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Showing papers by "Purdue University published in 1999"


Proceedings ArticleDOI
06 Jul 1999
TL;DR: The experimental results show that the PSO is a promising optimization method and a new approach is suggested to improve PSO's performance near the optima, such as using an adaptive inertia weight.
Abstract: We empirically study the performance of the particle swarm optimizer (PSO). Four different benchmark functions with asymmetric initial range settings are selected as testing functions. The experimental results illustrate the advantages and disadvantages of the PSO. Under all the testing cases, the PSO always converges very quickly towards the optimal positions but may slow its convergence speed when it is near a minimum. Nevertheless, the experimental results show that the PSO is a promising optimization method and a new approach is suggested to improve PSO's performance near the optima, such as using an adaptive inertia weight.

3,976 citations


Journal ArticleDOI
TL;DR: In this paper, the authors measured the effective thermal conductivity of mixtures of Al 2O3 and CuO, dispersed in water, vacuum pump, engine oil, and ethylene glycol.
Abstract: Effective thermal conductivity of mixtures of e uids and nanometer-size particles is measured by a steady-state parallel-plate method. The tested e uids contain two types of nanoparticles, Al 2O3 and CuO, dispersed in water, vacuum pump e uid, engine oil, and ethylene glycol. Experimental results show that the thermal conductivities of nanoparticle ‐e uid mixtures are higher than those of the base e uids. Using theoretical models of effective thermal conductivity of a mixture, we have demonstrated that the predicted thermal conductivities of nanoparticle ‐e uid mixtures are much lower than our measured data, indicating the dee ciency in the existing models when used for nanoparticle ‐e uid mixtures. Possible mechanisms contributing to enhancement of the thermal conductivity of the mixtures are discussed. A more comprehensive theory is needed to fully explain the behavior of nanoparticle ‐e uid mixtures. Nomenclature cp = specie c heat k = thermal conductivity L = thickness Pe = Peclet number P q = input power to heater 1 r = radius of particle S = cross-sectional area T = temperature U = velocity of particles relative to that of base e uids ® = ratio of thermal conductivity of particle to that of base liquid ¯ = .® i 1/=.® i 2/ ° = shear rate of e ow Ω = density A = volume fraction of particles in e uids Subscripts

2,156 citations


Journal ArticleDOI
TL;DR: The relationship between first- and second-order barriers is discussed and specific strategies for circumventing, overcoming, and eliminating the changing barriers teachers face as they work to achieve technology integration are described.
Abstract: Although teachers today recognize the importance of integrating technology into their curricula, efforts are often limited by both external (first-order) and internal (second-order) barriers. Traditionally, technology training, for both preservice and inservice teachers, has focused on helping teachers overcome first-order barriers (e.g., acquiring technical skills needed to operate a computer). More recently, training programs have incorporated pedagogical models of technology use as one means of addressing second-order barriers. However, little discussion has occurred that clarifies the relationship between these different types of barriers or that delineates effective strategies for addressing different barriers. If pre- and inservice teachers are to become effective users of technology, they will need practical strategies for dealing with the different types of barriers they will face. In this paper, I discuss the relationship between first- and second-order barriers and then describe specific strategies for circumventing, overcoming, and eliminating the changing barriers teachers face as they work to achieve technology integration.

1,834 citations


Journal ArticleDOI
TL;DR: This paper provides a comprehensive review that synthesizes existing results for the single period problem and develops additional results to enrich the existing knowledge base, and reviews and develops insight into a dynamic inventory extension of this problem.
Abstract: In the newsvendor problem, a decision maker facing random demand for a perishable product decides how much of it to stock for a single selling period. This simple problem with its intuitively appealing solution is a crucial building block of stochastic inventory theory, which comprises a vast literature focusing on operational efficiency. Typically in this literature, market parameters such as demand and selling price are exogenous. However, incorporating these factors into the mode l can provide an excellent vehicle for examining how operational problems interact with marketing issues to influence decision making at the firm level. In this paper we examine an extension of the newsvendor problem in which stocking quantity and selling price are set simultaneously. We provide a comprehensive review that synthesizes existing results for the single period problem and develop additional results to enrich the existing knowledge base. We also review and develop insight into a dynamic inventory extension of this problem, and motivate the applicability of such models.

1,579 citations


Journal ArticleDOI
TL;DR: The present review sought to determine the magnitude and overall pattern of responses typically found in cue-reactivity research and which, if any, learning-based model of cue reactivity is best supported by the findings.
Abstract: Aims. The cue-reactivity procedure exposes addicts to a variety of drug-related stimuli while self-report of craving and physiological responses are monitored. The present review sought to determine the magnitude and overall pattern of responses typically found in cue-reactivity research and which, if any, learning-based model of cue reactivity is best supported by the findings. Design. Meta-analytical techniques were used to select and evaluate results from 41 cue-reactivity studies that compared responses of alcoholics, cigarette smokers, cocaine addicts or heroin addicts to drug-related versus neutral stimuli. Effect sizes were calculated, separately by addict type, for self-report of craving and physiological responses (heart rate, sweat gland activity and skin temperature). Findings. Across all addict groups, the effect size for craving was +0.92. Alcoholics had a significantly smaller craving effect size (+0.53) compared to other addict groups (+1.18 to +1.29). Relatively smaller effect sizes were found for physiological responses. The general profile of effect sizes across all addict groups was increased heart rate (+0.26) and sweat gland activity (+0.40) and decreased skin temperature (-0.24) when addicts were presented with drug-related stimuli. Conclusions. The cuereactivity paradigm can produce a stable profile of significant effects and, therefore, has a number of potential applications for investigating addictive phenomena. The implications of these findings for conditioning-based models of cue-reactivity phenomena are discussed.

1,493 citations


Journal ArticleDOI
01 Jun 1999
TL;DR: The shikimate pathway links metabolism of carbohydrates to biosynthesis of aromatic compounds, the precursor of the aromatic amino acids and many aromatic secondary metabolites, and is the sole target for the herbicide glyphosate.
Abstract: The shikimate pathway links metabolism of carbohydrates to biosynthesis of aromatic compounds. In a sequence of seven metabolic steps, phosphoenolpyruvate and erythrose 4-phosphate are converted to chorismate, the precursor of the aromatic amino acids and many aromatic secondary metabolites. All pathway intermediates can also be considered branch point compounds that may serve as substrates for other metabolic pathways. The shikimate pathway is found only in microorganisms and plants, never in animals. All enzymes of this pathway have been obtained in pure form from prokaryotic and eukaryotic sources and their respective DNAs have been characterized from several organisms. The cDNAs of higher plants encode proteins with amino terminal signal sequences for plastid import, suggesting that plastids are the exclusive locale for chorismate biosynthesis. In microorganisms, the shikimate pathway is regulated by feedback inhibition and by repression of the first enzyme. In higher plants, no physiological feedback inhibitor has been identified, suggesting that pathway regulation may occur exclusively at the genetic level. This difference between microorganisms and plants is reflected in the unusually large variation in the primary structures of the respective first enzymes. Several of the pathway enzymes occur in isoenzymic forms whose expression varies with changing environmental conditions and, within the plant, from organ to organ. The penultimate enzyme of the pathway is the sole target for the herbicide glyphosate. Glyphosate-tolerant transgenic plants are at the core of novel weed control systems for several crop plants.

1,193 citations


Journal ArticleDOI
20 May 1999-Nature
TL;DR: A matrix-free strategy forbiomolecular mass spectrometry based on pulsed-laser desorption–ionization from a porous silicon surface that offers good sensitivity as well as compatibility with silicon-based microfluidics and microchip technologies.
Abstract: Desorption mass spectrometry has undergone significant improvements since the original experiments were performed more than 90 years ago1. The most dramatic change occurred in the early1980s with the introduction of an organic matrix2,3,4 to transfer energy to the analyte. This reduces ion fragmentation but also introduces background ions from the matrix. Here we describe a matrix-free strategy forbiomolecular mass spectrometry based on pulsed-laser desorption–ionization from a porous silicon5 surface. Our method uses porous silicon to trap analytes deposited on the surface, and laser irradiation to vaporize and ionize them. We show that the method works at femtomole and attomole levels of analyte, and induces little or no fragmentation, in contrast to what is typically observed with other such approaches6,7,8,9,10,11. The ability to perform these measurements without a matrix3,4,12,13 also makes itmore amenable to small-molecule analysis. Chemical14 and structural15 modification of the porous silicon has enabled optimization of the ionization characteristics of the surface. Our technique offers good sensitivity as well as compatibility with silicon-based microfluidics and microchip technologies.

1,032 citations


Journal ArticleDOI
TL;DR: This paper uses a set of learning algorithms to create classifiers that serve as noise filters for the training data and suggests that for situations in which there is a paucity of data, consensus filters are preferred, whereas majority vote filters are preferable for situations with an abundance of data.
Abstract: This paper presents a new approach to identifying and eliminating mislabeled training instances for supervised learning. The goal of this approach is to improve classification accuracies produced by learning algorithms by improving the quality of the training data. Our approach uses a set of learning algorithms to create classifiers that serve as noise filters for the training data. We evaluate single algorithm, majority vote and consensus filters on five datasets that are prone to labeling errors. Our experiments illustrate that filtering significantly improves classification accuracy for noise levels up to 30%. An analytical and empirical evaluation of the precision of our approach shows that consensus filters are conservative at throwing away good data at the expense of retaining bad data and that majority filters are better at detecting bad data at the expense of throwing away good data. This suggests that for situations in which there is a paucity of data, consensus filters are preferable, whereas majority vote filters are preferable for situations with an abundance of data.

877 citations


Journal ArticleDOI
08 Oct 1999-Science
TL;DR: The first x-ray structure of a calicivirus capsid, which consists of 180 copies of a single protein, has been determined by phase extension from a low-resolution electron microscopy structure that has a protruding (P) domain connected by a flexible hinge to a shell (S) domain that hasA classical eight-stranded beta-sandwich motif.
Abstract: Norwalk virus, a noncultivatable human calicivirus, is the major cause of epidemic gastroenteritis in humans. The first x-ray structure of a calicivirus capsid, which consists of 180 copies of a single protein, has been determined by phase extension from a low-resolution electron microscopy structure. The capsid protein has a protruding (P) domain connected by a flexible hinge to a shell (S) domain that has a classical eight-stranded beta-sandwich motif. The structure of the P domain is unlike that of any other viral protein with a subdomain exhibiting a fold similar to that of the second domain in the eukaryotic translation elongation factor-Tu. This subdomain, located at the exterior of the capsid, has the largest sequence variation among Norwalk-like human caliciviruses and is likely to contain the determinants of strain specificity and cell binding.

845 citations


Journal ArticleDOI
TL;DR: Three new heuristics, one for batch mode and two for immediate mode, are introduced as part of this research, revealing that the choice of which dynamic mapping heuristic to use in a given heterogeneous environment depends on parameters such as the structure of the heterogeneity among tasks and machines and the arrival rate of the tasks.

828 citations


Journal ArticleDOI
16 Apr 1999-Cell
TL;DR: A mutation is identified, net1-1, that bypasses the lethality of tem1 delta and is a key component of a multifunctional complex, denoted RENT (for regulator of nucleolar silencing and telophase), that also contains Cdc14 and the silencing regulator Sir2.

Journal ArticleDOI
TL;DR: The Annonaceous acetogenins are promising new antitumor and pesticidal agents that are found only in the plant family Annonaceae and exhibit their potent bioactivities through depletion of ATP levels via inhibiting complex I of mitochondria and inhibiting the NADH oxidase of plasma membranes of tumor cells.
Abstract: The Annonaceous acetogenins are promising new antitumor and pesticidal agents that are found only in the plant family Annonaceae. Chemically, they are derivatives of long-chain fatty acids. Biologically, they exhibit their potent bioactivities through depletion of ATP levels via inhibiting complex I of mitochondria and inhibiting the NADH oxidase of plasma membranes of tumor cells. Thus, they thwart ATP-driven resistance mechanisms. This review presents the progress made in the chemistry, biology, and development of these compounds since December 1995.

Journal ArticleDOI
01 Jul 1999
TL;DR: Digital watermarking techniques are described, known as perceptually based watermarks, that are designed to exploit aspects of the the human visual system in order to provide a transparent (invisible), yet robust watermark.
Abstract: The growth of new imaging technologies has created a need for techniques that can be used for copyright protection of digital images and video. One approach for copyright protection is to introduce an invisible signal, known as a digital watermark, into an image or video sequence. In this paper, we describe digital watermarking techniques, known as perceptually based watermarks, that are designed to exploit aspects of the the human visual system in order to provide a transparent (invisible), yet robust watermark. In the most general sense, any watermarking technique that attempts to incorporate an invisible mark into an image is perceptually based. However, in order to provide transparency and robustness to attack, two conflicting requirements from a signal processing perspective, more sophisticated use of perceptual information in the watermarking process is required. We describe watermarking techniques ranging from simple schemes which incorporate common-sense rules in using perceptual information in the watermarking process, to more elaborate schemes which adapt to local image characteristics based on more formal perceptual models. This review is not meant to be exhaustive; its aim is to provide the reader with an understanding of how the techniques have been evolving as the requirements and applications become better defined.

Journal ArticleDOI
David J. Denis1
TL;DR: In this article, the authors examine the equity ownership structure and board composition of a sample of 583 firms over the ten-year period 1983-1992 and find that a substantial fraction of firms exhibit large changes in ownership and board structure in any given year.

Proceedings ArticleDOI
12 Apr 1999
TL;DR: Three new heuristics, one for batch and two for on-line, are introduced as part of this research, revealing that the choice of mapping heuristic depends on parameters such as: the structure of the heterogeneity among tasks and machines, the optimization requirements, and the arrival rate of the tasks.
Abstract: Dynamic mapping (matching and scheduling) heuristics for a class of independent tasks using heterogeneous distributed computing systems are studied. Two types of mapping heuristics are considered: on-line and batch mode heuristics. Three new heuristics, one for batch and two for on-line, are introduced as part of this research. Simulation studies are performed to compare these heuristics with some existing ones. In total, five on-line heuristics and three batch heuristics are examined. The on-line heuristics consider; to varying degrees and in different ways, task affinity for different machines and machine ready times. The batch heuristics consider these factors, as well as aging of tasks waiting to execute. The simulation results reveal that the choice of mapping heuristic depends on parameters such as: (a) the structure of the heterogeneity among tasks and machines, (b) the optimization requirements, and (c) the arrival rate of the tasks.

Reference BookDOI
15 Oct 1999
TL;DR: In this paper, a case study of PARAMETER and QUANTILE ESTIMATION is presented, where the authors use moment ratio diagrams (MRDs) to estimate the probability of fit tests.
Abstract: INTRODUCTION Hydrologic Frequency Analysis General Aspects and Approaches Other Models Return Period, Probability, and Plotting Positions Flood Frequency Models Hydrologic Risk Regionalization Tests on Hydrologic Data SELECTION AND EVALUATION OF PARENT DISTRIBUTION: CONVENTIONAL MOMENTS Moments of Distributions and Their Sample Estimates Moment Ratio Diagrams (MRDs) Probability Plots Selection of Distributions Regional Homogeneity and Regionalization SELECTION AND EVALUATION OF PARENT DISTRIBUTIONS: PROBABILITY WEIGHTED MOMENTS AND L-MOMENTS Moments of Distributions and Their Sample Estimates L-Moment Ratio Diagrams Goodness of Fit Tests A Case Study PARAMETER AND QUANTILE ESTIMATION Introduction Parameter Estimation Quantile Estimation Confidence Intervals NORMAL AND RELATED DISTRIBUTIONS Normal Distribution Two-Parameter Lognormal (LN(2)) Distribution Three-Parameter Lognormal (LM(3)) Distribution GAMMA FAMILY Exponential Distribution Two-Parameter Gamma (G(2)) Distribution Pearson (2) Distribution Log-Pearson (3) Distribution U.S. Water Resources Council Method (WRCM) EXTREME VALUE DISTRIBUTIONS Generalized Extreme Value (GEV) Distribution The Extreme Value Type (EV(1) Distribution Weibul Distribution WAKEBY FAMILY The 5-Parameter Wakeby Distribution (WAK(5)) The 4-Parameter Wakeby Distribution (WAK(4)) The Generalized Pareto Distribution LOGISTIC DISTRIBUTIONS Logistic Distribution Generalized Logistic Distribution COMPUTER PROGRAM Introduction Description of Program REFERENCES

Journal ArticleDOI
TL;DR: In this article, undergraduates were randomly assigned to conditions crossing either a positive or negative outcome and a procedure which was either fair, biased in the participant's favor, or biased in favor of another, after which their emotional responses were assessed by self report.
Abstract: Research on organizational justice typically focuses on attitudinal, cognitive, or behavioral outcomes. Emotional reactions to justice have been suggested but not studied. The emotional appraisal literature provides a framework within which to analyze emotional reactions to just and unjust events. Undergraduates (67 females and 55 males) were randomly assigned to conditions crossing either a positive or negative outcome and a procedure which was either fair, biased in the participant's favor, or biased in favor of another, after which their emotional responses were assessed by self report. Results support predictions about discrete emotional reactions. As predicted by emotional-appraisal theories, reports of happiness were influenced only by outcome, whereas reports of guilt, anger, and to a lesser extent pride, were influenced by specific combinations of outcome and procedure. Results are discussed within an emotional appraisal framework.

Journal ArticleDOI
TL;DR: It is demonstrated that the S. pombe gene catalyzing GSH-dependent, heavy metal–activated synthesis of PCs in vitro demonstrated that both genes encode PC synthase activity, and a similar gene was identified in the nematode, Caenorhabditis elegans, suggesting that PCs may also be expressed in some animal species.
Abstract: Phytochelatins (PCs), a family of heavy metal–inducible peptides important in the detoxification of heavy metals, have been identified in plants and some microorganisms, including Schizosaccharomyces pombe , but not in animals. PCs are synthesized enzymatically from glutathione (GSH) by PC synthase in the presence of heavy metal ions. In Arabidopsis, the CAD1 gene, identified by using Cd-sensitive, PC-deficient cad1 mutants, has been proposed to encode PC synthase. Using a positional cloning strategy, we have isolated the CAD1 gene. Database searches identified a homologous gene in S. pombe , and a mutant with a targeted deletion of this gene was also Cd sensitive and PC deficient. Extracts of Escherichia coli cells expressing a CAD1 cDNA or the S. pombe gene catalyzing GSH-dependent, heavy metal–activated synthesis of PCs in vitro demonstrated that both genes encode PC synthase activity. Both enzymes were activated by a range of metal ions. In contrast, reverse transcription–polymerase chain reaction experiments showed that expression of the CAD1 mRNA is not influenced by the presence of Cd. A comparison of the two predicted amino acid sequences revealed a highly conserved N-terminal region, which is presumed to be the catalytic domain, and a variable C-terminal region containing multiple Cys residues, which is proposed to be involved in activation of the enzyme by metal ions. Interestingly, a similar gene was identified in the nematode, Caenorhabditis elegans , suggesting that PCs may also be expressed in some animal species.

Journal ArticleDOI
TL;DR: Overall, the ICSA and ICPC studies indicate that there are a number of receptors, neuronal pathways, and discrete CNS sites involved in brain reward mechanisms.

Journal ArticleDOI
TL;DR: This paper provides a detailed convergence analysis of the multiscale finite element method for solving second order elliptic equations with rapidly oscillating coefficients under the assumption that the oscillating coefficient is of two scales and is periodic in the fast scale.
Abstract: We propose a multiscale finite element method for solving second order elliptic equations with rapidly oscillating coefficients. The main purpose is to design a numerical method which is capable of correctly capturing the large scale components of the solution on a coarse grid without accurately resolving all the small scale features in the solution. This is accomplished by incorporating the local microstructures of the differential operator into the finite element base functions. As a consequence, the base functions are adapted to the local properties of the differential operator. In this paper, we provide a detailed convergence analysis of our method under the assumption that the oscillating coefficient is of two scales and is periodic in the fast scale. While such a simplifying assumption is not required by our method, it allows us to use homogenization theory to obtain a useful asymptotic solution structure. The issue of boundary conditions for the base functions will be discussed. Our numerical experiments demonstrate convincingly that our multiscale method indeed converges to the correct solution, independently of the small scale in the homogenization limit. Application of our method to problems with continuous scales is also considered.

Journal ArticleDOI
TL;DR: It is shown that diffusion controlled delivery of proteins from hydrogels containing poly(ethylene glycol) (PEG) can be possible and controlled by the three-dimensional structure.

Journal ArticleDOI
12 Feb 1999-Science
TL;DR: The formation and growth of crystal nuclei of zeolite A from clear solutions at room temperature were studied with low-dose, high-resolution transmission electron microscopy in field emission mode and with in situ dynamic light scattering to derive nanoscale single crystals embedded in amorphous gel particles.
Abstract: The formation and growth of crystal nuclei of zeolite A from clear solutions at room temperature were studied with low-dose, high-resolution transmission electron microscopy in field emission mode and with in situ dynamic light scattering Single zeolite A crystals nucleated in amorphous gel particles of 40 to 80 nanometers within 3 days at room temperature The resulting nanoscale single crystals (10 to 30 nanometers) were embedded in the amorphous gel particles The gel particles were consumed during further crystal growth at room temperature, forming a colloidal suspension of zeolite A nanocrystals of 40 to 80 nanometers On heating this suspension at 80°C, solution-mediated transport resulted in additional substantial crystal growth

Journal ArticleDOI
TL;DR: The reduction in functional I(Ca) density in myocytes from the atria of chronic AF patients may be an adaptive response to the arrhythmia-induced calcium overload, consistent with the concept that calcium overload is an important factor in the initiation of AF.
Abstract: Chronic atrial fibrillation (AF) is characterized by decreased atrial contractility, shortened action potential duration, and decreased accommodation of action potential duration to changes in activation rate. Studies on experimental animal models of AF implicate a reduction in L-type Ca2+ current (I(Ca)) density in these changes. To evaluate the effect of AF on human I(Ca), we compared I(Ca) in atrial myocytes isolated from 42 patients in normal sinus rhythm at the time of cardiac surgery with that of 11 chronic AF patients. I(Ca) was significantly reduced in the myocytes of patients with chronic AF (mean -3.35+/-0.5 pA/pF versus -9.13+/-1. 0 pA/pF in the controls), with no difference between groups in the voltage dependence of activation or steady-state inactivation. Although I(Ca) was lower in myocytes from the chronic AF patients, their response to maximal beta-adrenergic stimulation was not impaired. Postoperative AF frequently follows cardiac surgery. Half of the patients in the control group (19/38) of this study experienced postoperative AF. Whereas chronic AF is characterized by reduced atrial I(Ca), the patients with the greatest I(Ca) had an increased incidence of postoperative AF, independent of patient age or diagnosis. This observation is consistent with the concept that calcium overload may be an important factor in the initiation of AF. The reduction in functional I(Ca) density in myocytes from the atria of chronic AF patients may thus be an adaptive response to the arrhythmia-induced calcium overload.

Journal ArticleDOI
TL;DR: This survey provides a comprehensive analysis of new paradigms and enabler concepts for mobile client-server computing, including mobile-aware adaptation, extended client- server model, and mobile data access.
Abstract: Recent advances in wireless data networking and portable information appliances have engendered a new paradigm of computing, called mobile computing, in which users carrying portable devices have access to data and information services regardless of their physical location or movement behavior. In the meantime, research addressing information access in mobile environments has proliferated. In this survey, we provide a concrete framework and categorization of the various ways of supporting mobile client-server computing for information access. We examine characteristics of mobility that distinguish mobile client-server computing from its traditional counterpart. We provide a comprehensive analysis of new paradigms and enabler concepts for mobile client-server computing, including mobile-aware adaptation, extended client-server model, and mobile data access. A comparative and detailed review of major research prototypes for mobile information access is also presented.

Journal ArticleDOI
TL;DR: A Lyapunov-based stabilizing control design method for uncertain nonlinear dynamical systems using fuzzy models is proposed, finding sufficient conditions for stability and stabilizability of fuzzy models using fuzzy state feedback controllers.
Abstract: A Lyapunov-based stabilizing control design method for uncertain nonlinear dynamical systems using fuzzy models is proposed. The controller is constructed using a design model of the dynamical process to be controlled. The design model is obtained from the truth model using a fuzzy modeling approach. The truth model represents a detailed description of the process dynamics. The truth model is used in a simulation experiment to evaluate the performance of the controller design. A method for generating local models that constitute the design model is proposed. Sufficient conditions for stability and stabilizability of fuzzy models using fuzzy state feedback controllers are given. The results obtained are illustrated with a numerical example involving a four-dimensional nonlinear model of a stick balancer.

Journal ArticleDOI
TL;DR: It is proposed that PKL is a component of a gibberellin-modulated developmental switch that functions during germination to prevent reexpression of the embryonic developmental state.
Abstract: The life cycle of angiosperms is punctuated by a dormant phase that separates embryonic and postembryonic development of the sporophyte. In the pickle (pkl) mutant of Arabidopsis, embryonic traits are expressed after germination. The penetrance of the pkl phenotype is strongly enhanced by inhibitors of gibberellin biosynthesis. Map-based cloning of the PKL locus revealed that it encodes a CHD3 protein. CHD3 proteins have been implicated as chromatin-remodeling factors involved in repression of transcription. PKL is necessary for repression of LEC1, a gene implicated as a critical activator of embryo development. We propose that PKL is a component of a gibberellin-modulated developmental switch that functions during germination to prevent reexpression of the embryonic developmental state.

Journal ArticleDOI
TL;DR: The decrease in rates of production of cosmogenic nuclides occurs because of shielding of cosmic rays by mountains, sloped surfaces, and local rock formations that block them as discussed by the authors.

Journal ArticleDOI
Peggy A. Ertmer1, Paul Addison1, Molly Lane, Eva M. Ross1, Denise M. Woods1 
TL;DR: The authors examined the relationship between first-and second-order barriers to technology implementation by observing and interviewing several teachers within a single school who had achieved varying levels of integration, and found that teachers responded differently to these constraints based at least in part on their beliefs about what constitutes effective classroom practice.
Abstract: Although teachers today recognize the importance of integrating technology into their curricula, successful implementation often is hampered by both external (first-order) and internal (second-order) barriers. This study was designed to examine the relationship between first- and second-order barriers to technology implementation by observing and interviewing several teachers within a single school who had achieved varying levels of integration. Although first-order barriers constrained all teachers’ efforts in this school, teachers responded differently to these constraints based at least in part on their beliefs about what constitutes effective classroom practice. Strategies for technology staff development are discussed.

Journal ArticleDOI
TL;DR: It is postulated that apoE promotes both the deposition and fibrillization of Abeta, ultimately affecting clearance of protease-resistant Abeta/apoE aggregates.
Abstract: We quantified the amount of amyloid beta-peptide (Abeta) immunoreactivity as well as amyloid deposits in a large cohort of transgenic mice overexpressing the V717F human amyloid precursor protein (APP(V717F+/-) TG mice) with no, one, or two mouse apolipoprotein E (Apoe) alleles at various ages. Remarkably, no amyloid deposits were found in any brain region of APP(V717F+/-) Apoe(-/-) TG mice as old as 22 mo of age, whereas age-matched APP(V717F +/-) Apoe(+/-) and Apoe(+/+) TG mice display abundant amyloid deposition. The amount of Abeta immunoreactivity in the hippocampus was also markedly reduced in an Apoe gene dose-dependent manner (Apoe(+/+) > Apoe(+/-) >> Apoe(-/-)), and no Abeta immunoreactivity was detected in the cerebral cortex of APP(V717F+/-) Apoe(-/-) TG mice at any of the time points examined. The absence of apolipoprotein E protein (apoE) dramatically reduced the amount of both Abeta(1-40) and Abeta(1-42) immunoreactive deposits as well as the resulting astrogliosis and microgliosis normally observed in APP(V717F) TG mice. ApoE immunoreactivity was detected in a subset of Abeta immunoreactive deposits and in virtually all thioflavine-S-fluorescent amyloid deposits. Because the absence of apoE alters neither the transcription or translation of the APP(V717F) transgene nor its processing to Abeta peptide(s), we postulate that apoE promotes both the deposition and fibrillization of Abeta, ultimately affecting clearance of protease-resistant Abeta/apoE aggregates. ApoE appears to play an essential role in amyloid deposition in brain, one of the neuropathological hallmarks of Alzheimer's disease.

Journal ArticleDOI
TL;DR: Results showed that average levels of pleasant mood over the 16 days and VIE beliefs about the job made significant and independent contributions to the prediction of overall job satisfaction and did so over and above the contribution of dispositional happiness.