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Showing papers by "Michigan State University published in 1991"


Journal ArticleDOI
TL;DR: A texture segmentation algorithm inspired by the multi-channel filtering theory for visual information processing in the early stages of human visual system is presented, which is based on reconstruction of the input image from the filtered images.

2,351 citations


Journal ArticleDOI
TL;DR: The degree to which adaptation to a uniform environment among independently evolving asexual populations is associated with increasing divergence of those populations is assessed, consistent with theoretical expectations that do not invoke divergence due to multiple fitness peaks in a Wrightian evolutionary landscape.
Abstract: We assess the degree to which adaptation to a uniform environment among independently evolving asexual populations is associated with increasing divergence of those populations. In addition, we are concerned with the pattern of adaptation itself, particularly whether the rate of increase in mean fitness tends to decline with the number of generations of selection in a constant environment. The correspondence between the rate of increase in mean fitness and the within-population genetic variance of fitness, as expected from Fisher's fundamental theorem, is also addressed. Twelve Escherichia coli populations were founded from a single clonal ancestor and allowed to evolve for 2,000 generations. Mean fitness increased by about 37%. However, the rate of increase in mean fitness was slower in later generations. There was no statistically significant within-population genetic variance of fitness, but there was significant between-population variance. Although the estimated genetic variation in fitness within po...

1,523 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reviewed how the hydraulic design of trees influences the movement of water from roots to leaves and discussed some of the ecological and physiological trade-offs of specific structures.
Abstract: summary In this paper, we have reviewed how the hydraulic design of trees influences the movement of water from roots to leaves. The hydraulic architecture of trees can limit their water relations, gas exchange throughout the crown of trees, the distribution of trees over different habitats and, perhaps, even the maximum height that a particular species can achieve. Parameters of particular importance include: (1) the vulnerability of stems to drought-induced cavitation events because cavitation reduces the hydraulic conductance of stems, (2) the leaf specific conductivity-of stems because it determines the pressure gradients and most negative water potentials needed to sustain evaporation from leaves, (3) the water storage capacity of tissues because this might determine the ability of trees to survive long drought periods. All of these parameters are determined by the structure and function of anatomical components of trees. Some of the ecological and physiological trade-offs of specific structures are discussed.

1,461 citations


Journal ArticleDOI
TL;DR: The effects of sample size on feature selection and error estimation for several types of classifiers are discussed and an emphasis is placed on giving practical advice to designers and users of statistical pattern recognition systems.
Abstract: The effects of sample size on feature selection and error estimation for several types of classifiers are discussed. The focus is on the two-class problem. Classifier design in the context of small design sample size is explored. The estimation of error rates under small test sample size is given. Sample size effects in feature selection are discussed. Recommendations for the choice of learning and test sample sizes are given. In addition to surveying prior work in this area, an emphasis is placed on giving practical advice to designers and users of statistical pattern recognition systems. >

1,323 citations


Journal ArticleDOI
TL;DR: In this article, Bivariate GARCH models of cash and futures prices are estimated for the same six commodities and the optimal hedge ratio (OHR) is calculated as a ratio of the conditional covariance between Cash and futures to the conditional variance of futures.
Abstract: Six different commodities are examined using daily data over two futures contract periods. Cash and futures prices for all six commodities are found to be well described as martingales with near-integrated GARCH innovations. Bivariate GARCH models of cash and futures prices are estimated for the same six commodities. The optimal hedge ratio (OHR) is then calculated as a ratio of the conditional covariance between cash and futures to the conditional variance of futures. The estimated OHRs reveal that the standard assumption of a time-invariant OHR is inappropriate. For each commodity the estimated OHR path appears non-stationary, which has important implications for hedging strategies.

766 citations


Journal ArticleDOI
TL;DR: Two experiments assess adult age differences in the extent of inhibition or negative priming generated in a selective-attention task within the Hasher-Zacks (1988) framework, which proposes inhibition as a central mechanism determining the contents of working memory and consequently influencing a wide array of cognitive functions.
Abstract: Two experiments assess adult age differences in the extent of inhibition or negative priming generated in a selective-attention task. Younger adults consistently demonstrated negative priming effects; they were slower to name a letter on a current trial that had served as a distractor on the previous trial relative to one that had not occurred on the previous trial. Whether or not inhibition dissipated when the response to stimulus interval was lengthened from 500 ms in Experiment 1 to 1,200 ms in Experiment 2 depended upon whether young subjects were aware of the patterns across trial types. Older adults did not show inhibition at either interval. The age effects are interpreted within the Hasher-Zacks (1988) framework, which proposes inhibition as a central mechanism determining the contents of working memory and consequently influencing a wide array of cognitive functions. Language: en

698 citations


Journal ArticleDOI
TL;DR: The authors analyzes some of the controversies in the literature on media imperialism by drawing on two revised concepts: assymetrical interdependence as a more precise and complex way to frame the imperialism issues, and the idea of audiences actively searching for cultural proximity in cultural goods, as a way to reincorporate the role of audiences in the media imperialism debate.
Abstract: This paper analyzes some of the controversies in the literature on media imperialism by drawing on two revised concepts: the idea of assymetrical interdependence as a more precise and complex way to frame the imperialism issues, and the idea of audiences actively searching for cultural proximity in cultural goods, as a way to reincorporate the role of audiences in the media imperialism debate The focus is on limits imposed by dependence, growth in cultural industries, technological change, and reconceptualization of an active audience that is divided by class The study focuses on television flows vs national television production, on the primary case of Brazil, and on institutional and audience‐centered evidence

664 citations




Journal ArticleDOI
TL;DR: In this article, the authors describe a theoretical model for analyzing the motivational factors underlying individuals' decisions regarding achievement-related choices and evaluate the utility of this model for understanding gender differences in sport participation.
Abstract: With the growth of the field of sport psychology has come a growing interest and concern over gender differences in achievement and participation in various sports. Why do girls and boys differ from one another in their participation rates and participation patterns in sports? Over the past 10 years, Eccles and her colleagues have put together a theoretical model for analyzing the motivational factors underlying individuals' decisions regarding achievement-related choices. This paper describes this theoretical model and uses data from two studies, one focusing on adolescents, and one focusing on elementary school-aged children, to evaluate the utility of this model for understanding gender differences in sport participation. It reaches the following conclusions: (a) the Eccles et al. model holds for sport as well as, if not better than, it does for academic subjects; (b) gender differences in children's attitudes toward sport are quite strong and emerge at a very young age; and (c) these gender d...

626 citations


Journal ArticleDOI
TL;DR: This article reviewed 20 years' worth of empirical evidence on the "spatial mismatch" hypothesis and found that spatial mismatch is relevant for explaining black/white employment differences, though the magnitudes of these effects remain unclear.
Abstract: This paper reviews 20 years' worth of empirical evidence on the 'spatial mismatch' hypothesis. After briefly surveying the relevant models from urban and labour economics and recent trends in employment and population suburbanisation, the empirical evidence on spatial effects is examined. This literature includes evidence on the effects of residential segregation, residential suburbanisation and employment suburbanisation, and direct measures of 'access' (such as travel times). The most recent evidence suggests that spatial mismatch is relevant for explaining black/white employment differences, though the magnitudes of these effects remain unclear.

Journal ArticleDOI
TL;DR: The properties of PGH synthase are described, the enzyme which catalyzes the committed step in the synthesis of prostaglandins and thromboxane is described, and a model for the active site is proposed.

Journal ArticleDOI
TL;DR: In this paper, the authors studied a class of Banach space operators patterned after the weighted backward shifts on Hilbert space, and showed that any non-scalar operator in the commutant of one of these generalized backward shifts has a dense, invariant linear manifold whose non-zero members are cyclic vectors.

Journal ArticleDOI
TL;DR: In this article, a seasonal GARCH model is developed to describe the time-dependent volatility apparent in the percentage nominal return of each currency and the hourly patterns in volatility are found to be remarkably similar across currencies and appear to be related to the opening and closing of the worlds major markets.
Abstract: Four foreign exchange spot rate series, recorded on an hourly basis for a six-month period in 1986 are examined. A seasonal GARCH model is developed to describe the time-dependent volatility apparent in the percentage nominal return of each currency. Hourly patterns in volatility are found to be remarkably similar across currencies and appear to be related to the opening and closing of the worlds major markets. Robust LM tests designed to deal with the extreme leptokurtosis in the data fails to uncover any evidence of misspecification or the presence of volatility spillover effects between the currencies or across markets.

Journal ArticleDOI
TL;DR: In this paper, Salicylic acid was found to be an endogenous inducer of resistance in Cucumis sativus L. plants with Pseudomonas syringae Pathovar Syringae.
Abstract: Inoculation of one true leaf of cucumber (Cucumis sativus L.) plants with Pseudomonas syringae pathovar syringae results in the systemic appearance of salicylic acid in the phloem exudates from petioles above, below, and at the site of inoculation. Analysis of phloem exudates from the petioles of leaves 1 and 2 demonstrated that the earliest increases in salicylic acid occurred 8 hours after inoculation of leaf 1 in leaf 1 and 12 hours after inoculation of leaf 1 in leaf 2. Detaching leaf 1 at intervals after inoculation demonstrated that leaf 1 must remain attached for only 4 hours after inoculation to result in the systemic accumulation of salicylic acid. Because the levels of salicylic acid in phloem exudates from leaf 1 did not increase to detectable levels until at least 8 hours after inoculation with P. s. pathovar syringae, the induction of increased levels of salicylic acid throughout the plant are presumably the result of another chemical signal generated from leaf 1 within 4 hours after inoculation. Injection of salicylic acid into tissues at concentrations found in the exudates induced resistance to disease and increased peroxidase activity. Our results support a role for salicylic acid as an endogenous inducer of resistance, but our data also suggest that salicylic acid is not the primary systemic signal of induced resistance in cucumber.


Journal ArticleDOI
TL;DR: The experimental results indicated that transsaccadic memory is an undetailed, limited-capacity, long-lasting memory that is not strictly tied to absolute spatial position, similar to, and perhaps identical with, visual short-term memory.

Journal ArticleDOI
TL;DR: In this article, the magnetic and magneto-transport properties of Co/Cu multilayers prepared by sputtering were studied and a giant magnetoresistance was observed in the half-periods with antiferromagnetic interlayer coupling.

Journal ArticleDOI
TL;DR: This review questions the appropriateness of behavioral and dietary treatments of obesity in light of overwhelming evidence that they are ineffective in producing lasting weight loss.

Book ChapterDOI
01 Jan 1991

Journal ArticleDOI
TL;DR: The three major steps in prostanoid formation are discussed and the roles of aspirin and other nonsteroidal anti-inflammatory drugs, dexamethasone and other anti- inflammatory steroids, platelet-derived growth factor (PDGF), and interleukin-1 in prostaglandin metabolism are discussed.

Journal ArticleDOI
04 Jan 1991-Science
TL;DR: The mechanism of transcriptional activation by VP16 and other proteins may involve both ionic and specific hydrophobic interactions with target molecules.
Abstract: Virion protein 16 (VP16) of herpes simplex virus type 1 contains an acidic transcriptional activation domain. Missense mutations within this domain have provided insights into the structural elements critical for its function. Net negative charge contributed to, but was not sufficient for, transcriptional activation by VP16. A putative amphipathic alpha helix did not appear to be an important structural component of the activation domain. A phenylalanine residue at position 442 was exquisitely sensitive to mutation. Transcriptional activators of several classes contain hydrophobic amino acids arranged in patterns resembling that of VP16. Therefore, the mechanism of transcriptional activation by VP16 and other proteins may involve both ionic and specific hydrophobic interactions with target molecules.

Journal ArticleDOI
TL;DR: The experimental system constructed with the medically significant yersiniae provides a powerful basic model for comparative study of factors required for expression of acute versus chronic disease.
Abstract: The experimental system constructed with the medically significant yersiniae provides a powerful basic model for comparative study of factors required for expression of acute versus chronic disease. The system exploits the close genetic similarity between Yersinia pestis, the etiological agent of bubonic plague, and enteropathogenic Yersinia pseudotuberculosis and Yersinia enterocolitica. Y. pestis possesses three plasmids, of which one, shared by the enteropathogenic species, mediates a number of virulence factors that directly or indirectly promote survival within macrophages and immunosuppression. The two remaining plasmids are unique and encode functions that promote acute disease by enhancing bacterial dissemination in tissues and resistance to phagocytosis by neutrophils and monocytes. These properties are replaced in the enteropathogenic yersiniae by host cell invasins and an adhesin which promote chronic disease; the latter are cryptic in Y. pestis. Additional distinctions include specific mutational losses in Y. pestis which result in loss of fitness in natural environments plus gain of properties that facilitate transmission and infection via fleabite.


Journal ArticleDOI
TL;DR: The results suggest that the mutant is deficient in activity of a protein required to load phosphate into the xylem, suggesting that the phosphate deficiency is caused by a single nuclear recessive mutation at a locus designated pho1.
Abstract: A mutant of Arabidopsis thaliana deficient in the accumulation of inorganic phosphate has been isolated by screening directly for plants with altered quantities of total leaf phosphate. The mutant plants accumulate approximately 5% as much inorganic phosphate, and 24 to 44% as much total phosphate, as wild-type plants in aerial portions of the plant. Growth of the mutant is reduced, relative to wild type, and it exhibits other symptoms normally associated with phosphate deficiency. The phosphate deficiency is caused by a single nuclear recessive mutation at a locus designated pho1. The rate of phosphate uptake into the roots was similar between mutant and wild-type plants over a wide range of external phosphate concentrations. In contrast, when plants were grown in media containing 200 micromolar phosphate or less, phosphate transfer to the shoots of the mutant was reduced to 3 to 10% of the wild-type levels. The defect in phosphate transfer to the shoots could be overcome by providing higher levels of phosphate. Transfer of sulfate to the shoots was essentially normal in the mutant, indicating that the pho1 lesion was not a general defect in anion transport. Movement of phosphate through the xylem of the shoots was not impaired. The results suggest that the mutant is deficient in activity of a protein required to load phosphate into the xylem.

Journal ArticleDOI
TL;DR: Physically abusive families were significantly more often low income, had younger mothers with less education, more frequently reported a family history of child abuse, and were more likely to be abusing alcohol or drugs.

Journal ArticleDOI
TL;DR: The structure of a recombinant hirudin (variant 2, Lys47) human alpha-thrombin complex has been refined using restrained least-squares methods to a crystallographic R-factor of 0.173.


Journal ArticleDOI
TL;DR: Evidence is provided that ABA is synthesized by oxidative cleavage of epoxy-carotenoids (the "indirect pathway") and the carotenoid mutant the authors describe undergoes normal greening.
Abstract: The three mutant alleles of the ABA locus of Arabidopsis thaliana result in plants that are deficient in the plant growth regulator abscisic acid (ABA). We have used 18O2 to label ABA in water-stressed leaves of mutant and wild-type Arabidopsis. Analysis by selected ion monitoring and tandem mass spectrometry of [18O]ABA and its catabolites, phaseic acid and ABA-glucose ester (beta-D-glucopyranosyl abscisate), indicates that the aba genotypes are impaired in ABA biosynthesis and have a small ABA precursor pool of compounds that contain oxygens on the ring, presumably oxygenated carotenoids (xanthophylls). Quantitation of the carotenoids from mutant and wild-type leaves establishes that the aba alleles cause a deficiency of the epoxy-carotenoids violaxanthin and neoxanthin and an accumulation of their biosynthetic precursor, zeaxanthin. These results provide evidence that ABA is synthesized by oxidative cleavage of epoxy-carotenoids (the "indirect pathway"). Furthermore the carotenoid mutant we describe undergoes normal greening. Thus the aba alleles provide an opportunity to study the physiological roles of epoxy-carotenoids in photosynthesis in a higher plant.

Journal ArticleDOI
TL;DR: In this article, the authors measured the adsorption of aromatic hydrocarbons from water by organo-clays and found that the planar surfaces of the compounds adsorb directly to the clay surface.
Abstract: The nature of the siloxane surface in smectites was investigated by measuring the adsorption of aromatic hydrocarbons from water by organo-clays. The organo-clays were prepared by replacing the hydrophilic, inorganic exchange cations of a series of smectites with the small, hydrophobic organic cation, trimethylphenylammonium (TMPA). Smectites with a range in charge densities were used that resulted in different TMPA contents in the organo-clays. Adsorption isotherms of benzene, alkylbenzenes, and naphthalene from water by the TMPA-smectites indicated that sorption was inversely related to TMPA content. The Langmuir form of the isotherms suggests that the aromatic compounds adsorb to the clay surface. Possible adsorptive sites in TMPA-smectites are limited to the TMPA cations and the siloxane oxygen surfaces. Because sorption increased as layer charge and TMPA content decreased, the organic compounds must adsorb to the siloxane surfaces. Calculations based on an adsorbed compound monolayer, which was estimated by fitting adsorption data to the Langmuir equation, and the N2 specific surface area of each TMPA-clay, indicate that the surface area occupied by each adsorbed molecule increases as the planar area of the molecule increases. This strongly indicates that the planar surfaces of the compounds adsorb directly to the clay surface. Apparently, the TMPA cations function to keep the smectite interlayers open. Interactions between the phenyl groups of TMPA cations on opposing interlayer clay surfaces may act to increase the size of the adsorptive regions. These results show that the siloxane surfaces of smectites can effectively adsorb aromatic hydrocarbons from water if the hydrophilic, inorganic exchange cations are replaced with small, hydrophobic organic cations. The strong adsorption of hydrophobic organic molecules from water demonstrates the hydrophobicity of the siloxane surfaces in smectites.