Investigation of the Finite Element Software Packages at KSC

The useful and powerful features of NASTRAN and three real world problems for the testing of the capabilities of different NASTRAN versions are discussed. The test problems involve direct transient analysis, nonlinear analysis, and static analysis. The experiences in using graphics software packages are also discussed. It was found that MSC/XL can be more useful if it can be improved to generate picture files of the analysis results and to extend its capabilities to support finite element codes other than MSC/NASTRAN. It was found that the current version of SDRC/I-DEAS (version VI) may have bugs in the module 'Data Loader'

Quantum percolation in quantum spin Hall antidot systems

We study the influences of antidot-induced bound states on transport properties of two- dimensional quantum spin Hall insulators. The bound statesare found able to induce quantum percolation in the originally insulating bulk. At some critical antidot densities, the quantum spin Hall phase can be completely destroyed due to the maximum quantum percolation. For systems with periodic boundaries, the maximum quantum percolationbetween the bound states creates intermediate extended states in the bulk which is originally gapped and insulating. The antidot in- duced bound states plays the same role as the magnetic field inthe quantum Hall effect, both makes electrons go into cyclotron motions. We also draw an analogy between the quantum percolation phenomena in this system and that in the network models of quantum Hall effect

Deflections of anisotropic sandwich beams with variable face sheets and core thicknesses

A sandwich construction consists of a low-density core material with high strength face sheets bounded to the top and bottom surfaces. The construction has been widely used in the aerospace and marine industries due to its outstanding characteristics such as noise absorption, weight minimization, heat insulation, and better bending stiffness. In sandwich structures used in high-performance aircraft, the face sheets are often made of fiber-reinforced composite materials and the core is made of honeycomb. The structures may also have variable thickness so as to satisfy aerodynamic requirements. In the stress analysis, the constant-thickness face sheets are usually considered as membrane and the core is assumed to be inextensible but deformable in the thickness direction. The static behavior of variable-thickness, isotropic and homogeneous sandwich beams was successfully studied by employing a constant-thickness theory but allowing stiffnesses to vary in accordance with local thickness variations. It has been recently found in a refined theory that the analyses based on the constant thickness theory locally can lead to significant errors in structural responses if the sandwich beam is thickness-tapered and the cores are deformable in transverse shear. The errors arise mainly from two factors: (1) the transverse shear components of the membrane forces in the face sheets alter the transverse shears carried by the core; and (2) the face-sheet membrane strains arise from transverse shear deformation of the core. In practice the variable thickness may not only exist in core but also in face sheets. The thickness-variations may even be a type of step function. In this case the transverse shear stress in the face sheets and bending stress in the core should be taken into account in the refined theory mentioned. In the present study, energy principles are employed in deriving governing equations for general bending of anisotropic sandwich beams with variable thickness in both face sheets and cores. Solutions to these equations are based on a finite difference scheme. As an example in application, a simply supported thickness-tapered sandwich beam subject to a concentrated load at its center is considered. Let W' be the maximum deflection of the beam in which face sheets are considered as membrane, while W'' is that based on using the modified refined theory. It is found that W' is always larger than W'', however, the magnitude of (W'- W'') appears to be insensitive to the change of the taper of the beam

The Relationships Between Adolescents’ Future Aspirations and Postsecondary Enrollment: Finite Mixture Models

This study took person-centered statistical approaches to explore the multidimensional construct of adolescents\u27 future aspirations and its associations with three covariates (i.e., gender, race, and SES) and a binary, distal outcome measure, postsecondary enrollment. Fourteen survey items representing the multidimensionality of adolescents\u27 future aspirations were extracted from two-waves of Educational Longitudinal Study:2002 student data. The multidimensionality or the latent construct of the adolescents\u27 future aspirations were explored using two finite mixture models called latent class analysis (LCA) and latent transition analysis (LTA). Based on the students\u27 response patterns on the fourteen indicators, three latent classes representing three levels of aspiration emerged and were identified as High Aspiration (HA), Moderate Aspiration (MA), and Low Aspiration (LA) classes. Based on the LCA results, the likelihood to attend colleges was significantly higher for students classified into either the HA or MA classes than students in the LA class. Students\u27 SES was found to be statistically significantly associated with the class assignment postsecondary enrollment. In other words, parents\u27 higher income and higher educational attainment statistically improved the odds of postsecondary enrollment for students in all three aspirations classes. Furthermore, the LTA results found many students either became more ambitious or less ambitious as they started their senior year in high school. The students who changed their aspiration class were referred to as movers, and students who remained in the same aspiration class were the stayers. The likelihood of enrolling in a postsecondary institution was significantly decreased for students who changed their aspiration classes from time 1 to time 2. The changes in how some adolescents aspired about their future might be due to the impact of their family socioeconomic statuses or personal burnout. For future studies, school personnel, policymakers, and educators should investigate the associations between higher education and adolescents\u27 academic and non-academic aspirations and investigate the causes of changes in adolescents\u27 aspirations. Given the importance of college completion for future income and well-being, this study provided an ecological overview of how different social factors (e.g., school, family, community, personal, and peers) shaped adolescents\u27 attitudes about their future, including their impact on their higher educational attainment

Study of the available finite element software packages at KSC

The interaction among the three finite element software packages, SDRCI/I-DEAS, MSC/NASTRAN, and I/FEM, used at NASA, Kennedy Space Center is addressed. The procedures for using more than one of these application software packages to model and analyze a structure design are discussed. Design and stress analysis of a solid rocket booster fixture is illustrated by using four different combinations of the three software packages. Their results are compared and show small yet acceptable differences

Response of hydrological cycle to tiny random sea surface temperature disturbances

Thirteenth Conference on Hydrology, American Meteorological Society, J45-J4

Surface and Edge States in Topological Semi-metals

We study the topologically non-trivial semi-metals by means of the 6-band Kane model. Existence of surface states is explicitly demonstrated by calculating the LDOS on the material surface. In the strain free condition, surface states are divided into two parts in the energy spectrum, one part is in the direct gap, the other part including the crossing point of surface state Dirac cone is submerged in the valence band. We also show how uni-axial strain induces an insulating band gap and raises the crossing point from the valence band into the band gap, making the system a true topological insulator. We predict existence of helical edge states and spin Hall effect in the thin film topological semi-metals, which could be tested with future experiment. Disorder is found to significantly enhance the spin Hall effect in the valence band of the thin films