4,072 research outputs found
Near-infrared Variability among YSOs in the Star Formation Region Cygnus OB7
We present an analysis of near-infrared time-series photometry in J, H, and K
bands for about 100 epochs of a 1 square degree region of the Lynds 1003/1004
dark cloud in the Cygnus OB7 region. Augmented by data from the Wide-field
Infrared Survey Explorer (WISE), we identify 96 candidate disk bearing young
stellar objects (YSOs) in the region. Of these, 30 are clearly Class I or
earlier. Using the Wide-Field imaging CAMera (WFCAM) on the United Kingdom
InfraRed Telescope (UKIRT), we were able to obtain photometry over three
observing seasons, with photometric uncertainty better than 0.05 mag down to J
~17. We study detailed light curves and color trajectories of ~50 of the YSOs
in the monitored field. We investigate the variability and periodicity of the
YSOs and find the data are consistent with all YSOs being variable in these
wavelengths on time scales of a few years. We divide the variability into four
observational classes: 1) stars with periodic variability stable over long
timescales, 2) variables which exhibit short-lived cyclic behavior, 3) long
duration variables, and 4) stochastic variables. Some YSO variability defies
simple classification. We can explain much of the observed variability as being
due to dynamic and rotational changes in the disk, including an asymmetric or
changing blocking fraction, changes to the inner disk hole size, as well as
changes to the accretion rate. Overall, we find that the Class I:Class II ratio
of the cluster is consistent with an age of < 1Myr, with at least one
individual, wildly varying, source ~ 100,000 yr old. We have also discovered a
Class II eclipsing binary system with a period of 17.87 days.Comment: ApJ accepted: 44 pages includes 5 tables and 16 figures. Some figures
condensed for Astro/p
Non-thermal quantum engine in transmon qubits
The design and implementation of quantum technologies necessitates the
understanding of thermodynamic processes in the quantum domain. In stark
contrast to macroscopic thermodynamics, at the quantum scale processes
generically operate far from equilibrium and are governed by fluctuations.
Thus, experimental insight and empirical findings are indispensable in
developing a comprehensive framework. To this end, we theoretically propose an
experimentally realistic quantum engine that uses transmon qubits as working
substance. We solve the dynamics analytically and calculate its efficiency
Dissipation assisted Thouless pumping in the Rice-Mele model
We investigate the effect of dissipation from a thermal environment on
topological pumping in the periodically-driven Rice-Mele model. We report that
dissipation can improve the robustness of pumping quantisation in a regime of
finite driving frequencies. Specifically, in this regime, a low-temperature
dissipative dynamics can lead to a pumped charge that is much closer to the
Thouless quantised value, compared to a coherent evolution. We understand this
effect in the Floquet framework: dissipation increases the population of a
Floquet band which shows a topological winding, where pumping is essentially
quantised. This finding is a step towards understanding a potentially very
useful resource to exploit in experiments, where dissipation effects are
unavoidable. We consider small couplings with the environment and we use a
Bloch-Redfield quantum master equation approach for our numerics: Comparing
these results with an exact MPS numerical treatment we find that the quantum
master equation works very well also at low temperature, a quite remarkable
fact.Comment: 21 pages, 8 figure
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