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1.
The non-uniqueness of
distributions satisfying inert gas retention data without error is studied. The ability of such data to resolve blood flows
at particular
values is discussed through the application of linear programming and Backus-Gilbert theory. It is shown that the resolution
deteriorates away from the extremes of low and high
. 相似文献
2.
Didier G. Arqués Jean-Paul Fallot Christian J. Michel 《Bulletin of mathematical biology》1998,60(1):163-194
The self-complementary subset
∪{AAA,TTT} with
= {AAC, AAT, ACC, ATC, ATT, CAG, CTC, CTG, GAA, GAC, GAG, GAT, GCC, GGC, GGT, GTA, GTC, GTT, TAC, TTC} of 22 trinucleotides
has a preferential occurrence in the frame 0 (reading frame established by the ATG start trinucleotide) of protein (coding)
genes of both prokaryotes and eukaryotes. The subsets
∪{CCC} and
∪{GGG} of 21 trinucleotides have a preferential occurrence in the shifted frames 1 and 2 respectively (frame 0 shifted by
one and two nucleotides respectively in the 5′-3′ direction).
and
are complementary to each other. The subset
contains the subset
which has the rarity property (6 × 10−8) to be a complementary maximal circular code with two permutated maximal circular codes
and
in the frames 1 and 2 respectively.
is called a C3 code.
A quantitative study of these three subsets
in the three frames 0, 1, 2 of protein genes, and the 5′ and 3′ regions of eukaryotes, shows that their occurrence frequencies
are constant functions of the trinucleotide positions in the sequences. The frequencies of
in the frame 0 of protein genes are 49, 28.5 and 22.5% respectively. In contrast, the frequencies of
in the 5′ and 3′ regions of eukaryotes, are independent of the frame. Indeed, the frequency of
in the three frames of 5′ (respectively 3′) regions is equal to 35.5% (respectively 38%) and is greater than the frequencies
and
, both equal to 32.25% (respectively 31%) in the three frames.
Several frequency asymmetries unexpectedly observed (e.g. the frequency difference between
and
in the frame 0), are related to a new property of the subset
involving substitutions. An evolutionary analytical model at three parameters (p, q, t) based on an independent mixing of the 22 codons (trinucleotides in frame 0) of
with equiprobability (1/22) followed by t ≈ 4 substitutions per codon according to the proportions p ≈ 0.1; q ≈ 0.1 and r = 1 − p − q ≈ 0.8 in the three codon sites respectively, retrieves the frequencies of
observed in the three frames of protein genes and explains these asymmetries. Furthermore, the same model (0.1, 0.1, t) after t ≈ 22 substitutions per codon, retrieves the statistical properties observed in the three frames of the 5′ and 3′ regions.
The complex behaviour of these analytical curves is totally unexpected and a priori difficult to imagine. 相似文献
3.
Modelling the dynamics of West Nile Virus 总被引:1,自引:0,他引:1
Cruz-Pacheco G Esteva L Montaño-Hirose JA Vargas C 《Bulletin of mathematical biology》2005,67(6):1157-1172
In this work we formulate and analyze a mathematical model for the transmission of West Nile Virus (WNV) infection between
vector (mosquito) and avian population. We find the Basic Reproductive Number
in terms of measurable epidemiological and demographic parameters.
is the threshold condition that determines the dynamics of WNV infection: if
the disease fades out, and for
the disease remains endemic. Using experimental and field data we estimate
for several species of birds. Numerical simulations of the temporal course of the infected bird proportion show damped oscillations
approaching the endemic value. 相似文献
4.
M. -T. Linossier D. Dormois R. Fouquet A. Geyssant C. Denis 《European journal of applied physiology and occupational physiology》1996,74(5):420-427
A group of 15 untrained male subjects pedalled on a friction-loaded cycle ergometer as fast as possible for 5–7 s to reach
the maximal velocity (V{immax}) against different braking forces (F
B). Power was averaged during a complete crank rotation by adding the power dissipated againstF
B to the power necessary to accelerate the flywheel. For each sprint, determinations were made of peak power output (
) power output attained atV
max (
) calculated as the product ofV
max andF
B and the work performed to reachV
max expressed in mean power output (
). The relationships between these parameters andF
B were examined. A biopsy taken from the vastus lateralis muscle and tomodensitometric radiographs of both thighs were taken
at rest to identify muscle metabolic and morphometric properties. The
value was similar for allF
B. Therefore, the average of values was defined as corrected maximal power (
). This value was 11 higher than the maximal power output uncorrected for the acceleration. Whereas the
determination did not require high loads, the highest
value (
) was produced when loading was heavy, as evidenced by the
-F
B parabolic relationship. For each subject, the braking force (
) giving
was defined as optimal. The
, equal to 0.844 (SD 0.108) N · kg−1 bodymass, was related to thigh muscle area (r = 0.78,P < 0.05). The maximal velocity (
) reached against this force seemed to be related more to intrinsic fibre properties (% fast twitch b fibre area and adenylate
kinase activity). Thus, from the
determination, it is suggested that it should be possible to predict the conditions for optimal exercise on a cycle ergometer. 相似文献
5.
The present paper is an attempt to outline a possible approach to the study of concrete cellular systems in terms of relational
biology as developed by Rashevsky and Rosen. The basic ideas and the formalism of Rosen’s (M,R)-systems, proposed as a model of abstract biological systems, are used in order to represent the cellular protein biosynthesis.
A diagram corresponding to the activation of amino acids and synthesis of amino-acyl-transfer RNA, the attachment of
t
RNA to a specific codon of messenger RNA and peptide bond synthesis with the release of a protein molecule, is constructed.
The systemM thus obtained for the synthesis of a proteinp
k
receives a set of environmental inputs, that is, the twently naturally occurring amino acids and emits a single output, thep
k
protein. The problem of noncontractibility of inputs in the
system is then analyzed. In our context, it is found that the noncontractibility is not associated with the whole amino acid
setS
pk
but with an “essential amino acid set”
, so that
and
represent the set of amino acids which can be replaced or absent. According to our considerations, the biochemical concept
of “essential amino acid” acquires a new significance, that is, what seems “essential” is linked with the ability to form
a giventRNA
t
∼a
i
complex in a suitable augmented dependent set essential for the biosynthesis of a functional protein. Eventually the discussion
of re-establishability leads to some important biological implications concerning the existence of ambiguous codons and the
degeneracy phenomenon in the genetic code, as anecessary biochemical tool involved in adaptive processes. 相似文献
6.
Robert Rosen 《Bulletin of mathematical biology》1961,23(2):165-171
It is shown that a wide variety of structural alterations in both the “metabolic” and “genetic” apparatus of (
, ℜ)-systems can result from specific changes in the environment of such systems. A number of specific examples are investigated
in order to demonstrate the scope of these alterations. Certain biological applications of this discussion are suggested,
including a suggestion for a possible interpretation of the mitotic cycle.
This research was supported by the United States Air Force through the Air Force Office of Scientific Research of the Air
Research and Development Command, under Contract #AF 49 (638)-917. 相似文献
7.
Anthony F. Bartholomay 《Bulletin of mathematical biology》1958,20(3):175-190
A stochastic model for the basic unimolecular chemical reaction
is derived. This model provides a mathematical basis, altogether missing in the current kinetic theory, for the analysis
of inherent random fluctuations about the strict concentration-time course prescribed by the existing deterministic theory.
Limits on the extent of the predicted inherent variability are obtained and compared with those usually expected purely on
the basis of random experimental errors of extraneous origin (not associated with the mechanism of reaction). The results
support the extrapolation to chemical systems of a principle of statistical inaccuracy for physical systems which has been
called by E. Schroedinger “the
Law of Physics.” 相似文献
8.
We present a new model of the underlying dynamics of the oxygen uptake
kinetics for various exercise intensities. This model is in the form of a set of nonlinear coupled vector fields for the
and
, the derivative of the exercise intensity with respect to time. We also present a new and novel means for calculating the
oxygen demand, D(v, t), and hence also the oxygen deficit and debt, given the time series of the
. This enables us to give better predictions for these values especially for when exercising at or close to maximal exercise
intensities. Our model also allows us to predict the oxygen uptake time series given the time series for the exercise intensity
as well as to investigate the oxygen uptake response to nonlinear exercise intensities. Neither of these features is possible
using the currently used three-phase model. We also present a review of both the underlying physiology and the three-phase
model. This includes for the first time a complete set of the analytical solutions of the three-phase model for the oxygen
deficit and debt. 相似文献
9.
The second order nonlinear differential equation
arises from a kinetics model of abrin binding in an Epstein-Barr virus-transformed lymphocyte culture. Some results on the
dynamical behavior of this equation are given. These results are then discussed in relation to the known kinetics behavior
of abrin in an EBV-lymphocyte cell culture. 相似文献
10.
Water uptake by barley roots as affected by the osmotic and matric potential in the rhizosphere 总被引:2,自引:0,他引:2
U. Schleiff 《Plant and Soil》1986,94(1):143-146
Summary The water uptake rates of roots in saline soils are depressed by the simultaneously decreasing matric
and osmotic
water potentials in the soil surrounding the roots (rhizospheric soil). Unfortunately there are no reliable tools available
for direct measurements of the effect of decreasing water potentials in the rhizospheric soil on the uptake rate of soil water
by roots. This paper presents some results of a vegetation technique for studying the effect of different combinations of
osmotic and matric water potentials in the rhizospheric soil on the water uptake rates of barley roots.
Water uptake rates were reduced to a greater extent by decreasing soil matric water potentials than by decreasing soil osmotic
water potentials. According to the results of this experiment, there was no relationship between the total soil water potential
of a sandy soil and the water uptake rates when the roots were exposed to different combinations of
and
. 相似文献
11.
Jacopo P. Mortola anna Noworaj 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1985,155(2):171-176
Summary The resting oxygen consumption
and breathing pattern of nine newborn and adult species (ranging in body size from mouse to human) have been compared on the basis of data collected from the literature. Minute ventilation
is similarly linked to
at both ages, the percent of
extracted as O2
about 2.2. Tidal volume/kg is an interspecies constant in newborns and adults, approximately 8 ml/kg. Breathing frequency decreases with the increase in size in a different way at the two ages: large species have newborns breathing at rates 2–3 times above the corresponding adults' values, while in the small species newborns and adults breathe at almost the same rate. Therefore the newborns of the smallest species have both
and
below the expected values, implying a greater inability to cope with the external demands than newborns of larger species. Several considerations indicate that in the smallest newborns the mechanical properties of the respiratory system could be a constraint to resting ventilations larger than observed. It is therefore possible that their low
is the cause, and not the effect, of the relatively small
. 相似文献
12.
J. M. Bateman 《Bulletin of mathematical biology》1986,48(5-6):525-543
A theoretical study is made of three organ flow models with heterogeneity of capillary transit times. A new parametrization
of Rose and Goresky's Model III facilitates in many cases a reduction to Goresky's Model II, accomplished by a special time
shift. The shift parameter
defined here is critical in this analysis of Model III. A new expression of the series for outflow concentration in Model
III is given and proves useful in examining the model as an operator and in relating it to Models I and II. A result on parameter
optimization is given: if
then Model III cannot fit better than Model II. This is applied to some data from Rose and Goresky [Circulation Res.
39, 541–544 (1976)] and raises a new question about their model. A heart model of Levin and Bassingthwaighte based on regional
flow measurement is shown to be a discretized generalization of Model II.
This work supported in part by PHS Grant Nos. HL-19153 (SCOR for Pulmonary Vascular Disease) and HL-19370 at Vanderbilt University. 相似文献
13.
Gregory K. Snyder Wesley W. Weathers 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1977,117(3):291-301
Summary Resting rates of O2 consumption
against
, exercise endurance times and
during recovery from vigorous exercise were measured inSceloporus occidentalis captured near sea level and inS. graciosus captured above 2850 m. Oxygen consumption against
was also measured inS. occidentalis captured above 2850 m. When
was recorded continuously, as ambient
was slowly reduced from 155 Torr, it became directly dependent upon ambient
between 110 and 120 Torr. The critical
for the high altitude lizards was lower than that for the lowland lizards, which enabled the former to maintain relatively higher
's when ambient
was reduced below 120 Torr. The high altitude lizards also had significantly greater endurance when stimulated to exercise at 1600 m (
130 Torr). Both the higher
under hypoxia and the greater endurance roughly parallel a significantly greater maximum
in the high altitude lizards. At a simulated altitude of 3600 m (
100 Torr), maximum
and rate of recovery of the O2 debt calculated from post active
were significantly reduced in the lowland but not the high altitude lizards. The effects of simulated altitude conditions on the lowland but not the mountaine animals indicate adaptations to altitude in these sceloporine lizards. We did not find any consistent relationship between organ/body weight ratios or hematocrit and our measures of
endurance or the altitude at which the lizards were captured. 相似文献
14.
Summary The complete sequence of the 5S rRNA from the bioluminescent bacterium,Beneckea harveyi has been determined to be p U G C U U G G C G
C C A U A G C G A
U U-G G A C C C A
C U G A (U) C U U C
A U U C C-G A A C
C A G A A G U G A
A C G A A U U A-G
G C C G A U G G U
G U G U G G G G C
U-C C C C A U G U
A G A G U A G G A
A U C G-C C A G G
U (U)OH.Two sites of sensitivity to ribonuclease T2 cleavage were identified; at A41 and either A54 or A55. Comparison with existing sequence information fromEscherichia coli andPhotobacterium phosphoreum clarifies the amount of diversity among the bioluminescent bacteria and provides further insight into their phylogenetic position. Sequence heterogeneities were encountered and the importance of these in interpreting 5S rRNA data is discussed. 相似文献
15.
Evidence for four nonallelic structural genes for the γ chain of human fetal hemoglobin 总被引:4,自引:0,他引:4
T. H. J. Huisman W. A. Schroeder W. H. Bannister J. L. Grech 《Biochemical genetics》1972,7(2):131-139
An abnormal human fetal hemoglobin not only may be either aGγ- or anAγ-chain variant but also may be present in a different proportion of the total fetal hemoglobin.Gγ-Chain variants contribute either about one-fourth or one-eighth to the total production of HbF in the heterozygote, whereas
theAγ-chain variants approximate either one-eighth or one-sixteenth of the total HbF. These observations may indicate the presence
of four nonallelic Hbγ structural genes (termed
) which produce γ chains in an approximate ratio of 4 : 2 : 2 : 1. HbF Malta I is considered to be the product of a mutant
of the
locus, an undefined HbFx that of the
locus, HbF Hull and HbF Jamaica products of mutated
loci, and the newly discovered HbF Malta II a mutant of the
gene.
This work was supported in part by grants HL-05168 and HL-02558 from the National Institutes of Health, U.S. Public Health
Service. 相似文献
16.
Takayoshi Yoshida Junji Kamiya Kouji Hishimoto 《European journal of applied physiology and occupational physiology》1995,70(6):482-486
To assess the rate-limiting factor of oxygen uptake (
) kinetics at the onset of exercise, six healthy male sedentary subjects performed repeated one-legged constant-load cycle exercise. The one-legged constant-load exercise test consisted of two 5-min periods of pedalling at an exercise intensity of 50 W, with a 5-min rest between periods (these exercise periods, i.e. first and second exercises, were performed by the same leg). The exercise was then repeated using the other leg. In addition, two-legged incremental exercise was investigated to establish whether
kinetics were affected by slower heart rate kinetics. The incremental exercise test consisted of two-legged pedalling first with the cycle unloaded as a warm-up for 5 min followed by 50-W exercise for 5 min. The exercise intensity was then increased to 100 W for 5 min. During exercise, gas exchange parameters were determined by the breath-by-breath method and cardiac output (
) was determined continuously by an impedance technique with a computer-based automated system. To determine the kinetics of heart rate (HR),
and
, a best fit procedure was employed using least-squares criteria with a time delay, except during the initial increase. During the one-legged constant-load exercise test,
kinetics were significantly accelerated by repeated exercise using the same leg. On the other hand, when the exercise was changed to the other leg,
kinetics were significantly slower, although
kinetics continued to be faster. During the incremental exercise test, although the HR response was slower at the transition from 50-W to 100-W exercise than at the transition from warm-up to 50-W exercise, there were no significant changes in
kinetics. These findings suggest that
kinetics may be affected by metabolic conditions in the muscle, but not by blood flow (
and/or HR) kinetics. 相似文献
17.
B. Grubb G. E. Folk Jr. 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1978,128(2):185-188
Summary The rate of oxygen consumption (
) by skeletal muscle was investigated in isolated perfused hindlimbs of laboratory rats and lemmings (Lemmus). In both species,
increased in proportion to blood flow rate, even at flow rates 4–5 times above resting level. The slope of the line relating
to skeletal muscle blood flow was significantly greater in the lemming than in the rat. This may be related to the inverse relationship between body weight and metabolic rate. These data support the hypothesis that in small animals a dependent relationship exists between blood flow and skeletal muscle
. 相似文献
18.
Gerald Rosen 《Bulletin of mathematical biology》1984,46(5-6):967-969
It is observed that a dynamical continuity equation for biomass distribution yields the asymptotic steady-state exponential
dependencen=A exp(
) exhibited by certain fishery data, wherem is the biomass of an individual,n is the number of individuals per unit biomass interval, andA,
are positive constants. This dynamical approach to biomass distribution is an alternative to the global maximization principle
proposed recently by Lurié and Wagensberg. 相似文献
19.
Summary A set of three-dimensional triple-resonance experiments is described which provide
,
,
and
coupling constants. The pulse sequences generate E.COSY-like multiplet patterns and comprise a magnetization transfer from
the amide proton to the α-proton or vice versa via the directly bound heteronuclei. For residues with the 1Hα spin resonating close to the H2O signal, a modified HNCA experiment can be employed to measure the vicinal 1HN,1Hα couplings. Ambiguities associated with the conversion of
values into ϕ-angle constraints for protein structure determination can be resolved with the knowledge of the heteronuclear
3J-couplings. In favourable cases, stereospecific assignments of glycine α-protons can be obtained by employing the experiments
described here in combination with NOE data. The methods are applied to flavodoxin from Desulfovibrio vulgaris. 相似文献
20.
Hugo M. Martinez 《Bulletin of mathematical biology》1966,28(3):411-416
IfN(t) is the expected number of cells in a culture at timet,
the corresponding time derivative, andf(t−τ)dt the probability that a cell of aget−τ at timet will divide in the succeeding time intervaldt, then according to Hirsch and Engelberg (this issue) there obtains the integral equation
for describing the dynamics of the cell population. It is the purpose of this note to give two alternative derivations of
this equation, one based on the age density equation of Von Foerster, and the other based on a generalized form of the Harris-Bellman
equation describing the first moment of an age dependent, branching process. In addition, a probability model is posed from
which the Von Foerster equation and, hence, the Hirsch-Engelberg equation readily follows. 相似文献