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1.
We modify a simple mathematical model for natural selection originally formulated by Robert M. May in 1983 by permitting
one homozygote to have a larger selective advantage when rare than the other, and show that the new model exhibits dynamical
chaos. We determine an open region of parameter space associated with homoclinic points, and prove that there are infinite
sequences of period-doubling bifurcations along selected paths through parameter space. We also discuss the possibility of
chaos arising from imbalance in the homozygote fitnesses in more realistic biological situations, beyond the constraints of
the model.
Received 3 February 1995; received in revised form 1 November 1995 相似文献
2.
We studied the effects of host plant hybridization on the survival and mortality of the leaf-mining moth Phyllonorycter salicifoliella on hybrid and parental willow plants in the field and in a common garden experiment. P. salicifoliella survival differed significantly among three willow taxa in the field in 1994 but not in the field in 1995 or in the common
garden. Parasitism by eulophid wasps differed significantly among taxa in 1994 and appeared to account for the variation in
their survival. In the field in 1995, host feeding predation varied significant among taxa. The theory of tritrophic interactions
predicts that plant genotype can affect natural enemy impact, and this study supports this prediction. Significant variation
in survival and eulophid parasitism was also found among genotypes within taxa in the field in both years and in the common
garden experiment. The common garden results show that genetic differences in plants affect the herbivore-parasitoid interaction.
Variation among years in the patterns of survival and causes of mortality among field plants suggest that genotype by environment
interactions may be important.
Received: 1 March 1996 / Accepted: 4 November 1996 相似文献
3.
Cobra venom cytotoxins (CTX) have been shown to disrupt cells as different as immunocytes, skeletal myocytes, erythrocytes
and tumor cells. Nevertheless, even subpopulations of tumor cells are differentially susceptible to CTX by an order of magnitude.
In the present study, our objective was to compare CTX-specific binding with cytolytic potency for two disparate cell types
in vitro. We investigated the lytic activity of cytotoxin-III from Naja naja atra (NNA, fraction D) using heart cells and human leukemic T-cells (CEM cells). For both cell types, 50% cytolysis, assessed
by tetrazolium dye conversion, occurred with μm concentrations of toxin (EC50= 2.2 μm). We examined the binding of radiolabeled CTX III to both heart cells and CEM cells and found the apparent dissociation constant
(K
Dapp) to be 0.69 μm and 0.75 μm, for CEM and heart cells respectively. The B
max for the CEM cells was 1.0 fmoles/cell and that for heart cells was 5.2 fmoles/cell, both exhibiting positive cooperativity
between the sites (Hill coefficients 1.4, T-cells; 1.6, heart). Relatively modest dissociation constants plus high numbers
of binding sites per cell are consistent with a model of CTX binding to plasma membranes by interaction with phospholipids
in the bilayer. Our results suggest that the lytic activity of this cytotoxin follows its binding to a population of sites
on the cells in a cooperative fashion.
Received: 8 May 1995/Revised: 17 November 1995 相似文献
4.
A mathematical model of the HCO−
3-secreting pancreatic ductal epithelium was developed using network thermodynamics. With a minimal set of assumptions, the
model accurately reproduced the experimentally measured membrane potentials, voltage divider ratio, transepithelial resistance
and short-circuit current of nonstimulated ducts that were microperfused and bathed with a CO2/HCO−
3-free, HEPES-buffered solution, and also the intracellular pH of duct cells bathed in a CO2/HCO−
3-buffered solution. The model also accurately simulated: (i) the effect of step changes in basolateral K+ concentration, and the effect of K+ channel blockers on basolateral membrane potential; (ii) the intracellular acidification caused by a Na+-free extracellular solution and the effect of amiloride on this acidification; and (iii) the intracellular alkalinization
caused by a Cl−-free extracellular solution and the effect of DIDS on this alkalinization. In addition, the model predicted that the luminal
Cl− conductance plays a key role in controlling both the HCO−
3 secretory rate and intracellular pH during HCO−
3 secretion. We believe that the model will be helpful in the analysis of experimental data and improve our understanding of
HCO−
3-transporting mechanisms in pancreatic duct cells.
Received: 18 October 1995/Revised: 5 July 1996 相似文献
5.
Earthworm secondary production and N flux in agroecosystems: a comparison of two approaches 总被引:1,自引:0,他引:1
Production was estimated for Aporrectodea spp. and Lumbricus spp. populations in corn agroecosystems with a 5-year history of manure or inorganic fertilizer applications during 1994–1995
and 1995–1996. Earthworm biomass and production were greater in manure than inorganic fertilizer plots, although biomass and
production declined by about 50% between 1994–1995 and 1995–1996 due to unfavorable climatic conditions. Production was highest
during the spring and autumn when soil temperatures were between 4 and 22°C. Production was higher in Lumbricus spp. than Aporrectodea spp. populations due to greater Lumbricus spp. biomass. Aporrectodea spp. production was 3.47–16.14 g ash-free dry weight (AFDW) m–2 year–1, while Lumbricus spp. production was 6.09–18.11 g AFDW m–2 year–1, depending on the fertilizer treatment and the method used to estimate production. However, production estimates from the
instantaneous growth rate method were within 27% of the values calculated using the size-frequency method. Nitrogen flux through
earthworms was used to estimate efficiency quotients. Net production efficiency (P/A) ranged from 0.64 to 0.76, assimilation efficiency (A/C) ranged from 0.1 to 0.3, and gross production efficiency (P/C) ranged from 0.06 to 0.22. Annual N flux through earthworm populations was higher in manure than inorganic fertilizer plots,
and ranged from 2.95 to 5.47 g N m–2 year–1 in 1994–1995 and 1.76 to 2.92 g N m–2 year–1 in 1995–1996. The N flux through earthworms represented an amount equivalent to 16–30% of crop N uptake during 1994–1995
and 11–18% of crop N uptake during 1995–1996. We concluded that the effects of earthworms on N cycling in corn agroecosystems
were substantial, and that N flux through earthworms was influenced significantly by fertilizer amendments.
Received: 20 September 1999 / Accepted: 24 March 2000 相似文献
6.
Multiparametric bifurcations for a model in epidemiology 总被引:1,自引:0,他引:1
In the present paper we make a bifurcation analysis of an SIRS epidemiological model depending on all parameters. In particular
we are interested in codimension-2 bifurcations.
Received 8 April 1994; received in revised form 29 June 1995 相似文献
7.
Thomas Hillen 《Journal of mathematical biology》1996,35(1):49-72
If in the classical Turing model the diffusion process (Brownian motion) is replaced by a more general correlated random
walk, then the parameters describing spatial spread are the particle speeds and the rates of change in direction. As in the
Turing model, a spatially constant equilibrium can become unstable if the different species have different turning rates and
different speeds. Furthermore, a Hopf bifurcation can be found if the reproduction rate of the activator is greater than its
rate of change of direction, and oscillating patterns are possible.
Received 24 February 1995; received in revised form 6 September 1995 相似文献
8.
Recent evidence suggests that the formation and permeability of tight junctions are actively regulated by second-messenger-generating
systems involving G proteins and protein kinase C (PKC). A possible specific target for these regulatory proteins is the tight
junction protein ZO-1. An extensive immunocytochemical study was performed in cultured epithelial monolayers of MDCK and Caco-2
cells to identify which isoforms of G proteins and PKC are present at or near the zonula occludens complex. Antibodies against
α-subunits of each one of the four major subfamilies were used for the localization of the G proteins. For the PKC localization,
antibodies against eight different isoforms were used. In confluent monolayers, Gα12 and PKC ζ, were the only isoforms of these proteins present at the cell borders. In subconfluent monolayers, Gα12 and PKC ζ were found at the plasma membrane only along the areas of lateral cell-cell contact. These isoforms formed a pattern
of distribution very similar to the ZO-1 protein. The present findings indicate that Gα12 and PKC ζ may be part of the zonula occludens complex and may locally regulate formation and permeability of tight junctions.
Received: 29 July 1995/Revised: 13 October 1995 相似文献
9.
José Pires Lemos Filho Nilson Augusto Villa Nova Hilton Silveira Pinto 《International journal of biometeorology》1997,41(1):1-4
The aim of this study was to verify the applicability of a heat-sum model and an alternative model that included photoperiod
to describe Hevea bud growth. Considering 19° C as the base temperature, approx. 172 degree days were required for bud growth up to leaf blade
expansion. The applicability of the heat-sum model for Hevea bud growth was confirmed. The inclusion of day length as an exponential term in accumulated degree days resulted in the model
fitting much better for the spring than for the winter conditions.
Received: 21 May 1995 / Revised: 28 October 1996 / Accepted: 27 January 1997 相似文献
10.
Waltraud Huyer 《Journal of mathematical biology》1997,35(8):908-934
We consider a size-structured population model with discontinuous reproduction and feedback through the environmental variable
‘substrate’. The model admits solutions with finitely many cohorts and in that case the problem is described by a system of
ODEs involving a bifurcation parameter β. Existence of nontrivial periodic n-cohort solutions is investigated. Moreover, we discuss the question whether n cohorts (n≧2) with small size differences will tend to a periodic one-cohort solution as t→∞.
Received 16 March 1995; received in revised form 7 January 1997 相似文献
11.
B. Bastide T. Jarry-Guichard J.P. Briand J. Délèze D. Gros 《The Journal of membrane biology》1996,150(3):243-253
Cell-to-cell communication can be blocked by intracellular injections of antibodies raised against gap junction proteins,
but the mechanism of channel obstruction is unknown. Binding to connexins could lead to a conformational change, interfere
with regulatory domains or cause a steric hindrance. To address these questions, the effects on cell-to-cell communication
of affinity purified polyclonal antibodies raised against peptides reproducing the intracellular sequences 5–17, 314–322 and
363–382 of rat connexin43 were investigated in cultured rat ventricular cells. The antibodies against sequence 363–382 were
characterized by immunoblotting and immunocytochemistry. Characterization of antibodies 5–17 and 314–322 has been previously
reported. In a first series of experiments, the effect on gap junctional communication was assessed by injecting a junction-permeant
fluorescent dye into cells adjacent to one cell previously microinjected with antibodies. In a second series, junctional permeability
was quantitatively determined on records of fluorescence recovery after the photobleaching of 6-carboxyfluorescein-loaded
cells. Antibodies 5–17 marked a 43 kDa band on immunoblots, but did not immunolabel gap junctions and had no functional effect.
Antibodies 314–322 recognized the 43 kDa protein and labeled the intercalated disks, but failed to interfere with junctional
permeability. Antibodies to the nearby sequence 363–382, for which all immunospecific tests had been positive, caused a delayed
diffusional uncoupling in 50% of the microinjected cells. It is suggested that the blocking of junctional communication by
antibodies results from interference with a regulatory domain of the connexin.
Received: 25 July 1995/Revised: 21 December 1995 相似文献
12.
Using the whole-cell patch-clamp technique, we examined Cl−-selective currents manifested by strial marginal cells isolated from the inner ear of gerbils. A large Cl−-selective conductance of ∼18 nS/pF was found from nonswollen cells in isotonic buffer containing 150 mm Cl−. Under a quasi-symmetrical Cl− condition, the `instantaneous' current-voltage relation was close to linear, while the current-voltage relation obtained
at the end of command pulses of duration 400 msec showed weak outward rectification. The permeability sequence for anionic
currents was as SCN− > Br−≅ Cl− > F− > NO−
3≅ I− > gluconate−, corresponding to Eisenmann's sequence V. When whole-cell voltage clamped in isotonic bathing solutions, the cells exhibited
volume changes that were accounted for by the Cl− currents driven by the imposed electrochemical potential gradients. The volume change was elicited by lowered extracellular
Cl− concentration, anion substitution and altered holding potentials. The Cl− conductance varied in parallel with cell volume when challenged by bath anisotonicity. The whole-cell Cl− current was only partially blocked by both 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB, 0.5 mm) and diphenylamine-2-carboxylic acid (DPC, 1.0 mm), but 4-acetamido-4′-isothiocyanato-stilbene-2,2′-disulfonic acid (SITS, 0.5 mm) was without effect. The properties of the present whole-cell Cl− current resembled those of the single Cl− channel previously found in the basolateral membrane of the marginal cell (Takeuchi et al., Hearing Res.
83:89–100, 1995), suggesting that the volume-correlated Cl− conductance could be ascribed predominantly to the basolateral membrane. This Cl− conductance may function not only in cell volume regulation but also for the transport of Cl− and the setting of membrane potential in marginal cells under physiological conditions.
Received: 15 August 1995/Revised: 3 November 1995 相似文献
13.
G. M. Goulko V. V. Chumak N. I. Chepurny K. Henrichs P. Jacob I. A. Kairo I. A. Likhtarev V. S. Repin B. G. Sobolev G. Voigt 《Radiation and environmental biophysics》1996,35(2):81-87
The thyroid doses of 49 360 inhabitants of Pripjat evacuated after the accident at Chernobyl were reconstructed. During
their evacuation most of the evacuees passed through highly contaminated territories. The evaluation of a large-scale public
survey showed that only about 50% of the evacuees had left the contaminated areas within 5 days and that 30% of them stayed
there for more than 30 days. As a first step, the model of dose estimations was improved, and thyroid doses were assessed
for the group of evacuees for whom the 131I activity in the thyroids was measured. The 131I incorporation during the first 5 days after the accident was described by a single-intake model (inhalation); later incorporations
were assumed to be proportional to the radioiodine activity in milk. As a second step, the correlation between the calculated
doses and individual parameters (place of residence in Pripjat, intake of stable iodine, and age at the time of the accident) was described by
an empirical equation. This equation was applied to all evacuees who completed the questionnaires of the public survey. Previous
dose assessments were found to overestimate the thyroid doses especially for the younger evacuees. On the basis of these estimations,
collective doses and the resulting radiation risks for thyroid cancer were assessed for different age groups.
Received: 28 November 1995 / Accepted in revised form: 6 March 1996 相似文献
14.
Sebastian J. Schreiber 《Journal of mathematical biology》1996,35(1):37-48
Models of population growth in consumer-resource cascades (serially arranged containers with a dynamic consumer population,
v, receiving a flow of resource, u, from the previous container) with a functional response of the form h(u/v
b
) are investigated. For b∈[0, 1], it is shown that these models have a globally stable equilibrium. As a result, two conclusions can be drawn: (1) Consumer
density dependence in the functional or in the per-capita numerical response can result in persistence of the consumer population
in all containers. (2) In the absence of consumer density dependence, the consumer goes extinct in all containers except possibly
the first. Several variations of this model are discussed including replacing discrete containers by a spatial continuum and
introducing a dynamic resource.
Received 25 February 1995 / received in revised form 27 July 1995 相似文献
15.
Wei Feng 《Journal of mathematical biology》1997,35(6):683-694
We study a combined mathematical model of resource and sexual competition. The population dynamics in this model is analyzed
through a coupled system of reaction-diffusion equations. It is shown that strong sexual competition and low birth rate lead
to competitive exclusion of the biological species. If sexual competition is weak, then the persistence of the species is
possible, depending on the initial density functions and the growth rates of the species. When sexual competition affects
both species, persistence and competitive exclusion results are also obtained in terms of the ecological data in the model.
Received 1 November 1995; received in revised form 13 January 1996 相似文献
16.
Edoardo Beretta Fortunata Solimano Yasuhiro Takeuchi 《Journal of mathematical biology》1996,35(1):1-19
A mathematical model for the delivery of drug directly to the macrophages by using the phagocytosis of senescent red blood
cells is proposed. The model is based on the following assumption: At time t=0 a preassigned red blood cell population n(0, a)=φ(a), a>0, loaded by the drug, is injected in the blood circulation. Among the cells of that population only those with an age a≧ā (ā=120 days) will be phagocytosed by macrophages. Of course, the lifetime of the drug must be higher than ā. Within the
red blood cells it cannot be metabolized, neither can it diffuse through their membranes. The emphasis of the paper is on
the mathematical properties and on the formulation of the control problem.
Received 15 December 1994; received in revised form 20 July 1995 相似文献
17.
Horst Behncke 《Journal of mathematical biology》1997,35(4):375-390
In [2] the author has developed an optimization model for the force and energy in competitive running. In this paper the
energy processes in the muscle were described by a three-compartment hydraulic model. Here this is reviewed briefly and applied
to the current world records in order to determine the key parameters, maximal force, energy reserves and oxygen uptake. These
values agree well with those given in the literature and those obtained by other means. The velocity profiles for 100 m sprints
are described equally well. The model is then applied to older world records to deduce a relation between the force and energy
by linear regression. Finally the fully parameterized model is used to compute the effects of adverse wind and altitude. Inasmuch
as there are data available, there is a good agreement.
Received 19 July 1995; received in revised form 27 February 1996 相似文献
18.
Marion-Gabriele Ott Daniela N. Männel Harald Gallati Matthias Goerig Ulrich Raeth 《Cancer immunology, immunotherapy : CII》1996,42(1):31-37
Tumor necrosis factor α (TNFα) and interferon γ (IFNγ) are important immunomodulators. They are capable of acting in a synergistic
manner on tumor cells in vitro and in vivo. In a clinical phase I study 13 patients with malignant ascites due to abdominal
spread of different primary tumors received intraperitoneally (i. p.) TNFα and IFNγ once weekly over 3 – 8 weeks in order
to evaluate the effect of locoregionally administered TNFα/IFNγ on ascites formation. Therefore some peripheral and local
immunological functional parameters of peripheral blood and malignant ascites were investigated. Mononuclear lymphocytes and
natural killer (NK) cell activity of peripheral blood and ascites, TNF-inhibitory activity, soluble p55 and p75 TNF receptors,
and prostaglandin E2 values in ascites were measured immediately before and 24 h after each TNFα/IFNγ infusion. Peripheral mononuclear lymphocytes
and NK activity decreased significantly 24 h after i. p. TNFα/IFNγ application. However, over the entire treatment schedule,
peripheral NK activity in all responders showed a continuous increase, when compared to pre TNFα/IFNγ treatment levels. In
contrast, NK activity in non-responders constantly decreased. In contrast to non-responders, TNF-inhibitory activity and soluble
p55 TNF receptor levels, determined in ascites, decreased in responders. Taken together, our findings suggest, that successful
locoregional i. p. TNFα/IFNγ therapy induces systemic immunological reactions possibly after saturation of soluble p55 TNF
receptors in ascites, which leads to an increase of peripheral NK activity.
Received: 28 September 1995 / Accepted: 16 November 1995 相似文献
19.
R. Agerer 《Mycorrhiza》1998,8(2):109-111
This latest instalment of the index of unidentified ectomycorrhizae lists binomials and reference specimen characterizations
of ectomycorrhizae first described in 1995–1997.
Accepted: 14 May 1998 相似文献
20.
M. Sugita Takashi Izuno Masao Kanamori Kyoji Ogoshi Toshio Mitomi 《Cancer immunology, immunotherapy : CII》1996,42(4):251-254
Sometimes a specific treatment is effective in one subgroup but not in another. An indicator allowing quantitative comparison
of treatment effect in two subgroups would be useful in clinical medicine. We have developed such an indicator. It is obtained
by calculations using Cox’s proportional hazard or logistic model with therapy, subgroup, and confounding explanatory variables.
The parameter of the interaction between therapy and subgroup can be estimated and tested statistically. The exponential value
of the interaction parameter is what we tentatively call the “hazard ratio ratio”, meaning the ratio between the treatment
effects in two subgroups. The 95% confidence interval of the indicator can also be calculated. As a numerical example, the
hazard ratio between the survival times of postoperative gastric cancer patients treated by adjuvant immunochemotherapy and
patients without adjuvant immunochemotherapy in a subgroup with high serum glycosidically bound sialic acid (SA) level was
lower than that in a low-SA subgroup using an estimate for hazard ratio ratio of less than 0.5 with statistical significance.
We propose this indicator be used as a “responder/non-responder ratio” of therapy effect.
Received: 11 April 1995 / Accepted: 5 September 1995 相似文献