Evolution of the curvature perturbation during and after multi-field inflation

We study the evolution of the curvature perturbation on the super-horizon scales starting from the inflationary epoch until there remains only a single dynamical degree of freedom, presureless matter, in the universe. We consider the cosmic inflation driven by a multiple number of the inflaton fields, which decay into both radiation and pressureless matter components. We present a complete set of the exact background and perturbation equations which describe the evolution of the universe throughout its history. By applying these equations to the simple but reasonable model of multi-field chaotic inflation, we explicitly show that the total curvature perturbation is continuously varying because of the non-adiabatic components of the curvature perturbation generated by the multiple inflaton fields throughout the whole evolution of the universe. We also provide an useful analytic estimation of the total as well as matter and radiation curvature perturbations, assuming that matter is completely decoupled from radiation from the beginning. The resulting isocurvature perturbation between matter and radiation is at most sub-percent level when the masses of the inflaton fields are distributed between $10^{-6}m_{pl}$ and $10^{-5}m_{pl}$. We find that this result is robust unless we use non-trivial decay rates, and that thus, in general, it is hard to obtain large matter-radiation isocurvature perturbation. Also, by using the $\delta{N}$ formalism, we point out that the inflationary calculation, especially when involving multiple inflaton fields, is likely to lose the potentially important post-inflationary evolution which can modify the resulting curvature perturbation.Comment: 31 pages, 6 figures, Final version to appear in JCAP. Add calculation of power spectrum and spectral index. We provide more discussio

La Sémiotique de l'espace dans l'oeuvre de Le Clézio. Le cas de La Quarantaine

[Résumé] Le langage des relations spatiales peut etre un moyen pour rendre compte du reel, meme au niveau de la modelisation ideologique. Les concepts haut/bas, droit/gauche, ouvert/ferme, delimite/non delimite prennent le sens de valable/non valable, bon/mauvais, accessible/inaccessible, mortel/immortel etc. Pour demontrer cette etude, nous avons choisi La Quarantaine de Le Clezio dans lequel l’espace n’est pas un simple decor, mais une langue. La forme de l’opposition de deux valeurs spatiales comme le haut/le bas et la gauche/la droite est tres marque dans le texte.Et cela fonctionne en tant que mode d’expression de concepts non spatiaux comme les idees politiques, sociales, morales et religieuses. Or la valeur semantique acquise par la structure de l’espace n’est pas definitive la valeur positive peut changer en valeur negative d’apres les espaces ou les personnages se trouvent, et vice versa. De plus, la forme de l’opposition ne reste pas toujours opposee : la reunion des opposes se realice par la structure circulaire ou par le retour a l’origine et c’est le message de l’ecrivain

Effect of Communication and Time Spent with Children on the Parenting Difficulties of Single Parents in Korea

This research aims to analyze the effect of the time spent with children and the degree of communication with children on the difficulties of parenting children by single parents in Korea. As for the single parents\u27 parenting difficulties, economic hardships have been widely discussed. However, not many studies examined other psychosocial factors between single parents and children, such as the problem of communication between parents and children and the lack of time spent with parents and children, despite their importance in parenting children. This study claims that the focus of public policies, governmental support, and non-profit organizations\u27 roles to resolve the parenting difficulties faced by single parents needs to be changed and diversified toward addressing psychosocial factors. The data used for the analysis is the 2018 Single-parent Family Survey conducted by the Ministry of Gender Equality and Family, where 949 single-parent families with children aged 7 to 12 and 1,535 single-parent children aged 13 to 17 responded. The OLS regression analyses show several findings regarding the association between psychosocial factors and parenting challenges. First, the more difficult it is for single parents to communicate with children, the more difficult it is to raise children. Second, the more time single parents spend with their children, the less difficult it is to raise them. Third, when single parents are female, the greater the number of children, the more difficult it is to raise children. However, the age of single parents, the educational background of single parents, the period of becoming single parents, household income, and net assets do not significantly affect the stress of single parents\u27 childrearing. The research results highlight the importance of parents of single-parent family communicating with their children and securing time spend with their children in supporting single-parent families

Quantifying the Effects of Knee Joint Biomechanics on Acoustical Emissions

The knee is one of the most injured body parts, causing 18 million patients to be seen in clinics every year. Because the knee is a weight-bearing joint, it is prone to pathologies such as osteoarthritis and ligamentous injuries. Existing technologies for monitoring knee health can provide accurate assessment and diagnosis for acute injuries. However, they are mainly confined to clinical or laboratory settings only, time-consuming, expensive, and not well-suited for longitudinal monitoring. Developing a novel technology for joint health assessment beyond the clinic can further provide insights on the rehabilitation process and quantitative usage of the knee joint. To better understand the underlying properties and fundamentals of joint sounds, this research will investigate the relationship between the changes in the knee joint structure (i.e. structural damage and joint contact force) and the JAEs while developing novel techniques for analyzing these sounds. We envision that the possibility of quantifying joint structure and joint load usage from these acoustic sensors would advance the potential of JAE as the next biomarker of joint health that can be captured with wearable technology. First, we developed a novel processing technique for JAEs that quantify on the structural change of the knee from injured athletes and human lower-limb cadaver models. Second, we quantified whether JAEs can detect the increase in the mechanical stress on the knee joint using an unsupervised graph mining algorithm. Lastly, we quantified the directional bias of the load distribution between medial and lateral compartment using JAEs. Understanding and monitoring the quantitative usage of knee loads in daily activities can broaden the implications for longitudinal joint health monitoring.Ph.D

Comparing reactive and memory-one strategies of direct reciprocity

Direct reciprocity is a mechanism for the evolution of cooperation based on repeated interactions. When individuals meet repeatedly, they can use conditional strategies to enforce cooperative outcomes that would not be feasible in one-shot social dilemmas. Direct reciprocity requires that individuals keep track of their past interactions and find the right response. However, there are natural bounds on strategic complexity: Humans find it difficult to remember past interactions accurately, especially over long timespans. Given these limitations, it is natural to ask how complex strategies need to be for cooperation to evolve. Here, we study stochastic evolutionary game dynamics in finite populations to systematically compare the evolutionary performance of reactive strategies, which only respond to the co-player's previous move, and memory-one strategies, which take into account the own and the co-player's previous move. In both cases, we compare deterministic strategy and stochastic strategy spaces. For reactive strategies and small costs, we find that stochasticity benefits cooperation, because it allows for generous-tit-for-tat. For memory one strategies and small costs, we find that stochasticity does not increase the propensity for cooperation, because the deterministic rule of win-stay, lose-shift works best. For memory one strategies and large costs, however, stochasticity can augment cooperation.Comment: 18 pages, 7 figure

Measuring efficiency of lean six sigma project implementation using data envelopment analysis at NASA

Purpose: This study aims to review the implementation of the Lean Six Sigma project methodology in the Johnson Space Center (JSC) business environment of National Aeronautics and Space Administration (NASA) with an objective of evaluating performance of individual projects and to develop recommendation for strategies to improve operational efficiencies based on Data Envelopment Analysis (DEA). Design/methodology/approach: In this study, authors propose the Lean Six Sigma project performance evaluation model (LSS-PPEM) based on Data DEA where Critical Success Factors (CSFs) and Total Team Hours serve as inputs while Process Sigma and Cost avoidance are used as outputs. The CSFs are factors that critically affect the performance of LSS at JSC. Six of those are identified by the Black Belts through Analytical Hierarchical Process, and the values of those are decided by project leaders and Green Belts through survey. Eighteen LSS projects are evaluated, and their results are analyzed. Findings and Originality/value: Eventually, four out of the six CSFs are adopted for this study based upon Pearson correlation analysis, and those four include Project execution and follow up of results; Top management’s commitment and participation; The use of data analysis with easily obtainable data; Attention given to both long and short term targets. Using data between the years 2009 and 2011, seven of the eighteen projects are found to be efficient. The benchmark analysis and slack analysis are conducted to provide further recommendation for JSC managers. Three out of those seven efficient projects are most frequently used as an efficient peer. Practical implications: Traditionally, DEA has been considered as a data-driven approach. In this study, authors incorporate the survey-based CSFs into the DEA frame. Since many organizations may have different CSFs, the framework presented in this study can be easily applied to other organizations. Originality/value: This study provides a DEA-based framework and case study of LSS project evaluation in the government sector, which is very unique application to author’s best knowledge. The framework is unique in terms of its input factor selection and quantification procedures.Peer Reviewe