市郊列车用全封闭式永磁同步电动机

风冷式感应电动机广泛用作铁道车辆的牵引电动机.但它们需要大修进行内部清洁,而且还是噪声的主要来源.为解决这些问题,建议使用全封闭式永磁同步电动机作牵引电动机,它具有与传统的风冷式感应电动机相同的功率-重量比.报告了温升试验、噪声测定和能耗计算的结果.结果表明噪声等级下降10 dB,能耗约降低10%.     

Model-scale experiments of symmetric ship collisions

This study was initiated due to the lack of experimental data on ship collisions. The feasibility of model-scale ship collision experiments was examined and a series of model-scale ship collision experiments is presented. The theoretical background for the analysis of experiments is given together with the principles of scaling. Proper scaling should assure physical similarity to the large-scale experiments conducted in the Netherlands. The Froude scaling law was followed, resulting in the improper scaling of some forces: the effects of this are discussed. The study concentrates on the dynamics of collisions. The structural response, properly scaled from the large-scale experiments, was modelled using polyurethane foam as the ship’s side structure. The collision process was analysed and the results of model-scale tests, large-scale experiments, and a simple analytical model were compared, showing that there was both quantitative and qualitative agreement in the results of the experiments conducted at different scales. The analytical model yielded good quantitative assessment of the deformation energy.     

Seasonal variability of the Black Sea chlorophyll-a concentration

The optimal spectral decomposition (OSD) method is used to reconstruct seasonal variability of the Black Sea horizontally averaged chlorophyll-a concentration from data collected during the NATO SfP-971818 Black Sea Project in 1980–1995. During the reconstruction, quality control is conducted to reduce errors caused by measurement accuracy, sampling strategy, and irregular data distribution in space and time. A bi-modal structure with winter/spring (February–March) and fall (September–October) blooms is uniquely detected and accurately documented. The chlorophyll-a enriched zone rises to 15 m depth in winter and June, and deepens to 40 m in April and 35 m in August. The June rise of the chlorophyll-a enriched zone is accompanying by near-continuous reduction of upper layer maximum chlorophyll-a concentration.     

Maritime policy, management and research: role and potential

This special issue of Maritime Policy and Management includes a collection of the best papers presented at the recent conference of the International Association of Maritime Economists (IAME) 2005. On the basis of a review and conceptual synthesis of the six papers selected for the special issue, this paper provides a discussion of the role and potential of research in informing managerial decision-making and policy-making in the context of the maritime industry and makes recommendations for elevating the discipline-related credentials of the maritime area as a field of study.     

Effects of small-scale turbulence on the growth of two diatoms of different size in a phosphorus-limited medium

The effect of turbulence on the nutrient flux towards osmotrophic cells is predicted to be size dependent. This should translate into growth. We experimentally followed and modelled the growth of two marine diatoms of different size (Thalassiosira pseudonana, 6 μm in diameter and Coscinodiscus sp., ca. 109 μm in diameter) under still water and turbulent conditions, using a shaker table. Experiments were done with phosphorus-limited cultures and lasted for ca. 5 days. Turbulence enhanced the growth of Coscinodiscus sp. in agreement with theory but not the growth of T. pseudonana, which was actually slightly lower under turbulence. At the end of the experiments there were about 1.7 times as many Coscinodiscus sp. cells in the turbulent treatment than in the still treatment, while for T. pseudonana almost the same cell concentration was found in both conditions. In addition, the Coscinodiscus sp. cells growing under still conditions presented a higher specific alkaline phosphatase activity than those growing in turbulence which indicates a higher need for phosphorus in the still cultures. A simple dynamic model, based on Michaelis–Menten nutrient uptake kinetics, needed nearly no optimisation other than using observed initial conditions of phosphate and cell concentrations. The model showed how an increased nutrient flux towards the cells translates non-linearly into cell growth, most likely by affecting the half-saturation constant (K_M). However, since Coscinodiscus sp. experienced significant mortality and cells partially settled to the bottom of the containers, unequivocal support for the size-dependent effect of turbulence on nutrient uptake will require further experiments and more sophisticated modelling. The mechanisms to connect an increased nutrient flux towards cells with population growth and whether this process is size dependent are important in parameterizing the effects of turbulence on marine plankton in coupled physical–biological models.     

Shipping finance: time to follow a new track?

In this paper we introduce, for the first time, a methodology from the most recent literature of finance to reveal the duration of shipping cycles and then show the benefit of the use of this information to make more successful shipping loans. This is so as banks are willing to finance, during boom periods, shipping loans for new buildings but by this way 'create' oversupply and thus depress the freight market by their own actions. The information about cycles, especially their forecasting, is mostly important as shipping loans are based on project financing/cash flow financing, which means that ship revenue is of utmost importance. The Rescaled Range Analysis is applied here to 379 monthly freight trips—made stationary—between 1971 and 2002 (July), due to Hurst 1 and elaborated and popularized by Mandelbrot 2. The most important effect, however, is that shipping freight series exhibit non-normality and long-run dependence rendering the use of random walk models such as GARCH (Generalized Autoregressive Conditional Heteroscedasticity) problematic. Thus an adequate literature review is carried out with criticism against the models used. The cycles have been calculated as equal to 4.5 years and 2.25 years. This is almost compatible with the most recent paper of Stopford 3. The Hurst exponent was found equal to 0.93, alternating over the periods examined (0.65, 0.73, 0.62, 0.59 and 0.55) and indicating long-term persistence but seriously away from normal/random walk domain. Most studies have said the same using the Jarque--Bera test for normality but provided no alternative.     

Estimates of Southern Ocean primary production—constraints from predator carbon demand and nutrient drawdown

In view of the wide range of estimates for the total primary production for the Southern Ocean south of the Subantarctic Front—current estimates range from 1.2 to 3.5 Gtonne C year⁻¹—we have examined two indirect methods for assessing primary production. First, we have estimated the primary production needed to sustain the carbon requirements of the endotherm top predators in the ecosystem. Estimation of the carbon requirements for crabeater seals of about 7 Mtonne C year⁻¹ is extrapolated to a value for all endotherm predators of 15–30 Mtonne C year⁻¹. Current data indicate that 70–80% of the diet of this suite of predators is zooplankton (predominantly the euphausiid krill), making for highly efficient transfer from primary production to top predators. Our best estimate of Southern Ocean primary production by this method is of the order of 1.7 Gtonne C year⁻¹, or an averaged areal primary production of about 30–40 g C m⁻² year⁻¹. Our second approach is to estimate primary production from the drawdown of inorganic nutrients, based on the limited suite of studies from which an annual nutrient deficit can be calculated. Again, this indicates annual primary production of the order of 1.5 Gtonne. Although both methods have inherent uncertainties, taken together they provide a relatively robust constraint on annual primary production. For both methods to underestimate primary production by the 1–1.5 Gtonne C implied by the higher current estimates, carbon export from the Southern Ocean pelagic ecosystem would need to be much higher than is normally found in other oceans.     

Dissolved organic matter studies in enclosed systems: Application of Hydrophobic fractionation for the assessment of organic nitrogen dynamics

The evolution of dissolved organic matter (DOM) in a non-axenic batch culture of the marine diatom Thalassiosira tumida was studied by hydrophobic fractionation during a three month experiment. DOM was fractionated with XAD-2 resin into hydrophobic (acid and neutral, “humic”) and hydrophilic fractions. The combined amino acid contents of unfractionated filtered seawater, XAD-fractions and particulate material were determined during the growth, stationary and degradation phases of the culture, and variations related to changes in dissolved organic nitrogen (DON) in XAD-fractions, dissolved inorganic nitrogen, algal and bacterial biomass. XAD-fractionation enabled the discrimination of simultaneously ocurring release and uptake of organic nitrogenous compounds: During the diatom growth there was a net increase of tolal DON concentrations, which was mostly accounted for by the hydrophilic fraction. A concurrent heterotrophic uptake of combined amino acids and other non-amino acid organic nitrogen was discernible by the decrease of their concentrations in the hydrophobic fractions. In the stationary phase, during the prevailing net consumption of total DON, the production of algal exudates could be detected in the hydrophobic fractions, while uptake mainly involved non-amino acid organic nitrogen from the hydrophilic fraction. During the degradation phase, after two months part of the particulate amino acid pool was transformed into hydrophilic DON, which in contrast to the stationary phase, was not adequate for supporting sustained bacterial growth. This suggests that the generation of recalcitrant substances may begin in the hydrophilic fraction of DOM. A slight increase of the hydrophobic acid fraction was indicative of the incipient formation of humic substances. XAD-2 was able to adsorb substances from fast changing DOM pools and thus should be a useful tool in studies concerned with phytoplankton and bacterial dynamics.     

采用更好的气体金属弧焊方法--采用一些简单措施使气体金属弧焊焊缝质量更好

焊工常常会问这样一个问题,"气体金属弧焊(GMAW)和熔化极惰性气体保护焊(MIG)之间有什么区别?"术语"熔化极惰性气体保护焊"主要指保护气体不会与焊接熔池里的其它元素化合.美国焊接学会(AWS)采纳"气体金属弧焊"一词,是因为目前所利用的保护气体未必是惰性的.在许多情况下,保护气体的成分会引起化学反应,促进焊接熔池里的化合,提高强度、熔深、熔化和可焊性.     

电动汽车驱动控制的PWM新技术

文章介绍了电动汽车交流驱动中采用确定脉宽调制(DPWM)技术和随机脉宽调制(RPWM)技术的比较研究结果.RPWM方法替代DPWM方法,采用Avant!公司先进的仿真软件SABER,其重点是降低电磁干扰(EMI).为了评估PWM技术对驱动性能的影响,同时对驱动效率,转矩脉动和电流控制系统动态响应进行了研究.文中考虑了逆变器开关频率随机变化定义的2种RPWM技术:一种技术是调制器的取样频率与开关频率同步变化;另一种技术是取样频率固定且等于平均开关频率.研究表明:在驱动性能几乎不受影响的同时,RPWM技术降低EMI的良好潜力,可使EMI下降10dB或更多.