arXiv subjects

Jiyu Liu

Publications and source records attributed to Jiyu Liu.

5 recordsLinked to original sources

arXiv2026

T2T: Captioning Smartphone Activities Using Mobile Traffic

This paper studies the creation of textual descriptions of user activities and interactions on smartphones. Our approach of referring to encrypted mobile traffic exceeds traditional smartphone activity classification methods in terms of model scalability and output readability. The paper addresses two obstacles to the realization of this idea: the semantic gap between traffic features and smartphone activity captions, and the lack of textually annotated traffic data. To overcome these challenges, we introduce a novel smartphone activity captioning system, called T2T (Traffic-to-Text). T2T consists of a flow feature encoder that converts low-level traffic characteristics into meaningful latent features and a caption decoder to yield readable transcripts of smartphone activities. In addition, T2T achieves the automatic textual annotation of mobile traffic by feeding synchronized screen capture videos into the Qwen-VL-Max vision-language model, and proposing multi-stage losses for effective cross-model training. We evaluate T2T on 40,000 traffic-description pairs collected in two real-world environments, involving 8 smartphone users and 20 mobile apps. T2T achieves a BLEU-4 score of 58.1, a METEOR score of 38.3, a ROUGE-L score of 70.5, and a CIDEr score of 108.7. The quantitative and qualitative analyses show that T2T can generate semantically accurate captions that are comparable to the vision-language model.

cs.CR↗

arXiv2026

A Fourth-Order Cut-cell Multigrid Method for Solving Elliptic Equations on Arbitrary Domains

To numerically solve a generic elliptic equation on two-dimensional domains with rectangular Cartesian grids, we propose a cut-cell geometric multigrid method that features (1) general algorithmic steps that apply to two-dimensional constant-coefficient elliptic equations with both divergence and non-divergence forms and all types of boundary conditions, (2) the versatility of handling both regular and irregular domains with arbitrarily complex topology and geometry, (3) the fourth-order accuracy even at the presence of ${\cal C}^1$ discontinuities on the domain boundary, and (4) the optimal complexity of $O(h^{-2})$.Test results demonstrate the generality, accuracy, efficiency, robustness, and excellent conditioning of the proposed method.

math.NA↗

arXiv2025

A fourth-order cut-cell method for solving the two-dimensional advection-diffusion equation with moving boundaries

We propose a fourth-order cut-cell method for solving the two-dimensional advection-diffusion equation with moving boundaries on a Cartesian grid. We employ the ARMS technique to give an explicit and accurate representation of moving boundaries, and introduce a cell-merging technique to overcome discontinuities caused by topological changes in cut cells and the small cell problem. We use a polynomial interpolation technique base on poised lattice generation to achieve fourth-order spatial discretization, and use a fourth-order implicit-explicit Runge-Kutta scheme for time integration. Numerical tests are performed on various moving regions, with advection velocity both matching and differing from boundary velocity, which demonstrate the fourth-order accuracy of the proposed method.

math.NA↗

arXiv2024

RFTrans: Leveraging Refractive Flow of Transparent Objects for Surface Normal Estimation and Manipulation

Transparent objects are widely used in our daily lives, making it important to teach robots to interact with them. However, it's not easy because the reflective and refractive effects can make depth cameras fail to give accurate geometry measurements. To solve this problem, this paper introduces RFTrans, an RGB-D-based method for surface normal estimation and manipulation of transparent objects. By leveraging refractive flow as an intermediate representation, the proposed method circumvents the drawbacks of directly predicting the geometry (e.g. surface normal) from images and helps bridge the sim-to-real gap. It integrates the RFNet, which predicts refractive flow, object mask, and boundaries, followed by the F2Net, which estimates surface normal from the refractive flow. To make manipulation possible, a global optimization module will take in the predictions, refine the raw depth, and construct the point cloud with normal. An off-the-shelf analytical grasp planning algorithm is followed to generate the grasp poses. We build a synthetic dataset with physically plausible ray-tracing rendering techniques to train the networks. Results show that the proposed method trained on the synthetic dataset can consistently outperform the baseline method in both synthetic and real-world benchmarks by a large margin. Finally, a real-world robot grasping task witnesses an 83% success rate, proving that refractive flow can help enable direct sim-to-real transfer. The code, data, and supplementary materials are available at https://rftrans.robotflow.ai.

cs.CV↗

arXiv2016

Why are rapidly rotating M dwarfs in the Pleiades so (infra)red? New period measurements confirm rotation-dependent color offsets from the cluster sequence

Stellar rotation periods measured in open clusters have proved to be extremely useful for studying stars' angular momentum content and rotationally driven magnetic activity, which are both age- and mass-dependent processes. While period measurements have been obtained for hundreds of solar-mass members of the Pleiades, period measurements exist for only a few low-mass ($<$0.5 M$_{\odot}$) members of this key laboratory for stellar evolution theory. To fill this gap, we report rotation periods for 132 low-mass Pleiades members (including nearly 100 with M $\leq$ 0.45 M$_{\odot}$), measured from photometric monitoring of the cluster conducted by the Palomar Transient Factory in late 2011 and early 2012. These periods extend the portrait of stellar rotation at 125 Myr to the lowest-mass stars and re-establish the Pleiades as a key benchmark for models of the transport and evolution of stellar angular momentum. Combining our new rotation periods with precise BVIJHK photometry reported by Stauffer et al. and Kamai et al., we investigate known anomalies in the photometric properties of K and M Pleiades members. We confirm the correlation detected by Kamai et al. between a star's rotation period and position relative to the main sequence in the cluster's color-magnitude diagram. We find that rapid rotators have redder (V-K) colors than slower rotators at the same V, indicating that rapid and slow rotators have different binary frequencies and/or photospheric properties. We find no difference in the photometric amplitudes of rapid and slow rotators, indicating that asymmetries in the longitudinal distribution of starspots do not scale grossly with rotation rate.

astro-ph.SR↗