Characterization of a major permeability barrier in the zebrafish embryo

Fish embryos represent a class of multicompartmental biological systems that have not been successfully cryopreserved, primarily because of the lack of understanding of how water and cryoprotectants permeate the compartments. We are using the zebrafish embryo as a model to understand these kinetics. Zebrafish embryos have two major compartments, the blastoderm and the yolk, which is surrounded by the multinucleated yolk syncytial layer (YSL). We determined the water and cryoprotectant permeability in these compartments using two methods. First, we measured shrink/swell dynamics in optical volumetric experiments. Zebrafish embryos shrank over time and did not re-expand while immersed in dimethyl sulfoxide (DMSO) or propylene glycol. Second, we measured DMSO uptake with diffusion-weighted nuclear magnetic resonance spectroscopy. DMSO uptake was rapid during the first few minutes, then gradual thereafter. We used one- and two-compartment models to analyze the data and to determine the permeability parameters. We found that the two-compartment model provided a better fit to the data. On the basis of this model and in the presence of DMSO, the yolk and blastoderm had very similar water permeabilities (i.e., 0.01 and 0. 005 micron x min-1atm-1, respectively), but they had different DMSO permeabilities separated by three orders of magnitude (i.e., 相似文献   

Mangrove forests as a nature-based solution for coastal flood protection: Biophysical and ecological considerations

Nature-based coastal protection is increasingly recognised as a potentially sustainable and cost-effective solution to reduce coastal flood risk. It uses coastal ecosystems such as mangrove forests to create resilient designs for coastal flood protection. However, to use mangroves effectively as a nature-based measure for flood risk reduction, we must understand the biophysical processes that govern risk reduction capacity through mangrove ecosystem size and structure. In this perspective, we evaluate the current state of knowledge on local physical drivers and ecological processes that determine mangrove functioning as part of a nature-based flood defence. We show that the forest properties that comprise coastal flood protection are well-known, but models cannot yet pinpoint how spatial heterogeneity of the forest structure affects the capacity for wave or surge attenuation. Overall, there is relatively good understanding of the ecological processes that drive forest structure and size, but there is a lack of knowledge on how daily bed-level dynamics link to long-term biogeomorphic forest dynamics, and on the role of combined stressors influencing forest retreat. Integrating simulation models of forest structure under changing physical (e.g. due to sea-level change) and ecological drivers with hydrodynamic attenuation models will allow for better projections of long-term natural coastal protection.     

Ethnic differences in realising desires to leave urban neighbourhoods

Selective mobility into and out of urban neighbourhoods is one of the main driving forces of segregation. Earlier research has found group differences in who wants to leave or who leaves certain types of neighbourhoods. A factor that has received little attention so far is that some residents will have a desire to leave their neighbourhood, but are unable to do so. If there are differences between population groups in the realisation of desires to leave the neighbourhood, this might lead to involuntary segregation. This paper uses a unique combination of register data and survey data. We combine data from a large housing survey in the Netherlands (WoON) with longitudinal register data from the Netherlands (SSD) which contains individual-level information on residential mobility histories. This allows us to study whether households with a desire to leave their neighbourhood do realise this desire and which households are successful in leaving which neighbourhoods. A more thorough insight in who wants to leave which neighbourhoods but is unable to do so will contribute to a better understanding of selective mobility and segregation. We find that ethnic minorities and low-income households are less likely to realise a desire to leave their neighbourhood. We expected that ethnic minorities would be especially unsuccessful in realising desires to leave minority concentration neighbourhoods; however, for none of the ethnic groups we found an effect of neighbourhood ethnic composition on the realisation of desires to leave.     

Neighbourhood Restructuring and Residential Relocation: Towards a Balanced Perspective on Relocation Processes and Outcomes

This introductory paper to this special issue of Housing Studies questions whether various characteristics of the debate and research on gentrification, displacement and restructuring justify a largely negative perspective on the processes and outcomes of ‘forced’ residential relocation. We argue that a proper and fuller consideration of issues around policy, context, process and outcomes enable researchers and commentators to avoid ready characterisations and self-fulfilling investigations of restructuring which serve to present it as a singular (and somewhat suspicious or conspiratorial) phenomenon. For this purpose, we present a broad conceptual framework for restructuring and relocation studies, based on these four themes. Subsequently, we review major issues in restructuring and gentrification discourses, and briefly reflect upon some of the factors underlying the negative loading of the term displacement. We also identify caveats in the evidence base of relocation studies, both in the United States and in Europe. Finally, we introduce the papers in this special issue. The overall aim of this issue is to offer a more open, balanced starting position for analysis of urban restructuring processes and relocation outcomes, particularly in relation to areas of social housing.     

Multi-level Modeling of Silica–Template Interactions During Initial Stages of Zeolite Synthesis

Zeolite synthesis is driven by structure-directing agents, such as tetrapropyl ammonium ions (TPA⁺) for Silicalite-1 and ZSM-5. However, the guiding role of these organic templates in the complex assembly to highly ordered frameworks remains unclear, limiting the prospects for advanced material synthesis. In this work, both static ab initio and dynamic classical modeling techniques are employed to provide insight into the interactions between TPA⁺ and Silicalite-1 precursors. We find that as soon as the typical straight 10-ring channel of Silicalite-1 or ZSM-5 is formed from smaller oligomers, the TPA⁺ template is partially squeezed out of the resulting cavity. Partial retention of the template in the cavity is, however, indispensable to prevent collapse of the channel and subsequent hydrolysis.

Is bioethanol a sustainable energy source? An energy-, exergy-, and emergy-based thermodynamic system analysis

Biofuels are widely seen as substitutes for fossil fuels to offset the imminent decline of oil production and to mitigate the emergent increase in GHG emissions. This view is, however, based on too simple an analysis, focusing on only one piece in the whole mosaic of the complex biofuel techno-system, and such partial approaches may easily lead to ideological bias based on political preference. This study defines the whole biofuel techno-system at three scales, i.e., the foreground production (A), the background industrial network (B, including A), and the supporting Earth biosphere (C, including B). The thermodynamic concepts of energy, exergy and emergy measure various flows at these three scales, viz. primary resources, energy and materials products, and labor and services. Our approach resolves the confusion about scale and metric: direct energy demand and direct exergy demand apply at scale A; cumulative energy demand and cumulative exergy demand apply at scale B; and energy is applied at scale C, where it is named emergy, while exergy also can be applied at scale C. This last option was not examined in the present study.The environmental performance of the system was assessed using a number of sustainability indicators, including resource consumption, input renewability, physical benefit, and system efficiency, using ethanol from corn stover in the US as a technology case. Results were compared with available literature values for typical biofuel alternatives. We also investigated the influence of methodological choices on the outcomes, based on contribution analysis, as well as the sensitivity of the outcomes to emergy intensity. The results indicate that the techno-system is not only supported by commercial energy and materials products, but also substantially by solar radiation and the labor and services invested. The bioethanol techno-system contributes to the overall supply of energy/exergy resources, although in a less efficient way than the process by which the Earth system produces fossil fuels.Our results show that bioethanol cannot be simply regarded as a renewable energy resource. Furthermore, the method chosen for the thermodynamic analysis results in different outcomes in terms of ranking the contributions by various flows. Consequently, energy analysis, exergy analysis, and emergy analysis jointly provide comprehensive indications of the energy-related sustainability of the biofuel techno-system. This thermodynamic analysis can provide theoretical support for decision making on sustainability issues.     

Assessment of Load Transfer and Load Distribution in Bridges Utilizing FRP Panels

A primary means of demonstrating the feasibility and effectiveness of fiber-reinforced polymer (FRP) composite bridge materials is via in situ bridge load testing. For this study, the prescribed or assumed design factors for each of the study bridges were compared to those exhibited by the performance of the bridge. Specifically, the wheel load distribution factors and impact factors as defined by AASHTO were considered in order to assess the load transfer and distribution in structures utilizing FRP panels. The in situ testing configurations for the study bridges are outlined, including the truck and instrumentation placement to obtain the desired information. Furthermore, comparisons were drawn between the design values for deflection and those experienced by the structures during testing. It was found that although the deflections exhibited by the bridges were well within the design limits, further research is needed to be able to prescribe bridge design factors for FRP panels.     

An industrial view on compact modeling

Compact modeling is an area that gets more and more mature. Collaborations and standardization efforts have emerged. In this paper we present some special requirements that are important when constructing physics-based compact models. We will substantiate our statements on two recent examples, an inductor model and a MOSFET model.     

Effects of Daniella oliveri Wood Flour Characteristics on the Processing and Functional Properties of Wood Polymer Composites

The effects of particle sizes/distribution and contents on the processing, changes in microstructure and functional properties of wood polymer composites (WPCs) prepared from virgin high-density polyethylene (vHDPE) and sodium hydroxide (NaOH) treated Daniella oliveri wood flour via compression molding have been explored. Findings from this study suggested that an appropriate choice of wood flour characteristics could improve the interactions between the wood flour and the vHDPE matrix by eliminating incomplete wetting, segregation, and agglomeration of wood flour particles during processing while enhancing mechanical and thermal properties of the composites. Properties of the WPCs were optimized when wood flour of particle sizes/distribution and contents of +210–300 µm and 35 wt%, respectively, were blended with vHDPE matrix.     

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