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本文是文「5」在n=2时更进一步的讨论,模型由一个种群构成,此种群可在两个毒素环境中生存,且种群扩散仅与其所在自下而上环境中的(数量)密度决定,得到了比文「5」更精细的结论。 相似文献
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T S Tenforde 《Bioelectromagnetics》1986,7(3):341-346
Rectal temperatures were recorded in mice and rats during exposure to a stationary 7.55 Tesla (1 T = 10(4) Gauss) homogeneous magnetic field, and to magnetic field gradients ranging from 58.1 - 58.6 T/m. Contrary to observations reported recently by other investigators, no evidence was found for a change in the body temperature of rodents exposed to strong homogeneous or gradient magnetic fields. 相似文献
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Hayama M Kawakami Y Kaneko Y Sano K Ota H 《Journal of cellular and molecular medicine》2005,9(3):746-747
We investigated the effect of H. pylori infection on cell proliferation of gastric mucosa using immunostaining for H. pylori or Ki67. H. pylori cells attached to surface mucous cells covering luminal surface and the upper part of gastric foveolae, and up-regulated the proliferative activity of gastric epithelial cells without adhering to the proliferating epithelial cells. 相似文献
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A field strength dependent increase in the amplitude of the T-wave signal in the rat electrocardiogram (ECG) was observed during exposure to homogeneous, stationary magnetic fields. For 24 adult Sprague-Dawley and Buffalo rats of both sexes, the T-wave amplitude was found to increase by an average of 408% in a 2.0 Tesla (1 Tesla = 104 Gauss) field. No significant magnetically induced changes were observed in other components of the ECG record, including the P wave and the QRS complex. The minimum field level at which augmentation of the T wave could be detected was 0.3 Tesla. The magnetically induced increase in T-wave amplitude occurred instantaneously, and was immediately reversible after exposure to fields as high as 2.0 Tesla. No abnormalities in any component of the ECG record, including the T wave, were noted during a period of 3 weeks following cessation of a continuous 5-h exposure of rats to a 1.5-Tesla field. The heart rate and breathing rate of adult rats were not altered during, or subsequent to, application of fields up to 2.0 Tesla. The effect of animal orientation within the field was tested using juvenile rats 3–14 days old. The maximum increase in T-wave amplitude was observed when subjects were placed with the long axis of the body perpendicular to the lines of magnetic induction. These experimental observations, as well as theoretical considerations, suggest that augmentation of the signal amplitude in the T-wave segment of the ECG may result from a superimposed electrical potential generated by aortic blood flow in the presence of a stationary magnetic field. 相似文献
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Christos Rumbos Alexander Mendoza Richard Sikora Sebastian Kiewnick 《Biocontrol Science and Technology》2008,18(10):1041-1050
The persistence of the nematophagous fungus Paecilomyces lilacinus Samson strain 251 (PL251) and the effect of application rate, substrate type, as well as the presence of the nematode host on its dynamics after application to the soil were investigated under controlled conditions. In all experiments, increase of P. lilacinus colony forming units after application was not found. In contrast, a gradual decline in fungal densities over time was observed. Application rate had no significant effect on the dynamics of the fungal population. Likewise, P. lilacinus density decline in soil was not significantly affected by the presence of the nematode host. Substrate type had a significant effect on P. lilacinus persistence in soil. The fungal agent persisted longer in silty loam and clay soil, with reduced persistence when sand was added to field soil. Conversely, when organic substrate was added to pure sand, persistence was significantly increased. Although persistence of fungal biocontrol agents in soil depends on various biotic and abiotic conditions, baseline data on persistence such as those reported in this study are helpful for biocontrol and environmental risk assessment and merit further study. 相似文献
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Simultaneous measurements were made of the electrocardiogram (ECG) and the intraarterial blood pressure of adult male Macaca monkeys during acute exposures to homogeneous stationary magnetic fields ranging in strength up to 1.5 tesla. An instantaneous, field strength-dependent increase in the ECG signal amplitude at the locus of the T wave was observed in fields greater than 0.1 tesla. The temporal sequence of this signal in the ECG record and its reversibility following termination of the magnetic field exposure are consistent with an earlier suggestion that it arises from a magnetically induced aortic blood flow potential superimposed on the native T-wave signal. No measurable alterations in blood pressure resulted from exposure to fields up to 1.5 tesla. This experimental finding is in agreement with theoretical calculations of the magnetohydrodynamic effect on blood flow in the major arteries of the cardiovascular system. 相似文献
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Persistence and vulnerability: Retaining biodiversity in the landscape and in protected areas 总被引:1,自引:0,他引:1
An objective of biodiversity conservation activities is to minimize the exposure of biodiversity features to threatening processes
and to ensure, as far as possible, that biodiversity persists in the landscape. We discuss how issues of vulnerability and
persistence can and should be addressed at all stages of the conservation planning and implementation process. Procedures
for estimating the likelihood of persistence and for measuring degrees of vulnerability at different spatial and temporal
scales using subjective assessments, rules of thumb and analytical and simulation models are reviewed. The application of
information on vulnerability and persistence to conservation planning and management is discussed under the headings of natural
dynamics, replication of protection, levels of representation, source and sink population structures, refuges and critical
resources, reserve design, habitat fragmentation and levels of management. 相似文献
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Rhamnolipids are commonly produced using N-limited Pseudomonas aeruginosa fermentations, with active production in the stationary phase. The production, however, stops after certain period. This causes lower productivity and yield because of downtime between batches and the substrate consumed for cell growth. This discontinued production is the significant problem addressed in this study. Rhamnolipid synthesis involves complex regulatory mechanisms, including quorum-sensing systems and alternative sigma factors. Current knowledge on these mechanisms, however, cannot adequately explain the discontinued rhamnolipid production at extended stationary phase. Four hypotheses to causes of this discontinued production were examined here with carefully planned fermentation designs using different initial N-source concentrations and different ways of adding oil and nutrients. Results rejected three of the hypothetical causes: accumulation of rhamnolipids or other inhibitory metabolites, presence of high amounts of oil phase, and exhaustion of non-N nutrients, and supported the hypothesis that the stopped production was caused solely by the extended N-starvation experienced by the cells. The discontinued production was found to be fully reactivated by partial broth replacements with fresh media containing N-source. The finding is important to production economics and promotes new designs to maximize rhamnolipid productivity and yield using extended stationary-phase production instead of short repeated batches. 相似文献
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Humoral and cell-mediated immune responses were assayed following a 6-day exposure of LAF1/J mice to a 1.50 Tesla (1 T = 10(4) Gauss) stationary magnetic field. In tests of the immune response to sheep erythrocytes, the number of Jerne plaques formed by spleen lymphocytes and the level of serum IgM were not significantly different for the exposed mice in comparison with control animals. Tests for mitogen-induced lymphocyte proliferation also demonstrated no significant differences in the response of spleen lymphocytes from exposed and control groups of mice. 相似文献
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Jacqueline Jerney Salla Annika Ahonen Pivi Hakanen Sanna Suikkanen Anke Kremp 《Journal of phycology》2019,55(6):1226-1238
In seasonal environments, strong gradients of environmental parameters can shape life cycles of phytoplankton. Depending on the rate of environmental fluctuation, specialist or generalist strategies may be favored, potentially affecting life cycle transitions. The present study examined life cycle transitions of the toxin producing Baltic dinoflagellate Alexandrium ostenfeldii and their regulation by environmental factors (temperature and nutrients). This investigation aimed to determine whether genetic recombination of different strains is required for resting cyst formation and whether newly formed cysts are dormant. Field data (temperature and salinity) and sediment surface samples were collected from a site with recurrent blooms and germination and encystment experiments were conducted under controlled laboratory conditions. Results indicate a lack of seasonal germination pattern, set by an endogenous rhythm, as commonly found with other dinoflagellates from the Baltic Sea. Germination of quiescent cysts was triggered by temperatures exceeding 10°C and combined nutrient limitation of nitrogen and phosphorus or a drop in temperature from 16 to 10°C triggered encystment most efficiently. Genetic recombination was not mandatory for the formation of resting cysts, but supported higher numbers of resistant cysts and enhanced germination capacity after a resting period. Findings from this study confirm that A. ostenfeldii follows a generalist germination and cyst formation strategy, driven by strong seasonality, which may support its persistence and possibly expansion in marginal environments in the future, if higher temperatures facilitate a longer growth season. 相似文献
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When starved of essential nutrients, yeast cells cease mitotic division and enter an alternative state called the 'stationary phase'. In this paper, we report that stationary cells enter two major pathways: meiosis and apoptosis. Using transmission electron microscopy, five types of cell were identified in the stationary phase: (1) cells with chromosome condensed nuclei; (2) cells with normal, homogeneously stained nuclei; (3) sporulated cells; (4) apoptotic cells, in which chromatin, but not individual chromosomes, was condensed; and (5) dead cells, in which nuclei and cytoplasm were degraded. Further evidence using live cell imaging and mutation analysis suggested that cells with condensed chromosomes underwent meiosis, whereas chromatin condensed cells underwent apoptotic cell death. Cells with homogeneous nuclei are believed to be in the true resting state and undergo cell death when starvation continues. Chromosome or chromatin condensation may serve as a hallmark of life or death for stationary cells. 相似文献
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Bioassays were used to study the infectivity of cytoplasmic polyhedrosis viruses (CPVs), nuclear polyhedrosis viruses (NPVs) and entomopoxviruses (EPVs) contained in 16 nests of the paper waspPolistes hebraues F. in Réunion Island. Several virosis were propagated from 6 nest contents in 5 Lepidoptera:Catopsilia thauruma Saalmüller,Catopsilia florella F.,Callixena versicolora Mabille,Polydesma umbricola Boisduval andEagris sabadius Boisduval. Each of the previous species supported the development of one or two virosis and therefore, wasp nests must be considered as accumulating centres where infectivity of occluded entomoviruses is preserved. The accurate origin of the virosis propagated through bioassays was searched for using ecological investigations on similar natural diseases, REN analysis and a cross-transmission test onSpodoptera mauritia Boisduval. The nuclear polyhedrosis and one cytoplasmic polyhedrosis appearing in bioassays can be assigned respectively to viruses produced byC. thauruma andC. versicolora; the other virosis must be considered as developing in alternate or substitution hosts. Wasp nests could therefore be used to detect the presence of specific viruses in an environment and to collect new virus isolates. 相似文献
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G. D. Griffin 《Journal of nematology》1991,23(3):306-315
Persistence of dormant Ranger and nondormant Moapa alfalfas, both susceptible to Ditylenchus dipsaci, varied with stand age and cutting frequency. Stand reduction increased with cutting frequency. In D. dipsaci-infested soil, stand reductions in Ranger 1, 4, and 5 years old exceeded reductions in stands 2 and 3 years old; persistence was greatest in 2-year-old stands. In Moapa alfalfa, D. dipsaci reduced stands the most in years 2 and 3; whereas persistence was greatest in 1-year-old stands. Harvesting Ranger alfalfa one, two, three, and four times during the growing season reduced 2-year-old stands by 10, 14, 19, and 29% in D. dipsaci-infested soil and by 2, 4, 4, and 7% in uninfested soil, respectively. Comparable reductions in Moapa alfalfa were 13, 16, 18, and 38% in infested soil and 0, 2, 4, and 6% in uninfested soil. Cutting frequency had less effect on persistence of resistant semidormant Lahontan grown in D. dipsaci-infested soil relative to susceptible cultivars. Increasing the number of cuttings per year decreased storage of total nonstructural carbohydrate and adversely affected persistence of alfalfa stands and yields; the greatest negative effects occurred on both resistant and susceptible alfalfa in D. dipsaci-infested soil. 相似文献
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An extensive study of the behavior of three chiral stationary phases (CSP) used in liquid chromatography (LC) is presented for the stereoselective determination of methadone. The following chromatographic columns were selected: a cellulose, Chiralcel OJ; a modified cyclodextrin, Cyclobond I 2000 RSP, and a protein, Chiral‐AGP. Retention factors, enantioselectivity, efficiency, and resolution were tested by modifying the composition of the mobile phase as well as the temperature. The mechanism for the chiral recognition of methadone on each support was discussed. Optimal chromatographic parameters were obtained for the three supports tested, and methadone enantiomers were separated in less than 20 minutes. The cellulose‐based column gave the best resolution, but this CSP was not adapted to clinical analyses of methadone. Under optimized conditions, the cyclodextrin‐ and protein‐based columns allowed an excellent separation of methadone enantiomers, but no interference with the primary metabolite was found only with Chiral‐AGP. Chirality 11:319–325, 1999. © 1999 Wiley‐Liss, Inc. 相似文献
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New brush-type chiral stationary phases (CSP I-IV) comprising N-3,5,6-trichloro-2,4-dicyanophenyl-L-alpha-amino acids (1-4) were prepared by binding of chiral selectors 1-4 to gamma-aminopropyl silica gel. To check the role of excess free aminopropyl groups, CSP V was prepared by binding N-3,5,6-trichloro-2,4-dicyanophenyl-L-alanyl-(3-triethoxysilyl)propylamide to unmodified silica gel. The best separation of racemic 2-aryloxypropionic acids (TR-1-13) was obtained with CSP I; the -(-)-S enantiomer were regularly eluted first, as determined by a CD detector. The mechanism of chiral recognition implies a synergistic interaction of carboxylic acid analyte with the chiral selector and achiral free gamma-aminopropyl units on silica. In fact, CSP V, which is lacking an achiral aminopropyl spacer, shows a lower separation ability for 2-aryloxypropionic acids, but a similar enantioselective discrimination of esters TR-19-20, in comparison with CSP I. CSP I-IV retain unaltered separation ability after a few months of continuous work using a large number of various mobile phases. 相似文献
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Abstract The electrophoretic analysis of nuclear proteins extracted from root meristems at different times of germination puts in evidence the variations of content of specific proteins. Several nuclear proteins are phosphorylated by endogenous protein kinase and often the maximum rate of phosphorylation it has been observed in proteins present in the nucleus at low concentrations. Moreover also the phosphorylation rate of specific proteins changes at different times of germination. It is interesting the fact that both variations of concentration and phosphorylation in nuclear proteins occurr at the time when root meristems leave the quiescence to enter a proliferating state. We suggest that these variations play a role in this physiological event. 相似文献