Twin–twin transfusion syndrome: mathematical modelling

Twin–twin transfusion syndrome (TTTS) represents a pregnancy complication with a high risk for perinatal mortality and postnatal morbidity. Mathematical models have been utilized to examine the mechanisms of disease and potential treatment modalities. We developed four consecutive models based on pathophysiology mechanisms. Conceptually, these models remained simple, but with increased complexity in details. We present our models tutorially with the necessary equations expressed in words. The aetiology of TTTS was related to AV anastomoses from donor to recipient and their growth commensurate with placental growth. We assessed that natural growth of placenta and foetuses causes the diameter and length of the AV, as well as the AV's pressure gradient, to increase proportional to gestational age. The AV transfusion then increases faster than natural foetal growth. A progressively increasing discordance subsequently develops, not compensated for by foetal growth. A simulation is performed to show how this discordance in blood volumetric development causes successive discordances in other functions, particularly renal, circulatory, and cardio-vascular, resulting in disease progression to the various stages of TTTS. In conclusion, mathematical modelling of TTTS has provided an understanding of the sequence of events that leads to the various presentations of TTTS stages as well as the efficacy of therapies. Copyright © 2008 John Wiley & Sons, Ltd.     

OLAND生物脱氮系统运行及其硝化菌群的分子生物学检测

采用两阶段限氧自养硝化 -反硝化生物脱氮系统 (oxygen limitedautotrophicnitrificationanddenitrificationsystem ,以下简称OLAND)处理高氨氮、低COD的废水 .应用内浸式多聚醚砜中空膜 ,实现了污泥的完全截留 ,阻止了生物量的大量洗脱 ,并通过控制溶氧在 0 .1～ 0 .3mgL-1之间 ,实现了硝化阶段出水中氨氮与亚硝态氮浓度的比例达到最适值〔1 (1.2± 0 .2 )〕 ,从而为第二阶段的厌氧氨氧化提供理想的进水 ,进而获得较高的脱氮率 .同时应用荧光原位杂交技术对硝化阶段不同时期硝化菌群的变化进行分子生物学检测 ,揭示了随溶氧浓度的降低 ,氨氧化菌的数量基本保持恒定、亚硝酸氧化菌的数量略有减少的变化规律 ,并且发现 ,在两阶段限氧自养硝化 -反硝化生物脱氮系统中氨氮的氧化主要是由Nitrosomonassp .完成 ,亚硝酸的氧化主要由Nitrobactersp .完成 .图 4表 2参 2 2     

The influence of additives on the steam gasification of PVC waste

This study is concerned with the influence of additives on the steam gasification of polyvinyl chloride (PVC) waste. Three types of PVC waste, namely pipe waste, cable waste, and flooring, were tested. The presence of additives proved to have a profound effect on the carbon-to-gas conversion. Plasticizers and other organic additives caused an increase in carbon-to-gas conversion. Inorganic additives, especially calcium, caused a decrease in carbon-to-gas conversion, resulting in an overall decrease in the yield of syngas for all three types of waste. This decrease is probably caused by the deposition of Ca on the surface of the alumina bed material. In addition, calcium reacts with the HCl formed to give CaCl₂. This results in a decrease in the recovery of hydrochloric acid. Received: July 19, 2000 / Accepted: October 9, 2000     

Characteristics, treatment and utilization of residues from municipal waste incineration

Beneficial utilization of residues from municipal solid waste incineration is an important objective for integrated waste management in many jurisdictions. When residues are to be used as an aggregate substitute in construction applications, the release of constituents of concern to soils and water through leaching is an important environmental consideration. In this paper, residue characteristics that control constituent leaching and testing approaches for evaluating leaching are discussed. Quality control and potential improvement in case of beneficial application are addressed.     

The contemporary Oceania zinc cycle: one-year stocks and flows

The material flow approach provides a framework from which to address resource management and estimate gross environmental impacts, both spatially and temporally. In this article, the major flows of zinc in Oceania over its entire life-cycle are examined; these include production (mining, milling, and refining), fabrication and manufacturing of semi- and finished products, use, and the waste management system. Comprehensive mass balances were applied to determine the zinc flows, including the quantities of zinc entering stocks in waste and in-use reservoirs. The Oceania cycle shows that substantial amounts of zinc (about 1120Gg/year) are mined on the continent. The total flow of zinc in finished products entering the use stage is about 8.6kg/(capita.year), substantially exceeding the zinc flow in discarded products. This difference, about 7.2kgZn/(capita.year) on average, is added to the in-use reservoir, largely for galvanizing applications in domestic construction and transportation. Less than 60% of all discarded zinc entering the waste management system is recycled. Much of the remaining discarded zinc is diluted into other waste streams, where recovery and recycling are probably not economically feasible.     

Assessment of the Water Balance of European Forests: A Model Study

As part of the UN-ECE Intensive Monitoring Program, data on precipitation, throughfall and soil solution concentrations are measured on a regular basis in approximately 300 forest stands. These data were used to construct element budgets for European forests. To construct such budgets drainage fluxes have to be modeled. In this paper, the research chain from model selection to data derivation and application of the selected model to 245 of the 300 sites is described. To select a suitable hydrological model the Cl^- balance method, two capacity models (a multi and a single layer version) and a Darcy model have been applied to two forest sites. The results indicate that drainage fluxes calculated with the Darcy model are more accurate than fluxes derived with the capacity model, in particular in situations where water availability is limited. The Darcy model was applied to the sites using a mixture of generic data and site data. Despite the use of generic data, the calculated drainage fluxes appear feasible. Median transpiration fluxes were 350 mm and the lowest values are found in northern Europe and highest values are found in central Europe. Median drainage fluxes were 150 mm yr^-1 with the highest values in areas with high rainfall. Uncertainty analyses indicate that the use of local instead of interpolated meteorological data leads to lower drainage fluxes at 70% of the sites. The median deviation in calculated drainage fluxes is 20 mm yr^-1. The use of local soil data had little impact on the calculated fluxes.     

Modelling piloted ignition of wood and plastics

To gain insight in the startup of an incinerator, this article deals with piloted ignition. A newly developed model is described to predict the piloted ignition times of wood, PMMA and PVC. The model is based on the lower flammability limit and the adiabatic flame temperature at this limit. The incoming radiative heat flux, sample thickness and moisture content are some of the used variables. Not only the ignition time can be calculated with the model, but also the mass flux and surface temperature at ignition. The ignition times for softwoods and PMMA are mainly under-predicted. For hardwoods and PVC the predicted ignition times agree well with experimental results. Due to a significant scatter in the experimental data the mass flux and surface temperature calculated with the model are hard to validate. The model is applied on the startup of a municipal waste incineration plant. For this process a maximum allowable primary air flow is derived. When the primary air flow is above this maximum air flow, no ignition can be obtained.     

Some notes on Tubiluchus corallicola (Priapulida) from Barbados,West Indies

The occurrence of Tubiluchus corallicola (van der Land) in a lagoon on the East coast of Barbados, West Indies, is reported. 23 adult and 2 larval specimens were found in a sample taken from a subtidal stromatolite on which the animals presumably inhabited the algal surface layer. A comparison with data from earlier findings shows that the species is not confined to a particular type of substratum, yet morphologically it seems to be well adapted for a life in the interstitial sand habita. For the first time, living animals were observed and photographed. Their behavior and movements are briefly described and an account of morphological and histological details, as seen in squeezing preparations and photomicrographs, is presented.Supported in part by NSF Grant GB-7952     

Influence of light and temperature on the photosynthetic rate of marine benthic diatoms

The influence of light and temperature on photosynthetic rate as measured by C¹⁴O₂-fixation of marine benthic diatoms was investigated, using both intact sediment samples (Marshall et al., 1973) and suspensions of diatoms harvested by a lenstissue technique (Eaton and Moss, 1966). After C¹⁴-incubation, sediment samples were filtered, burned in a sample oxidizer, and their activity determined in a liquid scintillation counter. Photosynthetic rate of mixed field populations is saturated by a light intensity of approximately 10,000 lux; at still higher light intensities no photoinhibition was found. In contrast to the mixed field populations, unialgal cultures of the benthic diatom Amphiprora alata Kütz. exhibited strong photoinhibition at higher light intensities (10,000 to 60,000 lux). Within a range of 4° to 20°C, the photosynthetic rate increased about 10%/C^o. No differences in photosynthetic pattern were observed between epipelic and epipsammic species.