Consequences of different cutting regimes on regrowth and nutrient stoichiometry of Sparganium erectum L. and Potamogeton natans L.

Aquatic vegetation forms an essential component in freshwater ecosystems but due to changed environmental and anthropogenic conditions often needs management to reduce nuisance for human land‐use. In this paper, the authors looked at the regrowth of two macrophyte species (Potamogeton natans and Sparganium erectum) in two lowland rivers under different cutting treatments. After an initial cross‐sectional transect was manually removed from bank to bank at the beginning of the growth season, a monthly repetitive removal of biomass in plots on that transect was done during the rest of the growth season (testing frequency of mowing). Additional new transects were also cut in subsequent months (testing timing of mowing). Finally, biomass was repetitively removed in plots in those additional transects too (testing frequency of mowing × timing of mowing). The biomass at the end of the growth season was analysed for C, N, P, and Si. It was demonstrated that timing and frequency of vegetation cutting has an important effect on the capacity and rate of species' recovery and therefore on the efficiency of the applied management. Nutrient stoichiometry of the regrown biomass was directly affected by cutting. Caused by differences in the applied timing and frequency of the cutting, C/N and N/P ratios and BSi concentrations were highly variable. Yet, overall, there was a clear tendency towards a higher C/N ratio and BSi concentration and lower N/P ratio in biomass that recovered after cutting. This human impact on the quantity and quality of autochthonous organic matter may have knock‐on effects on the decomposers food web and mineralization process.     

Kinetics of the methanation of carbon dioxide over a supported Ni-La2O3 catalyst

The kinetics of the methanation of carbon dioxide was investigated using an alumina supported Ni-La₂O₂ catalyst in a differential and integral reactor. In the differential reactor the molar ratio of H₂ to CO₂ was varied from 0.6 to 30. In the integral reactor the rates were measured with up to 90% conversion. Both reactor tests were carried out at temperatures between 513 and 593 K. The experimental results were described by a Langmuir-Hinshelwood type equation. The kinetics can be explained by assuming equilibrium of dissociative carbon dioxide and hydrogen adsorption, and assuming hydrogenation of surface carbon as the rate determining step.     

Carbon Aerogels as Electrode Material in Supercapacitors

Due to their large specific surface area and their high electrical conductivity carbon aerogels are promising materials for electrodes in electrochemical double-layer capacitors (supercapacitor). The carbon aerogels were made via pyrolysis of resorcinol formaldehyde aerogels. The latter were prepared by supercritical and subcritical drying as well. The important findings of our investigation were, that the highest capacities of 46 F/cm³ were measured for samples with a density of about 800 kg/m³ pyrolyzed at 800°C. Also it was shown that RF-gels with molar resorcinol/catalyst ratios 1000 or higher can be dried subcritically without cracking or significant shrinkage. Carbon aerogels derived from these RF-aerogels have a small mesopore surface area, however an especially large micropore area. They provide electrical capacities which are most suitable for their use in supercapacitors.     

PVA-based activated carbon fibers with lotus root-like axially porous structure

A novel method was developed for the fabrication of activated carbon fiber (ACF) with wet spinning polyvinyl alcohol (PVA) fibers as the precursors. Through a combination of preoxidation, dehydration, carbonization and activation under a certain tension, PVA-based ACFs (PVA-ACFs) with high yields and good mechanical properties were obtained. The surface and cross-section morphologies, pore structures, surface geometries, surface functional groups and crystal structures of the PVA-ACFs were characterized using field emission scanning electron microscopy, low temperature nitrogen adsorption, Fourier transformed infrared spectrophotometry, X-ray photoelectron spectroscopy and X-ray power diffraction. All the PVA-ACF samples prepared had lotus root-like axially meso- and macroporous structures with the domination of micropores. Fractal geometries of PVA-ACFs deduced from nitrogen adsorption isotherms indicates that capillary force dominated in the interactions between nitrogen and the PVA-ACFs. The surface functional groups of the PVA-ACFs depend on the activating agents. Graphitoidal crystal structures were observed for the PVA-ACFs. The small crystal size and short range ordering between the crystallites ensured a high specific surface area of the PVA-ACFs.     

Chemical and Isotopic Tracer Evaluation of Water Mixing and Evaporation in a Dammed Texas River During Drought

The interaction between drought and river regulation is monitored to better understand river flow mixing, evaporation and surface‐groundwater exchange in changing regional climates and in increasingly regulated waterways. This study compared Brazos River stable isotope (δ¹⁸O and δD) and electrical conductivity values with reservoir, creek and aquifer samples in the Brazos watershed, the largest watershed in Texas. The combination of tributaries, rainfall and the Brazos River Alluvium Aquifer, on the one hand, and the Lake Whitney reservoir, on the other hand, represent endmembers of dilute run‐off water and evaporated saline water, respectively. A simple isotope mixing model that uses monthly river discharge, Lake Whitney discharge, historical monthly precipitation δ¹⁸O and pan evaporation accurately reconstructs river δ¹⁸O (±0.5‰ on average). Data and isotope balance modelling support continued evaporation of ¹⁸O‐enriched Lake Whitney water as it flows downstream, although the most evaporation took place in Lake Whitney. The difference between river and precipitation δ¹⁸O, or Δ¹⁸O_RIV‐_PPT, here a measurement of degree of evaporation, ranged from ?0.1‰ for a small creek, to 1.7‰ for the Brazos River, to at least 2.7‰ in Lake Whitney. This study indicates that drought in regulated rivers may enhance reservoir discharge dominance in river flows during peak drought conditions when combined run‐off and baseflow dominance would be expected in a similar undammed river. Copyright © 2016 John Wiley & Sons, Ltd.     

Carbonaceous adsorbents from sewage sludge and their application in a combined activated sludge-powdered activated carbon (AS-PAC) treatment

In this study, waste biological sludge is converted to an adsorbent by chemical activation with sulphuric acid. The adsorbent obtained is then applied to the aerated vessel of an activated sludge process treating glucose and phenol to improve the quality of the treated effluent. The sludge-based carbonaceous adsorbent was found to be mesoporous in nature, with a good adsorption capacity for large molecular weight compounds and limited removal efficiency for smaller molecules such as phenol. The addition of carbon, either sludge-based or commercial, enhanced phenol removal from 58% to 98.7% and from 87% to 93% the organic matter removal as measured by the chemical oxygen demand (COD) when operated with feed concentrations of 100 mg phenol/l and 2500 mg COD/l. No differences were found between the activated sludge-activated carbon bench scale continuous reactors operating with either commercial or sludge-based adsorbents in spite of the higher adsorption capacity of the former. It is suggested that powdered adsorbent bioregeneration in the combined AS-PAC system may be impaired by the obstruction of pores due to bacterial growth, the effect being more important for the commercial activated carbon with a narrower pore size distribution.     

碳纤维经氧等离子/KH550处理后的表面形态和结构

碳纤维(CF)表面经氧等离子、KH550和 LiAlH_4处理后,其物理和化学性能得以改善.由于提高了 CF 和树脂间的联结,使 CF 复合材料的层间剪切强度提高50%以上,在湿热下的强度保留率达94%以上.使用纤维接触角测定仪,SEM 和 XPS 等对 CF 表面的浸润性、形态和化学组成进行了研究.实验指出:CF 经等离子和 KH550处理后,其临界表面能有了提高;CF 本身仅受氧离子刻蚀,故其拉伸强度的损失小于其他处理方法.     

炭黑填充硬聚氯乙烯的改性

为使聚氯乙烯具有抗静电性能,采用加入具有导电性填料的方法,但加入大量的填料,会使硬聚氯乙烯的冲击性能降低,加工性能变差。本文是在以炭黑为填料的基础上,研究不同的改性剂和加工助剂改进硬聚氯乙烯的效果,结果表明,加入冲击改性剂和加工助剂后,大大增加了硬聚氯乙烯的冲击强度,且加工性能也得到改善,同时由于炭黑具有补强效果,其拉伸强度和弯曲强度在加入改性剂后也能满足使用要求。     

炭分子筛概述

阐述了炭分子筛分离的原理，并分别从其制备原料、制备方法、产品用途等方面综述了近年来炭分子筛的新进展。     

原子磁强计检测光闭环稳定系统设计

SERF态原子磁强计已实现人类历史上最高的0.16fT/Hz1/2的灵敏度。其检测方法主要是法拉第调制法。但法拉第调制法中光电流摄动或环境温度变化等干扰导致的检测光强的起伏会造成检测结果的不准确。为抑制检测光强起伏,设计了闭环原子磁强计检测光稳定系统。在法拉第调制法的基础上,增加了光路子系统和控制子系统对检测光强进行闭环稳定控制。通过对随机干扰进行闭环控制仿真与实验,验证本系统可以有效抑制各种干扰引起的光强起伏,使系统抗干扰能力提高1.2%,从而提高原子磁强计的检测精度。