Atto-Scale Noise Near-Infrared Organic Photodetectors Enabled by Controlling Interfacial Energetic Offset through Enhanced Anchoring Ability.

The near-infrared (NIR) sensor technology is crucial for various applications such as autonomous driving and biometric tracking. Silicon photodetectors (SiPDs) are widely used in NIR applications; however, their scalability is limited by their crystalline properties. Organic photodetectors (OPDs) have attracted attention for NIR applications owing to their scalability, low-temperature processing, and notably low dark current density (JD), which is similar to that of SiPDs. However, the still high JD (at NIR band) and few measurements of noise equivalent powers (NEPs) pose challenges for accurate performance comparisons. This study addresses these issues by quantitatively characterizing the performance matrix and JD generation mechanism using electron-blocking layers (EBLs) in OPDs. The energy offset at an EBL/photosensitive layer interface determines the thermal activation energy and directly affects JD. A newly synthesized EBL (3PAFBr) substantially enhances the interfacial energy barrier by forming a homogeneous contact owing to the improved anchoring ability of 3PAFBr. As a result, the OPD with 3PAFBr yields a noise current of 852 aA (JD = 12.3 fA cm⁻2 at V → -0.1 V) and several femtowatt-scale NEPs. As far as it is known, this is an ultralow of JD in NIR OPDs. This emphasizes the necessity for quantitative performance characterization.

Autoencoder-Based Target Detection in Automotive MIMO FMCW Radar System.

In general, a constant false alarm rate algorithm (CFAR) is widely used to automatically detect targets in an automotive frequency-modulated continuous wave (FMCW) radar system. However, if the number of guard cells, the number of training cells, and the probability of false alarm are set improperly in the conventional CFAR algorithm, the target detection performance is severely degraded. Therefore, we propose a method using a convolutional neural network-based autoencoder (AE) to replace the CFAR algorithm in the multiple-input and multiple-output FMCW radar system. In the AE, the entire detection result is compressed at the encoder side, and only significant signal components are recovered on the decoder side. In this work, by changing the number of hidden layers and the number of filters in each layer, the structure of the AE showing a high signal-to-noise ratio in the target detection result is determined. To evaluate the performance of the proposed method, the AE-based target detection result is compared with the target detection results of conventional CFAR algorithms. As a result of calculating the correlation coefficient with the data marked with the actual target position, the proposed AE-based target detection shows the highest similarity with a correlation of 0.73 or higher.

Experimental application of a zero-point charge based on pH as a simple indicator of microplastic particle aggregation.

Micro/nanoplastics - a useful but threatening material - continuously require fundamental research on its behaviors and properties for aggregation. Zeta potential (ζ) has been using as an indicator to determine the optimal aggregation for particle removal in water treatment processes. In the field work, however, an alternative method for streamlining these tasks and reducing the variability in processing efficiency is necessary. To improve practical utility in the field work, this study aimed at investigating applicability of the zero-point charge (ZPC) of the isoelectric point (IEP; ψpI) as an alternative indicator for aggregation in place of ζ. For the purpose, this study conducted laboratory experiments and model simulations. The experiments measured ψpI of microplastics in a trivalent-electrolyte aqueous solution using various concentrations of polyaluminum chloride (PAC) for reproducing the behavior of microplastics in natural water environments. As a result, ψpI for polyethylene (PE) and polyvinylchloride (PVC) were found to be pH 6.59 and 6.43, respectively. The removal rates (r) depended on the aggregation at the initial pH and optimal PAC concentration. The experimental attachment efficiency (αE), 0.14 to 0.4, showed a good correlation of over 95% with r, 0.04 to 0.84, both based on the pH change and PAC concentration and differing slightly with the type and size of the plastic. The highest αE was achieved with the highest r when ψpI was close to zero in the pH range of 6-8 using the optimized PAC concentration. Based on the experimental results, the model confirmed the applicability of ψpI instead of ζ as an indicator of the aggregation by simulating αE based on ψpI and ionic strength, which are themselves based on the change in pH. Therefore, this study provides some insights into behaviors of microplastics by using the isoelectric point (IEP, ψpI) as an indicator of aggregation of microplastics in place of ζ. The IEP method is limited by initial pH, optimal dosage of coagulant, and type and size of microplastics, but it will increase practical utility in the field.

Enhancement of Transgene Expression by Mild Hypothermia Is Promoter Dependent in HEK293 Cells.

Mild hypothermia has been widely used to enhance transgene expression and improve the cellular productivity of mammalian cells. This study investigated mild hypothermia-responsive exogenous promoters in human embryonic kidney 293 (HEK293) cells using site-specific integration of various promoter sequences, including CMV, EF1α, SV40, and TK promoters, into the well-known genomic safe harbor site, AAVS1. EGFP expression driven by the CMV promoter increased up to 1.5-fold at 32 °C versus 37 °C under stable expression, while others showed no hypothermic response. Integration of short CMV variants revealed that the CMV-enhancer region is responsible for the positive hypothermic response. CMV-enhancer-specific transcription factors (TFs) were then predicted through in silico analysis and RNA-sequencing analysis, resulting in the selection of one TF, NKX3-1. At 37 °C, overexpression of NKX3-1 in recombinant HEK293 cells expressing EGFP through the CMV promoter (CMV-EGFP) increased EGFP expression up to 1.6-fold, compared with that in CMV-EGFP, the expression level of which was comparable to that of CMV-EGFP at 32 °C. Taken together, this work demonstrates promoter-dependent hypothermia responses in HEK293 cells and emphasizes interactions between endogenous TFs and promoter sequences.

Osseointegration of Plasma Jet Treated Titanium Implant Surface in an Animal Model.

Osseointegration of titanium implant is important for the success of both dental and medical implants. Previous studies have attempted to improve osseointegration by considering the use of plasma jet technology, where information with animal models and parameters related to osseointegration is still lacking. Therefore, this study investigated the effects of non-thermal atmospheric pressure plasma jet (NTAPPJ) treatment on titanium implants in terms of osseointegration in mongrel dogs. A total of 41 implants; 21 NTAPPJ treated and 20 control, were placed in the maxilla and mandible of six mongrel dogs for either 4 or 8 weeks. The bone volume (BV) and bone-to-implant contact (BIC) ratio were determined by region of interest (ROI). Statistical analysis was performed with the Wilcoxon rank-sum test. The NTAPPJ group at 4 weeks showed higher numbers in both BV and BIC (p < 0.05) compared to the control group. However, at 8 weeks there were less significant differences between the control or experimental group as the control group had caught up with the experimental group. Hence, NTAPPJ may be an effective treatment for the initial healing period which is critical to ensure reliable long-term predictability. The BV and BIC have been clinically proven to accelerate in the initial stages with the use of NTAPPJ to aid in the healing and initial stability of implants.

Identification of Human Motion Using Radar Sensor in an Indoor Environment.

In this paper, we propose a method of identifying human motions, such as standing, walking, running, and crawling, using a millimeter wave radar sensor. In our method, two signal processing is performed in parallel to identify the human motions. First, the moment at which a person's motion changes is determined based on the statistical characteristics of the radar signal. Second, a deep learning-based classification algorithm is applied to determine what actions a person is taking. In each of the two signal processing, radar spectrograms containing the characteristics of the distance change over time are used as input. Finally, we evaluate the performance of the proposed method with radar sensor data acquired in an indoor environment. The proposed method can find the moment when the motion changes with an error rate of 3%, and also can classify the action that a person is taking with more than 95% accuracy.

Movement Patterns and Diel Activity of Anguilla japonica in the Middle Part of a Large River in South Korea.

To investigate movement patterns and diel activities of Anguilla japonica in the freshwater ecosystem, we applied acoustic telemetry on A. japonica in the Geum River, a large river in South Korea. The acoustic tags were attached on 19 individuals of A. japonica (12 with a depth sensor) in May and October 2015 and tracked at approximately 100-km sections from an estuary barrage by 20 automatic listening stations. Only four individuals showed longitudinal movement (mean, 5.2 km), and others were detected by the receivers at release sites; therefore, A. japonica showed high site fidelity. We did not identify seaward migration during the study period (May to November). Conversely, A. japonica showed active diel movement. The number of detections (p = 0.002) and movement distance (p = 0.004) were higher at night-time (18:00-06:00). As most individuals were actively moving at nighttime, we confirmed that A. japonica is nocturnal, although few individuals also showed daytime movement. Although the population and habitats of A. japonica have been decreasing simultaneously, the East-Asian countries are still severely exploiting rivers and streams to use water resources, and result in habitat simplification generated. Therefore, these results contribute to effective A. japonica management regarding habitat and population conservation and restoration.

Trophic response to ecological conditions of habitats: Evidence from trophic variability of freshwater fish.

To adapt to ecological and environmental conditions, species can change their ecological niche (e.g., interactions among species) and function (e.g., prey-predation, diet competition, and habitat segregation) at the species and guild levels. Stable isotope analysis of bulk carbon and nitrogen of organisms has conventionally been used to evaluate such adaptabilities in the scenopoetic and bionomic views as the isotopic niche width.Compound-specific stable isotope analysis (CSIA) of nitrogen within amino acids provides trophic information without any disruption of scenopoetic views in the isotope ratios, unlike conventional bulk isotope analysis provides both information and therefore frequently hinders its usefulness for trophic information.We performed CSIA of amino acids to understand the trophic variability of the pike gudgeon Pseudogobio esocinus and largemouth bass Micropterus salmoides as representative specialist and generalist fish species, respectively, from 16 ecologically variable habitats in the four major rivers of Korea.There was little variation (1σ) in the trophic position (TP) among habitats for P. esocinus (± 0.2); however, there was considerably large variation for M. salmoides (± 0.6). The TP of M. salmoides was negatively correlated with the benthic invertebrate indices of the habitats, whereas the TP of P. esocinus showed no significant correlation with any indices. Thus, these two representative fish species have different trophic responses to ecological conditions, which is related to known differences in the trophic niche between specialists (i.e., small niche width) and generalists (i.e., large niche width).Over the past four decades, the conventional bulk isotope analysis has not been capable of deconvoluting "scenopoetic" and "bionomic" information. However, in the present study, we demonstrated that the CSIA of amino acids could isolate trophic niches from the traditional ecological niche composed of trophic and habitat information and evaluated how biological and ecological indices influence the trophic response of specialists and generalists.

A broadband ultraviolet light source using GaN quantum dots formed on hexagonal truncated pyramid structures.

Group III-nitride semiconductor-based ultraviolet (UV) light emitting diodes have been suggested as a substitute for conventional arc-lamps such as mercury, xenon and deuterium arc-lamps, since they are compact, efficient and have a long lifetime. However, in previously reported studies, group III-nitride UV light emitting diodes did not show a broad UV spectrum range as conventional arc-lamps, which restricts their application in fields such as medical therapy and UV spectrophotometry. Here, we propose GaN quantum dots (QDs) grown on different facets of hexagonal truncated pyramid structures formed on a conventional (0001) sapphire substrate. A hexagonal truncated GaN pyramid structure includes {101̄1} semipolar facets as well as a (0001) polar facet, which have intrinsically different piezoelectric fields and growth rates of GaN QDs. Consequently, we successfully demonstrated a plateau-like broadband UV spectrum ranging from ∼400 nm (UV-A) to ∼270 nm (UV-C) from the GaN QDs. In addition, at the top-edge of the truncated pyramid structure, a strain was locally suppressed compared to the center of the truncated pyramid structure. As a result, various emission wavelengths in the UV range were achieved from the GaN QDs grown on the sidewall, top-edge and top-center of hexagonal truncated pyramid structures, which ultimately provide a broadband UV spectrum with high efficiency.

Interplay of strain and intermixing effects on direct-bandgap optical transition in strained Ge-on-Si under thermal annealing.

The influence of thermal annealing on the properties of germanium grown on silicon (Ge-on-Si) has been investigated. Depth dependencies of strain and photoluminescence (PL) were compared for as-grown and annealed Ge-on-Si samples to investigate how intermixing affects the optical properties of Ge-on-Si. The tensile strain on thermally annealed Ge-on-Si increases at the deeper region, while the PL wavelength becomes shorter. This unexpected blue-shift is attributed to Si interdiffusion at the interface, which is confirmed by energy dispersive X-ray spectroscopy and micro-Raman experiments. Not only Γ- and L-valley emissions but also Δ2-valley related emission could be found from the PL spectra, showing a possibility of carrier escape from Γ valley. Temperature-dependent PL analysis reveals that the thermal activation energy of Γ-valley emission increases at the proximity of the Ge/Si interface. By comparing the PL peak energies and their activation energies, both SiGe intermixing and shallow defect levels are found to be responsible for the activation energy increase and consequent efficiency reduction at the Ge/Si interface. These results provide an in-depth understanding of the influence of strain and Si intermixing on the direct-bandgap optical transition in thermally annealed Ge-on-Si.

[Development of Koreans Gut Quotient Measurement Scales].

BACKGROUND/AIMS: The aim of this study was to develop 'Koreans Gut Quotient Measurement Scales (GQ)', in which Koreans respond to questionnaires about the subjective feelings and symptoms of their intestinal health status. METHODS: Among 66 items pooled from previous studies and 4 items that were added following a focus group interview, 15 items were chosen using the Delphi survey. The content validity was evaluated using the content validity ratio. Data collected from 1,120 people from the general public in Korea were analyzed to verify the reliability and validity of GQ. RESULTS: The finalized GQ consisted of 17 items (including two exploratory measurement items) that were classified into three independent factors based on exploratory factor analysis (EFA): 'perceived intestine discomfort', 'bowel movement discomfort', and 'bowel movement control discomfort'. The discriminant and convergent validity of GQ were identified using EFA, reliability test, and confirmatory factor analysis. In addition, the criterion-related validity of GQ was identified using correlation and multiple regression analysis. CONCLUSIONS: The GQ, which is a simplified intestinal health index developed based on an easy questionnaire for the public to understand, can be used as a tool for the public to evaluate their own intestinal health and determine when to visit clinics.

Effect of tungsten on the oxidation of alumina-forming austenitic stainless steel.

As more W replaced Mo in alumina-forming austenitic stainless steels, weight gain by oxidation decreased after 336 h at 1053 K. Electron microscopy revealed slower growth of scale in the presence of more numerous second phases by W addition. The retardation of oxidation was attributed to the necessary partitioning of W in front of the metal-oxide interface. The W-rich second phases interacted with growing oxides and finally transformed to fine particles of metallic W alloy within the scale.

Three-dimensional GaN dodecagonal ring structures for highly efficient phosphor-free warm white light-emitting diodes.

Warm and natural white light (i.e., with a correlated colour temperature <5000 K) with good colour rendition (i.e., a colour rendering index >75) is in demand as an indoor lighting source of comfortable interior lighting and mood lighting. However, for warm white light, phosphor-converted white light-emitting diodes (WLEDs) require a red phosphor instead of a commercial yellow phosphor (YAG:Ce3+), and suffer from limitations such as unavoidable energy conversion losses, degraded phosphors and high manufacturing costs. Phosphor-free WLEDs based on three-dimensional (3D) indium gallium nitride (InGaN)/gallium nitride (GaN) structures are promising alternatives. Here, we propose a new concept for highly efficient phosphor-free warm WLEDs using 3D core-shell InGaN/GaN dodecagonal ring structures, fabricated by selective area growth and the KOH wet etching method. Electrically driven, phosphor-free warm WLEDs were successfully demonstrated with a low correlated colour temperature (4500 K) and high colour rendering index (Ra = 81). From our findings, we believe that WLEDs based on dodecagonal ring structures become a platform enabling a high-efficiency warm white light-emitting source without the use of phosphors.

Selective engineering of oxygen-containing functional groups using the alkyl ligand oleylamine for revealing the luminescence mechanism of graphene oxide quantum dots.

Oxygen-containing functional groups such as epoxy, hydroxyl, carboxylic, and carboxyl groups have a great influence on the luminescence properties of graphene oxide quantum dots (GOQDs). Understanding their roles is essential for the design and optimization of GOQD performance. Herein, we investigate the effect of epoxide functional groups in GOQDs on the luminescence mechanism through passivation of the epoxide functional groups using the alkyl ligand oleylamine. Luminescence in the as-synthesized GOQDs has two separate origins: intrinsic states derived from localized sp2 carbon subdomains and extrinsic states formed by oxygen-functional groups. When the oleylamine ligand is conjugated on the GOQDs, intrinsic PL emission from the localized sp2 carbon subdomains decreases. This is discussed in detail, based on optical characterization and first-principles density functional theory calculations, which reveal that the role of the epoxide functional groups is to form localized sp2 carbon subdomains emitting intrinsic PL. To the best of our knowledge, this is the first investigation of the role of epoxide functional groups on the luminescence mechanism in GOQDs.

Electrically driven, highly efficient three-dimensional GaN-based light emitting diodes fabricated by self-aligned twofold epitaxial lateral overgrowth.

Improvements in the overall efficiency and significant reduction in the efficiency droop are observed in three-dimensional (3D) GaN truncated pyramid structures fabricated with air void and a SiO2 layer. This 3D structure was fabricated using a self-aligned twofold epitaxial lateral overgrowth technique, which improved both the internal quantum efficiency and the light extraction efficiency. In addition, a reduced leakage current was observed due to the effective suppression of threading dislocations. While this study focuses primarily on the blue emission wavelength region, this approach can also be applied to overcome the efficiency degradation problem in the ultraviolet, green, and red emission regions.

The complete mitochondrial genome sequence of Squalidus multimaculatus (Cypriniformes: Cyprinidae).

This study determined the complete mitogenome sequence of Squalidus multimaculatus (Cypriniformes: Cyprinidae). The mitogenome of S. multimaculatus is 16,597 bp in length, including 13 protein-coding genes, 22 transfer RNAs, 2 ribosomal RNA genes, and a non-coding control region. NCR is 925 bp in length, is located between tRNApro and tRNAphe. The overall base composition of S. multimaculatus is 27.9% for A, 18.9% for G, 25% for T, 28.2% for C, with a slight AT bias (52.9%). These results will provide the data required for phylogenetic studies of the Squalidus species.

Extraordinary Strong Fluorescence Evolution in Phosphor on Graphene.

Optical transition between singlet and triplet is observed in phosphorescent platinum octaethylporphyrin (PtOEP), on a graphene substrate. PtOEP on single layer of graphene not only modulates the dominant emission wavelength but also enhances the emission intensity. This result addresses new light-matter interactions of the hybrid structure of graphene and a single molecule.

Giant Rabi Splitting of Whispering Gallery Polaritons in GaN/InGaN Core-Shell Wire.

The hybrid nature of exciton polaritons opens up possibilities for developing a new concept nonlinear photonic device (e.g., polariton condensation, switching, and transistor) with great potential for controllability. Here, we proposed a novel type of polariton system resulting from strong coupling between a two-dimensional exciton and whispering gallery mode photon using a core-shell GaN/InGaN hexagonal wire. High quality, nonpolar InGaN multiple-quantum wells (MQWs) were conformally formed on a GaN core nanowire, which was spatially well matched with whispering gallery modes inside the wire. Both high longitudinal-transverse splitting of nonpolar MQWs and high spatial overlap with whispering gallery modes lead to unprecedented large Rabi splitting energy of ∼180 meV. This structure provides a robust polariton effect with a small footprint; thus, it could be utilized for a wide range of interesting applications.

Is the Chain of Oxidation and Reduction Process Reversible in Luminescent Graphene Quantum Dots?

Graphene-based quantum dots (QDs) have received a tremendous amount of attention as a new type of light-emitting materials. However, their luminescence origins remain controversial due to extrinsic states of the impurities and disorder structures. Especially, the function of oxygen-contents should be understood and controlled as a crucial element for tuning the optical properties of graphene-based QDs. Herein, a series of graphene oxide QDs (GOQDs) with different amounts of oxygen-contents are first synthesized via a direct oxidation route of graphite nanoparticle and thoroughly compared with a series of reduced GOQDs (rGOQDs) prepared by the conventional chemical reduction. Irreversible emission and different carrier dynamics are observed between the GOQDs and rGOQDs, although both routes show a similar tendency with regard to the variation of oxygen-functional components. Their luminescence mechanisms are closely associated with different atomic structures. The mechanism for the rGOQDs can be associated with a formation of small sp(2) nanodomains as luminescent centers, whereas those of GOQDs may be composed of oxygen-islands with difference sizes depending on oxidation conditions surrounded by a large area of sp(2) bonding. Important insights for understanding the optical properties of graphene-based QDs and how they are affected by oxygen-functional groups are shown.

Primary hepatocyte imaging by multiphoton luminescent graphene quantum dots.

Water soluble GQDs were systematically characterized as a multiphoton fluorophore and a cell imaging probe. When mouse primary hepatocytes were incubated with GQDs, no significant cytotoxicity was observed up to the treatment concentration of 100 µg ml(-1). Using these GQDs, mouse primary hepatocytes were successfully imaged by multiphoton fluorescence.