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Accurate predictions of coastal ocean chlorophyll -a (Chl -a) concentrations are necessary for dynamic water quality monitoring, with eutrophication as a critical factor. Prior studies that used the driven-data method have typically overlooked the relationship between Chl -a and marine particulate carbon. To address this gap, marine particulate carbon was incorporated into machine learning (ML) and deep learning (DL) models to estimate Chl -a concentrations in the Yang Jiang coastal ocean of China. Incorporating particulate organic carbon (POC) and particulate inorganic carbon (PIC) as predictors can lead to successful Chl -a estimation. The Gaussian process regression (GPR) model significantly outperforming the DL model in terms of stability and robustness. A lower POC/Chl -a ratio was observed in coastal areas, in contrast to the higher ratios detected in the southern regions of the study area. This study highlights the efficacy of the GPR model for estimating Chl -a and the importance of considering POC in modeling Chl -a concentrations. • The Gaussian process regression (GPR) model outperformed the deep learning (DL) model in estimating coastal Chlorophyll- a (Chl- a). • Taking the particulate carbon as model inputs can estimate the Chl- a successfully. • The Chl- a concentration was higher in the coastal areas than in the open ocean. • Particulate organic carbon (POC) is the main driver of POC/Chl- a change. [ABSTRACT FROM AUTHOR]

Abstract: A three-dimensional chiral metamaterial consisting of arrays of the multi-layered mutually twisted metallic spirals is proposed. We theoretically demonstrate such a chiral spiral structure exhibiting negative refractive index at terahertz frequencies. The chirality with varied refractive index can be obtained by change of configurations of the structure. The presented design offers flexibility for investigation of electromagnetic properties of chiral metamaterials in the terahertz regime and thus leads to a unique route to terahertz device applications. [Copyright &y& Elsevier]

Abstract: The stress-optic law is fundamental to photoelasticity, and has been a prevalent method for measuring stress. However, its effectiveness in the terahertz (THz) regime has not been completely characterized. In this paper, the effects of uniaxial tensile stress on THz transmission through a polytetrafluoroethylene (PTFE) sample are investigated. Specifically, THz time domain spectroscopy (THz-TDS) has been used to measure the phase delay of transmitted THz radiation for different PTFE stress states. Differences in the refractive index of the PTFE are calculated from the measured phase delay. The calculated refractive index grows linearly with the applied stress, which can be considered a verification of the uniaxial stress-optic law in the terahertz frequency regime. [Copyright &y& Elsevier]

[Display omitted] • Nifedipine/isonicotinamide cocrystal polymorphs display THz spectral fingerprints. • Each THz fingerprint shows distinct frequency shift as temperature decreases. • DFT calculations assign each fingerprint to specific collective vibrational modes. • Hydrogen bond vibrations are important to stabilize polymorphic cocrystal structures. • Rotations of methyl group in nifedipine contribute to the steric recognition. Cocrystal is constructed to improve physicochemical properties of active pharmaceutical ingredient and prevent polymorphism via intermolecular interactions. However, recent examples on cocrystal polymorphs display significantly different properties. Even though some analytical techniques have been used to characterize the cocrystal polymorphic system, it remains unclear how intermolecular interactions drive and stabilize the structure. In this work, we study the cocrystal polymorphs of nifedipine (NFD) and isonicotinamide (INA) using terahertz (THz) spectroscopy. Form I and form II of NFD-INA cocrystals show spectral fingerprints in THz region. Temperature-dependent THz spectra display distinguished frequency shifts of each fingerprint. Combined with solid-state density functional theory (DFT) calculations, the experimental fingerprints and their distinct responses to temperature are elucidated by specific collective vibrational modes. The vibrations of hydrogen bonding between dihydropyridine ring of NFD and INA are generally distributed below 1.5 THz, which play important roles in stabilizing cocrystal and preventing the oxidation of NFD. The rotations of methyl group in NFD are widely distributed in the range of 1.5–4.0 THz, which helps the steric recognition. The results demonstrate that THz spectroscopy is a sensitive tool to discriminate cocrystal polymorphs. It has the potential to be used as a non-invasive technique for pharmaceutical screening. [ABSTRACT FROM AUTHOR]