61 research outputs found
Asymmetric sequential Landau-Zener dynamics of Bose condensed atoms in a cavity
We explore the asymmetric sequential Landau-Zener (LZ) dynamics in an
ensemble of interacting Bose condensed two-level atoms coupled with a cavity
field. Assuming the couplings between all atoms and the cavity field are
identical, the interplay between atom-atom interaction and detuning may lead to
a series of LZ transitions. Unlike the conventional sequential LZ transitions,
which are symmetric to the zero detuning, the LZ transitions of Bose condensed
atoms in a cavity field are asymmetric and sensitively depend on the photon
number distribution of the cavity. In LZ processes involving single excitation
numbers, both the variance of the relative atom number and the step slope of
the sequential population ladder are asymmetric, and the asymmetry become more
significant for smaller excitation numbers. Furthermore, in LZ processes
involving multiple excitation numbers, there may appear asymmetric population
ladders with decreasing step heights. During a dynamical LZ process, due to the
atom-cavity coupling, the cavity field shows dynamical collapse and revivals.
In comparison with the symmetric LZ transitions in a classical field, the
asymmetric LZ transitions in a cavity field originate from the
photon-number-dependent Rabi frequency. The asymmetric sequential LZ dynamics
of Bose condensed atoms in a cavity field may open up a new way to explore the
fundamental many-body physics in coupled atom-photon systems.Comment: 14 pages, 6 figure
Active spheroids in viscosity gradients
In this paper, we explore the hydrodynamics of spheroidal active particles in
viscosity gradients. This work provides a more accurate modeling approach, in
comparison to spherical particles, for anisotropic organisms like Paramecium
swimming through inhomogeneous environments, but more fundamentally examines
the influence of particle shape on viscotaxis. We find that spheroidal
squirmers generally exhibit dynamics consistent with their spherical analogs,
irrespective of the classification of swimmers as pushers, pullers, or neutral
swimmers. However, the slenderness of the spheroids tends to reduce the impact
of viscosity gradients on their dynamics; when swimmers become more slender,
the viscosity difference across their body is reduced, which leads to slower
reorientation. We also derive the mobility tensor for passive spheroids in
viscosity gradients generalizing previous results for spheres and slender
bodies. This work enhances our understanding of how shape factors into the
dynamics of passive and active particles in viscosity gradients, and offers new
perspectives that could aid the control of both natural and synthetic swimmers
in complex fluid environments.Comment: 19 pages, 5 figure
Facile synthesis of solid-state fluorescent organosilica nanoparticles with a photoluminescence quantum yield of 73.3% for fingerprint recognition and white-light-emitting diodes
Polymer-like coated OSiNPs with a solid-state PLQY of up to 73.3% for applications in WLEDs and fingerprint recognition are fabricated by a simple hydrothermal method
Pedestrian Accessible Infrastructure Inventory: Assessing Zero-Shot Segmentation on Multi-Mode Geospatial Data for All Pedestrian Types
In this paper, a Segment Anything Model (SAM)-based pedestrian infrastructure
segmentation workflow is designed and optimized, which is capable of
efficiently processing multi-sourced geospatial data including LiDAR data and
satellite imagery data. We used an expanded definition of pedestrian
infrastructure inventory which goes beyond the traditional transportation
elements to include street furniture objects that are important for
accessibility but are often omitted from the traditional definition. Our
contributions lie in producing the necessary knowledge to answer the following
two questions. First, which data representation can facilitate zero-shot
segmentation of infrastructure objects with SAM? Second, how well does the
SAM-based method perform on segmenting pedestrian infrastructure objects? Our
findings indicate that street view images generated from mobile LiDAR point
cloud data, when paired along with satellite imagery data, can work efficiently
with SAM to create a scalable pedestrian infrastructure inventory approach with
immediate benefits to GIS professionals, city managers, transportation owners,
and walkers, especially those with travel-limiting disabilities, such as
individuals who are blind, have low vision, or experience mobility
disabilities
Improving Input-label Mapping with Demonstration Replay for In-context Learning
In-context learning (ICL) is an emerging capability of large autoregressive
language models where a few input-label demonstrations are appended to the
input to enhance the model's understanding of downstream NLP tasks, without
directly adjusting the model parameters. The effectiveness of ICL can be
attributed to the strong language modeling capabilities of large language
models (LLMs), which enable them to learn the mapping between input and labels
based on in-context demonstrations. Despite achieving promising results, the
causal nature of language modeling in ICL restricts the attention to be
backward only, i.e., a token only attends to its previous tokens, failing to
capture the full input-label information and limiting the model's performance.
In this paper, we propose a novel ICL method called Repeated Demonstration with
Sliding Causal Attention, (RdSca). Specifically, we duplicate later
demonstrations and concatenate them to the front, allowing the model to
`observe' the later information even under the causal restriction. Besides, we
introduce sliding causal attention, which customizes causal attention to avoid
information leakage. Experimental results show that our method significantly
improves the input-label mapping in ICL demonstrations. We also conduct an
in-depth analysis of how to customize the causal attention without training,
which has been an unexplored area in previous research
Controlling the polarization of nitrogen ion lasing
Air lasing provides a promising technique to remotely produce coherent
radiation in the atmosphere and attracts continuous attention. However, the
polarization properties of N2+ lasing with seeding has not been understood
since it was discovered ten years ago, in which the behaviors appear disordered
and confusing. Here, we performed an experimental and theoretical investigation
on the polarization properties of N2+ lasing and successfully revealed its
underlying physical mechanism. We found that the optical gain is anisotropic
owing to the permanent alignment of N2+ induced by the preferential ionization
of the pump light. As a result, the polarization of N2+ lasing tends to align
with that of the pump light after amplification, which becomes more pronounced
with increasing amplification factor. Based on the permanent alignment of N2+,
we built a theoretical model that analytically interpreted and numerically
reproduced the experimental observations, which points out the key factors for
controlling the polarization of N2+ lasing.Comment: 12 pages, 4 figure
Masked Spatial-Spectral Autoencoders Are Excellent Hyperspectral Defenders
Deep learning methodology contributes a lot to the development of
hyperspectral image (HSI) analysis community. However, it also makes HSI
analysis systems vulnerable to adversarial attacks. To this end, we propose a
masked spatial-spectral autoencoder (MSSA) in this paper under self-supervised
learning theory, for enhancing the robustness of HSI analysis systems. First, a
masked sequence attention learning module is conducted to promote the inherent
robustness of HSI analysis systems along spectral channel. Then, we develop a
graph convolutional network with learnable graph structure to establish global
pixel-wise combinations.In this way, the attack effect would be dispersed by
all the related pixels among each combination, and a better defense performance
is achievable in spatial aspect.Finally, to improve the defense transferability
and address the problem of limited labelled samples, MSSA employs spectra
reconstruction as a pretext task and fits the datasets in a self-supervised
manner.Comprehensive experiments over three benchmarks verify the effectiveness
of MSSA in comparison with the state-of-the-art hyperspectral classification
methods and representative adversarial defense strategies.Comment: 14 pages, 9 figure
Amplification of light pulses with orbital angular momentum (OAM) in nitrogen ions lasing
Nitrogen ions pumped by intense femtosecond laser pulses give rise to optical
amplification in the ultraviolet range. Here, we demonstrated that a seed light
pulse carrying orbital angular momentum (OAM) can be significantly amplified in
nitrogen plasma excited by a Gaussian femtosecond laser pulse. With the
topological charge of +1 and -1, we observed an energy amplification of the
seed light pulse by two orders of magnitude, while the amplified pulse carries
the same OAM as the incident seed pulse. Moreover, we show that a spatial
misalignment of the plasma amplifier with the OAM seed beam leads to an
amplified emission of Gaussian mode without OAM, due to the special spatial
profile of the OAM seed pulse that presents a donut-shaped intensity
distribution. Utilizing this misalignment, we can implement an optical switch
that toggles the output signal between Gaussian mode and OAM mode. This work
not only certifies the phase transfer from the seed light to the amplified
signal, but also highlights the important role of spatial overlap of the
donut-shaped seed beam with the gain region of the nitrogen plasma for the
achievement of OAM beam amplification.Comment: 10 pages, 7 figure
PreQuant: A Task-agnostic Quantization Approach for Pre-trained Language Models
While transformer-based pre-trained language models (PLMs) have dominated a
number of NLP applications, these models are heavy to deploy and expensive to
use. Therefore, effectively compressing large-scale PLMs becomes an
increasingly important problem. Quantization, which represents high-precision
tensors with low-bit fix-point format, is a viable solution. However, most
existing quantization methods are task-specific, requiring customized training
and quantization with a large number of trainable parameters on each individual
task. Inspired by the observation that the over-parameterization nature of PLMs
makes it possible to freeze most of the parameters during the fine-tuning
stage, in this work, we propose a novel ``quantize before fine-tuning''
framework, PreQuant, that differs from both quantization-aware training and
post-training quantization. PreQuant is compatible with various quantization
strategies, with outlier-aware parameter-efficient fine-tuning incorporated to
correct the induced quantization error. We demonstrate the effectiveness of
PreQuant on the GLUE benchmark using BERT, RoBERTa, and T5. We also provide an
empirical investigation into the workflow of PreQuant, which sheds light on its
efficacy.Comment: Findings of ACL202
- …