5,773 research outputs found
Identifiability of Normal and Normal Mixture Models With Nonignorable Missing Data
Missing data problems arise in many applied research studies. They may
jeopardize statistical inference of the model of interest, if the missing
mechanism is nonignorable, that is, the missing mechanism depends on the
missing values themselves even conditional on the observed data. With a
nonignorable missing mechanism, the model of interest is often not identifiable
without imposing further assumptions. We find that even if the missing
mechanism has a known parametric form, the model is not identifiable without
specifying a parametric outcome distribution. Although it is fundamental for
valid statistical inference, identifiability under nonignorable missing
mechanisms is not established for many commonly-used models. In this paper, we
first demonstrate identifiability of the normal distribution under monotone
missing mechanisms. We then extend it to the normal mixture and mixture
models with non-monotone missing mechanisms. We discover that models under the
Logistic missing mechanism are less identifiable than those under the Probit
missing mechanism. We give necessary and sufficient conditions for
identifiability of models under the Logistic missing mechanism, which sometimes
can be checked in real data analysis. We illustrate our methods using a series
of simulations, and apply them to a real-life dataset
Your Room is not Private: Gradient Inversion Attack on Reinforcement Learning
The prominence of embodied Artificial Intelligence (AI), which empowers
robots to navigate, perceive, and engage within virtual environments, has
attracted significant attention, owing to the remarkable advancements in
computer vision and large language models. Privacy emerges as a pivotal concern
within the realm of embodied AI, as the robot accesses substantial personal
information. However, the issue of privacy leakage in embodied AI tasks,
particularly in relation to reinforcement learning algorithms, has not received
adequate consideration in research. This paper aims to address this gap by
proposing an attack on the value-based algorithm and the gradient-based
algorithm, utilizing gradient inversion to reconstruct states, actions, and
supervision signals. The choice of using gradients for the attack is motivated
by the fact that commonly employed federated learning techniques solely utilize
gradients computed based on private user data to optimize models, without
storing or transmitting the data to public servers. Nevertheless, these
gradients contain sufficient information to potentially expose private data. To
validate our approach, we conduct experiments on the AI2THOR simulator and
evaluate our algorithm on active perception, a prevalent task in embodied AI.
The experimental results demonstrate the effectiveness of our method in
successfully reconstructing all information from the data across 120 room
layouts.Comment: 7 pages, 4 figures, 2 table
Long-term Blood Pressure Prediction with Deep Recurrent Neural Networks
Existing methods for arterial blood pressure (BP) estimation directly map the
input physiological signals to output BP values without explicitly modeling the
underlying temporal dependencies in BP dynamics. As a result, these models
suffer from accuracy decay over a long time and thus require frequent
calibration. In this work, we address this issue by formulating BP estimation
as a sequence prediction problem in which both the input and target are
temporal sequences. We propose a novel deep recurrent neural network (RNN)
consisting of multilayered Long Short-Term Memory (LSTM) networks, which are
incorporated with (1) a bidirectional structure to access larger-scale context
information of input sequence, and (2) residual connections to allow gradients
in deep RNN to propagate more effectively. The proposed deep RNN model was
tested on a static BP dataset, and it achieved root mean square error (RMSE) of
3.90 and 2.66 mmHg for systolic BP (SBP) and diastolic BP (DBP) prediction
respectively, surpassing the accuracy of traditional BP prediction models. On a
multi-day BP dataset, the deep RNN achieved RMSE of 3.84, 5.25, 5.80 and 5.81
mmHg for the 1st day, 2nd day, 4th day and 6th month after the 1st day SBP
prediction, and 1.80, 4.78, 5.0, 5.21 mmHg for corresponding DBP prediction,
respectively, which outperforms all previous models with notable improvement.
The experimental results suggest that modeling the temporal dependencies in BP
dynamics significantly improves the long-term BP prediction accuracy.Comment: To appear in IEEE BHI 201
Research of Coordinated Control Strategy for Multi-UHVDC in AC/DC Hybrid Power Grid
AbstractThe control strategy and modulation scheme of DC system have great effect on transient stability and dynamical stability in AC/DC hybrid power grid. In order to decrease the effect of UHVDC blocks and AC lines faults, a coordinated control strategy of emergency power modulation and small signal modulation is put forward by making use of the fast controllability and the overload capability of HVDC system. Simulation results show that the coordinated control strategy may decrease power loss and improve the dynamical stability of the AC/DC hybrid system
Full-range Gate-controlled Terahertz Phase Modulations with Graphene Metasurfaces
Local phase control of electromagnetic wave, the basis of a diverse set of
applications such as hologram imaging, polarization and wave-front
manipulation, is of fundamental importance in photonic research. However, the
bulky, passive phase modulators currently available remain a hurdle for
photonic integration. Here we demonstrate full-range active phase modulations
in the Tera-Hertz (THz) regime, realized by gate-tuned ultra-thin reflective
metasurfaces based on graphene. A one-port resonator model, backed by our
full-wave simulations, reveals the underlying mechanism of our extreme phase
modulations, and points to general strategies for the design of tunable
photonic devices. As a particular example, we demonstrate a gate-tunable THz
polarization modulator based on our graphene metasurface. Our findings pave the
road towards exciting photonic applications based on active phase
manipulations
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