bluuebunny/crossref_metadata_2025 huggingface dataset:
Integrated modelling and simulation method of hybrid systems based on X language
Authors: Xie Kunyu , Zhang Lin , Wang Xiaohan , Wang Kunyu , Li Yingjie
Published: December 2024

Model‐based systems engineering is now leading the way in supporting the design of complex products or systems. The integration of modelling and simulation of continuous‐discrete hybrid systems is the key of model‐based systems engineering. But the existing languages, formalisms and tools cannot support the unified modelling and simulation of hybrid systems and therefore reduces the efficiency of complex system development. To address this issue, this paper develops a design method of complex hybrid systems, which integrates modelling and simulation of the continuous‐discrete hybrid behaviour. Specifically, the authors provided a modelling method of hybrid systems based on the X language, a simulation method based on XDEVS, and a compilation algorithm to transform the hybrid model constructed with X language into XDEVS simulation files. In this way, the X language hybrid model can be automatically translated into XDEVS simulation files by a compiler. The simulation files can then be simulated by the XDEVS simulation engine. The obtained simulation results will be used to verify whether the design scheme meets the design requirements of the hybrid system. Finally, the correctness and feasibility of the proposed method are verified using a car‐driving model.
Training improvement methods of ANN trajectory predictors in power systems
Authors: Kim Sangwon
Published: December 2024

This paper proposes training improvement methods of artificial neural networks (ANN) trajectory predictors. First, a dynamic power system time‐series trajectory is split into several different segments to simplify the original ANN training problem. Moreover, the time‐derivative of the trajectory is included to obtain an augmented loss function. Compared to previous studies which mainly focused on increasing the prediction accuracy, the aim of these novel techniques is to reduce the computational burden where the ANN output performance is still acceptable. The effectiveness of the developed methods is validated based on the WSCC three‐machine nine‐bus and IEEE 39‐bus system models. The mean absolute error (MAE) and trajectory prediction results are analysed, in which the numbers of neurons, hidden layers, and training epochs are constrained during the ANN training process. Rotor‐angle difference between generators and the system frequency are investigated as the dynamic trajectories of the power system models. The approaches are revealed to be effective when the ANN architecture and epochs are constrained. The MAE results can be reduced by up to 65% in the power system models depending on the ANN hyperparameters and training epochs. The ANN training results can better reflect the original trajectory as well.
Automated surgical skill assessment in endoscopic pituitary surgery using real‐time instrument tracking on a high‐fidelity bench‐top phantom
Authors: Das Adrito , Sidiqi Bilal , Mennillo Laurent , Mao Zhehua , Brudfors Mikael , Xochicale Miguel , Khan Danyal Z. , Newall Nicola , Hanrahan John G. , Clarkson Matthew J. , Stoyanov Danail , Marcus Hani J. , Bano Sophia
Published: December 2024

Improved surgical skill is generally associated with improved patient outcomes, although assessment is subjective, labour intensive, and requires domain‐specific expertise. Automated data‐driven metrics can alleviate these difficulties, as demonstrated by existing machine learning instrument tracking models. However, these models are tested on limited datasets of laparoscopic surgery, with a focus on isolated tasks and robotic surgery. Here, a new public dataset is introduced: the nasal phase of simulated endoscopic pituitary surgery. Simulated surgery allows for a realistic yet repeatable environment, meaning the insights gained from automated assessment can be used by novice surgeons to hone their skills on the simulator before moving to real surgery. Pituitary Real‐time INstrument Tracking Network (PRINTNet) has been created as a baseline model for this automated assessment. Consisting of DeepLabV3 for classification and segmentation, StrongSORT for tracking, and the NVIDIA Holoscan for real‐time performance, PRINTNet achieved 71.9% multiple object tracking precision running at 22 frames per second. Using this tracking output, a multilayer perceptron achieved 87% accuracy in predicting surgical skill level (novice or expert), with the ‘ratio of total procedure time to instrument visible time’ correlated with higher surgical skill. The new publicly available dataset can be found at https://doi.org/10.5522/04/26511049.
Die Hemisektion unterer zweiter Milchmolaren bei Unterzahl der
zweiten Prämolaren – Geschichte, Anwendung und klinisches
Vorgehen
Authors: Langer Lisa Josefine , Finke Christian , Becker Kathrin
Published: December 2024

Der Umgang mit Nicht-Anlagen bleibender Zähne ist eine anspruchsvolle Aufgabe im
Praxisalltag. Die weltweite Prävalenz der Nicht-Anlage eines oder mehrerer Zähne
variiert stark und liegt unter Ausschluss der 3. Molaren bei 0,15% – 16,18%
1
2.
Die zweiten Prämolaren im Unterkiefer sind hierbei die häufigsten nicht
angelegten Zähne 3
4
5
6
7
8. Die Prävalenz der Nicht-Anlage der unteren
zweiten Prämolaren beträgt je nach Studie und untersuchter Population zwischen
1,02% – 3,5% 9
10
11. Patientinnen sind in der
Regel häufiger betroffen als Patienten 9
11
12. Insofern es indiziert und erwünscht ist einen
kieferorthopädischen Lückenschluss in dieser Region anzustreben, sollte bei
Extraktion der Zähne 75 und 85 eine übermäßige Atrophie des Alveolarfortsatzes
verhindert werden, da diese einen Lückenschluss erschwert beziehungsweise
verlangsamt 13. Bereits sechs Monate nach
erfolgter Extraktion kann sich der Alveolarfortsatz bis zu 1,87 mm in der Breite
und zwischen 1,24–2,03 mm in der Höhe reduzieren 14
15.

Die Hemisektion unterer Milchmolaren bei Nicht-Anlage der unteren zweiten
Prämolaren schafft es durch den Verbleib eines Zahnanteils, die Knochenatrophie
zu vermindern und stellt außerdem eine nebenwirkungsarme und effektive
Alternative einer kieferorthopädischen Verankerungsmöglichkeit dar.

Ziel dieses Artikels ist es, auf die Geschichte der Hemisektion in der
Kieferorthopädie einzugehen, Anwendungsbereiche aufzuzeigen und Indikationen zu
erläutern.
Indirektes Kleben unter Anwendung von
CAD/CAM-Technologie
Authors: Sabbagh Hisham , Becker Kathrin , Jungbauer Rebecca
Published: December 2024

Digitale Technologien haben zur Entwicklung neuer Ansätze in der indirekten
Bracketplatzierung geführt. Dabei kann die Bracketplatzierung virtuell in
Softwareprogrammen durchgeführt werden, wobei verschiedene Simulations- und
Individualisierungmöglichkeiten angewendet werden können. Anschließend ist eine
modellfreie Herstellung der Bracketübertragungsschienen mithilfe von 3D-Druck
Verfahren möglich.

Dieser Artikel fasst den Hintergrund und aktuelle Literatur zum
CAD/CAM-Indirect-Bonding zusammen und stellt den Arbeitsprozess anhand eines
Fallbeispiels dar.
3D-Druck palatinal verankerter Apparaturen: eine
Übersicht
Authors: Mücke Katharina , Küffer Maximilian , Wilmes Benedict , Becker Kathrin
Published: December 2024

Der 3D-Druck, oder auch additive Fertigung genannt, hat die Kieferorthopädie
erheblich verändert. Indem er die Herstellung präziser, individuell angepasster
Apparaturen ermöglicht, verbessert der 3D-Druck sowohl die Effizienz der
Behandlung als auch den Patientenkomfort. In den letzten Jahren haben sich
insbesondere der Einsatz von Computer-Aided Design (CAD)/Computer-Aided
Manufacturing (CAM)-Systemen und Metall-3D-Druckverfahren, wie das selektive
Laserschmelzen (SLM), durchgesetzt. In der Kieferorthopädie ermöglichen diese
Technologien, festsitzende Apparaturen (Brackets[1], Lingualretainer [2],
Hyrax-Expander[3], skelettal verankerte Apparaturen[4]), herausnehmbare
Apparaturen [5] und komplexe, individualisierte Apparaturen (multipurpose
Apparaturen) digital zu planen und direkt zu drucken, teilweise sogar bereits
ohne die Notwendigkeit physischer Modelle [6].
Pilotierung und Evaluation einer partizipativen, digitalen Akte für gerontopsychiatrische Patienten und ihre Care-Partner
Authors: Meier-Diedrich Eva , Dahling Volker , Esch Tobias , Hägglund Maria , Heinze Martin , Hochwarter Stefan , Wagener Marie , Schwarz Julian
Published: December 2024

Hintergrund Ältere Patienten sind in ihrer Gesundheitsversorgung häufig auf Angehörige, sog. „Care-Partner” (CP), angewiesen. Diese erhalten oft nur erschwert Zugang zu relevanten Gesundheitsdaten der Patienten und können deshalb nur begrenzt unterstützen. CP einen digitalen Zugang zur elektronischen Akte und zur klinischen Behandlungsdokumentation der Patienten zu geben, stellt einen innovativen Beitrag zur Lösung dieses Problems dar. Es werden die Barrieren und Chancen des Lösungsansatzes untersucht.

Methoden Ältere Patienten (n = 8) und deren CP (n = 8) erhalten online Zugang zur ärztlichen Behandlungsdokumentation via eines webbasierten Patientenportals. Es werden qualitative Interviews (n = 16) zu den Erfahrungen mit dem Zugang für CP geführt.

Ergebnisse Sowohl Patienten als auch CP erleben bei der Nutzung Barrieren und Chancen. Der Kontakt zu den Behandlern verbessert und vereinfacht sich. Patienten stehen in Arztgesprächen weniger unter Druck, da sie via Online-Zugang die Arztkontakte nach- und vorbereiten können. CP fühlen sich besser in die Gesundheitsversorgung einbezogen und entlastet. Einige Patienten gelang es aufgrund von technischen Schwierigkeiten und/oder fehlender digitaler Gesundheitskompetenz nicht, den Online-Zugang selbstständig zu nutzen, sodass Verantwortung an die CP abgegeben wurde.

Diskussion CP nehmen eine zentrale Rolle in der digitalen Gesundheitsversorgung von Patienten ein. Damit auch ältere Patienten als gleichberechtigte Partner an ihrem digitalen Gesundheitsmanagement teilhaben, ist es erforderlich, spezifische Angebote zu entwickeln, die sie in der Entwicklung digitaler Kompetenzen unterstützen.
Equilibrium vortex lattice in a rotating superfluid
Authors: Krasnov Yu. K.
Published: December 2024

We study an equilibrium vortex lattice with the thermodynamically most favorable as well as with an arbitrary number, of Onsager–Feynman vortices, and determine the equilibrium vortex distribution, size of the irrotational region, and the region of stability of the lattice. It is proved that from the thermodynamic viewpoint, the most favorable equilibrium lattice with respect to the normal component of He II is the Onsager–Feynman vortex condensate. We discuss the first-order phase transition from the equilibrium vortex-free rotation of He II to an equilibrium rotation with vortices.
Superconducting properties of V/AI–AlxOy–Pb tunnel junctions
Authors: Rybal’chenko L F.
Published: December 2024

Vanadium-based junctions with aluminum oxide barriers are experimentally investigated. The characteristics of such junctions are shown to be close to ideal. A dependence of the broadening of the single-particle current jump on the ratio of the coherence length ξ(T) to the vanadium film thickness is observed. It is shown that the suppression of the order parameter at the vanadium film surface is caused by its oxides. It is experimentally confirmed that the dip in the density of states above the gap is caused by the normal layer at the superconductor surface.
Transport phenomena in dense binary systems. Mixtures of simple cryogenic fluids
Authors: Aznakaev É. G.
Published: December 2024

A description of transport phenomena in dense binary mixtures is proposed which takes into account both single-particle and collective molecular motions. Agreement between the calculated and experimental values of the shear viscosity is demonstrated for the example of the liquified gas system Ar−CH4. The law of corresponding states is shown to hold for the kinetic coefficients of a dense binary mixture.
Effect of N−S interface on critical depairing current
Authors: Kashchei V. A.
Published: December 2024

In terms of the heat balance equation for conduction electrons, the paper considers the critical current in a one-dimensional system consisting of a superconductor and a normal metal. It is shown that in the temperature range T≲Th (Th is the temperature at which hysteresis arises in the critical current of the superconductor) the main reason why the critical current decreases (in comparison with that of a completely superconducting sample) lies in the thermal energy flux across the interface into the superconductor. This flux and the corresponding critical current are studied as functions of the microscopic parameters of the consituent metals. The distinctive features of the mechanisms responsible for the breakdown of the ground state of such a system are explained.
Frequency agile photonic integrated external cavity laser
Authors: Lihachev Grigory , Bancora Andrea , Snigirev Viacheslav , Tian Hao , Riemensberger Johann , Shadymov Vladimir , Siddharth Anat , Attanasio Alaina , Wang Rui Ning , Visani Diego A. , Voloshin Andrey , Bhave Sunil A. , Kippenberg Tobias J.
Published: December 2024

Recent advances in the development of ultra-low loss silicon nitride integrated photonic circuits have heralded a new generation of integrated lasers capable of reaching fiber laser coherence. However, these devices are presently based on self-injection locking of distributed feedback laser diodes, increasing both the cost and requiring tuning of laser setpoints for their operation. In contrast, turn-key legacy laser systems use reflective semiconductor optical amplifiers (RSOAs). While this scheme has been utilized for integrated photonics-based lasers, so far, no cost-effective RSOA-based integrated lasers exist that are low noise and simultaneously feature fast, mode-hop-free, and linear frequency tuning as required for frequency modulated continuous wave (FMCW) LiDAR or for laser locking in frequency metrology. Here we overcome this challenge and demonstrate a RSOA-based, frequency agile integrated laser, that can be tuned with high speed, with high linearity at low power. This is achieved using monolithic integration of piezoelectrical actuators on ultra-low loss silicon nitride photonic integrated circuits in a Vernier filter-based laser scheme. The laser operates at 1550 nm, features a 6 mW output power and a 400 Hz intrinsic laser linewidth, and allows ultrafast wavelength switching within 7 ns rise time and 75 nW power consumption. In addition, we demonstrate the suitability for FMCW LiDAR by showing laser frequency tuning over 1.5 GHz at 100 kHz triangular chirp rate with a nonlinearity of 0.25% after linearization and use the source for measuring a target scene 10 m away with a 8.5 cm distance resolution.
Hybrid filter for lock-in amplifiers
Authors: Lindemuth Jeffrey , Codecido Emilio , Faust Noah , Fortney Houston , Daughton David
Published: December 2024

Lock-in amplifiers are instrumental in the precise measurement of extremely small AC signals within high-noise environments. Traditionally, noise reduction in these instruments relies on infinite impulse response (IIR) filters, which can necessitate prolonged settling times to ensure the acquisition of accurate, statistically independent data. While moving average filters offer faster settling times, their non-monotonic frequency response may not be optimal for noise reduction. Conversely, IIR filters frequently realized as N-pole RC filters exhibit a monotonic frequency response conducive to effective noise reduction. This study presents a hybrid filter architecture that combines a short IIR filter with a longer moving average finite impulse response filter. The objective is to enhance noise reduction as quantified by the filter’s equivalent noise bandwidth (ENBW). Theoretical analysis is provided to derive the step response, settling time, frequency response, and ENBW of the hybrid filter configuration. Design methodologies are outlined for hybrid filters that either match the settling time of an N-pole RC filter while achieving a lower ENBW or maintain the ENBW of an N-pole RC filter but with significantly faster settling time. The performance of the hybrid filter is validated through noise measurements of low-value resistors and thermal noise of larger resistors, with results compared to theoretical predictions.
Inferring fusion nuclear burnwidths with low gain photomultiplier impulse response functions
Authors: Meaney K. D. , Jeet J. , Carrera J. , Mariscal E. , Schlossberg D. , Moore A. , Eckart M. , Milnes J. , Hink P. , Hillyard P. , Holdener D. , Herrmann H. , Geppert-Kleinrath H. , Kim Y.
Published: December 2024

When an inertial confinement fusion implosion is compressed, it maintains thermonuclear density and temperatures for a very short time scale, about 100 ps. The Gamma Reaction History diagnostic measures the time evolution of the fusion burn, but its temporal resolution is limited by the use of a photomultiplier tube (PMT) to amplify the photon signal. Multichannel plate-based PMTs have a fast (∼120 ps) full-width at half-max impulse response function (IRF), but the time scale is similar to the incoming physics signal. An analysis routine is used to remove the effect of the PMT IRF and infer the incident fusion burnwidth. With the National Ignition Facility achieving ignition and creating much brighter signals, the PMTs are run at gains three orders of magnitude lower than nominal operation. Calibration at these settings shows the PMT IRFs get ∼15% wider. Taking the gain-dependent IRF can affect the inferred nuclear burnwidths by up to ∼15%.
Quasi-longitudinal whistler propagation in presence of finite ion response
Authors: Barsagade Gayatri , Sharma Devendra
Published: December 2024

In recent studies, quasi-longitudinal whistlers propagating along the resonance cone were identified to develop a steep density structure as a result of longitudinal resonant excitations in the upper-hybrid regime that are nonlinearly modified. The question of whether the ion response to these resonant whistlers in the lower hybrid regime, shared by them with ion excitations, leads to a stronger resonant coupling of quasi-longitudinal whistlers to electrostatic fluctuations remains unexplored and addressed by incorporating finite ion mobility (i.e., departure from mi→∞ limit) in present coherent quasi-longitudinal whistler simulations. At moderate angles, the ion response shows modification of lower hybrid ion excitations at the stage of evolution where the longitudinal electrostatic field of both modes grows comparable. The ratio of electron density fluctuation associated with whistler and plasma density fluctuation associated with ion response is, however, recovered to be small and confirmed analytically. In propagation along the resonance cone at high density, the ion fluctuations approach lower hybrid resonance without density steepening. Excited at equal wave numbers, they complement the longitudinal electrostatic field of the quasi-longitudinal whistlers. At higher densities, steep sharp electron density fluctuations are found recurrent and in equilibrium with the coherent lower-hybrid ion density structures.
Development of a diagnostic system for atomic processes in the whole divertor region of HL-3
Authors: Ma Huicong , Cai Laizhong , Gao Jinming , Fan Dongmei , He Zongyuhui , Du Hailong , Wang Dezhen
Published: December 2024

The atomic processes are important for understanding the mechanisms of divertor detachment physics. The developed diagnostic system for atomic processes aims to present the atomic process distributions of ionization and recombination in the whole divertor region of HL-3, which is equipped with the multi-channel visible imaging optics, two SCMOS cameras having identical parameters, and bandpass filters. This configuration enables high spatiotemporal resolution measurements of Balmer lines across the entire divertor region. The maximum frequency of the cameras is 400 fps (512 pixel × 512 pixel), and the field of view covers the entire 1100 × 650 cm2 area of the divertor with the spatial resolution of 1 × 1 cm2. The intensity ratio of experimental measurements of Balmer lines can be used to assess the leading region of ionization, transition from ionization to recombination, and recombination from the Atomic Data and Analysis Structure database. The preliminary results show that ionization is primarily distributed near the last closed flux surface (LCFS), while the transition from ionization to recombination and recombination predominate within a limited region distant from the LCFS. Through the corresponding S/XB, the numbers of ionization and recombination per unit time within the divertor region are obtained. With the evolution of time, the electron density gradually increases, and the ionization region and ionization rate gradually increase. This holds immense significance in advancing our comprehension of the detachment mechanism, facilitating real-time control of divertor detachment and steady-state control technology of heat load in the future.
Finding Birkhoff averages via adaptive filtering
Authors: Ruth M. , Bindel D.
Published: December 2024

In many applications, one is interested in classifying trajectories of symplectic maps as invariant tori, islands, or chaos. Here, we introduce Birkhoff reduced rank extrapolation (RRE), a modified version of the RRE method, which efficiently obtains ergodic averages of invariant tori and islands in symplectic maps. In contrast, Birkhoff RRE does not efficiently converge in chaos, meaning its convergence rate can be used for trajectory classification. Furthermore, for the islands and invariant circles, Birkhoff RRE returns the number of islands and the rotation number. This allows us to find Fourier parameterizations of invariant circles and islands from a single trajectory. We show examples of Birkhoff RRE on the standard map and magnetic field line dynamics.
Emergent behaviors of two thermodynamically consistent inertial spin models
Authors: Ha Seung-Yeal , Jin Guanghui , Ma Youwei , Yoon Wook
Published: December 2024

We propose two thermodynamically consistent inertial spin models generalizing the inertial spin model for the ensemble of mechanical particles with spin. For the collective dynamics modeling consistent with an entropy principle, we use two modeling ideas based on Hamiltonian formulation and flocking formalism for the coupling of the inertial spin model and temperatures introduced by Ha and Ruggeri [Arch. Ration. Mech. Anal. 223, 1397 (2017)]. The resulting models admit several constants of motions and are consistent with the entropy principle. We present several sufficient frameworks leading to the asymptotic vanishing of spins and velocity alignment. We also implement several numerical simulations and compare them with analytical results.
Perspective on non-Hermitian elastodynamics
Authors: Christensen Johan , Haberman Michael R. , Srivastava Ankit , Huang Guoliang , Shmuel Gal
Published: December 2024

The manipulation of mechanical waves is a long-standing challenge for scientists and engineers, as numerous devices require their control. The current forefront of research in the control of classical waves has emerged from a seemingly unrelated field, namely, non-Hermitian quantum mechanics. By drawing analogies between this theory and those of classical systems, researchers have discovered phenomena that defy conventional intuition and have exploited them to control light, sound, and elastic waves. Here, we provide a brief perspective on recent developments, challenges, and intricacies that distinguish non-Hermitian elastodynamics from optics and acoustics. We close this perspective with an outlook on potential directions such as topological phases in non-Hermitian elastodynamics and broken Hermitian symmetry in materials with electromomentum couplings.
Efficiency droop of AlGaN-based deep-ultraviolet miniaturized light-emitting diodes under electrical stress
Authors: Zheng Xi , Ai Sidan , Lu Tingwei , Dai Yurong , Tong Changdong , Lu Yijun , Chen Zhong , Guo Weijie
Published: December 2024

The reduction on efficiency of AlGaN-based high-voltage (HV) deep ultraviolet light emitting diodes (DUV-LEDs) with quadra-serial connection and different geometries has been investigated under electrical stress. After the electrical aging, the Shockley–Read–Hall nonradiative recombination becomes more significant, while the Auger recombination is mitigated. The hexagonal HV DUV-LEDs reach a maximum external quantum efficiency of 6.1% and exhibit superior performance after aging. The results provide insights into the impacts of submesa geometry on reliability and UV light communication performance of HV DUV-LEDs.
Most probable trajectories of a birhythmic oscillator under random perturbations
Authors: Zhang Wenting , Xu Wei , Tang Yaning , Kurths Jürgen
Published: December 2024

This study investigates the most probable trajectories of a birhythmic oscillator under stochastic perturbations. The distinctive feature of the birhythmic oscillator is the coexistence of two stable limit cycles with different amplitudes and frequencies, separated by an unstable limit cycle. The path integral method was utilized to compute the instantaneous probability density. Based on the theory of most probable dynamics, by maximizing the probability density function, we present the time series of the most probable trajectories starting from different initial states. Furthermore, we conducted a detailed analysis of the noise-induced transitions between the two stable limit cycles under different parameter conditions. This approach enables us to understand and track the most probable escape time and specific most probable trajectories as the system transitions from the basin of attraction of one stable limit cycle to another. This work visualizes the most probable trajectories in stochastic systems and provides an innovative solution to the complex problem of noise-induced transitions between two stable limit cycles. Our research aims to provide a new perspective for studying complex stochastic dynamical systems.
Arnold tongues, shrimp structures, multistability, and ecological paradoxes in a discrete-time predator–prey system
Authors: Rajni  , Ghosh Bapan
Published: December 2024

This paper explores a discrete-time system derived from the well-known continuous-time Rosenzweig–MacArthur model using the piecewise constant argument. Examining the impact of increasing carrying capacity and harvesting efforts, we uncover intricate phenomena, such as periodicity, quasiperiodicity, period-doubling, period-bubbling, and chaos. Our analysis reveals that increasing the carrying capacity of prey species can lead to both system stabilization and destabilization. We delve into normal forms associated with different bifurcation types, accompanied by numerical examples, observing multistabilities with intricate basin structures. Bistable, tristable, and quadruple attractors characterize the model’s multistable states. Additionally, we find that enriching prey species negatively affects predator abundance, and increasing carrying capacity can lead to a sudden jump in predator population to the brink of extinction. Examining the two-parameter space of predator and prey harvesting efforts, we identify organized periodic structures: Arnold tongues and shrimp-like structures within quasiperiodic and chaotic regions. Arnold tongues exhibit a sequence of periodic adding. The shrimp structures indicate the existence of period-doubling and period-bubbling phenomena. Discussions on ecological interpretations of predator harvesting, including the paradoxical hydra effect, are provided.
Coherent IR-hyper-Raman four wave mixing spectroscopy
Authors: McDonnell Ryan P. , Kohler Daniel D. , Wright John C.
Published: December 2024

Nonlinear, four-wave mixing vibrational spectroscopies are commonly used to probe electron–vibration coupling in isotropic media. Most of these methods rely on infrared and/or Raman transitions, but methods involving hyper-Raman transitions are also possible. Hyper difference frequency generation (HDFG) spectroscopy is an underdeveloped four-wave mixing vibrational spectroscopy based upon both infrared absorption and hyper-Raman scattering transitions. Despite several experimental reports on HDFG, its spectroscopic properties have not been fully explored. To this end, we investigate the selection rules and behavior of HDFG spectroscopy as an upconverted infrared spectroscopy and as a probe of vibronic coupling in molecular systems. We discuss the similarities between HDFG, a four-wave mixing technique, and vibrational sum frequency generation (vSFG) spectroscopy, a three-wave mixing technique. vSFG and HDFG appear to provide similar output intensities, making HDFG feasible for vSFG practitioners. HDFG is shown to be a sensitive probe of vibronic coupling in bulk systems and provides an alternative method to investigate electronic-nuclear coordinate correlations.
Development of a rotary piezoelectric energy harvester using magnetic excitation inspired by the fan blade
Authors: Qi Ji , Ma Jun , Zhang Yaxun , Wang Liang
Published: December 2024

This work proposes a new rotary piezoelectric energy harvester using magnetic excitation inspired by the fan blade. The configuration and operating principle of the harvester are introduced. Then, the equivalent nonlinear model of the piezoelectric beam is established based on the Euler–Bernoulli theory and the Rayleigh–Ritz method. Finite element simulation is used to obtain the vibration performance of the piezoelectric beam, and the first order natural frequency is obtained as 22.059 Hz. A prototype of the proposed harvester is developed, and a series of experiments are carried out. The effect of magnet deflection angle, magnet mass, and the number of magnets on the output performance of the harvester is studied in detail by experiments. The experimental results proved that the harvester obtained a relatively better output performance when the deflection angle of the drive magnet is 30°. In addition, the harvester generated the maximum output voltage when the rotary speed is 165 rpm, which is consistent with the simulation result. The harvester achieved an average power of 43.5 mW when the resistance was 130 kΩ under the rotary speed of 165 rpm. The output power can satisfy the power consumption of low-power electronic devices, such as LEDs, calculators, and electronic meters.
Complexity measure of extreme events
Authors: Das Dhiman , Ray Arnob , Hens Chittaranjan , Ghosh Dibakar , Hassan Md. Kamrul , Dabrowski Artur , Kapitaniak Tomasz , Dana Syamal K.
Published: December 2024

Complexity is an important metric for appropriate characterization of different classes of irregular signals, observed in the laboratory or in nature. The literature is already rich in the description of such measures using a variety of entropy and disequilibrium measures, separately or in combination. Chaotic signal was given prime importance in such studies while no such measure was proposed so far, how complex were the extreme events when compared to non-extreme chaos. We address here this question of complexity in extreme events and investigate if we can distinguish them from non-extreme chaotic signal. The normalized Shannon entropy in combination with disequilibrium is used for our study and it is able to distinguish between extreme chaos and non-extreme chaos and moreover, it depicts the transition points from periodic to extremes via Pomeau–Manneville intermittency and, from small amplitude to large amplitude chaos and its transition to extremes via interior crisis. We report a general trend of complexity against a system parameter that increases during a transition to extreme events, reaches a maximum, and then starts decreasing. We employ three models, a nonautonomous Liénard system, two-dimensional Ikeda map and a six-dimensional coupled Hindmarsh–Rose system to validate our proposition.
Polyglot entrainment for higher dimensional neuronal models
Authors: Wijayasooriya Lawan , Khan Emel , Qasim Rakhshanda , Sanaei Pejman
Published: December 2024

The entrainment of biological oscillators is a classic problem in the field of dynamical systems and synchronization. This paper explores a novel type of entrainment mechanism referred to as polyglot entrainment [Khan et al., “The emergence of polyglot entrainment responses to periodic inputs in vicinities of Hopf bifurcations in slow–fast systems,” Chaos 32, 063137 (2022)] (multiple disconnected 1:1 regions for a range of forcing amplitude) for higher dimensional nonlinear systems. Polyglot entrainment has been recently explored only in two-dimensional slow–fast models in the vicinity of Hopf bifurcations (HBs). Heading toward generality, in this research, we investigate the phenomenon of polyglot entrainment in higher-dimensional conductance-based models including the four-dimensional Hodgkin-Huxley model and its reduced three-dimensional version. We utilize dynamical systems tools to uncover the mechanism of entrainment and geometric structure of the null surfaces to explore the conditions for the existence of polyglot entrainment in these models. In light of our findings, in the vicinity of HB, when an unforced system acts as a damped oscillator and the fixed point is located near a cubic-like manifold, polyglot entrainment is observed.
Efficient method for simulating ionic fluids between polarizable metal electrodes
Authors: Telles Igor M. , dos Santos Alexandre P. , Levin Yan
Published: December 2024

We introduce an efficient method for simulating Coulomb systems confined by conducting planar surfaces. The new approach is suitable for both coarse-grained models and all-atom simulations of ionic liquids between polarizable metal electrodes. To demonstrate its efficiency, we use the new method to study the differential capacitance of an ionic liquid. Our technique is at least two orders of magnitude faster than traditional Ewald-based methods for non-polarizable surfaces, when calculating the electrostatic energy between two ions. This advancement has significant potential to enhance understanding in fields such as materials science and electrochemistry, enabling efficient large-scale simulations of Coulomb systems confined by polarizable metal electrodes.
Thermo- and soluto-capillary convection and instability near the air–liquid interface
Authors: Wu Zuo-Bing
Published: December 2024

Steady thermo- and solute-capillary convection, instability, and pattern evolution near the air–liquid interface driven by point heat and mass sources are investigated. First, under the assumption of the conically similar viscous flow, an exact axi-symmetric solution of the steady thermo- and soluto-capillary convection near the air–liquid interface is determined due to the constant heat and mass fluxes. It is shown that the constant heat, mass fluxes, and the radial surface tension cause the divergent motion at the interface and the Marangoni convection beneath the interface. Then, the linear stability of the steady thermo- and soluto-capillary convection in response to the azimuthal disturbance is analyzed. At a given Peclet (or Schmidt), Marangoni (or Prandtl), and elasticity numbers, the steady basic flow loses its stability when Reynolds number is beyond the critical value. It is found that for small Schmidt numbers, a half-loop structure between the critical Reynolds number and the harmonic wave number of the azimuthal disturbance appears. For large Schmidt numbers, the critical Reynolds number monotonously increases as the harmonic wave number increases. The critical patterns of the velocity fields and the isothermal, iso-concentration lines in the three-dimensional flow system in response to the disturbance harmonic wave number are dominated by both the radial and azimuthal surface tensions. The results not only provide a valuable understanding of Marangoni convection and pattern information near the air–liquid interface but also inspire its potential practical applications in the material chemistry and biotechnology.
Deep learning via CNN for identification of blue core phenomenon in helicon plasma discharge
Authors: Yin Xianyi , Song Qinlong , Cheng Shiyang , Zhang Haibao
Published: December 2024

Based on deep learning image recognition techniques, a convolutional neural network model for discharge mode recognition of helicon plasma was trained. The accuracy of the model was evaluated using functions such as F1-scores and the confusion matrix. The final recognition accuracy was more than 98.18% after 30 iterations. Interpretable analysis was done using methods such as gradient-weighted class activation mapping to verify the model's robustness as well as repeatability. The model identification results were compared with Langmuir probe diagnostic results. It was found a good fit between the model and the probe results, corroborating the correctness of the model. The present model can well identify the critical power of entering W mode in the discharge process of helicon plasma. As the discharge database expands, it has great potential for recognizing the higher-order discharge modes based on deep learning.
Strange nonchaotic attractor in an unforced turbulent reactive flow system
Authors: Thonti Beeraiah , Tandon Shruti , Durairaj Premraj , Sujith R. I.
Published: December 2024

We discover strange nonchaotic attractor (SNA) through experiments in an unforced system comprising turbulent reactive flow. While models suggest SNAs are common in dynamical systems, experimental observations are primarily limited to systems with external forcing. We observe SNA prior to the emergence of periodic oscillations from chaotic fluctuations. In complex systems, self-organization can lead to order, and inherent nonlinearity can induce chaos. The occurrence of SNA, which is nonchaotic yet nonperiodic in one such complex system, is intriguing.
A computational fluid dynamics-based girth welding model for large-diameter pipeline to reveal vertical weld formation mechanism
Authors: Yun Ze , Li Yan , Wu Juanhui , Liu Xiaoben , Wang Hao , Zhang Hong
Published: December 2024

Welding quality significantly impacts the safety of large-diameter, long-distance pipelines. The molten pool flow, influenced by gravity, results in variations in the girth weld seam at different circumferential orientations. A three-dimensional transient computational fluid dynamics model was developed to study the multi-layer, multi-pass welding process of X80M pipeline, incorporating arc heat, droplet heat, gravity, and fluid flow in the molten pool. The model also simulates dual-torch automatic welding to examine heat transfer and flow characteristics. Notably, it reveals the morphological evolution of the girth weld seam from the 2 to 3 o'clock positions during continuous welding, an area lacking prior research. The results, validated by experiments, show good agreement between the simulation and thermal cycle curves. The weld pool solidifies from the sides toward the center, creating a concave shape due to downward metal flow, with dual-torch welding intensifying this effect. The second torch increases the concavity of filler layers, with depths rising by 21.81% and 32.20%. These findings offer new insights into pipeline girth welding.
Experimental research on heat transfer enhancement by a wall-proximity circular cylinder under an axial magnetic field
Authors: Wang Ze-Dong , Zhang Qi-Long , Yang Juan-Cheng , Lyu Ze , Ni Ming-Jiu , Zhang Nian-Mei , Hu Chen
Published: December 2024

This work experimentally investigates the flow and heat transfer of liquid metal around a cylinder in a rectangular channel with a heated bottom wall under an axial magnetic field. Wall electrical potential probes measure the streamwise and vertical velocity components, while an immersed array probe measures the temperature distribution in the vertical profile. The coupling effects of the gap ratio (ratio of the distance between the center of the cylinder and the wall to the diameter of the cylinder) and the magnetic field on heat transfer enhancement are studied. The experimental results suggest that the Lorentz force suppresses the wall recirculation zone from shedding secondary vortices and alters the trajectory of the vortex street, affecting the thermal boundary layer. The probability density function of temperature indicates that the magnetohydrodynamics effect causes a bimodal distribution due to a quasi-two-dimensional vortex street and a trimodal distribution due to additional secondary vortices. The vortex street notably reduces the thermal boundary layer thickness and the local temperature of the heated wall. The analysis of the correlation coefficients between velocity and temperature fluctuations and the frequency spectrum reveals the physical mechanism enhancing heat transfer. The wall-proximity effect and buoyancy strengthen flow fluctuations and enhance heat transfer. For Ha (Hartmann number) ranging from 161.6 to 646.4, optimal heat transfer occurs at G/d = 1.0, whereas for 808 ≤ Ha ≤ 1131.2, optimal heat transfer is achieved at G/d = 0.5, which is attributed to the coupling effect of the magnetic field and gap flow on vortex dynamics.
Investigation of flow interference and heat transfer characteristics of two staggered circular cylinders in cross flow
Authors: Wang Zhengdao , Zhao Feng , Wei Yikun
Published: December 2024

The flow and heat transfer characteristics around staggered cylinders are critical for optimizing thermal performance in engineering applications like heat exchangers. This study investigates the flow and heat transfer properties around two staggered cylinders at Re = 100 using a double-distributed lattice Boltzmann method. Eight typical flow patterns are recognized based on vortex and temperature fields, phase diagram, and St. The effects of gap flow, shear layer, vortex shedding, and wake evolution behaviors on heat transfer characteristic are discussed. Results demonstrate that when the wake is a single vortex street, the shear layer reattachment and the weaker gap flow both lead to a high temperature in the gap between the two cylinders, which subsequently adversely affects the heat transfer performance. Inversely, the vortex impingement and the stronger gap flow enhance the heat transfer performance. The deflected gap flow leads to a narrow and wide street in the wake, and the cylinder located on the opposite side of the gap flow deflection has better heat transfer performance. Furthermore, two coupled vortex streets in the wake can further improve the heat transfer performance of the cylinders. These findings provide valuable insights for enhancing thermal management strategies in engineering applications.
On the coupling effects of near-wall combustion and shock train in dual-mode scramjets
Authors: Peng Yuan , Xu Jinglei , Chen Kuangshi , Huang Shuai
Published: December 2024

For the purpose of combustion enhancement and viscous drag reduction, fuel tends to be injected into the upstream of a scramjet's internal flow path, and the coupling of near-wall combustion and shock train may occur under this situation. This study numerically investigates the influence of combustion in turbulent boundary layers on shock train structures and pressure gradients. The numerical results reveal that the modification of the boundary layer structure and the reduction in skin friction caused by combustion in turbulent boundary layers are the intrinsic reasons for the decrease in shock train pressure gradient. In particular, within nearly the same length of shock train, combustion in turbulent boundary layers leads to a 20% reduction in the back pressure tolerance at an equivalence ratio of 0.1. Moreover, three representative one-dimensional (1D) shock train models are assessed under the condition of combustion in turbulent boundary layers. Among them, the 1D models established directly based on skin friction exhibits greater accuracy. Meanwhile, the Waltrup−Billig correlation based on momentum thickness is not applicable, further confirming the importance of including skin friction in shock train modeling.
Analysis of flutter dynamics in thin flexible flags under streamlined and vortex-induced flows
Authors: Tripathi Dheeraj , Ghommem Mehdi , Abdelkefi Abdessattar , Romdhane Lotfi , Bourantas George C.
Published: December 2024

In this study, numerical and experimental investigations are conducted to gain a thorough understanding of the aeroelastic behavior of flexible steel flags at low air speeds. Numerical simulations are conducted using a two-dimensional computational fluid dynamics solver to analyze the vortex shedding mechanism from a circular bluff body and to assess its effect on a downstream slender body placed at different gap distances. Experiments on a low-speed wind tunnel are performed to examine the flow-induced flutter dynamics of thin flexible flags. Four different flag shapes, namely, triangular, square, rectangular, and trapezoidal, are tested both with and without an upstream bluff body. Under streamlined flow conditions, flutter instability is characterized by subcritical bifurcation routes, while the presence of a cylindrical bluff body induces supercritical bifurcation scenarios. The aeroelastic response of the flag is inspected while varying the gap distance, separating it from the cylindrical bluff body from 0.5 to 15 times the cylinder's diameter. Experimental results show that the shape of the flag significantly influences its dynamic behavior, especially when it is placed in close proximity to the bluff body. The triangular flag exhibits the highest limit cycle oscillation (LCO) amplitudes, while the square flag has the lowest flutter onset speed. A regime of period-2 LCOs is observed in the triangular flag configuration, which is not seen elsewhere. For flags positioned farther away, the dynamics resembles those observed under streamlined flow, due to the vortices weakening with the increasing gap size. Finally, a comparative analysis demonstrates the flow speed regimes of high-amplitude oscillations for different flag shapes and bluff body positions, which can be explored for low speed energy harvesting applications.
On unsteady flow characteristics in a water-jet pump based on proper orthogonal decomposition method under different inflow conditions
Authors: Liu Chao , Chen Hongxun , Ma Zheng
Published: December 2024

Considering the complex flow characteristics of the water-jet pump and the anisotropy of Reynolds stresses, a hybrid Reynolds-averaged Navier–Stokes/large-eddy simulation method based on von Kármán scale and nonlinear correction has been developed, while its effectiveness has also been verified. The proper orthogonal decomposition method is employed to study the unsteady flow characteristics inside a water-jet pump due to its advantages in flow field analysis. The internal and external characteristics of the water-jet pump under two kinds of inflow conditions are comparatively analyzed, and the intrinsic influence mechanism of nonuniform inflow on the performance of the water-jet pump is investigated. The results indicate that nonuniform inflow causes the overall decrease in the pump head curve, and occurs serious reverse flow at impeller outlet near blade tip region, which in turn generates a large energy dissipation. The flow state is relatively smooth under uniform inflow condition, while the nonuniform inflow makes tip leakage flow induce many unstable flow structures, causing large turbulent kinetic energy and low pressure difference between the pressure surfaces and suction surfaces of impeller blades. There are multiscale flow structures in the water-jet pump, with large scales corresponding to low-order modes, which play a dominant role in turbulent movement and can be used as an important element for evaluating hydraulic performance. The energy content of low-modes is lower and the distribution of flow structures in each-order mode is more chaotic in the water-jet pump for nonuniform inflow compared to the ones for uniform inflow.