305 research outputs found
RobustSense: Defending Adversarial Attack for Secure Device-Free Human Activity Recognition
Deep neural networks have empowered accurate device-free human activity
recognition, which has wide applications. Deep models can extract robust
features from various sensors and generalize well even in challenging
situations such as data-insufficient cases. However, these systems could be
vulnerable to input perturbations, i.e. adversarial attacks. We empirically
demonstrate that both black-box Gaussian attacks and modern adversarial
white-box attacks can render their accuracies to plummet. In this paper, we
firstly point out that such phenomenon can bring severe safety hazards to
device-free sensing systems, and then propose a novel learning framework,
RobustSense, to defend common attacks. RobustSense aims to achieve consistent
predictions regardless of whether there exists an attack on its input or not,
alleviating the negative effect of distribution perturbation caused by
adversarial attacks. Extensive experiments demonstrate that our proposed method
can significantly enhance the model robustness of existing deep models,
overcoming possible attacks. The results validate that our method works well on
wireless human activity recognition and person identification systems. To the
best of our knowledge, this is the first work to investigate adversarial
attacks and further develop a novel defense framework for wireless human
activity recognition in mobile computing research
Seismic pounding between adjacent buildings of unequal floor height
When the story heights of adjacent buildings are unequal, the inter-floor pounding maybe happen during earthquake. Employing substructures in pounding area, the analytical model of adjacent structures with unequal story height is developed, and the equations of motion considering pounding are derived. Based on analytical model, the inter-floor pounding responses of adjacent buildings with unequal story height are investigated. The corresponding parametrical studies are conducted and influence rules are concluded. The results show that the influences of inter-floor pounding in adjacent buildings on main structures are smaller than those of floor pounding. But the damages on pounding area are quite large. Moreover, the period ratio of structures, the initial gap and the pounding location have remarkable influence on responses of inter-floor pounding
TENT: Connect Language Models with IoT Sensors for Zero-Shot Activity Recognition
Recent achievements in language models have showcased their extraordinary
capabilities in bridging visual information with semantic language
understanding. This leads us to a novel question: can language models connect
textual semantics with IoT sensory signals to perform recognition tasks, e.g.,
Human Activity Recognition (HAR)? If so, an intelligent HAR system with
human-like cognition can be built, capable of adapting to new environments and
unseen categories. This paper explores its feasibility with an innovative
approach, IoT-sEnsors-language alignmEnt pre-Training (TENT), which jointly
aligns textual embeddings with IoT sensor signals, including camera video,
LiDAR, and mmWave. Through the IoT-language contrastive learning, we derive a
unified semantic feature space that aligns multi-modal features with language
embeddings, so that the IoT data corresponds to specific words that describe
the IoT data. To enhance the connection between textual categories and their
IoT data, we propose supplementary descriptions and learnable prompts that
bring more semantic information into the joint feature space. TENT can not only
recognize actions that have been seen but also ``guess'' the unseen action by
the closest textual words from the feature space. We demonstrate TENT achieves
state-of-the-art performance on zero-shot HAR tasks using different modalities,
improving the best vision-language models by over 12%.Comment: Preprint manuscript in submissio
Investigation of Langdon effect on the nonlinear evolution of SRS from the early-stage inflation to the late-stage development of secondary instabilities
In a laser-irradiated plasma, the Langdon effect can result in a
super-Gaussian electron energy distribution function (EEDF), imposing
significant influences on the stimulated backward Raman scattering (SRS). In
this work, the influence of a super-Gaussian EEDF on the nonlinear evolution of
SRS is investigated by three wave model simulation and Vlasov-Maxwell
simulation for plasma parameters covering a wide range of k{\lambda}De from
0.19 to 0.48 at both high and low intensity laser drives. In the early-stage of
SRS evolution, it is found that besides the kinetic effects due to electron
trapping [Phys. Plasmas 25, 100702 (2018)], the Langdon effect can also
significantly widen the parameter range for the absolute growth of SRS, and the
time for the absolute SRS to reach saturation is greatly shorten by Langdon
effect within certain parameter region. In the late-stage of SRS, when
secondary instabilities such as decay of the electron plasma wave to beam
acoustic modes, rescattering, and Langmuir decay instability become important,
the Langdon effect can influence the reflectivity of SRS by affecting the
secondary processes. The comprehension of Langdon effect on nonlinear evolution
and saturation of SRS would contribute to a better understanding and prediction
of SRS in inertial confinement fusion
A Robust Indoor Positioning System Based on the Procrustes Analysis and Weighted Extreme Learning Machine
Indoor positioning system (IPS) has become one of the most attractive research fields due to the increasing demands on location-based services (LBSs) in indoor environments. Various IPSs have been developed under different circumstances, and most of them adopt the fingerprinting technique to mitigate pervasive indoor multipath effects. However, the performance of the fingerprinting technique severely suffers from device heterogeneity existing across commercial off-the-shelf mobile devices (e.g., smart phones, tablet computers, etc.) and indoor environmental changes (e.g., the number, distribution and activities of people, the placement of furniture, etc.). In this paper, we transform the received signal strength (RSS) to a standardized location fingerprint based on the Procrustes analysis, and introduce a similarity metric, termed signal tendency index (STI), for matching standardized fingerprints. An analysis of the capability of the proposed STI to handle device heterogeneity and environmental changes is presented. We further develop a robust and precise IPS by integrating the merits of both the STI and weighted extreme learning machine (WELM). Finally, extensive experiments are carried out and a performance comparison with existing solutions verifies the superiority of the proposed IPS in terms of robustness to device heterogeneity
Research on isolation property of prestressed thick rubber bearings
To overcome the shortages of current laminated rubber bearings (RB), a new kind of isolator called Prestressed Rubber Bearing (PRB) is presented in this paper, which is invented by appropriately amplifying the thickness of rubber layers in conventional RB and employing prestress tendons. Based on the experimental study, a modified formula for vertical stiffness of PRB is established. Then the nonlinear analytical model for PRB’s horizontal stiffness is developed and the corresponding formulas are derived. Through the response history analysis of structures, the isolation capacities of PRBs are investigated. The results show that the horizontal stiffness of PRB is variable with the displacment. PRB not only has effective isolation capacity as conventional RBs but also has the favorable capacity of horizontal displacement limitation and vertical up resistance
Experimental study of mechanical property for prestressed rubber bearing
To overcome the shortages of existing Rubber Bearings (RBs), an innovative type of isolator, named as Prestressed Rubber Bearing (PRB), is presented in this paper. Base on conventional laminated Rubber Bearing (RB), PRB is developed by increasing the thickness of rubber layers, setting vertical ducts and installing prestress tendons. Through the vertical and horizontal monotonic loading test, the vertical and horizontal stiffness of PRBs are investigated. The empirical formulas for stiffness are proposed. Moreover, the hysteresis behavior and the energy dissipation capacity of PRBs are studied by reversed cyclic loading test. The results show that PRBs not only have the horizontal isolating capacity as conventional RBs, but also have the capacity of horizontal displacement-limitation and improved capacity of energy dissipation
AutoFi: Towards Automatic WiFi Human Sensing via Geometric Self-Supervised Learning
WiFi sensing technology has shown superiority in smart homes among various
sensors for its cost-effective and privacy-preserving merits. It is empowered
by Channel State Information (CSI) extracted from WiFi signals and advanced
machine learning models to analyze motion patterns in CSI. Many learning-based
models have been proposed for kinds of applications, but they severely suffer
from environmental dependency. Though domain adaptation methods have been
proposed to tackle this issue, it is not practical to collect high-quality,
well-segmented and balanced CSI samples in a new environment for adaptation
algorithms, but randomly-captured CSI samples can be easily collected.
{\color{black}In this paper, we firstly explore how to learn a robust model
from these low-quality CSI samples, and propose AutoFi, an annotation-efficient
WiFi sensing model based on a novel geometric self-supervised learning
algorithm.} The AutoFi fully utilizes unlabeled low-quality CSI samples that
are captured randomly, and then transfers the knowledge to specific tasks
defined by users, which is the first work to achieve cross-task transfer in
WiFi sensing. The AutoFi is implemented on a pair of Atheros WiFi APs for
evaluation. The AutoFi transfers knowledge from randomly collected CSI samples
into human gait recognition and achieves state-of-the-art performance.
Furthermore, we simulate cross-task transfer using public datasets to further
demonstrate its capacity for cross-task learning. For the UT-HAR and Widar
datasets, the AutoFi achieves satisfactory results on activity recognition and
gesture recognition without any prior training. We believe that the AutoFi
takes a huge step toward automatic WiFi sensing without any developer
engagement.Comment: The paper has been accepted by IEEE Internet of Things Journa
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