Physical and biological correlates of virus dynamics in the southern Beaufort Sea and Amundsen Gulf

As part of the Canadian Arctic Shelf Exchange Study (CASES), we investigated the spatial and seasonal distributions of viruses in relation to biotic (bacteria, chlorophyll-a (chl a)) and abiotic variables (temperature, salinity and depth). Sampling occurred in the southern Beaufort Sea Shelf in the region of the Amundsen Gulf and Mackenzie Shelf, between November 2003 and August 2004. Bacterial and viral abundances estimated by epifluorescence microscopy (EFM) and flow cytometry (FC) were highly correlated (r² = 0.89 and r² = 0.87, respectively), although estimates by EFM were slightly higher (FC = 1.08 × EFM + 0.12 and FC = 1.07 × EFM + 0.43, respectively). Viral abundances ranged from 0.13 × 10⁶ to 23 × 10⁶ ml^− 1, and in surface waters were ~ 2-fold higher during the spring bloom in May and June and ~ 1.5-fold higher during July and August, relative to winter abundances. These increases were coincident with a ~ 6-fold increase in chl a during spring and a ~ 4-fold increase in bacteria during summer. Surface viral abundances near the Mackenzie River were ~ 2-fold higher than in the Mackenzie Shelf and Amundsen Gulf regions during the peak summer discharge, concomitant with a ~ 5.5-fold increase in chl a (up to 2.4 μg l^− 1) and a ~ 2-fold increase in bacterial abundance (up to 22 × 10⁵ ml^− 1). Using FC, two subgroups of viruses and heterotrophic bacteria were defined. A low SYBR-green fluorescence virus subgroup (V2) representing ~ 71% of the total viral abundance, was linked to the abundance of high nucleic acid fluorescence (HNA) bacteria (a proxy for bacterial activity), which represented 42 to 72% of the bacteria in surface layers. A high SYBR-green fluorescence viral subgroup (V1) was more related to high chl a concentrations that occurred in surface waters during spring and at stations near the Mackenzie River plume during the summer discharge. These results suggest that V1 infect phytoplankton, while most V2 are bacteriophages. On the Beaufort Sea shelf, viral abundance displayed seasonal and spatial variations in conjunction with chl a concentration, bacterial abundance and composition, temperature, salinity and depth. The highly dynamic nature of viral abundance and its correlation with increases in chl a concentration and bacterial abundance implies that viruses are important agents of microbial mortality in Arctic shelf waters.     

Hydrography and biogeochemistry of the north western Bay of Bengal and the north eastern Arabian Sea during winter monsoon

The north eastern Arabian Sea and the north western Bay of Bengal within the Indian exclusive economic zone were explored for their environmental characteristics during the winter monsoons of 2000 and 2001 respectively. The two regions were found to respond paradoxically to comparable intensities of the atmospheric forcing. There is an asymmetry in the net heat exchange of these two basins with atmosphere because of the varying thickness of barrier layer. During winter, the convective mixing in the Arabian Sea is driven by net heat loss from the ocean, whereas the Bay of Bengal does not contribute to such large heat loss to the atmosphere. It appears that the subduction of high saline Arabian Sea water mass is the mechanism behind the formation of a barrier layer in the northeast Arabian Sea; whereas that in the Bay of Bengal and the southeast Arabian Sea are already established as due to low saline water mass. The weak barrier layer in the Arabian Sea yields to the predominance of convective mixing to bring in nitrate-rich waters from the deeper layers to the surface, thereby supporting enhanced biological production. On the other hand, the river discharge into the Bay of Bengal during this period results in the formation of a thick and stable barrier layer, which insulates vertical mixing and provide oligotrophic condition in the Bay.     

Experimental evaluation of a vehicle steering assist controller using a driving simulator

Human-in-the-loop driving simulator experiments are conducted to evaluate a proposed robust steering assist controller that is designed on the basis of driver uncertainty modelling. A nominal controller (NC) that is designed without consideration of driver model uncertainty is also tested for comparison. Two types of experiments are proposed: a long driving task with nominal configurations and a short driving task with initially large lateral position error. The data are analysed using both time domain and frequency domain metrics. In the time domain, the standard deviation of lateral position error and percentage of road departure are used. In the frequency domain, the stability margins and crossover frequency are used. The driving simulator results indicate that statistically, the designed robust controller shows improvements in the short driving experiments. The improvements in the long driving experiments are less evident because of driver adaptation. The non-robust NC suffers from high gain and should be avoided. The benefits of considering driver model uncertainty in the design of vehicle steering assist controllers are, therefore, justified.     

Confidence bounds on structural reliability estimations for offshore platforms

Second-order estimates to measure platform reliability are generated and used to provide an additional space to select safety margins appropriate to the owner's perception or for risk-averse managers. The aleatory and epistemic uncertainties in the parameters of an offshore platform are explicitly considered in the reliability analysis and the platform structural reliability becomes a random variable, assessing then the beneficial effects of a reduction on these uncertainties. One of these benefits is for risk-aversive managers who often demand additional room to make conservative decisions regarding reliability estimations. Proposed here is a procedure to generate the frequency diagram of platform reliability with the use of confidence bounds to support reliability and cost decisions based on percentiles instead of mean values. The concepts are illustrated through a typical offshore platform in Mexico. The frequency diagram of the platform reliability index is built for several alternative designs and three levels of epistemic uncertainty. The results may be applied for decision making on new designs and also on the assessment and optimal inspection, retrofit, and decommissioning of existing platforms.     

Automotive transmission efficiency measurement using a chassis dynamometer

Automotive transmission efficiency measurements are usually performed on purpose-built rigs. A simple model was developed for calculating the overall transmission efficiency of passenger cars by using a chassis dynamometer. Wheel power and engine output were measured, and these values were used for calculations. The proposed method can only be employed for vehicles with manual drive because it requires constant speed measurements. Two case studies were investigated, with front-wheel and rear-wheel drive passenger cars. The results obtained from using the proposed model are in good agreement with data provided in the literature.     

应用于国Ⅲ摩托车的富钯涂层配方的研究

通过对不同催化作用涂层的对比，特别是针对小型摩托车活性、耐久性和贵金属成本的应用设计，提出以钯为主要或单一活性贵金属化合物涂料的研究数据，这些数据是通过使用合成气体反应器，对涂敷后的催化剂进行模拟发动机废气测试得到的。通过试验表明，较低成本的富钯催化涂料可用于小型摩托车的有效减排。此外，在110mL缸头补气与125mL中间补气摩托车上，按照摩托车欧Ⅲ和国Ⅲ排放法规运行ECER40冷起动循环，对不同配方催化剂的活性进行了测试，这些结果将与合成气体反应器测试结果相关联。     

Issues in the integration of active control turbochargers with internal combustion engines

The application of active control means to regulate the flow of exhaust gas in a turbocharger turbine is a concept developed by the Turbomachinery Group at Imperial College, London. It is a new concept the first results of which were made public in 2004. This paper presents the theoretical grounding behind the idea, its development and the elements required for a successful implementation of active control for a turbocharger turbine and the integration of such a turbocharger system within an internal combustion engine. This paper is intended to fill a gap in the theoretical understanding of the issues pertaining to the concept of Active Control for Turbocharger Turbines. The discussion is led towards a theory summarising the flow physics and their effect on the behaviour of the exhaust gas flow occurring during turbocharger turbine inlet geometrical changes and the implications from the periodic nature of these geometric changes in particular with respect to cycle performance results both for the turbocharger and for the engine. This paper is written with the purpose of presenting a realistic context of ACT operation by identifying and considering those parameters relevant to the operation and successful application of ACT to an internal combustion engine. In addition, the requirements for a dedicated ACT control strategy which can be effective in the ACT-engine integrated environment are, also, highlighted.     

Climate–ocean variability and Pacific hake: A geostatistical modeling approach

Climate forcing of the California Current has been known to impact the distribution and abundance of a number of local fish populations, but the mechanisms involved remain poorly understood. Climate metrics such as the Pacific Decadal Oscillation (PDO) and the El Niño Southern Oscillation (ENSO) are usually used to represent climate processes and direct links are made between climate forcing and production variability. This involves aggregation of impacts across large spatial scales and range of species. However, fluctuations in productivity are often the result of changes in physical habitat. In order to fully understand the relationship between climate and productivity, habitat changes should be addressed. In this study we use a geostatistical approach to quantify adult Pacific hake habitat during different climate regimes. Several authors have suggested that the distribution and intensity of the sub-surface poleward flow (the undercurrent) plays a key role in defining adult hake habitat along the west coast of North America. Here we build a model designed to predict hake habitat distribution in space based on sub-surface poleward flow distribution and bottom depth. Our results show that hake habitat expands in 1998 El Niño year compared to 1995. Given the important predatory role that hake plays in the CC, the amount and distribution of adult hake habitat has large implications for the Pacific Northwest food web and could thus serve as an ecosystem indicator representing important physical–biological interactions. Spatially based ecosystem indicators such as the one we develop here address two important yet neglected areas in the ‘Ecosystem Indicators debate’: the importance of developing metrics explicitly representing spatial and environmental processes shaping ecosystem structure. Without these, our power to fully describe ecosystems will be limited.     

Application of a SEEK filter to a 1D biogeochemical model of the Ligurian Sea: Twin experiments and real in-situ data assimilation

The Singular Evolutive Extended Kalman (SEEK) filter has been implemented to assimilate in-situ data in a 1D coupled physical-ecosystem model of the Ligurian Sea. The biogeochemical model describes the partly decoupled nitrogen and carbon cycles of the pelagic food web. The GHER hydrodynamic model (1D version) is used to represent the physical forcings. The data assimilation scheme (SEEK filter) parameterizes the error statistics by means of a set of empirical orthogonal functions (EOFs). Twin experiments are first performed with the aim to choose the suitable experimental protocol (observation and estimation vectors, number of EOFs, frequency of the assimilation,…) and to assess the SEEK filter performances. This protocol is then applied to perform real data assimilation experiments using the DYFAMED data base. By assimilating phytoplankton observations, the method has allowed to improve not only the representation of the phytoplankton community, but also of other variables such as zooplankton and bacteria that evolve with model dynamics and that are not corrected by the data assimilation scheme. The validation of the assimilation method and the improvement of model results are studied by means of suitable error measurements.