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排序方式: 共有1417条查询结果,搜索用时 187 毫秒
101.
Combining Upscaling and Downscaling of Methane Emissions from Rice Fields: Methodologies and Preliminary Results 总被引:1,自引:0,他引:1
H.A.C. Denier van der Gon P.M. van Bodegom S. Houweling P.H. Verburg N. van Breemen 《Nutrient Cycling in Agroecosystems》2000,58(1-3):285-301
The uncertainty in the methane (CH4) source strength of rice fields is among the highest of all sources in the global CH4 budget. Methods to estimate the source strength of rice fields can be divided into two scaling categories: bottom-up (upscaling) and top-down (downscaling). A brief review of upscaling and downscaling methodologies is presented. The combination of upscaling and downscaling methodologies is proposed as a potential method to reduce the uncertainty in the regional CH4 source strength of rice fields. Some preliminary results based on upscaling and downscaling are presented and the limitations of the approaches are discussed. The first case study focuses on upscaling by using a field-scale model in combination with spatial databases to calculate CH4 emissions for the island of Java. The reliability of upscaling results is limited by the uncertainty in model input parameters such as soil properties and organic carbon management. Because controlling variables such as harvested rice area may change on relatively short time scales, a land use change model (CLUE) was used to quantify the potential land use changes on Java in the period 1994–2010. The predicted changes were evaluated using the CH4 emission model. Temporal scaling by coupling land use change models and emission models is necessary to answer policy-related questions on future greenhouse gas emissions. In a downscaling case study, we investigate if inverse modeling can constrain the emissions from rice fields by testing a standard CH4 from rice scenario and a low CH4 from rice scenario (80 and 30 Tg CH4 yr–1, respectively). The results of this study are not yet conclusive; to obtain fine-resolution CH4 emission estimates over the Southeast Asian continent, the monitoring network atmospheric mixturing ratios need to be extended and located closer to the continental sources. 相似文献
102.
R Santos F Oliveira J Fernandes S Gon?alves F Macieira M Cadete 《Water science and technology》2005,52(8):177-180
Mycobacteria have emerged as a major cause of opportunistic infections. Until the present, only a few studies have characterized mycobacteria present in the water distribution system of urban areas. In this study, we characterize these microorganisms in the Lisbon water distribution system. Our results indicate a high rate of positivities (90.5%) with mainly saprophytic mycobacteria. Around 63% of these results belong to strains of Mycobacterium gordonae indicating a generalized proliferation of this species in the Lisbon water distribution system. A total of 21.05% of the isolates are from M. kansasii, M. intracellulare and M. chelonae. 相似文献
103.
Berta Gonçalves Ana Paula Silva José Moutinho-Pereira Eunice Bacelar Eduardo Rosa Anne S. Meyer 《Food chemistry》2007,103(3):976-984
The relationship between colour parameters and anthocyanins of four sweet cherry cultivars, Burlat, Saco, Summit and Van was studied. The colour (L∗, a∗, b∗, chroma and hue angle parameters) and anthocyanins were analysed during two different years at two different ripening stages (partially ripe, and ripe, respectively). The cherries were analysed at harvest and after storage at 1.5 ± 0.5 °C and 15 ± 5 °C for 30 and 6 days, respectively. The colour was measured by tristimulus colourimetry (CIELAB system) directly on the fruits, while anthocyanins were quantified by HPLC-DAD analysis on methanolic extracts of freeze-dried samples of the fresh cherries and on the differently stored cherries. L∗, chroma, and hue angle values were always lower for the ripe than for the partially ripe cherries. All of the cultivars were found to contain cyanidin-3-rutinoside and cyanidin-3-glucoside as the major anthocyanins. The total anthocyanin content in fruits of the different cultivars varied in the order Burlat > Saco > Van > Summit. The concentration of anthocyanins increased at both temperatures of storage in both ripe and partially ripe cherries, but the extent of increase varied among cultivars. Cherries stored at 15 ± 5 °C showed higher reduction of L∗, chroma and hue angle than fruits stored at 1.5 ± 0.5 °C. L∗, a∗, b∗, chroma and hue angle correlated negatively (P < 0.001) with the total anthocyanins levels, but not with the total phenols. These results show that chromatic functions of chroma and hue correlate closely with the evolution of colour and anthocyanins levels during storage of sweet cherries and indicate that colour measurements can be used to monitor pigment evolution and anthocyanin contents of cherries (and vice versa). 相似文献
104.
105.
The purpose of this article is to give a short mathematical introduction to the analysis of EEG signals by means of frequency-selective filters. Besides the resonant frequency, three characteristics of practical filters turn out to be of primary importance. These characteristics are: 1) the time selectivity (width of the window function), indicating the duration of the part of the signal under investigation; 2) the frequency selectivity as bandwidth of the filter; 3) the efficiency, i.e., the ratio of the standard deviation of the filter output to the mean output, in case random noise is fed into the filter. 相似文献
106.
Kuiwon Choi Gon Khang Steven A. Goldstein 《Journal of Mechanical Science and Technology》2001,15(7):1022-1031
The elastic modulus and fatigue properties of canine and human trabecular bone tissues (single trabeculae) were experimentally determined on a microstructural level using four-point bending cyclic test, and they were compared based on microstructural characteristics and mineral density. The results showed that canine trabecular bone tissue had significantly lower modulus and lower fatigue strength than human tissue. The observed microstructural differences between the two tissues may be more responsible for the differences, although the lower mineral density in canine tissue might also have contributed to the lower modulus and fatigue strength. 相似文献
107.
An effect of ZnO concentration at the surface of brass-plated steel cord on the adhesion property between a rubber compound
and a brass-plated steel cord was investigated. Cord composition was determined by an Auger microscope with Ar ion sputtering.
Two different steel cords were prepared; one (cord A) had higher ZnO concentration at the cord surface compared to the other
(cord B). Pull-out force of unaged adhesion sample of cord A was lower than that of cord B. But the adhesion durability of
the humidity-aged adhesion sample of cord A was better than the latter. Rubber coverage of the pull out cord for the unaged
adhesion samples of cord A was poor, indicating insufficient formation of an adhesion layer. Pull-out force of the thermal-aged
adhesion samples decreased with increasing aging time and that of cord A was lower than that of cord B. The enhancement of
rubber coverage during initial aging period could be explained by an additional formation of copper sulfide at the adhesion
interphase and an increase of modulus of rubber compound adjacent to the adhesion layer. With further increases of aging time,
adhesion interphase grew excessively and the physical property of rubber compound deteriorated significantly, such that rubber
coverage of adhesion samples decreased markedly with increasing aging time. 相似文献
108.
Films of aluminium oxide have been formed on single crystal silicon substrates using AlCl3-CO2-H2 gas mixtures in a cold-walled chemical vapour deposition (CVD) reactor. The nucleation and subsequent growth of the deposit have been observed under the varying process parameters. It is found that the nucleation and growth of the Al2O3 are dependent on the H2O flux and H2O supersaturation. An activation energy of 34.8 Kcal mol–1 is obtained for the growth rate indicating that the CVD of Al2O3 on silicon is a thermally activated process and limited by surface reaction. Scanning electron micrographs (SEM) show that the deposited films are amorphous at low temperature, 850° C, but change to fine grained polycrystalline structure at high temperature, 1000° C. 相似文献
109.
Rogério Mendes Carla Pestana Amparo Gonçalves 《International Journal of Food Science & Technology》2008,43(11):2000-2009
Sardine (Sardina pilchardus) is a species that for its abundance assumes great importance in the Portuguese fishing sector. In order to contribute for a better utilisation of this species, the aim of this study was to investigate the effect of the pre‐treatment with soluble gas stabilisation (SGS) (100% CO2 at 2 bar, during 15 and 30 min) on the quality and shelf‐life of sardine fillets, packed in air (AP), vacuum (VP) and modified atmosphere (MAP: 5% O2/35% CO2/60% N2). During the chilled storage, the quality changes were evaluated by sensory evaluation, chemical and microbiological analysis. The total volatile basic nitrogen content remained almost constant, between 16 and 19 mg N/100 g muscle, during the storage period, for all samples. The TBARs values increased with storage time, for all batches and storage conditions. The application of SGS treatment to sardine fillets, resulted in a bacteriostatic effect, contributing to the improvement of the microbiological quality of fillets. Considering a sensory criteria, the shelf‐life of SGS pre‐treated sardine fillets was found to be 5 days in AP and MAP while in VP‐treated fillets a shelf‐life of 8 days was reported. At sensory rejection, sardine fillets presented a K‐value of 30% in AP and MAP batches and 40% in VP batch. 相似文献
110.
New measurements are reported for the density and viscosity of tetralin and trans-decalin. The density was determined from room temperature to 60°C for tetralin and to 95°C for trans-decalin. The kinematic viscosity was measured up to temperatures slightly above 100°C. Our results improve upon the values recommended by the American Petroleum Institute for these liquids. 相似文献