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Impact of income and leisure on optimal portfolio, consumption, and retirement decisions under exponential utility
No full textWe study an optimal control problem encompassing investment, consumption, and retirement decisions under exponential (CARA-type) utility. The financial market comprises a bond with constant drift and a stock following geometric Brownian motion. The agent receives continuous income, consumes over time, and has the option to retire irreversibly, gaining increased leisure post-retirement compared to pre-retirement. The objective is to maximize the expected exponential utility of weighted consumption and leisure over an infinite horizon. Using a martingale approach and dual value function, we derive implicit solutions for the optimal portfolio, consumption, and retirement time. The analysis highlights key contributions: first, the equivalent condition for no retirement is characterized by a retirement income threshold; second, the influence of income and leisure levels on optimal portfolio, consumption, and retirement decisions is thoroughly examined. These results provide valuable insights into the interplay between financial and lifestyle choices in retirement planning.
Nitrogen-enriched porous organic polymers for high-performance CO2/N2 separation in mixed-matrix membranes
No full textThe development of high-performance mixed matrix membranes (MMMs) for CO2/N2 separation requires fillers that simultaneously enhance gas permeability and selectivity without introducing interfacial defects. In this study, we report the synthesis of nitrogen-containing porous organic polymers (POPs) via a one-step Friedel-Crafts polymerization, designed to introduce CO2-philic functional groups directly into the polymer backbone while preserving intrinsic porosity. Structural and gas sorption analyses confirmed that the synthesized POPs exhibit high microporosity, surface area, and nitrogen content, which together enhance CO2 adsorption affinity. When incorporated into Matrimid-based MMMs, the POPs significantly improved CO2 permeability and CO2/N2 selectivity, with the pp-tpta filler (containing the highest nitrogen content) delivering the most pronounced performance enhancement. Further optimization using a high-permeability 6FDA-DAM polyimide matrix yielded a membrane with a CO2 permeability of 1967 Barrer and a selectivity of 33.4 at 20 wt% pp-tpta loading, surpassing the 2008 Robeson Upper Bound. Solubility-diffusivity analyses, supported by both experimental measurements and molecular dynamics simulations, revealed that the pp-tpta filler enhances CO2/N2 separation primarily by increasing CO2 solubility and diffusivity within the membrane matrix. These results underscore the potential of rationally designed, nitrogen-rich POP fillers as effective, scalable materials for advanced gas separation membranes.
Automorphism groups of the fields of definition of torsion points of elliptic curves in characteristic ≥ 5
No full textFor a field K of characteristic p >= 5, let Es,t : y2 = x3+sx+t be an elliptic curve defined over the function field K (s, t) in two variables sand t. For a non-negative positive integer e and a positive integer N which is not divisible by p, we prove that if K superset of Falg p , then the automorphism group of the normal extension K (s, t) (Es,t [peN]) over K (s, t) is isomorphic to (Z/peZ)x x SL2 (Z/NZ). Applying this result, we also determine the automorphism group of the normal extension K (s, t) (Es,t [peN]) for a general field K of characteristic p >= 5. (c) 2025 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.
Improved variance estimation in steady-state and time-dependent Monte Carlo neutron transport using history-based batch method in the iMC code
No full textThe presence of intercycle correlations in the fission source distribution (FSD) is known to mathematically underestimate the sample variance of tally means in Monte Carlo (MC) steady-state simulations. To address this issue, the history-based batch method (HBM) estimates the variance using history-based batches, which are subsets of neutron histories grouped according to common ancestor fission neutrons, to stifle intercycle correlations. The HBM framework can also be extended to Dynamic Monte Carlo (DMC) simulations for time-dependent neutron transport, enabling direct variance estimation without relying on the replica scheme. Recently, HBM capabilities have been implemented in the iMC Monte Carlo code, developed at the Korea Advanced Institute of Science and Technology (KAIST), supporting both steady-state and time-dependent MC transport analyses. This work presents benchmark results that verify the correctness of the implementation and demonstrates the applicability of HBM to fast-spectrum reactor problems, which have not been previously explored. The dynamic MC algorithm in the iMC code is also discussed, with particular attention to the treatment of delayed neutron precursors. The results confirm that HBM offers improved variance estimation over conventional sample variance methods in both thermal and fast-spectrum reactor systems.
A Simple yet Effective Approach to Generate P-I Diagrams for RC Beams
No full textThis paper presents a straightforward yet effective methodology to generate flexural and shear P-I diagrams for arbitrary reinforced concrete (RC) beams using a linear interpolation procedure that eliminates the need to conduct multiple blast analyses through rigorous nonlinear time-history approaches. The flexural and shear P-I diagrams for a limited number of RC beams have been constructed and serve as reference P-I diagrams for the linear interpolation process. A total of 24 representative RC beam cases have been incorporated into the database, with plans for expansion through the continual addition of RC beam data. Since the P-I diagram is formulated based on the blast analyses of RC beams subjected to uniform blast pressure, this paper proposes an additional method to determine the equivalent uniform pressure-time history resulting from TNT explosions, whose effects may vary along the beam span. Furthermore, this paper introduces a method to account for the influence of changing boundary conditions on the P-I diagrams. By utilizing the proposed methods for evaluating equivalent uniform pressure-time histories and the suggested linear interpolation procedure, along with adjustments for variations in boundary conditions, bending and shear P-I diagrams for arbitrary RC beams can be effectively determined. The effectiveness of the proposed interpolation approach has been validated through comparisons between the interpolated P-I diagrams and P-I diagrams derived directly from blast analyses, along with additional parametric studies to investigate the influence of various design variables on the P-I diagrams. The proposed methodology can be effectively used to assess whether to remove or retain explosion-damaged RC beams for which flexural or shear P-I diagrams are not available, as well as to determine the sectional dimensions and steel ratios of RC beams during the preliminary stages of explosion-proof design.
Soil-tunnel interaction for segmental linings with non-planar longitudinal joints via centrifuge modeling
No full textSegmental tunnel linings can develop uneven internal forces and excessive deformation when nearby construction or groundwater fluctuations weaken their joints, threatening long-term durability. Conventional planar longitudinal joints often slip or rotate excessively under asymmetric, multidirectional loads, yet alternative geometries to overcome this vulnerability remain underexplored. This study proposes a novel design with nonplanar, topologically interlocking longitudinal joints and evaluates its performance against a planar counterpart. A 50g geotechnical centrifuge test imposed asymmetric surcharge loading on both linings. Ground responses, including surface settlement, soil stiffness, and stress redistribution, were monitored alongside structural responses such as bending moment and hoop force. The non-planar joints promoted more uniform hoop force distribution, limited peak bending moments, and stiffened the soil-tunnel system. Correspondingly, lining displacement and ground surface settlement decreased relative to the planar case. Key metrics, such as the loadsharing ratio and the equivalent radial spring stiffness of the system, quantify these performance gains. The highfidelity dataset clarifies the load transfer mechanisms and supports the establishment of sophisticated numerical models required for comparative design optimization. These findings demonstrate that non-planar interlocking joints enhance system resilience and provide a practical pathway toward more robust segmental linings.
SET-DGCN: An end-to-end electroencephalography-based fatigue detection method for young drivers
No full textDriver fatigue poses a critical threat to global road safety, particularly among young drivers. Nevertheless, policy-level interventions remain fragmented due to the lack of reliable and deployable detection technologies. Bridging this gap requires accurate, interpretable, and real-time fatigue monitoring systems capable of informing practical decision-making in transportation safety management. To address this challenge, we propose an end-to-end EEG-based fatigue detection model, Scale-Enhanced Transformer and Dynamic Graph Convolutional Network (SET-DGCN). The model captures multi-scale temporal dependencies and spatial brain-region interactions by integrating convolutional embeddings, attention mechanisms, and learnable graph structures. Extensive evaluations on both a driving simulation dataset and the publicly available SEED-VIG dataset confirm that SET-DGCN outperforms mainstream convolutional neural network (CNN)-based, graph convolutional network (GCN)-based, and Transformer-based models in terms of accuracy and F1-score, while maintaining strong cross-subject generalization. To enhance both interpretability and application relevance, a component-level attribution method (COAR) is employed to evaluate the functional contribution of model modules, while SHapley Additive exPlanations (SHAP) analysis is used to uncover brain region-specific patterns across fatigue stages. Based on these neural insights, a set of multi-level policy and design recommendations is proposed, ranging from infrastructure enhancements to adaptive in-vehicle systems and individualized interventions, to provide a comprehensive framework for mitigating fatigue among young drivers in real-world transportation contexts.
Prediction of Amyloid Positivity in Lewy Body Disease Using Early-Phase 18F-FP-CIT PET Images
No full textPurpose: To explore whether alterations in regional cerebral perfusion observed on early-phase F-18-FP-CIT PET imaging could predict beta-amyloid positivity in patients with Lewy body disease (LBD). Methods: We enrolled 132 patients with LBD (78 dementia with Lewy bodies and 54 Parkinson disease) who underwent dual-phase F-18-FP-CIT PET and 18F-FBB PET scans at initial assessment. Patients were divided into the amyloid-positive (n=69) and amyloid-negative (n=63) groups. We compared regional uptake on early-phase F-18-FP-CIT PET images between the 2 groups, whereas a linear discriminant analysis (LDA) was performed to predict beta-amyloid positivity based on the standard uptake value ratios (SUVRs) of each region of interest. Mediation analyses were performed to evaluate whether regional cerebral perfusion mediated the association between beta-amyloid load and longitudinal changes in the Mini-Mental State Examination (MMSE) scores. Results: There were no significant differences in age, sex, educational attainment, MMSE scores, motor deficits, or striatal dopamine depletion between the amyloid-positive and amyloid-negative groups. The amyloid-positive group exhibited decreased uptake in the parietal, precuneus, middle/inferior temporal, and isthmus cingulate cortices, as well as increased uptake in the caudate, compared with the amyloid-negative group on early-phase F-18-FP-CIT PET images. LDA prediction model demonstrated that SUVRs of the inferior parietal cortex and caudate optimally distinguished the 2 groups. Greater beta-amyloid burden was associated with a more rapid decline in MMSE scores, which was partially mediated by inferior parietal hypoperfusion. Conclusions: Alterations in regional cerebral perfusion on early-phase F-18-FP-CIT PET imaging may serve as a useful biomarker for predicting beta-amyloid deposition in LBD.
Spin and stability of on-surface synthesized Ni-organic complexes on Au (111)
No full textPlanar metal-organic complexes of transition metals and it-conjugated ligands are of broad interest due to their high electric conductivity and functional tunability. The electronic and spin states of the transition metals play a central role in defining their functional properties. While Ni is generally expected to exhibit no magnetic moment upon donating two electrons, new cases with magnetic moment induced by surface environments have been reported, calling for further experimental examples. Here, we investigated the electronic and spin states of on-surface synthesized metal-organic complexes composed of Ni atoms and deprotonated 2,3,6,7,10,11-hexahy-droxytriphenylene (HHTP) on Au(111) using scanning tunneling microscopy and spectroscopy. Several structures including one with a three-blade fan shape were observed with two distinct Ni sites-bridge and end positions. Density functional theory calculations reveal that the bridge-position Ni is non-magnetic, while the end-position Ni is magnetic, explaining the peaks observed in experiments. Our calculation results also showed that the Au(111) surface significantly stabilized the structures compared to vacuum conditions. This study highlights the crucial role of Au(111) surface in determining the spin and stability properties of on-surface synthesized metal-organic complexes.
Towards improving the self-updated four-node finite element
No full textRecently, the self-updated finite element proposed by Jung et al. (2022) was developed to improve the solution accuracy of the four-node solid finite element using an iterative solution procedure. The stiffness matrices of the self-updated finite element are iteratively updated using optimal bending modes through the iterative procedure to minimize shear locking. Excellent performance of the self-updated finite element was shown in various numerical examples, even with coarse and highly distorted meshes. However, a critical issue was subsequently observed: the numerical accuracy deteriorated under some combined loading conditions, which originated from the iterative solution procedure. To overcome this issue, a new iterative solution procedure is proposed using a load decomposition strategy, in which the external load is decomposed into bending-induced and the remaining parts. The new self-updated finite element passes the patch and zero-energy mode tests. The improved performance of the new self-updated finite element is demonstrated through several numerical examples.