Showing papers by "University of Illinois at Urbana–Champaign published in 1998"

Floral dip: a simplified method for Agrobacterium-mediated transformation of Arabidopsis thaliana

Abstract: Summary The Agrobacterium vacuum infiltration method has made it possible to transform Arabidopsis thaliana without plant tissue culture or regeneration. In the present study, this method was evaluated and a substantially modified transformation method was developed. The labor-intensive vacuum infiltration process was eliminated in favor of simple dipping of developing floral tissues into a solution containing Agrobacterium tumefaciens, 5% sucrose and 500 microliters per litre of surfactant Silwet L-77. Sucrose and surfactant were critical to the success of the floral dip method. Plants inoculated when numerous immature floral buds and few siliques were present produced transformed progeny at the highest rate. Plant tissue culture media, the hormone benzylamino purine and pH adjustment were unnecessary, and Agrobacterium could be applied to plants at a range of cell densities. Repeated application of Agrobacterium improved transformation rates and overall yield of transformants approximately twofold. Covering plants for 1 day to retain humidity after inoculation also raised transformation rates twofold. Multiple ecotypes were transformable by this method. The modified method should facilitate high-throughput transformation of Arabidopsis for efforts such as T-DNA

Converging measurement of horizontal and vertical individualism and collectivism

Abstract: The constructs of horizontal (H) and vertical (V) individualism (I) and collectivism (C) were theoretically defined and empirically supported. Study 1 confirmed, via factor analysis, that the 4 constructs, HI, VI, HC, and VC, which were previously found in the United States, which has an individualist culture, also were found in Korea, which has a collectivist culture. Study 2 investigated multimethod-multitrait matrices measuring the constructs and generally supported their convergent and divergent validity. Study 3 showed how these 4 constructs relate to previously identified components by H. C. Triandis and colleagues. Study 4 showed the relationships of the measurement of the 4 constructs to some of the measures used by other researchers.

Adolescent sexual behavior, drug use, and violence: increased reporting with computer survey technology

Abstract: Surveys of risk behaviors have been hobbled by their reliance on respondents to report accurately about engaging in behaviors that are highly sensitive and may be illegal. An audio computer-assisted self-interviewing (audio-CASI) technology for measuring those behaviors was tested with 1690 respondents in the 1995 National Survey of Adolescent Males. The respondents were randomly assigned to answer questions using either audio-CASI or a more traditional self-administered questionnaire. Estimates of the prevalence of male-male sex, injection drug use, and sexual contact with intravenous drug users were higher by factors of 3 or more when audio-CASI was used. Increased reporting was also found for several other risk behaviors.

Equation of state of nucleon matter and neutron star structure

Abstract: Properties of dense nucleon matter and the structure of neutron stars are studied using variational chain summation methods and the new Argonne ${v}_{18}$ two-nucleon interaction, which provides an excellent fit to all of the nucleon-nucleon scattering data in the Nijmegen database. The neutron star gravitational mass limit obtained with this interaction is 1.67${M}_{\ensuremath{\bigodot}}.$ Boost corrections to the two-nucleon interaction, which give the leading relativistic effect of order ${(v/c)}^{2},$ as well as three-nucleon interactions, are also included in the nuclear Hamiltonian. Their successive addition increases the mass limit to 1.80 and 2.20 ${M}_{\ensuremath{\bigodot}}.$ Hamiltonians including a three-nucleon interaction predict a transition in neutron star matter to a phase with neutral pion condensation at a baryon number density of $\ensuremath{\sim}0.2 {\mathrm{fm}}^{\ensuremath{-}3}.$ Neutron stars predicted by these Hamiltonians have a layer with a thickness on the order of tens of meters, over which the density changes rapidly from that of the normal to the condensed phase. The material in this thin layer is a mixture of the two phases. We also investigate the possibility of dense nucleon matter having an admixture of quark matter, described using the bag model equation of state. Neutron stars of 1.4${M}_{\ensuremath{\bigodot}}$ do not appear to have quark matter admixtures in their cores. However, the heaviest stars are predicted to have cores consisting of a quark and nucleon matter mixture. These admixtures reduce the maximum mass of neutron stars from 2.20 to 2.02 (1.91) ${M}_{\ensuremath{\bigodot}}$ for bag constant $B=200 (122) {\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{f}\mathrm{m}}^{3}.$ Stars with pure quark matter in their cores are found to be unstable. We also consider the possibility that matter is maximally incompressible above an assumed density, and show that realistic models of nuclear forces limit the maximum mass of neutron stars to be below 2.5${M}_{\ensuremath{\bigodot}}.$ The effects of the phase transitions on the composition of neutron star matter and its adiabatic index $\ensuremath{\Gamma}$ are discussed.

Statistical Properties of X-Ray Clusters: Analytic and Numerical Comparisons

Abstract: We compare the results of Eulerian hydrodynamic simulations of cluster formation against virial scaling relations between four bulk quantities: the cluster mass, the dark matter velocity dispersion, the gas temperature, and the cluster luminosity. The comparison is made for a large number of clusters at a range of redshifts in three different cosmological models (cold plus hot dark matter, cold dark matter, and open cold dark matter). We find that the analytic formulae provide a good description of the relations between three of the four numerical quantities. The fourth (luminosity) also agrees once we introduce a procedure to correct for the fixed numerical resolution. We also compute the normalizations for the virial relations and compare extensively to the existing literature, finding remarkably good agreement. The Press-Schechter prescription is calibrated with the simulations, again finding results consistent with other authors. We also examine related issues such as the size of the scatter in the virial relations, the effect of metallicity with a fixed passband, and the structure of the halos. All of this is done in order to establish a firm groundwork for the use of clusters as cosmological probes. Implications for the models are briefly discussed.

Relevance feedback: a power tool for interactive content-based image retrieval

Abstract: Content-based image retrieval (CBIR) has become one of the most active research areas in the past few years. Many visual feature representations have been explored and many systems built. While these research efforts establish the basis of CBIR, the usefulness of the proposed approaches is limited. Specifically, these efforts have relatively ignored two distinct characteristics of CBIR systems: (1) the gap between high-level concepts and low-level features, and (2) the subjectivity of human perception of visual content. This paper proposes a relevance feedback based interactive retrieval approach, which effectively takes into account the above two characteristics in CBIR. During the retrieval process, the user's high-level query and perception subjectivity are captured by dynamically updated weights based on the user's feedback. The experimental results over more than 70000 images show that the proposed approach greatly reduces the user's effort of composing a query, and captures the user's information need more precisely.

Ultrafiltration and Microfiltration Handbook

Abstract: Each chapter ends with a section of references. Introduction Definition and classification of membrane separation processes Historical developments Physical chemistry of membrane separations: Chemical potential and osmosis, Vapor pressure, Osmotic pressure and chemical potential Membrane Chemistry Definitions and classification: Depth vs. screen filters, Microporous vs. asymmetric membranes General methods of membrane manufacture: Phase Inversion Process of Membrane Manufacture Polymers used in membrane manufacture: Cellulose Acetate, Polyamide membranes, Polysulfone membranes, Other polymeric materials Composite membranes Inorganic membranes: Properties of inorganic membranes Membrane Properties Pore size: Bubble point and pressure techniques, Direct microscopic observation Predicting flux from pore statistics Passage (challenge) tests: Microfiltration membranes, Ultrafiltration membranes Factors affecting retentivity of membranes: Size of the molecule, Shape of the molecule, Membrane material, Presence of other solutes, Operating parameters, Lot-to-lot variability, Membrane configuration, Fouling and adsorption effects, The microenvironment Performance and Engineering Models The velocity boundary layer The concentration boundary layer Models for predicting flux: the pressure-controlled region Concentration polarization Mass transfer (film theory) model: Determining the mass transfer coefficient, Example The resistance model Osmotic pressure model for limiting flux Factors affecting flux: operating parameters: Feed concentration, Temperature, Flow rate and turbulence Physical properties of liquid streams: Density, Viscosity, Diffusion coefficients Experiment vs. theory: the "flux paradox" Design factors affecting flux Equipment Laboratory scale devices Industrial equipment: Tubular modules, Hollow fibers, Plate units, Spiral-wound Special modules: Rotary modules, Vibrating modules, Dean Vortices Summary Fouling and Cleaning Characteristics of fouling: Water flux Consequences of fouling Mathematical models of fouling Factors affecting fouling: Membrane properties, Solute properties, Process engineering factors affecting fouling Flux enhancement: Turbulence promoters/inserts/baffles, Back-flushing, -pulsing, -shocking and washing, Uniform transmembrane pressure/co-current permeate flow, Permeate back-pressure, Intermittent jets, Pulsatile flow, Electrical methods Summary: Membrane Fouling Cleaning membranes: Important factors during cleaning, Typical foulants and soils, Cleaning chemicals, Sanitizers Process Design Physics of the ultrafiltration process: Example Modes of operation: Discontinuous diafiltration (DD), Continuous diafiltration (CD), Dialysis ultrafiltration Batch vs. continuous operation: Batch operation, Single pass, Feed-and-bleed, Multistage operations, Example, Control methods Minimum process time Fractionation of macromolecules Energy requirements: Example Cost and process economics: Arrays and configurations, System cost Summary Applications Electrocoat paint The dairy industry: Fluid milk and fermented products, Cheese manufacture, Milk microfiltration, Cheese whey ultrafiltration, Microfiltration of whey Water treatment Wastewaters: Oily wastewater, Stillage from bioethanol plants, Caustic and acid recovery, Brine recovery, Printing ink, Laundry wastewater, Micellar-enhanced ultrafiltration Textile industry Latex emulsions Pulp and paper industry Tanning and leather industries Sugar refining Soybean and other vegetable proteins Vegetable oils: Degumming, Deacidification, Bleaching, Removal of metals, Dewaxing, Clarifying Frying Oils Corn and other grains: Dextrose clarification, Protein processing Animal products: Red meat, Gelatin, Egg processing, Fish processing, Poultry industry Biotechnology applications: Separation and harvesting of microbial cells, Enzyme recovery, Affinity ultrafiltration, Membrane bioreactors Fruit juices and extracts Alcoholic beverages: Wine, Beer Appendices List of manufacturers of membrane equipment Conversion factors Books and general Glossary of terms Index More than 350 Tables and Figures Useful reference data is provided in 85 tables. Numerous schematics illustrate membranes, modules, equipment, and processes. Micrographs illustrate membranes and filtration. Here is a small sampling of this supplementary material. * Tables: Characteristics of membrane processes Comparison of energy requirements and costs between evaporation and membrane processes Methods of manufacture of synthetic membranes Materials used for the manufacture of membranes Properties of membrane filters requiring standardization Morphological parameters and bubble points for selected MF membranes-Pore size and surface porosity of ultrafiltration membranes Selected values of gel concentration-Diffusion coefficients-Relationship between channel size and surface area:volume ratio of membrane modules Hollow fibers from various manufacturers-Specifications of spiral-wound membranes from various manufacturers-Typical cleaning reagents and their modes of action-Operating economy of UF plants processing whole milk for cheese manufacture-Water purification process comparison Examples of affinity ultrafiltration Figures: Useful ranges of various separation processes-Classification of filters-Micrograph of multistage depth filter-Schematic representation of ultrastructure of an asymmetric (skinned) membrane-Typical structures of polyamide membranes-Comparison of the performance of commercial cellulose acetate and thin-film composite (polyamide) membranes-Ceramic membrane modules in their housing-Relationship between pore size, molecular weight of ideal solutes, and ratings of ideal and real membranes Permeability of large and small molecules through large and small pore membranes-Schematic representation of the cross section of typical asymmetric UF or MF membrane-Schematic of concentration polarization during UF of colloidal and macromolecular solutes . . .-Schematic of typical plate type membrane module-Multistage filtration sowing several feed-and-bleed systems connected in series-Membrane processing of cheese whey-Selection criteria of separation methods in biopro- cessing

The Effects of Price-Comparison Advertising on Buyers’ Perceptions of Acquisition Value, Transaction Value, and Behavioral Intentions:

Abstract: The authors expand and integrate prior price-perceived value models within the context of price comparison advertising. More specifically, the conceptual model explicates the effects of advertised ...

Model Based Inference in the Life Sciences: A Primer on Evidence

Abstract: Introduction: Science Hypotheses and Science Philosophy.- Data and Models.- Information Theory and Entropy.- Quantifying the Evidence About Science Hypotheses.- Multimodel Inference.- Advanced Topics.- Summary.

The shifting basis of life satisfaction judgments across cultures: Emotions versus norms.

Abstract: The relative importance of emotions versus normative beliefs for life satisfaction judgments was compared among individualist and collectivist nations in 2 large sets of international data (in total, 61 nations, N = 62,446). Among nations, emotions and life satisfaction correlated significantly more strongly in more individualistic nations (r = .52 in Study 1; r = .48 in Study 2). At the individual level, emotions were far superior predictors of life satisfaction to norms (social approval of life satisfaction) in individualist cultures, whereas norms and emotions were equally strong predictors of life satisfaction in collectivist cultures. The present findings have implications for future studies on cultural notions of well-being, the functional value of emotional experiences, and individual differences in life satisfaction profiles. Across the world, is the "good life" attained mostly by doing what a person would like to do or by doing what a person thinks he or she should do? More broadly, are internal processes, such as attitudes, beliefs, emotions, and the like, or external pro

A particle image velocimetry system for microfluidics

Abstract: A micron-resolution particle image velocimetry (micro-PIV) system has been developed to measure instantaneous and ensemble-averaged flow fields in micron-scale fluidic devices. The system utilizes an epifluorescent microscope, 100–300 nm diameter seed particles, and an intensified CCD camera to record high-resolution particle-image fields. Velocity vector fields can be measured with spatial resolutions down to 6.9×6.9×1.5 μm. The vector fields are analyzed using a double-frame cross-correlation algorithm. In this technique, the spatial resolution and the accuracy of the velocity measurements is limited by the diffraction limit of the recording optics, noise in the particle image field, and the interaction of the fluid with the finite-sized seed particles. The stochastic influence of Brownian motion plays a significant role in the accuracy of instantaneous velocity measurements. The micro-PIV technique is applied to measure velocities in a Hele–Shaw flow around a 30 μm (major diameter) elliptical cylinder, with a bulk velocity of approximately 50 μm s-1.

The complete genome of the hyperthermophilic bacterium Aquifex aeolicus

Abstract: Aquifex aeolicus was one of the earliest diverging, and is one of the most thermophilic, bacteria known. It can grow on hydrogen, oxygen, carbon dioxide, and mineral salts. The complex metabolic machinery needed for A. aeolicus to function as a chemolithoautotroph (an organism which uses an inorganic carbon source for biosynthesis and an inorganic chemical energy source) is encoded within a genome that is only one-third the size of the E. coli genome. Metabolic flexibility seems to be reduced as a result of the limited genome size. The use of oxygen (albeit at very low concentrations) as an electron acceptor is allowed by the presence of a complex respiratory apparatus. Although this organism grows at 95 degrees C, the extreme thermal limit of the Bacteria, only a few specific indications of thermophily are apparent from the genome. Here we describe the complete genome sequence of 1,551,335 base pairs of this evolutionarily and physiologically interesting organism.

Are Insiders' Trades Informative?

Abstract: We document insider trading activities of all companies listed on the NYSE, Amex, and Nasdaq exchanges during the 1975-1995 period. Insider trading is common, and in more than half the sample firms, there is at least some insider activity in a given year. In general, very little market movement is observed when insiders trade and when they report their trades to the SEC. Insiders in aggregate are contrarian investors. However, they predict market movements better than simple contrarian strategies. Insiders also seem to be able to predict cross-sectional stock returns. The result, however, is driven by insider's ability to predict returns in smaller firms. In addition, insider purchases are more informative than insider sales.

Electron transfer by domain movement in cytochrome bc1.

Abstract: The cytochrome bc1 is one of the three major respiratory enzyme complexes residing in the inner mitochondrial membrane. Cytochrome bc1 transfers electrons from ubiquinol to cytochrome c and uses the energy thus released to form an electrochemical gradient across the inner membrane. Our X-ray crystal structures of the complex from chicken, cow and rabbit in both the presence and absence of inhibitors of quinone oxidation, reveal two different locations for the extrinsic domain of one component of the enzyme, an iron-sulphur protein. One location is close enough to the supposed quinol oxidation site to allow reduction of the Fe-S protein by ubiquinol. The other site is close enough to cytochrome c1 to allow oxidation of the Fe-S protein by the cytochrome. As neither location will allow both reactions to proceed at a suitable rate, the reaction mechanism must involve movement of the extrinsic domain of the Fe-S component in order to shuttle electrons from ubiquinol to cytochrome c1. Such a mechanism has not previously been observed in redox protein complexes.

From Embedded Knowledge to Embodied Knowledge: New Product Development as Knowledge Management:

Abstract: Because new product development (NPD) teams are engaged in knowledge creation, NPD management should emphasize cognitive team processes rather than purely social processes. Using the notions of tac...

Anatomy of protein pockets and cavities: Measurement of binding site geometry and implications for ligand design

Abstract: Identification and size characterization of surface pockets and occluded cavities are initial steps in protein structure-based ligand design. A new program, CAST, for automatically locating and measuring protein pockets and cavities, is based on precise computational geometry methods, including alpha shape and discrete flow theory. CAST identifies and measures pockets and pocket mouth openings, as well as cavities. The program specifies the atoms lining pockets, pocket openings, and buried cavities; the volume and area of pockets and cavities; and the area and circumference of mouth openings. CAST analysis of over 100 proteins has been carried out; proteins examined include a set of 51 monomeric enzyme-ligand structures, several elastase-inhibitor complexes, the FK506 binding protein, 30 HIV-1 protease-inhibitor complexes, and a number of small and large protein inhibitors. Medium-sized globular proteins typically have 10-20 pockets/cavities. Most often, binding sites are pockets with 1-2 mouth openings; much less frequently they are cavities. Ligand binding pockets vary widely in size, most within the range 10(2)-10(3)A3. Statistical analysis reveals that the number of pockets and cavities is correlated with protein size, but there is no correlation between the size of the protein and the size of binding sites. Most frequently, the largest pocket/cavity is the active site, but there are a number of instructive exceptions. Ligand volume and binding site volume are somewhat correlated when binding site volume is < or =700 A3, but the ligand seldom occupies the entire site. Auxiliary pockets near the active site have been suggested as additional binding surface for designed ligands (Mattos C et al., 1994, Nat Struct Biol 1:55-58). Analysis of elastase-inhibitor complexes suggests that CAST can identify ancillary pockets suitable for recruitment in ligand design strategies. Analysis of the FK506 binding protein, and of compounds developed in SAR by NMR (Shuker SB et al., 1996, Science 274:1531-1534), indicates that CAST pocket computation may provide a priori identification of target proteins for linked-fragment design. CAST analysis of 30 HIV-1 protease-inhibitor complexes shows that the flexible active site pocket can vary over a range of 853-1,566 A3, and that there are two pockets near or adjoining the active site that may be recruited for ligand design.

The universal ancestor

Abstract: A genetic annealing model for the universal ancestor of all extant life is presented; the name of the model derives from its resemblance to physical annealing. The scenario pictured starts when "genetic temperatures" were very high, cellular entities (progenotes) were very simple, and information processing systems were inaccurate. Initially, both mutation rate and lateral gene transfer levels were elevated. The latter was pandemic and pervasive to the extent that it, not vertical inheritance, defined the evolutionary dynamic. As increasingly complex and precise biological structures and processes evolved, both the mutation rate and the scope and level of lateral gene transfer, i.e., evolutionary temperature, dropped, and the evolutionary dynamic gradually became that characteristic of modern cells. The various subsystems of the cell "crystallized," i.e., became refractory to lateral gene transfer, at different stages of "cooling," with the translation apparatus probably crystallizing first. Organismal lineages, and so organisms as we know them, did not exist at these early stages. The universal phylogenetic tree, therefore, is not an organismal tree at its base but gradually becomes one as its peripheral branchings emerge. The universal ancestor is not a discrete entity. It is, rather, a diverse community of cells that survives and evolves as a biological unit. This communal ancestor has a physical history but not a genealogical one. Over time, this ancestor refined into a smaller number of increasingly complex cell types with the ancestors of the three primary groupings of organisms arising as a result.

Tame Topology and O-minimal Structures

Abstract: Following their introduction in the early 1980s o-minimal structures were found to provide an elegant and surprisingly efficient generalization of semialgebraic and subanalytic geometry. These notes give a self-contained treatment of the theory of o-minimal structures from a geometric and topological viewpoint, assuming only rudimentary algebra and analysis. The book starts with an introduction and overview of the subject. Later chapters cover the monotonicity theorem, cell decomposition, and the Euler characteristic in the o-minimal setting and show how these notions are easier to handle than in ordinary topology. The remarkable combinatorial property of o-minimal structures, the Vapnik-Chervonenkis property, is also covered. This book should be of interest to model theorists, analytic geometers and topologists.

Numerical integration of Einstein’s field equations

Abstract: Many numerical codes now under development to solve Einstein's equations of general relativity in $(3+1)$-dimensional spacetimes employ the standard ADM form of the field equations. This form involves evolution equations for the raw spatial metric and extrinsic curvature tensors. Following Shibata and Nakamura, we modify these equations by factoring out the conformal factor and introducing three ``connection functions.'' The evolution equations can then be reduced to wave equations for the conformal metric components, which are coupled to evolution equations for the connection functions. We evolve small amplitude gravitational waves and make a direct comparison of the numerical performance of the modified equations with the standard ADM equations. We find that the modified form exhibits much improved stability.

Children's interpersonal behaviors and the teacher-child relationship.

Abstract: Relations between kindergartners' (N = 199; M age = 5 years 6 months) behavioral orientations and features of their 1st-grade teacher-child relationships (i.e., conflict, closeness, dependency) were examined longitudinally. Early behavioral orientations predicted teacher-child relationship quality in that (a) unique associations emerged between children's early antisocial behavior and features of their 1st-grade teacher-child relationships (i.e., negative relation with closeness, positive relation with conflict and dependency) and between asocial behavior and teacher-child dependency, and (b) prosocial behavior was correlated with but not uniquely related to any feature of children's 1st-grade teacher-child relationships. In addition, specific features of the teacher-child relationship (e.g., conflict) predicted changes in children's behavioral adjustment (e.g., decreasing prosocial behavior).

An overview of quality of service routing for next-generation high-speed networks: problems and solutions

Abstract: The upcoming gigabit-per-second high-speed networks are expected to support a wide range of communication-intensive real-time multimedia applications. The requirement for timely delivery of digitized audio-visual information raises new challenges for next-generation integrated services broadband networks. One of the key issues is QoS routing. It selects network routes with sufficient resources for the requested QoS parameters. The goal of routing solutions is twofold: (1) satisfying the QoS requirements for every admitted connection, and (2) achieving global efficiency in resource utilization. Many unicast/multicast QoS routing algorithms have been published, and they work with a variety of QoS requirements and resource constraints. Overall, they can be partitioned into three broad classes: (1) source routing, (2) distributed routing, and (3) hierarchical routing algorithms. We give an overview of the QoS routing problem as well as the existing solutions. We present the strengths and weaknesses of different routing strategies, and outline the challenges. We also discuss the basic algorithms in each class, classify and compare them, and point out possible future directions in the QoS routing area.

Learning by Association? Interorganizational Networks and Adaptation to Environmental Change

Abstract: A study of 230 private colleges over 16 turbulent years supports two arguments: (1) Strong ties to other organizations mitigate uncertainty and promote adaptation by increasing communication and in...

Electronic liquid-crystal phases of a doped Mott insulator

Abstract: The character of the ground state of an antiferromagnetic insulator is fundamentally altered following addition of even a small amount of charge1. The added charge is concentrated into domain walls across which a π phase shift in the spin correlations of the host material is induced. In two dimensions, these domain walls are ‘stripes’ which can be insulating2,3 or conducting4,5,6 — that is, metallic ‘rivers’ with their own low-energy degrees of freedom. However, in arrays of one-dimensional metals, which occur in materials such as organic conductors7, interactions between stripes typically drive a transition to an insulating ordered charge-density-wave (CDW) state at low temperatures. Here it is shown that such a transition is eliminated if the zero-point energy of transverse stripe fluctuations is sufficiently large compared tothe CDW coupling between stripes. As a consequence, there should exist electronic quantum liquid-crystal phases, which constitute new states of matter, and which can be either high-temperature superconductors or two-dimensional anisotropic ‘metallic’ non-Fermi liquids. Neutron scattering and other experiments in the copper oxide superconductor La1.6−xNd0.4SrxCuO4 already provide evidence for the existence of these phases in at least one class of materials.

Response inhibition in AD/HD, CD, comorbid AD/HD + CD, anxious, and control children: A meta-analysis of studies with the stop task.

Abstract: The aim of this study was to investigate whether impaired response inhibition is uniquely related to AD/HD or whether deficits in response inhibition are also evident in other psychopathological disorders. Furthermore, the suggestion was examined that anxiety disorders are associated with abnormally high levels of response inhibition. This paper presents the results of a meta-analysis of eight studies in which response inhibition was assessed with the so-called stop task in five groups of children: children with attention deficit/hyperactivity disorder (AD/HD), children with conduct disorder (CD), children with AD/HD + CD, children with anxiety disorders, and control children. A total of 456 children participated in the 8 studies. All children were in the age range 6-12 years. Consistent and robust evidence was found for a response inhibition deficit in AD/HD. However, response inhibition deficits did not distinguish children with AD/HD from children with CD, nor from children with comorbid AD/HD + CD. Contrary to predictions, anxious children did not demonstrate enhanced levels of response inhibition.

Ownership Structure, Speculation, and Shareholder Intervention

Abstract: An institution holding shares in a firm can use information about the firm both for trading ("speculation") and for deciding whether to intervene to improve firm performance. Intervention increases the value of the institution's existing shareholdings, but intervention only increases the institution's trading profits if it; enhances the precision of the institution's information relative to that of uninformed traders. Thus, the ability to speculate can increase or decrease institutional intervention. We examine key factors that affect the intervention decision, the usefulness of "short-swing" provisions and restricted shares in encouraging institutional intervention, and implications for ownership structure across different firms. INSTITUTIONAL INVESTORS HOLD an ever-greater fraction of Corporate America's equity. Traditionally, these institutions were "stock pickers" who tried to beat the market through trading; if a firm whose stock they held seemed headed for trouble, these investors headed for the door ("the Wall Street rule"). More recently, some of these institutions have been using the ownership rights attached to their shares to pressure firms to act in the shareholders' interest. Some have even argued that there is a synergy between gathering information for use in trading shares ("speculation") and intelligently pressuring firms to improve performance ("intervention"). We argue that these motives can also conflict. Analyzing these motives allows us to predict which firms are most likely to attract institutional intervention, which in turn has crosssectional implications for firm ownership structure. Recent examples suggest that institutional investors with large stakes sometimes intervene and sometimes follow the Wall Street rule, so that there is indeed a choice to be studied. In the early 1990s, there was a wave of activism by a variety of large institutional investors, among them CalPERS, the California public employees pension fund, Putnam Management, a mutual fund manager, and J.P. Morgan, a bank holding company.' These institu