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排序方式: 共有463条查询结果,搜索用时 156 毫秒
1.
Fuel cell electric vehicles and hydrogen refuelling infrastructure are developing quickly in Europe, the USA and Asia. Hydrogen quality for transport applications requires compliance with ISO 14687-2: 2012 and EN 17124:2018 - this needs representative sampling, at the hydrogen production process and at hydrogen dispenser nozzle (which typically fill vehicles to a Nominal Working Pressure of either 35 or 70 MPa). The low thresholds in ISO 14687-2 for oxygen and water can be exceeded if the sampling procedure fails to purge the system sufficiently, which would lead to false results (60% in this study). Purging requirements to remove water were studied using a low pressure sampling rig. For hydrogen dispenser sampling using the Linde H2 Qualitizer (suitable for dispensing pressures up to 70 MPa), purging number and the effect of the initial fill level of a vehicle compressed hydrogen storage system were investigated experimentally to avoid hydrogen quality violation due to oxygen false positive. The study procedure reduces from 60% to 0% hydrogen quality violation. The next challenges highlighted are safe purging and reliable sampling of reactive contaminants in gas cylinders.  相似文献   
2.
The St. Clair-Detroit River System contains a world-class Great Lakes muskellunge (Esox masquinongy) fishery that has avoided the declines observed in many Great Lakes muskellunge populations. Muskellunge are an upper trophic level predator, and therefore a naturally low-density species. Limited fishery-independent data exist on which to base management decisions. To remedy this, we initiated an acoustic telemetry study in May of 2016, in collaboration with the Great Lakes Acoustic Telemetry Observation System. Our objective was to describe patterns of movement of muskellunge in this large and open system to better understand their spatial ecology. We acoustically tagged 133 muskellunge in the Detroit River and Lake St. Clair, and movements of 58 fish that passed our data quality control screens were analyzed. We utilized mixed modelling to assess the effects of sex, length, release location, and season on daily movement rates. We found that movement rates only differed among seasons, with highest movement rates occurring in the fall and lowest movement rates in the winter. Muskellunge tagged at different locations exhibited distinct residency patterns, and fish frequently crossed jurisdictional and waterbody boundaries. Ultimately our study highlights the scope and patterns of muskellunge movement in a large, unimpounded system and demonstrates that management of these fish would benefit from consideration of their full distribution covering multiple management jurisdictions.  相似文献   
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4.
Concentrations of total mercury (THg) in the axial musculature of northern pike (Esox lucius), walleye (Sander vitreus), lake whitefish (Coregonus clupeaformis), and sauger (Sander canadensis) were analyzed from several regions of Lake Winnipeg and three main inflows, focusing on Mossy Bay in the North Basin of the lake. Length-standardized means (standard means) indicated THg concentrations in pike of 550 mm fork length (0.44 ppm) and walleye measuring 400 mm (0.38 ppm) from Mossy Bay were highest in 1971 and declined to 0.13 and 0.22 ppm, respectively, by 1974. Standard means of both these species have been similar since 2010 (walleye; approximately 0.11 ppm) and 2013 (pike; approximately 0.17 ppm), except for a significant increase to 0.15 ppm in walleye in 2019, potentially related to concurrent changes in trophic interactions with invasive fish and invertebrate species. Standard means of 300 mm long sauger (0.23–0.29 ppm) did not decline significantly between 1971 and 1974, and those of 350 mm long whitefish ranged from 0.006 to 0.028 ppm from 1983 to 2016 with no clear temporal trend. In concert with data from other areas of Lake Winnipeg and the three inflows for 2000–2019, these results indicate higher contemporary concentrations in the South Basin of the lake. This latitudinal gradient in fish THg is assumed to be a result of continuous mercury inputs from the Red and the Winnipeg River, whereas a former point source of industrial mercury in the Saskatchewan River is no longer relevant. According to human consumption limits based on tolerable daily intake calculations and current THg concentrations of fish from Mossy Bay, substantial quantities of whitefish, pike, and walleye fish can be safely eaten.  相似文献   
5.
While nutrient loading has affected all levels of Lake Winnipeg’s ecology, its greatest influence has likely been on the microbial community. In addition to eutrophication, zebra mussels (Dreissena polymorpha) have recently invaded the ecosystem and threaten food web dynamics. Their filter-feeding predation and association with bacteria, specifically phototrophs, was investigated. A sampling trip to Lake Winnipeg in October 2017, focused on the isolation, enumeration, and identification of aerobic anoxygenic phototrophs in littoral water, sediment, and tissues of mussels. Gimli, Patricia, and Grand beaches, separated by >15 km across the South Basin, had similar bacterial counts when cultivated on rich organic, BG-11, purple non-sulphur, and K2TeO3-supplemented media. Culture-based enumeration on rich organic medium revealed 1.74% of heterotrophs from littoral waters were aerobic anoxygenic phototrophs, and represented 13.98% within sediments. In contrast, 0.48, 1.15, and 0.16% of cultured heterotrophs were aerobic anoxygenic phototrophs within zebra mussel gill, gut, and gonadal tissues, respectively. High-throughput sequencing of bacterial 16S V4 rDNA maintained similar trends in respective bivalve organs, where 0.22, 1.13, and 0.20% of total 16S genes belonged to these phototrophs. Several Sphingomonadaceae isolates were recovered from gut tissues, all with filamentous morphology large enough for predation. Bioaccumulation of metals was also studied in D. polymorpha. All tested associated aerobic anoxygenic phototrophs were capable of resisting the metalloid oxide tellurite. The consistent distribution of aerobic anoxygenic phototrophs within microbial communities across Lake Winnipeg, and their predominance in the gut tissues of zebra mussels suggested bacterial consumption by this invasive species.  相似文献   
6.
Joint photographic experts group (JPEG) can provide good quality with small file size but also eliminate extensively the redundancies of images. Therefore, hiding data into JPEG images in terms of maintaining high visual quality at small file sizes has been a great challenge for researchers. In this paper, an adaptive reversible data hiding method for JPEG images containing multiple two-dimensional (2D) histograms is proposed. Adaptability is mainly reflected in three aspects. The first one is to preferentially select sharper histograms for data embedding after K histograms are established by constructing the kth (k{1,2,,K}) histogram using the kth non-zero alternating current (AC) coefficient of all the quantized discrete cosine transform blocks. On the other hand, to fully exploit the strong correlation between coefficients of one histogram, the smoothness of each coefficient is estimated by a block smoothness estimator so that a sharply-distributed 2D-histogram is constructed by combining two coefficients with similar smoothness into a pair. The pair corresponding to low complexity is selected priorly for data embedding, leading to high embedding performance while maintaining low file size. Besides, we design multiple embedding strategies to adaptively select the embedding strategy for each 2D histogram. Experimental results demonstrate that the proposed method can achieve higher rate–distortion performance which maintaining lower file storage space, compared with previous studies.  相似文献   
7.
A direct formate microfluidic fuel cell with cotton thread-based electrodes is proposed. The palladium catalyst is directly coated on cotton threads by repeated dipping method to prepare electrodes, which integrates the flow channel and electrode together and provides exposed active sites for enhancing the mass transfer on the anode and cathode. The aqueous anolyte and catholyte transport through cotton threads by capillary force with aid of gravity, eliminating the use of any external pump and facilitating the integration and miniaturization of the whole system. In the experiment, a three-flow channel structure is employed. The fuel is sodium formate and the oxidant is hydrogen peroxide. 1 M Na2SO4 solution is introduced into the middle channel formed by cotton threads with no catalyst to alleviate the reactant crossover. Performance is evaluated under various catalyst loadings, fuel concentrations and differences in height between the inlet and outlet. Results show that the fuel cell produces an open circuit voltage (OCV) of 1.41 V. The maximum current density of 74.56 mA cm−2 and the peak power density of 24.75 mW cm−2 are yielded when the palladium loading is 1 mg cm−1 and the difference in height between the inlet and outlet is 7 cm, using 4 M HCOONa as fuel. Furthermore, the performance of the fuel cell increases first and then decreases with increasing the palladium loading. The same variation is observed with increasing the fuel concentration. However, the performance gradually increases with increasing the difference in height from 3 cm to 7 cm. The proposed microfluidic fuel cell with cotton thread-based electrodes shows enormous potential as a micro power source for portable devices.  相似文献   
8.
Pang Y  Gordon R 《Nano letters》2012,12(1):402-406
We experimentally demonstrate the optical trapping of a single bovine serum albumin (BSA) molecule that has a hydrodynamic radius of 3.4 nm, using a double-nanohole in an Au film. The strong optical force in the trap not only stably traps the protein molecule but also unfolds it. The unfolding of the BSA is confirmed by experiments with changing optical power and with changing solution pH. The detection of the trapping event has a signal-to-noise ratio of 33, which shows that the setup is extremely sensitive to detect the presence of a protein, even at the single molecule level.  相似文献   
9.
Two shallow-angled symmetric and asymmetric skins, with off-axis fiber angles of less than 45°, were proposed and employed to a 5 MW wind turbine blade. For the symmetric configuration, shallow-angled skins were applied to both the pressure and suction sides of the blade, while, for the asymmetric configuration, only the pressure side was implemented with a shallow-angled skin, keeping the conventional 45-degree-angled skin for the suction side. The blade tip deflection, modal frequencies, buckling stability, and failure index were computed for off-axis fiber angles of 45°, 35°, and 25°. The use of shallow-angled skins improved blade bending stiffness and strength. The buckling resistance decreased for symmetric skins and remained unchanged for asymmetric skins; the former case was compensated for by increasing the core thickness. For both skin configurations, a reduction in the blade failure index of up to 18% and 38%, and mass reductions of up to 8% and 13% were demonstrated for the 35° and 25° shallow-angled skins, respectively.  相似文献   
10.
Large eddy simulations of a model scale tidal turbine encountering inflow turbulence have been performed. This has allowed both unsteady blade loading and hydrodynamic noise radiation to be predicted. The study is motivated by the need to assess environmental impact of tidal devices, in terms of their acoustic impact on marine species.Inflow turbulence was accounted for using a synthetic turbulence generator, with statistics chosen to represent the gross features of a typical tidal flow. The turbine is resolved in a fully unsteady manner using a sliding interface technique within the OpenFOAM® libraries. Acoustic radiation is estimated using a compact source approximation of the Ffowcs Williams–Hawkings equation.It is observed that the long streamwise length scale of the inflow turbulence results in characteristic ‘humps’ in the turbine thrust and torque spectra. This effect is also evident in the far-field noise spectra. The acoustic sources on the blades are visualised in terms of sound pressure level and “Powell's source term”. These measures show that the dominant sources are concentrated at the blade leading edges towards the tip. This results from the high loading of the turbine blades, and causes the sound to radiate more akin to a monopole than a dipole.The full scale source level, obtained from scaling of the simulation results, is found to be lower than comparable measured data reported in the literature; this is attributed to additional sources not included in the present study. Based on the predicted source level, no physical impact on fish is expected.  相似文献   
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