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Abstract Optical phonon engineering through nonlinear effects has been utilized in ultrafast control of material properties. However, nonlinear optical phonons typically exhibit rapid decay due to strong mode-mode couplings, limiting their effectiveness in temperature or frequency sensitive applications. Here we report the observation of long-lived nonlinear optical phonons through the spontaneous formation of phonon frequency combs in the van der Waals material CrXTe₃(X=Ge, Si) using high-resolution Raman scattering. Unlike conventional optical phonons, the highestA_gmode in CrGeTe₃splits into equidistant, sharp peaks forming a frequency comb that persists for hundreds of oscillations and survives up to 200K. These modes correspond to localized oscillations of Ge₂Te₆clusters, isolated from Cr hexagons, behaving as independent quantum oscillators. Introducing a cubic nonlinear term to the harmonic oscillator model, we simulate the phonon time evolution and successfully replicate the observed comb structure. Similar frequency comb behavior is observed in CrSiTe₃, demonstrating the generalizability of this phenomenon. Our findings demonstrate that Raman scattering effectively probes high-frequency nonlinear phonon modes, offering insight into the generation of long-lived, tunable phonon frequency combs with potential applications in ultrafast material control and phonon-based technologies. 

Abstract The recent Far-Infrared Polarimetric Large-Area Central Molecular Zone Exploration (FIREPLACE) survey with SOFIA has mapped plane-of-sky magnetic field orientations within the Central Molecular Zone (CMZ) of the Milky Way. Applying the Histogram of Relative Orientations analysis to the FIREPLACE data, we find that the relative orientation between magnetic fields and column density structures is random in low-density regions ( $2\times 10^{22}\lesssim N_{{\mathrm{H}}_2}\lesssim 10^{23}{\mathrm{cm}}^{-2}$) but becomes preferentially parallel in high-density regions (≳10²³cm⁻²). This trend is in contrast with that of the nearby molecular clouds, where the relative orientation transitions from parallel to perpendicular with increasing column densities. However, the relative orientation varies between individual CMZ clouds. Comparisons with magnetohydrodynamic simulations specific to the CMZ conditions suggest that the observed parallel alignment is intrinsic, rather than artifacts caused by the projection effect. The origin of this parallel configuration may arise from the fact that most dense structures in the CMZ are not self-gravitating, as they are in supervirial states, except for the ministarburst region Sgr B2. These findings are consistent with the low star formation efficiency observed in the CMZ compared to that in the Galactic disk. 

Abstract We report the first arcsecond-resolution observations of the magnetic field in the ministarburst complex Sgr B2. SMA polarization observations revealed magnetic field morphology in three dense cores of Sgr B2 N(orth), M(ain), and S(outh). The total plane-of-sky magnetic field strengths in these cores are estimated to be 4.3–10.0 mG, 6.2–14.7 mG, and 1.9–4.5 mG derived from the angular dispersion function method after applying the correction factors of 0.21 and 0.5. Combining with analyses of the parsec-scale polarization data from Stratospheric Observatory for Infrared Astronomy, we found that a magnetically supercritical condition is present from the cloud scale (∼10 pc) to core scale (∼0.2 pc) in Sgr B2, which is consistent with the burst of star formation activities in the region likely resulting from a multiscale gravitational collapse from the cloud to dense cores. 

eal-time systems with hard timing constrains require known upper bounds on each task’s worst-case execution time (WCET) to determine if all deadlines can be met. One challenge in predictable execution is that Dynamic Random Access Memory (DRAM) cells must be refreshed periodically to maintain data validity, yet memory remains blocked during refresh, which results in overly pessimistic WCET bounds. This work contributes “Colored Refresh” to hide DRAM refresh overhead while preserving real-time schedulability for cyclic executives, which are widely used in highly critical systems. Colored Refresh partitions DRAM memory at rank granularity such that refreshes rotate round-robin from rank to rank. Real-time tasks are assigned different ranks via colored memory allocation. By cooperatively scheduling real-time tasks and refresh operations, memory requests no longer suffer from refresh interference. This reduces memory access latencies for tasks irrespective of DRAM density and size. Hence, Colored Refresh reduces a task’s WCET and makes its execution more predictable. 

Bounding each task’s worst-case execution time (WCET) accurately is essential for real-time systems to determine if all deadlines can be met. Yet, access latencies to Dynamic Random Access Memory (DRAM) vary significantly due to DRAM refresh, which blocks access to memory cells. Variations further increase as DRAM density grows. This work contributes the “Colored Refresh Server” (CRS), a uniprocessor scheduling paradigm that partitions DRAM in two distinctly colored groups such that refreshes of one color occur in parallel to the execution of real-time tasks of the other color. By executing tasks in phase with periodic DRAM refreshes with opposing colors, memory requests no longer suffer from refresh interference. Experimental results confirm that refresh overhead