Additional Degrees Research Articles

Advanced absorbing boundaries for elastodynamic finite element analysis: The added degree of freedom method

Absorbing boundaries are essential in engineering simulations, especially for elastodynamic problems, to ensure accuracy, reliability and numerical stability. In this paper, the added degree of freedom method (ADM) is developed as a novel approach to address absorbing boundary challenges in finite element analysis. In ADM, additional degrees of freedom (DOFs) are introduced within the absorbing domain to attenuate outgoing elastic waves. For the proposed ADM to implement the absorbing boundary, the stiffness and mass properties of both the added DOFs and conventional DOFs within the absorbing domain are adjusted. This adjustment aims to reduce the propagation speed of elastic waves within the medium, and to prolong the duration of interaction between elastic waves and the surrounding medium. Consequently, the vibrations of nodes can be effectively attenuated by applying damping forces to the added DOFs. The numerical results show that the ADM has the ability to absorb one-dimensional and two-dimensional elastic waves across a broad range of frequencies. Therefore, the proposed ADM offers an innovative solution for modeling absorbing boundaries in various scientific and engineering applications, addressing the challenges of simulating wave propagation within finite computational domains.

Pauli blockade catalogue and three- and four-particle Kondo effect in bilayer graphene quantum dots

Pauli blockade is a fundamental quantum phenomenon that also serves as a powerful tool for qubit manipulation and readout. While most systems exhibit a simple even-odd pattern of double-dot Pauli spin blockade due to the preferred singlet pairing of spins, the additional valley degree of freedom offered by bilayer graphene greatly alters this pattern. Inspecting bias-triangle measurements at double-dot charge degeneracies with up to four electrons in each dot reveals a much richer double-dot Pauli blockade catalog with both spin and/or valley blockade. In addition, we use single-dot Kondo effect measurements to substantiate our understanding of the three- and four-particle state spectra by analyzing their magnetic field dependence. With high controllability and reported long valley- and spin-relaxation times, bilayer graphene is a rising platform for hosting semiconductor quantum dot qubits. A thorough understanding of state spectra is crucial for qubit design and manipulation, and the rich Pauli blockade catalog provides an abundance of qubit operational possibilities and opportunities to explore intriguing spin and valley physics. Published by the American Physical Society 2024

A yarn-scale woven fabric model including significant slippage formulated within the Arbitrary Lagrangian Eulerian framework

A numerical model is proposed to simulate significant yarn slippage and unweaving in woven fabrics using the Arbitrary Lagrangian Eulerian (ALE) method. Woven fabrics were modeled at the yarn scale using 1D ALE elements with additional slip displacement degrees of freedom (DOF). The relatively weak bending stiffness of the yarn was included using a rotation-free approach. A weave kinematic constraint between crossing yarns allowed an efficient description of the deformation modes due to the yarn assembly such as in-plane shear. In particular, normal compaction at weave points was taken into account using an additional crimp amplitude DOF and couplings of the fabric’s cohesion with the normal and lateral compaction were considered. To deal with yarn unweaving, a specific void-ALE 1D element was developed in order to avoid remeshing, time-step reduction (explicit scheme) and early deactivation of the weave kinematic constraint. To demonstrate the capabilities of this numerical model, common characterization tests such as in-plane and out-of-plane pullouts, which induced unweaving were simulated. Finally, a first forming simulation on a hemisphere was performed to verify whether the cohesion of the fabric remained well represented in situations without loss of cohesion before simulating forming on a prismatic punch involving significant yarn slippage.

Sculpting ultrastrong light-matter coupling through spatial matter structuring.

The central theme of cavity quantum electrodynamics is the coupling of a single optical mode with a single matter excitation, leading to a doublet of cavity polaritons which govern the optical properties of the coupled structure. Especially in the ultrastrong coupling regime, where the ratio of the vacuum Rabi frequency and the quasi-resonant carrier frequency of light, ΩR/ω c, approaches unity, the polariton doublet bridges a large spectral bandwidth 2ΩR, and further interactions with off-resonant light and matter modes may occur. The resulting multi-mode coupling has recently attracted attention owing to the additional degrees of freedom for designing light-matter coupled resonances, despite added complexity. Here, we experimentally implement a novel strategy to sculpt ultrastrong multi-mode coupling by tailoring the spatial overlap of multiple modes of planar metallic THz resonators and the cyclotron resonances of Landau-quantized two-dimensional electrons, on subwavelength scales. We show that similarly to the selection rules of classical optics, this allows us to suppress or enhance certain coupling pathways and to control the number of light-matter coupled modes, their octave-spanning frequency spectra, and their response to magnetic tuning. This offers novel pathways for controlling dissipation, tailoring quantum light sources, nonlinearities, correlations as well as entanglement in quantum information processing.

Who Are the Mentors of the Future Endourologist? An Analysis of Endourological Society Program Directors.

Introduction: Surgical training programs are pivotal in shaping skilled and compassionate surgeons, with mentors playing a crucial role in instilling clinical competence and essential attributes. This study aims to describe the characteristics of the program directors of Endourological Society-accredited fellowship programs. Methodology: The Endourological Society's website was used to identify program directors. The following data points were extracted: year of graduation from medical school, year of completing residency, if they had attended fellowship training or held additional degrees such as (PhD, MS, MBA, MSc, etc.), and number of publications on Scopus. Descriptive statistics were used to analyze the data. Results: A total of 84 fellowship programs and 115 program directors were identified. Geographically, 77.4% (n = 65) were in North America, 8.3% (n = 7) in Asia, 8.3% (n = 7) in the Middle East, 3.6% (n = 3) in Europe, and 2.4% (n = 2) in South America. Of the 115 program directors, 94.8% were male, and only 5.2% were female. Program directors graduated medical school with a median year of 1998 (1966-2015). Eighty percent attended fellowship programs, and 19.1% held additional degrees (PhD, MS, MBA, MSc, etc.). The median number of publications was 79 (4-1963), with a median citation of 1607 (1-43,565). The median H-index was 23 (range: 1-110). Conclusion: Most program directors of Endourological Society-accredited fellowship programs are fellowship-trained and a notable number held a second degree. However, a pronounced gender disparity is observed, with limited female representation among program directors. This assessment contributes valuable insights into the urology and endourology mentorship, emphasizing the need for broader diversity and inclusivity in leadership roles.

A magnetically actuated dynamic labyrinthine transmissive ultrasonic metamaterial

Currently, space-coiling acoustic metamaterials are static, requiring manual reconfiguration for sound-field modulation. Here, we introduce an approach to enable active reconfiguration, using standalone dynamic space-coiling unit cells called dynamic meta-bricks. Unlike their static counterparts, these meta-bricks, house an actuatable soft robotic-inspired magnetorheological elastomeric flap. This flap operates like a switch to directly control the transmitted ultrasound. For scalability, we present a hybrid stacking method, which vertically combines static and dynamic meta-bricks. This allows us to form a surface-integrated metasurface through concatenating variations of either fully static or hybrid stacks. By actuating dynamic metasurface sections, we experimentally demonstrate accurate modulation of λ/4 (≈2 mm) between two acoustic twin traps. We shift a levitated bead between the traps, validating that full-array operational dynamicity is achievable with partial, localised actuation. This work showcases the synergy between active and passive reconfigurability, opening possibilities to develop multifunctional metamaterials with additional degrees of freedom in design and control.

Propagation of Lorentz-Gaussian elliptical multi-Gaussian correlated Schell-Model beam in uniaxial crystal

The evolution behavior of the intensity profile, beam spreading, and spectral degree of coherence of the Lorentz-Gaussian elliptical multi-Gaussian correlated Schell-Model beam propagating in uniaxial crystal are studied. The expression of the cross spectral density of the beam in uniaxial crystal is obtained based on Huygens-Fresnel integration, and the expressions of spectral coherence and root mean square (rms) beam width are derived. The beam spot is circular or elliptical while the ordinary and extraordinary refractive indices of the crystal are equal or unequal, respectively. The ellipticity of the light spot is affected by the Lorentz parameters. The larger the ratio of ordinary to extraordinary refractive index in uniaxial crystal is, the larger the spectral coherence of beam and rms beam waist width is. The spectral coherence increases with the increase of the Gaussian beam waist and the decrease of the Lorentz parameters. The rms beam width of the beam increases with the increase of the Gaussian beam width and Lorentz partial parameters. With the increase of the transmission distance, the influence of the light source parameters on the rms beam width gradually weakens. The total number of terms of multi-Gaussian correlated Schell-Model (MGSM) source and the spatial coherence lengths add additional degree of freedom for adjusting the spot pattern inside crystal.

Scalar and vector electromagnetic solitary waves in nonlinear hyperbolic media

In this paper, we investigate the problem of electromagnetic wave propagation in hyperbolic nonlinear media. To address this problem, we consider the scalar hyperbolic nonlinear Schrödinger system and its coupled version, namely hyperbolic Manakov type equations. These hyperbolic systems are shown as non-integrable. Then, we examine the propagation properties of both the scalar and vector electromagnetic solitary waves by deriving their exact analytical forms through the Hirota bilinear method. A detailed analysis shows that the presence of hyperbolic transverse dispersion provides an additional degree of freedom to prevent the formation of singularity in both the scalar and vector solitary wave structures in this hyperbolic nonlinear media. Besides this, we realize that the solitary waves in this media possess fascinating propagation properties which cannot be observed in conventional nonlinear media. We believe that the present study will be very useful in analyzing electromagnetic wave propagation in hyperbolic nonlinear metamaterials.

Research on the electronic phase transitions in strongly correlated oxides and multi-field regulation

External-field-triggered multiple electronic phase transitions within correlated oxides open up a new paradigm to explore exotic physical functionalities and new quantum transitions via regulating the electron correlations and the interplay in the degrees of freedom, which makes the multidisciplinary fields have the promising application prospects, such as neuromorphic computing, magnetoelectric coupling, smart windows, bio-sensing, and energy conversion. This review presents a comprehensive picture of regulating the electronic phase transitions for correlated oxides via multi-field covering the VO<sub>2</sub> and <i>Re</i>NiO<sub>3</sub>, thus highlighting the critical role of external field in exploring the exotic physical property and designing new quantum states. Beyond conventional semiconductors, the complex interplay in the charge, lattice, orbital and spin degrees of freedom within correlated oxides triggers abundant correlated physical functionalities that are rather susceptible to the external field. For example, hydrogen-related electron-doping Mottronics makes it possible to discover new electronic phase and magnetic ground states in the hydrogen-related phase diagram of correlated oxides. In addition, filling-controlled Mottronics by using hydrogenation triggers multiple orbital reconfigurations for correlated oxides away from the correlated electronic ground state that results in new quantum transitions via directly manipulating the d-orbital configuration and occupation, such as unconventional Ni-based superconductivity. The transition metals of correlated oxides are generally substituted by dopants to effectively adjust the electronic phase transitions via introducing the carrier doping and/or lattice strain. Imparting an interfacial strain to correlated oxides introduces an additional freedom to manipulate the electronic phase transition via distorting the lattice framework, owing to the interplay between charge and lattice degrees of freedom. In recent years, the polarization field associated with BiFeO<sub>3</sub> or PMN-PT material triggered by a cross-plane electric field has been used to adjust the electronic phase transition of correlated oxides that enriches the promising correlated electronic devices. The exotic physical phenomenon as discovered in the correlated oxides originates from the non-equilibrium states that are triggered by imparting external fields. Nevertheless, the underneath mechanism as associated with the regulation in the electronic phase transitions of correlated oxides is still in a long-standing puzzle, owing to the strong correlation effect. As a representative case, hydrogen-associated Mottronic transition introduces an additional ion degree of freedom into the correlated oxides that is rather difficult to decouple from the correlated system. In addition, from the perspective of material synthesis, the above-mentioned correlated oxides are expected to be compatible with conventional semiconducting process, by which the prototypical correlated electronic devices can be largely developed. The key point that accurately adjusts and designs the electronic phase transitions for correlated oxides via external fields is presented to clarify the basic relationship between the microscopic degrees of freedom and macroscopic correlated physical properties. On the basis, the multiple electronic phase transitions as triggered by external field within correlated oxides provide new guidance for designing new functionality and interdisciplinary device applications.

Accuracy of Invisalign® aligners in adult patients: a retrospective study of angular tooth movements.

This retrospective study aimed to assess the predictability of Invisalign® aligners regarding rotational, mesio-distal and buccal-lingual tip movements. Two materials were included in the analysis - EX30, used until 2013; and SmartTrack, in current use. The study comprised 56 adult patients treated with Invisalign Comprehensive. Data sample were assessed on three sets of digital models; model 1 - initial, model 2 - predicted, and model 3 - achieved. Sixty reference points were marked in each dental arch, and two reference planes assisted the superimposition. The degree of rotation, mesio-distal and buccal-lingual tip was obtained via trigonometric calculations, through a previously published validated method. The accuracy of outcomes was compared according to the types of tooth movement and teeth groups,and the influence of predetermined variables on movement accuracy was also investigated. Rotation and mesio-distal tip did not present any significant difference when comparing EX30 and SmartTrack groups. Only buccal-lingual tip presented a significant difference, incisor and canine groups treated with EX30 aligners presented an increase in accuracy (p= 0.007 and p = 0.007, respectively). For each additional degree planned for rotation movements, there was an increase of 0.35° in the discrepancy, and an increase of 0.40° and 0.41° for mesio-distal and buccal-lingual tip, respectively. EX30 and SmartTrack discrepancies were compared by multilevel linear regression. EX30 aligners reached higher accuracy for buccal-lingual tip in anterior teeth. However, for rotation and mesio-distal tip, SmartTrack and EX30 are similarly accurate. The total amount of planned movement has a significant impact on accuracy rates, with a decrease in accuracy for every additional degree.

Bonus or Penalty? Designing Service-Level Agreements for a Decentralized Supply Chain: The Implication of Return on Investment

We study the coordination of two-echelon supply chains via service level-dependent bonus and penalty contracts and assume that the manufacturer maximizes its profit while enabling the supplier to achieve its performance target. Profit and return on investment (ROI) are considered as the supplier’s performance measures. We compute optimal contract parameters and perform a numerical study. In addition, we perform a simulation-based study to analyze the profit risk of the considered parties. For supplier profit targets, bonus and penalty contracts lead to the same profit for both parties, but bonus contracts lead to lower costs, hence, a higher ROI. For supplier ROI targets, bonus contracts always lead to higher manufacturer profit, and no optimal penalty contracts exist. For every contract service level, optimal bonus contracts exist that maximize profit and ROI of the manufacturer simultaneously. Thus, we analyze the profit risk for the manufacturer and the supplier and show that it can be significantly reduced by setting an appropriate contract service level. The manufacturer usually should prefer bonus contracts. They allow to optimize profit and ROI simultaneously and even offer an additional degree of freedom to reduce the profit risk.

Securing the Future of Digital Marketing through Advanced Cybersecurity Approaches and Consumer Data Protection Privacy and Regulatory Compliance

The SecureDigitalGuard framework gets recognition for its all-encompassing strategy, which combines strict consumer data protection laws with state-of-the-art security safeguards with ease. This all-encompassing approach is designed to guarantee the longevity of digital marketing in the face of constantly changing cyberthreats. This cutting-edge system is based on three key strategies: the Behavioural Threat Detection (BTD) algorithm, the Adaptive Access Control (AAC) algorithm, and the Homomorphic Privacy Guard (HPG) programme. The vital task of dynamically controlling user access levels in response to continuing risk evaluations is taken on by the AAC algorithm. This dynamic control technique improves the framework's capacity to adjust to constantly shifting security circumstances. However, the BTD algorithm is proactive in spotting abnormalities in user behaviour, allowing for quick reactions to any dangers. The SecureDigitalGuard architecture gains an additional degree of protection from this preventive method. In addition, the HPG programme is responsible for doing analytics while maintaining user privacy. This careful approach shows a dedication to finding a fine balance between user protection and data analysis, making sure the framework complies with the strictest privacy regulations. Test results provide empirical evidence that SecureDigitalGuard is effective and that it can keep up with the dynamic and often changing nature of cyber threats. As a result, the architecture makes traditional cybersecurity techniques outdated. In an increasingly complex and dynamic cybersecurity world, SecureDigitalGuard provides a strong solution for protecting digital marketing through the seamless integration of state-of-the-art technology and strict adherence to privacy regulations.

A 4-DOF Exosuit Using a Hybrid EEG-Based Control Approach for Upper-Limb Rehabilitation.

Rehabilitation devices, such as traditional rigid exoskeletons or exosuits, have been widely used to rehabilitate upper limb function post-stroke. In this paper, we have developed an exosuit with four degrees of freedom to enable users to involve more joints in the rehabilitation process. Additionally, a hybrid electroencephalogram-based (EEG-based) control approach has been developed to promote active user engagement and provide more control commands.The hybrid EEG-based control approach includes steady-state visual evoked potential (SSVEP) paradigm and motor imagery (MI) paradigm. Firstly, the rehabilitation movement was selected by SSVEP paradigm, and the multivariate variational mode decomposition (MVMD) and canonical correlation analysis (CCA) method was used for SSVEP EEG recognition; then, the motion intention was obtained by MI paradigm, and the convolutional neural network (CNN) and long short-term memory network (LSTM) were used to build a CNN-LSTM model for MI EEG recognition; finally, the recognition results were translated into control commands of Bowden cables to achieve multi-degree-of-freedom rehabilitation.Experimental results show that the average classification accuracy of the CNN-LSTM model reaches to 90.07% ± 2.23%, and the overall accuracy of the hybrid EEG-based control approach reaches to 85.26% ± 1.95%. The twelve subjects involved in the usability assessment demonstrated an average system usability scale (SUS) score of 81.25 ± 5.82. Additionally, four participants who underwent a 35-day rehabilitation training demonstrated an average 10.33% increase in range of motion (ROM) across 4 joints, along with a 11.35% increase in the average electromyography (EMG) amplitude of the primary muscle involved.The exosuit demonstrates good accuracy in control, exhibits favorable usability, and shows certain efficacy in multi-joint rehabilitation. Our study has taken into account the neuroplastic principles, aiming to achieve active user engagement while introducing additional degrees of freedom, offering novel ideas and methods for potential brain-computer interface (BCI)-based rehabilitation strategies and hardware development.Clinical impact: Our study presents an exosuit with four degrees of freedom for stroke rehabilitation, enabling multi-joint movement and improved motor recovery. The hybrid EEG-based control approach enhances active user engagement, offering a promising strategy for more effective and user-driven rehabilitation, potentially improving clinical outcomes.Clinical and Translational Impact Statement: By developing an exosuit and a hybrid EEG-based control approach, this study enhances stroke rehabilitation through better user engagement and multi-joint capabilities. These innovations consider neuroplasticity principles, integrating rehabilitation theory with rehabilitation device.

Three-dimensional spatial orbital angular momentum holography

The degree of freedom of orbital angular momentum of light has been used as a new information carrier in optical holographic information processing technology. However, current research on orbital angular momentum holography mainly focuses on two-dimensional orbital angular momentum holography, where the reconstructed two-dimensional holographic image is located in a certain plane in three-dimensional space. How to further implement three-dimensional spatial orbital angular momentum holographic technology and use it to increase the information capacity of holographic communication is still a blank. Here, we implement three-dimensional spatial orbital angular momentum holographic technology based on the degrees of freedom of orbital angular momentum and the positional degrees of freedom of reconstructed two-dimensional images in three-dimensional space. In other words, in the three-dimensional spatial orbital angular momentum holography, the acquisition of the target object image requires not only the correct orbital angular momentum state used for decoding, but also the correct spatial position where the object’s image is detected. In addition, we further investigate the three-dimensional spatial orbit angular momentum holographic multiplexing technology and point out that this multiplexing technology can be used for information encryption. Compared with traditional two-dimensional orbital angular momentum holography, three-dimensional spatial orbital angular momentum holography uses an additional degree of freedom. Therefore, the encryption scheme based on three-dimensional spatial orbital angular momentum holographic technology can further improve the security level of information. Our simulation results and experimental results have verified the feasibility of three-dimensional spatial orbit angular momentum holographic technology and three-dimensional spatial orbit angular momentum holographic encryption technology.

Interplay between wall slip and shear banding in a thixotropic yield stress fluid.

We study the local dynamics of a thixotropic yield stress fluid that shows a pronounced non-monotonic flow curve. This mechanically unstable behavior is generally not observable from standard rheometry tests, resulting in a stress plateau that stems from the coexistence of a flowing band with an unyielded region below a critical shear rate c. Combining ultrasound velocimetry with standard rheometry, we discover an original shear-banding scenario in the decreasing branch of the flow curve of model paraffin gels, in which the velocity profile of the flowing band is set by the applied shear rate  instead of c. As a consequence, the material slips at the walls with a velocity that shows a non-trivial dependence on the applied shear rate. To capture our observations, we propose a differential version of the so-called lever rule, describing the extent of the flowing band and the evolution of wall slip with shear rate. This phenomenological model holds down to very low shear rates, at which the dimension of the flowing band becomes comparable to the size of the individual wax particles that constitute the gel microstructure, leading to cooperative effects. Our approach provides a framework where constraints imposed in the classical shear-banding scenario can be relaxed, with wall slip acting as an additional degree of freedom.

Neuromuscular Interfacing for Advancing Kinesthetic and Teleoperated Programming by Demonstration of Collaborative Robots.

This study addresses the challenges of Programming by Demonstration (PbD) in the context of collaborative robots, focusing on the need to provide additional degrees of programming without hindering the user's ability to demonstrate trajectories. PbD enables an intuitive programming of robots through demonstrations, allowing non-expert users to teach robot skills without coding. The two main PbD modalities, observational and kinesthetic, have limitations when it comes to programming the diverse functionalities offered by modern collaborative robots. To overcome these limitations, the study proposes the use of a wearable human-robot interface based on surface Electromyography (sEMG) to measure the forearm's muscle co-contraction level, enabling additional programming inputs through hand stiffening level modulations without interfering with voluntary movements. Vibrotactile feedback enhances the operator's understanding of the additional programming inputs during PbD tasks. The proposed approach is demonstrated through experiments involving a collaborative robot performing an industrial wiring task. The results showcase the effectiveness and intuitiveness of the interface, allowing simultaneous programming of robot compliance and gripper grasping. The framework, applicable to both teleoperation and kinesthetic teaching, demonstrated effectively in an industrial wiring task with a 100% success rate over the group of subjects. Furthermore, the presence of vibortactile feedback showed an average decrease of programming errors of 33%, and statistical analyses confirmed the subjects' ability to correctly modulate co-contraction levels. This innovative framework augments programming by demonstration by integrating neuromuscular interfacing and introducing structured programming logics, providing an intuitive human-robot interaction for programming both gripper and compliance in teleoperation and kinesthetic teaching.

An Efficient Goal-Oriented Adaptive Finite Element Method for Accurate Simulation of Complex Electromagnetic Radiation Problems

A goal-oriented adaptive frequency domain finite element method for solving electromagnetic radiation problems including complex structures is presented in this paper. Compared with the traditional adaptive finite element method, the goal-oriented method can flexibly control the refined regions according to the parameters of interest; therefore it has better convergence and has made significant progress in scattering problems and eigenvalue problems. To simulate complex antennas, this paper proposes an error indicator with high accuracy and low computational cost, and it uses the adjoint problem to weight element residuals without additional degrees of freedom. Moreover, high-quality mesh refinement algorithms adapted to this indicator are developed using a suitable point insertion strategy for multiscale structures. By simulating two practical antennas, comparisons with the traditional goal-oriented FEM and the well-developed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</i> -adaptive finite element method in commercial software demonstrate the accuracy and efficiency of the proposed method.

Large piezoelectric responses and ultra-high carrier mobility in Janus HfGeZ3H (Z = N, P, As) monolayers: a first-principles study.

Breaking structural symmetry in two-dimensional layered Janus materials can result in enhanced new phenomena and create additional degrees of piezoelectric responses. In this study, we theoretically design a series of Janus monolayers HfGeZ3H (Z = N, P, As) and investigate their structural characteristics, crystal stability, piezoelectric responses, electronic features, and carrier mobility using first-principles calculations. Phonon dispersion analysis confirms that HfGeZ3H monolayers are dynamically stable and their mechanical stability is also confirmed through the Born-Huang criteria. It is demonstrated that while HfGeN3H is a semiconductor with a large bandgap of 3.50 eV, HfGeP3H and HfGeAs3H monolayers have narrower bandgaps being 1.07 and 0.92 eV, respectively. When the spin-orbit coupling is included, large spin-splitting energy is found in the electronic bands of HfGeZ3H. Janus HfGeZ3H monolayers can be treated as piezoelectric semiconductors with the coexistence of both in-plane and out-of-plane piezoelectric responses. In particular, HfGeZ3H monolayers exhibit ultra-high electron mobilities up to 6.40 × 103 cm2 V-1 s-1 (HfGeAs3H), indicating that they have potential for various applications in nanoelectronics.

Modeling fatigue-assisted pitting in pipeline steel with PCA-XFEM

We present a localized corrosion and cracking damage mechanism (initiation of the pit, propagation of the pit, pit-to-crack transition, and stable cracking) in a pipeline steel under the application of fatigue loading by using sequential coupling of Probabilistic Cellular Automata (PCA) and eXtended Finite Element Method (XFEM). PCA is utilized for describing the localized corrosion damage mechanism. XFEM is used to simulate arbitrary inhomogeneities (cracks, voids, and soft/hard material interfaces (inclusions)) with the help of Level Set Methods (LSM). In the XFEM, the standard finite element is enriched by additional degrees of freedom by invoking the notion of the partition of unity, which alleviates the burden of mesh conformity to the internal boundaries and avoids re-meshing. LSM is used to locate the voids and material interfaces and track the crack propagation location. A localized strain criterion initiates cracks from the pit surface when the pit reaches a critical strain value.The coupling of PCA and XFEM demonstrates good agreement with experimental data regarding stress-assisted pitting corrosion and pit-induced fatigue cracking in the pipeline steel. The study also investigates the effects of boundaries, and initial pit size on fatigue crack initiation and growth. Boundary effects significantly influence crack initiation life and growth behavior, highlighting the importance of considering both defect characteristics and boundary conditions in assessing fatigue performance and structural integrity. Various initial pit sizes and geometric features further affect crack initiation location and transition time. Furthermore, the PCA-XFEM model effectively captures crack behavior in both short and long crack regimes, demonstrating good agreement with experimental data for a selected pit width of 140μm. By incorporating crack driving parameters derived from experiments, the model accurately predicts crack propagation, further enhancing its reliability and predictive capabilities in assessing fatigue crack behavior. Overall, this approach provides valuable insights for predicting the service life and integrity of pipelines subjected to similar loading conditions, thus aiding in designing and maintaining these critical infrastructure components.

Performance evaluation of a novel monofilar helical antenna with tapered cross-section wire fabricated via metal additive manufacturing

This paper presents a novel formulation for a generalized helical antenna that incorporates non-uniform helix diameters, non-uniform helix spacing, and non-uniform wire cross-section, providing additional degrees of freedom for optimization. By carefully defining the transition between the helix and the center feed point, a thicker wire was used at the base to enhance the antenna’s operating bandwidth capability and mechanical strength, eliminating the need for additional support structures. The fabrication process utilized metal additive manufacturing (MAM) with Maraging steel. The results demonstrate that the helical antenna with a tapered cross-section wire (with a thicker base and a thinner tip) exhibits significantly better performance compared to the control models for operation in the X-band. This design amalgamates impedance matching from antennas with uniform thick wires and radiation characteristics from antennas with uniform thin wires. The major contribution of this work is the demonstration that employing tapered wire cross-sections can enhance helical antenna performance, thereby introducing a new design parameter in metal additive manufacturing. Specifically, we present an eight-turn helical antenna that achieved a measured reflection coefficient less than −10 dB and axial ratio less than 1 dB over the X band, with a peak realized gain in RHCP of 10.8 dBic.