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1. A Machine Learning Driven Ultrafast Mid-Infrared Spectroscopic System for Mixed Plastic Characterization

   https://doi.org/10.65569/FQZE6459  

   Long, Fei; Bar-Ziv, Saar; Idrisi, Amir Hussain; Adekunle, Adeyinka; Bar-Ziv, Ezra (January 2025, REMADE Institute)

   The U.S. Environmental Protection Agency estimates that over 35.6 million tons of plastic waste are generated annually in the United States, yet only 8.7% is recycled, with approximately 75% ending up in landfills. Among the landfilled plastic waste, 15%—equivalent to more than 2.5 million tons annually—comprise black and dark-colored plastics. This high disposal rate is primarily due to the inability of existing optical sensors, such as near-infrared (NIR) and camera systems used in Material Recovery Facilities, to detect black plastics due to their low reflectivity in the near-visible wavelength range. Mid-infrared (MIR) technology has the potential to overcome this limitation by providing accurate compositional information independent of plastic color. However, traditional MIR systems suffer from slow measurement speeds, limiting their applicability in industrial settings. To address this challenge, we developed a ultra high-speed MIR characterization system capable of measuring of up 400-10,000 infrared spectra per second, integrated with a belt conveyor operating at 20-600 feet per minute. This innovation bridges the gap between laboratory-grade MIR analysis and the operational requirements of industrial recycling facilities. To ensure reliable performance despite the low signal-to-noise ratio inherent to high-speed MIR measurements, we implemented robust wavelet data preprocessing techniques. Additionally, we developed a lightweight machine learning (ML) model that achieves over 95%-99% accuracy in characterizing mixed plastic waste, including black plastics. Our ML model is designed for efficiency and operation without reliance on large-scale data centers, enabling seamless integration into industrial control systems. By facilitating the accurate identification and recovery of black plastics, our MIR characterization system offers a practical solution to increase recycling rates and reduce landfill waste. This innovation supports the development of a sustainable and circular economy in plastic recycling, addressing critical environmental challenges and unlocking new opportunities for resource recovery. 

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2. Mid- and Far-infrared Color–Color Relations within Local Galaxies

   https://doi.org/10.3847/1538-4357/ac558a  

   Gregg, Benjamin; Calzetti, Daniela; Heyer, Mark (March 2022, The Astrophysical Journal)

   Abstract We present an extensive archival analysis of a sample of local galaxies, combining multiwavelength data from GALEX, Spitzer, and Herschel to investigate “blue-side” mid-infrared (MIR) and “red-side” far-infrared (FIR) color–color correlations within the observed infrared spectral energy distributions. Our sample largely consists of the KINGFISH galaxies, with the important addition of a select few including NGC 5236 (M83) and NGC 4449. With data from the far-ultraviolet (∼0.15 μ m) through 500 μ m convolved to common angular resolution, we measure the photometry of kiloparsec-scale star-forming regions 36″ × 36″ in size. Star formation rates (SFRs), stellar masses, and metallicity distributions are derived throughout our sample. Focusing on the f 70 / f 500 “FIR” and f 8 / f 24 “MIR” flux density ratios (colors), we find that a subsample of galaxies demonstrate a strong IR color–color correlation within their star-forming regions, while others demonstrate uncorrelated colors. This division is driven by two main effects: (1) the local strength of star formation (SF) and (2) the metal content of the interstellar medium (ISM). Galaxies uniformly dominated by high surface densities of SF (e.g., NGC 5236) demonstrate strong IR color–color correlations, while galaxies that exhibit lower levels of SF and mixed environments (e.g., NGC 5457) demonstrate weaker or no correlation—explained by the increasing effect of varying ISM heating and metal content on the IR colors, specifically in the MIR. We find large dispersion in the SFR– L 8 (8 μ m luminosity) relation that is traced by the metallicity distributions, consistent with extant studies, highlighting its problematic use as an SFR indicator across diverse systems/samples. 

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3. Ground-based and JWST Observations of SN 2022pul. I. Unusual Signatures of Carbon, Oxygen, and Circumstellar Interaction in a Peculiar Type Ia Supernova

   https://doi.org/10.3847/1538-4357/ad0975  

   Siebert, Matthew R; Kwok, Lindsey A; Johansson, Joel; Jha, Saurabh W; Blondin, Stéphane; Dessart, Luc; Foley, Ryan J; Hillier, D John; Larison, Conor; Pakmor, Rüdiger; et al (December 2023, The Astrophysical Journal)

   Abstract Nebular-phase observations of peculiar Type Ia supernovae (SNe Ia) provide important constraints on progenitor scenarios and explosion dynamics for both these rare SNe and the more common, cosmologically useful SNe Ia. We present observations from an extensive ground- and space-based follow-up campaign to characterize SN 2022pul, a super-Chandrasekhar mass SN Ia (alternatively “03fg-like” SN), from before peak brightness to well into the nebular phase across optical to mid-infrared (MIR) wavelengths. The early rise of the light curve is atypical, exhibiting two distinct components, consistent with SN Ia ejecta interacting with dense carbon–oxygen (C/O)-rich circumstellar material (CSM). In the optical, SN 2022pul is most similar to SN 2012dn, having a low estimated peak luminosity (M_B= −18.9 mag) and high photospheric velocity relative to other 03fg-like SNe. In the nebular phase, SN 2022pul adds to the increasing diversity of the 03fg-like subclass. From 168 to 336 days after peakB-band brightness, SN 2022pul exhibits asymmetric and narrow emission from [Oi]λλ6300, 6364 (FWHM ≈ 2000 km s⁻¹), strong, broad emission from [Caii]λλ7291, 7323 (FWHM ≈ 7300 km s⁻¹), and a rapid Feiiito Feiiionization change. Finally, we present the first ever optical-to-MIR nebular spectrum of an 03fg-like SN Ia using data from JWST. In the MIR, strong lines of neon and argon, weak emission from stable nickel, and strong thermal dust emission (withT≈ 500 K), combined with prominent [Oi] in the optical, suggest that SN 2022pul was produced by a white dwarf merger within C/O-rich CSM. 

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4. PHANGS–JWST First Results: A Global and Moderately Resolved View of Mid-infrared and CO Line Emission from Galaxies at the Start of the JWST Era

   https://doi.org/10.3847/2041-8213/acab01  

   Leroy, Adam K.; Bolatto, Alberto D.; Sandstrom, Karin; Rosolowsky, Erik; Barnes, Ashley. T.; Bigiel, F.; Boquien, Médéric; den Brok, Jakob S.; Cao, Yixian; Chastenet, Jérémy; et al (February 2023, The Astrophysical Journal Letters)

   Abstract We explore the relationship between mid-infrared (mid-IR) and CO rotational line emission from massive star-forming galaxies, which is one of the tightest scalings in the local universe. We assemble a large set of unresolved and moderately (∼1 kpc) spatially resolved measurements of CO (1–0) and CO (2–1) intensity, I CO , and mid-IR intensity, I MIR , at 8, 12, 22, and 24 μ m. The I CO versus I MIR relationship is reasonably described by a power law with slopes 0.7–1.2 and normalization I CO ∼ 1 K km s −1 at I MIR ∼ 1 MJy sr −1 . Both the slopes and intercepts vary systematically with choice of line and band. The comparison between the relations measured for CO (1–0) and CO (2–1) allow us to infer that R 21 ∝ I MIR 0.2 , in good agreement with other work. The 8 μ m and 12 μ m bands, with strong polycyclic aromatic hydrocarbon (PAH) features, show steeper CO versus mid-IR slopes than the 22 and 24 μ m, consistent with PAH emission arising not just from CO-bright gas but also from atomic or CO-dark gas. The CO-to-mid-IR ratio correlates with global galaxy stellar mass ( M ⋆ ) and anticorrelates with star formation rate/ M ⋆ . At ∼1 kpc resolution, the first four PHANGS–JWST targets show CO-to-mid-IR relationships that are quantitatively similar to our larger literature sample, including showing the steep CO-to-mid-IR slopes for the JWST PAH-tracing bands, although we caution that these initial data have a small sample size and span a limited range of intensities. 

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5. Aromaticity versus regioisomeric effect of β-substituents in porphyrinoids

   https://doi.org/10.1039/C9CP01177C  

   Yao, Yuhang; Rao, Yu; Liu, Yiwei; Jiang, Liang; Xiong, Jin; Fan, Ying-Jie; Shen, Zhen; Sessler, Jonathan L.; Zhang, Jun-Long (May 2019, Physical Chemistry Chemical Physics)

   The photophysical properties of naturally occurring chlorophylls depend on the regioisomeric nature of the β-pyrrolic substituents. Such systems are the “gold standard” by which such effects are judged. However, simple extrapolations from what has been learned with chlorophylls may not be appropriate for other partially reduced porphyrinoids. Here we report the synthesis of a series of cis / trans -porphodilactones ( cis / trans -1) and related derivatives ( cis / trans 2–5) designed to probe the effect of regioisomeric substitution in porphyrinoids that incorporate degrees of unsaturation through the β-pyrrolic periphery that exceed those of chlorophyll. These test systems were obtained through β-pyrrolic modifications of the tetrapyrrolic core, which included reduction of β-diazalone to the corresponding dilactol moieties and 1,3-dipolar cycloadditions. In the case of cis - vs. trans -3 bearing two pyrrolidine-fused β-rings we found an unprecedented Δ Q L up to ca. 71 nm (2086 cm −1 ), where Δ Q L ( Q L means the lowest energy transfer band, also the S 0 → S 1 transition band, which is often assigned as Q y (0,0) band) refers to the transition energy difference between the corresponding cis / trans -isomers. The Δ Q L values for these and other systems reported here were found to depend on the differences in the HOMO–LUMO energy gap and to be tied to the degeneracy and energy level splitting of the FMOs, as inferred from a combination of MCD spectral studies and DFT calculations. The aromaticity, estimated from the chemical shifts of the N–H protons and supported by theoretical calculations ( e.g. , AICD plots and NICS(1) values), was found to correlate with the extent of porphyrin periphery saturation resulting from the specific β-modifications. The aromaticity proved inversely proportional to the degree to which the regioisomerism affected the photophysical properties as noted from plots of Δ Q L s in cm −1 vs. the average NICS(1) values for 1–5. Such a finding is not something that can be easily interpolated from prior work and thus reveals how aromaticity may be used to fine-tune photophysical effects in reduced porphyrinoids. 

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