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We propose the use of a second-order sliding-mode controller (2-SMC) to stabilize an autonomous underwater vehicle (AUV) which is subject to modeling errors and often suffers from unknown environmental disturbances. The 2-SMC is effective in compensating for the uncertainties in the hydrodynamic and hydrostatic parameters of the vehicle and rejecting the unpredictable disturbance effects due to ocean waves, tides, and currents. The 2-SMC is comprised of an equivalent controller and a switching controller to suppress the parameter uncertainties and external disturbances, and its closed-loop system is exponentially stable in the presence of parameter uncertainties and unknown disturbances. We performed numerical simulations to validate the proposed control approach, and experimental tests using Cyclops AUV were conducted to demonstrate its practical feasibility. The proposed controller increased the accuracy of trajectory tracking for an AUV in the presence of uncertain hydrodynamics and unknown disturbances. [ABSTRACT FROM AUTHOR]

Abstract: Conventional underwater manipulation is performed by a remotely operated vehicle (ROV) equipped with a rigidly connected multi-link arm. However, accurate manipulation requires the ROV to have excellent maneuverability, which limits the design flexibility and capabilities of the vehicle. This paper instead proposes the use of a small, deployable, and highly maneuverable agent ROV as an end effector, which is connected to the main vehicle by a flexible smart cable. This cable tracks the relative position of the agent, thus eliminating the need for additional positioning sensors and allowing significant size reduction for the agent. In addition, to compensate for the limited lifting capability of the small agent, it is equipped with active buoyancy control. The proposed system can be applied to common autonomous underwater vehicles (AUVs) with minimal modification for coarse station-keeping. The whole system is operated as a conventional AUV under normal operating conditions, but the agent is deployed when manipulation or precise monitoring is necessary. Numerical simulations were performed for dynamic analysis and prototype design of the agent vehicle, and this design was implemented as a model-scale system for experiments in a test tank. This implementation confirmed the feasibility and potential capabilities of the proposed manipulation system concept. [Copyright &y& Elsevier]

This paper proposes a method for mapping the height information on an area around a vehicle and of identifying a drivable area by fusing a stereo camera and a laser sensor. A SOM (Self Organizing Map) clustering algorithm obtained from the depth information of the stereo camera is used to analyze the front part area of a vehicle in forms of several candidate planes. In addition, an IMU indicating the current pose of a vehicle is applied to detect a drivable plane. A laser sensor installed on a vehicle's roof scans the front part with a single line and informs a distance value. A drivable plane detected is utilized to calculate height value in the normal direction detected by the laser scan data. Additionally, when the height already mapped has a value higher than that of the threshold, it is regarded as an obstacle and the vehicle is prevented from coming into contact with it. Regarding the vehicle position estimation, a Kalman filter method is used for real-time mapping during driving. The moving location of the vehicle is dead reckoned based on steering angle and velocity, and this value is compensated using the position value received from the GPS. The vehicle's position and mapping coordinates are converted into latitude and longitude values. This study demonstrates that it is possible to generate a precise 2D height map by conducting a test in a real road environment with various slope angles and obstacles. [ABSTRACT FROM AUTHOR]

Abstract: Automation of complicated underwater tasks require acoustic image based object recognition. This paper presents an acoustic image based real-time object recognition system. We proposed an acoustic image predictor to estimate an object''s shape in advance. Depending on the acoustic camera''s position, the predictor generates optimal template for recognition. The proposed method is implemented in our autonomous marine vehicle. For real-time processing, efficient recognition strategies are addressed. The vehicle detects an object and localizes it for recognition. In the detection process, the acoustic image''s specific characteristics are used as the detection cues. In the localization process, the vehicle''s horizontal and vertical positioning strategies are described. Efficient template generation method to minimize computing power is addressed. This realizes real-time recognition using the vehicle. To estimate the proposed system''s accuracy and reliability, a recognition test was carried out in the field. The vehicle successfully recognized two different objects with high accuracy. [Copyright &y& Elsevier]

This work reports a series of new organic electro‐optic salt crystals possessing unusual orthogonal dipole‐coupling assembly that act as dimple‐free THz generators. In the new crystals, optically anisotropic aromatic anions introducing highly electronegative fluorinated substituents are orthogonally assembled with optically anisotropic nonlinear optical benzothiazolium cations. These orthogonal cation–anion assembled crystals exhibit strong suppression of intrinsic THz phonon modes along the polar axis, which results in a wide THz absorption‐free range from 1.5 to 4.0 THz without substantial absorption peaks. This is sharply in contrast to previous benchmark crystals with parallel cation–anion assembly; for example, in analogous crystals, several strong absorption peaks appear in this frequency range. This absence of strong absorption peaks is attributed to the orthogonal cation–anion dipole coupling assembly, the formation of fluorinate‐induced strong interionic interactions, and a high packing ability of uniaxial anions. With top‐level macroscopic optical nonlinearity, new orthogonal‐dipole assembled crystals make dimple‐free THz wave generation possible in the range of about 1.5–4.0 THz, which is very beneficial for characterizing signature peaks related to molecular phonon motions of analytes in THz spectroscopy. Therefore, orthogonal molecular assembly of optically highly anisotropic molecules provides an efficient way to substantially reduce and control intrinsic THz phonon modes. [ABSTRACT FROM AUTHOR]

In this study, we develop new organic benzothiazolium crystals possessing very large off-diagonal optical nonlinearity. In these crystals, benzothiazolium-based 2-(4-(4-(hydroxymethyl)piperidin-1-yl)styryl)-3-methylbenzothiazol-3-ium (PMB) cations with large molecular optical nonlinearity are incorporated with two anions: 4-(trifluoromethoxy)benzenesulfonate (TFO) with an orthogonal non-planar shape and 5-bromothiophene-2-sulfonate (BTS) with a planar shape. Both PMB-TFO and PMB-BTS crystals exhibit state-of-the-art off-diagonal effective hyperpolarizability (~105 × 10−30 esu) that results from the V-shape and X-shape alignments of PMB chromophores, respectively. Newly developed PMB crystals indicate excellent characteristics for second-order nonlinear optical applications such as difference-frequency generation (e.g. optical rectification) and sum-frequency generation (e.g. second-harmonic generation), which are comparable to current benchmark organic crystals. Newly developed PMB-based crystals exhibit state-of-the-art off-diagonal effective hyperpolarizability and show excellent frequency conversion characteristics, including efficient optical-to-THz conversion using the large off-diagonal optical nonlinearity. [Display omitted] • New benzothiazolium crystals exhibit state-of-the-art off-diagonal optical nonlinearity. • Large off-diagonal optical nonlinearity of new benzothiazolium crystals originates from different ordering of chromophores. • New benzothiazolium crystals indicate excellent performance in second-order nonlinear optical processes. [ABSTRACT FROM AUTHOR]

This paper proposes a sonar-based underwater object classification method for autonomous underwater vehicles (AUVs) by reconstructing an object's three-dimensional (3D) geometry. The point cloud of underwater objects can be generated from sonar images captured while the AUV passes over the object. Then, a neural network can predict the class given the generated point cloud. By reconstructing the 3D shape of the object, the proposed method can classify the object accurately through a straightforward training process. We verified the proposed method by performing simulations and field experiments. [ABSTRACT FROM AUTHOR]

Plastic waste worldwide is becoming a serious pollution problem for the planet. Various physical and chemical methods have been tested in attempts to remove plastic dumps. However, these have usually resulted in secondary pollution issues. Recently, the biodegradation of plastic by fungal and bacterial strains has been spotlighted as a promising solution to remove plastic wastes without generating secondary pollution. We have previously reported that a Pseudomonas aeruginosa strain isolated from the gut of a superworm is capable of biodegrading polystyrene (PS) and polyphenylene sulfide (PPS). Herein, we demonstrate the extraordinary biodegradative power of P. aeruginosa in efficiently depolymerizing four different types of plastics: PS, PPS, polyethylene (PE) and polypropylene (PP). We further compared biodegradation rates for these four plastic types and found that PE was biodegraded fastest, whereas the biodegradation of PP was the slowest. Moreover, the growth rates of P. aeruginosa were not always proportional to biodegradation rates, suggesting that the rate of bacterial growth could be influenced by the composition and properties of intermediate molecules produced during plastic biodegradation, and these may supply useful cellular precursors and energy. In conclusion, an initial screening system to select the most suitable bacterial strain to biodegrade certain types of plastic is particularly important and may be necessary to solve plastic waste problems both presently and in the future. [ABSTRACT FROM AUTHOR]

Three-dimensional reconstruction is a crucial technique for mapping and object-search tasks, but it is challenging in sonar imaging because of the nature of acoustics. In underwater sensing, many advanced studies have introduced approaches that have included feature-based methods and multiple imaging at different locations. However, most existing methods are prone to environmental conditions, and they are not adequate for continuous data acquisition on moving autonomous underwater vehicles (AUVs). This paper proposes a sensor fusion method for 3D reconstruction using acoustic sonar data with two sonar devices that provide complementary features. The forward-looking multibeam sonar (FLS) is an imaging sonar capable of short-range scanning with a high horizontal resolution, and the profiling sonar (PS) is capable of middle-range scanning with high reliability in vertical information. Using both sonars, which have different data acquisition planes and times, we propose a probabilistic sensor fusion method. First, we extract the region of interest from the background and develop a sonar measurement model. Thereafter, we utilize the likelihood field generated by the PS and estimate the elevation ambiguity using importance sampling. We also present the evaluation of our method in a ray-tracing-based sonar simulation environment and the generation of the pointclouds. The experimental results indicate that the proposed method can provide a better accuracy than that of the conventional method. Because of the improved accuracy of the generated pointclouds, this method can be expanded for pointcloud-based mapping and classification methods. [ABSTRACT FROM AUTHOR]

New organic electro‐optic crystals containing orthogonally oriented electron‐withdrawing groups are developed for efficient and gap‐free THz wave generation with a very flat broadband spectral shape. These crystals consist of 2‐(4‐hydroxystyryl)‐1‐methylquinolinium (OHQ) cationic chromophores and nonplanar 4‐(trifluoromethoxy)benzenesulfonate (TFO) anions with orthogonally oriented highly electronegative trifluoromethoxy groups capable of strong hydrogen bonds. OHQ‐TFO crystals exhibit enhanced macroscopic optical nonlinearity with a second harmonic generation efficiency 2.3 times greater than that of benchmark OHQ‐based crystals with conventional planar anions. This enhancement is attributed to reduced edge‐to‐face π–π interactions between cations and anions due to the orthogonal orientation and electron‐withdrawing characteristics of trifluoromethoxy groups. Moreover, OHQ‐TFO crystals exhibit excellent THz wave characteristics generated by optical rectification; 0.52 mm thick OHQ‐TFO crystal generate a peak‐to‐peak THz electric field 15 times higher than that of inorganic standard 1.0 mm thick ZnTe crystal and a broader spectrum with an upper cut‐off frequency near 8 THz at pump wavelengths of 1140–1500 nm. Unlike previously reported state‐of‐the‐art organic electro‐optic salt crystals with strong phonon absorption in the frequency range of 0.8–3 THz, OHQ‐TFO crystals facilitate gap‐free broadband THz wave generation without strong absorption modulations due to the strong hydrogen bond ability of trifluoromethoxy groups. [ABSTRACT FROM AUTHOR]

A strategic approach to develop efficient ultra‐broadband terahertz (THz) crystals involves the incorporation of different electron donating groups (EDGs) into cationic chromophores. In contrast to the widely utilized non‐cyclic 4‐(dimethylamino)phenyl (DA) EDG, cyclic 5‐membered 4‐(2‐(hydroxymethyl)pyrrolidine‐1‐yl)phenyl (PB) and cyclic 6‐membered 4‐(3‐(hydroxymethyl)piperidin‐1‐yl)phenyl (PN) EDGs exhibit an asymmetrical shape with a strongly interacting hydroxymethyl group at the chiral center. Notably, the PB EDG shows narrower intrinsic vibrational states with lower conformational flexibility and smaller ring flips compared to the PN EDG. In the crystalline state, introducing the PB EDG leads to the formation of a new class of nonlinear optical assembly, the so‐called stair‐type cation‐anion assembly. This assembly demonstrates optimal chromophore alignment with state‐of‐the‐art effective first hyperpolarizability (209 × 10−30 esu). Furthermore, the PB EDG‐based crystals exhibit significantly lower THz absorption compared to previously reported benchmark crystals. In THz wave generation experiments, PB EDG‐based crystals demonstrate state‐of‐the‐art efficiency and ultrabroad spectral bandwidth, featuring a cut‐off frequency of up to 16 THz. [ABSTRACT FROM AUTHOR]

The symmetry reduction of molecular shape of cationic chromophores as a design strategy to develop organic terahertz (THz) generators is used. Electron donating group (EDG) with an asymmetric shape is introduced into two types of cationic styryl‐quinolinium chromophores, leading to the development of several novel non‐centrosymmetric crystals with high macroscopic optical nonlinearity. In contrast, when an EDG with a symmetric shape is introduced, centrosymmetric crystal structure is obtained in all investigated crystals. For THz wave generation, crystals based on asymmetrically shaped EDG exhibit several optimal crystal characteristics, including a plate‐shape morphology, a large size, and an in‐plane polar axis. Furthermore, over the entire range of molecular phonon vibrations, 0.5–4 THz, the steric hindrance group in the asymmetrically shaped EDG has a strong influence on the suppression of THz phonon vibrations, leading to a low THz absorption coefficient. The crystals based on asymmetrically shaped EDG generate an ≈40 times stronger THz electric field than the inorganic ZnTe crystal and very broad THz spectra, extending up to 16 THz. Thus, the symmetry reduction of the molecular shape of cationic chromophores through the introduction of an asymmetrically shaped EDG is an effective design approach for the development of novel organic THz crystals. [ABSTRACT FROM AUTHOR]

Given the prevalence of MP contamination in marine environments and the potential for ingestion, this study focused on detecting MPs in widely consumed omega-3 supplements. We developed and validated a testing method for analyzing microplastics (MPs) in omega-3 dietary supplements using micro-Fourier-transform infrared spectroscopy (μ-FT-IR). For sample preparation, 30% H 2 O 2 pretreatment and 20 μm stainless-steel filtration were adopted to digest omega-3 samples. A total of 88 omega-3 products were collected and examined, including animal- and plant-origin omega-3 with different packaging materials. Recovery test using reference MP materials was conducted to enhance the reliability of the method. As a result, the recovery was more than 70.4%, and relative standard deviation was below 36.9% in three laboratories. MPs (>20 μm) were detected in all the samples. The number of MPs were 9.5 ± 5.3 particles/g and 16.3 ± 8.1 particles/serving size. The developed method can be applied to MP analysis of omega-3 supplements. • Developed μ-FT-IR method for microplastic (MP) analysis in omega-3 supplements. • Detected MPs in all samples; average quantity: 16.3 ± 8.1 particles/daily serving size. • Proposed testing method with acceptable recovery results in three laboratories. [ABSTRACT FROM AUTHOR]

In this study, an organic nonlinear optical salt crystal, 4‐(4‐methoxystyryl)‐1‐methylpyridinium 4‐bromobenzenesulfonate (MOS‐BBS), is newly reported. MOS‐BBS crystals exhibit perfectly parallel molecular ordering of 4‐(4‐methoxystyryl)‐1‐methylpyridinium (MOS) cationic chromophores with noncentrosymmetric P1 space group symmetry, which provides an optimal configuration for maximizing the macroscopic second‐order optical nonlinearity. The macroscopic optical nonlinearity of the MOS‐BBS crystals is very large, with the diagonal effective first hyperpolarizability of 160 × 10−30 esu. Furthermore, the MOS‐BBS crystals exhibit a high thermal crystal‐phase stability. The lowest phase transition temperature of the MOS‐BBS crystals is 265°C, which is ~90°C higher than that of previously reported MOS‐based crystals. [ABSTRACT FROM AUTHOR]

Solid‐state molecular phonons play a crucial role in the performance of diverse photonic and optoelectronic devices. In this work, new organic terahertz (THz) generators based on a catechol group that acts as a phonon suppressing intermolecular adhesive are developed. The catechol group is widely used in mussel‐inspired mechanical adhesive chemistry. Newly designed organic electro‐optic crystals consist of catechol‐based nonlinear optical 4‐(3,4‐dihydroxystyryl)‐1‐methylpyridinium (DHP) cations and 4‐(trifluoromethyl)benzenesulfonate anions (TFS), which both have multiple interionic interaction capability. Interestingly, compared to benchmark organic crystals for THz generators, DHP‐TFS crystals concomitantly achieve top level values of the lowest void volume and the highest crystal density, resulting in an exceptionally small amplitude of solid‐state molecular phonons. Simultaneously achieving small molecular phonon amplitude, large optical nonlinearity and good phase matching at infrared optical pump wavelengths, DHP‐TFS crystals are capable of generating broadband THz waves of up to 16 THz with high optical‐to‐THz conversion efficiency; one order of magnitude higher than commercial inorganic THz generators. [ABSTRACT FROM AUTHOR]

Newly designed halogenated organic quinolinium crystals proposed in this work provide fully optimized molecular ordering for maximizing the optical nonlinearity and high‐performance broadband terahertz (THz) wave generation. The ultralarge diagonal optical nonlinearity (almost 300 × 10−30 esu) of the new halogenated crystals is approximately two times larger than that of state‐of‐the‐art pyridinium‐based crystals. In contrast, nonhalogenated analogous crystals exhibit very low (or vanishing) diagonal optical nonlinearity. This is attributed to halogen‐induced unique interionic interactions and fine‐tuning of the space‐filling characteristics. In addition, the halogenated crystals show a good ability for bulk crystal growth of few millimeters lateral size with plate‐like morphology and high thermal stability that are finally required for real‐world applications. The new halogenated quinolinium crystals exhibit excellent THz wave generation characteristics, significantly surpassing the limit of conversion efficiency and spectral bandwidth of inorganic benchmark crystals. A 0.16 mm thick chlorinated crystal generates a 29‐times larger THz field than 1.0 mm thick inorganic ZnTe crystals at 1500 nm pump wavelength with a flat and broadband spectrum extending up to ≈8 THz. Therefore, introducing halogen substituents is a potential design strategy for designing new organic crystals showing ultralarge macroscopic hyperpolarizability and high‐performance THz wave generation. [ABSTRACT FROM AUTHOR]

Ultra‐broadband THz photonics covering the 0.3–20 THz range provides a very attractive foundation for a wide range of basic research and industrial applications. However, the lack of ultra‐broadband THz devices has yet to be overcome. In this work, high‐density organic electro‐optic crystals are newly developed for efficient THz wave generation in a very broad THz spectral range and are successfully used for a broadband THz time‐domain spectroscopy. The new organic THz generator crystals, namely the OHP‐TFS crystals, have very low void volume, high density, and are shown to cover the ultra‐broadband THz spectrum up to about 15 THz, which cannot be easily accessed with the more widely used inorganic‐based THz generators. In addition to the very favorable broadband properties, the generated THz electric‐field amplitude at the pump wavelength of 1560 nm is about 40 times higher than that generated by a commercial inorganic THz generator (ZnTe crystal). By using the newly developed OHP‐TFS as generation crystal in a compact table‐top all‐organic THz time‐domain spectrometer based on a low‐cost telecom fiber laser, the optical characteristics of a model material are successfully determined in the broad 1.5–12.5 THz range with high accuracy. [ABSTRACT FROM AUTHOR]

New organic THz generators are designed herein by molecular engineering of the refractive index, phonon mode, and spatial asymmetry. These benzothiazolium crystals simultaneously satisfy the crucial requirements for efficient THz wave generation, including having nonlinear optical chromophores with parallel alignment that provide large optical nonlinearity; good phase matching for enhancing the THz generation efficiency in the near‐infrared region; strong intermolecular interactions that provide restraining THz self‐absorption; high solubility that promotes good crystal growth ability; and a plate‐like crystal morphology with excellent optical quality. Consequently, the as‐grown benzothiazolium crystals exhibit excellent characteristics for THz wave generation, particularly at near‐infrared pump wavelengths around 1100 nm, which is very promising given the availability of femtosecond laser sources at this wavelength, where current conventional THz generators deliver relatively low optical‐to‐THz conversion efficiencies. Compared to a 1.0‐mm‐thick ZnTe crystal as an inorganic benchmark, the 0.28‐mm‐thick benzothiazolium crystal yields a 19 times higher peak‐to‐peak THz electric field with a broader spectral bandwidth (>6.5 THz) when pumped at 1140 nm. The present work provides a valuable approach toward realizing organic crystals that can be pumped by near‐infrared sources for efficient THz wave generation. [ABSTRACT FROM AUTHOR]

Efficient broadband organic terahertz (THz) generators using X‐shaped alignment of the nonlinear optical chromophores, as an alternative to the parallel alignment of chromophores in benchmark organic crystals, are reported. All the developed six organic benzothiazolium crystals exhibit an isomorphic X‐shaped alignment of chromophores, resulting in an unprecedentedly large off‐diagonal optical nonlinearity (>100 × 10−30 esu), which presents one of the largest off‐diagonal optical nonlinearity of organic crystals. The benzothiazolium crystals exhibit efficient broadband THz wave generation employing the off‐diagonal optical nonlinearity, in contrast to the present state‐of‐the‐art organic THz generators that mostly utilize diagonal optical nonlinearity. For using off‐diagonal and diagonal optical nonlinearities, the polarization of the optical pump is perpendicular and parallel, respectively, to the polar axis of crystals. In addition to a large THz wave generation efficiency with one order of magnitude higher peak‐to‐peak THz electric field than that generated in a 1.0‐mm‐thick inorganic benchmark ZnTe crystal, the benzothiazolium crystals generate broadband THz spectra with an upper cut‐off frequency of near 8 THz, and the absence of strong absorption dimples in the range of 0.5−4 THz. Therefore, the X‐shaped alignment of chromophores presents an interesting potential alternative for efficient broadband organic THz generators. [ABSTRACT FROM AUTHOR]

A new approach for the molecular design of highly efficient nonlinear optical organic crystals is proposed by introducing substituents that form σ‐holes on both nonlinear optical cationic chromophores and aromatic anions. Introducing chlorinated substituents, in which a relatively positive σ‐hole and a negative belt coexist, provides selective reduction capability of specific π–π intermolecular interactions and simultaneous multiple secondary bonding capabilities. This leads to a crystalline state with enhanced first‐order hyperpolarizability βcrystal of chromophores that favors parallel chromophore alignment and suppression of molecular vibrations, which are optimal characteristics for electro‐optic and nonlinear optical applications, including efficient THz wave generation. Compared to benchmark nonhalogenated and fluorinated analogous crystals with state‐of‐the‐art macroscopic optical nonlinearity, σ‐hole containing chloro‐quinolinium crystals exhibit up to two times higher macroscopic nonlinear optical response and remarkably different crystal characteristics. As a result, a 0.16 mm thick chloro‐quinolinium crystal exhibits ≈22 times higher optical‐to‐THz conversion efficiency than the widely used 1.0 mm thick ZnTe inorganic crystal. Moreover, chloro‐quinolinium crystals exhibit very broad THz spectra, up to 8 THz with significantly different THz spectral shape compared to benchmark organic crystals, which is attributed to different phase matching between optical and THz frequencies and molecular vibration motions. [ABSTRACT FROM AUTHOR]

This study proposes a parent–child robot-based underwater manipulation system for underwater structure maintenance comprising two underwater vehicles with split roles. The larger autonomous underwater vehicle (AUV) acts as the base to transport and control a tethered child robot that is deployed to perform actual manipulation tasks. Conventional AUVs face several challenges when performing manipulation missions because of their large and massive body and the complexity of dynamic control with a rigid arm manipulator in the precise hovering state. To address this problem, we proposed an underwater manipulation system that uses a large parent AUV with high-performance sensors to navigate to the desired location and a child robot with high mobility to perform manipulation tasks. In this study, a parent–child robot-based manipulation system was developed and mathematically modeled considering hydrodynamics. Based on the system model, a nonlinear time delay (TD) controller was applied to the child robot to ensure robustness of the movement, and complementary sensing methods were proposed according to the observation distance. Subsequently, we detailed the mission process such that the manipulation tasks could be performed autonomously. To implement and verify the proposed method, we conducted three-dimensional (3D) simulations, water tank experiments, and sea trials. In the 3D simulation and water tank experiments, we evaluated the position control using a TD controller during a specific disturbance and performed an operational evaluation of the parent–child system. In the water tank, we performed the operation of the child robot with the tether length adjustment of the winch system and the manipulation task. In the sea trial, the predefined mission was successfully completed, which demonstrated the feasibility of properly operating both the robots. The results of the experiments demonstrated the high potential and capabilities of the proposed manipulation system. [ABSTRACT FROM AUTHOR]

New cationic chromophore HPR (4-(4-hydroxy-3-methoxystyryl)-1-(pyrimidin-2-yl)pyridin-1-ium), with large first hyperpolarizability of up to 264 × 10−30 esu, exhibits large off-diagonal macroscopic optical nonlinearity, which is approximately four times higher than that of the benchmark stilbazolium crystals. [Display omitted] • New cationic HPR chromophore based on N -pyrimidinyl stilbazolium was developed. • New HPR cationic chromophore exhibits large microscopic optical nonlinearity (264 × 10−30 esu). • HPR-based crystals exhibit large off-diagonal macroscopic optical nonlinearity, approximately four times higher than that of benchmark stilbazolium crystals. We report a new π-conjugated cationic chromophore based on phenolic N -pyrimidinyl stilbazolium and its corresponding non-centrosymmetric crystals. The new cationic chromophore, HPR (4-(4-hydroxy-3-methoxystyryl)-1-(pyrimidin-2-yl)pyridin-1-ium), consists of a strong electron donor, the 4-hydroxy-3-methoxyphenyl group based on two electron-donating groups, and a strong electron acceptor, the N -pyrimidinyl pyridinium group based on two electron-withdrawing groups. The HPR chromophore possesses large molecular optical nonlinearity with first hyperpolarizability of up to 264 × 10−30 esu, which is significantly larger than that of the benchmark stilbazolium chromophores. In solution, the HPR chromophore showed co-existence of phenol- and phenolate-like forms with two absorption bands (∼460 and ∼610 nm, respectively). In the crystalline state, all HPR-based derivatives with three different counter anions, N2S (naphthalene-2-sulfonate), VBS (4-vinylbenzenesulfonate), and NBS (3-nitrobenzenesulfonate), exhibit a macroscopic second-order nonlinear optical response. HPR-N2S crystals exhibit non-centrosymmetric monoclinic Pn space group symmetry and large off-diagonal effective macroscopic optical nonlinearity (94 × 10−30 esu), which is approximately four times higher than that of the benchmark stilbazolium crystals. Therefore, the newly developed HPR-based crystals are highly promising materials for second-order nonlinear optical applications. [ABSTRACT FROM AUTHOR]

In this paper, a hovering-type autonomous underwater vehicle called Cyclops is introduced. Because of the symmetric body structure and thruster configuration of Cyclops, it is specially designed to utilize a lawnmower trajectory without changing its heading direction. This movement is effective at reducing the dead reckoning error and obtaining source images with homogeneous optical characteristics for underwater image mosaicing. [ABSTRACT FROM AUTHOR]

Pseudomonas sp. isolated from soil, are bioremediating microorganisms that are capable of degrading various types of plastics. Polyphenylene sulfide (PPS) has the most excellent structural stability among general plastics and thus is extremely difficult to break down using physical or chemical methods. This study demonstrates the efficient biodegradation of PPS by Pseudomonas sp., which exists in the gut of superworms. Compared with the conventional film-type of plastic, the degradation efficiencies to the bead form of plastic were significantly improved and thus the biodegradation time was dramatically shortened. Therefore, instead of film-type plastics, we used 300 μm diameter plastic beads for the measurement of Pseudomonas sp.-mediated biodegradation of PPS during a 10-day period. This method not only can be used for comparison and verification of the biodegradation efficiency of different types of plastics within a short reaction time of 10 days, but also provides the possibility to develop a new and more efficient screening system to rapidly identify the most efficient species of bacteria for the biodegradation of various types of plastics. Unlabelled Image • Pseudomonas sp. biodegrades polyethylene much faster than polyphenylene sulfide • Bacteria-mediated biodegradation of bead-type plastics proceeds faster than film-types • New rapid screen system is available for research of bacterial plastic biodegradation. [ABSTRACT FROM AUTHOR]