Showing papers by "Arizona State University published in 2004"

Confidence Limits for the Indirect Effect: Distribution of the Product and Resampling Methods.

Abstract: The most commonly used method to test an indirect effect is to divide the estimate of the indirect effect by its standard error and compare the resulting z statistic with a critical value from the standard normal distribution. Confidence limits for the indirect effect are also typically based on critical values from the standard normal distribution. This article uses a simulation study to demonstrate that confidence limits are imbalanced because the distribution of the indirect effect is normal only in special cases. Two alternatives for improving the performance of confidence limits for the indirect effect are evaluated: (a) a method based on the distribution of the product of two normal random variables, and (b) resampling methods. In Study 1, confidence limits based on the distribution of the product are more accurate than methods based on an assumed normal distribution but confidence limits are still imbalanced. Study 2 demonstrates that more accurate confidence limits are obtained using resampling methods, with the bias-corrected bootstrap the best method overall.

Prospects for inferring very large phylogenies by using the neighbor-joining method

Abstract: Current efforts to reconstruct the tree of life and histories of multigene families demand the inference of phylogenies consisting of thousands of gene sequences. However, for such large data sets even a moderate exploration of the tree space needed to identify the optimal tree is virtually impossible. For these cases the neighbor-joining (NJ) method is frequently used because of its demonstrated accuracy for smaller data sets and its computational speed. As data sets grow, however, the fraction of the tree space examined by the NJ algorithm becomes minuscule. Here, we report the results of our computer simulation for examining the accuracy of NJ trees for inferring very large phylogenies. First we present a likelihood method for the simultaneous estimation of all pairwise distances by using biologically realistic models of nucleotide substitution. Use of this method corrects up to 60% of NJ tree errors. Our simulation results show that the accuracy of NJ trees decline only by ≈5% when the number of sequences used increases from 32 to 4,096 (128 times) even in the presence of extensive variation in the evolutionary rate among lineages or significant biases in the nucleotide composition and transition/transversion ratio. Our results encourage the use of complex models of nucleotide substitution for estimating evolutionary distances and hint at bright prospects for the application of the NJ and related methods in inferring large phylogenies.

Social Influence: Compliance and Conformity

Abstract: This review covers recent developments in the social influence literature, focusing primarily on compliance and conformity research published between 1997 and 2002. The principles and processes underlying a target's susceptibility to outside influences are considered in light of three goals fundamental to rewarding human functioning. Specifically, targets are motivated to form accurate perceptions of reality and react accordingly, to develop and preserve meaningful social relationships, and to maintain a favorable self-concept. Consistent with the current movement in compliance and conformity research, this review emphasizes the ways in which these goals interact with external forces to engender social influence processes that are subtle, indirect, and outside of awareness.

Understanding HRM–Firm Performance Linkages: The Role of the “Strength” of the HRM System

Abstract: Theory building has lagged on the intermediate linkages responsible for the relationship between HRM and firm performance. We introduce the construct “strength of the HRM system” and describe the meta-features of an HRM system that result in a strong organizational climate, analogous to Mischel's “strong situation,” in which individuals share a common interpretation of what behaviors are expected and rewarded. The strength of the HRM system can help explain how individual employee attributes accumulate to affect organizational effectiveness.

A route to high surface area, porosity and inclusion of large molecules in crystals

Abstract: One of the outstanding challenges in the field of porous materials is the design and synthesis of chemical structures with exceptionally high surface areas Such materials are of critical importance to many applications involving catalysis, separation and gas storage The claim for the highest surface area of a disordered structure is for carbon, at 2,030 m2 g(-1) (ref 2) Until recently, the largest surface area of an ordered structure was that of zeolite Y, recorded at 904 m2 g(-1) (ref 3) But with the introduction of metal-organic framework materials, this has been exceeded, with values up to 3,000 m2 g(-1) (refs 4-7) Despite this, no method of determining the upper limit in surface area for a material has yet been found Here we present a general strategy that has allowed us to realize a structure having by far the highest surface area reported to date We report the design, synthesis and properties of crystalline Zn4O(1,3,5-benzenetribenzoate)2, a new metal-organic framework with a surface area estimated at 4,500 m2 g(-1) This framework, which we name MOF-177, combines this exceptional level of surface area with an ordered structure that has extra-large pores capable of binding polycyclic organic guest molecules--attributes not previously combined in one material

An empirical evaluation of alternative methods of estimation for confirmatory factor analysis with ordinal data.

Abstract: Confirmatory factor analysis (CFA) is widely used for examining hypothesized relations among ordinal variables (e.g., Likert-type items). A theoretically appropriate method fits the CFA model to polychoric correlations using either weighted least squares (WLS) or robust WLS. Importantly, this approach assumes that a continuous, normal latent process determines each observed variable. The extent to which violations of this assumption undermine CFA estimation is not well-known. In this article, the authors empirically study this issue using a computer simulation study. The results suggest that estimation of polychoric correlations is robust to modest violations of underlying normality. Further, WLS performed adequately only at the largest sample size but led to substantial estimation difficulties with smaller samples. Finally, robust WLS performed well across all conditions.

Efficient Feature Selection via Analysis of Relevance and Redundancy

Abstract: Feature selection is applied to reduce the number of features in many applications where data has hundreds or thousands of features. Existing feature selection methods mainly focus on finding relevant features. In this paper, we show that feature relevance alone is insufficient for efficient feature selection of high-dimensional data. We define feature redundancy and propose to perform explicit redundancy analysis in feature selection. A new framework is introduced that decouples relevance analysis and redundancy analysis. We develop a correlation-based method for relevance and redundancy analysis, and conduct an empirical study of its efficiency and effectiveness comparing with representative methods.

How many steps/day are enough? Preliminary pedometer indices for public health.

Abstract: readily being used by researchers and practitioners to assess and motivate physical activity behaviours. Pedometer-determined physical activity indices are needed to guide their efforts. Therefore, the purpose of this article is to review the rationale and evidence for general pedometer-based indices for research and practice purposes. Specifically, we evaluate popular recommendations for steps/day and attempt to translate existing physical activity guidelines into steps/day equivalents. Also, we appraise the fragmented evidence currently available from associations derived from cross-sectional studies and a limited number of interventions that have documented improvements (primarily in body composition and/or blood pressure) with increased steps/day. A value of 10 000 steps/day is gaining popularity with the media and in practice and can be traced to Japanese walking clubs and a business slogan 30+ years ago. 10 000 steps/day appears to be a reasonable estimate of daily activity for apparently healthy adults and studies are emerging documenting the health benefits of attaining similar levels. Preliminary evidence suggests that a goal of 10 000 steps/day may not be sustainable for some groups, including older adults and those living with chronic diseases. Another concern about using 10 000 steps/ day as a universal step goal is that it is probably too low for children, an important target population in the war against obesity. Other approaches to pedometer-determined physical activity recommendations that are showing promise of health benefit and individual sustainability have been based on incremental improvements relative to baseline values. Based on currently available evidence, we propose the following preliminary indices be used to classify pedometer-determined physical activity in healthy adults: (i) 12 500 steps/day are likely to be classified as ‘highly active’.

A Framework to Analyze the Robustness of Social-ecological Systems from an Institutional Perspective

Abstract: What makes social-ecological systems (SESs) robust? In this paper, we look at the institutional configurations that affect the interactions among resources, resource users, public infrastructure providers, and public infrastructures. We propose a framework that helps identify potential vulnerabilities of SESs to disturbances. All the links between components of this framework can fail and thereby reduce the robustness of the system. We posit that the link between resource users and public infrastructure providers is a key variable affecting the robustness of SESs that has frequently been ignored in the past. We illustrate the problems caused by a disruption in this link. We then briefly describe the design principles originally developed for robust common-pool resource institutions, because they appear to be a good starting point for the development of design principles for more general SESs and do include the link between resource users and public infrastructure providers.

Understanding the meaning of collaboration in the supply chain

Abstract: Despite its infancy, some authors are already suggesting that the writing may be on the wall for supply chain collaboration. It has been reported that supply chain collaboration has proved difficult to implement; there has been an over‐reliance on technology in trying to implement it; a failure to understand when and with whom to collaborate; and fundamentally a lack of trust between trading partners. This paper proposes that a supply chain segmentation approach, based on customer buying behaviour and service needs, is the most appropriate context for collaboration. The paper also proposes the need for a greater understanding of the elements that make up supply chain collaboration, and in particular how the relevant cultural, strategic and implementation elements inter‐relate with each other.

Subspace clustering for high dimensional data: a review

Abstract: Subspace clustering is an extension of traditional clustering that seeks to find clusters in different subspaces within a dataset. Often in high dimensional data, many dimensions are irrelevant and can mask existing clusters in noisy data. Feature selection removes irrelevant and redundant dimensions by analyzing the entire dataset. Subspace clustering algorithms localize the search for relevant dimensions allowing them to find clusters that exist in multiple, possibly overlapping subspaces. There are two major branches of subspace clustering based on their search strategy. Top-down algorithms find an initial clustering in the full set of dimensions and evaluate the subspaces of each cluster, iteratively improving the results. Bottom-up approaches find dense regions in low dimensional spaces and combine them to form clusters. This paper presents a survey of the various subspace clustering algorithms along with a hierarchy organizing the algorithms by their defining characteristics. We then compare the two main approaches to subspace clustering using empirical scalability and accuracy tests and discuss some potential applications where subspace clustering could be particularly useful.

Dynamical models of tuberculosis and their applications.

Abstract: The reemergence of tuberculosis (TB) from the 1980s to the early 1990s instigated extensive researches on the mechanisms behind the transmission dynamics of TB epidemics. This article provides a detailed review of the work on the dynamics and control of TB. The earliest mathematical models describing the TB dynamics appeared in the 1960s and focused on the prediction and control strategies using simulation approaches. Most recently developed models not only pay attention to simulations but also take care of dynamical analysis using modern knowledge of dynamical systems. Questions addressed by these models mainly concentrate on TB control strategies, optimal vaccination policies, approaches toward the elimination of TB in the U.S.A., TB co-infection with HIV/AIDS, drug-resistant TB, responses of the immune system, impacts of demography, the role of public transportation systems, and the impact of contact patterns. Model formulations involve a variety of mathematical areas, such as ODEs (Ordinary Differential Equations) (both autonomous and non-autonomous systems), PDEs (Partial Differential Equations), system of difference equations, system of integro-differential equations, Markov chain model, and simulation models.

The cultural adaptation of prevention interventions: resolving tensions between fidelity and fit.

Abstract: A dynamic tension has developed in prevention science regarding two imperatives: (a) fidelity of implementation—the delivery of a manualized prevention intervention program as prescribed by the program developer, and (b) program adaptation—the modification of program content to accommodate the needs of a specific consumer group. This paper examines this complex programmatic issue from a community-based participatory research approach for program adaptation that emphasizes motivating community participation to enhance program outcomes. Several issues, key concepts, and implementation strategies are presented under a strategic approach to address issues of fidelity and adaptation. Despite the noted tension between fidelity and adaptation, both are essential elements of prevention intervention program design and they are best addressed by a planned, organized, and systematic approach. Towards this aim, an innovative program design strategy is to develop hybrid prevention programs that “build in” adaptation to enhance program fit while also maximizing fidelity of implementation and program effectiveness.

Structure of Calcium Silicate Hydrate (C‐S‐H): Near‐, Mid‐, and Far‐Infrared Spectroscopy

Abstract: The mid-, near-, and far-infrared (IR) spectra of synthetic, single-phase calcium silicate hydrates (C-S-H) with Ca/Si ratios (C/S) of 0.41–1.85, 1.4 nm tobermorite, 1.1 nm tobermorite, and jennite confirm the similarity of the structure of these phases and provide important new insight into their H2O and OH environments. The main mid-IR bands occur at 950–1100, 810–830, 660–670, and 440–450 cm−1, consistent with single silicate chain structures. For the C-S-H samples, the mid-IR bands change systematically with increasing C/S ratio, consistent with decreasing silicate polymerization and with an increasing content of jennite-like structural environments of C/S ratios >1.2. The 950–1100 cm−1 group of bands due to Si-O stretching shifts first to lower wave number due to decreasing polymerization and then to higher wave numbers, possibly reflecting an increase in jennite-like structural environments. Because IR spectroscopy is a local structural probe, the spatial distribution of the jennite-like domains cannot be determined from these data. A shoulder at ∼1200 cm−1 due to Si-O stretching vibrations in Q3 sites occurs only at C/S lessthan equal to 0.7. The 660–670 cm−1 band due to Si-O-Si bending broadens and decreases in intensity for samples with C/S > 0.88, consistent with depolymerization and decreased structural order. In the near-IR region, the combination band at 4567 cm−1 due to Si-OH stretching plus O-H stretching decreases in intensity and is absent at C/S greater than ∼1.2, indicating the absence of Si-OH linkages at C/S ratios greater than this. The primary Si-OH band at 3740 cm-1 decreases in a similar way. In the far-IR region, C-S-H samples with C/S ratio greater than ∼1.3 have increased absorption intensity at ∼300 cm−1, indicating the presence of CaOH environments, even though portlandite cannot be detected by X-ray diffraction for C/S ratios <1.5. These results, in combination with our previous NMR and Raman spectroscopic studies of the same samples, provide the basis for a more complete structural model for this type of C-S-H, which is described.

Ecosystem stability and compensatory effects in the Inner Mongolia grassland

Abstract: Numerous studies have suggested that biodiversity reduces variability in ecosystem productivity through compensatory effects; that is, a species increases in its abundance in response to the reduction of another in a fluctuating environment. But this view has been challenged on several grounds. Because most studies have been based on artificially constructed grasslands with short duration, long-term studies of natural ecosystems are needed. On the basis of a 24-year study of the Inner Mongolia grassland, here we present three key findings. First, that January-July precipitation is the primary climatic factor causing fluctuations in community biomass production; second, that ecosystem stability (conversely related to variability in community biomass production) increases progressively along the hierarchy of organizational levels (that is, from species to functional group to whole community); and finally, that the community-level stability seems to arise from compensatory interactions among major components at both species and functional group levels. From a hierarchical perspective, our results corroborate some previous findings of compensatory effects. Undisturbed mature steppe ecosystems seem to culminate with high biodiversity, productivity and ecosystem stability concurrently. Because these relationships are correlational, further studies are necessary to verify the causation among these factors. Our study provides new insights for better management and restoration of the rapidly degrading Inner Mongolia grassland.

Evidence toward an expanded model of organizational identification

Abstract: Recent research on organizational identification has called for the consideration of an expanded model of identification, which would include a more thorough treatment of the ways an individual could derive his or her identity from the organization. This paper begins to answer that call by testing operationalizations of the four dimensions of the expanded model: identification, disidentification, ambivalent identification, and neutral identification. Survey results from 330 employed adults support the discriminability of the four dimensions. This exploratory study also begins to establish the criterion-related validity of the model by examining organizational, job-related, and individual difference variables associated with the four dimensions of the model, and suggests implications for the expanded model's strong potential for applications in organizational identification research. Copyright © 2004 John Wiley & Sons, Ltd.

Effects of changing scale on landscape pattern analysis: scaling relations

Abstract: Landscape pattern is spatially correlated and scale-dependent. Thus, understanding landscape structure and functioning requires multiscale information, and scaling functions are the most precise and concise way of quantifying multiscale characteristics explicitly. The major objective of this study was to explore if there are any scaling relations for landscape pattern when it is measured over a range of scales (grain size and extent). The results showed that the responses of landscape metrics to changing scale fell into two categories when computed at the class level (i.e., for individual land cover types): simple scaling functions and unpredictable behavior. Similarly, three categories were found at the landscape level, with the third being staircase pattern, in a previous study when all land cover types were combined together. In general, scaling relations were more variable at the class level than at the landscape level, and more consistent and predictable with changing grain size than with changing extent at both levels. Considering that the landscapes under study were quite diverse in terms of both composition and configuration, these results seem robust. This study highlights the need for multiscale analysis in order to adequately characterize and monitor landscape heterogeneity, and provides insights into the scaling of landscape patterns.

In situ evidence for an ancient aqueous environment at Meridiani Planum, Mars.

Abstract: Sedimentary rocks at Eagle crater in Meridiani Planum are composed of fine-grained siliciclastic materials derived from weathering of basaltic rocks, sulfate minerals (including magnesium sulfate and jarosite) that constitute several tens of percent of the rock by weight, and hematite. Cross-stratification observed in rock outcrops indicates eolian and aqueous transport. Diagenetic features include hematite-rich concretions and crystal-mold vugs. We interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history. The environmental conditions that they record include episodic inundation by shallow surface water, evaporation, and desiccation. The geologic record at Meridiani Planum suggests that conditions were suitable for biological activity for a period of time in martian history.

Functional brain abnormalities in young adults at genetic risk for late-onset Alzheimer's dementia

Abstract: Fluorodeoxyglucose positron emission tomography (PET) studies have found that patients with Alzheimer's dementia (AD) have abnormally low rates of cerebral glucose metabolism in posterior cingulate, parietal, temporal, and prefrontal cortex We previously found that cognitively normal, late-middle-aged carriers of the apolipoprotein E epsilon4 allele, a common susceptibility gene for late-onset Alzheimer's dementia, have abnormally low rates of glucose metabolism in the same brain regions as patients with probable AD We now consider whether epsilon4 carriers have these regional brain abnormalities as relatively young adults Apolipoprotein E genotypes were established in normal volunteers 20-39 years of age Clinical ratings, neuropsychological tests, magnetic resonance imaging, and PET were performed in 12 epsilon4 heterozygotes, all with the epsilon3/epsilon4 genotype, and 15 noncarriers of the epsilon4 allele, 12 of whom were individually matched for sex, age, and educational level An automated algorithm was used to generate an aggregate surface-projection map that compared regional PET measurements in the two groups The young adult epsilon4 carriers and noncarriers did not differ significantly in their sex, age, educational level, clinical ratings, or neuropsychological test scores Like previously studied patients with probable AD and late-middle-aged epsilon4 carriers, the young epsilon4 carriers had abnormally low rates of glucose metabolism bilaterally in the posterior cingulate, parietal, temporal, and prefrontal cortex Carriers of a common Alzheimer's susceptibility gene have functional brain abnormalities in young adulthood, several decades before the possible onset of dementia

The Thermal Emission Imaging System (THEMIS) for the Mars 2001 Odyssey mission

Abstract: The Thermal Emission Imaging System (THEMIS) on 2001 Mars Odyssey will investigate the surface mineralogy and physical properties of Mars using multi-spectral thermal-infrared images in nine wavelengths centered from 6.8 to 14.9 μm, and visible/near-infrared images in five bands centered from 0.42 to 0.86 μm. THEMIS will map the entire planet in both day and night multi-spectral infrared images at 100-m per pixel resolution, 60% of the planet in one-band visible images at 18-m per pixel, and several percent of the planet in 5-band visible color. Most geologic materials, including carbonates, silicates, sulfates, phosphates, and hydroxides have strong fundamental vibrational absorption bands in the thermal-infrared spectral region that provide diagnostic information on mineral composition. The ability to identify a wide range of minerals allows key aqueous minerals, such as carbonates and hydrothermal silica, to be placed into their proper geologic context. The specific objectives of this investigation are to: (1) determine the mineralogy and petrology of localized deposits associated with hydrothermal or sub-aqueous environments, and to identify future landing sites likely to represent these environments; (2) search for thermal anomalies associated with active sub-surface hydrothermal systems; (3) study small-scale geologic processes and landing site characteristics using morphologic and thermophysical properties; and (4) investigate polar cap processes at all seasons. THEMIS follows the Mars Global Surveyor Thermal Emission Spectrometer (TES) and Mars Orbiter Camera (MOC) experiments, providing substantially higher spatial resolution IR multi-spectral images to complement TES hyperspectral (143-band) global mapping, and regional visible imaging at scales intermediate between the Viking and MOC cameras.

Social Capital and Knowledge Creation: Diminishing Returns of the Number and Strength of Exchange Relationships

Abstract: This study analyzed the relationship between social capital and knowledge creation at the individual level. Our limited theory of knowledge creation encompasses the number and strength of the relat...

Emotion-related regulation: Sharpening the definition

Abstract: Cole, Martin, and Dennis (this issue) considered many important conceptual and methodological issues in their discussion of emotion regulation. Although it may be necessary to develop an integrated definition of the construct of emotion regulation, the definition provided in the Cole et al. article is too encompassing. It is important to differentiate emotion regulation from the effects of emotions on others and to differentiate among (a) regulation that stems from individuals external to the child versus behavior that is accomplished by the child, (b) behavior that is goal oriented versus unintentional, and (c) regulation that is voluntary versus behavior that is less voluntarily controlled. An alternate definition of emotion-related self-regulation is provided.

Use and misuse of landscape indices

Abstract: Landscape ecology has generated much excitement in the past two decades. One reason was that it brought spatial analysis and modeling to the forefront of ecological research. However, high expectations for landscape analysis to improve our understanding and prediction of ecological processes have largely been unfulfilled. We identified three kinds of critical issues: conceptual flaws in landscape pattern analysis, inherent limitations of landscape indices, and improper use of pattern indices. For example, many landscape analyses treat quantitative description of spatial pattern as an end itself and fail to explore relationships between pattern and process. Landscape indices and map data are sometimes used without testing their ecological relevance, which may not only confound interpretation of results, but also lead to meaningless results. In addition, correlation analysis with indices is impeded by the lack of data because of difficulties in large-scale experimentation and by complicated behavior of indices because of their varying responses to changes in scale and spatial pattern. These problems represent significant challenges to landscape pattern analysis, especially in terms of relating pattern to process. In this perspective paper, we examine the underlying problems of these challenges and offer some solutions.

A phylogeny of legumes (Leguminosae) based on analysis of the plastid matK gene resolves many well-supported subclades within the family.

Abstract: Phylogenetic analysis of 330 plastid matK gene sequences, representing 235 genera from 37 of 39 tribes, and four outgroup taxa from eurosids I supports many well-resolved subclades within the Leguminosae. These results are generally consistent with those derived from other plastid sequence data (rbcL and trnL), but show greater resolution and clade support overall. In particular, the monophyly of subfamily Papilionoideae and at least seven major subclades are well-supported by bootstrap and Bayesian credibility values. These subclades are informally recognized as the Cladrastis clade, genistoid sensu lato, dalbergioid sensu lato, mirbelioid, millettioid, and robinioid clades, and the inverted-repeat-lacking clade (IRLC). The genistoid clade is expanded to include genera such as Poecilanthe, Cyclolobium, Bowdichia, and Diplotropis and thus contains the vast majority of papilionoids known to produce quinolizidine alkaloids. The dalbergioid clade is expanded to include the tribe Amorpheae. The mirbelioids include the tribes Bossiaeeae and Mirbelieae, with Hypocalypteae as its sister group. The millettioids comprise two major subclades that roughly correspond to the tribes Millettieae and Phaseoleae and represent the only major papilionoid clade marked by a macromorphological apomorphy, pseudoracemose inflorescences. The robinioids are expanded to include Sesbania and members of the tribe Loteae. The IRLC, the most species-rich subclade, is sister to the robinioids. Analysis of the matK data consistently resolves but modestly supports a clade comprising papilionoid taxa that accumulate canavanine in the seeds. This suggests a single origin for the biosynthesis of this most commonly produced of the nonprotein amino acids in legumes.

The Natural History of Nitrogen Fixation

Abstract: In recent years, our understanding of biological nitrogen fixation has been bolstered by a diverse array of scientific techniques. Still, the origin and extant distribution of nitrogen fixation has been perplexing from a phylogenetic perspective, largely because of factors that confound molecular phylogeny such as sequence divergence, paralogy, and horizontal gene transfer. Here, we make use of 110 publicly available complete genome sequences to understand how the core components of nitrogenase, including NifH, NifD, NifK, NifE, and NifN proteins, have evolved. These genes are universal in nitrogen fixing organisms-typically found within highly conserved operons-and, overall, have remarkably congruent phylogenetic histories. Additional clues to the early origins of this system are available from two distinct clades of nitrogenase paralogs: a group composed of genes essential to photosynthetic pigment biosynthesis and a group of uncharacterized genes present in methanogens and in some photosynthetic bacteria. We explore the complex genetic history of the nitrogenase family, which is replete with gene duplication, recruitment, fusion, and horizontal gene transfer and discuss these events in light of the hypothesized presence of nitrogenase in the last common ancestor of modern organisms, as well as the additional possibility that nitrogen fixation might have evolved later, perhaps in methanogenic archaea, and was subsequently transferred into the bacterial domain.