Including gravity and wettability effects, a full analytical solution for the frontal flow period for 1D counter-current spontaneous
imbibition of a wetting phase into a porous medium saturated initially with non-wetting phase at initial wetting phase saturation
is presented. The analytical solution applicable for liquid–liquid and liquid–gas systems is essentially valid for the cases
when the gravity forces are relatively large and before the wetting phase front hits the no-flow boundary in the capillary-dominated
regime. The new analytical solution free of any arbitrary parameters can also be utilized for predicting non-wetting phase
recovery by spontaneous imbibition. In addition, a new dimensionless time equation for predicting dimensionless distances
travelled by the wetting phase front versus dimensionless time is presented. Dimensionless distance travelled by the waterfront
versus time was calculated varying the non-wetting phase viscosity between 1 and 100 mPas. The new dimensionless time expression
was able to perfectly scale all these calculated dimensionless distance versus time responses into one single curve confirming
the ability for the new scaling equation to properly account for variations in non-wetting phase viscosities. The dimensionless
stabilization time, defined as the time at which the capillary forces are balanced by the gravity forces, was calculated to
be approximately 0.6. The full analytical solution was finally used to derive a new transfer function with application to
dual-porosity simulation. 相似文献
Population pressure increasingly endangers high-mountain ecosystems such as the pastures in the Eastern Pamirs and the mountain forests on Mt. Kilimanjaro. At the same time, these ecosystems constitute the economic basis for millions of people living there. In our study, we, therefore, aimed at characterising the land-use effects on soil degradation and N-cycling by determining the natural abundance of (15)N. A short review displays that δ(15)N of plant-soil systems may often serve as an integrated indicator of N-cycles with more positive δ(15)N values pointing towards N-losses. Results for the high-mountain pastures in the Eastern Pamirs show that intensively grazed pastures are significantly enriched in (15)N compared to the less-exploited pastures by 3.5 ‰, on average. This can be attributed to soil organic matter degradation, volatile nitrogen losses, nitrogen leaching and a general opening of the N-cycle. Similarly, the intensively degraded savanna soils, the cultivated soils and the soils under disturbed forests on the foothill of Mt. Kilimanjaro reveal very positive δ(15)N values around 6.5 ‰. In contrast, the undisturbed forest soils in the montane zone are more depleted in (15)N, indicating that here the N-cycle is relatively closed. However, significantly higher δ(15)N values characterise the upper montane forest zone at the transition to the subalpine zone. We suggest that this reflects N-losses by the recently monitored and climate change and antropogenically induced increasing fire frequency pushing the upper montane rainforest boundary rapidly downhill. Overall, we conclude that the analysis of the (15)N natural abundance in high-mountain ecosystems is a purposeful tool for detecting land-use- or climate change-induced soil degradation and N-cycle opening. 相似文献
Population pressure increasingly endangers high-mountain ecosystems such as the pastures in the Eastern Pamirs and the mountain forests on Mt. Kilimanjaro. At the same time, these ecosystems constitute the economic basis for millions of people living there. In our study, we, therefore, aimed at characterising the land-use effects on soil degradation and N-cycling by determining the natural abundance of 15N. A short review displays that δ15N of plant–soil systems may often serve as an integrated indicator of N-cycles with more positive δ15N values pointing towards N-losses. Results for the high-mountain pastures in the Eastern Pamirs show that intensively grazed pastures are significantly enriched in 15N compared to the less-exploited pastures by 3.5 ‰, on average. This can be attributed to soil organic matter degradation, volatile nitrogen losses, nitrogen leaching and a general opening of the N-cycle. Similarly, the intensively degraded savanna soils, the cultivated soils and the soils under disturbed forests on the foothill of Mt. Kilimanjaro reveal very positive δ15N values around 6.5 ‰. In contrast, the undisturbed forest soils in the montane zone are more depleted in 15N, indicating that here the N-cycle is relatively closed. However, significantly higher δ15N values characterise the upper montane forest zone at the transition to the subalpine zone. We suggest that this reflects N-losses by the recently monitored and climate change and antropogenically induced increasing fire frequency pushing the upper montane rainforest boundary rapidly downhill. Overall, we conclude that the analysis of the 15N natural abundance in high-mountain ecosystems is a purposeful tool for detecting land-use- or climate change-induced soil degradation and N-cycle opening. 相似文献
The mutual influence between anion–π and chalcogen bond interactions is studied by ab initio calculations at the MP2/6-311++G** level of theory. These effects are analysed in detail in terms of the structural, energetic, charge-transfer and electron density properties of the complexes. Interesting cooperativity effects are found when anion–π and chalcogen-bonding interactions coexist in the same complex. The effect of anion–π on the properties of chalcogen bonding is larger than that of chalcogen bonding on the properties of anion–π. The cooperative mechanism is analysed in terms of the electrostatic potentials, orbital interaction and electron density analysis. 相似文献
The main objective of investigation was to study the effect of pulsating electrospray of high viscous and non-Newtonian sodium alginate on mono-dispersity of droplets. In the jet mode, employing the pulsating DC electric field at a critical frequency led to narrow size distribution of beads, produced from the droplets. Above the critical frequency, the size of beads was distributed over a wider range. The relationship between the dimensionless group representing diameter and the groups including: Weber, Reynolds, Electric Field and Frequency numbers was modeled according to genetic algorithm. The experimental results were found in good agreement with the model. 相似文献
Wireless Personal Communications - In this paper, we consider a mixed dual-hop RF-FSO communication system, where RF link is subjected to Rice fading, while FSO link experience double generalized... 相似文献
Research on Chemical Intermediates - In this research, Co/Ca–Al2O3 composite as a heterogeneous nanocatalyst was synthesized by the co-precipitation method. The effect of Ca addition on the... 相似文献
Among the proposed models for land mobile satellite (LMS) channels, the shadowed Rice model proposed originally by Loo, has
found wide applications in different frequency bands. In Loo’s model, it is assumed that the received signal is affected by
nonselective Rice fading with lognormal shadowing on the direct component only, while the diffuse scattered component has
constant average power level. The resulting composite probability density function (PDF) includes an infinite-range integral
and is not available in closed-form, thereby making the performance evaluation of LMS communication links in these channels
cumbersome. To bypass this problem, in this paper an approximation method is developed which makes it possible to describe
the envelope PDF as a sum of weighted Rice’s PDFs. Therefore, in contrast with Loo’s PDF, the proposed method leads to an
easy-to-use, closed-form approximate expression for the PDF and also for the most statistical characteristics, such as cumulative
distribution function and moments of the signal envelop in shadowed Rice channels. Based on the derived expressions, the performance
analysis of a single receiver operating over lognormally shadowed Rice channel is investigated in terms of the outage probability.
Numerically evaluated results show the good accuracy of the proposed approximation method. 相似文献
EIS (electrolyte-insulator-semiconductor) sensors based on the functionalization of uncoated gold nanoparticles supported on a Si/SiO2 structure are presented. Oxygen plasma etching at moderate power (<200 W) provides a convenient and efficient way to remove organic capping agents from the gold nanoparticles without significant damage. Higher power intensities destroy the linkage between the SiO2 and the gold nanoparticles, and some of the gold nanoparticles are removed from the surface. The flat-band potential shift, i.e. the pH dependence of the gold-coated EIS sensors is similar (33 mV/pH) to the uncoated EIS pH-sensor. Lead, penicillin and glucose sensors were prepared by immobilization of β-cyclodextrin, penicillinase and glucose oxidase by various immobilization techniques.