243 research outputs found
Guarding a Non-Maneuverable Translating Line with an Attached Defender
In this paper we consider a target-guarding differential game where the
defender must protect a linearly translating line-segment by intercepting an
attacker who tries to reach it. In contrast to common target-guarding problems,
we assume that the defender is attached to the target and moves along with it.
This assumption affects the defenders' maximum speed in inertial frame, which
depends on the target's direction of motion. Zero-sum differential game of
degree for both the attacker-win and defender-win scenarios are studied, where
the payoff is defined to be the distance between the two agents at the time of
game termination. We derive the equilibrium strategies and the Value function
by leveraging the solution for the infinite-length target scenario. The
zero-level set of this Value function provides the barrier surface that divides
the state space into defender-win and attacker-win regions. We present
simulation results to demonstrate the theoretical results.Comment: 8 pages, 8 figures. arXiv admin note: text overlap with
arXiv:2207.0409
Output Feedback Adaptive Optimal Control of Affine Nonlinear systems with a Linear Measurement Model
Real-world control applications in complex and uncertain environments require
adaptability to handle model uncertainties and robustness against disturbances.
This paper presents an online, output-feedback, critic-only, model-based
reinforcement learning architecture that simultaneously learns and implements
an optimal controller while maintaining stability during the learning phase.
Using multiplier matrices, a convenient way to search for observer gains is
designed along with a controller that learns from simulated experience to
ensure stability and convergence of trajectories of the closed-loop system to a
neighborhood of the origin. Local uniform ultimate boundedness of the
trajectories is established using a Lyapunov-based analysis and demonstrated
through simulation results, under mild excitation conditions.Comment: 16 pages, 5 figures, submitted to 2023 IEEE Conference on Control
Technology and Application
The McDonald Observatory search for pulsating sdA stars : asteroseismic support for multiple populations
Context. The nature of the recently identified “sdA” spectroscopic class of stars is not well understood. The thousands of known sdAs have H-dominated spectra, spectroscopic surface gravity values between main sequence stars and isolated white dwarfs, and effective temperatures below the lower limit for He-burning subdwarfs. Most are likely products of binary stellar evolution, whether extremely low-mass white dwarfs and their precursors or blue stragglers in the halo. Aims. Stellar eigenfrequencies revealed through time series photometry of pulsating stars sensitively probe stellar structural properties. The properties of pulsations exhibited by sdA stars would contribute substantially to our developing understanding of this class. Methods. We extend our photometric campaign to discover pulsating extremely low-mass white dwarfs from the McDonald Observatory to target sdA stars classified from SDSS spectra. We also obtain follow-up time series spectroscopy to search for binary signatures from four new pulsators. Results. Out of 23 sdA stars observed, we clearly detect stellar pulsations in 7. Dominant pulsation periods range from 4.6 min to 12.3 h, with most on timescales of approximately one hour. We argue specific classifications for some of the new variables, identifying both compact and likely main sequence dwarf pulsators, along with a candidate low-mass RR Lyrae star. Conclusions. With dominant pulsation periods spanning orders of magnitude, the pulsational evidence supports the emerging narrative that the sdA class consists of multiple stellar populations. Since multiple types of sdA exhibit stellar pulsations, follow-up asteroseismic analysis can be used to probe the precise evolutionary natures and stellar structures of these individual subpopulations
Spin and Rotations in Galois Field Quantum Mechanics
We discuss the properties of Galois Field Quantum Mechanics constructed on a
vector space over the finite Galois field GF(q). In particular, we look at
2-level systems analogous to spin, and discuss how SO(3) rotations could be
embodied in such a system. We also consider two-particle `spin' correlations
and show that the Clauser-Horne-Shimony-Holt (CHSH) inequality is nonetheless
not violated in this model.Comment: 21 pages, 11 pdf figures, LaTeX. Uses iopart.cls. Revised
introduction. Additional reference
I Spy Transits and Pulsations: Empirical Variability in White Dwarfs Using Gaia and the Zwicky Transient Facility
We present a novel method to detect variable astrophysical objects and
transient phenomena using anomalous excess scatter in repeated measurements
from public catalogs of Gaia DR2 and Zwicky Transient Facility (ZTF) DR3
photometry. We first provide a generalized, all-sky proxy for variability using
only Gaia DR2 photometry, calibrated to white dwarf stars. To ensure more
robust candidate detection, we further employ a method combining Gaia with ZTF
photometry and alerts. To demonstrate the efficacy, we apply this latter
technique to a sample of roughly white dwarfs within 200 pc centered
on the ZZ Ceti instability strip, where hydrogen-atmosphere white dwarfs are
known to pulsate. Through inspecting the top samples ranked by these
methods, we demonstrate that both the Gaia-only and ZTF-informed techniques are
highly effective at identifying known and new variable white dwarfs, which we
verify using follow-up, high-speed photometry. We confirm variability in all 33
out of 33 () observed white dwarfs within our top highest-ranked
candidates, both inside and outside the ZZ Ceti instability strip. In addition
to dozens of new pulsating white dwarfs, we also identify five white dwarfs
highly likely to show transiting planetary debris; if confirmed, these systems
would more than triple the number of white dwarfs known to host transiting
debris.Comment: 30 pages, 14 figures, revised and accepted to ApJ on March 11, 202
Genomic, Pathway Network, and Immunologic Features Distinguishing Squamous Carcinomas
This integrated, multiplatform PanCancer Atlas study co-mapped and identified distinguishing
molecular features of squamous cell carcinomas (SCCs) from five sites associated with smokin
Pan-Cancer Analysis of lncRNA Regulation Supports Their Targeting of Cancer Genes in Each Tumor Context
Long noncoding RNAs (lncRNAs) are commonly dys-regulated in tumors, but only a handful are known toplay pathophysiological roles in cancer. We inferredlncRNAs that dysregulate cancer pathways, onco-genes, and tumor suppressors (cancer genes) bymodeling their effects on the activity of transcriptionfactors, RNA-binding proteins, and microRNAs in5,185 TCGA tumors and 1,019 ENCODE assays.Our predictions included hundreds of candidateonco- and tumor-suppressor lncRNAs (cancerlncRNAs) whose somatic alterations account for thedysregulation of dozens of cancer genes and path-ways in each of 14 tumor contexts. To demonstrateproof of concept, we showed that perturbations tar-geting OIP5-AS1 (an inferred tumor suppressor) andTUG1 and WT1-AS (inferred onco-lncRNAs) dysre-gulated cancer genes and altered proliferation ofbreast and gynecologic cancer cells. Our analysis in-dicates that, although most lncRNAs are dysregu-lated in a tumor-specific manner, some, includingOIP5-AS1, TUG1, NEAT1, MEG3, and TSIX, synergis-tically dysregulate cancer pathways in multiple tumorcontexts
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