Showing papers by "Brigham Young University published in 2017"

Evaluating significance in linear mixed-effects models in R

Abstract: Mixed-effects models are being used ever more frequently in the analysis of experimental data. However, in the lme4 package in R the standards for evaluating significance of fixed effects in these models (i.e., obtaining p-values) are somewhat vague. There are good reasons for this, but as researchers who are using these models are required in many cases to report p-values, some method for evaluating the significance of the model output is needed. This paper reports the results of simulations showing that the two most common methods for evaluating significance, using likelihood ratio tests and applying the z distribution to the Wald t values from the model output (t-as-z), are somewhat anti-conservative, especially for smaller sample sizes. Other methods for evaluating significance, including parametric bootstrapping and the Kenward-Roger and Satterthwaite approximations for degrees of freedom, were also evaluated. The results of these simulations suggest that Type 1 error rates are closest to .05 when models are fitted using REML and p-values are derived using the Kenward-Roger or Satterthwaite approximations, as these approximations both produced acceptable Type 1 error rates even for smaller samples.

Guidelines for Family-Centered Care in the Neonatal, Pediatric, and Adult ICU.

Abstract: Objective:To provide clinicians with evidence-based strategies to optimize the support of the family of critically ill patients in the ICU.Methods:We used the Council of Medical Specialty Societies principles for the development of clinical guidelines as the framework for guideline development. We a

Rare coding variants in PLCG2, ABI3, and TREM2 implicate microglial-mediated innate immunity in Alzheimer's disease

Abstract: We identified rare coding variants associated with Alzheimer's disease in a three-stage case–control study of 85,133 subjects. In stage 1, we genotyped 34,174 samples using a whole-exome microarray. In stage 2, we tested associated variants (P < 1 × 10−4) in 35,962 independent samples using de novo genotyping and imputed genotypes. In stage 3, we used an additional 14,997 samples to test the most significant stage 2 associations (P < 5 × 10−8) using imputed genotypes. We observed three new genome-wide significant nonsynonymous variants associated with Alzheimer's disease: a protective variant in PLCG2 (rs72824905: p.Pro522Arg, P = 5.38 × 10−10, odds ratio (OR) = 0.68, minor allele frequency (MAF)cases = 0.0059, MAFcontrols = 0.0093), a risk variant in ABI3 (rs616338: p.Ser209Phe, P = 4.56 × 10−10, OR = 1.43, MAFcases = 0.011, MAFcontrols = 0.008), and a new genome-wide significant variant in TREM2 (rs143332484: p.Arg62His, P = 1.55 × 10−14, OR = 1.67, MAFcases = 0.0143, MAFcontrols = 0.0089), a known susceptibility gene for Alzheimer's disease. These protein-altering changes are in genes highly expressed in microglia and highlight an immune-related protein–protein interaction network enriched for previously identified risk genes in Alzheimer's disease. These genetic findings provide additional evidence that the microglia-mediated innate immune response contributes directly to the development of Alzheimer's disease.

Weight and Metabolic Outcomes 12 Years after Gastric Bypass

Abstract: BackgroundFew long-term or controlled studies of bariatric surgery have been conducted to date. We report the 12-year follow-up results of an observational, prospective study of Roux-en-Y gastric bypass that was conducted in the United States. MethodsA total of 1156 patients with severe obesity comprised three groups: 418 patients who sought and underwent Roux-en-Y gastric bypass (surgery group), 417 patients who sought but did not undergo surgery (primarily for insurance reasons) (nonsurgery group 1), and 321 patients who did not seek surgery (nonsurgery group 2). We performed clinical examinations at baseline and at 2 years, 6 years, and 12 years to ascertain the presence of type 2 diabetes, hypertension, and dyslipidemia. ResultsThe follow-up rate exceeded 90% at 12 years. The adjusted mean change from baseline in body weight in the surgery group was −45.0 kg (95% confidence interval [CI], −47.2 to −42.9; mean percent change, −35.0) at 2 years, −36.3 kg (95% CI, −39.0 to −33.5; mean percent change, −28...

The genome of Chenopodium quinoa

Abstract: Chenopodium quinoa (quinoa) is a highly nutritious grain identified as an important crop to improve world food security. Unfortunately, few resources are available to facilitate its genetic improvement. Here we report the assembly of a high-quality, chromosome-scale reference genome sequence for quinoa, which was produced using single-molecule real-time sequencing in combination with optical, chromosome-contact and genetic maps. We also report the sequencing of two diploids from the ancestral gene pools of quinoa, which enables the identification of sub-genomes in quinoa, and reduced-coverage genome sequences for 22 other samples of the allotetraploid goosefoot complex. The genome sequence facilitated the identification of the transcription factor likely to control the production of anti-nutritional triterpenoid saponins found in quinoa seeds, including a mutation that appears to cause alternative splicing and a premature stop codon in sweet quinoa strains. These genomic resources are an important first step towards the genetic improvement of quinoa.

Advancing Social Connection as a Public Health Priority in the United States

Abstract: A robust body of scientific evidence has indicated that being embedded in high-quality close relationships and feeling socially connected to the people in one's life is associated with decreased risk for all-cause mortality as well as a range of disease morbidities. Despite mounting evidence that the magnitude of these associations is comparable to that of many leading health determinants (that receive significant public health resources), government agencies, health care providers and associations, and public or private health care funders have been slow to recognize human social relationships as either a health determinant or health risk marker in a manner that is comparable to that of other public health priorities. This article evaluates current evidence (on social relationships and health) according to criteria commonly used in determining public health priorities. The article discusses challenges for reducing risk in this area and outlines an agenda for integrating social relationships into current public health priorities. (PsycINFO Database Record

A common haplotype lowers PU.1 expression in myeloid cells and delays onset of Alzheimer's disease.

Abstract: A genome-wide survival analysis of 14,406 Alzheimer's disease (AD) cases and 25,849 controls identified eight previously reported AD risk loci and 14 novel loci associated with age at onset. Linkage disequilibrium score regression of 220 cell types implicated the regulation of myeloid gene expression in AD risk. The minor allele of rs1057233 (G), within the previously reported CELF1 AD risk locus, showed association with delayed AD onset and lower expression of SPI1 in monocytes and macrophages. SPI1 encodes PU.1, a transcription factor critical for myeloid cell development and function. AD heritability was enriched within the PU.1 cistrome, implicating a myeloid PU.1 target gene network in AD. Finally, experimentally altered PU.1 levels affected the expression of mouse orthologs of many AD risk genes and the phagocytic activity of mouse microglial cells. Our results suggest that lower SPI1 expression reduces AD risk by regulating myeloid gene expression and cell function.

The Potential Public Health Relevance of Social Isolation and Loneliness: Prevalence, Epidemiology, and Risk Factors

Abstract: Our social relationships are widely considered crucial to emotional well-being; however, the possibility that social connection may be a biological need, vital to physical wellbeing and even survival, is commonly unrecognized. Still, extreme examples clearly illustrate infants in custodial care who lack human contact fail to thrive and often die (UNICEF, 1997), and social isolation is so distressing that solitary confinement has been used as a form of punishment and even torture. Yet an increasing portion of the U.S. population now experiences isolation regularly. News headlines from many nations, including the United States, Germany, Australia, and the United Kingdom, suggest that we are facing a loneliness epidemic (http://www.campaigntoendloneliness.org/loneliness-research, http://www.spiegel.de/ international/germany/germany-faces-epidemic-of-lonelyand-isolated-seniors-a-876635.html, https://startsat60.com/ health/new-survey-reveals-australias-loneliness-epidemic, http://www.huffingtonpost.com.au/tania-de-jong/lonelinessis-the-global-epidemic-of-our-times), leading to the important question of whether there is evidence to support such a claim and, if so, whether we are facing a public health crisis. Recently my work has systematically examined and summarized the available evidence supporting the public health prioritization of social connections (Holt-Lunstad, Robles, & Sbarra, 2017). Here I will summarize data on prevalence rates, epidemiological evidence of risk, and potential risk factors.

Custom 3D printer and resin for 18 μm × 20 μm microfluidic flow channels

Abstract: While there is great interest in 3D printing for microfluidic device fabrication, to-date the achieved feature sizes have not been in the truly microfluidic regime (<100 μm). In this paper we demonstrate that a custom digital light processor stereolithographic (DLP-SLA) 3D printer and a specifically-designed, low cost, custom resin can readily achieve flow channel cross sections as small as 18 μm × 20 μm. Our 3D printer has a projected image plane resolution of 7.6 μm and uses a 385 nm LED, which dramatically increases the available selection of UV absorbers for resin formulation compared to 3D printers with 405 nm LEDs. Beginning with 20 candidate absorbers, we demonstrate the evaluation criteria and process flow required to develop a high-resolution resin. In doing so, we introduce a new mathematical model for characterizing the resin optical penetration depth based only on measurement of the absorber's molar absorptivity. Our final resin formulation uses 2-nitrophenyl phenyl sulfide (NPS) as the UV absorber. We also develop a novel channel narrowing technique that, together with the new resin and 3D printer resolution, enables small flow channel fabrication. We demonstrate the efficacy of our approach by fabricating 3D serpentine flow channels 41 mm long in a volume of only 0.12 mm3, and by printing high aspect ratio flow channels <25 μm wide and 3 mm tall. These results indicate that 3D printing is finally positioned to challenge the pre-eminence of methods such as soft lithography for microfluidic device prototyping and fabrication.

What is the physiological time to recovery after concussion? A systematic review.

Abstract: Aim or objective The aim of this study is to consolidate studies of physiological measures following sport-related concussion (SRC) to determine if a time course of postinjury altered neurobiology can be outlined. This biological time course was considered with respect to clinically relevant outcomes such as vulnerability to repeat injury and safe timing of return to physical contact risk. Design Systematic review. Data sources PubMed, CINAHL, Cochrane Central, PsychINFO. Eligibility criteria for selecting studies Studies were included if they reported original research on physiological or neurobiological changes after SRC. Excluded were cases series Results A total of 5834 articles were identified, of which 80 were included for full-text data extraction and review. Relatively few longitudinal studies exist that follow both physiological dysfunction and clinical measures to recovery. Summary/conclusions Modalities of measuring physiological change after SRC were categorised into the following: functional MRI, diffusion tensor imaging, magnetic resonance spectroscopy, cerebral blood flow, electrophysiology, heart rate, exercise, fluid biomarkers and transcranial magnetic stimulation. Due to differences in modalities, time course, study design and outcomes, it is not possible to define a single ‘physiological time window’ for SRC recovery. Multiple studies suggest physiological dysfunction may outlast current clinical measures of recovery, supporting a buffer zone of gradually increasing activity before full contact risk. Future studies need to use generalisable populations, longitudinal designs following to physiological and clinical recovery and careful correlation of neurobiological modalities with clinical measures.

A giant planet undergoing extreme-ultraviolet irradiation by its hot massive-star host

Abstract: The amount of ultraviolet irradiation and ablation experienced by a planet depends strongly on the temperature of its host star. Of the thousands of extrasolar planets now known, only six have been found that transit hot, A-type stars (with temperatures of 7,300–10,000 kelvin), and no planets are known to transit the even hotter B-type stars. For example, WASP-33 is an A-type star with a temperature of about 7,430 kelvin, which hosts the hottest known transiting planet, WASP-33b (ref. 1); the planet is itself as hot as a red dwarf star of type M (ref. 2). WASP-33b displays a large heat differential between its dayside and nightside, and is highly inflated–traits that have been linked to high insolation. However, even at the temperature of its dayside, its atmosphere probably resembles the molecule-dominated atmospheres of other planets and, given the level of ultraviolet irradiation it experiences, its atmosphere is unlikely to be substantially ablated over the lifetime of its star. Here we report observations of the bright star HD 195689 (also known as KELT-9), which reveal a close-in (orbital period of about 1.48 days) transiting giant planet, KELT-9b. At approximately 10,170 kelvin, the host star is at the dividing line between stars of type A and B, and we measure the dayside temperature of KELT-9b to be about 4,600 kelvin. This is as hot as stars of stellar type K4 (ref. 5). The molecules in K stars are entirely dissociated, and so the primary sources of opacity in the dayside atmosphere of KELT-9b are probably atomic metals. Furthermore, KELT-9b receives 700 times more extreme-ultraviolet radiation (that is, with wavelengths shorter than 91.2 nanometres) than WASP-33b, leading to a predicted range of mass-loss rates that could leave the planet largely stripped of its envelope during the main-sequence lifetime of the host star.

Local Genetic Correlation Gives Insights into the Shared Genetic Architecture of Complex Traits

Abstract: Although genetic correlations between complex traits provide valuable insights into epidemiological and etiological studies, a precise quantification of which genomic regions disproportionately contribute to the genome-wide correlation is currently lacking. Here, we introduce ρ-HESS, a technique to quantify the correlation between pairs of traits due to genetic variation at a small region in the genome. Our approach requires GWAS summary data only and makes no distributional assumption on the causal variant effect sizes while accounting for linkage disequilibrium (LD) and overlapping GWAS samples. We analyzed large-scale GWAS summary data across 36 quantitative traits, and identified 25 genomic regions that contribute significantly to the genetic correlation among these traits. Notably, we find 6 genomic regions that contribute to the genetic correlation of 10 pairs of traits that show negligible genome-wide correlation, further showcasing the power of local genetic correlation analyses. Finally, we report the distribution of local genetic correlations across the genome for 55 pairs of traits that show putative causal relationships.

Mechanisms and mediators of the skeletal muscle repeated bout effect

Abstract: Skeletal muscle adapts to exercise-induced damage by orchestrating several but still poorly understood mechanisms that endow protection from subsequent damage Known widely as the repeated bout effect, we propose that neural adaptations, alterations to muscle mechanical properties, structural remodeling of the extracellular matrix, and biochemical signaling work in concert to coordinate the protective adaptation

Prophage-mediated defence against viral attack and viral counter-defence.

Abstract: Temperate phages are common, and prophages are abundant residents of sequenced bacterial genomes. Mycobacteriophages are viruses that infect mycobacterial hosts including Mycobacterium tuberculosis and Mycobacterium smegmatis, encompass substantial genetic diversity and are commonly temperate. Characterization of ten Cluster N temperate mycobacteriophages revealed at least five distinct prophage-expressed viral defence systems that interfere with the infection of lytic and temperate phages that are either closely related (homotypic defence) or unrelated (heterotypic defence) to the prophage. Target specificity is unpredictable, ranging from a single target phage to one-third of those tested. The defence systems include a single-subunit restriction system, a heterotypic exclusion system and a predicted (p)ppGpp synthetase, which blocks lytic phage growth, promotes bacterial survival and enables efficient lysogeny. The predicted (p)ppGpp synthetase coded by the Phrann prophage defends against phage Tweety infection, but Tweety codes for a tetrapeptide repeat protein, gp54, which acts as a highly effective counter-defence system. Prophage-mediated viral defence offers an efficient mechanism for bacterial success in host-virus dynamics, and counter-defence promotes phage co-evolution.

Review of Research on Student-Facing Learning Analytics Dashboards and Educational Recommender Systems

Abstract: This article is a comprehensive literature review of student-facing learning analytics reporting systems that track learning analytics data and report it directly to students. This literature review builds on four previously conducted literature reviews in similar domains. Out of the 945 articles retrieved from databases and journals, 93 articles were included in the analysis. Articles were coded based on the following five categories: functionality, data sources, design analysis, student perceptions, and measured effects. Based on this review, we need research on learning analytics reporting systems that targets the design and development process of reporting systems, not only the final products. This design and development process includes needs analyses, visual design analyses, information selection justifications, and student perception surveys. In addition, experiments to determine the effect of these systems on student behavior, achievement, and skills are needed to add to the small existing body of evidence. Furthermore, experimental studies should include usability tests and methodologies to examine student use of these systems, as these factors may affect experimental findings. Finally, observational study methods, such as propensity score matching, should be used to increase student access to these systems but still rigorously measure experimental effects.

Maximization of the annual energy production of wind power plants by optimization of layout and yaw‐based wake control

Abstract: This paper presents a wind plant modeling and optimization tool that enables the maximization of wind plant annual energy production (AEP) using yaw-based wake steering control and layout changes. The tool is an extension of a wake engineering model describing the steady-state effects of yaw on wake velocity profiles and power productions of wind turbines in a wind plant. To make predictions of a wind plant's AEP, necessary extensions of the original wake model include coupling it with a detailed rotor model and a control policy for turbine blade pitch and rotor speed. This enables the prediction of power production with wake effects throughout a range of wind speeds. We use the tool to perform an example optimization study on a wind plant based on the Princess Amalia Wind Park. In this case study, combined optimization of layout and wake steering control increases AEP by 5%. The power gains from wake steering control are highest for region 1.5 inflow wind speeds, and they continue to be present to some extent for the above-rated inflow wind speeds. The results show that layout optimization and wake steering are complementary because significant AEP improvements can be achieved with wake steering in a wind plant layout that is already optimized to reduce wake losses. Copyright © 2016 John Wiley & Sons, Ltd.

Overcoming the loss of blue sensitivity through opsin duplication in the largest animal group, beetles.

Abstract: Opsin proteins are fundamental components of animal vision whose structure largely determines the sensitivity of visual pigments to different wavelengths of light. Surprisingly little is known about opsin evolution in beetles, even though they are the most species rich animal group on Earth and exhibit considerable variation in visual system sensitivities. We reveal the patterns of opsin evolution across 62 beetle species and relatives. Our results show that the major insect opsin class (SW) that typically confers sensitivity to “blue” wavelengths was lost ~300 million years ago, before the origin of modern beetles. We propose that UV and LW opsin gene duplications have restored the potential for trichromacy (three separate channels for colour vision) in beetles up to 12 times and more specifically, duplications within the UV opsin class have likely led to the restoration of “blue” sensitivity up to 10 times. This finding reveals unexpected plasticity within the insect visual system and highlights its remarkable ability to evolve and adapt to the available light and visual cues present in the environment.

Hybrid Concentrated Solar Thermal Power Systems: A Review

Abstract: Concentrated solar power (CSP), or solar thermal power, is an ideal technology to hybridize with other energy technologies for power generation. CSP shares technology with conventional power generation and can be readily integrated with other energy types into a synergistic system, which has many potential benefits including increased dispatchability and reliability, improved efficiency, reduced capital costs through equipment sharing, and the opportunity for flexible operation by alternating between energy sources, which can lead to improved overall efficiency through synergy of the different energy sources. Another advantage of CSP technology is the ability to readily store via thermal energy storage (TES), making the intermittent solar resource dispatchable. A review of CSP hybridization strategies with coal, natural gas, biofuels, geothermal, photovoltaic (PV), and wind is given. An overview of different configurations for hybridizing CSP with these other energy sources is also provided. Hybridized CSP plants present different types and levels of synergy, depending on the hybrid energy source, the location of the plant, the CSP technology used, and the plant configuration. Coal, natural gas, and biofuel hybrids with CSP present many opportunities to inject solar heat at various temperatures. These combustible fuels provide reliability, dispatchability, and flexibility but are not entirely renewable solutions (with the exception of biofuels). Geothermal, wind, and PV hybrid designs with CSP can be entirely renewable, but lack some of the benefits of hydrocarbon fuels. Effective geothermal-CSP hybrid designs require low temperature operation where efficiency is limited by the power cycle. Wind-CSP and PVT (photovoltaic/thermal) lack dispatchability, but have other advantages. The pursuit of ideal CSP hybrid systems is an important research topic as it allows for further development of CSP technologies while providing an immediate solution that increases the use of solar power.

Addressing the Elephant in the Room: Disentangling Family Heterogeneity to Advance Family Business Research

Abstract: Over the years, thoughtful scholars have left us compelling reminders that differences among families shape family business goals, behaviors, and outcomes (Aldrich & Cliff, 2003; Dyer, 2006; Olson et al., 2003; Rogoff & Heck, 2003). Yet the integration of prevalent family differences in theory building and empirical testing in the context of family business is still in its infancy (Combs et al., in press; Danes, 2014; James, Jennings, & Breitkreuz, 2012; Martinez & Aldrich, 2003; Powell et al., in press). One reason for the status quo is that many scholars commonly apply management theories that include neither the family nor its heterogeneity as an element. With the growing heterogeneity of family patterns within and across societies around the world, in this essay we highlight different dimensions and approaches to capture family heterogeneity and discuss how researchers might begin to build and test richer theory to extend and refine our knowledge of family firms. The discipline of “family science,” which draws from anthropology, sociology, psychology, and education, among others, provides us with abundant theories that include and illuminate families (Jaskiewicz, Combs, Shanine, & Kacmar, 2016). Pioneering studies have already highlighted the relevance of family structures (Aldrich & Cliff, 2003) and the family system (Olson et al., 2003) for family business behavior and outcomes, and one recent study discussed the implications of family science theories for family business research (Jennings, Breitkreuz, & James, 2013). However, we still lack a comprehensive overview that ties together dimensions of family heterogeneity that are relevant for family business research and the prominent family science theories (Jaskiewicz et al., 2016) that might help us theorize how these family dimensions affect family business behaviors and outcomes. With this essay, we aim to fill this gap. Ignoring differences among families in family business research is problematic because the results of our work may be misleading. Therefore, while reading this essay, we encourage researchers to reflect on the sources of family heterogeneity, the ways to account for them in future research, and their potential impact on family business outcomes.

Mechanisms and kinetics of CO2 hydrogenation to value-added products: A detailed review on current status and future trends

Abstract: Global warming, fossil fuel depletion and energy security are driving scientists to investigate the mechanism of hydrocarbons production from CO 2 hydrogenation. The need for more comprehensive understanding on mechanism of CO 2 hydrogenation to hydrocarbons remains controversial because of the complex reaction mechanism and a large number of involved species. The micro mechanism of CO 2 hydrogenation to hydrocarbons has been considered as a possible remedy to fulfill the requirements. This review comprehensively discusses two processes: reverse water gas shift (RWGS) and CO 2 hydrogenation to hydrocarbons. The review includes reaction mechanisms and catalyst effects on yields and rates. In addition, the review outlines each of the Fischer-Tropsch (FT) micro mechanisms. The review infers some mechanisms from existing work and proposes a new mechanism that improves several predictions. These mechanisms form the design basis for optimal reactor design.

Ambient Air Pollution and Cancer Mortality in the Cancer Prevention Study II.

Abstract: Background: The International Agency for Research on Cancer classified both outdoor air pollution and airborne particulate matter as carcinogenic to humans (Group 1) for lung cancer. There may be a...

Data Augmentation for Recognition of Handwritten Words and Lines Using a CNN-LSTM Network

Abstract: We introduce two data augmentation and normalization techniques, which, used with a CNN-LSTM, significantly reduce Word Error Rate (WER) and Character Error Rate (CER) beyond best-reported results on handwriting recognition tasks (1) We apply a novel profile normalization technique to both word and line images (2) We augment existing text images using random perturbations on a regular grid We apply our normalization and augmentation to both training and test images Our approach achieves low WER and CER over hundreds of authors, multiple languages and a variety of collections written centuries apart Image augmentation in this manner achieves state-of-the-art recognition accuracy on several popular handwritten word benchmarks

Transethnic genome-wide scan identifies novel Alzheimer's disease loci

Abstract: Introduction Genetic loci for Alzheimer's disease (AD) have been identified in whites of European ancestry, but the genetic architecture of AD among other populations is less understood. Methods We conducted a transethnic genome-wide association study (GWAS) for late-onset AD in Stage 1 sample including whites of European Ancestry, African-Americans, Japanese, and Israeli-Arabs assembled by the Alzheimer's Disease Genetics Consortium. Suggestive results from Stage 1 from novel loci were followed up using summarized results in the International Genomics Alzheimer's Project GWAS dataset. Results Genome-wide significant (GWS) associations in single-nucleotide polymorphism (SNP)–based tests ( P −8 ) were identified for SNPs in PFDN1/HBEGF , USP6NL/ECHDC3 , and BZRAP1-AS1 and for the interaction of the (apolipoprotein E) APOE e4 allele with NFIC SNP. We also obtained GWS evidence ( P −6 ) for gene-based association in the total sample with a novel locus, TPBG ( P = 1.8 × 10 −6 ). Discussion Our findings highlight the value of transethnic studies for identifying novel AD susceptibility loci.

The Ideational Approach to Populism

Abstract: Although the study of populism has traditionally been the domain of Latin Americanists, research here has become increasingly comparative. One of the most important payoffs of this comparative work is conceptual. Rather than defining populism in structuralist, economic, or political-strategic terms, a growing number of scholars around the world are using an ideational conceptualization that draws heavily from earlier discursive theories. By employing the ideational approach, scholars have been able to provide empirical measures of populist discourse. In this article we explain and show the advantages of this ideational approach to a Latin American audience by presenting a new historical dataset measuring the discourse of Argentine, Chilean, and Peruvian presidents across the twentieth century. Our main intent is to clarify the ideational approach as well as to enliven the conceptual debate. While we are critical of alternative definitions, we acknowledge and reassess their theoretical insights. Resumen Aun cuando el estudio del populismo ha sido tradicionalmente un campo de los latinoamericanistas, la investigacion al respecto se ha vuelto cada vez mas comparativa. Uno de los beneficios mas importantes de los trabajos comparados es conceptual. En vez de definir al populismo en terminos estructurales, economicos o politico-estrategicos, un creciente numero de academicos alrededor del mundo utilizan una conceptualizacion ideacional vinculada con previas teorias discursivas. Mediante el uso del enfoque ideacional academicos han sido capaces de proveer mediciones empiricas de discurso populista. En este articulo explicamos y mostramos las ventajas del enfoque ideacional mediante la discusion de una nueva base de datos que mide el discurso de los presidentes de Argentina, Chile y Peru durante el siglo veinte. Nuestra principal intension es clarificar el enfoque ideacional y a su vez avivar el debate conceptual. Si bien es cierto que somos criticos de definiciones alternativas, reconocemos y reconsideramos sus aportes teoricos.

Investigating student engagement in blended learning settings using experience sampling and structural equation modeling

Abstract: We investigated activity-level student engagement in blended learning classes at the university level. We used intensive longitudinal methodology to collect activity level engagement data throughout a semester for 68 students enrolled in six blended courses across two universities. We used structural equation modeling to gain a holistic understanding of learning environments, including the influence of personal characteristics, course design, and student perceptions of the learning experience on in-the-moment cognitive and emotional engagement. To investigate longitudinal relationships between emotional and cognitive engagement, we employed cross-lagged modeling techniques. Findings showed that course design and student perception variables had a greater influence on engagement than individual student characteristics and that student multitasking had a strong negative influence on engagement. Students' perceptions of the importance of the activity had a strong positive influence on both cognitive and emotional engagement. An important outcome of engagement was the students' perceptions that they were learning and improving.