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Showing papers by "Michigan State University published in 1981"


Journal ArticleDOI
TL;DR: The properties of oxygenevolving PS II preparations obtained by detergent resolution of chloroplast thylakoid membranes are reported.

1,866 citations


Journal ArticleDOI
TL;DR: It is demonstrated that even when pre-formed in the presence of CAP-cAMP, the polymerase-promoter open complex becomes unstable if CAP is then selectively removed, and this gel method is applied to the study of the E. coli lactose operon regulatory system.
Abstract: The use of gel electrophoresis for quantitative studies of DNA-protein interactions is described. This rapid and simple technique involves separation of free DNA from DNA-protein complexes based on differences in their electrophoretic mobilities in polyacrylamide gels. Under favorable conditions both unbound DNA and DNA associated with protein can be quantified. This gel method is applied to the study of the E. coli lactose operon regulatory system. At ionic strengths in the physiological range, the catabolite activator protein (CAP) is shown to form a long-lived complex with the wild type lac promotor, but not with a CAP-insensitive mutant. Formation of a stable "open" or "melted-in" complex of RNA polymerase with the wild type promoter requires the participation of CAP and cyclic AMP. Further, it is demonstrated that even when pre-formed in the presence of CAP-cAMP, the polymerase-promoter open complex becomes unstable if CAP is then selectively removed.

1,759 citations


Journal ArticleDOI
01 Oct 1981-Ecology
TL;DR: Habitat use of large bluegills was shown to maximize foraging return as fish switched from utilizing vegetation- living prey to utilizing open-water zooplankton as relative foraging profitabilities in the two habitats changed across the summer.
Abstract: A foraging model was developed to predict the optimal diet breadth and maximum energetic intake of a given-sized fish foraging in each of three aquatic habitats: the open water, vegetation, and bare sediments. Model parameters of prey encounter rates and prey handling times were quantified as functions of fish size, prey density, and prey size through a series of laboratory feeding experiments using the bluegill sunfish (Lepomis macrochirus). Results of these experiments show both searching ability and prey handling efficiency to increase with increasing fish size. Predictions of prey size selection and optimal habitat use based upon maximizing energetic gain were then examined in a small Michigan lake for three size classes of bluegills. Bluegills >100 mm standard length were highly size selective in their feeding and their diets closely matched predictions of an optimal diet model. From two estimates of relative prey visibilities I show that these fish selected larger prey items than would be predicted if prey were consumed "as encountered." Habitat use of large bluegills was also shown to maximize foraging return as fish switched from utilizing vegetation- living prey to utilizing open-water zooplankton as relative foraging profitabilities in the two habitats changed across the summer. Bluegills < 100 mm standard length were restricted in their habitat use, remaining in or near the vegetation despite demonstrated increases in foraging return available in the open-water habitat. Size-related predation risk apparently accounts for differences in habitat use between bluegill size classes, and its consequences for intra- and interspecific competition between size classes are discussed.

905 citations


Journal ArticleDOI
TL;DR: In this paper, a framework for organizing role conflict and ambiguity research is proposed, which may assist in consolidating the field and providing an understanding of where we are, what is left to be done and, therefore, direction for future role conflict/ambiguity research.
Abstract: Although research on role conflict and ambiguity has been extensive, there has been only moderate consistency in the focus and results of the research, while several areas of role conflict and ambiguity research are still relatively unexamined. This paper suggests that a framework for organizing the recent research may assist in consolidating the field and providing an understanding of where we are, what is left to be done and, therefore, direction for future role conflict and ambiguity research.

700 citations


Journal ArticleDOI
01 Dec 1981-Nature
TL;DR: In photosynthetic membranes isolated from pea leaves, the redox state of the plastoquinone pool controls both the level of phosphorylation of the chloroplast light-harvesting pigment–protein complex (LHC) and distribution of absorbed excitation energy between the two photosystems.
Abstract: In photosynthetic membranes isolated from pea leaves, the redox state of the plastoquinone pool controls both the level of phosphorylation of the chloroplast light-harvesting pigment–protein complex (LHC) and distribution of absorbed excitation energy between the two photosystems. Phosphorylation of LHC polypeptides is proposed as the regulatory mechanism by which photosynthetic systems adapt to changing wavelengths of light.

660 citations


Journal ArticleDOI
TL;DR: Numerical solutions to a mathematical model of denitrification based on Michaelis-Menten kinetics showed that differences in reduction rates of the nitrogenous compounds were sufficient to account for the observed patterns of nitrite, nitric oxide, and nitrous oxide accumulation.
Abstract: The kinetics of denitrification and the causes of nitrite and nitrous oxide accumulation were examined in resting cell suspensions of three denitrifiers. An Alcaligenes species and a Pseudomonas fluorescens isolate characteristically accumulated nitrite when reducing nitrate; a Flavobacterium isolate did not. Nitrate did not inhibit nitrite reduction in cultures grown with tungstate to prevent formation of an active nitrate reductase; rather, accumulation of nitrite seemed to depend on the relative rates of nitrate and nitrite reduction. Each isolate rapidly reduced nitrous oxide even when nitrate or nitrite had been included in the incubation mixture. Nitrate also did not inhibit nitrous oxide reduction in Alcaligenes odorans, an organism incapable of nitrate reduction. Thus, added nitrate or nitrite does not always cause nitrous oxide accumulation, as has often been reported for denitrifying soils. All strains produced small amounts of nitric oxide during denitrification in a pattern suggesting that nitric oxide was also under kinetic control similar to that of nitrite and nitrous oxide. Apparent Km values for nitrate and nitrite reduction were 15 μM or less for each isolate. The Km value for nitrous oxide reduction by Flavobacterium sp. was 0.5 μM. Numerical solutions to a mathematical model of denitrification based on Michaelis-Menten kinetics showed that differences in reduction rates of the nitrogenous compounds were sufficient to account for the observed patterns of nitrite, nitric oxide, and nitrous oxide accumulation. Addition of oxygen inhibited gas production from 13NO3− by Alcaligenes sp. and P. fluorescens, but it did not reduce gas production by Flavobacterium sp. However, all three isolates produced higher ratios of nitrous oxide to dinitrogen as the oxygen tension increased. Inclusion of oxygen in the model as a nonspecific inhibitor of each step in denitrification resulted in decreased gas production but increased ratios of nitrous oxide to dinitrogen, as observed experimentally. The simplicity of this kinetic model of denitrification and its ability to unify disparate observations should make the model a useful guide in research on the physiology of denitrifier response to environmental effectors.

587 citations


Journal ArticleDOI
TL;DR: In this article, the authors used Raman scattering and x-ray diffraction measurements to correlate finite-size effects on the Raman spectra of nonpolar vibrational modes in BN.
Abstract: Raman scattering and x-ray diffraction measurements are used to correlate finite-size effects on the Raman spectra of nonpolar vibrational modes in BN. The BN microcrystalline samples used exhibited domain sizes varying from 4.4 to 78.5 nm in the plane and 1.5 and 47.5 nm perpendicular to the planes. The Raman measurements indicated that the high-frequency ${E}_{2g}$ mode shifted to higher frequency and broadened as the crystallite size decreased. A formulation of the Raman cross section for scattering from nonpolar microcrystals is presented. The development includes evaluation of the susceptibility correlation function over a limited spatial extent. The results indicate that spectral changes are related to the phonon dispersion, and the wave-vector uncertainty is accounted for. The formulation is applied to describe the BN light scattering results, and good agreement was obtained to describe the observed shift in frequency.

520 citations


Journal ArticleDOI
28 Aug 1981-Science
TL;DR: A single topical application of benzoyl peroxide produced a marked epidermal hyperplasia and induced a large number of dark basal keratinocytes, effects similar to those produced by the potent tumor promoter 12-O-tetradecanoyl phorbol-13-acetate.
Abstract: Benzoyl peroxide, a widely used free radical-generating compound, promoted both papillomas and carcinomas when it was topically applied to mice after 7,12-dimethylbenz[a]anthracene initiation. Benzoyl peroxide was inactive on the skin as a complete carcinogen or as a tumor initiator. A single topical application of benzoyl peroxide produced a marked epidermal hyperplasia and induced a large number of dark basal keratinocytes, effects similar to those produced by the potent tumor promoter 12-O-tetradecanoyl phorbol-13-acetate. Benzoyl peroxide, like other known tumor promoters, also inhibited metabolic cooperation (intercellular communication) in Chinese hamster cells. In view of these results caution should be recommended in the use of this and other free radical-generating compounds.

484 citations


Journal ArticleDOI
05 Jun 1981-Science
TL;DR: The activity of the lysosomal proteinase cathepsin B is significantly elevated in a variant of the B16 melanoma with high metastatic potential.
Abstract: Although lysosomal enzymes are implicated in the processes of tumor invasion and metastasis, their cellular origin within the tumor is unclear. The activity of the lysosomal proteinase cathepsin B is significantly elevated in a variant of the B16 melanoma with high metastatic potential. The cathepsin B activity is localized to the lysosomes of the tumor cells.

376 citations


Journal ArticleDOI
TL;DR: In this paper, Polonius observes that Hamlet is in deep grief and despair over the recent death of his father, King of Denmark, and many have called him mad.
Abstract: Few works in the English language are as rich as Shakespeare's Hamlet. One phrase is of particular interest . Hamlet is in deep grief and despair over the recent death of his father, King of Denmark. In his melancholy he has been acting rather strangely and many have called him mad. Yet, Polonius observes of H a m l e t , \"Though th i s be madness , yet there is method in it.\" What does Shakespeare wish to convey with this phrase? How can the apparent lack of coherence or sanity of Hamlet ' s behavior be c h a r a c t e r i z e d by me thod? To assert that something has method is to claim that there is an order, a regularity, obscure though it may be, which underlies an apparent d i s o r d e r , t h u s r e n d e r i n g i t meaningful. Method is the attribute which distinguishes research activity from mere observation and speculation. When adversaries argue about the nature of the world or the best approach to some particular human endeavor, we typically find ourselves evaluating their respective claims through examining the methods they used to reach their conclusions. There are few subjects tha t generate as much passion among scientists as arguments over method. This is not surpr is ing , since scholars who agree on matters of method can

371 citations


Journal ArticleDOI
TL;DR: The interpretation is that the rapidly growing end of all axonal microtubules is distal to the cell body, which supports Kirschner's hypothesis on microtubule organizing centers.
Abstract: The polarity orientation of cellular microtubules is widely regarded to be important in understanding the control of microtubule assembly and microtubule-based motility in vivo. We have used a modification of the method of Heidemann and McIntosh (Nature (Lond.). 286:517-519) to determine the polarity orientation of axonal microtubules in postganglionic sympathetic fibers of the cat. In fibers from three cats we were able to visualize the polarity of 68% of the axonal microtubules; of these, 96% showed the same polarity orientation. Our interpretation is that the rapidly growing end of all axonal microtubules is distal to the cell body. We support Kirschner's hypothesis on microtubule organizing centers. (J. Cell Biol. 86:330-334), although this interpretation raises questions about the continuity of axonal microtubules. Our results are inconsistent with a number of models for axonal transport based on force production on the surface of microtubules in which the direction of force is determined by the polarity of microtubules.

Journal ArticleDOI
21 Aug 1981-Science
TL;DR: Despite the common somato-dendritic morphology of the neostriatal projection neurons, two different distribution patterns of efferent axons were observed, indicating the presence of functionally different medium spiny neurons in the nestriatum.
Abstract: Intracellularly labeled rat neostriatal projection neurons were analyzed with both light and electron microscopy. The axons of medium spiny neurons were traced into the globus pallidus and were found to make synaptic contacts with pallidal dendrites. Despite the common somato-dendritic morphology of the neostriatal projection neurons, two different distribution patterns of efferent axons were observed, indicating the presence of functionally different medium spiny neurons in the neostriatum.

Journal ArticleDOI
14 Aug 1981-Science
TL;DR: Intracellular recordings from pairs of neurons in slices of rat hippocampus directly demonstrate electrotonic coupling between neurons in the mammalian brain and indicate that some fast prepotentials are coupling potentials.
Abstract: Intracellular recordings from pairs of neurons in slices of rat hippocampus directly demonstrated electronic coupling between CA3 pyramidal cells. When two neurons were impaled simultaneously (as verified by subsequent double staining with horseradish peroxidase), current pulses injected into one cell caused voltage changes in other cells. These interactions were bidirectional. Fast prepotentials, historically thought to represent spike activity in dendrites, resulted from action potentials in other electronically coupled pyramidal cells. These data directly demonstrate electrotonic coupling between neurons in the mammalian brain and indicate that some fast prepotentials are coupling potentials. Coupling between pyramidal cells could mediate synchronization of normal rhythmic activity and of burst discharges during seizures.

Journal ArticleDOI
TL;DR: The combined technique of intrACEllular recording and intracellular labeling of neurons with H R P was employed to assess the nature of cortical inputs to the subthalamic nucleus and it was reported that the lesions of the primary sensorimotor areas in cats produced degeneration of terminal boutons containing small vesicles synapsing mainly on spines and small dendrites ofsubthalamic neurons.

Journal ArticleDOI
01 Oct 1981-Ecology
TL;DR: In this paper, the authors introduced a new model of gases gas transport wherein the gases move through waterlilies in a mass flow, and the internal gas spaces in Nuphar constitute a pressurized flow-through system, with ambient air entering the youngest emergent leaves against a small gradient in total gas pressure.
Abstract: Current models of gas transport in aquatic plants hold that gases diffuse in an essentially static gas phase within the lacunae according to gradients in their individual partial pressures. This study introduces a new model of gases gas transport wherein the gases move through waterlilies in a mass flow. The internal gas spaces in Nuphar constitute a pressurized flow—through system, with ambient air entering the youngest emergent leaves against a small gradient in total gas pressure. This pressurization phenomenon is the result of purely physical processes driven by the gradients in temperature (thermal transpiration) and water vapor (hygrometric pressure) between the atmosphere and the lacunae of the youngest emergent leaves. The lacunae are continuous throughout the entire plant, and the older leaves vent the elevated pressure generated by the younger leaves. This arrangement gives rise to a flow—through pattern, accelerating both the rate of O2 supply from the atmosphere to the roots, and the rate of CO2 and CH4 transport from the roots towards the atmosphere. This ventilation system represents an important adaptation by the waterlily to life in anaerobic sediments.

Proceedings ArticleDOI
01 Dec 1981
TL;DR: In this paper, a quadratic-type Lyapunov function for a singularly perturbed system is obtained as a weighted sum of quadratically-type LSTM functions of two lower order systems.
Abstract: Asymptotic and exponential stability of nonlinear singularly perturbed systems are investigated via Lyapunov stability techniques. A quadratic-type Lyapunov function for a singularly perturbed system is obtained as a weighted sum of quadratic-type Lyapunov functions of two lower order systems. Estimates of domain of attraction, of upper bound on perturbation parameter, and of degree of exponential stability are obtained. The method is illustrated by studying the stability of a synchronous generator connected to an infinite bus.

Journal ArticleDOI
TL;DR: The fate of a rosette appears to be independent of its age although in populations where the probability of death is high for individuals above the minimum size for flowering, the age of arosette may influence its fate to some extent.
Abstract: Individual plants were marked in field populations of four biennial plant species, Verbascum thapsus L., Oenothera biennis L., Daucus carota L., and Tragopogon dubius Scop., and followed for 2 or 3 years. The relationship of both rosette size and age to the probability of an individual dying, remaining vegetative, or flowering was determined for each species. In all four species, a minimum size must be reached before flowering can be induced and above that minimum the probability of flowering increases directly with rosette size. Conversely, the probability of dying decreases with increasing rosette size. In general, the fate of a rosette appears to be independent of its age although in populations where the probability of death is high for individuals above the minimum size for flowering, the age of a rosette may influence its fate to some extent.

Journal ArticleDOI
TL;DR: The structured deme model explains the evolution of altruism by the differential productivity of trait groups, in which the dispersal pool represents the deme as a whole, and the breeding group in each resource patch is a "trait group."
Abstract: In 1930 R. A. Fisher proposed an evolutionary model to explain why so many species produce roughly equal numbers of male and female offspring at birth. Very simply, since each offspring has a male and female parent (or grandparent, for haplodiploids), whichever sex is in short supply has the greater fecundity. A genotype that produces an excess of the minority sex among its own offspring is favored by natural selection, until an equilibrium is reached at a 1:1 population sex ratio (assuming male and female offspring cost the same to produce). Charnov (1979) and Maynard Smith (1978) have recently reviewed the subject. As with many other traits for which fitness is frequency dependent, the evolution of sex ratio is influenced by the spatial structure of the population. To see this, consider an organism that depends upon some patchy resource. The patches themselves are temporary, but last long enough for the organism to complete one or more generations before dispersal to new patches becomes necessary. Many small arthropods, parasites, and successional species fit this pattern well, and vertebrates that undergo extreme periodic fluctuations in density approximate it. Now suppose that the genotype of each female determines the sex ratio of her progeny: one allele codes for a female-biased sex ratio, and another for equal numbers of sons and daughters, with total fecundity the same for both alleles. If mating is random within each patch, the local frequency of the biased sex ratio allele will decline in every generation in every patch. This is simply a case of Fisher's principle, which operates with equal force regardless of the size of the breeding group (Colwell, 1981). However, patches will vary by chance in the frequency of the two alleles among the initial colonists. Defining the occupants of a single patch as a "group," those groups that have a higher initial frequency of the female-biasing allele will produce more grandprogeny, simply because a greater number of the founders' progeny are females. If the local groups continue to grow in size, the effect will persist through successive generations of local mating, so that a group initiated with a higher than average frequency of the biased sex ratio allele eventually produces a higher than average number of dispersers. Moreover, the dispersers from such a patch still carry a higher than average frequency of the allele, in spite of its local decline within every group during each generation of local mating. Consequently, the frequency of the biased sex ratio allele can nonetheless increase in the global population, to the degree that the differential productivity of groups (group selection) counters the effect of Fisher's principle (individual selection). This process is shown diagrammatically in Figure 1. It is an example of the structured deme model of population genetics (Uyenoyama and Feldman, 1980; Wilson, 1980), in which the dispersal pool represents the deme as a whole, and the breeding group in each resource patch is a "trait group." In general, the structured deme model explains the evolution of altruism by the differential productivity of trait groups. In the present case, any female

Journal ArticleDOI
TL;DR: Determination of flux response curves on leaves in the normal position or in the inverted position led to the conclusion that the photoreceptors for blue as well as for red light are located on or near the surfaces of the leaves; presumably they are in the guard cells themselves.
Abstract: Flux response curves were determined at 16 wavelengths of light for the conductance for water vapor of the lower epidermis of detached leaves of Xanthium strumarium L An action spectrum of stomatal opening resulted in which blue light (wavelengths between 430 and 460 nanometers) was nearly ten times more effective than red light (wavelengths between 630 and 680 nanometers) in producing a conductance of 15 centimoles per square meter per second Stomata responded only slightly to green light An action spectrum of stomatal responses to red light corresponded to that of CO2 assimilation; the inhibitors of photosynthetic electron transport, cyanazine (2-chloro-4[1-cyano-1-methylethylamino]-6-ethylamino-s-triazine) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea, eliminated the response to red light This indicates that light absorption by chlorophyll is the cause of stomatal sensitivity to red light Determination of flux response curves on leaves in the normal position (upper epidermis facing the light) or in the inverted position (lower epidermis facing the light) led to the conclusion that the photoreceptors for blue as well as for red light are located on or near the surfaces of the leaves; presumably they are in the guard cells themselves


Journal ArticleDOI
TL;DR: In this paper, the authors measured the effects of style, tempo, and performing medium on fifth-rade students' expressed music listening preference and found a strong effect for style, which was notice ably suppressed by performance in the instrumental medium.
Abstract: The purpose of this study was to measure the effects of style, tempo, and performing medium on fifth-rade students' expressed music listening preference. A listening test was administered to 107 students in four classes in central Michigan. Test reliability was evaluated in terms of common factor concentration and stability across time, and behavior observation was used to help interpret results. A preference hierarchy emerged in which the popular styles were most favored and correlation analysis indicated that style was most strongly related to preference. A three-way repeated measures analysis of variance disclosed a significant three-way interaction. An examination of charted cell means indicated a strong effect for style, which was notice ably suppressed by performance in the instrumental medium. Across pooled styles there was a slight preference for faster tempos and the instrumental medium.

Journal ArticleDOI
TL;DR: Examples are provided showing how simple models predicting prey choice can be used to relate behavioral and morphological differences between species and questions at higher levels such as the nature of species interactions and community structure.
Abstract: Synopsis. The application of optimal foraging theory to questions of predator behavior, and evidence bearing on the utility of this construct, are reviewed. Experimental tests of simple models predicting prey choice are examined with particular reference to the sizeselection of prey by fish. Laboratory estimates of model parameters are then used to predict prey choice in the field and data from several field tests are presented which corroborate these predictions. When parameters are habitat specific this permits predic? tions of net return from foraging in different habitats and consequendy predictions of habitat use and switching. Field data gathered to test these predictions demonstrate that fish feed in the richer habitats and switch habitats when the profitability of one drops below that of another. Examples are provided showing how these models can then be used to relate behavioral and morphological differences between species and questions at higher levels such as the nature of species interactions and community structure. It is suggested that this may be one of the more useful applications of optimal foraging theory. Finally, some of the criticisms of the theory and important questions requiring further study are discussed.

Journal ArticleDOI
TL;DR: Rotavirus infection was uncommon in the first six months of life, but by two years of age, 62% of the infants had had at least one infection, and neither breast feeding nor the presence of antibody to rotavirus in cord blood appeared to be protective.
Abstract: Diarrhea in neonates, followed as a cohort, and their families was studied prospectively. The families were followed for an average of 16.3 months. Stool and serum specimens were obtained at least every three months. Stool specimens were examined for viruses by electron microscopy and cultured for enteropathogens, and serum specimens were tested for antibodies to rotavirus and Norwalk virus. During the study, 237 episodes of gastroenteritis were observed in 104 infants and their 62 siblings. Rotavirus, detected 82 times in 72 children, was by far the most common enteropathogen. It was associated with gastrointestinal symptoms in 72% (with diarrhea in 65%). Rotavirus diarrhea occurred mostly in winter months and was significantly more frequently associated with respiratory symptoms than were diarrheas with other etiologies. Rotavirus infection was uncommon in the first six months of life, but by two years of age, 62% of the infants had had at least one infection. Neither breast feeding nor the presence of antibody to rotavirus in cord blood appeared to be protective.

Journal ArticleDOI
TL;DR: Research since 1955 that contributed to understanding mammary function was reviewed and areas that seem likely to provide new methods for regulation of milk production efficiency are molecular biology, hormone receptors, harvesting milk, endocrine-nutrient metabolism, genetic and environmental basis of hormonal control of lactation.

Journal ArticleDOI
TL;DR: Symbiotic recycling of uric acid N appears to be important to N conservation in these oligonitrotrophic insects, either directly via glutamine synthetase activity of fat body tissue or indirectly through microbe assimilation.
Abstract: Reticulitermes flavipes termites synthesize uric acid via purine-nucleoside phosphorylase (purine-nucleoside: orthophosphate ribosyltransferase, EC 2.4.2.1) and xanthine dehydrogenase (xanthine:NAD+ oxidoreductase, EC 1.2.1.37), but their tissues lack uricase (urate:oxygen oxidoreductase, EC 1.7.3.3) or any other enzyme that degrades uric acid. Nevertheless, uricolysis occurs in termites, but as an anaerobic process mediated by hindgut bacteria. 14C-Tracer experiments showed that termites transport uric acid from the site of synthesis and storage (fat body tissue) to the site of degradation (hindgut microbiota) via Malpighian tubules. Moveover, [1,3-15N]uric acid dissimilated by gut bacteria in vivo leads to assimilation of 15N into termite tissues. NH3, a product of uricolysis, is a potential N source for termites, either directly via glutamine synthetase [L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2] activity of fat body tissue or indirectly through microbe assimilation. Symbiotic recycling of uric acid N appears to be important to N conservation in these oligonitrotrophic insects.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the inconsistency of the Tobit model with heteroskedastic error terms in a constant-term-only model and showed that the inconsistency is larger when the error terms are heterogeneous.

Journal ArticleDOI
TL;DR: Several experiments reported in here show that the proposed performance measure puts an order on different partitions of the same data which is consistent with the error rate of a classifier designed on the basis of the obtained cluster labelings.
Abstract: Clustering is primarily used to uncover the true underlying structure of a given data set and, for this purpose, it is desirable to subject the same data to several different clustering algorithms. This paper attempts to put an order on the various partitions of a data set obtained from different clustering algorithms. The goodness of each partition is expressed by means of a performance measure based on a fuzzy set decomposition of the data set under consideration. Several experiments reported in here show that the proposed performance measure puts an order on different partitions of the same data which is consistent with the error rate of a classifier designed on the basis of the obtained cluster labelings.

Journal ArticleDOI
TL;DR: A non-orthogonal helical co-ordinate system is introduced and it is found that both curvature and torsion induce non-negligible effects when the Reynolds number is less than about 40.
Abstract: A non-orthogonal helical co-ordinate system is introduced to study the effect of curvature and torsion on the flow in a helical pipe. It is found that both curvature and torsion induce non-negligible effects when the Reynolds number is less than about 40. When the Reynolds number is of order unity, torsion induces a secondary flow consisting of one single recirculating cell while curvature causes an increased flow rate. These effects are quite different from the two recirculating cells and decreased flow rate at high Reynolds numbers.

Journal ArticleDOI
TL;DR: This article showed that group members' motivation for certain types of tasks declines as group size increases, and two experiments examined alternative explanations for this effect: the "me first" explanation and the "hide-in-the-crowd" explanation.
Abstract: Recent work suggests that group members' motivation for certain types of tasks declines as group size increases. Two experiments examined alternative explanations for this effect. The results of the first study disconfirmed the "me first" explanation, which holds that the effect occurs only when an individual performs in several different size groups. The second experiment supported the "hide-in—the crowd"explanation, which holds that member anonymity increases with group size for the tasks which have yielded the effect.

Journal ArticleDOI
13 Mar 1981-Science
TL;DR: Intracellular injection of the fluorescent dye Lucifer Yellow into single magnocellular neurons in slices of rat hypothalamus resulted in dye transfer between these cells, suggesting that some mammalian neuropeptidergic cells are electrotonically coupled, providing a possible means for recruitment and synchronization of their electrical activity.
Abstract: Most magnocellular neurosecretory cells that terminate in the posterior pituitary secrete either vasopressin, oxytocin, or enkephalin. Intracellular injection of the fluorescent dye Lucifer Yellow into single magnocellular neurons in slices of rat hypothalamus resulted in dye transfer between these cells. Freeze-fracture replicas of these cells occasionally revealed gap junctions, which presumably contain channels that mediate the dye coupling. These two independent techniques strongly suggest that some mammalian neuropeptidergic cells are electrotonically coupled, providing a possible means for recruitment and synchronization of their electrical activity.