10,041 research outputs found
Orbits for eighteen visual binaries and two double-line spectroscopic binaries observed with HRCAM on the CTIO SOAR 4m telescope, using a new Bayesian orbit code based on Markov Chain Monte Carlo
We present orbital elements and mass sums for eighteen visual binary stars of
spectral types B to K (five of which are new orbits) with periods ranging from
20 to more than 500 yr. For two double-line spectroscopic binaries with no
previous orbits, the individual component masses, using combined astrometric
and radial velocity data, have a formal uncertainty of ~0.1 MSun. Adopting
published photometry, and trigonometric parallaxes, plus our own measurements,
we place these objects on an H-R diagram, and discuss their evolutionary
status. These objects are part of a survey to characterize the binary
population of stars in the Southern Hemisphere, using the SOAR 4m
telescope+HRCAM at CTIO. Orbital elements are computed using a newly developed
Markov Chain Monte Carlo algorithm that delivers maximum likelihood estimates
of the parameters, as well as posterior probability density functions that
allow us to evaluate the uncertainty of our derived parameters in a robust way.
For spectroscopic binaries, using our approach, it is possible to derive a
self-consistent parallax for the system from the combined astrometric plus
radial velocity data ("orbital parallax"), which compares well with the
trigonometric parallaxes. We also present a mathematical formalism that allows
a dimensionality reduction of the feature space from seven to three search
parameters (or from ten to seven dimensions - including parallax - in the case
of spectroscopic binaries with astrometric data), which makes it possible to
explore a smaller number of parameters in each case, improving the
computational efficiency of our Markov Chain Monte Carlo code.Comment: 32 pages, 9 figures, 6 tables. Detailed Appendix with methodology.
Accepted by The Astronomical Journa
Localization and the effects of symmetries in the thermalization properties of one-dimensional quantum systems
We study how the proximity to an integrable point or to localization as one
approaches the atomic limit, as well as the mixing of symmetries in the chaotic
domain, may affect the onset of thermalization in finite one-dimensional
systems. We consider systems of hard-core bosons at half-filling with nearest
neighbor hopping and interaction, and next-nearest neighbor interaction. The
latter breaks integrability and induces a ground-state superfluid to insulator
transition. By full exact diagonalization, we study chaos indicators and
few-body observables. We show that when different symmetry sectors are mixed,
chaos indicators associated with the eigenvectors, contrary to those related to
the eigenvalues, capture the onset of chaos. The results for the complexity of
the eigenvectors and for the expectation values of few-body observables confirm
the validity of the eigenstate thermalization hypothesis in the chaotic regime,
and therefore the occurrence of thermalization. We also study the properties of
the off-diagonal matrix elements of few-body observables in relation to the
transition from integrability to chaos and from chaos to localization.Comment: 12 pages, 13 figures, as published (Fig.09 was corrected in this
final version
Assessing Learning Outcomes in Middle-Division Classical Mechanics: The Colorado Classical Mechanics/Math Methods Instrument
Reliable and validated assessments of introductory physics have been
instrumental in driving curricular and pedagogical reforms that lead to
improved student learning. As part of an effort to systematically improve our
sophomore-level Classical Mechanics and Math Methods course (CM 1) at CU
Boulder, we have developed a tool to assess student learning of CM 1 concepts
in the upper-division. The Colorado Classical Mechanics/Math Methods Instrument
(CCMI) builds on faculty consensus learning goals and systematic observations
of student difficulties. The result is a 9-question open-ended post-test that
probes student learning in the first half of a two-semester classical mechanics
/ math methods sequence. In this paper, we describe the design and development
of this instrument, its validation, and measurements made in classes at CU
Boulder and elsewhere.Comment: 11 pages, 6 figures, 1 tabl
Two-dimensional Lattice Gauge Theories with Superconducting Quantum Circuits
A quantum simulator of U(1) lattice gauge theories can be implemented with
superconducting circuits. This allows the investigation of confined and
deconfined phases in quantum link models, and of valence bond solid and spin
liquid phases in quantum dimer models. Fractionalized confining strings and the
real-time dynamics of quantum phase transitions are accessible as well. Here we
show how state-of-the-art superconducting technology allows us to simulate
these phenomena in relatively small circuit lattices. By exploiting the strong
non-linear couplings between quantized excitations emerging when
superconducting qubits are coupled, we show how to engineer gauge invariant
Hamiltonians, including ring-exchange and four-body Ising interactions. We
demonstrate that, despite decoherence and disorder effects, minimal circuit
instances allow us to investigate properties such as the dynamics of electric
flux strings, signaling confinement in gauge invariant field theories. The
experimental realization of these models in larger superconducting circuits
could address open questions beyond current computational capability.Comment: Published versio
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