arXiv subjects

Cong Yu

Publications and source records attributed to Cong Yu.

At least 37 records · Page 2Linked to original sources

arXiv2025

Exoplanet Ephemerides Change Observations (ExoEcho). II. Transit timing variation analysis of Brown Dwarfs around Solar-type Stars

Transit timing variation (TTV) is a useful tool for studying the orbital properties of transiting objects. However, few TTV studies have been done on transiting brown dwarfs (BDs) around solar-type stars. Here we study the long-term TTV of a population of close BD companions around solar-type stars using TESS data. We use the measured orbital period change rate to constrain the tidal interaction strength between the host star and the BD companion and put limits on the destruction timescale of these transiting BDs. However, we find no statistically significant evidence of orbital decay or expansion in our sample based on the current data. This may be due to either poor observational data or inherently weak tidal dissipation. We then perform simulations to investigate future observation strategies for detecting orbital decay of transiting BDs, which show NGTS-7A b, TOI-263~b and LP 261-75 b are the most promising targets in the next few years. Our study demonstrates the potential of TTV technique to probe the formation and evolution of close BD companions around solar-type stars.

astro-ph.EP↗

arXiv2025

Agent-Q: Fine-Tuning Large Language Models for Quantum Circuit Generation and Optimization

Large language models (LLMs) have achieved remarkable outcomes in complex problems, including math, coding, and analyzing large amounts of scientific reports. Yet, few works have explored the potential of LLMs in quantum computing. The most challenging problem is to leverage LLMs to automatically generate quantum circuits at a large scale. Fundamentally, the existing pre-trained LLMs lack the knowledge of quantum circuits. In this paper, we address this challenge by fine-tuning LLMs and injecting the domain-specific knowledge of quantum computing. We describe Agent-Q, an LLM fine-tuning system to generate and optimize quantum circuits. In particular, Agent-Q implements the mechanisms to generate training data sets and constructs an end-to-end pipeline to fine-tune pre-trained LLMs to generate parameterized quantum circuits for various optimization problems. Agent-Q provides 14,000 quantum circuits covering a large spectrum of the quantum optimization landscape: 12 optimization problem instances and their optimized QAOA, VQE, and adaptive VQE circuits. Based thereon, Agent-Q fine-tunes LLMs and constructs syntactically correct parametrized quantum circuits in OpenQASM 3.0. We have evaluated the quality of the LLM-generated circuits and parameters by comparing them to the optimized expectation values and distributions. Experimental results show superior performance of Agent-Q, compared to several state-of-the-art LLMs and better parameters than random. Agent-Q can be integrated into an agentic workflow, and the generated parametrized circuits with initial parameters can be used as a starting point for further optimization, e.g., as templates in quantum machine learning and as benchmarks for compilers and hardware.

quant-ph↗

arXiv2025

Dust Growth in ALMA Rings: II. Dusty Rossby Wave Instability

Annular substructures serve as ideal venues for planetesimal formation. In this series, we investigate the linear stage of dust growth within rings. The first paper examines the global streaming instability, while this study focuses on the dusty Rossby wave instability (DRWI). We perform a linear analysis of the two-fluid equations on a background pressure bump, representing annular substructures. The spectral code \textsc{Dedalus} is used to solve the linear eigenvalue problem. We identify two distinct DRWI modes: Type I, which originates from dust-modified gas RWI, and Type II, which results from dust-gas coupling. These modes never coexist for a given azimuthal wavenumber $\ky$, but transition between each other as $\ky$ varies. Type I modes are driven by the advection of background vorticity, whereas Type II modes involve two primary waves: Rossby waves, driven by advection, and thin waves, driven by dust-gas drag. Finally, we assess the relevance of DRWI in ALMA rings using DSHARP sources. Our findings suggest that Type I modes could explain the absence of azimuthal asymmetries in many ALMA disks, whereas Type II modes are entirely absent in all eight observed rings, implying that unresolved narrow rings or alternative mechanisms may play a role in dust growth within annular substructures.

astro-ph.EP↗

arXiv2025

Irradiated Atmospheres III : Radiative-Convective-Mixing Equilibrium for Non-Grey Picket-Fence Model

The non-grey picket-fence model predicts more accurately the temperatures in low-density regions compared to semi-grey models. This study investigates how the vertical mixing and convection fluxes modify the picket-fence model. The usual radiative-convective-equilibrium (RCE) is now extended to radiative-convective-mixing-equilibrium (RCME). The temperature profile, characterized by an increase with pressure in the upper region and an inversion in the lower, is influenced by Rosseland opacity, spectral bands, and chemical composition. The atmosphere consists of five distinct layers: a pseudo-adiabatic zone shaped by mixing flux, two convective layers driven by convective flux with a smaller adiabatic gradient, and two radiative layers. In scenarios with lower Rosseland opacity, vertical mixing significantly reduces the width of temperature inversion, counteracting the cooling effect of the convective layers and driving the deep convective layer inward. The convective flux lowers the upper temperature and expands the upper convective layer. In the low-Rosseland-opacity five-band model, these fluxes significantly cool the mid-atmosphere when temperature increases with pressure, enlarging the pseudo-adiabatic region. Without TiO/VO, the pseudo-adiabatic region shrinks, indicating that TiO/VO enhances the mixing effect. Moreover, less mixing intensity is essential to maintain a stable five-layer structure. Therefore, future studies of chemical equilibrium with multi-frequency atmospheric opacity should clearly define the constraints on vertical mixing.

astro-ph.EP↗

arXiv2025

Irradiated Atmospheres II: Interplay Between Scattering and Vertical-Mixing induced Energy Transport

The scattering is crucial for the atmospheric thermal profiles. The energy transport by the vertical mixing plays an essential role for the greenhouse or anti-greenhouse effect. This work explores the interaction between scattering and vertical mixing, specifically whether these processes enhance or mitigate each other's effects on atmospheric temperature. The interaction between mixing flux and scattering is nonlinear. Our calculations indicate that thermal scattering intensifies the greenhouse effects caused by vertical mixing in the middle atmosphere but reduces it in the lower layers. In the middle atmosphere, increased vertical mixing enhances the warming effect of the thermal scattering while diminishing the cooling effect of visible scattering. In the lower atmosphere, it enhances the anti-greenhouse effect linked to visible scattering and diminishes the greenhouse effect produced by thermal scattering. The combined influence of thermal scattering and vertical mixing on the lower atmosphere's greenhouse effect is weaker than their separate impacts, akin to $1+1<2$. It is also interesting to note that the joint effect may also influence chemistry and cloud formation, altering the thermal structure.

astro-ph.EP↗

arXiv2025

Feature-Based Dual Visual Feature Extraction Model for Compound Multimodal Emotion Recognition

This article presents our results for the eighth Affective Behavior Analysis in-the-wild (ABAW) competition.Multimodal emotion recognition (ER) has important applications in affective computing and human-computer interaction. However, in the real world, compound emotion recognition faces greater issues of uncertainty and modal conflicts. For the Compound Expression (CE) Recognition Challenge,this paper proposes a multimodal emotion recognition method that fuses the features of Vision Transformer (ViT) and Residual Network (ResNet). We conducted experiments on the C-EXPR-DB and MELD datasets. The results show that in scenarios with complex visual and audio cues (such as C-EXPR-DB), the model that fuses the features of ViT and ResNet exhibits superior performance.Our code are avalible on https://github.com/MyGitHub-ax/8th_ABAW

cs.CV↗

arXiv2025

Exoplanet Ephemerides Change Observations (ExoEcho). I. Transit Timing Analysis of Thirty-Seven Exoplanets using HST/WFC3 Data

The ExoEcho project is designed to study the photodynamics of exoplanets by leveraging high-precision transit timing data from ground- and space-based telescopes. Some exoplanets are experiencing orbital decay, and transit timing variation (TTV) is a useful technique to study their orbital period variations. In this study, we have obtained transit middle-time data from the Hubble Space Telescope (HST) observations for 37 short-period exoplanets, most of which are hot Jupiters. To search for potential long- and short-term orbital period variations within the sample, we conduct TTV model fitting using both linear and quadratic ephemeris models. Our analysis identifies two hot Jupiters experiencing strong periodic decays. Given the old age of the host stars of the hot Jupiter population, our findings call for a scenario where HJs are continuously being destructed and created. Our study demonstrates the importance of incorporating high-precision transit timing data to TTV study in the future.

astro-ph.EP↗

arXiv2024

New record-breaking binary linear codes constructed from group codes

In this paper, we employ group rings and automorphism groups of binary linear codes to construct new record-breaking binary linear codes. We consider the semidirect product of abelian groups and cyclic groups and use these groups to construct linear codes. Finally, we obtain some linear codes which have better parameters than the code in \cite{bib5}. All the calculation results and corresponding data are listed in the paper or posted online.

cs.IT↗

arXiv2024

Streaming Torque with Turbulent Diffusion

Fast type-I migration of (proto)planets poses a challenging problem for the core accretion formation scenario. We found that the dust-induced ``Streaming Torque (ST)'' may slow down or even reverse the planet migration in \cite{Hou2024}. But in realistic protoplanetary disks, dust diffusion induced by gas turbulence may have important influences on ST. We perform linear analysis to investigate the effects of dust diffusion on ST. The dependence of ST on the dust diffusion may provide better constraints on the turbulence strength and the stopping time $\tau$. We derive the dispersion relation for all the wave modes in the two-fluid system. The dust diffusion will smooth the short-wavelength structure of the the quasi-drift mode and split it into two predominant D-drift modes with opposite directions. The outgoing D-drift mode will contribute to a negative torque on planets, particularly when $\tau \sim 0.1$, which slightly shifts the zero-torque turning point. We explore how ST depends on the regimes of aerodynamic drag, dust mass fraction and disk scale height. We compare the radial wavenumbers of D-drift modes under different formulations of dust diffusion and find qualitative agreement. In all cases, $\tau$ at the zero-torque turning point, which determines the direction of planetary migration, consistently remains on the order of $\sim 0.1$, corresponding to large pebble-sized dust grains. This suggests that rapid dust coagulation can inhibit the inward migration of planets, implying that weak gas turbulence may enhance the survival of protoplanets.

astro-ph.EP↗

arXiv2024

Vortex-Induced Rings and Gaps within Protoplanetary Disks

Observations of protoplanetary disks have revealed the presence of both crescent-shaped and ring-like structures in dust continuum emission. These crescents are thought to arise from dust-trapping vortices generated by the Rossby Wave Instability (RWI), which induces density waves akin to those caused by planets. These vortices have the potential to create gaps and rings within the disk, resulting from the dissipation of their density waves. We carry out 2D hydrodynamic simulations in the shearing box to investigate vortex-disk interaction. We find that long-lived vortices can produce dust rings and gaps in inviscid discs detectable by ALMA, and a more elongated vortex produces rings at larger separations. Vortex-induced density waves carry over two orders of magnitude higher angular momentum flux compared to planet-induced ones that shock at the same location, making the former much more effective at producing dust gaps and rings far away.

astro-ph.EP↗

arXiv2024

Irradiated Atmospheres I: Heating by Vertical-Mixing Induced Energy Transport

Observations have revealed unique temperature profiles in hot Jupiter atmospheres. We propose that the energy transport by vertical mixing could lead to such thermal features. In our new scenario, strong absorbers, TiO and VO are not necessary. Vertical mixing could be naturally excited by atmospheric circulation or internal gravity wave breaking. We perform radiative transfer calculations by taking into account the vertical mixing driven energy transport. The radiative equilibrium (RE) is replaced by radiative-mixing equilibrium (RME). We investigate how the mixing strength, $K_{\rm zz}$, affects the atmospheric temperature-pressure profile. Strong mixing can heat the lower atmosphere and cool the upper atmosphere. This effect has important effects on the atmosphere thermal features that would form without mixing. In certain circumstances, it can induce temperature inversions in scenarios where the temperature monotonically increases with increasing pressure under conditions of lower thermal band opacity. Temperature inversions show up as $K_{\rm zz}$ increases with altitude due to shear interaction with the convection layer. The atmospheric thermal structure of HD~209458b can be well fitted with $K_{\rm zz} \propto (P/1\ {\rm bar})^{-1/2}\ {\rm cm}^{2} \ {\rm s}^{-1}$. Our findings suggest vertical mixing promotes temperature inversions and lowers $K_{\rm zz}$ estimates compared to prior studies. Incorporating chemical species into vertical mixing will significantly affect the thermal profile due to their temperature sensitivity.

astro-ph.EP↗

arXiv2024

Constraining the Presence of Companion Planets in Hot Jupiter Planetary System Using TTV Observation from TESS

The presence of another planetary companion in a transiting exoplanet system can impact its transit light curve, leading to sinusoidal transit timing variations (TTV). By utilizing both $\chi^2$ and RMS analysis, we have combined the TESS observation data with an N-body simulation to investigate the existence of an additional planet in the system and put a limit on its mass. We have developed CMAT, an efficient and user-friendly tool for fitting transit light curves and calculating TTV with a theoretical period, based on which we can give a limit on its hidden companion's mass. We use 260 hot Jupiter systems from the complete TESS data set to demonstrate the use of CMAT. Our findings indicate that, for most systems, the upper mass limit of a companion planet can be restricted to several Jupiter masses. This constraint becomes stronger near resonance orbits, such as the 1:2, 2:1, 3:1, and 4:1 mean motion resonance, where the limit is reduced to several Earth masses. These findings align with previous studies suggesting that a lack of companion planets with resonance in hot Jupiter systems could potentially support the high eccentricity migration theory. Additionally, we observed that the choice between $\chi^2$ or {root mean square (RMS)} method does not significantly affect the upper limit on companion mass; however, $\chi^2$ analysis may result in weaker restrictions but is statistically more robust compared to RMS analysis in most cases.

astro-ph.EP↗

arXiv2024

Morphology and Behavior Co-Optimization of Modular Satellites for Attitude Control

The emergence of modular satellites marks a significant transformation in spacecraft engineering, introducing a new paradigm of flexibility, resilience, and scalability in space exploration endeavors. In addressing complex challenges such as attitude control, both the satellite's morphological architecture and the controller are crucial for optimizing performance. Despite substantial research on optimal control, there remains a significant gap in developing optimized and practical assembly strategies for modular satellites tailored to specific mission constraints. This research gap primarily arises from the inherently complex nature of co-optimizing design and control, a process known for its notorious bi-level optimization loop. Conventionally tackled through artificial evolution, this issue involves optimizing the morphology based on the fitness of individual controllers, which is sample-inefficient and computationally expensive. In this paper, we introduce a novel gradient-based approach to simultaneously optimize both morphology and control for modular satellites, enhancing their performance and efficiency in attitude control missions. Our Monte Carlo simulations demonstrate that this co-optimization approach results in modular satellites with better mission performance compared to those designed by evolution-based approaches. Furthermore, this study discusses potential avenues for future research.

cs.RO↗

arXiv2024

Vertical Shear Instability with Partially Reflecting Boundary Conditions

The vertical shear instability (VSI) is widely believed to be effective in driving turbulence in protoplanetary disks. Prior studies on VSI exclusively exploit the reflecting boundary conditions (BCs) at the disk surfaces. VSI depends critically on the boundary behaviors of waves at the disk surfaces. We extend earlier studies by performing a comprehensive numerical analysis of VSI with partially reflecting BCs for both the axisymmetric and non-axisymmetric unstable VSI modes. We find that the growth rates of the unstable modes diminish when the outgoing component of the flow is greater than the incoming one for high-order body modes. When the outgoing wave component dominates, the growth of VSI is notably suppressed. We find that the non-axisymmetric modes are unstable and they grow at a rate that decreases with the azimuthal wavenumber. The different BCs at the lower and upper disk surfaces naturally lead to non-symmetric modes relative to the disk midplane. The potential implications of our studies for further understanding planetary formation and evolution in protoplanetary disks (PPDs) are also briefly discussed.

astro-ph.EP↗

arXiv2024

Boundary Layers of Circumplanetary Disks around Spinning Planets II. Global Modes with Azimuthal Magnetic Fields

The accretion of material from disks onto weakly magnetized objects invariably involves its traversal through a material surface, known as the boundary layer (BL). Our prior studies have revealed two distinct global wave modes for circumplanetary disks (CPDs) with BLs exhibit opposite behaviors in spin modulation.We perform a detailed analysis about the effect of magnetic fields on these global modes, highlighting how magnetic resonances and turning points could complicate the wave dynamics. The angular momentum flux becomes positive near the BL with increasing magnetic field strength. We also examine the perturbation profile to demonstrate the amplification of magnetic fields within the BL. The dependence of growth rates on the magnetic field strength, and the spin rate are systematically investigated. We find that stronger magnetic fields tend to result in lower terminal spin rates. We stress the potential possibility for the formation of angular momentum belts and pressure bumps. The implication for the spin evolution and quasi-period oscillations observed in compact objects are also briefly discussed. Our calculations advance the understanding of magnetohydrodynamical (MHD) accretion processes and lays a foundation for observational studies and numerical simulations.

astro-ph.EP↗

arXiv2024

Streaming Torque in Dust-Gas Coupled Protoplanetary Disks

We investigate the migration of low-mass protoplanets embedded in dust-gas coupled protoplanetary disks. Linear calculations are performed with respect to the NSH (Nakagawa-Sekiya-Hayashi 1986) equilibrium within a shearing sheet. We find that the dusty quasi-drift mode dominates the dynamical behaviors in close proximity to the protoplanet. This mode exhibits an extremely short radial wavelength, characterized by a dispersion relation of $ \tilde{\omega} = \left( 1 + \mu \right) \boldsymbol{W}_s \cdot \boldsymbol{k}$. The emergence of this mode leads to a wake with a short radial length-scale ahead of protoplanets, contributing to a positive torque, termed as ``Streaming Torque (ST)''. Furthermore, both Lindblad torque and corotation torque are affected by the NSH velocity. The total torque and planetary migration are contingent upon the coupling strength between dust and gas. In most scenarios, ST predominates, inducing outward migration for planets, thereby addressing the issue of rapid inward migration in their formation paradigm.

astro-ph.EP↗

arXiv2024

Rossby wave instability in weakly ionized protoplanetary disks. I. azimuthal or vertical B-fields

Rossby wave instability (RWI) is considered the underlying mechanism to crescent-shaped azimuthal asymmetries, discovered in (sub-)millimeter dust continuum of many protoplanetary disks. Previous works on linear theory were conducted in the hydrodynamic limit. Nevertheless, protoplanetary disks are likely magnetized and weakly ionized. We examine the influence of magnetic fields and non-ideal magnetohydrodynamic (MHD) effects - namely, Ohmic resistivity, Hall drift, and ambipolar diffusion - on the RWI unstable modes. We perform radially global linear analyses, employing constant azimuthal ($B_\phi$) or vertical ($B_z$) background magnetic fields. It is found that, in the ideal MHD regime, magnetism can either enhance or diminish RWI growth. Strong non-ideal MHD effects cause RWI growth rates to recover hydrodynamic results. The sign of Hall Els\"{a}sser number subtly complicates the results, and vertical wavenumbers generically diminish growth rates.

astro-ph.EP↗

arXiv2024

The Impact-driven Atmospheric Loss of Super-Earths around Different Spectral Type Host Stars

The planet's mass loss is important for the planet's formation and evolution. The radius valley (RV) is believed to be triggered by evaporation-induced mass loss. As an alternative mechanism for the RV, the mass loss of post-impact planets is thoroughly investigated in this work. The impact energy is converted to the planet's internal energy, enhancing its core energy and accelerating mass loss and orbital migration. As the host star changes from K-type to F-type, the planet's mass loss and orbital migration increase. When the initial gas-to-core mass ratio (GCR) is small, the migration efficiency for planets around K-type stars will increase, which helps to suppress mass loss and retain the planet's mass and radius within a specific range. On the contrary, planets around more massive F-type stars experience more substantial mass loss, potentially leading to complete mass loss, and migrate to orbits with longer periods. Our calculation shows that planets around different spectral types of host stars give rise to an RV ranging from 1.3-2.0 $R_{\oplus}$, consistent with the observed range of 1.3-2.6 $R_{\oplus}$. Despite the presence of uncertain parameters, the planetesimal impact can promote the RV establishment for planets around host stars of different spectral types.

astro-ph.EP↗