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1.
A new failure model is introduced in the form of a four-parameter nonlinear differential equation, with failure probability as the dependent variable and failure time as the independent variable. The first parameter characterizes the location, the second the scale, and the other two the shape of the model. The type of the accompanying hazard function is immediately read off the shape parameters. The new model approximates the classical failure models with rather high precision, but also models cases where the failure density is skewed to the left. It can be used to analyze survival data objectively, based on the shape of the failure distribution. The computation of quantiles and moments is easy and fast. Nonlinear regression methods are used to estimate parameter values. 相似文献
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Stoichiometries, equilibrium constants and optical extinction coefficients of calcium-antipyrylazo III (An) complexing are determined with the analytical method described in article I of this series. Spcctrophotometric Ca titrations of An at the wavelengths 595 and 710 nm indicate overall dissociation equilibrium constants for the complexes CaAn, CaAn2 and Ca2An to be 4.5 × 10?4 M, 1.1 × 10?8 M2 and 1.5× 10?6 M2, respectively, extrapolated to zero ionic strength. Ca titrations of solutions containing An plus acetylcholine receptor protein give clear evidence that An binds to the protein to a large extent in the presence of Ca2+; furthermore, addition of acetylcholine results in release of protein-bound Ca and An. This is the first reported indication that antipyrylazo III binds to biological material and questions the usefulness of this dye as a Ca indicator in biological systems. 相似文献
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Konrad J. Böhm Wolfram Vater Heinz Fenske Eberhard Unger 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,800(2):119-126
In order to demonstrate the effect of microtubule-associated proteins on the protofilament number of microtubules, we used different systems of microtubule formation in vitro in which these proteins are either functionally eliminated (by DNA or glycerol) or absent (purified tubulin). The results obtained by electron microscopy of ultrathin-sectioned material indicate that under standard conditions in the presence of microtubule-associated proteins microtubules are formed consisting predominantly of 14 protofilaments. In cases of deficiency of microtubule-associated proteins, the mean value of the protofilament number is lower, and the protofilament number within the microtubule population varies remarkably. On the other hand, the action of microtubule-associated proteins is enhanced by histones resulting in increased protofilament numbers. A model is proposed illustrating that the quality and the quantity of microtubule-associated proteins bound to microtubules determine the curvature between the protofilaments and restrict the variety of their binding angles. In this way the microtubule-associated proteins may be regarded as an important factor in determining the structural fidelity of microtubules. 相似文献
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The most suitable way for standardizing biovolume based assemblage analysis using the Utermöhl technique for counting combined with biomass conversion has not yet been found even though this method has been successfully used in plankton studies for many years. Due to the complexity of the approach easily applicable steps to initially meet primary standard end point or target counts for intra-laboratory standardization tested here seem promising. Examples from count validation and biometric data from the large datasets of three laboratories are given. The first two examples initially intended to quantify the taxon specific scatter of counts by (A) using identical replica of field samples combined with a half-chamber count (scan of every second transect) and the 30 random field approach, respectively, and (B) the replication of transect counts in one sample. Both examples identified relatively low minimum count thresholds to delimit counting errors for single cell counts. The third example identifies shape variability and allometric relationships of the main axes and shows a way to improve taxon specific biomass estimates with special reference to cell thickness. However improved precision of quantitative phytoplankton analysis requires optimization of combined counting strategy and biovolume assessment methods. 相似文献
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Serial sections of 13 embryos and fetuses of the harbor porpoise from 10 mm crown-rump length up to 167 mm total length were studied. Unlike the adult animals, ontogenetic stages of 18–27 mm crown-rump length still show a typical mammalian olfactory bulb. The olfactory bulb primordium is penetrated by olfactory nerve fibers, the latter passing through the cribriform plate. However, the olfactory bulb anlage is gradually reduced in later stages, its placodal component being largely uncoupled from the telencephalon. As a ganglionlike structure, the remains of the placodal component stay in contact with the nasal septum and mucosa via thin bundles of nerve fibers. The ganglion and plexus can be traced within the meninges until the adult stage of the porpoise. There is strong evidence that they represent the material of the terminalis system, which cannot be distinguished from the olfactory system in earlier stages. A vomeronasal organ could not be detected in the embryonal and fetal material investigated. 相似文献
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Eberhard Gischler 《Facies》2010,56(2):173-177
Shallow fore-reef areas worldwide are usually characterized by spurs and grooves. A comparison of examples from the three
world oceans suggests that Indo-Pacific spurs and grooves are shaped predominantly by erosion, whereas western Atlantic spur
and groove systems are largely a product of constructive processes. I propose that this difference is caused by regional differences
in Holocene sea-level change, which controlled exposure to waves and currents, and reef-accretion rates. The transgressive–regressive
sea-level curve in the Indo-Pacific realm, i.e., the Mid-to-Late Holocene sea-level fall in these areas has maintained high-energy
conditions in the shallow fore reef. Higher exposure to waves and currents favors erosion and leads to a dominance of crustose
coralline algae that have relatively slow growth rates. In the western Atlantic, the transgressive Holocene sea level has
caused Mid-to-Late Holocene deepening and has maintained accommodation space for reef accretion. Fast-growing acroporid corals
thrive under lower exposure and are more common than coralline algae. The fossil record of the spur and groove system is rather
poor, which is probably a consequence of the need of excellent, three-dimensional outcrops for identification. 相似文献
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Summary In the adenohypophysis of Zonotrichia leucophrys gambelii two types of cells with butylcholinesterase(BuChE) activity can be demonstrated histochemically. Type I occurs in the cephalic lobe of the pars distalis and in the pars tuberalis; it consists of oval and round cells. It is a distinctive cell type that is identical with the amphophilic cells described by Matsuo, Vitums, King and Farner (1969). Whereas castration or inhibition of thyroid gland activity causes only minor changes in these cells, blocking of adrenal cortex activity, or adrenalectomy, causes conspicuous hyperplasia and hypertrophy suggesting that these cells are involved in the production or release of ACTH. The second type, which occurs in both cephalic and caudal lobes, consists mostly of irregularly formed cells. Various observations indicate that it is a composite group, consisting, at least in part, of degenerating cells.These investigations were supported by grants from the National Institutes of Health (S ROI NB 06812) and the National Science Foundation (GB 5969) to Professor Farner. 相似文献