A model for the complex permittivity of water at frequencies below 1 THz

Experimental permittivity data of liquid water, compiled from the open literature, were selectively applied to support a modeling strategy. Frequencies up to 1 THz and atmospheric temperatures are covered with an expression made up by two relaxation (Debye) terms. The double-Debye model reduces to one term when the high frequency limit is set at 100 GHz, and the model can be extended to 30 THz by adding two resonance (Lorentzian) terms. The scheme was carried out by employing nonlinear least-squares fitting routines to data we considered reliable.     

Exploring the future impacts of urbanization and climate change on groundwater in Arusha,Tanzania

ABSTRACT

We combine satellite imagery, urban growth modelling, groundwater modelling and hydrogeological field expeditions to estimate the potential impacts in 2050 of rapid urbanization and climate change on groundwater in Arusha, Tanzania, and by extension similar areas in Sub-Saharan Africa. Our analysis suggests that a reduction of groundwater recharge by 30–44% will cause groundwater levels to drop by up to 75 m, mainly due to increased evapotranspiration and to an expansion in paved surface. If this scenario becomes reality, we predict that wells will run dry, creating health, social and environmental risks.     

The challenge of predicting spinnability: Investigating benefits of adding lignin to cellulose solutions in air-gap spinning

In this study, the underlying mechanism for improved spinnability when mixing lignin and cellulose in solution was investigated. Co-processing of lignin and cellulose has previously been identified as a potential route for production of inexpensive and bio-based carbon fibers. The molecular order of cellulose contributes to the strength of the fibers and the high carbon content of lignin improves the yield during conversion to carbon fibers. The current work presents an additional benefit of combining lignin and cellulose; solutions that contain both lignin and cellulose could be air-gap spun at substantially higher draw ratios than pure cellulose solutions, that is, lignin improved the spinnability. Fibers were spun from solutions containing different ratios of lignin, from 0 to 70 wt%, and the critical draw ratio was determined at various temperatures of solution. The observations were followed by characterization of the solutions with shear and elongational viscosity and surface tension, but none of these methods could explain the beneficial effect of lignin on the spinnability. However, by measuring the take-up force it was found that lignin seems to stabilize against diameter fluctuations during spinning, and plausible explanations are discussed.     

The Pupal Parasitoid Trichopria drosophilae Is Attracted to the Same Yeast Volatiles as Its Adult Host

Journal of Chemical Ecology - There is increasing evidence that microorganisms, particularly fungi and bacteria, emit volatile compounds that mediate the foraging behaviour of insects and therefore...     

Partition Into Triangles on Bounded Degree Graphs

We consider the Partition Into Triangles problem on bounded degree graphs. We show that this problem is polynomial-time solvable on graphs of maximum degree three by giving a linear-time algorithm. We also show that this problem becomes $\mathcal{NP}$ -complete on graphs of maximum degree four. Moreover, we show that there is no subexponential-time algorithm for this problem on graphs of maximum degree four unless the Exponential-Time Hypothesis fails. However, the Partition Into Triangles problem on graphs of maximum degree at most four is in many cases practically solvable as we give an algorithm for this problem that runs in $\mathcal{O}(1.02220^{n})$ time and linear space.     

Elimination and accumulation of polycyclic aromatic hydrocarbons in urban stormwater wet detention ponds

The concentrations of polycyclic aromatic hydrocarbons (PAHS) in water and sediments of seven wet detention ponds receiving urban stormwater were investigated. The ponds comprised traditional wet detention ponds with a permanent wet volume and a storage volume as well as ponds that were expanded with sand filters and other means to improve the removal of micropollutants. The concentrations of sigmaPAH in the sediments varied between 6 +/- 5 and 2,222 +/- 603 ng g(-1) dry weight (mean +/- standard deviation), and were highest in the ponds with lower pond volume per catchment area and did not clearly reflect different activities in the catchments. In general, the concentrations of PAHS in the sediments decreased from inlet to outlet, especially in the systems with good conditions for sedimentation such as systems with flow perpendicular sand dikes and extensive submerged vegetation. High molecular weight PAHs were predominant in the sediments indicating the pyrogenic origin of the PAHS. There was no correlation between PAH species concentrations in water or sediments and their hydrophobicity (log K(ow)). PAH concentrations in water fluctuated in response to intensity and frequency of rain events, whereas concentrations in the sediments integrated the pollutant load over time. Pond systems expanded with sand filters and other technologies to enhance removal of micropollutants consistently had concentrations of PAHS in the effluents below the detection level.     

基于中子成像的水泥基材料毛细吸水动力学研究

总结了国内外有关水泥基材料毛细吸水的动力学机理及其现有模型,应用中子成像技术对其毛细吸水过程进行了可视化再现,对水分侵入的空间分布规律进行了定量分析。结果表明,在毛细孔吸附力作用下,水分前锋不断向水泥基材料内部推进,在吸水初期速度较快,后趋于平缓直至稳定;水分侵入曲线在深度和含量上同时增 长,可以由线性+反S形模型来描述其空间分布特点,并与实测结果吻合良好;现有的 “时间开方” 及其修正模型对毛细吸水的后期预测不太合理,本文提出的渗透系数双曲线衰减模型更符合真实结果。     

Matrix Interpretations for Proving Termination of Term Rewriting

We present a new method for automatically proving termination of term rewriting. It is based on the well-known idea of interpretation of terms where every rewrite step causes a decrease, but instead of the usual natural numbers we use vectors of natural numbers, ordered by a particular nontotal well-founded ordering. Function symbols are interpreted by linear mappings represented by matrices. This method allows us to prove termination and relative termination. A modification of the latter, in which strict steps are only allowed at the top, turns out to be helpful in combination with the dependency pair transformation. By bounding the dimension and the matrix coefficients, the search problem becomes finite. Our implementation transforms it to a Boolean satisfiability problem (SAT), to be solved by a state-of-the-art SAT solver.