Science China Physics, Mechanics & Astronomy最新文献

The possible existence of an exotic phase of matter, rigid like a solid but able to sustain persistent and dissipation-less flow like a superfluid, a “supersolid”, has been the subject of intense theoretical and experimental efforts since the discovery of superfluidity in Helium-4. Recently, it has been proposed that nonlinear periodic modulations known as cnoidal waves, that naturally emerge in Bose-Einstein condensates, provide a promising platform to find and study supersolidity in non-equilibrium phases of matter. Nevertheless, so far the analysis has been limited to a one-dimensional zero-temperature system. By combining the dissipative Gross-Pitaevskii equation with a finite temperature holographic model, we show that the proposed cnoidal wave supersolid phases of matter are dynamically unstable at finite temperature. We ascribe this instability to the dynamics of the “elastic” Goldstone mode, which arises as a direct consequence of translational order in the presence of dissipation, and establish a direct connection between the elastic-mode instability of the supersolid state and the nucleation of topological excitations during the relaxation towards a homogeneous equilibrium state, which resembles the Landau instability in superfluids. Finally, we numerically confirm the dominant role of the elastic-mode instability in the collision between cnoidal waves in the strong dissipation limit.

We experimentally and numerically investigated the hydrodynamics, fragmentation mechanisms, and debris distribution arising from the interaction of nanosecond laser pulses with a gallium-indium-tin (Ga-In-Sn) liquid film of micron-scale thickness. High-speed stroboscopic shadow photography was employed to visualize the splash crown and ejection of debris. The velocities of this debris, ranging from 329 to 4211 m s⁻¹, were found to scale with laser pulse energy (E_p = 0.9–36 mJ) and film thickness (h) according to U ∝ E ^5/9_p /h. This velocity was accurately described by a modified ablation and propulsion model. The numerical simulations provided insights into the underlying physics, including the expansion of high-pressure plasma zone, shock wave propagation, and the formation of significant negative pressure regions conducive to cavitation. Furthermore, the direction of minimal debris deposition is found to align with peak plasma luminous intensity, which is normal to the liquid film.

Magnetic soft continuum robots (MSCRs) offer transformative potential for minimally invasive procedures due to their high flexibility and magnetic responsiveness. However, reliable and efficient programming of MSCRs for anatomical adaptability and precise tip manipulation remains a key challenge, particularly in navigating tortuous pathways and targeting hard-to-reach lesions. Addressing this, we propose a unified inverse programming framework based on Physics-Informed Neural Networks (PINNs) that simultaneously tackles two critical design objectives in MSCR applications: shape morphing and tip trajectory control. The shape morphing problem involves programming magnetization distributions during fabrication to achieve desired global geometries, while trajectory control is realized by designing time-varying magnetic fields to guide the robot tip along prescribed paths. Leveraging the hard-magnetic elastica model, we reformulate the inverse design challenge into solving a nonlinear ordinary differential equation (ODE). The proposed PINN-based framework seamlessly integrates physical priors into the learning process, enabling rapid convergence while requiring only sparse data. We validate our approach using complex geometries, including shapes resembling the letters “USTC”, and benchmark the results against finite difference (FDM) and finite element method (FEM) simulations. The strong agreement across methods confirms the reliability and accuracy of the PINN-based framework. Our method offers a versatile and computationally efficient tool for the inverse design and control of programmable MSCRs and opens new pathways for data-free, high-fidelity, multi-objective optimization in magnetically actuated soft robotics.

Photolithography-assisted chemo-mechanical etching (PLACE), a dedicated fabrication methodology for high-quality (high-Q) large-scale photonic integrated circuits (PICs) on thin-film lithium niobate (TFLN), has enabled the realization of diverse PICs spanning from high-Q micro-resonators to waveguide amplifiers and programmable photonic circuits. To advance high-throughput TFLN PICs manufacturing, we developed a laser lithography technique employing a high repetition-rate femtosecond laser and a high-speed polygon scanner, achieving a lithography throughput of 2.4 cm²/h and optical propagation loss below 0.1 dB/cm. System capabilities are further evidenced by the demonstration of wafer-scale fabricated TFLN photonic devices, confirming the scalability and performance of this lithographic platform.

The nature of dark matter (DM) remains mysterious despite the substantial evidence from astrophysical and cosmological observations. While the majority of DM in our universe is non-relativistic, collisionless and its equation of state (EoS) is approximately pressureless p ≃ 0, DM becomes relativistic near the massive black holes (BHs) in galactic center. Yet its EoS is seldom discussed in the relativistic regime. Here we initially explore the possible EoS for DM in the vicinity of Schwarzschild BHs. We work in a spherical and quasi-static background spacetime, and describe DM as a perfect fluid in equilibrium. By numerically solving the Tolman-Oppenheimer-Volkoff equations with physical spatial initial conditions, we show that DM can have static profiles near BHs and its pressure should be negative in order to support the viable density profiles ρ. We illustrate with two simple general EoSs, namely the polytropic–like p ∝ ρ^γ and the radius-dependent p ∝ r · ρ, and compare them with the observations of the Milky Way. Our findings provide insights into the model-building of DM, which should incorporate the possibility of negative pressure in the relativistic regime around BHs if such shallower DM profiles are probed by future gravitational-wave detectors in space.

This paper reviews the recent advances of practical techniques within different method frameworks for improved uncertainty propagation in orbital dynamics. The uncertainty propagation problem has been explored in many applications in orbital dynamics, such as orbit determination, relative motion, space debris removal, and small body exploration. In recent years, to further improve the accuracy and efficiency of uncertainty propagation, many practical techniques have been presented within different method frameworks. Among these, most techniques are within the frameworks of the continuity equation, the Gaussian mixture model, and the surrogate model. To facilitate the research work for nonlinear uncertainty propagation in orbital dynamics, a classification of the present method frameworks and the practical techniques for improved uncertainty propagation within different method frameworks is given and discussed in this paper.

Broadband undistorted transmission is one of the criteria to preserve the information carried by incident waves and pulses, allowing imaging formation and source detection. For transmission through artificial materials like metasurfaces, undistorted transmission usually requires each meta-atom to possess exactly the same transmission amplitude and phase. Here, we consider a special acoustic metasurface consisting of meta-atoms with the same transmission phase but different transmittance. Interestingly, we find that when the meta-atoms are of subwavelength scale, the difference in transmittance would not induce substantial distortion in the transmitted wavefront. Based on this observation, we numerically and experimentally demonstrate acoustic metasurfaces that exhibit undistorted transmission and configurable arbitrary reflection. Two distinct types of reflection, i.e., anomalous reflection and diffuse reflection, are numerically and experimentally demonstrated with the transmission wavefront undistorted through a broad spectrum. Our work reveals a more general condition for realizing broadband undistorted transmission and configurable reflection with metasurfaces, which has potential implications in acoustic field manipulation and novel sonar domes.

The Lunar Orbital VLBI Experiment (LOVEX) is a scientific component of the Chinese Lunar Exploration Project (CLEP) Chang’E-7. The spaceborne component of LOVEX is implemented onboard the relay satellite QueQiao-2, which was launched on 20 March 2024, and later placed into an elliptical selenocentric orbit. The LOVEX-specific payload consists of an X-band cryogenic receiver, a hydrogen maser frequency standard, and VLBI data formatting and acquisition electronics. Several components of the QueQiao-2 nominal onboard instrumentation, such as the 4.2-m antenna, the data storage device, and the downlink communication system, contribute to the overall spaceborne VLBI instrumentation. This allows us to form a space radio telescope capable of co-observing with Earth-based radio telescopes in VLBI mode. In this space VLBI system, the length of the baseline extends up to approximately 380000 km. This paper presents the LOVEX scientific objectives, architecture, instrumentation, prelaunch tests, in-flight verification and calibration, and the first in-flight detections of interferometric response (“fringes”) achieved through observations of the quasar AO 0235+164 and the Chang’E-6 orbital module, positioned at the Sun-Earth Lagrange point L2. These initial results demonstrate the successful performance of LOVEX, verifying its capability for both astronomical and spacecraft tracking observations at ultra-long VLBI baselines.