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排序方式: 共有98条查询结果,搜索用时 31 毫秒
1.
V. A. A. Jansen 《Journal of mathematical biology》1995,34(2):195-224
The aim of this paper is to understand how dispersal in a patchy environment influences the stability properties of tri-trophic metapopulations. Differential equation models for tri-trophic metapopulations are formulated and analysed. The patchy nature of the metapopulations is incorporated through dispersal phases. Two variants are studied: one with a dispersal phase for the top and one with a dispersal phase for the middle level. A complete characterisation of stable and unstable equilibria is given and the possibility of invasion in these food chains is studied. A dispersal phase for the middle level can destabilize the bottom level-middle level interaction, because of the delay that dispersal causes in the reaction to the resource. When the middle level is not efficiently controlled by the top level, the unstable bottom level-middle level pair can destabilize the entire food chain. Dispersal for the top level can destabilize in the same way. A characterisation of the long term behaviour of the models is given. Bistability with a stable three species equilibrium and a stable limit cycle is one of the possibilities. 相似文献
2.
3.
Hou SM Van Dam FJ de Zwart F Warnock C Mognato M Turner J Podlutskaja N Podlutsky A Becker R Barnett Y Barnett CR Celotti L Davies M Hüttner E Lambert B Tates AD 《Mutation research》1999,431(2):211-221
The T-cell cloning assay, which enables the enumeration and molecular analysis of 6-thioguanine resistant (HPRT-negative) mutant T-cells, has been extensively used for studying human somatic gene mutation in vivo. However, large inter-laboratory variations in the HPRT mutant frequency (MF) call for further investigation of inter-laboratory differences in the experimental methodology, and development of an optimal but easy uniform cloning protocol. As part of the EU Concerted Action on HPRT Mutation (EUCAHM), we have carried out two Ring tests for the T-cell cloning assay. For each test, duplicate and coded samples from three buffy coats were distributed to five laboratories for determination of MF using six different protocols. The results indicated a good agreement between split samples within each laboratory. However, both the cloning efficiencies (CEs) and MFs measured for the same blood donors showed substantial inter-laboratory variations. Also, different medium compositions used in one and the same laboratory resulted in a remarkable difference in the level of MF. A uniform operating protocol (UOP) was proposed and compared with the traditional protocols in the second Ring test. The UOP (preincubation) increased the CE in laboratories traditionally using preincubation, but decreased the CE in laboratories traditionally using priming. Adjusted for donor, use of different protocols contributed significantly to the overall variation in lnCE (P=0.0004) and lnMF (P=0.03), but there was no significant laboratory effect on the lnCE (P=0.38) or lnMF (P=0.14) produced by the UOP alone. Finally, a simplified version of the UOP using the serum-free medium X-Vivo 10 and PMA was tested in one laboratory, and found to produce a considerable increase in CE. This modified UOP needs to be further evaluated in order to be used for future databases on HPRT MFs in various populations. 相似文献
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5.
Room temperature sterilization of surfaces and fabrics with a One Atmosphere Uniform Glow Discharge Plasma 总被引:8,自引:0,他引:8
K Kelly-Wintenberg T C Montie C Brickman J R Roth A K Carr K Sorge L C Wadsworth P P Y Tsai 《Journal of industrial microbiology & biotechnology》1998,20(1):69-74
We report the results of an interdisciplinary collaboration formed to assess the sterilizing capabilities of the One Atmosphere
Uniform Glow Discharge Plasma (OAUGDP). This newly-invented source of glow discharge plasma (the fourth state of matter) is
capable of operating at atmospheric pressure in air and other gases, and of providing antimicrobial active species to surfaces
and workpieces at room temperature as judged by viable plate counts. OAUGDP exposures have reduced log numbers of bacteria,
Staphylococcus aureus and Escherichia coli, and endospores from Bacillus stearothermophilus and Bacillus subtilis on seeded solid surfaces, fabrics, filter paper, and powdered culture media at room temperature. Initial experimental data
showed a two-log10 CFU reduction of bacteria when 2 × 102 cells were seeded on filter paper. Results showed ≥3 log10 CFU reduction when polypropylene samples seeded with E. coli (5 × 104) were exposed, while a 30 s exposure time was required for similar killing with S. aureus-seeded polypropylene samples. The exposure times required to effect ≥6 log10 CFU reduction of E. coli and S. aureus on polypropylene samples were no longer than 30 s. Experiments with seeded samples in sealed commercial sterilization bags
showed little or no differences in exposure times compared to unwrapped samples. Plasma exposure times of less than 5 min
generated ≥5 log10 CFU reduction of commercially prepared Bacillus subtilis spores (1 × 106); 7 min OAUGDP exposures were required to generate a ≥3 log10 CFU reduction for Bacillus stearothermophilus spores. For all microorganisms tested, a biphasic curve was generated when the number of survivors vs time was plotted in dose-response cures. Several proposed mechanisms of killing at room temperature by the OAUGDP are discussed.
Received 06 June 1997/ Accepted in revised form 01 November 1997 相似文献
6.
Elizabeth M. Hartgers G.H. Aalderink Paul J. Van den Brink Ronald Gylstra J. Wilfred F. Wiegman Theo C.M. Brock 《Aquatic Ecology》1998,32(2):135-152
Twelve indoor, plankton-dominated, freshwater microcosms (600 l) were used to study the effect of a mixture of herbicides
on structural and functional aspects of these ecosystems. The EC50, 72 h values of the most susceptible standard test alga
Selenastrum capricornutum (EC50, atrazine=54 μg l−1, EC50, diuron=15 μg l−1, EC50, metolachlor=56 μg l−1) were used as a starting
point for the dosage applied in the microcosms (dosages: 0, 0.01, 0.03, 0.1, 0.3, 1× EC50). The microcosms were exposed to
chronic levels for 28 days and subsequently monitored for 4 more weeks.
The following effects were observed: (1) direct effects became apparent from an initial drop in photosynthesis efficiency,
pH and oxygen concentration and a decrease in the abundance of several phytoplankton taxa at the 0.3 × EC50 treatment level
and higher. (2) Fourteen days post application an increase in the abundance of several phytoplankton taxa (Chlamydomonas sp.
and Stephanodiscus/Cyclotella) was observed; oxygen concentrations recovered while alkalinity, conductivity and total inorganic
nitrogen were elevated. (3) Effects on fauna were minor. Daphnia galeata showed a decreasing trend and the cyclopoid copepods
an increasing trend at the end of the experiment.
Multivariate statistical analyses demonstrated no effects of any treatment level on the zooplankton community. Effects were
reported for the phytoplankton community at dose levels of 0.3 × EC50 and higher. On species level the most sensitive taxon
was Chlorophyceae coccales. For this taxon a NOEC at the dose level of 0.01 × EC50 was calculated. This effect however was
relatively small in magnitude and merely based on an increase in numbers in the control and lowest treated microcosms rather
than a decrease in numbers in all other treatments. The standards based on algal toxicity data, as adopted by the Uniform
Principles, consist of a safety factors of 0.1 to be multiplied with the EC50. The NOEC of coccales was lower than 0.1 × EC50.
All other observed variables in this aquatic ecosystem were sufficiently protected against the mixture of herbicides by the
safety factor as proposed in the Uniform Principles.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
8.
The optimal distribution of biocatalyst in a fixed bed operating at steady state was determined to minimize the length of
the bed for a fixed conversion of 95%. The distribution in terms of the biocatalyst loading on an inert support depends upon
the axial distance from the bed entrance (continuous solution) as well as a set of dimensionless parameters that reflect the
bed geometry, the bulk flow, reaction kinetics and diffusional characteristics. A mathematical model of the system with the
following features was used to obtain the results: (1) convective mass transfer and dispersion in the bulk phase; (2) mass
transfer from the bulk phase to the surface of the catalyst particle; and (3) simultaneous diffusion and chemical reaction
in the catalyst particle with Michaelis–Menton kinetics and a reliable diffusion model (Zhao and DeLancey in Biotechnol Bioeng
64:434–441, 1999, 2000). The solution to the mathematical model was obtained with Mathematica utilizing the Runge Kutta 4–5 method. The dimensionless
length resulting from the continuous solution was compared with the optimal length restricted to a uniform or constant cell
loading across the entire bed. The maximum difference in the dimensionless length between the continuous and uniform solutions
was determined to be 6.5%. The model was applied to published conversion data for the continuous production of ethanol that
included cell loading (Taylor et al. in Biotechnol Prog 15:740–751, 2002). The data indicated a minimum production cost at a catalyst loading within 10% of the optimum predicted by the mathematical
model. The production rate versus cell loading in most cases displayed a sufficiently broad optimum that the same (non-optimal)
rate could be obtained at a significantly smaller loading such as a rate at 80% loading being equal to the rate at 20% loading.
These results are particularly important because of the renewed interest in ethanol production (Novozymes and BBI International,
Fuel ethanol: a technological evolution, 2004). 相似文献
9.
Testing for multimodality with dependent data 总被引:1,自引:0,他引:1
10.