Showing papers by "Michigan State University published in 1995"

A neutral templating route to mesoporous molecular sieves.

Abstract: A neutral templating route for preparing mesoporous molecular sieves is demonstrated based on hydrogen-bonding interactions and self-assembly between neutral primary amine micelles (S degrees ) and neutral inorganic precursors (l degrees ). The S degrees l degrees templating pathway produces ordered mesoporous materials with thicker framework walls, smaller x-ray scattering domain sizes, and substantially improved textural mesoporosities in comparison with M41S materials templated by quaternary ammonium cations of equivalent chain length. This synthetic strategy also allows for the facile, environmentally benign recovery of the cost-intensive template by simple solvent extraction methods. The S degrees 1 degrees templating route provides for the synthesis of other oxide mesostructures (such as aluminas) that may be less readily accessible by electrostatic templating pathways.

Unraveling Nanotubes: Field Emission from an Atomic Wire

Abstract: Field emission of electrons from individually mounted carbon nanotubes has been found to be dramatically enhanced when the nanotube tips are opened by laser evaporation or oxidative etching. Emission currents of 0.1 to 1 microampere were readily obtained at room temperature with bias voltages of less than 80 volts. The emitting structures are concluded to be linear chains of carbon atoms, Cn, (n = 10 to 100), pulled out from the open edges of the graphene wall layers of the nanotube by the force of the electric field, in a process that resembles unraveling the sleeve of a sweater.

Templating of Mesoporous Molecular Sieves by Nonionic Polyethylene Oxide Surfactants

Abstract: Mesoporous silica molecular sieves have been prepared by the hydrolysis of tetraethylorthosilicate in the presence of low-cost, nontoxic, and biodegradable polyethylene oxide (PEO) surfactants, which act as the structure-directing (templating) agents. This nonionic, surfactant-neutral, inorganic-precursor templating pathway to mesostructures uses hydrogen bonding interactions between the hydrophilic surfaces of flexible rod- or worm-like micelles and Si(OC 2 H 5 ) 4-x (OH) x hydrolysis products to assemble an inorganic oxide framework. Disordered channel structures with uniform diameters ranging from 2.0 to 5.8 nanometers have been obtained by varying the size and structure of the surfactant molecules. Metal-substituted silica and pure alumina mesostructures have also been prepared by the hydrolysis of the corresponding alkoxides in the presence of PEO surfactants. These results suggest that nonionic templating may provide a general pathway for the preparation of mesoporous oxides.

Studies of Individualism-Collectivism: Effects on Cooperation in Groups

Abstract: Data from 492 college students indicated that group size and individuals' identifiability, sense of shared responsibility, and levels of individualism or collectivism influenced peer-rated cooperation in classroom groups. Levels of individualism or collectivism moderated the effects of size and identifiability on cooperation but not those of shared responsibility. These findings suggest that models of free riding and social loafing provide insights into individualistic cooperation in groups but are limited in their ability to explain the cooperation of collectivists.

Toward a better definition of the restless legs syndrome

Abstract: A large International Restless Legs Syndrome (RLS) Study Group has been formed. As its first task, the group has taken upon itself the role of definig the clinical features of the RLS. As minimal criteria for diagnosis, the group proposes the following four features: (a) desire to move the extremities, often associated with paresthesias/dysesthesias; (b) motor restlessness; (c) worsening of symptoms at rest with at least temporary relief by activity, and (d) worsening of symptoms in the evening or night. Other features commonly seen in RLS include sleep disturbance, periodic limb movements in sleep and similar involuntary movements while awake, a normal neurological examination in the idiopathic from, a tendency for the symptoms to be worse in middle to older age, and, in some cases, a family history suggestive of an autosomal dominant mode of inheritance.

Observation of top quark production in p̄p collisions with the collider detector at fermilab

Abstract: We establish the existence of the top quark using a $67{\mathrm{pb}}^{\ensuremath{-}1}$ data sample of $\overline{p}p$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ collected with the Collider Detector at Fermilab (CDF). Employing techniques similar to those we previously published, we observe a signal consistent with $t\overline{t}$ decay to $\mathrm{WWb}\overline{b}$, but inconsistent with the background prediction by $4.8\ensuremath{\sigma}$. Additional evidence for the top quark is provided by a peak in the reconstructed mass distribution. We measure the top quark mass to be $176\ifmmode\pm\else\textpm\fi{}8(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}10(\mathrm{syst})\mathrm{GeV}{/c}^{2}$, and the $t\overline{t}$ production cross section to be ${6.8}_{\ensuremath{-}2.4}^{+3.6}\mathrm{pb}$.

Geometrical percolation threshold of overlapping ellipsoids

Abstract: A recurrent problem in materials science is the prediction of the percolation threshold of suspensions and composites containing complex-shaped constituents. We consider an idealized material built up from freely overlapping objects randomly placed in a matrix, and numerically compute the geometrical percolation threshold ${\mathit{p}}_{\mathit{c}}$ where the objects first form a continuous phase. Ellipsoids of revolution, ranging from the extreme oblate limit of platelike particles to the extreme prolate limit of needlelike particles, are used to study the influence of object shape on the value of ${\mathit{p}}_{\mathit{c}}$. The reciprocal threshold 1/${\mathit{p}}_{\mathit{c}}$ (${\mathit{p}}_{\mathit{c}}$ equals the critical volume fraction occupied by the overlapping ellipsoids) is found to scale linearly with the ratio of the larger ellipsoid dimension to the smaller dimension in both the needle and plate limits. Ratios of the estimates of ${\mathit{p}}_{\mathit{c}}$ are taken with other important functionals of object shape (surface area, mean radius of curvature, radius of gyration, electrostatic capacity, excluded volume, and intrinsic conductivity) in an attempt to obtain a universal description of ${\mathit{p}}_{\mathit{c}}$. Unfortunately, none of the possibilities considered proves to be invariant over the entire shape range, so that ${\mathit{p}}_{\mathit{c}}$ appears to be a rather unique functional of object shape. It is conjectured, based on the numerical evidence, that 1/${\mathit{p}}_{\mathit{c}}$ is minimal for a sphere of all objects having a finite volume.

Characteristics of plant cell walls affecting intake and digestibility of forages by ruminants.

Abstract: Even under the intensive concentrate feeding systems of ruminant animal production in the United States, forages continue to represent the single most important feed resource. Cell-wall concentration and digestibility limit the intake potential and energy availability of forage crops in beef and dairy production. Identification of cell-wall characteristics that should be targets of genetic modification is required if plant breeders and molecular biologists are to successfully improve forages for livestock feeding. As the forage plant cell develops, phenolic acids and lignin are deposited in the maturing cell wall in specific structural conformations, and in a strict developmental sequence. Lignin is the key element that limits cell-wall digestibility, but cross-linkage of lignin and wall polysaccharides by ferulic acid bridges may be a prerequisite for lignin to exert its affect. Lignin composition and p-coumaric acid in the wall are less likely to affect digestibility. Voluntary intake of forages is a critical determinant of animal performance and cell-wall concentration is negatively related to intake of ruminants consuming high-forage diets. Cell walls affect intake by contributing to ruminal fill. A simple model of cell-wall digestion and passage in which ruminal fill is a function of rates of digestion and passage, as well as the indigestible fraction of the cell-wall indicates that cell-wall concentration and rate of passage are the most critical parameters determining ruminal fill. Plant factors that affect rate of passage include those that affect particle size reduction by chewing and those that affect particle buoyancy in the rumen. The latter is primarily affected by 1) the ability of the particulate matter to retain gases, which is probably related to plant anatomy and rate of digestion of the plant tissue, and 2) the rate at which the gas is produced, which is affected by the potentially digestible fraction of the particulate matter and the rate of digestion of this fraction. Increasing rate of digestion should increase rate of passage by diminishing the gas produced and increasing density over time. A reduction in the indigestible cell-wall fraction is beneficial because this will decrease fill and increase digestibility. Animal production and economic benefits from reduced cell-wall concentration and increased digestibility are significant. Because of the high cell-wall concentration and large digestible cell-wall fraction of grasses, reduction in cell-wall concentration would probably be of greater value than improving digestibility in these species. Legumes represent the opposite situation and may benefit more from improvements in the digestibility of their cell walls.

The crystal structure of urease from Klebsiella aerogenes

Abstract: The crystal structure of urease from Klebsiella aerogenes has been determined at 2.2 A resolution and refined to an R factor of 18.2 percent. The enzyme contains four structural domains: three with novel folds playing structural roles, and an (alpha beta)8 barrel domain, which contains the bi-nickel center. The two active site nickels are 3.5 A apart. One nickel ion is coordinated by three ligands (with low occupancy of a fourth ligand) and the second is coordinated by five ligands. A carbamylated lysine provides an oxygen ligand to each nickel, explaining why carbon dioxide is required for the activation of urease apoenzyme. The structure is compatible with a catalytic mechanism whereby urea ligates Ni-1 to complete its tetrahedral coordination and a hydroxide ligand of Ni-2 attacks the carbonyl carbon. A surprisingly high structural similarity between the urease catalytic domain and that of the zinc-dependent adenosine deaminase reveals a remarkable example of active site divergence.

Goal-directed evaluation of binarization methods

Abstract: This paper presents a methodology for evaluation of low-level image analysis methods, using binarization (two-level thresholding) as an example. Binarization of scanned gray scale images is the first step in most document image analysis systems. Selection of an appropriate binarization method for an input image domain is a difficult problem. Typically, a human expert evaluates the binarized images according to his/her visual criteria. However, to conduct an objective evaluation, one needs to investigate how well the subsequent image analysis steps will perform on the binarized image. We call this approach goal-directed evaluation, and it can be used to evaluate other low-level image processing methods as well. Our evaluation of binarization methods is in the context of digit recognition, so we define the performance of the character recognition module as the objective measure. Eleven different locally adaptive binarization methods were evaluated, and Niblack's method gave the best performance.

Artificial neural networks for feature extraction and multivariate data projection

Abstract: Classical feature extraction and data projection methods have been well studied in the pattern recognition and exploratory data analysis literature. We propose a number of networks and learning algorithms which provide new or alternative tools for feature extraction and data projection. These networks include a network (SAMANN) for J.W. Sammon's (1969) nonlinear projection, a linear discriminant analysis (LDA) network, a nonlinear discriminant analysis (NDA) network, and a network for nonlinear projection (NP-SOM) based on Kohonen's self-organizing map. A common attribute of these networks is that they all employ adaptive learning algorithms which makes them suitable in some environments where the distribution of patterns in feature space changes with respect to time. The availability of these networks also facilitates hardware implementation of well-known classical feature extraction and projection approaches. Moreover, the SAMANN network offers the generalization ability of projecting new data, which is not present in the original Sammon's projection algorithm; the NDA method and NP-SOM network provide new powerful approaches for visualizing high dimensional data. We evaluate five representative neural networks for feature extraction and data projection based on a visual judgement of the two-dimensional projection maps and three quantitative criteria on eight data sets with various properties. >

The relationship between work experience and job performance: a conceptual and meta‐analytic review

Abstract: A gap in the conceptual development of the work experience construct was addressed by creating a framework specifying two dimensions along which work experience measures can vary The dimensions of measurement mode (amount, time, and type) and level of specificity (task, job, organizational) formed nine separate categories of measures of work experience The usefulness of the conceptual framework was tested by conducting a meta-analytic review of the existing literature on work experience using the dimensions in the framework as potential moderators of the experience-performance relationship Results of the meta-analysis (N= 25,911; K= 44) revealed an estimated population correlation of 27 between experience and performance after correcting for sampling error and criterion unreliability In addition, the results showed that amount (Mp= 43) and task-level (Mp= 41) measures of work experience had the highest correlations with measures of job performance In addition, work experience had the highest correlations with hard (eg work samples) as opposed to soft (eg ratings) measures of job performance (Mp= 39 vs Mp= 24) Implications and directions for future research are discussed

A multivariate hierarchical model for studying psychological change within married couples.

Abstract: This article illustrates new statistical methods for the study of psychological change in married couples. The design involves time-series data on each partner. The analysis combines longitudinal methods for studies of individual change with cross-sectional methods for the study of matched pairs. Each person is viewed as changing over time as a function of an individual growth curve or change function. As in previous studies of individual change, a person's trajectory depends on time-invarian t personal background characteristics and time-varying changes in the environment. However, unlike typical studies of individual change, a person's changing psychological profile depends, in part, on the influence of that person's partner. These methods apply directly to other types of longitudinal studies on families (e.g., studies that use teacher and parent reports of a child's social behavior). The methodology is flexible in allowing randomly missing data, varying spacing of time points, unbalanced designs, and time-varying and time-invariant covariates. The study of psychological change of married partners involves two basic features that have implications for conceptual and statistical models. First, each individual changes over time. Second, the change trajectories of partners are likely to be related. At minimum, the relational character of change in couples must not be ignored; it may, in fact, be of central interest in many studies. To represent this process, a pair of change functions is first specified for each couple in a Level 1 or "within-couple" model. At Level 2,

The clinical manifestations of bovine viral diarrhea infection.

Abstract: Infection of cattle with bovine viral diarrhea virus (BVDV) occurs frequently. The outcome of BVDV infection is a wide range of clinical manifestations. The form of clinical disease observed depends on the agent, host, and environmental factors, as well as interaction of these factors. The clinical manifestations are reviewed in terms of BVDV infection in animals that are immuno-competent to BVDV, fetal infections, and cattle that are immuno-tolerant to BVDV.

Adaptive control of a class of nonlinear discrete-time systems using neural networks

Abstract: Layered neural networks are used in a nonlinear self-tuning adaptive control problem. The plant is an unknown feedback-linearizable discrete-time system, represented by an input-output model. To derive the linearizing-stabilizing feedback control, a (possibly nonminimal) state-space model of the plant is obtained. This model is used to define the zero dynamics, which are assumed to be stable, i.e., the system is assumed to be minimum phase. A linearizing feedback control is derived in terms of some unknown nonlinear functions. A layered neural network is used to model the unknown system and generate the feedback control. Based on the error between the plant output and the model output, the weights of the neural network are updated. A local convergence result is given. The result says that, for any bounded initial conditions of the plant, if the neural network model contains enough number of nonlinear hidden neurons and if the initial guess of the network weights is sufficiently close to the correct weights, then the tracking error between the plant output and the reference command will converge to a bounded ball, whose size is determined by a dead-zone nonlinearity. Computer simulations verify the theoretical result. >

Recruiting Minorities Into Clinical Trials Toward a Participant-Friendly System

Abstract: The purpose of this review is to describe the state of the art in recruiting participants for clinical trials designed to test new methods of treatment or disease prevention. The ultimate objective of this review is to provide a summary of key issues in recruiting diverse populations into clinical trials, particularly ethnic and racial minorities. An overview of general issues related to clinical trial participation is followed by a detailed discussion of specific issues that must be addressed by investigators as they recruit minority populations for clinical trial. To date, the majority of clinical trials have included a limited segment of the U.S. population: middle-class, married white males. These trials have faced many problems in their efforts to recruit participants, including barriers to physician participation, barriers to subject participation, barriers to planning and implementing effective recruitment strategies, and costs of the recruitment phase of clinical trials. Following this general introduction is a discussion of the definition of diverse populations. The first step investigators must take as they prepare to recruit study participants is to develop a relevant definition of the subject populations. A detailed review of investigators' experiences in recruiting minorities into clinical trials is presented, including barriers to minority recruitment, barriers inherent in study design, researcher bias, barriers to minority physician participation, as well as strategies for minority recruitment, modifications of study design, and cost issues. Formal evaluation of recruitment strategies has been limited. Most investigators present descriptive reports of their experience in recruiting diverse populations into clinical trials. Research into the issues presented and rigorous testing of specific strategies is needed. A series of steps that are essential to effective clinical trials recruitment of diverse populations is presented.

Characterization of inducible cyclooxygenase in rat brain

Abstract: Considerable debate exists regarding the cellular source of prostaglandins in the mammalian central nervous system (CNS). At least two forms of prostaglandin endoperoxide synthase, or cyclooxygenase (COX), the principal enzyme in the biosynthesis of these mediators, are known to exist. Both forms have been identified in the CNS, but only the distribution of COX 1 has been mapped in detail. In this study, we used Western blot analysis and immunohistochemistry to describe the biochemical characterization and anatomical distribution of the second, mitogen-inducible form of this enzyme, COX 2 in the rat brain. COX 2-like immunoreactive (COX 2-ir) staining occurred in dendrites and cell bodies of neurons, structures that are typically postsynaptic. It was noted in distinct portions of specific cortical laminae and subcortical nuclei. The distribution in the CNS was quite different from COX 1. COX 2-ir neurons were primarily observed in the cortex and allocortical structures, such as the hippocampal formation and amygdala. Within the amygdala, neurons were primarily observed in the caudal and posterior part of the deep and cortical nuclei. In the diencephalon, COX 2-ir cells were also observed in the paraventricular nucleus of the hypothalamus and in the nuclei of the anteroventral region surrounding the third ventricle, including the vascular organ of the lamina terminalis. COX 2-ir neurons were also observed in the subparafascicular nucleus, the medial zona incerta, and pretectal area. In the brainstem, COX 2-ir neurons were observed in the dorsal raphe nucleus, the nucleus of the brachium of the inferior colliculus, and in the region of the subcoeruleus. The distribution of COX 2-ir neurons in the CNS suggests that COX 2 may be involved in processing and integration of visceral and special sensory input and in elaboration of the autonomic, endocrine, and behavioral responses.

A Meta-Analysis of Cohesion and Performance Effects of Level of Analysis and Task Interdependence

Abstract: This study extends previous work reviewing the cohesion-performance relationship by using meta-analytic techniques to assess the effects of level of analysis and task interdependence on the cohesio...

Checkerboard patterns in layout optimization

Abstract: Effective properties of arrangements of strong and weak materials in a checkerboard fashion are computed. Kinematic constraints are imposed so that the displacements are consistent with typical finite element approximations. It is shown that when four-node quatrilateral elements are involved, these constraints result in a numerically induced, artificially high stiffness. This can account for the formation of checkerboard patterns in continuous layout optimization problems of compliance minimization.

The Estimation of School Effects

Abstract: The increasing public demand to hold schools accountable for their effects on student outcomes lends urgency to the task of clarifying statistical issues pertaining to studies of school effects. Th...

A longitudinal investigation of newcomer expectations, early socialization outcomes, and the moderating effects of role development factors

Abstract: This longitudinal study examined hypothesized moderating effects of role development on the link between unmet expectations and socialization outcomes. Data were collected from 248 new hires before organizational entry and at an average of 4 weeks after entry. Three role expectations-conflict, clarity, and acceptance-were measured at both data collections. Two role development constructs-leader-member exchange (LMX) and team-member exchange (TMX)-and three socialization outcomes-organizational commitment, turnover intention, and job satisfaction-were measured after entry. Results showed that met expectations, LMX, and TMX were significant predictors of all outcomes. In addition, LMX and TMX significantly moderated several relationships, such that favorable role development relationships with supervisors or work groups ameliorated the negative effects of unmet expectations. Research and applied implications are discussed.

Experimental tests of the roles of adaptation, chance, and history in evolution

Abstract: The contributions of adaptation, chance, and history to the evolution of fitness and cell size were measured in two separate experiments using bacteria. In both experiments, populations propagated in identical environments achieved similar fitnesses, regardless of prior history or subsequent chance events. In contrast, the evolution of cell size, a trait weakly correlated with fitness, was more strongly influenced by history and chance.