In this article, the authors developed a common strategy for identifying differential item functioning (DIF) items that can be implemented in both the mean and covariance structures method (MACS) and ...item response theory (IRT). They proposed examining the loadings (discrimination) and the intercept (location) parameters simultaneously using the likelihood ratio test with a free-baseline model and Bonferroni corrected critical
p
values. They compared the relative efficacy of this approach with alternative implementations for various types and amounts of DIF, sample sizes, numbers of response categories, and amounts of impact (latent mean differences). Results indicated that the proposed strategy was considerably more effective than an alternative approach involving a constrained-baseline model. Both MACS and IRT performed similarly well in the majority of experimental conditions. As expected, MACS performed slightly worse in dichotomous conditions but better than IRT in polytomous cases where sample sizes were small. Also, contrary to popular belief, MACS performed well in conditions where DIF was simulated on item thresholds (item means), and its accuracy was not affected by impact.
Eigenmodes of averaged small-amplitude perturbations to a turbulent channel flow – which is one of the most fundamental canonical flows – are identified for the first time via an extensive set of ...high-fidelity graphics processing unit accelerated direct numerical simulations. While the system governing averaged small-amplitude perturbations to turbulent channel flow remains unknown, the fact such eigenmodes can be identified constitutes direct evidence that it is linear. Moreover, while the eigenvalue associated with the slowest-decaying anti-symmetric eigenmode mode is found to be real, the eigenvalue associated with the slowest-decaying symmetric eigenmode mode is found to be complex. This indicates that the unknown linear system governing the evolution of averaged small-amplitude perturbations cannot be self-adjoint, even for the case of a uni-directional flow. In addition to elucidating aspects of the flow physics, the findings provide guidance for development of new unsteady Reynolds-averaged Navier–Stokes turbulence models, and constitute a new and accessible benchmark problem for assessing the performance of existing models, which are used widely throughout industry.
Polynomial sum of squares in fluid dynamics: a review with a look ahead Chernyshenko, S. I.; Goulart, P.; Huang, D. ...
Philosophical transactions - Royal Society. Mathematical, Physical and engineering sciences/Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences,
07/2014, Letnik:
372, Številka:
2020
Journal Article
Recenzirano
Odprti dostop
The first part of this paper reviews the application of the sum-of-squares-of-polynomials technique to the problem of global stability of fluid flows. It describes the known approaches and the latest ...results, in particular, obtaining for a version of the rotating Couette flow a better stability range than the range given by the classic energy stability method. The second part of this paper describes new results and ideas, including a new method of obtaining bounds for time-averaged flow parameters illustrated with a model problem and a method of obtaining approximate bounds that are insensitive to unstable steady states and periodic orbits. It is proposed to use the bound on the energy dissipation rate as the cost functional in the design of flow control aimed at reducing turbulent drag.
The purpose of this study was to identify the underlying structure of the trait domain of Conscientiousness using scales drawn from 7 major personality inventories. Thirty‐six scales conceptually ...related to Conscientiousness were administered to a large community sample (N= 737); analyses of those scales revealed a hierarchical structure with 6 factors: industriousness, order, self‐control, responsibility, traditionalism, and virtue. All 6 factors demonstrated excellent convergent validity. Three of the 6 factors, industriousness, order, and self‐control, showed good discriminant validity. The remaining 3 factors—responsibility, traditionalism and virtue—appear to be interstitial constructs located equally between Conscientiousness and the remaining Big Five dimensions. In addition, the 6 underlying factors had both differential predictive validity and provided incremental validity beyond the general factor of Conscientiousness when used to predict a variety of criterion variables, including work dedication, drug use, and health behaviors.
Two conceptual frameworks for the origin of the streaky pattern in near-wall developed turbulent flows are compared. According to the framework that dominated the research over several decades, the ...pattern of streaks is dictated by the pattern of wall-normal motions via the lift-up mechanism. Various concepts within this framework describe the wall-normal motions as induced by longitudinal vortices, hairpin vortices, vortex packets, etc. According to the newly emerging conceptual framework, the combined action of lift-up of the mean profile, mean shear, and viscous diffusion has its own pattern-forming properties. The pattern of streaks is dictated by these linear effects to a much greater extent than by the pattern of the wall-normal motions. Numerical results supporting the new conceptual framework are presented. An approximate approach for calculating the streak spacing within the new framework is proposed. It is shown to have a significant predictive ability.
The well-known background flow method for finding bounds for time-averaged characteristics of dynamical systems, proposed by Doering and Constantin (1994, 1995) is a special case of the auxiliary ...functional method of Chernyshenko et al. (2014). Chernyshenko (2022) proved that bounds obtained by the direct method described by Seis (2015) can be obtained also by the auxiliary functional method and, therefore, by the background flow method when the auxiliary functional is quadratic. This brief note outlines the technique by which the background flow and more generally the auxiliary functional can be obtained when a proof of a bound for infinite time average by the direct method is known, by applying this technique to the case of the bound on the Nusselt number for infinite-Prandtl-number Rayleigh–Bénard convection obtained by Otto and Seis (2011).
•Bound on Nusselt number for Rayleigh–Bénard convection is rederived.•Auxiliary functional and background flow for the bound are found.•Recent Otto and Seis approach reduced to background flow method.
Parkinson’s disease (PD) is a neurodegenerative pathology resulting from the degeneration of dopaminergic (DA) neurons in the substantia nigra (SN). Neurotrophic factors (NTFs) and their receptors ...are key regulators of the survival, differentiation, and development of neurons. However, the role of these factors in the pathogenesis of PD is still unclear. Here, we analyzed the expression of NTFs and their receptors in human induced pluripotent stem cells (iPSCs) derived from the fibroblasts of patients with PD and healthy donors (HDs). Four PD-derived iPSC lines with different mutations and three cell lines from HDs at different stages of neuronal differentiation were used for RT-qPCR analysis and ELISA. We found that the mRNA levels of most analyzed genes were altered in PD-derived cells compared with those in HD-derived cells at all stages. Importantly, irrespective of PD-associated mutations, the mRNA levels of the
BDNF
and
GDNF
genes were mostly increased or unchanged in predominantly DA terminally differentiated neurons (TDNs) compared with those in HD-derived cells. Strikingly, in contrast to BDNF and GDNF mRNA levels, BDNF and GDNF protein levels were lower in almost all PD-derived TDNs than in HD-derived cells, thus indicating the dysregulation of NTF expression at the post-transcriptional level. We suggest that this dysregulation is one of the important signs of PD development.
Linearized Navier–Stokes equations are solved to investigate the impact on the growth of near-wall turbulent streaks that arises from streamwise-travelling waves of spanwise wall velocity. The ...percentage change in streak amplification due to the travelling waves, over a range of wave parameters, is compared to published direct numerical simulation (DNS) predictions of turbulent skin-friction reduction; a clear correlation between the two is observed. Linearized simulations at a much higher Reynolds number, more relevant to aerospace applications, produce results that show no marked differences to those obtained at low Reynolds number. It is also observed that there is a close correlation between DNS data of drag reduction and a very simple characteristic of the ‘generalized’ Stokes layer generated by the streamwise-travelling waves.
With the goal of providing the first example of application of a recently proposed method, thus demonstrating its ability to give results in principle, global stability of a version of the rotating ...Couette flow is examined. The flow depends on the Reynolds number and a parameter characterizing the magnitude of the Coriolis force. By converting the original Navier-Stokes equations to a finite-dimensional uncertain dynamical system using a partial Galerkin expansion, high-degree polynomial Lyapunov functionals were found by sum-of-squares of polynomials optimization. It is demonstrated that the proposed method allows obtaining the exact global stability limit for this flow in a range of values of the parameter characterizing the Coriolis force. Outside this range a lower bound for the global stability limit was obtained, which is still better than the energy stability limit. In the course of the study, several results meaningful in the context of the method used were also obtained. Overall, the results obtained demonstrate the applicability of the recently proposed approach to global stability of the fluid flows. To the best of our knowledge, it is the first case in which global stability of a fluid flow has been proved by a generic method for the value of a Reynolds number greater than that which could be achieved with the energy stability approach.
This study seeks to enhance the distal-proximal modeling of personality trait–leader emergence relationships by (1) distinguishing between the motivation to lead (i.e., the reasons why a person seeks ...leadership roles) and leadership intention (i.e., one’s expressed desire to claim a leadership role) and by (2) examining how the Dark Triad traits add to the Big Five personality factors in predicting three motivation to lead factors and leadership intentions. Using personality and careers aspiration data collected from 750 university students, we found that affective-identity and social-normative motivation to lead mediate the effects of distal traits on intentions. In contrast, non-calculative motivation to lead does not contribute to leadership intentions, which has important implications for organizations seeking selfless leaders. Narcissism explains variance in leadership intentions over and above that explained by extraversion; this contrasts with the studies of leader emergence, where the effect of narcissism disappears once extraversion is controlled. Overall, our findings validate the three-factor conceptualization of motivation to lead and illuminate the roles of both bright and dark personality factors in understanding individual desire to attain leadership roles.
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