WEE1 Is a Biological Target of the miR-17-92 Cluster in Leukemia

MicroRNAs are noncoding RNAs that bind to the 3\u27 untranslated region of their mRNA targets, which causes downregulation of target gene expression. Previous studies have shown that the miR-17-92 cluster, which encodes six miRNAs, is overexpressed in leukemias arising from chromosomal translocations of the Mixed Lineage Leukemia (MLL) gene. In the present study, prediction algorithms identified WEE1, a kinase that inhibits cell cycle progression, as a possible target of five of the six miRNAs. Through luciferase reporter assays, we found that miR-17, miR-20a, and miR-18a specifically target nucleotides 465 to 487 of the 3\u27 UTR of WEE1, while miR-19a and miR-19b target nucleotides 1069 to 1091. Notably, while we did not detect a relationship between MLL rearrangement status and miR-17-92 expression in the leukemia cell lines tested, we observed a negative correlation between endogenous miR-17-92 and endogenous WEE1. These results suggest that WEE1 is a target of the miR-17-92 cluster

End-of-life disposal of libration point orbit spacecraft

In this work we investigate end-of-life trajectories for spacecraft in orbit about the Sun-Earth L 1 and L 2 libration points. A plan for decommission is often re- quired during the mission design process. We study the spacecraft's natural dynamics in both a high- delity model and the circular restricted three-body problem. In particular, we consider the role of the unstable manifold and forbidden regions in determin- ing disposal outcomes. A simple maneuver scheme to prevent returns to the Earth vicinity is also an- alyzed. We include discussion on potential collision orbit schemes.Postprint (published version

Dynamics of offset bearings: parametric studies

Novel "offset" designs offer greatly improved durability in applications fo

Computation of Quasi-Periodic Tori and Heteroclinic Connections in Astrodynamics Using Collocation Techniques

Many astrodynamical systems exhibit both ordered and chaotic motion. The invariant manifold structure organizes these behaviors and is a valuable tool for the design of spacecraft trajectories. The study of a system\u27s dynamics often begins with the computation of its invariant tori (equilibrium points, periodic orbits, quasi-periodic orbits) and associated stable and unstable manifolds. Periodic orbits, in particular, have been used effectively for the design of low-energy transfers in the circular restricted 3-body problem (CR3BP). Quasi-periodic orbits offer similar benefits and are often more prevalent in the phase space, but additional complexities are involved in their computation. The foundation of this work is the development of a numerical method for computing two-dimensional quasi-periodic tori. The approach is applicable to a general class of Hamiltonian systems. Using a Fourier discretization and Gauss-Legendre collocation, a continuous representation of the torus is obtained. Included in the scheme is the computation of the torus\u27s stable and unstable manifolds. These manifolds can then be used for the design of natural transfers. Two methods are presented for locating and continuing families of heteroclinic connections between quasi-periodic orbits in the CR3BP. A collocation-based approach for transitioning trajectories to a higher-fidelity ephemeris model is also included

Oral History Interview, Steven Olikara (1240)

In this interview, Steven Olikara outlines his leadership experiences he had as an undergraduate student and also discusses his relationship with his mentor and former UW Chancellor, Biddy Martin. To learn more about this oral history, download & review the index first (or transcript if available). It will help determine which audio file(s) to download & listen to.In his 2012 interview with Vicki Tobias, Steven Olikara details his leadership experiences as an undergraduate student at UW-Madison. Olikara describes initiatives in which he participated, as well as those that he spearheaded. He also focusses on his relationship with his mentor and former UW Chancellor, Biddy Martin

Computation of quasi-periodic tori in the circular restricted three-body problem

Quasi-periodic orbits lying on invariant tori in the circular restricted three-body problem offer a broad range of mission design possibilities, but their computation is more complex than that of periodic orbits. A preliminary framework for directly computing two-dimensional invariant tori is presented including a natural parameterization and a continuation scheme. The approach is based on a scheme designed for generic dynamical systems. Modifications are included to account for the special family structure in the circular restricted three-body problem. A discretized partial differential equation is solved along with constraint equations to compute members of the family and their associated frequencies. The continuation process is initialized from a linear estimate of a quasi-periodic torus. A regularization scheme is included for computing invariant tori that pass close to a primary body. A method to generate a quasi-periodic trajectory lying on the surface of the invariant torus is also presented. The numerical methodology is demonstrated by generating families of quasi-periodic tori with fixed Jacobi constant values that emanate from periodic orbits in the vicinity of the Earth-Moon libration points

Fully Numerical Methods for Continuing Families of Quasi-Periodic Invariant Tori in Astrodynamics

Quasi-periodic invariant tori are of great interest in astrodynamics because of their capability to further expand the design space of satellite missions. However, there is no general consent on what is the best methodology for computing these dynamical structures. This paper compares the performance of four different approaches available in the literature. The first two methods compute invariant tori of flows by solving a system of partial differential equations via either central differences or Fourier techniques. In contrast, the other two strategies calculate invariant curves of maps via shooting algorithms: one using surfaces of section, and one using a stroboscopic map. All of the numerical procedures are tested in the co-rotating frame of the Earth as well as in the planar circular restricted three-body problem. The results of our numerical simulations show which of the reviewed procedures should be preferred for future studies of astrodynamics systems