Mixture modeling for lifespan developmental research

As part of the Generalized Structural Equation Modeling framework, mixture models are person-centered analyses seeking to identify distinct subpopulations, or profiles, of participants differing quantitatively and qualitatively from one another on a configuration of indicators and/or relations among these indicators. Mixture models are typological (resulting in a classification system), probabilistic (each participant having a probability of membership into all profiles based on prototypical similarity), and exploratory (the optimal model is typically selected based on a comparison of alternative specifications) in nature, and can take different forms. Latent profile analyses seek to identify subpopulations of participants differing from one another on a configuration of indicators and can be extended to factor mixture analyses allowing for the incorporation of latent factors to the model. In contrast, mixture regression analyses seek to identify subpopulations of participants’ differing from one another in terms of relations among profile indicators. These analyses can be extended to the multiple-group and/or longitudinal analyses, allowing researchers to conduct tests of profile similarity across different samples of participants or time points, and latent transition analyses can be used to assess probabilities of profiles transition over time among a sample of participants (i.e., within person stability and change in profile membership). Finally, growth mixture analyses are built from latent curve models and seek to identify subpopulations of participants following quantitatively and qualitatively distinct trajectories over time. All of these models can accommodate covariates, used either as predictors, correlates, or outcomes, and can even be extended to tests of mediation and moderation

Generalizability of achievement goal profiles across five cultural groups : more similarities than differences

Previous results have shown possible cultural differences in students’ achievement goals endorsement and in their relations with various predictors and outcomes. In this person-centered study, we sought to identify achievement goal profiles and to assess the extent to which these configurations and their associations with predictors and outcomes generalize across cultures. We used a new statistical approach to assess latent profile similarities across adolescents from five cultural backgrounds (N = 2643, including Non-Indigenous Australians, Indigenous Australians, Indigenous American, Middle Easterners, and Asians). Our results supported the cross-cultural generalizability of the profiles, their predictors, and their outcomes. Five similar profiles were identified in each cultural group, but their relative frequency differed across cultures. The results revealed advantages of exploring multidimensional goal profiles

Thermodynamic metrics and optimal paths

A fundamental problem in modern thermodynamics is how a molecular-scale machine performs useful work, while operating away from thermal equilibrium without excessive dissipation. To this end, we derive a friction tensor that induces a Riemannian manifold on the space of thermodynamic states. Within the linear-response regime, this metric structure controls the dissipation of finite-time transformations, and bestows optimal protocols with many useful properties. We discuss the connection to the existing thermodynamic length formalism, and demonstrate the utility of this metric by solving for optimal control parameter protocols in a simple nonequilibrium model.Comment: 5 page

BIM for the sub-surface : challenges

Most existing BIM 3D models show the ground as a grey amorphous mass, if it is shown at all. The ground is inherently more variable than other construction materials and, in an integrated multidisciplinary BIM project, it is important that this can be appropriately conveyed in order to avoid poor decision making

Nonperturbative Matching for Field Theories with Heavy Fermions

We examine a paradox, suggested by Banks and Dabholkar, concerning nonperturbative effects in an effective field theory which is obtained by integrating out a generation of heavy fermions, where the heavy fermion masses arise from Yukawa couplings. They argue that light fermions in the effective theory appear to decay via instanton processes, whereas their decay is forbidden in the full theory. We resolve this paradox by showing that such processes in fact do not occur in the effective theory, due to matching corrections which cause the relevant light field configurations to have infinite action.Comment: 10 pages, no figures, uses harvmac, Harvard University Preprint HUTP-93/A03

A polynomial bound for untangling geometric planar graphs

To untangle a geometric graph means to move some of the vertices so that the resulting geometric graph has no crossings. Pach and Tardos [Discrete Comput. Geom., 2002] asked if every n-vertex geometric planar graph can be untangled while keeping at least n^\epsilon vertices fixed. We answer this question in the affirmative with \epsilon=1/4. The previous best known bound was \Omega((\log n / \log\log n)^{1/2}). We also consider untangling geometric trees. It is known that every n-vertex geometric tree can be untangled while keeping at least (n/3)^{1/2} vertices fixed, while the best upper bound was O(n\log n)^{2/3}. We answer a question of Spillner and Wolff [arXiv:0709.0170 2007] by closing this gap for untangling trees. In particular, we show that for infinitely many values of n, there is an n-vertex geometric tree that cannot be untangled while keeping more than 3(n^{1/2}-1) vertices fixed. Moreover, we improve the lower bound to (n/2)^{1/2}.Comment: 14 pages, 7 figure

Achievement goal profiles among adolescent males and females.

Achievement goal theory has long been a dominant model in the study of student motivation. However, a relatively small number of researchers have investigated gender differences in achievement goals or have considered the possible role that social and extrinsic goals may play in student academic motivation. Adopting a person-centered multiple goals perspective based on personal investment theory, this longitudinal study investigated whether males and females shared similar goal profiles, and whether the predictors (facilitating conditions) and outcomes (learning processes, task perseverance, and future aspirations) of these profiles were equivalent across genders. Profiles were extracted from 8 types of academic goals, based on a large sample of Hong Kong high school students (N 7,848). Findings revealed 5 distinctive profiles for both males and females. Although the relative size of these profiles differed across samples of male and female students, the results show that 4 of these profiles were mostly equivalent across genders. Predictors of membership into these profiles were also equivalent across genders, whereas their relative outcomes were specific to gender

Decays of ℓ=1\ell=1 Baryons --- Quark Model versus Large-NcN_c

We study nonleptonic decays of the orbitally excited, \su6 \rep{70}-plet baryons in order to test the hypothesis that the successes of the nonrelativistic quark model have a natural explanation in the large-$N_c$ limit of QCD. By working in a Hartree approximation, we isolate a specific set of operators that contribute to the observed s- and d-wave decays in leading order in $1/N_c$. We fit our results to the current experimental decay data, and make predictions for a number of allowed but unobserved modes. Our tentative conclusion is that there is more to the nonrelativistic quark model of baryons than large-$N_c$.Comment: LaTeX 49pp. (38 pp. landscape), PicTex, PrePicTex, PostPicTex required for 3 figures, Harvard Preprint HUTP-94/A008. (Two additional operators are included, but conclusions are unchanged.

Predictors of improvement in subjective sleep quality reported by older adults following group-based cognitive behavior therapy for sleep maintenance and early morning awakening insomnia

ObjectiveCognitive behavior therapy is an effective nonpharmacologic treatment for insomnia. However, individualized administration is costly and often results in substantial variability in treatment response across individual patients, particularly so for older adults. Group-based administration has demonstrated impressive potential for a brief and inexpensive answer to the effective treatment of insomnia in the older population. It is important to identify potential predictors of response to such a treatment format to guide clinicians when selecting the most suitable treatment for their patients. The aim of our study was to identify factors that predict subjective sleep quality of older adults following group-based administration of cognitive behavior therapy for insomnia (CBT-I).MethodsEighty-six adults (41 men; mean age, 64.10 y; standard deviation [SD], 6.80) with sleep maintenance or early morning awakening insomnia were selected from a community-based sample to participate in a 4-week group-based treatment program of CBT-I. Participants were required to complete 7-day sleep diaries and a comprehensive battery of questionnaires related to sleep quality and daytime functioning. Hierarchical multiple regression analyses were used to identify factors predicting subjective sleep quality immediately following treatment and at 3-month follow-up. Sleep diaries reported average nightly sleep efficiency (SE), which was used as the outcome measure of sleep quality.Results and conclusionsParticipants with the greatest SE following treatment while controlling for pretreatment SE were relatively younger and had more confidence in their ability to sleep at pretreatment. These characteristics may be useful to guide clinicians when considering the use of a group-based CBT-I for sleep maintenance or early morning awakening insomnia in older adults.Nicole Lovato, Leon Lack, Helen Wright, David J. Kennawa