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To address the need for robust investment strategies in an increasingly uncertain global market, this study focuses on an ambiguity-averse insurer facing exchange rate uncertainty while investing in a foreign stock market. The insurer’s surplus is modeled via a classical compound Poisson process, and exchange rate dynamics are captured using an Ornstein–Uhlenbeck process for the drift component. Within the framework of maximizing expected exponential utility of terminal wealth, we derive and solve the Hamilton–Jacobi–Bellman equation to characterize the optimal investment strategy and the associated value function. Finally, a numerical example illustrates how varying model parameters influences the insurer’s optimal investment behavior.

In this paper, we consider the optimal dividend problem for the renewal risk model with phase-type distributed interclaim times and exponentially distributed claim sizes. Assume that the phases of the interclaim times can be observed. The goal is to find the optimal dividend policy to maximize the cumulative discounted dividend before ruin. To explore the optimal strategy, we first present an algorithm and then for each particular phase-type distributed interclaim times example, the optimality of phase-wise barrier strategy as well as the convergence of the algorithm is proved. Then we theoretically analyze some properties of the value function and the optimal phase-wise barriers should fulfill. Furthermore, we specifically analyze the concavity of the value function and the barrier size comparison in the case of 2-order distributed interclaim times. In the last, we theoretically show that the phase with the highest barrier is the one with the highest intensity to the next claim.

The correct prediction of the wind speed and turbulence levels over complex terrain is essential for accurately assessing wind turbine wake recovery, power production, safety, and wind farm design. In this paper, two modified RANS turbulence models are proposed, which are innovative variants of the conventional SST k-ω model and the linear Reynolds stress model (RSM) featuring optimized closure constants. Then, these two modified models and their origin models are applied to compare and analyze wind flows from a 3D hill wind tunnel experiment and two field measurements over typical complex terrain, including Askervein hill and Bolund island, with the aim of analyzing the sensitivity of wind flows to different RANS turbulence models. The study focuses on analyzing the effects of different turbulence models on the self-sustainability of wind speed and turbulent kinetic energy upstream of the computational domain and on the accuracy of wind flow prediction over complex terrain. The results show that our modified RSM model shows better agreement with the available experimental data on the upstream and leeward sides of all simulated hills. The wind speed on the leeward slope is particularly sensitive to the turbulence model, with a maximum difference in the relative root mean square error (RRMSE) that can reach 11% among the four models. The accuracy of the turbulent kinetic energy depends on the self-sustainability of the upstream turbulent kinetic energy and the predictive ability of the turbulence model for separated flows, and the maximum difference in the RRMSE of the four models can reach 47%. In addition, the advantages and disadvantages of the tested models are discussed to provide guidance for model selection during wind flow simulations in complex terrain.

This paper deals with a credit derivative pricing problem using the martingale approach. We generalize the conventional reduced-form credit risk model for a credit default swap market, assuming that the firms’ default intensities depend on the default states of counterparty firms and that the stochastic interest rate follows a jump-diffusion Cox–Ingersoll–Ross process. First, we derive the joint Laplace transform of the distribution of the vector process (rt,Rt) by applying piecewise deterministic Markov process theory and martingale theory. Then, using the joint Laplace transform, we obtain the explicit pricing of defaultable bonds and a credit default swap. Lastly, numerical examples are presented to illustrate the dynamic relationships between defaultable securities (defaultable bonds, credit default swap) and the maturity date.

Agricultural headwater ditches are an important source of indirect agricultural nitrous oxide (N 2 O) emissions, but their contribution is difficult to quantify. In the present study, the static chamber-gas chromatography technique was used for measurement of N 2 O emissions from vegetated (V, the whole ditch ecosystem) and non-vegetated (NV, the sediment-water interface only) zones in an agricultural headwater ditch in the Central Sichuan Basin in Southwestern China during 2014–2015. Annual N 2 O emissions from the agricultural headwater ditch were similar to direct N 2 O emissions from an adjacent N-fertilized purple soil cropland, suggesting nitrogen (N)-enriched ditches are important anthropogenic N 2 O sources. Mean cumulative N 2 O emissions during summer and autumn were higher than those in spring and winter. Overlying water nitrate (NO 3 − -N) concentration and sediment-water interface temperature were primary factors affecting seasonal N 2 O emissions. Heavy precipitation transported NO 3 − -N from cropland and increase NO 3 − -N in the agricultural headwater ditch water, and subsequently stimulate N 2 O emissions. A literature review of EF 5r (the indirect N 2 O emission factor for rivers) revealed a mean value of 0.23%, similar to our values (0.27%), and also the default value (0.25%) proposed by the Intergovernmental Panel on Climate Change. The number of studies on indirect N 2 O emissions remains limited, and more in situ measurements are needed to have more accurate values of EF 5r .

Remote stimuli‐responsive movable soft robots without the need for complex 3D deformation processes and specific working environments is an unsolved problem and urgent need. In this work, under the inspiration of mother nature, a novel strategy of simple combination of the bionic bristles structure and the photothermal‐driven reversible shape change liquid crystal polymer (LCP) actuator is proposed to work out this difficulty. The combination structure is designed as unique three parts with two bionic bristle units at the two ends and one LCP unit in the center with a soft connection between them. After matching the driving force and the resistance, the prepared soft robot can realize the earthworm‐like unidirectionally crawl on the paper surface upon near‐infrared light irradiation through the contracting and stretching of LCP with a maximum average speed of 4.4 mm min−1. What's more, the crawling speed of the soft robot can be regulated by varying the irradiation distance of near‐infrared light or the length of the actuators. This strategy realizes the type of remote wireless control soft robot and has potential application ability in other soft robots with various demands. A novel strategy of simple combination of bionic bristles and photothermal‐driven liquid crystal polymer (LCP) actuator is presented. This combination has two bristle units at the ends and one LCP unit in the center with soft connection. The crawling speed of the robot can be regulated by varying irradiation distance of near‐infrared light or the length of the actuators.

Sertoli cell-only syndrome (SCOS) is the most severe and common pathological type of non-obstructive azoospermia. The etiology of SCOS remains largely unknown to date despite a handful of studies reported in this area. According to the gene expression of testicular tissue samples in six datasets from the Gene Expression Omnibus, we detected 1441 differentially expressed genes (DEGs) between SCOS and obstructive azoospermia (OA) testicular tissue samples. Enriched GO terms and KEGG pathways for the downregulated genes included various terms and pathways related to cell cycle and reproduction, while the enrichment for the upregulated genes yielded many inflammation-related terms and pathways. In accordance with the protein-protein interaction (PPI) network, all genes in the most critical module belonged to the downregulated DEGs, and we obtained nine hub genes, including CCNB1, AURKA, CCNA2, BIRC5, TYMS, UBE2C, CDC20, TOP2A, and OIP5. Among these hub genes, six were also found in the most significant SCOS-specific module obtained from consensus module analysis. In addition, most of SCOS-specific modules did not have a consensus counterpart. Based on the downregulated genes, transcription factors (TFs) and kinases within the upstream regulatory network were predicted. Then, we compared the difference in infiltrating levels of immune cells between OA and SCOS samples and found a significantly higher degree of infiltration for most immune cells in SCOS than OA samples. Moreover, CD56 bright natural killer cell was significantly associated with six hub genes. Enriched hallmark pathways in SCOS had remarkably more upregulated pathways than the downregulated ones. Collectively, we detected DEGs, significant modules, hub genes, upstream TFs and kinases, enriched downstream pathways, and infiltrated immune cells that might be specifically implicated in the pathogenesis of SCOS. These findings provide new insights into the pathogenesis of SCOS and fuel future advances in its theranostics.

Spermatozoa exit the testis in an immotile and immature state, and obtain motility and maturity in the epididymis with the most abundant functions acquired in its initial segment (IS). The reshaping of polystyrene nanoplastics (PS-NPs) exposure on the epididymis, however, has never been studied in detail yet, let alone from a multi-omic perspective. Herein, we utilized single-cell transcriptomics, untargeted metabolomics and in vivo experiments to explore PS-NPs-induced cellular remodeling of rat IS. A dose-dependent decrease in the epithelial thickness was merely observed in the IS (Control vs. low vs. medium vs. high group, 38.33 ± 2.52 vs. 32.67 ± 3.15 vs. 21.67 ± 3.58 vs. 11.08 ± 1.67 μm, respectively; P  < 0.001) instead of the other three epididymal segments. PS-NPs exposure inhibited the acidification of epididymal luminal fluid (Control vs. low vs. medium vs. high group, pH, 6.05 ± 0.19 vs. 6.35 ± 0.14 vs. 6.57 ± 0.23 vs. 6.70 ± 0.24, respectively; P  < 0.001), downregulated sperm acrosome reaction (Control vs. low vs. medium vs. high group, 42.67 ± 4.62% vs. 36.38 ± 4.04% vs. 28.07 ± 3.46% vs. 17.69 ± 2.52%, respectively; P  < 0.05), and reduced sperm motility (Control vs. low vs. medium vs. high group, 83.08 ± 4.02% vs. 76.33 ± 2.08% vs. 70.67 ± 3.79% vs. 65.33 ± 2.89%, respectively; P  < 0.01). Cell apoptosis after exposure existed across the IS without cell type-specificity. Besides, we found altered metabolic landscape and dysregulatory amino acid metabolites after exposure. Interestingly, cell-cell communication together with pseudotime trajectory delineated that PS-NPs facilitated NK cell differentiation towards cytotoxic and proliferative subtypes, during which ICAM and TNF signalings were upregulated. Moreover, PS-NPs exposure upregulated AQP9 through activating ERK1/2 in principal cells. Furthermore, we observed dysfunctions and ultrastructural defects of blood-epididymal barrier with downregulated protein levels of tight junction (VIM, SOX9, KRT5 and β-catenin) and upregulated ROS levels in basal cells. In summary, we offer previously unidentified insights into the contribution of PS-NPs in epididymal IS and extend on existing knowledge of environmental contaminant-induced epididymis damage that merits future investigation. Graphical abstract

In this paper, we study the optimal dividend problem assuming that the underlying reserve process follows the Sparre Andersen model. In this model, there is no constant restriction on the dividend rates, i.e., the optimization problem is of singular type. In this case, the value function is no longer bounded and the associated Hamilton–Jacobi–Bellman equation is a variational inequality involving a first-order integro-differential operator and a gradient constraint. We prove the regularity properties for the value function by constructing strategies and show that the value function is a constrained viscosity solution of the associated Hamilton–Jacobi–Bellman equation. In addition, we prove that the value function is the upper semicontinuous envelope of the supremum for a class of subsolutions.

The indiscriminate use of antibiotics has resulted in a growing resistance to drugs in Pseudomonas aeruginosa . The identification of antibiotic resistance genes holds considerable clinical significance for prompt diagnosis. In this study, we established and optimized a Recombinase-Aided Amplification (RAA) assay to detect two genes associated with drug resistance, oprD and arr , in 101 clinically collected P. aeruginosa isolates. Through screening for the detection or absence of oprD and arr , the results showed that there were 52 Imipenem-resistant P. aeruginosa (IRPA) strains and 23 Rifampin-resistant P. aeruginosa (RRPA) strains. This method demonstrated excellent detection performance even when the sample concentration is 10 copies/μL at isothermal conditions and the results could be obtained within 20 minutes. The detection results were in accordance with the results of conventional PCR and Real-time PCR. The detection outcomes of the arr gene were consistently with the resistance spectrum. However, the antimicrobial susceptibility results revealed that 65 strains were resistant to imipenem, while 49 strains sensitive to imipenem with oprD were identified. This discrepancy could be attributed to genetic mutations. In summary, the RAA has higher sensitivity, shorter time, and lower-cost instrument requirements than traditional detection methods. In addition, to analyze the epidemiological characteristics of the aforementioned drug-resistant strains, we conducted Multilocus Sequence Typing (MLST), virulence gene, and antimicrobial susceptibility testing. MLST analysis showed a strong correlation between the sequence types ST-1639, ST-639, ST-184 and IRPA, while ST-261 was the main subtype of RRPA. It was observed that these drug-resistant strains all possess five or more virulence genes, among which exoS and exoU do not coexist, and they are all multidrug-resistant strains. The non-coexistence of exoU and exoS in P.aeruginosa is related to various factors including bacterial regulatory mechanisms and pathogenic mechanisms. This indicates that the relationship between the presence of virulence genes and the severity of patient infection is worthy of attention. In conclusion, we have developed a rapid and efficient RAA (Recombinase-Aided Amplification) detection method that offers significant advantages in terms of speed, simplicity, and cost-effectiveness (especially in time and equipment aspect). This novel approach is designed to meet the demands of clinical diagnostics.