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161.
We consider establishment success (and extinction risk of small populations) in fluctuating environments, by means of an inhomogeneous branching process model. In this model it is assumed that individuals reproduce asexually during discrete reproduction periods. Within each period individuals reproduce independently and have random numbers of offspring. Expected numbers of offspring vary over reproduction periods due to random environmental changes. Previous simulation results indicated that there is a positive autocorrelation between the establishment probabilities of invaders in successive reproduction periods when environmental states are independently distributed. This result was never formally proved. In this paper we prove that this is indeed true, regardless of the form of the distribution of environmental states or the offspring distribution (under a monotonicity condition, which holds for biologically realistic models). Furthermore, we prove that it is also true for positively autocorrelated environmental states. We show by a counterexample that in environments with a strong negative autocorrelation establishment probabilities can be negatively autocorrelated. This was further examined through simulations. Our results imply that in independent, positively autocorrelated and weakly negatively autocorrelated environments the probability of success of invasion in different independently varying sites is the highest, followed by sequential invasion. For environments with a strong negative autocorrelation, sequential invasion has the highest probability of success. Effects of autocorrelation were further examined with simulations. From the results it appears that the expected length of 'runs of bad luck' is the most crucial factor for establishment success. 相似文献
162.
Arsenic content was assayed in the samples of the femur head of the people living in southern and central Poland (Kraków,
n=13; Silesian region, n=13; Łódź, n=12). The average age being 68.7±8.7 yr. Arsenic content in the femur head was determined applying the hydride generation
atomic absorption spectrometry (HG-AAS) method after microwave mineralization. The average arsenic contents in the femur head
of the residents of the Łódź, Kraków, and Silesian regions were 0.41 μg/g, 0.37 μg/g, and 0.18 μg/g, respectively. No correlation
has been found between arsenic content in the femur head and the content of other metals. Neither the age nor sex of the people
tested affected the arsenic content in the femur head. 相似文献
163.
El-Laithy HM 《AAPS PharmSciTech》2003,4(1):80-89
The performance of dioctyl sodium sulfosuccinate (aerosol OT) in the development of a pharmaceutically acceptable, stable,
self-emulsifying water continuous microemulsion with high dilution efficiency was assessed. A pseudoternary microemulsion
system was constructed using aerosol OT/medium-chain triglycerides with oleic acid/glycerol monooleate and water. The model
microemulsion was characterized with regard to its electroconductive behavior, eosin sodium absorption, interfacial tension,
and droplet size measurements after dilution with water. The percolation transition law, which makes it possible to determine
the percolation threshold and to identify bicontinuous structures, was applied to the system. The interfacial tension changes
associated with the microemulsion formation revealed ultralow values up to 30% oil at a surfactant/cosurfactant ratio of 3∶1.
Moreover, the investigated particle size and polydispersity using photon correlation spectroscopy after dilution with excess
of the continuous phase proved the efficiency of the microemulsion system as a drug carrier that ensures an infinitely dilutable,
homogeneous, and thermodynamically stable system. 相似文献
164.
The 15N-HSQC spectra of low-spin cyano-met-myoglobin and high-spin fluoro-met-myoglobin were assigned and dipole-dipole-Curie-spin cross-correlated relaxation rates measured. These cross-correlation rates originating from the dipolar 1H-15N interaction and the dipolar interaction between the 1H and the Curie spin of the paramagnetic center contain long-range angular information about the orientation of the 1H-15N bond with respect to the iron-1H vector, with information measurable up to 11 Å from the metal for the low-spin complex, and between 10 to 25 Å for the high-spin complex. Comparison of the experimental data with predictions from crystal structure data showed that the anisotropy of the magnetic susceptibility tensor in low spin cyano-met-myoglobin significantly influences the cross-correlated dipole-dipole-Curie-spin relaxation rates. 相似文献
165.
van Rossum BJ Castellani F Pauli J Rehbein K Hollander J de Groot HJ Oschkinat H 《Journal of biomolecular NMR》2003,25(3):217-223
In this paper, we present a strategy for the 1HN resonance assignment in solid-state magic-angle spinning (MAS) NMR, using the -spectrin SH3 domain as an example. A novel 3D triple resonance experiment is presented that yields intraresidue HN-N-C correlations, which was essential for the proton assignment. For the observable residues, 52 out of the 54 amide proton resonances were assigned from 2D (1H-15N) and 3D (1H-15N-13C) heteronuclear correlation spectra. It is demonstrated that proton-driven spin diffusion (PDSD) experiments recorded with long mixing times (4 s) are helpful for confirming the assignment of the protein backbone 15N resonances and as an aid in the amide proton assignment. 相似文献
166.
167.
Methods are presented for modeling dose-related effects in proportion data when extra-binomial variability is a concern. Motivation is taken from experiments in developmental toxicology, where similarity among conceptuses within a litter leads to intralitter correlations and to overdispersion in the observed proportions. Appeal is made to the well-known beta-binomial distribution to represent the overdispersion. From this, an exponential function of the linear predictor is used to model the dose-response relationship. The specification was introduced previously for econometric applications by Heckman and Willis; it induces a form of logistic regression for the mean response, together with a reciprocal biexponential model for the intralitter correlation. Large-sample, likelihood-based methods for estimating and testing the joint proportion-correlation response are studied. A developmental toxicity data set illustrates the methods. 相似文献
168.
I McIntosh S D Dreyer M V Clough J A Dunston W Eyaid C M Roig T Montgomery S Ala-Mello I Kaitila A Winterpacht B Zabel M Frydman W G Cole C A Francomano B Lee 《American journal of human genetics》1998,63(6):1651-1658
Nail-patella syndrome (NPS), a pleiotropic disorder exhibiting autosomal dominant inheritance, has been studied for >100 years. Recent evidence shows that NPS is the result of mutations in the LIM-homeodomain gene LMX1B. To determine whether specific LMX1B mutations are associated with different aspects of the NPS phenotype, we screened a cohort of 41 NPS families for LMX1B mutations. A total of 25 mutations were identified in 37 families. The nature of the mutations supports the hypothesis that NPS is the result of haploinsufficiency for LMX1B. There was no evidence of correlation between aspects of the NPS phenotype and specific mutations. 相似文献
169.
A note on generating correlated binary variables 总被引:1,自引:0,他引:1
170.
Employing a set of 43 othologous mouse and rat genes, Hughes and Yeager (J. Mol. Evol. 45:125–130, 1997) reported (1) no correlation between synonymous and nonsynonymous rates of nucleotide substitution, (2)
a positive correlation between intronic GC contents (GC
i) and intronic substitution rates (K
i), (3) that the average K
i value was very similar to the average K
s value, and (4) that the compositional correlation between the rat and the mouse genes is stronger at the third codon position
(GC3) than at the first and second codon positions (GC12). We have examined the robustness of these results to alterations in substitution rate estimation protocol, alignment protocol,
and statistical procedure. We find that a significant correlation between K
a and K
s is observed either if a rank correlation statistic is used instead of regression analysis, if one outlier is excluded from
the analysis, or if a regression weighted by gene size is employed. The correlation between K
i and GC
i we find to be sensitive to changes in alignment protocol and disappears on the use of weighted means. The finding that K
s and K
i are approximately the same is dependent on the method for estimating K
s values. Finally, the variance around the regression line of rat GC3 versus mouse GC3 we find to be significantly higher than that in GC12. The source of the discrepancy between this and Hughes and Yeager's result is unclear. The variance around the line for GC4 is higher still, as might be expected. Using a methodology that may be considered preferable to that of Hughes and Yeager,
we find that all four of their results are contradicted. More importantly this analysis reinforces the need for caution in
assembling and analyzing data sets, as the degree of sensitivity to what many might consider minor methodological alterations
is unexpected.
Received: 2 February 1998 / Accepted: 23 March 1998 相似文献