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81.
Global stability of an SIR epidemic model with time delays   总被引:11,自引:0,他引:11  
An SIR disease transmission model is formulated under the assumption that the force of infection at the present time depends on the number of infectives at the past. It is shown that a disease free equilibrium point is globally stable if no endemic equilibrium point exists. Further the endemic point (if it exists) is globally stable with respect to the whole state space except the neighborhood of the disease free state.Research partly supported by the Ministry of Education, Science and Culture, Japan, Grant 05640256  相似文献   
82.
Cotyledons excised from dark-grown seedlings of cucumber (Cucumis sativus L.) were cultured in vitro under UV radiation at different wavelengths, obtained by passage of light through cut-off filters with different transmittance properties. Growth and the synthesis of chlorophyll (Chl) in cotyledons were inhibited and malondialdehyde was accumulated upon irradiation at wavelengths below 320 nm. Exogenous application of scavengers of free radicals reversed the growth inhibition induced by UV-B. Measurement of the fluorescence of Chl a suggested that electron transfer in photosystems was affected by UV-B irradiation. On the basis of these results, the involvement is postulated of active species of oxygen in damages to thylakoid membranes and the growth inhibition that are induced by UV-B irradiation.Abbreviations Chl chlorophyll - Fm maximal fluorescence (dark) - Fm maximal fluorescence (light) - Fv variable fluorescence (dark) - Fv variable fluorescence (light) - MDA malondialdehyde - O2 Superoxide radical - PS photosystem - qN non-photochemical quenching of fluorescence - qP photochemical quenching of fluorescence - UV-BBE biologically effective UV-B radiation - WL(T = 0.5) wavelength at which 50% transmittance occurs  相似文献   
83.
Uptake of glucose-6-phosphate by microsomes of hepatocyte in rats, human controls and patients with glycogen storage disease type Ia and Ib was studied. In rat the uptake of glucose-6-phosphate increased rapidly and reached to a plateau, but mannose-6-phosphate was not accumulated. These findings indicate that a glucose-6-phosphate specific transport system exists in the microsomal membrane. In human controls and patients with glycogen storage disease type Ia the uptake of glucose-6-phosphate was clearly observed. On the other hand, no accumulation of it was detected in a patient with glycogen storage disease type Ib. These data provide a direct evidence of the defect in the glucose-6-phosphate transport system of hepatic microsomal membrane in glycogen storage disease type Ib.  相似文献   
84.
Aspergillus saitoi acid carboxypeptidase hydrolyzed C-terminal peptidyl-L-proline bonds and released the C-terminal proline from Z-Gly-Pro-Leu-Gly-Pro and Z-Gly-Pro at pH 3.3. Proline liberated by the enzymic reaction was measured by a sensitive colorimetric ninhydrin method in glacial acetic acid at 513 nm. A Km value of 1.0 mM and a kcat value of 0.09 s-1 for Z-Gly-Pro-Leu-Gly-Pro hydrolysis, and a Km value of 5.0 mM and a kcat value of 0.0045 s-1 for Z-Gly-Pro hydrolysis were calculated from Lineweaver-Burk plots.  相似文献   
85.
86.
The effects of nineteen AHPA* derivatives were examined on morphine analgesia by tail-flick test in rats and on enkephalinase inhibition which was based on the formation of tyrosyl-glycyl-glycine from met-enkephalin. The correlation between the enhancement of morphine analgesia in vivo and enkephalinase inhibition in vitro was analyzed. The different analogs varied considerably in the degree of enhancement of morphine analgesia and inhibition of enkephalinase. A close relationship between enkephalinase inhibition expressed by IC50 in vitro and enhancement of morphine analgesia in vivo was observed in thirteen out of nineteen AHPA derivatives examined. One of other six AHPA derivatives which showed weak effectiveness in potentiating on morphine analgesia but was highly potent as an enkephalinase inhibitor, caused potent analgesic action when it was applied intracisternally indicating poor penetration of the blood brain barrier. The possibility was discussed that some of other compounds excluded from the linear relationship might act on other enkephalin degrading enzymes such as aminopeptidase.  相似文献   
87.
Four outbreaks of botulism in waterfowl were encountered over a five-year period of 1973 to 1977 in Japan. In all the outbreaks toxin was detected from all 12 sera, twenty-three of 24 gizzard contents from diseased or dead birds and one of three maggots. It was neutralized with Clostridium botulinum type C antitoxin serum, regardless of its origin. By using CO2 gas jet method, C. botulinum was isolated from four of 11 gizzards from diseased birds, five of 7 ones from dead birds, one of one maggot and one of one sludge sample, that is, eleven of 20 specimens in total. All 20 strains were identical with C. botulinum type C in biological properties. Most of the isolates showed a toxin titer ranging from 1,000 to 200,000 LD50 for mice. Four of them were identified as type C by mouse neutralization tests with antitoxin sera. The toxic suspensions of a strain 1-15 were administered orally to Chinese spot-billed ducks, which died when more than 200,000 LD50 mouse toxin was administered. Environmental conditions for occurrences of waterfowl botulism were discussed.  相似文献   
88.
The influences of two water soluble contrast media, meglumine iothalamate and meglumine iocarmate, on the neuronal excitability and on the neuronal sensitivity to putative transmitters were examined in comparison with those of sucrose using two identifiable giant neurones of Achatina fulica Férussac (the TAN and the PON). A relatively low increase of osmotic pressure of the extracellular fluid, produced by the application of contrast media, reversed the Cl- dependent inhibition caused by a putative transmitter. The same increase of this osmotic pressure, however, did not influence the Cl- independent inhibition and the excitation of the neurone examined. The hyperpolarization of neuromembrane was caused by an increase of osmotic pressure of the extracellular fluid. Its relatively high increase was necessary to make spontaneous spike discharges disappear totally. All effects of the two contrast media, observed in this study, were due to the increase of osmotic pressure of the extracellular fluid ; no specific effect of the contrast media containing the iodine on the indicators used was observed.  相似文献   
89.
90.
GABA, three of its derivatives (l-GABOB, d-GABOB and delta-amino valeric acid), acetycholine (Ach), dopamine (DA) and l-Phe-Tyr all inhibit an identifiable giant neurone (the TAN, tonically autoactive neurone) of Achatina fulica. These effects were examined by microdrop application in two different conditions: in physiological solution and in the absence of chloride ions. The results show that the relatively transient (rapid) inhibitions caused by GABA, by its derivatives and by Ach are dependent on chloride ions; the relatively maintained (long-lasting) inhibitions, caused by DA and l-Phe-Tyr, are independent of chloride ions.  相似文献   
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