2,891 research outputs found
Amplitude Variations in Pulsating Yellow Supergiants
It was recently discovered that the amplitudes of pulsating red giants and
supergiants vary significantly on time scales of 20-30 pulsation periods. Here,
we analyze the amplitude variability in 29 pulsating yellow supergiants (5 RVa,
4 RVb, 9 SRd, 7 long-period Cepheid, and 4 yellow hypergiant stars), using
visual observations from the AAVSO International Database, and Fourier and
wavelet analysis using the AAVSO's VSTAR package. We find that these stars vary
in amplitude by factors of up to 10 or more (but more typically 3-5), on a mean
time scale (L) of 33 +/- 4 pulsation periods (P). Each of the five sub-types
shows this same behavior, which is very similar to that of the pulsating red
giants, for which the median L/P was 31. For the RVb stars, the lengths of the
cycles of amplitude variability are the same as the long secondary periods, to
within the uncertainty of each.Comment: To be submitted to JAAVS
Alien Registration- Davis, Percy R. (Presque Isle, Aroostook County)
https://digitalmaine.com/alien_docs/33493/thumbnail.jp
Kinematically redundant robot manipulators
Research on control, design and programming of kinematically redundant robot manipulators (KRRM) is discussed. These are devices in which there are more joint space degrees of freedom than are required to achieve every position and orientation of the end-effector necessary for a given task in a given workspace. The technological developments described here deal with: kinematic programming techniques for automatically generating joint-space trajectories to execute prescribed tasks; control of redundant manipulators to optimize dynamic criteria (e.g., applications of forces and moments at the end-effector that optimally distribute the loading of actuators); and design of KRRMs to optimize functionality in congested work environments or to achieve other goals unattainable with non-redundant manipulators. Kinematic programming techniques are discussed, which show that some pseudo-inverse techniques that have been proposed for redundant manipulator control fail to achieve the goals of avoiding kinematic singularities and also generating closed joint-space paths corresponding to close paths of the end effector in the workspace. The extended Jacobian is proposed as an alternative to pseudo-inverse techniques
Forty Years of Linking Variable Star Research with Education
In this review, I reflect on four decades of my experience in linking
astronomy research and education by supervising variable-star research projects
by undergraduates, and by outstanding senior high school students. I describe
the evolution of my experience, the students I have supervised, the nature of
their projects, the educational contexts of the projects, the need for "best
practices", the journals in which we publish, and the special role of the
American Association of Variable Star Observers (AAVSO). I then describe our
recent research on pulsating red giants and related objects, including three
astrophysical mysteries that we have uncovered. Finally, I suggest how my
projects might be scaled up or extended by others who supervise student
research.Comment: Submitted to the proceedings of the conference "Remote Telescopes,
Student Research, and Education
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