The Bandaiko hot spring, located in Kusatsu Town, Gunma Prefecture, is characterized by its hyper-acidic nature with a pH level of 1.7 and remarkable flow rate of approximately nine tons per minute. Gunma Prefecture is exploring the possibility of modifying its existing heat exchange system to establish a binary power generation facility utilizing this hyper-acidic hot spring, marking a potential first in the world. However, in the existing heat exchange facility, scale accumulation of the current facility necessitates water washing roughly once a month, but the type of scale and the rate of accumulation rate are still unknown. To address this, hot spring water was sampled and chemically analyzed, and field tests simulating scale adhesion were conducted using this water. For evaluation, quartz glass coupons and a batch-type scale sensor were utilized. The accumulated scale was identified as elemental sulfur. The use of quartz glass coupons did not enable an assessment of the scale deposition rate based on weight changes. By contrast, an 18-d immersion test with batch-type scale sensor indicated a gradual decrease in transmittance over time. The decrease in this sensor's transmittance serves as a proxy indicator for material accumulation under static immersion conditions. As it is not possible to analyze the scale adhering to the titanium heat exchanger during operation, it does not directly indicate the rate of scale deposition. Analysis of deposits on the sensor surface and scale recovered during the water washing of the heat exchanger revealed that the scale was elemental sulfur. Further analysis revealed that the elemental sulfur, derived from the chemical composition of the hot spring water, was undersaturated within the tested temperature range. The hot spring water is transported via pipeline to the heat exchange facility after gas-liquid separation at the source—located 2 km away—yet it is determined that atmospheric air enters the water at the source. This suggests that the precipitation of sulfur is caused either by the oxidation of trace amounts of H2S in the hot spring water by atmospheric oxygen or, alternatively, by bacterial activity. A subsequent bacterial analysis detected sulfur-oxidizing bacteria. These findings suggest that the formation of elemental sulfur scale likely results from the precipitation of sulfur caused by H2S oxidation—driven either by microbial activity or atmospheric oxygen—during the transport of the hot spring water. While installing sterilization equipment is an option for inhibiting bacterial activity, it entails significant costs. Given that the periodic water cleaning currently employed effectively restores heat exchange efficiency, this method remains the most appropriate approach for the time being. However, if the concentration of H2S in the hot spring water increases, reconsideration of a sterilization approach will be necessary. The novelty of this study is to connect observed sulfur scale, water chemistry, field sensor testing, equilibrium modelling, and microbial evidence in an actual utilization setting.
Although considerable advances have been made in directly converting ethanol to butadiene (ETB), the catalyst deactivation mechanism remains incompletely understood. Herein, ZnZr/Si-beta catalyst was chosen as a model catalyst to elucidate the carbon deposition induced deactivation mechanism. The comprehensive characterization revealed that the primary cause of deactivation is the accumulation of coke deposits on the catalyst surface or within the pores. The significant accumulation of acetaldehyde results from inhibited aldol condensation, caused by carbon deposits covering the active sites. The accumulated acetaldehyde undergoes aldol condensation to form acetone. Subsequently, the generated acetone and acetaldehyde participate in self- and cross-condensation reaction, generating long-chain unsaturated aldehydes and ketones. Subsequent cyclization reaction of these compounds generates complex compounds such as 2,4-dimethylbenzaldehyde, dibenzofuran, and fluorene, which ultimately poison the catalyst by blocking its active sites. These insights offer valuable theoretical guidance for designing novel catalysts for the direct ethanol-to-butadiene conversion.
The evolution behavior of reaction intermediates plays a pivotal role in directing the performance of dry reforming of methane (DRM), yet precise control strategies remain limited. Herein, we present a laser-etching technique for the controllable synthesis of defective carbon-supported Ni (Ni/C) catalysts. Comprehensive characterization and density functional theory (DFT) simulations collectively reveal that tuning the laser etching power enables the precise regulation of defect density in the carbon support. A moderate defect density not only optimizes the electronic states and particle size of Ni sites but also maintains the size stability of Ni nanoparticles. Such synergistic effects achieve an optimal balance between deep dehydrogenation and oxidation of CH x * intermediates, delivering CH4 and CO2 conversion of 73 and 75%, respectively. This work provides a novel and effective approach for enhancing the DRM performance of carbon-supported Ni-based catalysts.
The contractile apparatus of striated muscle, including both skeletal and cardiac muscle, intrinsically exhibits self-sustained oscillatory behavior under intermediate activation states between contraction and relaxation. This phenomenon, termed SPOC (spontaneous oscillatory contraction), provides unique insights into the dynamic regulation of force generation. In this review, we first highlight experimental findings that characterize SPOC and then focus on theoretical frameworks developed to capture its essential features. A key feature of these models is the assumption that the lattice spacing, that is, the distance between the thick and thin filaments, varies dynamically during muscle contraction and that actomyosin activity depends on this spacing. This assumption naturally explains the emergence of SPOC. Particular attention is given to models constructed for single sarcomeres, isolated myofibrils, and small bundles of myofibrils, through which the underlying mechanisms of SPOC can be systematically understood. Finally, by extending the mathematical structure of these models, we propose that SPOC may exhibit chaotic properties, thereby providing a comprehensive understanding of its mechanisms and physiological significance.
Previous extended x-ray absorption fine structure (EXAFS) studies have shown evidence of anomalous contributions in the atomic background function whose origin was debated in the literature. The present study presents advanced multiple scattering calculations aimed to put to a test the existence and origin of the so-called atomic XAFS (AXAFS) contribution, discussed in details in some previous works. We show with specific examples that the muffin-tin approximation normally used in EXAFS calculations is inappropriate to study this phenomenon as spurious oscillations in the atomic background are related to the potential truncation at the border of the muffin-tin spheres. We thus employed a more sophisticated approach beyond the muffin-tin approximation based on the full-potential multiple scattering theory and self-consistent charge densities. The comparison of EXAFS calculations with previous experimental results allowed us to exclude the presence of the AXAFS as due to modulations of the charge density as previously suggested. This study confirms the importance of a proper account of the atomic background in EXAFS data analysis, which may contain effects beyond the single-electron approximation but are found not affected by AXAFS. We conclude that the contribution of AXAFS in EXAFS experiments, if existing at all, is negligible and should not be considered in EXAFS data analysis.
