2,208 research outputs found
Does the non-force-freeness matter for the extrapolation of solar magnetic field?
Magnetic field extrapolation is a fundamental tool to reconstruct the
three-dimensional solar coronal magnetic field. However, the prevalently used
force-free field model might not be applicable in the lower atmosphere, where
plasma \b{eta} is greater than 1. In this work, we perform extrapolation in
active region 12158, based on an updated magnetohydrostatic (MHS) method. By
comparing the results with those from the force-free field method of
Current-Field Iteration in Spherical Coordinates (CFITS), we find that the
overall properties, which are characterized by the magnetic free energy and
helicity, are roughly the same after volume integral. The major differences lie
in the magnetic configuration and the twist number of magnetic flux rope (MFR).
A coherent MFR with twist around 1 is reproduced from CFITS. In another manner,
two sets of MFR, which are highly twisted and slightly coupled, are derived by
the MHS method. The latter one is better constrained by the high-resolution
observations, such as the filament fibrils, pre-eruptive braiding
characteristics and the eruptive double-J shaped hot channel. Overall, our work
shows the MHS method is more promising to reproduce the magnetic fine
structures that can well match the observations not only in the chromosphere
but also in the corona. This initiates the necessity of reconsidering the
simplification of low atmosphere for currently widely used nonlinear force-free
extrapolation method, since such assumption will not only omit the magnetic
structures at low atmosphere but also affect those obtained in the corona, and
therefore bringing in ambiguity in interpreting the solar eruption.Comment: 19 pages, 6 figures, accepted by Ap
Efficient generation of relativistic near-single-cycle mid-infrared pulses in plasmas
Ultrashort intense optical pulses in the mid-infrared (mid-IR) region are very important for broad applications ranging from super-resolution spectroscopy to attosecond X-ray pulse generation and particle acceleration. However, currently, it is still difficult to produce few-cycle mid-IR pulses of relativistic intensities using standard optical techniques. Here, we propose and numerically demonstrate a novel scheme to produce these mid-IR pulses based on laser-driven plasma optical modulation. In this scheme, a plasma wake is first excited by an intense drive laser pulse in an underdense plasma, and a signal laser pulse initially at the same wavelength (1 micron) as that of the drive laser is subsequently injected into the plasma wake. The signal pulse is converted to a relativistic multi-millijoule near-single-cycle mid-IR pulse with a central wavelength of ~5 microns via frequency-downshifting, where the energy conversion efficiency is as high as approximately 30% when the drive and signal laser pulses are both at a few tens of millijoules at the beginning. Our scheme can be realized with terawatt-class kHz laser systems, which may bring new opportunities in high-field physics and ultrafast science
Adaptive Hierarchical Origami Metastructures
Shape-morphing capabilities are crucial for enabling multifunctionality in
both biological and artificial systems. Various strategies for shape morphing
have been proposed for applications in metamaterials and robotics. However, few
of these approaches have achieved the ability to seamlessly transform into a
multitude of volumetric shapes post-fabrication using a relatively simple
actuation and control mechanism. Taking inspiration from thick origami and
hierarchies in nature, we present a new hierarchical construction method based
on polyhedrons to create an extensive library of compact origami
metastructures. We show that a single hierarchical origami structure can
autonomously adapt to over 103 versatile architectural configurations, achieved
with the utilization of fewer than 3 actuation degrees of freedom and employing
simple transition kinematics. We uncover the fundamental principles governing
theses shape transformation through theoretical models. Furthermore, we also
demonstrate the wide-ranging potential applications of these transformable
hierarchical structures. These include their uses as untethered and autonomous
robotic transformers capable of various gait-shifting and multidirectional
locomotion, as well as rapidly self-deployable and self-reconfigurable
architecture, exemplifying its scalability up to the meter scale. Lastly, we
introduce the concept of multitask reconfigurable and deployable space robots
and habitats, showcasing the adaptability and versatility of these
metastructures
Anomalous Floquet non-Hermitian skin effect in a ring resonator lattice
We present a one-dimensional coupled ring resonator lattice exhibiting a
variant of the non- Hermitian skin effect (NHSE) that we call the anomalous
Floquet NHSE. Unlike existing approaches to achieving the NHSE by engineering
gain and loss on different ring segments, our design uses fixed on-site gain or
loss in each ring. The anomalous Floquet NHSE is marked by the existence of
skin modes at every value of the Floquet quasienergy, allowing for broadband
asymmetric transmission. Varying the gain/loss induces a non-Hermitian
topological phase transition, reversing the localization direction of the skin
modes. An experimental implementation in an acoustic lattice yields good
agreement with theoretical predictions, with a very broad relative bandwidth of
around 40%.Comment: 7 pages, 3 figure
Multi-Modal Automatic Prosody Annotation with Contrastive Pretraining of SSWP
In the realm of expressive Text-to-Speech (TTS), explicit prosodic boundaries
significantly advance the naturalness and controllability of synthesized
speech. While human prosody annotation contributes a lot to the performance, it
is a labor-intensive and time-consuming process, often resulting in
inconsistent outcomes. Despite the availability of extensive supervised data,
the current benchmark model still faces performance setbacks. To address this
issue, a two-stage automatic annotation pipeline is novelly proposed in this
paper. Specifically, in the first stage, we propose contrastive text-speech
pretraining of Speech-Silence and Word-Punctuation (SSWP) pairs. The
pretraining procedure hammers at enhancing the prosodic space extracted from
joint text-speech space. In the second stage, we build a multi-modal prosody
annotator, which consists of pretrained encoders, a straightforward yet
effective text-speech feature fusion scheme, and a sequence classifier.
Extensive experiments conclusively demonstrate that our proposed method excels
at automatically generating prosody annotation and achieves state-of-the-art
(SOTA) performance. Furthermore, our novel model has exhibited remarkable
resilience when tested with varying amounts of data.Comment: Submitted to ICASSP 202
TranssionADD: A multi-frame reinforcement based sequence tagging model for audio deepfake detection
Thanks to recent advancements in end-to-end speech modeling technology, it
has become increasingly feasible to imitate and clone a user`s voice. This
leads to a significant challenge in differentiating between authentic and
fabricated audio segments. To address the issue of user voice abuse and misuse,
the second Audio Deepfake Detection Challenge (ADD 2023) aims to detect and
analyze deepfake speech utterances. Specifically, Track 2, named the
Manipulation Region Location (RL), aims to pinpoint the location of manipulated
regions in audio, which can be present in both real and generated audio
segments. We propose our novel TranssionADD system as a solution to the
challenging problem of model robustness and audio segment outliers in the trace
competition. Our system provides three unique contributions: 1) we adapt
sequence tagging task for audio deepfake detection; 2) we improve model
generalization by various data augmentation techniques; 3) we incorporate
multi-frame detection (MFD) module to overcome limited representation provided
by a single frame and use isolated-frame penalty (IFP) loss to handle outliers
in segments. Our best submission achieved 2nd place in Track 2, demonstrating
the effectiveness and robustness of our proposed system
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