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Machine learning is a promising tool to reconstruct time-series phenomena, such as variability of active galactic nuclei (AGN), from sparsely-sampled data. Here we use three Continuous Auto-Regressive Moving Average (CARMA) representations of AGN variability – the Damped Random Walk (DRW) and (over/under-)Damped Harmonic Oscillator (DHO) – to simulate 10-year AGN light curves as they would appear in the upcoming Vera Rubin Observatory Legacy Survey of Space and Time (LSST), and provide a public tool to generate these for any survey cadence. We investigate the impact on AGN science of five proposed cadence strategies for LSST’s primary Wide-Fast-Deep (WFD) survey. We apply for the first time in astronomy a novel Stochastic Recurrent Neural Network (SRNN) algorithm to reconstruct input light curves from the simulated LSST data, and provide a metric to evaluate how well SRNN can help recover the underlying CARMA parameters. We find that the light curve reconstruction is most sensitive to the duration of gaps between observing season, and that of the proposed cadences, those that change the balance between filters, or avoid having long gaps in the g-band perform better. Overall, SRNN is a promising means to reconstruct densely sampled AGN light curves and recover the long-term Structure Function of the DRW process (SF∞) reasonably well. However, we find that for all cadences, CARMA/SRNN models struggle to recover the decorrelation timescale (τ) due to the long gaps in survey observations. This may indicate a major limitation in using LSST WFD data for AGN variability science.

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We present a robust simultaneous multiwavelength bulk laser based on Yb:LaMgB5O10 (Yb:LMB) crystal, including its continuous-wave (CW) and ultrafast pulsed regimes. CW dual wavelengths at 1077 nm and 1091 nm with an average output power of 2.67 W were achieved with a 1% output coupling (OC). A maximum output power of 4.42 W with triple wavelengths of 1056, 1077, and 1091 nm was generated with 3% OC. In the case of 25% OC, the Yb:LMB laser can operate with four wavelengths (1025.1, 1031.4, 1033.2, and 1053.3 nm), producing an average output power of up to 4.44 W. Furthermore, 568 fs pulses with an average power of 470 mW were obtained at 1057.4, 1079.2, and 1092.4 nm from a synchronous tri-wavelength mode-locked Yb:LMB laser. These pulses are the shortest ever reported from a synchronous tri-wavelength mode-locked bulk laser. The detected frequency beating pulses had a primary interval of 0.11 ps and a full width at half maximum of 77 fs. Results indicated that equal spectral separation between each wavelength is not an essential factor for establishing a synchronous tri-wavelength mode-locking operation.

Hydrous materials such as clays, cements, hydroxyapatite, and metal hydroxides have been known and extensively used since antiquity. However, experimental elucidation of hydrogen in hydrous materials remains challenging due to the intrinsic insensitivity, limited accessibility, sample damage, or poor spectral resolution of many characterization methods. 1 H solid-state NMR spectroscopy has evolved into an ideal site-specific characterization tool of hydrogen-containing materials, but its current application in hydrous materials is hampered by the low resolution of 1 H NMR spectra in the solid state due to the presence of intense dipolar coupling networks and a narrow 1 H chemical shift range. Herein, a significant advance in the characterization of hydrogens in hydrous materials is reported. A combination of magic-angle spinning (MAS) NMR, moderate 2 H substitution, and high magnetic fields has unlocked the capacity of identifying many chemically similar while crystallographically distinct hydrogen sites in a prototypical hydrous material Y 4 (OH) 10 Br 2 •3H 2 O (LYH-Br) by 1D 1 H solid-state NMR experiments. 1 H NMR peaks were first tentatively assigned in accordance with the density functional theory (DFT) calculation results, and the assignment was further refined by 2D 1 H− 89 Y heteronuclear correlation (HETCOR) and 1 H− 1 H doublequantum (DQ) MAS NMR data. The order of 1 H chemical shift (δ iso ) values provides valuable information on the relative strength of hydrogen bond for ten hydroxide hydrogen sites. The power of very high spectral resolution is further described by observing all triple-quantum (TQ) coherences in the 2D 1 H− 1 H TQ MAS NMR spectrum, in which all spatial proximities among three hydrogen sites are resolved. This demonstration of the very high spectral resolution obtained in 1D and 2D 1 H solid-state NMR experiments illustrates how scientists in various communities can now study the multiple hydrous species of hydrous materials and obtain previously inaccessible fine structural information.