49 research outputs found
An Algebraic Method to Fidelity-based Model Checking over Quantum Markov Chains
Fidelity is one of the most widely used quantities in quantum information
that measure the distance of quantum states through a noisy channel. In this
paper, we introduce a quantum analogy of computation tree logic (CTL) called
QCTL, which concerns fidelity instead of probability in probabilistic CTL, over
quantum Markov chains (QMCs). Noisy channels are modelled by super-operators,
which are specified by QCTL formulas; the initial quantum states are modelled
by density operators, which are left parametric in the given QMC. The problem
is to compute the minimumfidelity over all initial states for conservation. We
achieve it by a reduction to quantifier elimination in the existential theory
of the reals. The method is absolutely exact, so that QCTL formulas are proven
to be decidable in exponential time. Finally, we implement the proposed method
and demonstrate its effectiveness via a quantum IPv4 protocol
A Sample-Driven Solving Procedure for the Repeated Reachability of Quantum CTMCs
Reachability analysis plays a central role in system design and verification.
The reachability problem, denoted , asks whether the system
will meet the property after some time in a given time interval .
Recently, it has been considered on a novel kind of real-time systems --
quantum continuous-time Markov chains (QCTMCs), and embedded into the
model-checking algorithm. In this paper, we further study the repeated
reachability problem in QCTMCs, denoted , which
concerns whether the system starting from each \emph{absolute} time in will
meet the property after some coming \emph{relative} time in . First
of all, we reduce it to the real root isolation of a class of real-valued
functions (exponential polynomials), whose solvability is conditional to
Schanuel's conjecture being true. To speed up the procedure, we employ the
strategy of sampling. The original problem is shown to be equivalent to the
existence of a finite collection of satisfying samples. We then present a
sample-driven procedure, which can effectively refine the sample space after
each time of sampling, no matter whether the sample itself is successful or
conflicting. The improvement on efficiency is validated by randomly generated
instances. Hence the proposed method would be promising to attack the repeated
reachability problems together with checking other -regular properties
in a wide scope of real-time systems
Calibration of Time-Series Forecasting Transformers: Detecting and Adapting Context-Driven Distribution Shift
Recent years have witnessed the success of introducing Transformers to time
series forecasting. From a data generation perspective, we illustrate that
existing Transformers are susceptible to distribution shifts driven by temporal
contexts, whether observed or unobserved. Such context-driven distribution
shift (CDS) introduces biases in predictions within specific contexts and poses
challenges for conventional training paradigm. In this paper, we introduce a
universal calibration methodology for the detection and adaptation of CDS with
a trained Transformer model. To this end, we propose a novel CDS detector,
termed the "residual-based CDS detector" or "Reconditionor", which quantifies
the model's vulnerability to CDS by evaluating the mutual information between
prediction residuals and their corresponding contexts. A high Reconditionor
score indicates a severe susceptibility, thereby necessitating model
adaptation. In this circumstance, we put forth a straightforward yet potent
adapter framework for model calibration, termed the "sample-level
contextualized adapter" or "SOLID". This framework involves the curation of a
contextually similar dataset to the provided test sample and the subsequent
fine-tuning of the model's prediction layer with a limited number of steps. Our
theoretical analysis demonstrates that this adaptation strategy is able to
achieve an optimal equilibrium between bias and variance. Notably, our proposed
Reconditionor and SOLID are model-agnostic and readily adaptable to a wide
range of Transformers. Extensive experiments show that SOLID consistently
enhances the performance of current SOTA Transformers on real-world datasets,
especially on cases with substantial CDS detected by the proposed
Reconditionor, thus validate the effectiveness of the calibration approach
Insight-HXMT observations of Swift J0243.6+6124 during its 2017-2018 outburst
The recently discovered neutron star transient Swift J0243.6+6124 has been
monitored by {\it the Hard X-ray Modulation Telescope} ({\it Insight-\rm HXMT).
Based on the obtained data, we investigate the broadband spectrum of the source
throughout the outburst. We estimate the broadband flux of the source and
search for possible cyclotron line in the broadband spectrum. No evidence of
line-like features is, however, found up to . In the absence of
any cyclotron line in its energy spectrum, we estimate the magnetic field of
the source based on the observed spin evolution of the neutron star by applying
two accretion torque models. In both cases, we get consistent results with
, and peak luminosity of which makes the source the first Galactic ultraluminous
X-ray source hosting a neutron star.Comment: publishe
Overview to the Hard X-ray Modulation Telescope (Insight-HXMT) Satellite
As China's first X-ray astronomical satellite, the Hard X-ray Modulation
Telescope (HXMT), which was dubbed as Insight-HXMT after the launch on June 15,
2017, is a wide-band (1-250 keV) slat-collimator-based X-ray astronomy
satellite with the capability of all-sky monitoring in 0.2-3 MeV. It was
designed to perform pointing, scanning and gamma-ray burst (GRB) observations
and, based on the Direct Demodulation Method (DDM), the image of the scanned
sky region can be reconstructed. Here we give an overview of the mission and
its progresses, including payload, core sciences, ground calibration/facility,
ground segment, data archive, software, in-orbit performance, calibration,
background model, observations and some preliminary results.Comment: 29 pages, 40 figures, 6 tables, to appear in Sci. China-Phys. Mech.
Astron. arXiv admin note: text overlap with arXiv:1910.0443