基于CFD-DEM的旋风除尘器内气固流动特性研究

为了研究旋风除尘器内气固流动特性,采用CFD-DEM耦合算法研究不同入口气体速度下旋风除尘器内颗粒流态、静压、径向速度及轴向速度分布特征。结果表明:煤屑颗粒在离心力和径向曳力的作用下以螺旋颗粒条带靠近除尘器的壁面稳定向下移动,随着入口风速的增加煤屑颗粒条带变宽,条带与除尘器的第1次接触的拐点上移,螺距减小;除尘器内部压力轴向变化较小,径向变化较大,随着入口气体速度增加,除尘器壁面附近高压区范围和压力也随之增加,除尘器上方和下方的负压区变宽并朝轴向方向延伸;随入口气体速度增加,除尘器内径向速度和轴向速度逐渐增加,煤屑颗粒在除尘器中部聚集较多,煤屑停留时间变长,入口气体速度为15 m/s时,煤屑颗粒在除尘器内停留时间最长。     

Seasonal changes in the diving parameters of king penguins (Aptenodytes patagonicus)

Contrasting conditions at-sea are likely to affect the foraging behaviour of seabirds. However, the effect of season on the dive parameters of penguins is poorly known. We report here on an extensive study of the diving behaviour of king penguins (Aptenodytes patagonicus) over the bird's complete annual cycle at the Crozet Islands. Time-depth recorders were used to record dive duration, bottom duration, post-dive interval, ascent rate and descent rate in breeding adults during different seasons in 1995 and 1996. Seasons included summer (n=6, incubation; n=6, chick brooding), autumn and winter (n=5 and n=3, respectively, chick at the crèche stage), and spring (n=4, birds at the post-moult stage). In all seasons dive duration increased with dive depth, but, for a given depth, dives were longer in winter (6.8 min when averaged over the 100-210 m depth layer) than in spring (4.6 min) and summer (4.4 min). The time spent at the bottom of the dives, which probably represents a substantial part of the feeding time, was much longer in winter (2.5 min per dive for dives over the 100-210 m layer) than during other seasons (1.0-1.4 min), i.e. there was a 2.5-fold augmentation for similar diving depths. Ascent and descent rates increased with increasing dive depth, but no difference in the relationships between rates of ascent and descent and dive depth was found among seasons. Furthermore, for all dive depths, ascent and descent rates were independent of the bottom duration. In all seasons post-dive intervals increased with dive duration and with dive depth, but they were longer in spring (2.3 min for dives over the 100-210 m layer) and summer than in autumn and winter (1.6-1.8 min). The diving efficiency decreased with increasing dive depth and was higher in autumn and winter (0.22-0.29) than in summer and spring (0.15-0.18). The large increase in bottom and dive duration from spring to winter is in agreement with the seasonal drop in prey density, with penguins spending more time searching for prey. In contrast, the consistency of the vertical velocity during contrasting conditions at-sea suggests that the transit time to depth is an important component of the foraging behaviour (scanning of the water column) that is independent of the prey availability. The time budget of the penguins during diving in a fluctuating environment appears to vary primarily during the bottom phase of the dives, with bottom duration increasing with diminishing prey supplies, while post-dive intervals shorten in the same time.     

Observations sur le développement larvaire de Meganyctiphanes norvegica (Crustacea: Euphausiacea) au laboratoire

Larvae of Meganyctiphanes norvegica (M. Sars), caught with a plankton net, were reared in the laboratory from the calyptopis phase onwards, under different temperature and trophic conditions. Eyestalk ablation was performed on the first furciliae. Data are presented on growth, moulting rate and ontogenesis of the larvae as a function of the varying experimental conditions, and on larval morphology, pigmentation and diet. Recent modifications of larval nomenclature in euphausiids are discussed.

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Observations sur le développement larvaire de Meganyctiphanes norvegica (Crustacea: Euphausiacea) au laboratoire

     

Biodegradation of shells of the black pearl oyster,Pinctada margaritifera var. cumingii,by microborers and sponges of French Polynesia

The composition, distribution and infestation sequence of organisms that destroy the commercially valuable shells of the black oyster Pinctada margaritifera var. cumingii Jameson, 1901 were studied. Three ecologically different groups of boring (euendolithic) organisms were identified: (1) phototrophic boring microorganisms (cyanobacteria, Hyella caespitosa, Hyella sp., Mastigocoleus testarum, Plectonema terebrans, and green algae, Phaeophila dendroides, Ostreobium quekettii); (2) heterotrophic boring microorganisms (fungi, Ostracoblabe implexa); (3) filter-feeding boring organisms (sponges, Cliona margaritiferae, C. vastifica). The phototrophic endoliths dominate the external pristmatic region of the shell, whereas the valuable interior nacreous region is attacked mainly by heterotrophs. Boring patterns reflect in part the shape and behaviour of the organisms and in part the structural properties of the shell, and inflict different types of damage. Infestation starts with microbial borers, which prepare the conditions for later invasion by more damaging clionid sponges. The infestation begins always at the apex, the oldest part of the shells, from which the periostracum is often removed by natural attrition or by cleaning procedure. The rate of bioerosion in 1 yr-old hatchery shells is 36 times higher than in natural populations.     

Arsenic in groundwaters of the Lower Mekong

Increasing incidence and awareness of arsenic in many alluvial aquifers of South-east Asia has raised concern over possible arsenic in the Lower Mekong Basin. Here, we have undertaken new research and reviewed many previous small-scale studies to provide a comprehensive overview of the status of arsenic in aquifers of Cambodia and the Cuu Long Delta of Vietnam. In general natural arsenic originates from the Upper Mekong basin, rather than from the local geology, and is widespread in soils at typical concentrations of between 8 and 16 ppm; (dry weight). Industrial and agricultural arsenic is localised and relatively unimportant compared to the natural alluvial arsenic. Aquifers most typically contain groundwaters of no more than 10 μg L⁻¹, although scattered anomalous areas of 10 to 30 μg L⁻¹ are also quite common. The most serious, but possibly ephemeral arsenic anomalies, of up to 600 μg L⁻¹, are associated with iron and organic-rich flood-plain sediments subject to very large flood-related fluctuations in water level, resulting in transient arsenopyrite dissolution under oxidizing conditions. In general, however, high-arsenic groundwaters result from the competing interaction between sorption and dissolution processes, in which arsenic is only released under reducing and slightly alkaline conditions. High arsenic groundwaters are found both in shallow water-tables, and in deeper aquifers of between 100 and 120 m depth. There is no evidence of widespread arsenicosis, but there are serious localised health-hazards, and some risk of low-level arsenic ingestion through indirect pathways, such as through contaminated rice and aquaculture. An almost ubiquitous presence of arsenic in soils, together with the likelihood of greatly increased groundwater extraction in the future, will require continuing caution in water resources development throughout the region.     

Studying crop sequences with CarrotAge,a HMM-based data mining software

We have developed a knowledge discovery system based on high-order hidden Markov models for analyzing spatio-temporal data bases. This system, named CarrotAge , takes as input an array of discrete data – the rows represent the spatial sites and the columns the time slots – and builds a partition together with its a posteriori probability. CarrotAge has been developed for studying the cropping patterns of a territory. It uses therefore an agricultural drench database, named Ter-Uti , which records every year the land-use category of a set of sites regularly spaced. The results of CarrotAge are interpreted by agronomists and used in research works linking agricultural land use and water management. Moreover, CarrotAge can be used to find out and study crop sequences in large territories, that is a main question for agricultural and environmental research, as discussed in this paper.     

Analysis of chromium and copper by cathodic stripping voltammetry with mixed ligands

Cathodic adsorptive stripping voltammetry is one of the most sensitive analytical methods for ultratrace analysis. The detection limit is usually lower than 10⁻⁹ mol/L. Most adsorptive stripping procedures have been focused on the one ligand/one analyte approach. In order to reduce analysis time and sample volume, the possibility of simultaneously determining several metals by cathodic stripping voltammetry using a mixture of ligands was explored, e.g., by Colombo and van den Berg (1997). Here, we describe a new procedure for quantifying chromium and copper using 2,2′-bipyridine and 8-hydroxyquinoline (oxine). The effect of various operational parameters such as buffer type, ligand concentration, potential and time collection were assessed and optimized. Possible interferences by trace metals and organic matter were also investigated. Applicability for fresh water is illustrated. Electronic Publication     

Amino acid uptake and respiration by marine heterotrophs

The concentration and turnover of dissolved free amino acids were measured in samples from 25 and 100 m on three occasions at a station 6 miles off the California (USA) coast. Individual amino acid concentrations varied from undetectable (<0.05 g/l) to 3 g/l, the total amino acid concentration from 1.8 to 8.5 g/l. The greater concentration of total amino acids was always found at 25 m. The predominant amino acids were serine, lysine, aspartate, glutamate and alanine; reliable analyses could not be made for glycine because of a high blank. For the 10 individual amino acids studied, the rate of heterotrophic turnover ranged from undetectable to 1.2 g/l day^-1; serine, aspartate, alanine and glutamate showed the highest rates. In samples from 25 m, the rates were 15 to 20 times higher than those taken from 100 m. The total calculated flux of the amino acids studied varied from 0.015 to 3.2 g/l day^-1 and amounted to 1–10% of photosynthetic carbon dioxide fixation.     

Small-scale spatial and temporal interactions among benthic crustaceans and one fish species in the Bay of Biscay

In the summer of 2004, a video survey was carried out in the northern part of the central mud bank (Grande Vasière) of the Bay of Biscay to study the small scale relationship between the dominant crustacean megafauna Nephrops norvegicus, Munida rugosa and Goneplax rhomboides and juvenile hake (Merluccius merluccius). Using a towed body, high-resolution videos were recorded in six sampling sites. Statistical modelling using generalised additive models (GAM) revealed variations in activity patterns for two species. More N. norvegicus were observed outside their burrows at dawn and somewhat at dusk (no observations during night) while G. rhomboides was less observed in the morning. In addition, reduced spatial overlap between G. rhomboides and N. norvegicus suggested reduced competition for food but also space as both are burrowing species. The observed temporal and spatial activity patterns may contribute to regulating assemblage structure as competing species may be actively foraging at different times and locations thus reducing direct competition.     

Asynchronous deposition of dense skeletal bands in Porites lutea

Alternate dense and less-dense skeletal bands in massive corals have been used for many years to record the history of growth in species such as Porites lutea and Montastrea annularis, based on the assumption that one dense band and one less-dense band is equivalent to a year's growth. This report demonstrates that specimens of Porites lutea Edwards and Haime (collected from the same neighbourhood in Phuket, Thailand, from November 1983 through November 1984) produce skeletal bands asynchronously and that one year's growth in corals from certain sites may regularly consist of four bands of varying density. The annual banding pattern observed at all sites includes the deposition of a dense band in response to high sedimentation loads and, probably, reduced light levels.