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排序方式: 共有792条查询结果,搜索用时 15 毫秒
52.
A new one-dimensional mixed-culture biofilm model was derived based on a hypothesis that each particulate component would have different space occupancy within biofilm. Contrary to conventional density-based modeling approaches, in this model the volume change of the biofilm is described with the space occupancies of the particulate components, new model parameters introduced here. The unique feature of this model is that internal pore development during biofilm growth can be predicted implicitly so that the changes of effective diffusivities of soluble components depending on internal porosity are readily implemented in the model. Simulation studies revealed that the presented biofilm model could reasonably describe several important aspects of biofilm growth phenomena. In a mixed-culture biofilm system where heterotrophs and autotrophs were involved, the overall biofilm growth pattern was governed by microbial competition depending on influent composition. In a thick heterotrophic biofilm, a simulated biomass distribution and internal porosity profile showed higher total biomass concentration, lower active cell fraction, and lower internal porosity in the bottom layers of the biofilm, which are well coincident with the experimental data reported previously. All these phenomena can be explained by the proceeding of biofilm consolidation, which happens due to the inter-conversions of the particulate components having different space-occupancy values. The presented biofilm model suggests that the space occupancy of EPS may be a key model parameter to decide the overall biofilm growth pattern by regulating the extent of biofilm consolidation. 相似文献
53.
Wieliczko RJ Williamson JH Cursons RT Lacy-Hulbert SJ Woolford MW 《Journal of dairy science》2002,85(9):2149-2154
The discriminatory power of two polymerase chain reaction-based DNA fingerprinting methods, random amplified polymorphic DNA and repetitive extragenic palindrome were compared by subtyping 128 isolates of Streptococcus uberis cultured from cows in six different dairy herds in New Zealand. The typing results demonstrated that the majority of isolates possessed unique fingerprint profiles except on occasions where multiple isolates were obtained from individual cows. On these occasions, individual quarters of the mammary gland were generally, but not exclusively, infected by the same strain of bacteria. Both random amplified polymorphic DNA and repetitive extragenic palindromic typing assays were simple to perform, relatively inexpensive ($11.00 per reaction), and provided reliable and reproducible results. Furthermore, when these assays were used in conjunction with each other, they provided a means of confirmation of the specific DNA fingerprint patterns obtained. 相似文献
54.
A biofilm model for flowing systems in the food industry 总被引:1,自引:0,他引:1
den Aantrekker ED Vernooij WW Reij MW Zwietering MH Beumer RR van Schothorst M Boom RM 《Journal of food protection》2003,66(8):1432-1438
When bacteria attach to the walls of pipelines, they can form biofilms, which can cause the recontamination of food products. In order to quantify such recontamination, a one-dimensional biofilm model was developed taking into account adsorption, desorption, and the growth of cells. The model consisted of two mass balances describing increases in biofilm formation at the wall and the accumulation of cells in the liquid phase. The necessary parameters for the model were obtained in laboratory biofilm experiments. These experiments involved a flowing system and the use of Staphylococcus aureus as a model pathogen and silicon tubing as a testing material. S. aureus was inoculated into the system for 2 h, and then the system was changed to a sterile medium. Both biofilm formation and the release of cells into the flowing liquid were measured until steady-state conditions were reached (for up to 9 days). The experiments were performed in duplicate for different flow conditions (i.e., for Reynolds numbers of 3.2, 32, and 170). It was shown that at higher Reynolds numbers, the biofilm developed faster, probably owing to an increase in the transfer of nutrients to the surface. The proposed biofilm model was capable of describing the data obtained for the three different flow conditions with the use of the specific growth rate in the biofilm and the desorption coefficient as fit parameters. The specific growth rates were 0.16, 0.27, and 0.49 h(-1) for Reynolds numbers of 3.2, 32, and 170, respectively, and the desorption coefficients were about 1% of these values. 相似文献
55.
The internalization and persistence of a bioluminescent Escherichia coli O157:H7 Ph1 was investigated in growing spinach plants that had been either biologically or mechanically damaged. In control (undamaged) plants cultivated in soil microcosms inoculated with E. coli O157:H7 Phl, the bacterium was recovered from surface-sterilized root tissue but not from leaves. Mechanical disruption of the seminal root and root hairs of the plants did not result in the internalization of the pathogen into the aerial leaf tissue. When imprints of the root tissue were made on plates of tryptic soy agar plus ampicillin, no colonies of E. coli O157:H7 were observed around damaged tissue. The roots of growing plants were exposed to the northern root-knot nematode, Meloidogyne hapla, in the presence of E. coli O157:H7. Although this treatment caused knot formation on the roots, it did not enhance the internalization of the bacterium into the plant vascular system. Coinoculation of intact leaves with E. coli O157:H7 and the phytopathogen Pseudomonas syringae DC3000 resulted in localized necrosis, but the persistence of the human pathogen was not affected. The mechanical disruption of roots does not result in the internalization of E. coli O157:H7 into the aerial tissue of spinach, and there does not appear to be any effect of P. syringae in terms of enhancing the persistence of E. coli O157:H7 in spinach leaves. 相似文献
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59.
Room-temperature high on/off ratio in suspended graphene nanoribbon field-effect transistors 总被引:1,自引:0,他引:1
Lin MW Ling C Zhang Y Yoon HJ Cheng MM Agapito LA Kioussis N Widjaja N Zhou Z 《Nanotechnology》2011,22(26):265201
We have fabricated suspended few-layer (1-3 layers) graphene nanoribbon field-effect transistors from unzipped multi-wall carbon nanotubes. Electrical transport measurements show that current annealing effectively removes the impurities on the suspended graphene nanoribbons, uncovering the intrinsic ambipolar transfer characteristic of graphene. Further increasing the annealing current creates a narrow constriction in the ribbon, leading to the formation of a large bandgap and subsequent high on/off ratio (which can exceed 10(4)). Such fabricated devices are thermally and mechanically stable: repeated thermal cycling has little effect on their electrical properties. This work shows for the first time that ambipolar field-effect characteristics and high on/off ratios at room temperature can be achieved in relatively wide graphene nanoribbons (15-50 nm) by controlled current annealing. 相似文献
60.
Meaney PM Paulsen KD Geimer SD Haider SA Fanning MW 《IEEE transactions on bio-medical engineering》2002,49(7):708-720
Two-dimensional (2-D) approaches to microwave imaging have dominated the research landscape primarily due to the moderate levels of measurement data, data-acquisition time, and computational costs required. Three-dimensional (3-D) approaches have been investigated in simulation, phantom, and animal experiments. While 3-D approaches are certainly important in terms of the potential to improve image quality, their associated costs are significant at this time. In addition, benchmarks are needed to evaluate these new generation systems as more 3-D methods begin to appear. In this paper, we present a systematic series of experiments which assess the capability of our 2-D system to image classical 3-D geometries. We demonstrate where current methods suffer from 3-D effects but also identify situations where they remain quite useful. Comparisons between reconstructions utilizing phantom measurements and simulated 3-D data are also shown to validate the results. These findings suggest that for certain biomedical applications, 2-D approaches remain quite attractive. 相似文献