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1.
Kung-Jong Lui Duane Steffey Jamie K. Pugh 《Biometrical journal. Biometrische Zeitschrift》1993,35(6):677-688
Calculating the required sample size for a desired power at a given type I error level, we often assume that we know the exact time of all subject responses whenever they occur during our study period. It is very common, however, in practice that we only monitor subjects periodically and, therefore, we know only whether responses occur or not during an interval. This paper includes a quantitative discussion of the effect resulting from data grouping or interval censoring on the required sample size when we have two treatment groups. Furthermore, with the goal of exploring the optimum in the number of subjects, the number of examinations per subject for test responses, and the total length of a study time period, this paper also provides a general guideline about how to determine these to minimize the total cost of a study for a desired power at a given α-level. A specified linear cost function that incorporates the costs of obtaining subjects, periodic examinations for test responses of subjects, and the total length of a study period, is assumed, primarily for illustrative purpose. 相似文献
2.
Nonparametric spline regression with prior information 总被引:1,自引:0,他引:1
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Selective deposition of BaSO4 in the tight junctions (TJs) of frog skins led to profound and reversible functional alterations of these structures, as revealed by changes of tissue conductance (G), clamping current (I), and fluxes of extracellular markers (sulfate (JSO
4) and sucrose (JSUC)). Experiments were performed with nominally Ca2+ -free simple salt solutions on the apical side (usually KCl) and Na2SO4-Ringer on the inner side of skins. The deposition of BaSO4 in the TJs was obtained by diffusion and/or migration through the paracellular path of Ba2+ from the apical solution and SO
4
2–
from the inner solution. A brief presence (2 to 6 min) of apical Ba2+ (Ba2+ pulse) is followed (i.e., when Ba2+ is removed from the apical fluid) by a large increase of G, I, JSO
4 and JSUC, above pre-Ba2+ levels. These attain a steady state within 15 to 30 min (overshoot phase), characterizing a conspicuous increase of the paracellular permeability. During the overshoot phase, a second Ba2+ pulse blocks the paracellular route while apical Ba2+ is present, leading to a new and larger overshoot when the Ba2+ pulse is terminated. Addition of apical Ca2+ triggers the resealing of the TJs, resulting in a full recovery of G, I, JSO
4 and JSUC. This Ca2+ -induced recovery persists when apical Ca2+ is removed. The presence of a normal Ca2+ concentration in the inner bathing Ringer does not induce the recovery process. Tissues remain viable after being submitted to the Ba2+ treatment and the subsequent overshoot. Experiments performed in the urinary bladder of Rana catesbeiana and skins and urinary bladders of Bufo marinus indicate that Ba2+ effect can also be elicited in these tissues. The above results seem to report general properties of the TJs. Incidentally, they warn about the use of Ba2+ as an ion channel blocker in epithelial membranes in association with SO
4
2–
-containing solutions on the contralateral side.This project was supported by grants from Fundação de Amparo à Pesquisa do Estado de São Paulo (91/0293-7 to F.L.V., and 90/1788-1 to A.S.), and Conselho Nacional de Desenvolvimento Científico e Tecnológico (410068/90-0 and 303633-85/BF to F.L.V.). J.A.C. received a doctoral fellowship from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior/Fundação Universidade do Rio Grande. We thank Dr. Alice T. Ferreira for help in the measurements of free Ca2+ concentration. 相似文献
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The potential for and constraints on the evolution of compensatory ability in Asclepias syriaca 总被引:2,自引:0,他引:2
To investigate the potential for and constraints on the evolution of compensatory ability, we performed a greenhouse experiment
using Asclepias syriaca in which foliar damage and soil nutrient concentration were manipulated. Under low nutrient conditions, significant genetic
variation was detected for allocation patterns and for compensatory ability. Furthermore, resource allocation to storage was
positively, genetically correlated both with compensatory ability and biomass when damaged, the last two being positively,
genetically correlated with each other. Thus, in the low nutrient environment, compensatory ability via resource allocation
to storage provided greater biomass when damaged. A negative genetic correlation between compensatory ability and plant biomass
when undamaged suggests that this mechanism entailed an allocation cost, which would constrain the evolution of greater compensatory
ability when nutrients are limited. Under high nutrient conditions, neither compensatory ability nor allocation patterns predicted
biomass when damaged, even though genetic variation in compensatory ability existed. Instead, plant biomass when undamaged
predicted biomass when damaged. The differences in outcomes between the two nutrient treatments highlight the importance of
considering the possible range of environmental conditions that a genotype may experience. Furthermore, traits that conferred
compensatory ability did not necessarily contribute to biomass when damaged, demonstrating that it is critical to examine
both compensatory ability and biomass when damaged to determine whether selection by herbivores can favor the evolution of
increased compensation.
Received: 2 April 1999 / Accepted: 21 September 1999 相似文献
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《Journal of biological dynamics》2013,7(4):318-334
In this paper, we study a two-species competitive system where both the species produce toxin against each other at some cost to their growth rates. A much wider set of outcomes is possible for our system. These outcomes are important contrasts to competitive exclusion or bistable attractors that are often the outcomes for competitive systems. We show that toxin helps to gain an advantage in competition for toxic species whenever the cost of toxin production remains within some moderate value; otherwise it may result in the extinction of the species itself. 相似文献
10.
The cost of interspecific competition in two gerbil species 总被引:5,自引:1,他引:4