Estimation of copepod production in a flooded savanna of Venezuela

This is the first contribution to the copepod production in Venezuelan tropical savannas. Total abundance, biomass, production and mean P/B ratio of nauplii, copepodids and adults were determined in interdaily samples from a flooded, embanked savanna during February and March (end of dry season), and May (beginning of rainy season). Highest values of biomass and total production were recorded during dry season (61.5 mg m⁻³, 153.8 mg m⁻³ day⁻¹, respectively), compared to the rainy season (5.6 mg m⁻³, 45.9 mg m⁻³ day⁻¹). The last values are related to a low population density found during rainy season. Highest production were observed in copepodids at the end of the dry season. Significant differences of production between nauplii and copepodid stages, as well as between nauplii and adults, were also found.     

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.     

(Law for the Promotion of Competition and Consumer Protection) was passed in early 1995. The impact this law will eventually have, however, is uncertain because rules for its implementation have not yet been established.

Governments in their port reform efforts have experimented with liberalization and commercialization to improve port operations. Because of their failure to meet expectations or because of changing competitive environments, these options have generally been discarded in favour of privatization. In mature large-volume port systems, privatization was a relatively obvious solution, because interport or interterminal competition would be achieved to the extent that the monopolistic tendencies characteristic of their predecessor organizations would cease to exist. In countries with a limited number of ports having relatively small cargo volumes, however, the case is quite different. These countries would have to pursue strategies that would still induce competition in spite of their limited cargo volumes if they hoped to achieve the same privatization benefits and market disciplines enjoyed in other countries. This article examines the port reform approaches used in three distinct competitive settings;the experiences in these countries offer some guidance on how to assure that ports will feel competitive pressures even under conditions of limited cargo volumes.     

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.     

Seabirds utilizing the Northeast Water polynya

A small seabird community depends on the resources of the Northeast Water (NEW) polynya. In spring, at least 1000 King Eiders and 2500 Common Eiders form pre-breeding congregations at Ob Bank before dispersing in mid June to breeding areas. The most abundant species is the Fulmar, which breeds in six colonies with a total of 2550 “apparently occupied sites”, corresponding to approx. 1475 active pairs in 1993. Kittiwakes occupied almost 900 sites at Mallemukfjeld, with an estimated 733 breeding pairs. The entire NEW area probably holds 400–500 pairs of Ivory Gulls, and about 500 individuals were associated with a colony on Henrik Krøyer Holme; this is one of the world's largest known colonies. Sabine's Gulls breed at the same islands and on Kilen (approx. 50 pairs in each place). Small colonies (total less than 1000 birds) of Arctic Terns are distributed along the edge of the polynya, with the largest colony of about 100 pairs on Henrik Krøyer Holme. The Black Guillemot is the only breeding auk species (< 20 pairs) in the area. Small numbers of Red Phalaropes were observed in the polynya in 1992 and 1993, and the species may have bred at Henrik Krøyer Holme in 1993; the polynya area may also serve as a staging area for transpolar migrants. In late summer a few hundreds of Ross's Gull—non-breeding adults and immatures—show up in and around the polynya, and in recent years a few cases of breeding have also been recorded. The relatively small seabird populations are evidence of a generally low carrying capacity of the polynya area.Apart from the benthic foraging eiders and the Black Guillemot, the seabird community of NEW consists of surface feeders—Fulmars and gulls—dependent on small fish and zooplankton. During their stay in the NEW area, the five most abundant surface feeders will annually consume approximately 243,000 kg (wet weight) of food, of which the Fulmars alone take 67%. Food demand in relation to area of open water in the polynya is highest in spring (approx. 0.2 kg/km²), which is     

基于自适应STFT的货车滚动轴承故障诊断

带故障的铁路货车滚动轴承振动信号表现为低频平稳信号与高频的周期性冲击信号的叠加。采用以三阶B样条函数作为窗函数的自适应短时傅立叶变换(STFT)对货车滚动轴承振动信号进行时频分析和故障信息提取。与传统的固定带宽的STFT相比,自适应STFT在不同频段自适应选取窗长,大大提高了振动信号的时频分辨率。应用该方法对197726型货车滚动轴承在内圈剥离、外圈剥离两种故障状态下的振动信号做了分析,求得故障频率分别为61.32 Hz和46.36 Hz,与内外圈的理论故障频率相符,可以有效地诊断出铁路货车滚动轴承内外圈故障。     

G1206型大功率液力传动内燃机车

Ｇ１２０６型机车是ＶＳＦＴ公司的ＲＡＧ公司生产的标准大功率液力传动内燃机车，它的最显著的特点是功率大、工作可靠、适应重载牵引和调车作业。对该型机车的主要结构部件，如柴油机、液力换向传动装置、空压机、转向架、中央控制器等均作了介绍。     

Longitudinal Tire Dynamics

This article begins with a brief review of the traditional concept of lateral relaxation length. The review illustrates that this concept yields a useful approximation which can be used with semi-empirical tire models which assume lateral forces are a function of steady-state slip angles. The article then presents an analogous derivation for longitudinal slip. Like its lateral counterpart, the derivation yields an approximation for transient longitudinal slip which can be used with tire models which assume longitudinal forces are a function of steady-state longitudinal slip. It is shown that, like the relaxation-length-based lateral slip angle, this formulation for longitudinal slip yields the ability to compute shear forces at the tire/road interface for either high or low speed applications, a necessary feature of simulations which support human in the loop driving simulation. Like traditional kinematically-based longitudinal slip, the transient formulation presented here is coupled with the wheel spin equation, and it shares the characteristic that it is very stiff compared to the equations of vehicle motion. This characteristic is a challenge impeding the real-time calculations required for driving simulation. The paper shows that local linearization of the wheel spin equations coupled with analytical solutions of the transient longitudinal slip formulation provide the basis for both insight into the longitudinal dynamics of the tire and for integrating the model in real-time.     

德国城市轨道交通建设投资的有关法规

介绍了德国城市轨道交通建设投资的有关法规，包括投资来源、投资规模、投资管理及投资准确性检验等方面内容，并举例加以说明。