5,008 research outputs found
Radio Frequency Interference Mitigation
Radio astronomy observational facilities are under constant upgradation and
development to achieve better capabilities including increasing the time and
frequency resolutions of the recorded data, and increasing the receiving and
recording bandwidth. As only a limited spectrum resource has been allocated to
radio astronomy by the International Telecommunication Union, this results in
the radio observational instrumentation being inevitably exposed to undesirable
radio frequency interference (RFI) signals which originate mainly from
terrestrial human activity and are becoming stronger with time. RFIs degrade
the quality of astronomical data and even lead to data loss. The impact of RFIs
on scientific outcome is becoming progressively difficult to manage. In this
article, we motivate the requirement for RFI mitigation, and review the RFI
characteristics, mitigation techniques and strategies. Mitigation strategies
adopted at some representative observatories, telescopes and arrays are also
introduced. We also discuss and present advantages and shortcomings of the four
classes of RFI mitigation strategies, applicable at the connected causal
stages: preventive, pre-detection, pre-correlation and post-correlation. The
proper identification and flagging of RFI is key to the reduction of data loss
and improvement in data quality, and is also the ultimate goal of developing
RFI mitigation techniques. This can be achieved through a strategy involving a
combination of the discussed techniques in stages. Recent advances in high
speed digital signal processing and high performance computing allow for
performing RFI excision of large data volumes generated from large telescopes
or arrays in both real time and offline modes, aiding the proposed strategy.Comment: 26 pages, 10 figures, Chinese version accepted for publication in
Acta Astronomica Sinica; English version to appear in Chinese Astronomy and
Astrophysic
Stability of braneworlds with non-minimally coupled multi-scalar fields
Linear stability of braneworld models constructed with multi-scalar fields is
very different from that of single-scalar field models. It is well known that
both the tensor and scalar perturbation equations of the later can always be
written as a supersymmetric Schr\"{o}dinger equation, so it can be shown that
the perturbations are stable at linear level. However, in general it is not
true for multi-scalar field models and especially there is no effective method
to deal with the stability problem of the scalar perturbations for braneworld
models constructed with non-minimally coupled multi-scalar fields. In this
paper we present a method to investigate the stability of such braneworld
models. It is easy to find that the tensor perturbations are stable. For the
stability problem of the scalar perturbations, we present a systematic
covariant approach. The covariant quadratic order action and the corresponding
first-order perturbed equations are derived. By introducing the orthonormal
bases in field space and making the Kaluza-Klein decomposition, we show that
the Kaluza-Klein modes of the scalar perturbations satisfy a set of coupled
Schr\"{o}dinger-like equations, with which the stability of the scalar
perturbations and localization of the scalar zero modes can be analyzed
according to nodal theorem. The result depends on the explicit models. For
superpotential derived barane models, the scalar perturbations are stable, but
there exist normalizable scalar zero modes, which will result in unaccepted
fifth force on the brane. We also use this method to analyze the
braneworld model with an explicit solution and find that the scalar
perturbations are stable and the scalar zero modes can not be localized on the
brane, which ensure that there is no extra long-range force and the Newtonian
potential on the brane can be recovered.Comment: 13 pages, 3 figure
Study on the mechanism of open-flavor strong decays
The open-flavor strong decays are studied based on the interaction of
potential quark model. The decay process is related to the s-channel
contribution of the same scalar confinment and one-gluon-exchange(OGE)
interaction in the quark model. After we adopt the prescription of massive
gluons in time-like region from the lattice calculation, the approximation of
four-fermion interaction is applied. The numerical calculation is performed to
the meson decays in , , light flavor sector. The analysis of the
ratios of and show
that the scalar interaction should be dominant in the open-flavor decays
Lamb wave signal retrieval by wavelet ridge
Lamb wave testing is one of the important methods in ultrasonic nondestructive testing. One of the key technologies in the Lamb wave testing is to get a clear signal. In this paper, a signal retrieval method for the Lamb wave signal from noisy signals is presented on the basis of its wavelet ridge analysis. After the wavelet transformation, the wavelet ridge of the Lamb wave signal is extracted and the signal is reconstructed by using its ridge as the characteristic parameter. Experimental results show that the Lamb wave signal is retrieved in the case of the white noise, the transient noise and the sine noise. The proposed method can retrieve the ultrasonic Lamb wave signal effectively
Waiting, Banning, and Embracing: An Empirical Analysis of Adapting Policies for Generative AI in Higher Education
Generative AI tools such as ChatGPT have recently gained significant
attention in higher education. This study aims to understand how universities
establish policies regarding the use of AI tools and explore the factors that
influence their decisions. Our study examines ChatGPT policies implemented at
universities around the world, including their existence, content, and issuance
dates. Specifically, we analyzed the top 500 universities according to the 2022
QS World University Rankings. Our findings indicate that there is significant
variation in university policies. Less than one-third of the universities
included in the study had implemented ChatGPT policies. Of the universities
with ChatGPT policies, approximately 67 percent embraced ChatGPT in teaching
and learning, more than twice the number of universities that banned it. The
majority of the universities that ban the use of ChatGPT in assessments allow
individual instructors to deviate from this restrictive policy. Our empirical
analysis identifies several factors that are significantly and positively
correlated with a university's likelihood of having a ChatGPT policy, including
the university's academic reputation score, being in an English-speaking
country, and the general public attitudes toward ChatGPT. In addition, we found
that a university's likelihood of having a ban policy is positively associated
with faculty student ratio, citations, and the English-speaking country dummy,
while negatively associated with the number of peer universities within the
same country that have banned ChatGPT. We discuss the challenges faced by
universities based our empirical findings.Comment: 33 pages with 2 figure
Probing nuclear symmetry energy at high densities using pion, kaon, eta and photon productions in heavy-ion collisions
The high-density behavior of nuclear symmetry energy is among the most
uncertain properties of dense neutron-rich matter. Its accurate determination
has significant ramifications in understanding not only the reaction dynamics
of heavy-ion reactions especially those induced by radioactive beams but also
many interesting phenomena in astrophysics, such as the explosion mechanism of
supernova and the properties of neutron stars. The heavy-ion physics community
has devoted much effort during the last few years to constrain the high-density
symmetry using various probes. In particular, the pion-/pion+ ratio has been
most extensively studied both theoretically and experimentally. All models have
consistently predicted qualitatively that the pion-/pion+ ratio is a sensitive
probe of the high-density symmetry energy especially with beam energies near
the pion production threshold. However, the predicted values of the pion-/pion+
ratio are still quite model dependent mostly because of the complexity of
modeling pion production and reabsorption dynamics in heavy-ion collisions,
leading to currently still controversial conclusions regarding the high-density
behavior of nuclear symmetry energy from comparing various model calculations
with available experimental data. As more pion-/pion+ data become available and
a deeper understanding about the pion dynamics in heavy-ion reactions is
obtained, more penetrating probes, such as the kaon+/kaon0 ratio, eta meson and
high energy photons are also being investigated or planned at several
facilities. Here, we review some of our recent contributions to the community
effort of constraining the high-density behavior of nuclear symmetry energy in
heavy-ion collisions. In addition, the status of some worldwide experiments for
studying the high-density symmetry energy, including the HIRFL-CSR external
target experiment (CEE) are briefly introduced.Comment: 10 pages, 10 figures, Contribution to the Topical Issue on Nuclear
Symmetry Energy in EPJA Special Volum
Deterministic and Efficient Quantum Cryptography Based on Bell's Theorem
We propose a novel double-entanglement-based quantum cryptography protocol
that is both efficient and deterministic. The proposal uses photon pairs with
entanglement both in polarization and in time degrees of freedom; each
measurement in which both of the two communicating parties register a photon
can establish one and only one perfect correlation and thus deterministically
create a key bit. Eavesdropping can be detected by violation of local realism.
A variation of the protocol shows a higher security, similarly to the six-state
protocol, under individual attacks. Our scheme allows a robust implementation
under current technology.Comment: 4 pages, 1 figure; published version with a note adde
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