With the long-term operation of nuclear power plants, evaluating the integrity of reactor pressure vessels (RPVs) against neutron irradiation has become increasingly important. In the context of pressurized thermal shock (PTS) evaluation, the flaw stability of the reactor vessel has been assessed using fracture mechanics for a postulated flaw. Neutron irradiation may reduce the safety margins of certain plants, potentially raising concerns regarding nuclear safety. For this countermeasure, the applicability of the Beremin model, which is a statistical procedure considering the stress multi-axiality, has been investigated to mitigate excessive conservatism in the conventional fracture mechanics and to perform a realistic fracture evaluation using a physical model for cleavage fracture. In this paper, the applicability of a model coupled with the Beremin model with the Gurson-Tvergaard-Needleman (GTN) models was examined to establish a more precise fracture evaluation method for realistic structures in which cleavage fracture occurs after a small ductile crack growth in the ductile-brittle transition temperature (DBTT) region. After determining the parameters of the Beremin model to characterize cleavage fracture and the GTN model parameters to characterize ductile fracture with the C(T) and SE(B) specimens, these parameter values were used in the coupled model to predict the 5% and 95% confidence limits of critical cleavage fracture of a surface-flawed plate specimen with a thickness of 50 mm under bending or tensile load with nearly the same constraint as a reactor vessel. When the fracture tests using a flat plate with a surface flaw of depth/thickness 0.1 under bending or tensile load were performed at temperatures -80 degrees C and -120 degrees C, most of all the critical Ks of the specimens were within the upper and lower bounds of the predicted critical K values. At the temperature -80 degrees C which caused a small ductile crack, the predicted critical K values by the coupled model were better than those by the Beremin model comparing with the test data. As a result, it was confirmed that the coupled model was a proper procedure for the cleavage fracture associated with small ductile crack growth.
In Japan, the "Comparable Sales Approach" is the most common method for real estate appraisal. However, this approach often fails to adequately reflect regional characteristics. This study constructs a region-specific price prediction model using LightGBM with transaction data of pre-owned condominiums in Minato Ward, Tokyo. The model extracts the importance of price-determining factors (features), which are then compared across regions. Differences in the influence of factors such as distance to the nearest station, building age, floor level, floor area, and view conditions were identified, highlighting both interregional variations and deviations from overall trends. Furthermore, by employing generative AI for analysis, this study clarifies region-specific determinants and demonstrates the potential to enhance transparency, foster trust among property owners, and improve the practical application of real estate sales appraisals. Our results show the importance of incorporating region-specific determinants, contributing to greater transparency and trust in property markets.
One-way functions play fundamental role in public-key cryptography. In this paper, one-way functions proposed by Anshel and Goldfeld in 1997 are reformulated, and their computational complexity and applications are discussed. Their one-way functions are constructed using Lfunctions associated with elliptic curves defined over the rational number field. Their functions are unique and also have potential applications in post-quantum cryptography.
In the event of a major Nankai Trough earthquake, which is predicted to occur with high probability in the near future, there is concern that long-term-period seismic motions having a significant impact on supertalls will be strongly excited in the Kanto Plain where central Tokyo is located. In order to design a supertall satisfying extremely high building performance under such a severe seismic environment, authors have developed a new response control system, the Damped Braced Tube System, and adopted it for the 385 meters tall Torch Tower, which have commenced construction as the primary building of TOKYO TORCH redevelopment project in central Tokyo. This paper describes an overview of the Damped Braced Tube System and introduces how it is adopted to the structural design of the Torch Tower. Additionally, the Damped Braced Tube System is shown to meet the high seismic design goals for the severe seismic environment in central Tokyo.
This paper proposes a method for minimizing a Gerber-Shiu-like penalty function using a and reinsurance strategies. The Gerber-Shiu-like penalty function considers both the probability of ruin and the magnitude of loss when ruin occurs. To apply the MBSPG, we derive an unbiased estimator of the gradient via Malliavin calculus and establish Holder continuity of the gradient. Numerical experiments demonstrate the effectiveness of our proposed method.
