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CO₂, CH₄, and N₂O (GHG) emissions are globally important in China, but few field observations have been made in freshwater lakes. In this paper, we measured the GHG effluxes from 44 sampling locations among four sub-regions in Poyang Lake in China in October 2010 using floating chambers. The mean CO₂, CH₄, and N₂O effluxes were 0.23 μmol m⁻²·s⁻¹, 3.0 nmol·m⁻²·s⁻¹, and 0.11 nmol m⁻²·s⁻¹, ranging from -0.25 to 0.54 μmol·m⁻²·s⁻¹, 1.4 to 8.9 nmol m⁻²·s⁻¹, and 0.012 to 0.21 nmol·m⁻²·s⁻¹ for the CO₂, CH₄, and N₂O efflux, respectively. We found differently related tendencies between GHG effluxes and environmental parameters for each sub-region and, totally, four sub-regions together. The 16 environmental factors explained the GHG effluxes with 55%, 70%, and 89% of the variation in CO₂, CH₄, and N₂O efflux, respectively, in Poyang Lake. Our analysis revealed that sediment C/N ratio, water depth, and the difference of air-water temperature were significantly contributing variables for GHG effluxes in the lake.
This study was conducted to evaluate the predictions of dry matter intake (DMI), average daily gain (ADG), and faecal nitrogen (N) excretion by the Cornell Net Carbohydrate and Protein System Version 6.1.26 (CNCPSv6) in China. A total of 71 bulls from two imported breeds, Limousin and Simmental, and three local breeds: Luxi, Jinnan and Qinchuan were selected in China. Data required by the CNCPSv6 model were collected, and model predictions were generated for animals of each breed. The regression equation between observed and predicted DMI for these cattle was: YOBS = 0.93XCNCPS + 0.48 (R2 = 0.94; P < 0.001), with an intercept not different from zero and a slope not different from unity. The proportion of deviation points lying within the range –0.4 to 0.4 kg · d–1 was 90.1%. The regression equation between observed and predicted ADG was: YOBS = 1.07XCNCPS – 0.05 (R2 = 0.92; P < 0.001), with an intercept not different from zero and a slope not different from unity. About 78.9% of points fell within the range –0.1 to 0.1 kg/d for these cattle. Model-predicted faecal N excretion for the cattle breeds was close to the observed values. The regression equation between observed and predicted faecal N excretion was: YOBS = 1.04XCNCPS – 1.48 (R2 = 0.94; P < 0.001), with an intercept not different from zero and a slope not different from unity. About 73.3% of the points fell within −4 and 4 g per day. These results show that the CNCPSv6 model using actual feed fractions can give good predictions of DMI, ADG and faecal N excretion with different beef cattle breeds in China.
Annular cavitator with water injection is one of the key parts of the long-range supercavitating vehicle powered by water ramjet. In this paper, hydrodynamic properties of annular cavitator are studied numerically. The standard k ~ ε turbulence model is coupled with the Reynolds Averaged Navier-Stokes (RANS) equations to model the natural supercavitation process. The multiphase flow is considered as a mixture of varying density and modeled by the mass exchange equations. To fully understand this process, numerical simulations were performed for different annular cavitators. Computational Fluid Dynamics (CFD) results, including the pressure distribution and forces acting on the cavitator surface, mass flow and pressure loss of water injection, various supercavity sizes, were obtained and analyzed. The pressure distribution on the cavitator surface was significantly changed which resulted in 4 ~ 6% increase of the total drag of the vehicle. The results show that the mass flow and velocity of the injection water is mainly dependent on the tube size, while the total pressure loss of the water injection is mostly related to the outlet pressure. Supercavity generated by annular cavitator is smaller than that of the discal one. Based on the correlation analysis of the supercavity size and other factors, it could be concluded that the contraction of the cavity size is mainly caused by the diffluent mass flow of the water injection
His296 of Zymomonas mobilis levansucrase (EC 2.4.1.10) is crucial for the catalysis of the transfructosylation reaction. The three-dimensional structures of levansucrases revealed the His296 is involved in the substrate recognition and binding. In this study, nine mutants were created by site-directed mutagenesis, in which His296 was substituted with amino acids of different polarity, charge and length. The substitutions of His296 with Arg or Trp retained partial hydrolysis and transfructosylation activities. The positively charged Lys substitution resulted in a 2.5-fold increase of sucrose hydrolysis. Substitutions with short (Cys or Ser), negatively charged (Glu) or polar (Tyr) amino acids virtually abolished both the activities. Analysis of transfructosylation products indicated that the mutants synthesized different oligosaccharides, suggesting that amino acid substitutions of His296 strongly affected both the enzyme activity and transfructosylation products.
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