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Pruned branches from persimmon trees are a largely untapped agricultural waste resource. This study explores the conversion of these branches into an enhanced fuel source through hydrothermal carbonization. The branches were subjected to hydrothermal treatment under various conditions to identify the optimal parameters. Higher temperatures and longer treatment durations increased the carbon content to 69.2% and reduced the oxygen content to 20.4%. A Van Krevelen diagram showed that dehydration was the primary reaction, with decarboxylation occurring at 250 °C. The energy value increased from 18.2 MJ/kg for raw branches to 28.5 MJ/kg under the optimal conditions, indicating a 57% improvement. These findings demonstrate that hydrothermal carbonization effectively utilizes persimmon pruning waste, offering a sustainable method for converting biomass into energy and aiding agricultural waste management.

In future 6G systems, integrated sensing and communication (ISAC) in the terahertz (THz) band are emerging as a key technology. Photomixing-based approaches offer advantages for the generation and control of THz waves due to their wide bandwidth and frequency tunability. This paper proposes and experimentally demonstrates a THz-band ISAC system that employs high-speed wavelength tunable lasers. Leveraging the rapid wavelength tunability of the laser, the system simultaneously generates a frequency-modulated continuous-wave (FMCW) radar signal and a frequency-shift keying (FSK) communication signal. Experimental results show successful ranging with a centimeter-level distance measurement error using a 7.9 GHz sweep-bandwidth THz-FMCW signal. The system achieves a short repetition period of 800 ns, significantly enhancing real-time performance in dynamic environments. Moreover, 2FSK communication at 2 Gbit/s was demonstrated without the use of an external modulator, achieving a BER below the HD-FEC threshold. These results confirm that radar and communication functionalities can be integrated into a single transmitter. The proposed system contributes to reducing system complexity and cost and offers a promising solution for 6G applications.

The photomixing of two lightwaves is one of the promising methods of generating a terahertz (THz) wave. The conventional photomixing system consisting of two lasers and a modulator results in large transmitter volumes and high power consumption. To solve this issue, we devised a novel THz wave generation and modulation system based on photomixing using a single wavelength-tunable laser in combination with delayed self-multiplexing. We successfully demonstrated the feasibility of 300-GHz wave generation and modulation.

Background and Objectives: Autologous bone grafting is the first choice for reconstructive surgery in bone defects due to trauma or malignant tumors. However, there is an increasing demand for minimally invasive alternatives involving bone regeneration using artificial materials. Biomimetic materials that replicate the body’s microscopic structure, such as Cellnest®, are gaining attention. Cellnest is a xeno-free recombinant peptide based on human type I collagen, containing a rich Arg-Gly-Asp (RGD) motif related to cell adhesion. The aim of this study was to compare the effects of Cellnest with existing collagen materials (Pelnac®, Integra®, Terudermis®) on bone regeneration and elucidate the underlying mechanisms. Materials and Methods: In vivo experiments involved a rat model of calvarial bone defects, in which Cellnest and other collagen materials were implanted into the defect area. Bone formation was assessed after 4 weeks using micro-computed tomography (micro-CT) and histological analysis. In vitro experiments included the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), adhesion, and migration assays, and a real-time polymerase chain reaction using rapidly expanding cells (RECs) to explore the mechanisms of Cellnest’s bone regenerative capacity. Results: The micro-CT analysis showed that the regenerated bone area was significantly greater in the Cellnest group (72.3%) than in the Pelnac® (25.5%), Integra® (31.6%), and Terudermis® (38.3%) groups. The histological analysis confirmed similar trends, with Cellnest showing 42.2% bone regeneration, outperforming the other materials. The in vitro assays revealed that Cellnest promoted cell proliferation, adhesion, and migration. Gene expression analysis demonstrated that Cellnest significantly increased the levels of the bone formation markers ALP and COL1. Conclusions: Cellnest, a human type I collagen-like peptide rich in RGD motifs, enhances bone regeneration by promoting MSC adhesion and migration, and bone formation-related gene expression. The findings suggest its potential as an effective material for bone defect reconstruction.

A photomixing-based frequency-hopping spread spectrum (FHSS) system is effective for future secure terahertz (THz) wireless communications. Conventional photomixing systems are typically composed of two lasers, which result in an increased system size and power consumption. To address this issue, we applied our proposed THz wave generation method, using a single wavelength-tunable laser, to the FHSS system. In the experiments, we successfully demonstrated a J-band (220–330 GHz) FHSS system with a frequency-hopped interval of 400 ns.

Future wireless communications require higher security as well as a higher data rate. We have been studying physically secured wireless transmission systems and previously proposed encryption/decryption techniques based on the AND operation caused by coherent detection between two encrypted data sequences on two different terahertz carriers. Furthermore, we suggested that by employing the XOR operation as the decryption, the proposed system can be made more secure because XOR increases the computational complexity for eavesdroppers to recover the plaintext. In this paper, we propose the XOR operation between two data sequences on FSK-modulated terahertz waves. By constructing the XOR encryption transmitters/receivers, which consisted of high-speed wavelength tunable lasers and arrayed uni-traveling-carrier photodiodes (UTC-PDs), we successfully demonstrated the XOR operation between two data sequences on 200 GHz waves from the two transmitters.

The authors developed a mirror‐based out‐of‐plane optical coupler (MOOC) for InP photonic integrated circuits (PICs). The coupler has the coupling loss and alignment tolerance comparable to those of a conventional edge coupler. An asymmetric Mach–Zehnder interferometer (a‐MZI) with the MOOC exhibits little wavelength‐dependent loss (WDL) and a high extinction ratio (ER) of >20 dB over 100‐nm wavelength bandwidth. In addition, the temperature‐independent transmittance spectra were obtained. Finally, the authors fabricated a 4‐ch MOOC array with the pitch of 40 μm, which corresponds to the core pitch of practical multi‐core fibre (MCF). We developed a mirror‐based out‐of‐plane optical coupler (MOOC) for InP photonic integrated circuits. The coupler has the coupling loss and alignment tolerance comparable to those of a conventional edge coupler. A small wavelength‐dependent loss was observed over the 100‐nm wavelength bandwidth at chip temperatures of 25, 45, and 65°C.

The poor stickiness of silicate dust grains is a major obstacle to the formation of rocky planetesimals. In this study, we examine the possibility that silicate grains with an organic mantle, which we call Organic-Mantled Grains (OMGs), form planetesimals through direct coagulation. Organic mantles are commonly found in interplanetary dust particles, and laboratory experiments show that they are softer than silicates, in particular in warm environments. This, combined with the theory of particle adhesion, implies that OMGs are stickier than bare silicate grains. Because organic mantles can survive up to 400 K, silicate grains inside the water snow line in protoplanetary disks can in principle hold such mantles. We construct a simple grain adhesion model to estimate the threshold collision velocity below which aggregates of OMGs can grow. The model shows that aggregates of 0.1 \\micron-sized OMGs can overcome the fragmentation barrier in protoplanetary disks if the mantles are as thick as those in interplanetary dust particles and if the temperature is above \\(\\sim\\) 200 K. We use this adhesion model to simulate the global evolution of OMG aggregates in the inner part of a protoplanetary disk, demonstrating that OMG aggregates can indeed grow into planetesimals under favorable conditions. Because organic matter is unstable at excessively high temperatures, rocky planetesimal formation by the direct sticking of OMGs is expected to occur in a disk annulus corresponding to the temperature range \\( \\sim\\) 200--400 K. The organic-rich planetesimals may grow into carbon-poor rocky planetesimals by accreting a large amount of carbon-poor chondrules.

We have proposed and developed a new type of electroabsorption modulator (EAM) that employs both optical absorption and interferometric extinction. The EAM operates at a record-low voltage of 0.2 Vat 25.8-Gbit/s modulation, which can reduce optical transmitter power consumption and allows the adoption of cost-effective CMOS drivers.