Construction of molecule-selective mixed matrix membranes with confined mass transfer structure

Extraordinary mass transfer phenomenon is usually found when the small molecules pass through a confined structure, whose effective size is commensurate with the mean free path of the molecules. Small changes in the confined mass transfer structure (including size, morphology and properties) will lead to significant fluctuations of the mass transfer coefficient. The mass transfer of the penetrant molecules in the dense membranes for pervaporation, gas separation and so on, is located in the scope of confined mass transfer. Incorporating nanofillers into polymer matrix to construct mixed matrix membranes (MMMs) is an effective approach to tune the confined mass transfer structure and enhance the performance of the widely used polymeric membranes. This reviewfocuses on the construction andmanipulation of the confined structure in the polymeric membranes via incorporating one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) fillers.The comparison of the MMMs for pervaporation is summarized, and the research prospective of the MMMs is provided.     

Second generation anticoagulant rodenticides in tawny owls (Strix aluco) from Great Britain

Secondary exposure of vertebrate predators to second generation anticoagulant rodenticides (SGARs) is widespread in Britain. Tawny owl (Strix aluco) populations in the UK are thought to have declined since the 1970s, when SGARs were first introduced, and these compounds may have contributed to any decline in owl numbers. Our aims were to conduct the first systematic survey of SGAR exposure in tawny owls and ascertain whether there had been a change in the proportion of exposed birds that was concurrent with the decline in the population. Liver difenacoum, bromadiolone, flocoumafen and brodifacoum concentrations in British tawny owls from two periods (1990-1993 and 2003-2005) were quantified. In total, some 20% of birds contained detectable residues of one or more SGAR. The extent of exposure (% of birds exposed, magnitude of residues) to different SGARs did not change consistently between time periods. Of the raptors analysed to date in Britain, tawny owls had the lowest proportion of individuals that contained detectable liver residues and so appear to be the least vulnerable to exposure and/or assimilation of SGARs. We found no clear evidence to implicate SGARs as a major factor affecting tawny owl numbers in Britain between 1990 and 2005.     

A Review of the 1995–96 Drought in the North West

As environmental regulator, the Environment Agency seeks the best balance between essential needs of water supply and the environment, whilst taking into account costs and benefits; nowhere is this balance more focused than in the management of droughts. The drought of 1995–96 was the most severe on record in the North West, and presented a major challenge to both the water company and the Environment Agency in safeguarding essential water supplies and minimizing the risks to the environment.
This paper describes the management of the drought from the Agency's perspective.     

Reversible end-to-end assembly of gold nanorods using a disulfide-modified polypeptide

Directing the self-assembly of colloidal particles into nanostructures is of great interest in nanotechnology. Here, reversible end-to-end assembly of gold nanorods (GNR) is induced by pH-dependent changes in the secondary conformation of a disulfide-modified poly(L-glutamic acid) (SSPLGA). The disulfide anchoring group drives chemisorption of the polyacid onto the end of the gold nanorods in an ethanolic solution. A layer of poly(vinyl pyrrolidone) is adsorbed on the positively charged, surfactant-stabilized GNR to screen the surfactant bilayer charge and provide stability for dispersion of the GNR in ethanol. For comparison, irreversible end-to-end assembly using a bidentate ligand, namely 1,6-hexanedithiol, is also performed. Characterization of the modified GNR and its end-to-end linking behavior using SSPLGA and hexanedithiol is performed using dynamic light scattering (DLS), UV-vis absorption spectroscopy and transmission electron microscopy (TEM). Experimental results show that, in a colloidal solution of GNR-SSPLGA at a pH～3.5, where the PLGA is in an α-helical conformation, the modified GNR self-assemble into one-dimensional nanostructures. The linking behavior can be reversed by increasing the pH (>8.5) to drive the conformation of the polypeptide to a random coil and this reversal with pH occurs rapidly within minutes. Cycling the pH multiple times between low and high pH values can be used to drive the formation of the nanostructures of the GNR and disperse them in solution.     

Two-dimensional simulations of bulk heterojunction solar cell characteristics

We present a two-dimensional model of a bulk heterojunction solar cell in which we include the effects of optical interference, exciton diffusion, charge separation via the formation of polaron pairs, and charge transport in two separate interpenetrating phases. Our model shows that the current is increased by an order of magnitude with a full optical model compared to assuming that absorbed photons have a Lambertian profile, and depends much more strongly on applied bias when dissociation via polaron pairs is considered. We find a power efficiency at solar intensities of 1-3% depending on the morphology, and show that the fill factor decreases from 40% at low intensities to 20% at solar intensities because of the increase in the open circuit voltage and decreases much more rapidly at higher intensities due to the decrease in the power efficiency.     

FRP包裹钢筋混凝土柱抗震加固的耐久性设计

虽然FRP材料已经越来越多地被采用在土木建设方面,但依然缺乏长期的耐久性试验数据,以及在结构水平上的明确的、长期劣化设计理论方法。针对一组试验数据,在材料水平上评定了FRP护套抗震计算的长期劣化标准。共测试了三种不同的系统,快速试验结果被用于材料长期性能的预测,以此分析在四种特殊工况下抗震加固的效果。显而易见,劣化的影响可用预期寿命对应的包裹厚度的增长值来表达。将结果与ACI-440的推荐值以及随时间变化的材料劣化模型结果进行比较,表明ACI的失效推荐值在考虑50年周期时有些保守。通过采用前面所提到的材料耐久性预测方法和FRP防护层厚度设计分析工具,不仅能够更好地对防护层厚度进行估算,而且可以对选择防护层厚度的主要控制机理进行评定。其中,防护层厚度随着暴露时间的长短而改变。快速试验的结果与自然露天测试结果的关系可以用一系列相关的系数来表达。     

A simplified model for estimating population-scale energy impacts of building envelope air tightening and mechanical ventilation retrofits

Changing the air exchange rate of a home affects the annual thermal conditioning energy. Large-scale changes to air exchange rates of the housing stock can significantly alter the residential sector's energy consumption. However, the complexity of existing residential energy models is a barrier to the accurate quantification of the impact of policy changes on a state or national level. The Incremental Ventilation Energy (IVE) model introduced here combines the output of simple air exchange models with a limited set of housing characteristics to estimate the associated change in energy demand of homes. The IVE model was designed specifically to enable modellers to use existing databases of housing characteristics to determine the impact of ventilation policy change on a population scale. The IVE model estimates of energy change when applied to US homes with limited parameterization are shown to be comparable to the estimates of a well-validated, complex residential energy model.     

A Nonparametric Model for Stationary Time Series

Stationary processes are a natural choice as statistical models for time series data, owing to their good estimating properties. In practice, however, alternative models are often proposed that sacrifice stationarity in favour of the greater modelling flexibility required by many real‐life applications. We present a family of time‐homogeneous Markov processes with nonparametric stationary densities, which retain the desirable statistical properties for inference, while achieving substantial modelling flexibility, matching those achievable with certain non‐stationary models. A latent extension of the model enables exact inference through a trans‐dimensional Markov chain Monte Carlo method. Numerical illustrations are presented.     

High-contrast plasma-electrode Pockels cell

A plasma-electrode Pockels cell (PEPC) has been developed for use on the OMEGA extended performance (EP) laser system that can be used in a high-contrast optical switch, as required for isolation of the system from retroreflected pulses. Contrast ratios reliably exceeded 500:1 locally everywhere in the clear aperture. The key to achieving this improvement was the use of circular windows simply supported on compliant O rings, which is shown to produce very low stress-induced birefringence despite vacuum loading. Reliable operation was achieved operating at a relatively high operating pressure, low operating pressures being found to be strongly correlated to occurrences of local loss of plasma density.