1,649 research outputs found
Topological Strings and Quantum Spectral Problems
We consider certain quantum spectral problems appearing in the study of local
Calabi-Yau geometries. The quantum spectrum can be computed by the
Bohr-Sommerfeld quantization condition for a period integral. For the case of
small Planck constant, the periods are computed perturbatively by deformation
of the Omega background parameters in the Nekrasov-Shatashvili limit. We
compare the calculations with the results from the standard perturbation theory
for the quantum Hamiltonian. There have been proposals in the literature for
the non-perturbative contributions based on singularity cancellation with the
perturbative contributions. We compute the quantum spectrum numerically with
some high precisions for many cases of Planck constant. We find that there are
also some higher order non-singular non-perturbative contributions, which are
not captured by the singularity cancellation mechanism. We fix the first few
orders formulas of such corrections for some well known local Calabi-Yau
models.Comment: 47 pages, 3 figures. v2: journal version, typos correcte
What can be learnt from a highly informative X-ray occultation event in NGC 6814? A marvellous absorber
A unique X-ray occultation event in NGC 6814 during an XMM-Newton observation
in 2016 has been reported, providing useful information of the absorber and the
corona. We revisit the event with the aid of the hardness ratio (HR) - count
rate (CR) plot and comparison with two other absorption-free XMM exposures in
2009 and 2021. NGC 6814 exhibits a clear "softer-when-brighter" variation
pattern during the exposures, but the 2016 exposure significantly deviates from
the other two in the HR - CR plot. While spectral fitting does yield transient
Compton-thin absorption corresponding to the eclipse event in 2016, rather than
easing the tension between exposures in the HR - CR plot, correcting the
transient Compton-thin absorption results in new and severe deviation within
the 2016 exposure. We show that the eclipsing absorber shall be clumpy (instead
of a single Compton-thin cloud), with an inner denser region composed of both
Compton-thin and Compton-thick clouds responsible for the previously identified
occultation event, and an outer sparser region with Compton-thin clouds which
eclipses the whole 2016 exposure. With this model, all the tension in the HR -
CR plots could be naturally erased, with the observed spectral variability
during the 2016 exposure dominated by the variation of absorption. Furthermore,
the two warm absorbers (with different ionization and column densities but
similar outflowing velocities) detected in the 2016 exposure shall also
associate with the transient absorber, likely due to ablated or tidal
stretched/disrupted fragments. This work highlights the unique usefulness of
the HR - CR plot while analysing rare occultation events.Comment: 13 pages, 9 figures, accepted by MNRAS. For the video of the
eclipsing cloud, see
https://drive.google.com/file/d/1CEsPEWE-b5W8PfZINyI5K1sE6klHaYMa/view?usp=sharing
. Comments are welcome
Device modeling of superconductor transition edge sensors based on the two-fluid theory
In order to support the design and study of sophisticated large scale
transition edge sensor (TES) circuits, we use basic SPICE elements to develop
device models for TESs based on the superfluid-normal fluid theory. In contrast
to previous studies, our device model is not limited to small signal
simulation, and it relies only on device parameters that have clear physical
meaning and can be easily measured. We integrate the device models in design
kits based on powerful EDA tools such as CADENCE and OrCAD, and use them for
versatile simulations of TES circuits. Comparing our simulation results with
published experimental data, we find good agreement which suggests that device
models based on the two-fluid theory can be used to predict the behavior of TES
circuits reliably and hence they are valuable for assisting the design of
sophisticated TES circuits.Comment: 10pages,11figures. Accepted to IEEE Trans. Appl. Supercon
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