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941.
Methane release and coastal environment in the East Siberian Arctic shelf   总被引:1,自引:0,他引:1  
In this paper we present 2 years of data obtained during the late summer period (September 2003 and September 2004) for the East Siberian Arctic shelf (ESAS). According to our data, the surface layer of shelf water was supersaturated up to 2500% relative to the present average atmospheric methane content of 1.85 ppm, pointing to the rivers as a strong source of dissolved methane which comes from watersheds which are underlain with permafrost. Anomalously high concentrations (up to 154 nM or 4400% supersaturation) of dissolved methane in the bottom layer of shelf water at a few sites suggest that the bottom layer is somehow affected by near-bottom sources. The net flux of methane from this area of the East Siberian Arctic shelf can reach up to 13.7 × 104 g CH4 km− 2 from plume areas during the period of ice free water, and thus is in the upper range of the estimated global marine methane release. Ongoing environmental change might affect the methane marine cycle since significant changes in the thermal regime of bottom sediments within a few sites were registered. Correlation between calculated methane storage within the water column and both integrated salinity values (r = 0.61) and integrated values of dissolved inorganic carbon (DIC) (r = 0.62) suggest that higher concentrations of dissolved methane were mostly derived from the marine environment, likely due to in-situ production or release from decaying submarine gas hydrates deposits. The calculated late summer potential methane emissions tend to vary from year to year, reflecting most likely the effect of changing hydrological and meteorological conditions (temperature, wind) on the ESAS rather than riverine export of dissolved methane. We point out additional sources of methane in this region such as submarine taliks, ice complex retreat, submarine permafrost itself and decaying gas hydrates deposits.  相似文献   
942.
Whilst the world is much better prepared and equipped to combat major tanker spills than it was 30 years ago, it is still the case that responders are not able to overcome some of the fundamental technical problems. What is more regrettable is the fact that most significant oil spills are not dealt with as effectively as current technology should allow. This is frequently because insufficient account is taken by those in charge of preparedness programmes and response operations of the extensive technical knowledge and experience that is available around the world, especially in terms of the lessons that have been learnt from previous spills.  相似文献   
943.
铁路噪声对沿线居民影响的研究   总被引:2,自引:2,他引:0  
分析了铁路沿线居民对噪声的反应,并比较了铁路与交通运输噪声主观反应。结果表明,无论是高干扰率阈值的比较,或是从高干拢率与声级的回归方程比较,铁路和交通这两种运输噪声对人的主观反应干扰基本一样。  相似文献   
944.
The upper water column in the Irminger Sea is characterized by cold fresh arctic and subarctic waters and warm saline North Atlantic waters. In this study the local physical and meteorological preconditioning of the phytoplankton development over an annual cycle in the upper water column in four physical zones of the Irminger Sea is investigated. Data from four cruises of the UK's Marine Productivity programme are combined with results from a coupled biological–physical nitrogen–phytoplankton–zooplankton–detritus model run using realistic forcing. The observations and model predictions are compared and analyzed to identify the key parameters and processes which determine the observed heterogeneity in biological production in the Irminger Sea. The simulations show differences in the onset of the bloom, in the time of the occurrence of the maximum phytoplankton biomass and in the length of the bloom between the zones. The longest phytoplankton bloom of 90 days duration was predicted for the East Greenland Current of Atlantic origin zone. In contrast, for the Central Irminger Sea zone a phytoplankton bloom with a start at the beginning of May and the shortest duration of only 70 days was simulated. The latest onset of the phytoplankton bloom in mid May and the latest occurrence of the maximum biomass (end of July) were predicted for the Northern Irminger Current zone. Here the bloom lasted for 80 days. In contrast the phytoplankton bloom in the Southern Irminger Current zone started at the same time as in Central Irminger Sea, but peaked end of June and lasted for 80 days. For all four zones relatively low daily (0.3–0.5 g C m− 2d− 1) and annual primary production was simulated, ranging between 35.6 g C m− 2y− 1 in the East Greenland Current of Atlantic origin zone and 45.6 g C m− 2y− 1 in the Northern Irminger Current zone. The model successfully simulated the observed regional and spatial differences in terms of the maximum depth of winter mixing, the onset of stratification and the development of the seasonal thermocline, and the differences in biological characteristics between the zones. The initial properties of the water column and the seasonal cycle of physical and meteorological forcing in each of the zones are responsible for the observed differences during the Marine Productivity cruises. The timing of the transition from mixing to stratification regime, and the different prevailing light levels in each zone are identified as the crucial processes/parameters for the understanding of the dynamics of the pelagic ecosystem in the Irminger Sea.  相似文献   
945.
Current analytic models for optimizing urban bus transit systems tend to sacrifice geographic realism and detail in order to obtain their solutions. The models presented here shows how an optimization approach can be successful without oversimplifying spatial characteristics and demand patterns of urban areas and how a grid bus transit system in a heterogeneous urban environment with elastic demand is optimized. The demand distribution over the service region is discrete, which can realistically represent geographic variation. Optimal network characteristics (route and station spacings), operating headways and fare are found, which maximize the total operator profit and social welfare. Irregular service regions, many‐to‐many demand patterns, and vehicle capacity constraints are considered in a sequential optimization process. The numerical results show that at the optima the operator profit and social welfare functions are rather flat with respect to route spacing and headway, thus facilitating the tailoring of design variables to the actual street network and particular operating schedule without a substantial decrease in profit. The sensitivities of the design variables to some important exogenous factors are also presented.  相似文献   
946.
基于磁滞比较器和选择表的感应电机直接转矩控制(DTC),其开关频率可变,且转矩脉动大,特别在低速时.这是因为转矩和磁通的变化率以及转矩和磁通达到其上带和下带所花的时间随运行工况变化.文中提出了一种新型的开关频率固定的转矩控制器.新型控制器结构非常简单,其输出类似于传统的三点式磁滞比较器.就提出的控制器介绍了近似频域分析法,作为控制器参数选择的指南.介绍了感应电机直接转矩控制采用该转矩控制器进行的仿真和实验结果.结果表明提出的控制器可以保持开关频率恒定,并降低了转矩脉动,尤其在低速时.  相似文献   
947.
The main target of this work is to realize the function of pre-oxidizing NO from diesel engine’s exhaust by using self-designed double-dielectric Non-thermal Plasma (NTP) reactor. The majorized discharge frequency and discharge peak to peak voltage (Vp-p) range for NTP reactor were obtained through air discharge test. The diesel engine test bench was established to observe the effect of NTP on the volume fraction of NO. The results showed that there were more active substances and fewer by-products in NTP reactor when discharge frequency was 9 kHz and Vp-p was between 9 kV and 23 kV; Exhaust flows had insignificant effect on the performance of NTP pre-oxidizing NO; The ability of NTP to pre-oxidize NO gradually weakened with the increase of engine load, and when the engine load were 0 % and 25 %, the ratio of NO/NO2 could reach 1. In such working conditions, SCR system could improve the conversion rate of the NOx at low-temperature zone through quick reaction combined with NTP.  相似文献   
948.
Experimental coastdown analysis were performed on a full scale passenger car model FIAT Linea to obtain the drag coefficients for three different test configurations as engine-cooling airflow closed with smooth underbody, enginecooling airflow closed with detailed underbody, and engine-cooling airflow open with detailed underbody. The comparison of the drag coefficients for all three coastdown configurations were in good agreement with the CFD results and FIAT wind tunnel results. The coastdown tests predicted the model drag coefficients 5.3 % to 7.8 % less than FIAT wind tunnel drag coefficients for three test configurations. The contribution of the engine-cooling airflow and the detailed underbody configuration on the total drag coefficient were measured as 9.6 % ~ 10.4 % and 14.6 % ~ 16.7 %, respectively in the coastdown, FIAT wind tunnel tests and CFD analysis. In the CFD analysis,steady RANS equations were solved by STAR-CCM+ code. The turbulence model was selected as realizable k-ε two layer model. Model surface pressure contours were compared for all three test.  相似文献   
949.
This paper presents a novel sensor-less steering torque control method for applications to the steer-by-wire system. A steer-by-wire system has not any mechanical link to connect a steering wheel and a rack and pinion gear module. Instead of mechanical devices, two electric motors are used on each side. A one motor is attached to the steering wheel and the other is set on rack and pinion. The motor on the steering wheel works as a deliverer between a steering torque and load torque from the road. In this paper, we focus on motion control related to the steering feel based on impedance control. Therefore, the model of rack and pinion is not considered in this work. In most power steering systems, a torque sensor is used to set impedance effect on driver’s steering feel. In this paper, we proposed a novel steering control method without using any torque sensors. The effectiveness of a proposed method is confirmed from experimental results.  相似文献   
950.
This research investigates stochastic estimation of a look-ahead sensor scheme using the optimal preview control for an active suspension system of a full tracked vehicle (FTV). In this scheme, wheel disturbance input to the front wheels are estimated using the dynamic equations of the system. The estimated road disturbance input at the front wheels are utilized as preview information for the control of subsequently following wheels of FTV. The design of optimal preview control is used as a classical linear quadratic Gaussian problem by combining dynamics of the original system and estimation of previewed road inputs. The effectiveness of the preview controller is evaluated by comparing the estimated information with the measured information for different road profiles, where Kalman filter is used for the state-variables estimation of the FTV. This research also considers the reduced order estimation using commonly available sensors in order to decrease the number of sensors and measurements. The simulation results’ using an active suspension system with different preview information shows that the proposed system can be beneficial for the improvement of ride comfort of tracked vehicles without using any specialized sensors for preview information calculation.  相似文献   
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