Modeling municipal yields with (and without) bond insurance

YesWe develop an intensity-based model of municipal yields, making simultaneous use of the CDS premiums of the insurers and both insured and uninsured municipal bond transactions. We estimate the model individually for 61 municipal issuers by exploiting the dramatic decline in credit quality of the bond insurers from July 2007 to June 2008, and decompose the municipal yield spread based on the estimated parameters. The decomposition reveals a dominant role of the liquidity component as well as interactions between liquidity and default similar to those modeled by Chen et al. (2016) for corporate bonds. Towards the end of the sample period, our model also reproduces the "yield inversion" phenomenon documented by Bergstresser et al. (2010)

Credit risk prediction in an imbalanced social lending environment

© 2018, the Authors. Credit risk prediction is an effective way of evaluating whether a potential borrower will repay a loan, particularly in peer-to-peer lending where class imbalance problems are prevalent. However, few credit risk prediction models for social lending consider imbalanced data and, further, the best resampling technique to use with imbalanced data is still controversial. In an attempt to address these problems, this paper presents an empirical comparison of various combinations of classifiers and resampling techniques within a novel risk assessment methodology that incorporates imbalanced data. The credit predictions from each combination are evaluated with a G-mean measure to avoid bias towards the majority class, which has not been considered in similar studies. The results reveal that combining random forest and random under-sampling may be an effective strategy for calculating the credit risk associated with loan applicants in social lending markets

What We Don’t Know (Yet) about Human-AI Collaboration

New questions about how humans can – and should – collaborate with Artificial Intelligence (AI) are emerging rapidly with the emergence of generative AI solutions like “ChatGPT”. The AI solutions available today go far beyond previously considered IT because it can re-code procedures, transform data, generate content, and thus alter the process and outcomes of work at an unprecedented scale. The consequence of this development is the question of whether AI is outperforming and replacing humans at non-routine tasks such as knowledge work (KW). This is a non-trivial question because knowledge worker (KWers) and the knowledge-intensive organizations embedded in were, for a long time, seen to be seemingly unaffected by the technological developments stemming from AI. Today, however, there is very limited understanding of the ways that KWers adjust to, and integrate, AI at work. This includes questions addressing ethical concerns related whether technology inhibits or facilitates KWers. With these theoretical challenges in mind, this research in progress sets out to sets out to address the existing research gaps existing in human-AI collaboration within knowledge-intensive domain: 1) there is out-of-dated understanding of relationship between the use of technology and the evolution of KW; 2) how are KWers highly attached with technology influenced by AI; and 3) the expectation about how human-AI collaboration should shape the nature of KW still remain unclear. Thus, this research aims to revisit the concept of KW in light of ongoing AI technology progress, outline the AI-driven phenomenon in knowledge-intensive domain and generate in-depth insights on how human–AI collaboration is reshaping the nature of KW

Chitosan extracted from the Persian Gulf chiton shells: Induction of apoptosis in liver cancer cell line

Here for the first time, we investigated the cytotoxic effects of the chitosan extracted from the Persian Gulf Chiton shell (Acanthopleura vaillantii) on liver cancer cell line (HepG_2). Chitosan extraction was implemented following this method: chitin was produced by demineralization and deproteinization procedure, and the extracted chitin was converted into soluble chitosan using deacetylation method. The cytotoxic effects of extracted chitosan were evaluated using four different tests, including 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, Annexin V-FITC, propidium iodide (PI) staining, 4',6-diamidino-2-phenylindole (DAPI) staining, and Caspase activity analysis. The IC_50 inhibitory concentrations of chitosan were obtained at 250 µg/mL after 24 h. Chitosan clearly inhibited the growth of hepatocarcinoma cells in vitro in a dose-dependent manner. For detecting the induced cell apoptosis, HepG_2 cells were treated with 125, 250 and 500 µg/ml of chitosan for 24 h. According to the result of Annex in V/PI kit, in 125, 250, and 500 µg/ml of chitosan, 28.2, 49.1, and 83.3% of HepG_2 cells undergone late apoptosis, respectively. The morphology of treated cells by DAPI staining showed non uniform plasma membrane and DNA fragmentation compared to untreated cells with perfect nucleus. The analysis of cell cycle using flow cytometry demonstrated that the rate of sub-G1 peak was increased to 52.7%. Both caspase-3 and -9 activities increased by the extracted chitosan, but it was only significant for caspase-3. The results of the present study suggested that the extracted chitosan has efficient cytotoxicity on HepG_2 cells. Therefore, the extracted chitosan from the shell of the Chiton may be considered as a futuristic natural product regarding the treatment of liver cancer

Reversible energy absorption of elasto-plastic auxetic, hexagonal, and AuxHex structures fabricated by FDM 4D printing

The present study aims at introducing reconfigurable mechanical metamaterials by utilising four-dimensional (4D) printing process for recoverable energy dissipation and absorption applications with shape memory effects. The architected mechanical metamaterials are designed as a repeating arrangement of re-entrant auxetic, hexagonal, and AuxHex unit-cells and manufactured using 3D printing fused deposition modelling process. The AuxHex cellular structure is composed of auxetic re-entrant and hexagonal components. Architected cellular metamaterials are developed based on a comprehension of the elasto-plastic features of shape memory polylactic acid materials and cold programming deduced from theory and experiments. Computational models based on ABAQUS/Standard are used to simulate the mechanical properties of the 4D-printed mechanical metamaterials under quasi-static uniaxial compression loading, and the results are validated by experimental data. Research trials show that metamaterial with re-entrant auxetic unit-cells has better energy absorption capability compared to the other structures studied in this paper, mainly because of the unique deformation mechanisms of unit-cells. It is shown that mechanical metamaterials with elasto-plastic behaviors exhibit mechanical hysteresis and energy dissipation when undergoing a loading-unloading cycle. It is experimentally revealed that the residual plastic strain and dissipation processes induced by cold programming are completely reversible through simple heating. The results and concepts presented in this work can potentially be useful towards 4D printing reconfigurable cellular structures for reversible energy absorption and dissipation engineering applications

Bio-inspired design, modeling, and 3D printing of lattice-based scale model scooter decks

This research aims at enhancing the performance of scale-model scooter decks by investigating various architected cellular metamaterial and bio-inspired core structure designs, such as honeycomb, tetrachiral, re-entrant, arrowhead, and star-shaped arrangements. An initial effort is made toward the design and rapid prototyping of small-scale deck with a uniform honeycomb core structure. More specifically, polylactic acid is utilized to fabricate complex structures via fused filament fabrication technique. Investigation is then focused on its mechanical performance, such as its bending properties obtained through a three-point bending test. Simulations are also conducted with different core configurations using a geometrically non-linear finite element method which is implemented. Experiments are carried out to verify the numerical results. After validation, various patterns are modeled, and eventually, it is observed that the functionally graded arrowhead structure has the best bending resistance, compared to other bio-inspired and mechanical metamaterial structures. At a constant force of 845 N, the functionally graded arrowhead design lowers the deflection in the middle of the scale model of scooter deck by up to 14.7%, compared to the uniform arrowhead structure. Furthermore, comparing the tetrachiral and functionally graded arrowhead configurations at a constant force, a 30% reduction in central deflection was observed. Due to the lack of similar results and designs in the specialized literature, this work could potentially advance the state-of-the-art scooter core designs and provide designers with architectures that could enhance the performance and safety of scooters

Metamaterial boat fenders with supreme shape recovery and energy absorption/dissipation via FFF 4D printing

In maritime transportation, a fender acts like a bumper to absorb the kinetic energy of a boat berthing against a jetty, pier wall, or other boats. They have high energy absorption and low reaction forces, preventing damage to boats and berthing structures. The aim of this paper is to introduce a novel conceptual design for a new class of lightweight boat-fendering systems with superior energy absorption/dissipation and shape recovery features. Different metamaterials with honeycomb, re-entrant, and re-entrant chiral auxetic patterns are designed in the form of boat fender panels, and their thermo-mechanical behaviors are analyzed experimentally and numerically. A finite element modeling (FEM) is developed to investigate the compressive behaviors of boat fenders. Some of designs are 4D printed by fused filament fabrication of shape memory polylactic acid polymers and then tested thermo-mechanically. A good correlation is observed between numerical and experimental results, supporting the FEM accuracy. Results reveal that proposed boat fenders have considerable energy absorption/dissipation along with the capability to fully recover plastic deformations by simply heating up. The excellent mechanical property recovery of the proposed boat-fendering system is also shown under cycling loadings. Due to the absence of similar conceptual designs, models, and results in the specialized literature, this paper is expected to be instrumental towards 4D printing novel boat fenders with supreme energy absorption/dissipation and shape recovery properties promoting sustainability

Finite element analysis of patient-specific additive-manufactured implants

Introduction: Bone tumors, characterized by diverse locations and shapes, often necessitate surgical excision followed by custom implant placement to facilitate targeted bone reconstruction. Leveraging additive manufacturing, patient-specific implants can be precisely tailored with complex geometries and desired stiffness, enhancing their suitability for bone ingrowth.Methods: In this work, a finite element model is employed to assess patient-specific lattice implants in femur bones. Our model is validated using experimental data obtained from an animal study (n = 9).Results: The results demonstrate the accuracy of the proposed finite element model in predicting the implant mechanical behavior. The model was used to investigate the influence of reducing the elastic modulus of a solid Ti6Al4V implant by tenfold, revealing that such a reduction had no significant impact on bone behavior under maximum compression and torsion loading. This finding suggests a potential avenue for reducing the endoprosthesis modulus without compromising bone integrity.Discussion: Our research suggests that employing fully lattice implants not only facilitates bone ingrowth but also has the potential to reduce overall implant stiffness. This reduction is crucial in preventing significant bone remodeling associated with stress shielding, a challenge often associated with the high stiffness of fully solid implants. The study highlights the mechanical benefits of utilizing lattice structures in implant design for enhanced patient outcomes