Flexible Boundary Research Articles

A Novel Event-triggered Practical Prescribed-Time Control for four Complex coupled Duffing-type MEMS resonators with Prescribed Performance

This paper explores the dynamic characteristics and a novel event-triggered practical prescribed-time controller for four complex coupled Duffing-type MEMS resonators. Initially, the effects of mechanical coupling stiffness, electrostatic coupling stiffness, and internal system parameters on the system's dynamic behavior are examined. The analysis results provide guidance for selecting system parameters. Furthermore, the dynamic analysis reveals that chaotic oscillations may occur in the system without input, significantly affecting system performance. To mitigate these chaotic oscillations, a novel event-triggered practical prescribed-time controller with prescribed performance is proposed, utilizing interval type-3 fuzzy system (IT3FS) to estimate unknown nonlinear functions. By employing a more relaxed practical prescribed-time stability (PPTS) criterion and a novel time-varying scale transformation function (STF), the designed controller ensures that all signals converge within a prescribed time. Additionally, a prescribed performance function (PPF) is employed, allowing for more flexible convergence boundary settings. A dynamic event-triggered mechanism is implemented to reduce the frequency of control signal updates. The stability analysis demonstrates that all signals converge within a prescribed time, and the tracking errors remain within their prescribed boundary. Finally, simulations validate the effectiveness of the proposed scheme.

Implementation of time-dependent Hartree–Fock in real space

Abstract Time-dependent Hartree–Fock (TDHF) is one of the fundamental post-Hartree–Fock (HF) methods to describe excited states. In its Tamm-Dancoff form, equivalent to Configuration Interaction Singles, it is still widely used and particularly applicable to big molecules where more accurate methods may be unfeasibly expensive. However, it is rarely implemented in real space, mostly because of the expensive nature of the exact-exchange potential in real space. Compared to widely used Gaussian-type orbitals (GTO) basis sets, real space often offers easier implementation of equations and more systematic convergence of Rydberg states, as well as favorable scaling, effective domain parallelization, flexible boundary conditions, and ability to treat model systems. We implemented TDHF in the Octopus real-space code as a step toward linear-response hybrid time-dependent density-functional theory (TDDFT), other post-HF methods, and ensemble density-functional theory methods involving exact exchange. Calculation of HF’s non-local exact exchange is very expensive in real space. We overcome this limitation with Octopus’ implementation of Adaptively Compressed Exchange, and find the appropriate mixing scheme and starting point to complete the ground-state calculation in a practical amount of time, and thus enable TDHF. We compared our results to those from GTOs on a set of small molecules and confirmed close agreement of results, though with larger deviations than in the case of semi-local TDDFT. We find that convergence of TDHF demands a finer real-space grid than semi-local TDDFT. We also present the subtleties in benchmarking a real-space calculation against GTOs, relating to Rydberg and vacuum states.

Distributed event-triggered collision avoidance coordinated control for QUAVs based on flexible virtual tubes

In this paper, a distributed Event-Triggered (ET) collision avoidance coordinated control for Quadrotor Unmanned Aerial Vehicles (QUAVs) is proposed based on Virtual Tubes (VTs) with flexible boundaries in the presence of unknown external disturbances. Firstly, VTs are constructed for each QUAV, and the QUAV is restricted into the corresponding VT by the artificial potential field, which is distributed around the boundary of the VT. Thus, the collisions between QUAVs are avoided. Besides, the boundaries of the VTs are flexible by the modification signals, which are generated by the self-regulating auxiliary systems, to make the repulsive force smaller and give more buffer space for QUAVs without collision. Then, a novel ET mechanism is designed by introducing the concept of prediction to the traditional fixed threshold ET mechanism. Furthermore, a disturbance observer is proposed to deal with the adverse effects of the unknown external disturbance. On this basis, a distributed ET collision avoidance coordinated controller is proposed. Then, the proposed controller is quantized by the hysteresis uniform quantizer and then sent to the actuator only at the ET instants. The boundedness of the closed-loop signals is verified by the Lyapunov method. Finally, simulation and experimental results are performed to demonstrate the superiority of the proposed control method.

Multi-period optimisation of flexible natural gas production network infrastructure with an operational perspective: A mixed integer linear programming approach

With the increased complexities in end markets, advanced quantitative tools became essential for efficient decision-making. Traditional methods that implement average forecasted demand and prices often fail to account for the dynamic nature of network behaviour. Hence, this study introduces a multi-period mixed integer linear programming (MILP) model for flexible natural gas allocation in complex networks. The model was formulated based on Qatar as a case study, utilising a Qatar-based natural gas monetisation network that includes four direct and two indirect monetisation processes. By integrating flexible operational boundaries with annual demand and price forecasts, the model optimises annual allocation strategies to maximise profitability. A scenario-based evaluation of three cases demonstrated the model’s robustness and potential for enhancing profitability. Scenarios limited to operational constraints achieved the highest profitability, especially in allocating high-value commodities such as ammonia and urea. However, the proposed production capacities surpass the current infrastructure capabilities, requiring further infrastructure investments. The validation of results showed a slight profitability decrease of 1.2% when these investment costs were included. Notably the case considering fixed and operating cost variables together as a single cost variable in the objective function, referred to as annualised cost (case C), offered optimal cost quantification with relaxed technical constraints. Overall, the multi-level multi-period MILP model aids decision-makers in understanding system capabilities and explores the benefits of flexible operation in proactively addressing endogenous and exogenous uncertainties.

Permutation Tests to Identify Significant Constraint or Promotion Within Biological Scatterplots.

Scatterplots of biological datasets often have no-data zones, which suggest constraint or promotion of dependent variables. Although methods exist to estimate boundary lines-that is, to fit lines to the edges of scatters of data points-there are, to our knowledge, none available to assess the significance of the areal extents of no-data zones. Accordingly, we propose a flexible boundary line definition paired with a permutation test of the magnitude of no-data zones-rather than testing the shape or slope of the line as current methods do. Our proposed permutation test can be used with any method of defining a boundary line. We demonstrate our approach with empirical datasets, find no-data zones that methods such as quantile regressions fail to detect, and discuss how our approach can quantify constraint and promotion relationships that are not always apparent with other statistics.

Sensitivity-Aware Density Estimation in Multiple Dimensions.

We formulate an optimization problem to estimate probability densities in the context of multidimensional problems that are sampled with uneven probability. It considers detector sensitivity as an heterogeneous density and takes advantage of the computational speed and flexible boundary conditions offered by splines on a grid. We choose to regularize the Hessian of the spline via the nuclear norm to promote sparsity. As a result, the method is spatially adaptive and stable against the choice of the regularization parameter, which plays the role of the bandwidth. We test our computational pipeline on standard densities and provide software. We also present a new approach to PET rebinning as an application of our framework.

Emergent behaviors of buckling-driven elasto-active structures

Active systems of self-propelled agents, e.g., birds, fish, and bacteria, can organize their collective motion into myriad autonomous behaviors. Ubiquitous in nature and across length scales, such phenomena are also amenable to artificial settings, e.g., where brainless self-propelled robots orchestrate their movements into spatial-temporal patterns via the application of external cues or when confined within flexible boundaries. Like their natural counterparts, these approaches typically require many units to initiate collective motion, so controlling the ensuing dynamics is challenging. Here, we demonstrate a simple mechanism that leverages nonlinear elasticity to tame near-diffusive motile particles in forming structures capable of directed motion and other emergent behaviors. Our elasto-active system comprises two centimeter-sized self-propelled microbots connected with elastic beams. These microbots exert forces that suffice to buckle the beam and set the structure in motion. We first rationalize the physics of the interaction between the beam and the microbots. Then we use reduced-order models to predict the interactions of our elasto-active structures with boundaries, e.g., walls and constrictions, and demonstrate how they can exhibit remarkable emergent behaviors such as maze navigation. These findings demonstrate that allowing and understanding changes in body morphology can enhance the capabilities of active matter systems and enable the design of robotic materials capable of space exploration, adaptation, and complex interactions with their surrounding environment.

SIAT: Document-level Event Extraction via Spatiality-Augmented Interaction Model with Adaptive Thresholding

Document-level event extraction endeavors to automatically extract structural events from a given document. Many existing approaches focus on modeling entity interactions and decoding these interactions into events, assigning each entity as an event argument. However, these approaches encounter two primary limitations: they exclusively capture semantic dependencies to model entity interactions, overlooking the indication of the spatial distribution features of entities; they decode interactions imprecisely with a hard binary-classification boundary, potentially failing to calibrate micro differences in interactions. To overcome these limitations, we introduce a novel approach termed the S patiality-augmented I nteraction Model with A daptive T hresholding (SIAT). Our method addresses the first limitation by calculating the relative position encoding of entities to represent spatial interaction features. These features are then integrated with multi-granularity semantic interactions, enhancing the modeling of entity interactions for each entity pair. Furthermore, we introduce an adaptive event decoding mechanism, which establishes a more flexible decision boundary for different entity interactions. Additionally, an adaptive loss function for threshold learning is designed to further refine the model. Experimental results demonstrate that our proposed method achieves competitive performance compared to state-of-the-art methods on two public event extraction datasets while maintaining considerable training efficiency.

Study on the coupled hydro-mechanical model of gas-induced dilation effects in bentonite

IntroductionGas migration in low-permeability buffer materials is a crucial aspect of nuclear waste disposal. This study focuses on Gaomiaozi bentonite to investigate its behavior under various conditions.MethodsWe developed a coupled hydro-mechanical model that incorporates damage mechanisms in bentonite under flexible boundary conditions. Utilizing the elastic theory of porous media, gas pressure was integrated into the soil's constitutive equation. The model accounted for damage effects on the elastic modulus and permeability, with damage variables defined by the Galileo and Coulomb–Mohr criteria. We conducted numerical simulations of the seepage and stress fields using COMSOL and MATLAB. Gas breakthrough tests were also performed on bentonite samples under controlled conditions.ResultsThe permeability obtained from gas breakthrough tests and numerical simulations was within a 10% error margin. The experimentally measured gas breakthrough pressure aligned closely with the predicted values, validating the model's applicability.DiscussionAnalysis revealed that increased dry density under flexible boundaries reduced the damage area and influenced gas breakthrough pressure. Specifically, at dry densities of 1.4 g/cm³, 1.6 g/cm³, and 1.7 g/cm³, the corresponding gas breakthrough pressures were 5.0 MPa, 6.0 MPa, and 6.5 MPa, respectively. At a dry density of 1.8 g/cm³ and an injection pressure of 10.0 MPa, no continuous seepage channels formed, indicating no gas breakthrough. This phenomenon is attributed to the greater tensile and compressive strengths associated with higher dry densities, which render the material less susceptible to damage from external forces.

Investigating fracture mechanisms in glassy polymers using coupled particle-continuum simulations

We study the fracture behavior of glassy polymers using a multiscale simulation method that integrates a molecular dynamics (MD) system within a continuum domain. By employing a nonlinear viscoelastic constitutive model in the continuum domain, the MD system undergoes non-uniform deformation with flexible boundaries through interaction with the surrounding continuum. Systems with pre-defined double cracks are subjected to tensile stretch under various geometric constraints and bond breakage criteria. The simulation results show that geometric constraints primarily affect deformation behavior at small strains, but their influence diminishes at larger strains. In the stage of fracture, increased deformation correlates with a narrowing distribution of microscopic structures at molecular scales, such as bond length. This distribution converges across different systems just before fracture, irrespective of ultimate stress, fracture strain, bond breakage criteria, and geometric constraints. This convergence suggests that the distribution of microscopic structures is a fundamental property linked to the fracture behavior of glassy polymers.

Impact of rubber membrane on lunar regolith mechanical properties under low effective confining pressure

The existing lunar exploration activities and associated equipment interactions are limited to the surface environment, where the stress state of the lunar regolith is significantly lower than that in laboratory tests conducted on Earth. To address this, this paper proposes a new framework for discrete modeling of large-scale triaxial tests on lunar regolith under low confining pressure. The framework incorporates particle shapes from the Chang’E-5 mission (CE-5) and flexible boundary conditions. Firstly, the shape characteristics of the lunar regolith particles were adopted in the Discrete Element Method (DEM) model to reproduce the mechanical properties of the lunar regolith as accurately as possible. Then, experiments with varying membrane particle stiffness ratios were conducted to explore the effect of the rubber membrane’s properties on the mechanical characteristics of lunar regolith under low effective confining pressure. Topological Data Analysis (TDA) tools from persistent homology were utilized to quantify the dynamic response of particles during the onset and development of strain localization. The results indicate that under low effective confining pressure, selecting appropriate rubber membrane types is crucial for accurately determining the mechanical properties of lunar regolith.

Critical state uniqueness of dense granular materials using discrete element method in conjunction with flexible membrane boundary

An explanation of the meso-mechanism of sand granular materials for the uniqueness of critical state is presented by means of the discrete element method (DEM) under flexible boundary loading conditions. A series triaxial drainage shear test (DEM simulations), in conjunction with the flexible boundary technique, of were performed for sand samples subjected to various physical states and with different particle size distributions. After carefully investigating the critical status of the results of the numerical calculation, the macroscopic failure modes and shear band evolution of sand, as well as the velocity vector field due to different initial states, were explored and classified. Furthermore, the evaluation rules and discrepancies between overall void ratios of the specimen and local void ratios within the shear band under the critical state were recorded and analyzed. The results proved that a sample with a small void tends to form a shear band, and the rotation of the particles in the non-shear zone is negligible. Conversely, sandy soil with large initial void ratios exhibited limited development of significant shear bands, and the change in void ratios within the shear region and the non-shear area are not significant. Interestingly, the particle-size distribution exerts minimal influence on the evolution rule which the void ratio converges within the shear band and diverges outside the shear region for both multi-stage and single-stage specimens. The void ratio within the shear band and deviator stress ratio tend to exhibit consistently for the same specimen with different initial physical states, thereby distinguishing the critical state. There is a significantly higher change in void ratio within the shear band compared to outside of it, yet it remains stable within a relatively similar range. Additionally, the invariant of the fabric tensor used to describe the critical state characteristics also demonstrates a high degree of consistency within the shear band. These findings strongly indicate that the critical state exists within the shear failure surface and is highly likely to be unique.

Exponential stability for a classical structural acoustic model with thermoelastic boundary control

The uniform stabilization of a coupled system arising in the active control of noise in a cavity with a flexible boundary (strings under thermal effects) is considered. Unlike most articles on this subject, which employ the scalar wave equation when analyzing the asymptotic behavior of structural acoustic models, in this paper, we consider classical equations in terms of flow velocity and pressure to describe the acoustic vibrations of the fluid which fills the cavity. This allows to consider, for example, more realistic boundary conditions to model the coupling on the interface between the acoustic chamber and the wall. The main result of this paper, concerning the exponential stability of the model, is established by means of the frequency domain method and the semigroup theory. This method can be adapted to other first‐order hyperbolic dissipative systems as well.

Analyzing strain localization of Chang'E-5 lunar regolith through discrete element analysis

The current understanding of the geotechnical behavior of lunar in-situ resources, particularly lunar regolith (LR), is significantly limited due to its scarcity. To address this gap, this research utilized the morphological characteristics of LR particles obtained from the Chang'E-5 (CE-5) mission to construct numerical simulants using the discrete element method (DEM). This approach was then employed to investigate the mechanical properties of LR. Firstly, high-definition lunar particle images from the CE-5 mission were selected to capture the morphological characteristics and grain size distribution. These morphological characteristics were linked with the rolling resistance parameter and incorporated into the three-dimensional (3D) micromechanical contact model. Additionally, a flexible boundary condition was employed in the triaxial simulation to ensure the evolution of strain localization. The relative particle translation gradient (RPTG) concept was utilized to capture the onset and development of strain localization during the shear process. The results indicated that the numerical lunar simulants can effectively reproduce the mechanical response of LR. Furthermore, at the particle scale, particle shape characteristics play a crucial role in particle rotation and translation during the shear process. This study may establish a foundation for lunar resource exploration and utilization techniques.

Flexible membrane boundary condition DEM-FEM for drained and undrained monotonic and cyclic triaxial tests

Flexible membrane boundary condition DEM-FEM for drained and undrained monotonic and cyclic triaxial tests

YOLO V3 AND CCN FOR THE TRACKING AND CLASSIFICATION OF AERIAL OBJECT AND DRONES

The goal of this study is to give headways in aeronautical article ID that will help with making recognitions that are both more exact and more precise. Specifically, we revamp the meaning of the article recognition anchor enclose request to remember turns for expansion to level and width, and besides, we make it conceivable to have erratic four corner point structures. Furthermore, the consideration of new anchor boxes gives the model additional adaptability to address protests that are focused at a pivot of turn that gives a 45-degree point. By accomplishing these results, we can make an organization that considers negligible tradeoffs about speed and unwavering quality, while likewise giving more exact restrictions. The latest ways to deal with PC vision and article acknowledgment are for the most part dependent on brain organizations and different advances that utilize profound learning. This powerful field of study is utilized in various applications, including military and observation, aeronautical photography, independent driving, and airborne perception. To precisely locate the location of an item, contemporary object identification techniques make use of bounding boxes that are drawn over the object and have a rectangular form (horizontal and vertical). These orthogonal bounding boxes do not consider the posture of the object, which leads to a decrease in the amount of object localization and restricts subsequent tasks such as object comprehension and tracking. We have used the DOTA dataset to present all of the results, demonstrating the value of flexible object boundaries, particularly with rotated and non-rectangular objects. We have also achieved an accuracy of 98.47% for the detection and classification of aerial objects, with forty percent of the data being used for training and the remaining twenty percent being used for testing. There was a minimum of 2.8 seconds of processing time required for the whole program to be executed to categorize all of the aerial items that were parked on the base.

Saturation-tolerant prescribed control of MIMO nonlinear systems with actuator faults

This paper addresses the tracking control problem of a class of multiple-input–multiple-output nonlinear systems subject to actuator faults. Achieving a balance between input saturation and performance constraints, rather than conducting isolated analyses, especially in the presence of frequently encountered unknown actuator faults, becomes an interesting yet challenging problem. First, to enhance the tracking performance, Tunnel Prescribed Performance (TPP) is proposed to provide narrow tunnel-shape constraints instead of the common over-relaxed trumpet-shape performance constraints. A pair of non-negative signals produced by an auxiliary system is then integrated into TPP, resulting in Saturation-tolerant Prescribed Performance (SPP) with flexible performance boundaries that account for input saturation situations. Namely, SPP can appropriately relax TPP when needed and decrease the conservatism of control design. With the help of SPP, our developed Saturation-tolerant Prescribed Control (SPC) guarantees finite-time convergence while satisfying both input saturation and performance constraints, even under serious actuator faults. Simulations are conducted to illustrate the effectiveness of the proposed SPC.

Dynamic response analysis of submerged floating tunnel after anchor cables forces adjustment under impact load

Submerged Floating Tunnel (SFT) is a new type of cable-supported structural system for straight crossings. In this study, the initial state of the SFT was optimized based on the existing SFT cable-force adjustment method (relatively uniform cable forces, minimizing the support reaction forces at the abutment section). The responses of the SFT under static and seismic conditions before and after cable-force adjustment were compared, further verifying the optimization effect of the cable-force adjustment method on the structural performance of the SFT. In addition, a theoretical model (flexible support model) of the anchor cables was proposed to calculate the displacement after impact by sunken ships. A finite element model of the SFT was established using ABAQUS to prove the accuracy of the flexible boundary model. In addition, the flexible support stiffnesses of anchor cables at different positions were determined based on the finite element model. Finally, the SFT after the cable-force adjustment was analyzed to study the response patterns of the anchor cables at different positions under an impact load. The results demonstrate that a correlation between the distribution pattern of the flexible boundary stiffnesses of anchor cables and the regulation of the responses of the anchor cables to impact load.

A simple scheme to amplify inter-class discrepancy for improving few-shot fine-grained image classification

Few-shot image classification is a challenging topic in pattern recognition and computer vision. Few-shot fine-grained image classification is even more challenging, due to not only the few shots of labelled samples but also the subtle differences to distinguish subcategories in fine-grained images. A recent method called task discrepancy maximisation (TDM) can be embedded into the feature map reconstruction network (FRN) to generate discriminative features, by preserving the appearance details through reconstructing the query image and then assigning higher weights to more discriminative channels, producing the state-of-the-art performance for few-shot fine-grained image classification. However, due to the small inter-class discrepancy in fine-grained images and the small training set in few-shot learning, the training of FRN+TDM can result in excessively flexible boundaries between subcategories and hence overfitting. To resolve this problem, we propose a simple scheme to amplify inter-class discrepancy and thus improve FRN+TDM. To achieve this aim, instead of developing new modules, our scheme only involves two simple amendments to FRN+TDM: relaxing the inter-class score in TDM, and adding a centre loss to FRN. Extensive experiments on five benchmark datasets showcase that, although embarrassingly simple, our scheme is quite effective to improve the performance of few-shot fine-grained image classification. The code is available at https://github.com/Airgods/AFRN.git.

REVISITING HR FOR HYBRID WORKPLACES

The global pandemic has redefined work from home to work from anywhere. The remote or hybrid work arrangement - switching between working from office and remote working is there to stay. While hybrid work offers flexibility to workers it also adds a layer of complexity to operations. The post pandemic disruptions demand agility and resilience at workplaces. As organizations look into the future, they must be able to engage the "everywhere talent" and "everywhere customer", this means accessing new and diverse talent pools. This can be achieved by creating workplace cultures that empower employees to explore their full potential, a feeling of belongingness regardless of their demography. The challenges around hybrid work include employee's motivation, effectively driving collaboration and open communication across teams, and ensuring employees personal and professional lives remain balanced. At the same time the hybrid workplaces will emphasize on Collaboration, Agility & Resilience and Compassionate Leadership. Both the employer and the employee need to work on curating employee centered experience and therefore Hence HR leaders need to focus on building a strategy to ensure that employees engaged and productive while clearly aligning the organizations as well as their own goals, focusing on an inclusive atmosphere with mental wellness as a key priority.PurposeDigital renaissances have made the world so small that anyone can connect with another at any moment. This has been a major enabler of the quick adoption of work from home to work from anywhere, thereby paving way to future organizations characterized by everywhere talent and everywhere customers. Thus, future looking organizations will focus on accessing new and diverse talent pools. This can be achieved by creating workplace cultures that empower employees to explore their full potential, a feeling of belongingness regardless of their demography. This requires organizations to develop new measures to help remote and hybrid workers reestablish sustainable but flexible boundaries between their work responsibilities and their home responsibilities and personal time. MethodologyThe paper is based on systematic literature review of the advent of hybrid workplaces and the benefits and shortcomings of such workplaces that demand a revisit of HR strategies and policies for benefit of both the employer and employee. For this purpose, different articles, research papers available on open source were reviewed with prime focus on keywords for hybrid, work from home, employee engagement, flexibility, support. Explorative search in the articles is used to cover most of the aspects of hybrid workplaces. Findings During the study it was found that the hybrid workplaces to a large extent led to distance bias and deteriorating employee mental health and burnout. Despite the shortcomings Hybrid workplaces also come with promises of work-life balance and flexibility of work. Based on the literature review The Originality/value of paper: Organizations can leverage best practices of organizations promoting hybrid work to ensure improved employee productivity and consequently achievement of organizational goals.