Spatial and temporal variability of size-fractionated biomass and primary production in the Ross Sea (Antarctica) during austral spring and summer

The results of a study on the spatial and temporal dynamics of size-fractionated biomass and production of phytoplankton in the Ross Sea during the austral spring and summer are reported. The spring cruise took place in the offshore Ross Sea from 14 November to 14 December 1994. Sampling was carried out on a transect of 27 stations distributed from 76.5 to 72.0°S along 175°E, and covered the three main Antarctic environments of the polynya open waters, the marginal ice zone and the pack ice area. Three subsystems were identified. The subsystem of the polynya was characterised by the predominance of the micro- and nano-planktonic fractions, chlorophyll (Chl a) concentrations from 69.6 to 164.7 mg m⁻² and production rates from 0.68 to 1.14 g C m⁻² day⁻¹. The second subsystem, the marginal ice zone, showed a relative increase of the micro-planktonic fraction, high biomass levels (from 99.64 to 220 mg Chl m⁻²) and production rates from 0.99 to 2.7 g C m⁻² day⁻¹. The subsystem of the pack ice area had a phytoplankton community dominated by the pico-planktonic fraction and showed low biomasses (from 19.4 to 37.7 mg Chl m⁻²) and production rates (0.28 to 0.60 g C m⁻² day⁻¹). Selective grazing by krill is considered an important factor in determining the size structure of the phytoplankton communities. The summer study consisted of a time series carried out in inshore waters of Terra Nova Bay from 12 January to 8 February 1990. In a well stabilised water column and with high levels of PAR always available, the primary production rates of a community dominated by micro-plankton varied from 0.52 to 1.2 g C m⁻² day⁻¹ (average 0.84). A high P/B ratio, up to 3, and a remarkably elevated mean phaeopigment (Phaeo)/Chl a ratio of 2.4 indicated an active removal of biomass by grazing, confirmed by the presence of faecal pellets in quantities reaching 6000 m⁻³ in the upper 50 m. The peculiarities of the inshore versus offshore environments in terms of community size structure, production processes and their implications as regards the food web are discussed.     

新型快餐盒生物降解性能试验方法研究

通过固体培养微生物侵蚀试验、液体培养微生物侵蚀试验、降解过程中纤维素酶活性测定、纤维素酶侵蚀试验和降解过程中 Ｃ Ｏ２ 生成体积分数的测定等试验结果分析，认为固体培养微生物侵蚀试验、纤维素酶侵蚀试验及 Ｃ Ｏ２ 生成量测定试验可用于评价新型快餐盒生物降解性能。     

The change in soil cover on the exposed bed of the Aral Sea

Desiccation of the Aral Sea has led to the formation of new soil cover on the exposed seabed. Investigation of the newly formed dry land is very important since it is a source of dust storms and salts transferred to long distances. A soil map of the exposed seabed for 2000 has been produced on the basis of the map for the year 1990 (Institute of Soil Science, Uzbekistan), satellite images, and selected field observations of groundwater table. During the period 1990–2000, the sea recessed 20–32 km, thus changing the soil cover characteristics. The maps of soil cover with the detailed information on soil textures, the characterization of soil types, the soil formation trends, and the changes in soil types during the sea recession process are available. Attention has been paid to erosion tendencies and susceptibility to dust and salt transfers. As a whole, the soil cover was formed as a result of the replacement of excessive wetlands (salt-marsh), located in the form of strip along the sea, by hydromorphic and semi-hydromorphic, semi-automorphic and automorphic soils. The drying seabed has complicated lithological and morphologic composition. The territory of the exposed seabed is characterized by different hydrological conditions. Groundwater depth varies from 0.5 to 10 m. With the shore's recession, the water storage groundwater is approaching the surface. With general tendency towards desertification, the initial soil cover changes. The soils that did not reach the complete genetic formation, under the influence of quickly changing hydrogeological conditions, are transformed into the other types and subtypes. Often, while becoming dry, they are self-destructed and change into sands. Currently, the following types of soils are observed on the exposed seabed: automorphic solonchaks, semi-automorphic solonchaks, semi-hydromorphic solonchaks, hydromorphic solonchaks, desert sandy soils, sands.     

The trophic state of the Baltic Sea a century ago: a model simulation study

We apply a 3-D circulation model with a biogeochemical module (ERGOM) for the simulation of trophic conditions in the Baltic Sea a century ago. One aim is to provide reference or background data for nitrogen, phosphorus and chlorophyll, which is required for the implementation of the European Water Framework Directive (WFD). We assume that the situation a century ago serves this purpose well. Model input for this long-term simulation study are the regionally differentiated riverine and atmospheric nutrient loads to the Baltic Sea, which were compiled and calculated for a situation 100 years ago on the basis of various literature sources. For the mixed surface layer of the open Baltic Sea, we suggest maximum winter concentrations for dissolved phosphorus (dissolved inorganic nitrogen) of 0.23–0.35 (2.7–3.7) mmol/m³. Maximum chlorophyll-a concentrations are between 1.8 and 2.4 mg/m³. The concentrations of all parameters for different coastal waters vary in a wide range, depending on exposure to nutrient sources. Our nutrient concentrations for the situation a century ago are close to early measured data (1950–1960) and suggest that this data is suitable as reference data, as well.     

Practical Frequency and Time Optimal Design of Passive Linear Vibration Isolation Mounts

Summary In this paper we examine a linear one-degree of freedom vibration isolator mount. The linearity of the system allows us to analyze its frequency and time response characteristics analytically. Optimal damping and stiffness values for the isolator are obtained by minimizing certain cost functions, which are the Root Mean Square (RMS) of the absolute acceleration and the relative displacement. These RMS cost functions are used to create a design chart for the isolator parameters. This is very useful particularly in the presence of physical constraints such as a limit in relative displacement. The time response of the system for a unit step input is also considered to gain an insight into the transient characteristics of the system. We obtain an optimal value for the damping ratio of the system in order to minimize the transmitted acceleration. Combining the frequency and time response analyses leads to an optimal value for the mount natural frequency and damping ratio satisfying both time and frequency domains. The results are verified numerically using measured acceleration as input.     

Integral Recrystallization Modelling

1.IntroductionAlthoughmancanproducemetallicmaterialssincemorethan5(X)0yearsitisafundamentalfindingofonlythiscenturythatthePropertiesofamaterialarenotdeterminedbyanymacroscopicquantity,likeoverallcomposition,dimensions,strainortemperature,ratherthanbyitsmicrostructure,i.e.thespatialdistributionofelements,phases,orientationsanddefects.Thismicrosmicture,however,isliabletOchangeduringprocessingofamaterialfromtheliquidstatetothefinalproduct,anditcanbesubstantiallyaffectedbychangingtheprocessingcon…     

Measuring network reliability: A game theoretic approach

Despite the importance of assessing the reliability of transport networks in general there is a paucity of suitable techniques. In part this is due to the fact that network performance depends both on the state of the infrastructure and on the behaviour of network users, where user behaviour is governed by expectations about the state of the network. An approach based on game theory is proposed whereby the performance of the network is estimated for the case where network users are extremely pessimistic about the state of the network. Where the routes are prespecified and route utilities depend only on exogenously given scenarios, the estimation problem may be formulated as a linear program. A reformulation of the problem as a non-linear program allows the impact of the degree of user pessimism on expected network utility to be studied. The problems of implementing the method for large networks with multiple origins and destinations is discussed and an algorithm is proposed.     

High Speed Railway: Collecting Pantographs Active Control and Overhead Lines Diagnostic Solutions

The catenary-pantograph system and its dynamic behaviour play a decisive role for high speed trains from the power collecting point of view. The decisive criterion for assessing the contact quality is to reduce the contact force variability as far as possible. In this paper active pantograph elements are introduced in order to improve the system performance. The control strategy is based on Extended Kalman Filter technique, used to get a contact force estimation available for control feedback. The same estimation procedure based on the Extended Kalman Filter is also used to obtain some information useful to overhead line diagnostic purposes.     

Relationships between near-bottom dissolved oxygen and sediment profile camera measures

The United States Environmental Protection Agency (U.S. EPA) and other environmental authorities regulate concentrations of dissolved oxygen (DO) as a measure of nutrient-related eutrophication in estuarine and coastal waters. However, in situ DO concentrations are extremely variable, and their characterization requires an extensive sampling program to provide data over meaningful scales of time and space. In contrast, benthic faunal communities integrate the impacts of low DO over time, and can be rapidly assessed using benthic imaging. The goal of this study was to quantify the relationships between near-bottom dissolved oxygen and measures derived from benthic imaging with a sediment profile camera. We monitored three stations in Narragansett Bay (Rhode Island, USA) for DO and other water quality parameters 15–20 cm above the sediment surface on 15-minute intervals between July and November 2002, and regularly sampled these stations with a sediment profile camera throughout this time period. These soft-sediment stations encompassed several DO environments. We tested for relationships between near-bottom DO and several camera measures, including Nilsson and Rosenberg's Benthic Habitat Quality (BHQ) index, the apparent Redox Potential Discontinuity (aRPD) depth, and various faunal features that can be identified in sediment profile images. Camera measures were examined against a variety of methods of characterizing DO (including mean DO, and the percent of time under various DO thresholds), over a span of time scales from 1 day to 49 days. The best relationship (highest r²) between near-bottom DO and BHQ was found when DO was evaluated as the percent of time under a hypoxic threshold of 2.6 mg l^− 1 over a 28-day time scale (by examining DO records over the 28 days preceding each camera deployment). We found that, over several benthic settings, the BHQ index was successful at identifying environments that had experienced relatively high or low DO over the preceding four weeks. Our sediment profile data showed more variability with DO in the intermediate values of BHQ. We conclude that sediment profile camera measures correlate to DO in areas where low DO is the primary stressor, integrate DO over ecologically relevant time scales, and enable sampling over spatial scales that are meaningful for mapping by virtue of rapid deployment and analysis. We submit that sediment profile camera imagery is a useful assessment and mapping tool for environmental managers interested in benthic condition and in first-order quantitative estimates of near-bottom DO regimes in areas where low DO is the primary benthic stressor.     

Shipping freight derivatives: a survey of recent evidence

In an industry that is characterized by highly volatile prices, seasonality, strong business cycles, cyclicality and capital intensiveness, risk management is extremely important. Ship-owners and charterers face enormous risks, which emanate from fluctuations in freight rates, bunker prices, interest rates, foreign exchange rates and vessel values. These risks substantially affect the interplay between revenue and cost. Modern risk management techniques, involve the use of financial derivatives products, some of which have been developed exclusively for protecting (hedging) against the adverse price fluctuations of the aforementioned sources of risk in shipping. By using derivatives products, ship-owners and charterers can secure (stabilize) the level of their future income or costs and thus reduce uncertainty and unforeseen volatility of their cash-flow. To explore the importance of hedging freight rate risk in shipping operations, a survey of recent empirical evidence that has appeared in economic studies has been conducted. Developments over the past 20 years have been fast, with certain amount of research carried, which has helped to understand better the special features of these derivatives markets. They are all summarized in the current study, which can provide the stepping stone for further work in the area of shipping derivatives and risk management in shipping.