quick corrosion test, the bearing capacity test on eccentric short columns is implemented to investigate the variation rules in the bearing capacity of models with time. Influence of the corrosion degree of steel bars on the bearing capacity of models is also investigated. Based on the results of model tests, the acceleration ratio between the quick corrosion in laboratory test and the natural corrosion environments is established. Thus, the natural service life of subsea tunnel lining structures can be obtained by means of laboratory tests. Then, the proposed method using this modified model is employed to predict the service life of tunnel lining structures. Finally, the design and construction measures for improving the durability of lining structures of subsea tunnel are introduced. The proposed method in the present study based on a real engineering project is superior to those with only theoretical assumptions, and would be more suitable for similar projects.

Antibacterial activity of honey in north-west Pakistan against select human pathogens

OBJECTIVE:To investigate the antimicrobial activity of commercially available honey and raw honey samples in Khyber Pakhtunkhwa,Pakistan,against pathogenic bacterial strains.METHODS:Well diffusion assays were performed to screen pure and diluted honey samples for antibacterial activity against six Gram-negative and six Gram-positive bacterial strains.Zones of inhibition were measured and compared with 10 mg Gentamycin.RESULTS:When honey samples were diluted to20%-70%,the honey samples showed no activity to mild antibacterial activity.The highest antibacterial activity was recorded when 90%and pure undiluted honey samples were tested and compared with a control Gentamycin disc(10 mg).CONCLUSION:Commercially processed honey and raw honey samples from north-west of Pakistan possess good antimicrobial potential.