Numerous Observations Research Articles

Analytical, numerical and experimental observation of isolated branches of periodic orbits in 1DOF mechanical parametric oscillator

The aim of this study is to investigate the dynamic properties of an existing experimental stand of 1DOF mechanical parametric oscillator, with a focus on approximate analytical solutions of the observed isolated branches of periodic orbits. The experimental stand involves a cart moving along a rolling guide, with the stiffness consisting of two components: a time-varying linear element created by a rotating rod with a rectangular cross-section and a nonlinear hardening stiffness caused by magnetic springs. It was demonstrated that a rolling bearing’s nonlinear resistance to motion consists of viscous damping and a second component analytically compared to dry friction. The study utilises multiple scales and harmonic balancing methods to provide analytical solutions. It is then successfully validated using numerical simulations and experimental data. The study investigates how dry friction influences oscillator response and applies the modified Mathieu–Duffing equation to represent the system’s dynamics. Different branches of periodic orbits are researched to determine their function in energy harvesting and mechanical system improvement. This research demonstrates the distinctions across analytical, numerical, and experimental methodologies, providing a comprehensive understanding of investigating intricate nonlinear systems.

EFFECT Of DELAY IN A MUSCA DOMESTICA HOUSEFLIES MODEL: STABILITY AND GLOBAL HOPF BIFURCATION

The study focuses on the model of houseflies with discrete delay, which is examined both theoretically and numerically. The solution of the delayed system is bounded and positive. The delay is selected as the bifurcation parameter. Stability analysis, local and global Hopf bifurcation are given in theoretical aspect. Through computer simulations, various dynamic behaviors, such as supercritical Hopf bifurcation, are detected. The theoretical analysis and numerical observations in this research are significant contributions to the biomathematics research area.

Role of turbulent separatrix tangle in the improvement of the integrated pedestal and heat exhaust issue for stationary-operation tokamak fusion reactors

The magnetic separatrix surface is designed to provide the final and critical confinement to the hot stationary-operation core plasma in modern tokamak reactors in the absence of an external magnetic perturbation (MP) or transient magneto-hydrodynamic perturbation, while diverting the exhaust heat to divertor plates. All the stationary operational boundary plasma studies and reactor designs have been performed under this assumption. However, there has been a long-standing suspicion that a stationary-operation tokamak plasma even without external MPs or edge localized modes (ELMs) activities may not have a stable closed separatrix surface, especially near the magnetic X-point. Here, the first gyrokinetic numerical observation is reported that the divertor separatrix surface, due to homoclinic tangles caused by intrinsic electromagnetic turbulence, is not a stable closed surface in a stationary operation phase even without MPs or ELMs. Unlike the MP- or ELM-driven homoclinic tangles that could cause deleterious effects to core confinement or divertor plates, it is found that the micro-turbulence driven homoclinic tangles could connect the divertor plasma to the pedestal plasma in a constructive way by broadening the divertor heat-exhaust footprint and weakening the pedestal slope to the ELM-safe direction. Micro-turbulent homoclinic tangles can open a new research direction in understanding and controlling these two most troublesome and non-locally connected edge-plasma issues in a tokamak fusion reactor.

Living-donor Lobar Lung Transplantation - Initiation and Development - Secondary Publication.

Due to the difficulty of finding brain-dead donors, in October 1998, I performed the first living-donor lobar lung transplantation (LDLLT) for a ventilator-dependent 24-year-old female patient with bronchiectasis using lobes from her parents. The patient is still alive and in good health 25 years after the transplantation. Over time, the indications for LDLLT have expanded to include pulmonary hypertension, pulmonary fibrosis, congenital genetic diseases, pulmonary complications after stem cell transplantation, and, more recently, severe lung injury due to COVID-19 infection. In 2022, we successfully performed an ABO-incompatible LDLLT. To address size mismatches, we have developed new LDLLT techniques, such as right-to-left inverted transplantation, upper lobe-sparing transplantation, and segmental lung transplantation. Our published studies cover a range of topics, encompassing both basic and clinical research. Of particular significance is the observation that LDLLT offers immunological advantages over cadaveric lung transplantation (CLT). Having conducted 353 cases of lung transplantation, including 161 LDLLTs and 192 CLTs, our 5-year survival rates were 83% after LDLLT and 74% after CLT, surpassing the 55% 5-year survival rate reported by the International Society for Heart and Lung Transplantation. We have hosted numerous observers and research fellows from 15 countries. In addition, I have contributed to LDLLT procedures not only in Japan but also abroad. It brings me great satisfaction to think that my educational efforts may ultimately lead to saving the lives of those suffering from end-stage respiratory failure around the world.

Improvising the significance of vertical dimension of occlusion in patients with dentulous and edentulous condition–An update

One of the most contentious topics in dentistry has been altering the occlusal vertical dimension (OVD). When it becomes necessary to improve occlusal connections, accommodate planned restorations, and harmonize dentofacial esthetics, the OVD may need to be modified. Leonardo da Vinci made numerous observations and illustrations regarding facial proportions, specifically focusing on the lower third of the face. The calculation of the vertical dimension at occlusion involves numerous measurements of the face and body. There has been a great deal of progress in the techniques and materials used to measure vertical dimension, but little is known about an accurate assessment process for edentulous patients. Parafunctional habits that could alter the vertical dimension include abrasion, loss of teeth and molar support, and generalized attrition. It is still debatable whether or not to alter the vertical dimension of occlusion. Giving clinical criteria and subjective guidelines that a lab technician and physician should adhere to while treating patients with OVD anomalies is the aim of this paper.

Old-Aged groundwater contributes to mountain hillslope hydrologic dynamics

Understanding connectivity between the soil and deeper bedrock groundwater is needed to accurately predict a watershed’s response to perturbation, such as drought. Yet, the bedrock groundwater dynamics in mountainous environments are typically under-constrained and excluded from watershed hydrologic models. Here, we investigate the role of groundwater characterized with decadal and longer water ages on the hydrologic and mass-transport processes within a steep snow-dominated mountain hillslope in the Central Rocky Mountains (USA). We quantify subsurface and surface water mass-balance, groundwater flowpaths, and age distributions using the ParFlow-CLM integrated hydrologic and EcoSLIM particle tracking models, which are compared to hydrometric and environmental tracer observations. An ensemble of models with varied soil and hydrogeologic parameters reproduces observed groundwater levels and century-scale mean ages inferred from environmental tracers. The numerical models suggest soil water near the toe of the hillslope contains considerable (>60 % of the mass-flux) contributions from bedrock flowpaths characterized with water ages >10 years. Flowpath connectivity between the deeper bedrock and soil systems is present throughout the year, highlighting the potentially critical role of groundwater with old ages on processes such as evapotranspiration and streamflow generation. The coupled numerical model and groundwater age observations show the bedrock groundwater system influences the hillslope hydrodynamics and should be considered in mountain watershed conceptual and numerical models.

Quantitative and Qualitative Evaluation of Non-Metallic Inclusions in High-Silicon Steel after Hot Rolling

This paper presents an analysis of non-metallic inclusions occurring in high-silicon steels containing about 3% Si of terms of their type, volume fraction and morphology. The inclusions were divided into 3 main groups: oxides, sulfides, nitrides which together can also form complex. The work was based on numerous metallographic observations in two sections (longitudinal and transverse to the rolling direction). The study was performed on three casts differing in chemical composition. The analyzed casts were characterized by a different content of non-metallic inclusions, which can be associated with slight differences in chemical composition. The analyzed results showed that the most common inclusions were oxides and nitrides. Sulfides occurred sporadically.

Volume Structure Retrieval Using Drone-Based SAR Interferometry with Wide Fractional Bandwidth

Synthetic aperture radar (SAR) interferometry (InSAR) is a well-established remote sensing technique capable of providing accurate topographic information of an area. Multiple scattering occurring at different heights within a single resolution cell, however, cannot be resolved using a single baseline and results in a degradation of the height accuracy. Techniques such as polarimetric InSAR and SAR tomography tackle this problem using additional measurements to obtain the three-dimensional structure of the volume. However, polarimetry-based methods assume orthogonal and deterministic scattering mechanisms and tomography requires numerous observations. This paper presents a novel approach to retrieving the three-dimensional structure of semitransparent media using wide fractional bandwidth InSAR. The frequency dependency of the InSAR coherence is exploited to retrieve the three-dimensional structure, assuming that signals with wide fractional bandwidth are available, as is the case for unmanned aerial vehicles (UAVs) or drones. As the extinction is, in general, frequency-dependent, a third observation may improve the inversion results. Simulations of different scenarios show that the frequency profile can be inverted to obtain information about the three-dimensional scattering structure. The acquired data also enable retrieval of the phase center depth as a function of frequency. This method allows for frequent and accurate monitoring of semitransparent targets, e.g., forests and vegetation, using a swarm of two or three drones.

Development and validation of a phenomenological model for hydrogen fueled PFI internal combustion engines considering Thermo-Diffusive effects on flame speed propagation

This paper proposes a 1D numerical/experimental study on a single-cylinder research ICE equipped with a hydrogen Port Fuel Injection (PFI) system. The experimental campaign covered tests at the fixed speed of 1500 rpm and different levels of load, from 5 bar to 11 bar IMEP, and of air excess, with a relative air-to-fuel ratio ranging from 1.4 to 4.0. A 0D/1D model of the investigated ICE is developed, including detailed combustion, turbulence, and NOx emission sub-models. In particular, combustion model is based on the fractal approach, k-K-T model is adopted for describing turbulent phenomena and NOx emissions are predicted by the Zeldovich mechanism. A sub-model was developed to assess the influence of Thermo-Diffusive (TD) instabilities on the freely propagating flame speed accounting for equivalence ratio, variable transport coefficients and reaction orders. This evaluation considered the impact of TD instabilities commonly observed in lean premixed hydrogen combustion on the flame front. The engine model calibration process enabled the comparison between numerical predictions and experimental observations, encompassing pressure cycles, burn rate traces, and main engine performance (air flow rate, IMEP, indicated efficiency, and timing of main combustion events). The model replicated the IMEP with an average error of 2.5%, gross indicated efficiency with an average error of 1.6%, main combustion angles with an average error of 3.8 CAD on CA50, and NOx emissions satisfactorily, showing high sensitivity to operational parameters. Nonetheless, less accurate predictions occur in cases with significantly elevated λ values (λ>3.6), which were attributed to the presence of thickened flames, where some assumptions inherent to the adopted combustion model may fail. Finally, a comparison between the proposed approach and the one proposed in Ballerini et al. (2022) is presented, and readers are provided with recommendations for further development of future models that account for Thermo-Diffusive instabilities in lean hydrogen combustion.

The link between socially responsible human resource management and eco-helping behavior in aviation industry – a moderated mediation model

Purpose This study aims to propose a research model that emphasizes the moderating influence of ethical leadership (ELS) and the link between socially responsible human resource management (SRHRM) and leaders’ eco-helping behavior (LEH) in the aviation industry. Design/methodology/approach The authors used a time-lag research design. Data were gathered from 397 respondents working for aviation companies in Vietnam and analyzed using SmartPLS 4.0. Findings The findings show that SRHRM has a beneficial effect on LEH through employees’ voluntary workplace green behavior (EVB). Based on social cognitive theory, this study developed a theoretical model of how SRHRM influences LEH through EVB. The authors discovered that SRHRM increased LEH and that EVB mediated this favorable relationship. Furthermore, the results demonstrate that ELS mitigates the indirect impact of SRHRM on LEH via EVB. Research limitations/implications Future studies should assess constructs with numerous observations across time, with a larger sample size and in different industrial settings. Practical implications Volunteerism is one of the most important values in the aviation industry given that it is vulnerable to practices such as overbooking, delaying, postponing flights and pressure weather. Originality/value This study emphasized the impact of SRHRM and ELS on LEH while fulfilling their professional obligations. EVB may be best positioned to mediate the relationship between SRHRM and LEH.

Density of mode-locking property for quasi-periodically forced Arnold circle maps

Abstract We show that the mode-locking region of the family of quasi-periodically forced Arnold circle maps with a topologically generic forcing function is dense. This gives a rigorous verification of certain numerical observations in [M. Ding, C. Grebogi and E. Ott. Evolution of attractors in quasiperiodically forced systems: from quasiperiodic to strange nonchaotic to chaotic. Phys. Rev. A 39(5) (1989), 2593–2598] for such forcing functions. More generally, under some general conditions on the base map, we show the density of the mode-locking property among dynamically forced maps (defined in [Z. Zhang. On topological genericity of the mode-locking phenomenon. Math. Ann. 376 (2020), 707–72]) equipped with a topology that is much stronger than the $C^0$ topology, compatible with smooth fiber maps. For quasi-periodic base maps, our result generalizes the main results in [A. Avila, J. Bochi and D. Damanik. Cantor spectrum for Schrödinger operators with potentials arising from generalized skew-shifts. Duke Math. J.146 (2009), 253–280], [J. Wang, Q. Zhou and T. Jäger. Genericity of mode-locking for quasiperiodically forced circle maps. Adv. Math.348 (2019), 353–377] and Zhang (2020).

Doped holographic superconductors in the Gubser–Rocha model

We construct a doped holographic superconductor in the Gubser–Rocha model, and realize a superconducting dome in the middle of the temperature-doping phase diagram. It is worth noting that unlike in previous research, the profile of our dome shrinks inward near to zero temperature. From the numerical observation for the coupling dependence of the phase diagram, we find that the coupling between the two gauge fields plays a crucial role in the formation of the dome. We also analytically calculate the DC conductivity of the normal phase of the system in the momentum dissipation and obtain resistivity which is proportional to the temperature. The AC conductivity is calculated numerically.

Reconfigurable Multifunctional Transmission Metasurface Polarizer Integrated with PIN Diodes Operating at Identical Frequencies

Herein, a reconfigurable multifunctional transmission metasurface polarizer, structured with double Jerusalem crosses and integrated with four PIN diodes, is presented. The bottom Jerusalem cross is rotated by 35∘ with respect to the top cross. Both numerical and experimental observations reveal that a linearly polarized (LP) outgoing wave is transmitted at approximately 4.0 GHz when subjected to a left-handed circularly polarized (LCP) or right-handed circularly polarized (RCP) incident wave. The transmission efficiency reaches -2.5 dB when all elements are in the ON state. Furthermore, active control of switchable PIN diodes operating in various statuses unequivocally demonstrates the ability to convert an incident wave polarized in the x or y direction to a LCP or RCP wave, respectively, within the identical frequency band, spanning from 3.6 GHz to 4.3 GHz. This conversion is achieved with a transmission coefficient of -3.5 dB or -4.2 dB at the peak frequency. The proposed metasurface polarizer presents a potentially dynamic method for simultaneously manipulating various polarization conversions of electromagnetic (EM) waves within a desired frequency band.

A Twist for Graph Classification: Optimizing Causal Information Flow in Graph Neural Networks

Graph neural networks (GNNs) have achieved state-of-the-art results on many graph representation learning tasks by exploiting statistical correlations. However, numerous observations have shown that such correlations may not reflect the true causal mechanisms underlying the data and thus may hamper the ability of the model to generalize beyond the observed distribution. To address this problem, we propose an Information-based Causal Learning (ICL) framework that combines information theory and causality to analyze and improve graph representation learning to transform information relevance to causal dependence. Specifically, we first introduce a multi-objective mutual information optimization objective derived from information-theoretic analysis and causal learning principles to simultaneously extract invariant and interpretable causal information and reduce reliance on non-causal information in correlations. To optimize this multi-objective objective, we enable a causal disentanglement layer that effectively decouples the causal and non-causal information in the graph representations. Moreover, due to the intractability of mutual information estimation, we derive variational bounds that enable us to transform the above objective into a tractable loss function. To balance the multiple information objectives and avoid optimization conflicts, we leverage multi-objective gradient descent to achieve a stable and efficient transformation from informational correlation to causal dependency. Our approach provides important insights into modulating the information flow in GNNs to enhance their reliability and generalization. Extensive experiments demonstrate that our approach significantly improves the robustness and interpretability of GNNs across different distribution shifts. Visual analysis demonstrates how our method converts informative dependencies in representations into causal dependencies.

Deformation twinning and the role of stacking fault energy during cryogenic testing of Ni-based superalloy 625

Ni-based superalloys play a crucial role in various high-temperature applications, where their exceptional mechanical properties and resistance to corrosion are highly desirable. However, their response to low temperatures, especially concerning strain hardening, microstructural evolution, and deformation mechanisms, requires further scrutiny. In this study, we investigate the influence of temperature on the stacking fault energy (SFE) and its implications on deformation twinning in Alloy 625. Uniaxial tensile tests are performed at 298 K, 173 K and 77 K. The study reveals a notable increase in strain hardening at intermediate strain levels, suggesting the activation of a secondary deformation mechanism. To gain deeper insights, crystal plasticity-based simulations using the DAMASK framework are employed, complementing the experimental outcomes. Deformation twins are consistently observed at all temperatures, albeit with a small volume fraction and thickness. The critical strain for twinning decreased with decreasing temperature. Based on the numerous literature studies, experimental and computational observations, the SFE of the material is estimated to be constant over the studied temperature range.

Transformer‐based choice model: A tool for assortment optimization evaluation

AbstractAssessing the efficacy of algorithms plays a pivotal role in advancing various fields, both in theory and practice. Unlike the predictive models, due to the intricate relationship between decisions and the underlying data‐generating processes, the evaluation of decision algorithms cannot directly rely on real data. Hence, a simulator becomes indispensable for appraising decision algorithm effectiveness. In this paper, we aim to leverage assortment decisions, a widely used application in revenue management, to illustrate the utilization of a machine learning‐based simulation. The process can be summarised as: we utilize the modified Transformer‐based choice model, acting as a simulator, to generate a synthetic dataset that mimics consumer purchasing behavior. After training the MNL, DeepFM, and DeepFM‐a models, all of which can swiftly provide assortment decisions in real‐time, we utilize the simulator to evaluate the revenue generated by each assortment prescribed by different choice models. This approach mitigates the challenge of validating decision models that alter real‐world observed data. To show the benefit of such a simulation approach, we have conducted various numerical studies. These studies aim to examine the impact of outside option attractiveness, data size, the number of features, and cardinality. Admittedly, due to the close alignment between the simulator and complex consumer purchase choice datasets, some numerical observations may be challenging to explain. Nevertheless, by employing the simulator, we are able to contrast the differences between the MNL and DeepFM/DeepFM‐a models, shedding light on their respective model misspecifications.

A comprehensive investigation of thermal management strategies in dissimilar micro-friction stir welding (dissimilar µFSW): Insights from numerical simulation and experimental observations

The increased heat dissipation rate from thin sheets and differences in material properties lead to difficulties in controlling the heat input in dissimilar micro-friction stir welding (dissimilar µFSW). As a result, improper material mixing and defect formation significantly increase, which deteriorates weld performance and escalates its rejection rate. This issue of thermal mismanagement is mitigated in the present work by utilizing suitable material positioning and tool offset strategies during the dissimilar µFSW of 0.5 mm thick AA 2024-T3 and AA 6061-T6. To date, post-weld analysis was predominantly utilized to derive the physics for explaining these strategies in dissimilar µFSW. However, for proper utilization of these strategies, it is important to comprehend the underlying process physics by investigating the parameters that evolved during the process, such as temperature distribution, material flow velocity, and material intermixing. The literature currently available lacks a systematic investigation in this direction. For this purpose, a 3-D thermo-mechanical model based on coupled Eulerian-Lagrangian formulation was employed in this study. The numerical results showed that an optimal temperature difference between the advancing and retreating sides facilitates achieving a higher degree of velocity symmetry with a uniform higher magnitude of velocity vectors. Importantly, this degree of velocity symmetry showed a good agreement with experimentally determined weld characteristics, namely macro and microstructures, and mechanical performance. By appropriate thermal management, a joint efficiency of 77.3 % (weld strength = 243.58 MPa) was obtained upon tensile loading, and the weld fractured from the heat-affected zone of the AA 6061-T6 side, exhibiting characteristics of ductile failure.

Polymorphic transformations of titanium oxides contribute to economic uranium mineralization in sandstone

Abstract Sandstone-hosted uranium (U) deposits provide a significant U resource for nuclear energy worldwide. Driven by redox reactions, tetravalent uranium-bearing minerals are commonly associated with reductants (e.g., pyrite and organic matter). However, numerous observations have revealed that tetravalent uranium-bearing minerals can spatially coexist with chemically stabilized titanium oxides in sandstone-hosted U deposits, requiring a complementary mechanism to interpret these findings. We present a new model based on in situ texture, trace-element content, and titanium isotopic ratio, as well as polymorph type and related transformation for titanium oxides from the Yaojia Formation of the southwestern Songliao Basin in northeast China. Specifically, in our model, abundant nanopores were generated during the spontaneous transformation of anatase to rutile, producing a porous material for hexavalent U adsorption. Facilitated by a U-rich source rock, adsorbed U in porous titanium oxide from the lower Yaojia Formation was up to several thousand parts per million. In order to minimize surface energy, a subsequent decrease in surface area by merging small pores is inevitable. When the evolved surface area was small enough, hexavalent U would be desorbed and subsequently transformed to tetravalent U by local reductants, forming uraninite nanoparticles on the surface of U-rich rutile with relatively large pores. Our newly proposed mechanism not only contributes to a better understanding of economic U mineralization in sandstone, but also suggests that U occurred as uranium oxide instead of brannerite in sandstone-hosted U deposits, providing a nano-mineralogical perspective required for industrial processing.

Transient magnetohydrodynamic heat and mass transfer analysis of chemically reacting fluid flow over oscillatory permeable media

This study focuses on the numerical observation of the convective motion of chemically active magnetohydrodynamic (MHD) fluid through a vertically oriented permeable medium, incorporating variations in mass and heat transfer. The fluid type is assumed to be incompressible, chemically strongly ionized and viscous with some mass infusibility. The model associated with this problem is solved by a highly stable Implicit Finite Difference Method (IFDM). The method is used for small and large deflection of the physical parameters, which results in a noticeable fluid flow behavior. Numerical configuration is graphically depicted to scrutinize the fluid behavior. The momentum, energy, concentration diffusion, skin friction, Nusselt number and Sherwood number are investigated for numerous factors such as magnetic field, permeability and chemical reaction rate. The current study unveils significant findings, demonstrating that a heightened rate of chemical reaction in the presence of magnetic effects, coupled with specific porosity, diminishes ionization energy, resulting in a concurrent decrease in the concentration and momentum profiles of the fluid flow. The rise in the viscous diffusion rate is attributed to escalating values of the Schmidt number, causing an augmentation in dynamic viscosity and consequently resulting in an overall reduction in the momentum of the fluid flow.

Enhancing information freshness in multi-class mobile edge computing systems using a hybrid discipline

Timely status updating in mobile edge computing (MEC) systems has recently gained the utmost interest in internet of things (IoT) networks, where status updates may need higher computations to be interpreted. Moreover, in real-life situations, the status update streams may also be of different priority classes according to their importance and timeliness constraints. The classical disciplines used for priority service differentiation, preemptive and non-preemptive disciplines, pose a dilemma of information freshness dissatisfaction for the whole priority network. This work proposes a hybrid preemptive/non-preemptive discipline under an M/M/1/2 priority queueing model to regulate the priority-based contention of the status update streams in MEC systems. For this hybrid discipline, a probabilistic discretionary rule for preemption is deployed to govern the server and buffer access independently, introducing distinct probability parameters to control the system performance. The stochastic hybrid system approach is utilized to analyze the average age of information (AoI) along with its higher moments for any number of classes. Then, a numerical study on a three-class network is conducted by evaluating the average AoI performance and the corresponding dispersion. The numerical observations underpin the significance of the hybrid-discipline parameters in ensuring the reliability of the whole priority network. Hence, four different approaches are introduced to demonstrate the setting of these parameters. Under these approaches, some outstanding features are manifested: exploiting the buffering resources efficiently, conserving the aggregate sensing power, and optimizing the whole network satisfaction. For this last feature, a near-optimal low-complex heuristic method is proposed.