211 research outputs found
Hâ filter for flexure deformation and lever arm effect compensation in M/S INS integration
ABSTRACTOn ship, especially on large ship, the flexure deformation between Master (M)/Slave (S) Inertial Navigation System (INS) is a key factor which determines the accuracy of the integrated system of M/S INS. In engineering this flexure deformation will be increased with the added ship size. In the M/S INS integrated system, the attitude error between MINS and SINS cannot really reflect the misalignment angle change of SINS due to the flexure deformation. At the same time, the flexure deformation will bring the change of the lever arm size, which further induces the uncertainty of lever arm velocity, resulting in the velocity matching error. To solve this problem, a Hâ algorithm is proposed, in which the attitude and velocity matching error caused by deformation is considered as measurement noise with limited energy, and measurement noise will be restrained by the robustness of Hâ filter. Based on the classical âattitude plus velocityâ matching method, the progress of M/S INS information fusion is simulated and compared by using three kinds of schemes, which are known and unknown flexure deformation with standard Kalman filter, and unknown flexure deformation with Hâ filter, respectively. Simulation results indicate that Hâ filter can effectively improve the accuracy of information fusion when flexure deformation is unknown but non-ignorable
A trace alkaloid, oleraisoindole A from Portulaca oleracea L. and its anticholinesterase effect
International audienc
Energy-resolved Photoconductivity Mapping in a Monolayer-bilayer WSe2 Lateral Heterostructure
Vertical and lateral heterostructures of van der Waals materials provide
tremendous flexibility for band structure engineering. Since electronic bands
are sensitively affected by defects, strain, and interlayer coupling, the edge
and heterojunction of these two-dimensional (2D) systems may exhibit novel
physical properties, which can be fully revealed only by spatially resolved
probes. Here, we report the spatial mapping of photoconductivity in a
monolayer-bilayer WSe2 lateral heterostructure under multiple excitation
lasers. As the photon energy increases, the light-induced conductivity detected
by microwave impedance microscopy first appears along the hetero-interface and
bilayer edge, then along the monolayer edge, inside the bilayer area, and
finally in the interior of the monolayer region. The sequential emergence of
mobile carriers in different sections of the sample is consistent with the
theoretical calculation of local energy gaps. Quantitative analysis of the
microscopy and transport data also reveals the linear dependence of
photoconductivity on the laser intensity and the influence of interlayer
coupling on carrier recombination. Combining theoretical modeling, atomic scale
imaging, mesoscale impedance microscopy, and device-level characterization, our
work suggests an exciting perspective to control the intrinsic band-gap
variation in 2D heterostructures down to the few-nanometer regime.Comment: 18 pages, 5 figures; Nano Lett., Just Accepted Manuscrip
A new alkaloid from Portulaca oleracea L. and its antiacetylcholinesterase activity
International audienc
Reconstructive Neuron Pruning for Backdoor Defense
Deep neural networks (DNNs) have been found to be vulnerable to backdoor
attacks, raising security concerns about their deployment in mission-critical
applications. While existing defense methods have demonstrated promising
results, it is still not clear how to effectively remove backdoor-associated
neurons in backdoored DNNs. In this paper, we propose a novel defense called
\emph{Reconstructive Neuron Pruning} (RNP) to expose and prune backdoor neurons
via an unlearning and then recovering process. Specifically, RNP first unlearns
the neurons by maximizing the model's error on a small subset of clean samples
and then recovers the neurons by minimizing the model's error on the same data.
In RNP, unlearning is operated at the neuron level while recovering is operated
at the filter level, forming an asymmetric reconstructive learning procedure.
We show that such an asymmetric process on only a few clean samples can
effectively expose and prune the backdoor neurons implanted by a wide range of
attacks, achieving a new state-of-the-art defense performance. Moreover, the
unlearned model at the intermediate step of our RNP can be directly used to
improve other backdoor defense tasks including backdoor removal, trigger
recovery, backdoor label detection, and backdoor sample detection. Code is
available at \url{https://github.com/bboylyg/RNP}.Comment: Accepted by ICML2
Direct observation of nanometer-scale amorphous layers and oxide crystallites at grain boundaries in polycrystalline Sr1-xKxFe2As2 superconductors
We report here an atomic resolution study of the structure and composition of
the grain boundaries in polycrystalline Sr0.6K0.4Fe2As2 superconductor. A large
fraction of grain boundaries contain amorphous layers larger than the coherence
length, while some others contain nanometer-scale particles sandwiched in
between amorphous layers. We also find that there is significant oxygen
enrichment at the grain boundaries. Such results explain the relatively low
transport critical current density (Jc) of polycrystalline samples with respect
to that of bicrystal films.Comment: 12 pages, 4 figure
Layer-dependent anisotropic electronic structure of freestanding quasi-two dimensional MoS2
The anisotropy of the electronic transition is an important physical property
not only determining the materials' optical property, but also revealing the
underlying character of the electronic states involved. Here we used
momentum-resolved electron energy-loss spectroscopy to study the evolution of
the anisotropy of the electronic transition involving the low energy valence
electrons in the free-standing MoS2 systems as the layer thickness was reduced
to monolayer. We used the orientation and the spectral-density analysis to show
that indirect to direct band-gap transition is accompanied by a three- to
two-dimensional anisotropy cross-over. The result provides a logical
explanation for the large sensitivity of indirect transition to the change of
thickness compared with that for direct transition. By tracking the energy of
indirect transition, we also revealed the asymmetric response of the valence
band and conduction band to the quantum confinement effect. Our results have
implication for future optoelectronic applications of atomic thin MoS2
Analysis of compression/expansion stage on compressed air energy storage cogeneration system
Compressed Air Energy Storage (CAES) technology has risen as a promising approach to effectively store renewable energy. Optimizing the efficient cascading utilization of multi-grade heat can greatly improve the efficiency and overall system performance. Particularly, the number of compressor and expander stages is a critical factor in determining the systemâs performance. In this study, we focused on the Advanced Adiabatic Compressed Air Energy Storage system with Combined Heat and Power (AA-CAES -CHP). Both economic and thermodynamic models were established for the AA-CAES-CHP system. To systematically study the effects of compression and expansion stages, the influence of 3 different compressor stages and expander stages was comprehensively analyzed under 4 operating conditions. Key findings reveal that the count of compressor and expander stages have a notable impact on the exergy losses of the AA-CAES-CHP system. As for the investment cost, the proportion of investment cost for expanders decreases when the stage numbers of compressors and expanders are the same. Furthermore, both thermodynamic and economic characteristics allow us to optimize the AA-CAES-CHP systemâs performance. One of our cases demonstrates that doubling the air mass flow rate results in a doubled total energy output with a relatively modest increase (41.1%â65.1%) in the total investment cost
Cytotoxicity of hydroxydihydrobovolide and its pharmacokinetic studies in Portulaca oleracea L. extract
Hydroxydihydrobovolide (HDB) was for the first time isolated from Portulaca oleracea L. and then its cytotoxicity against SH-SYTY cells was studied. Moreover, a rapid and sensitive ultra-high performance liquid chromatographic (UHPLC) method with bergapten as internal standard (IS) was developed and validated to investigate the pharmacokinetics of HDB in rats after intravenous and oral administrations of extract (POE). The UHPLC analysis was performed on a Diamonsil C18 analytical column, using acetonitrile-water (35:65, v/v) as the mobile phase with UV detection at 220 nm. The calibration curve was linear over the range of 0.2-25 ”g/mL in rat plasma. The average extraction recovery was from 90.1 to 98.9%, and the relative standard deviations (RSDs) of the intra- and inter-day precisions were less than 4.7 and 4.1%, respectively. The results showed that 50 ”M HDB had significant cytotoxicity on the SH-SY5Y cells, which was rapidly distributed with a Tmax of 11 min after oral administration and presented a low absolute bioavailability, 4.12%
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