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Search Results (153)

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Keywords = relaxation oscillators

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20 pages, 1508 KB  
Article
Outlier-Robust Convergence of Integer- and Fractional-Order Difference Operators in Fuzzy-Paranormed Spaces: Diagnostics and Engineering Applications
by Muhammed Recai Türkmen
Fractal Fract. 2025, 9(10), 667; https://doi.org/10.3390/fractalfract9100667 (registering DOI) - 16 Oct 2025
Viewed by 113
Abstract
We develop a convergence framework for Grünwald–Letnikov (GL) fractional and classical integer difference operators acting on sequences in fuzzy-paranormed (fp) spaces, motivated by data that are imprecise and contain sporadic outliers. Fuzzy paranorms provide a resolution-dependent notion of proximity, while statistical and lacunary [...] Read more.
We develop a convergence framework for Grünwald–Letnikov (GL) fractional and classical integer difference operators acting on sequences in fuzzy-paranormed (fp) spaces, motivated by data that are imprecise and contain sporadic outliers. Fuzzy paranorms provide a resolution-dependent notion of proximity, while statistical and lacunary statistical convergence downweight sparse deviations by natural density; together, they yield robust criteria for difference-filtered signals. Within this setting, we establish uniqueness of fp–Δm statistical limits; an equivalence between fp-statistical convergence of Δm (and its GL extension Δα) and fp-strong p-Cesàro summability; an equivalence between lacunary fp-Δm statistical convergence and blockwise strong p-Cesàro summability; and a density-based decomposition into a classically convergent part plus an fp-null remainder. We also show that GL binomial weights act as an 1 convolution, ensuring continuity of Δα in the fp topology, and that nabla/delta forms are transferred by the discrete Q–operator. The usefulness of the criteria is illustrated on simple engineering-style examples (e.g., relaxation with memory, damped oscillations with bursts), where the fp-Cesàro decay of difference residuals serves as a practical diagnostic for Cesàro compliance. Beyond illustrative mathematics, we report engineering-style diagnostics where the fuzzy Cesàro residual index correlates with measurable quantities (e.g., vibration amplitude and energy surrogates) under impulsive disturbances and missing data. We also calibrate a global decision threshold τglob via sensitivity analysis across (α,p,m), where mN is the integer difference order, α>0 is the fractional order, and p1 is the Cesàro exponent, and provide quantitative baselines (median/M-estimators, 1 trend filtering, Gaussian Kalman filtering, and an α-stable filtering structure) to show complementary gains under bursty regimes. The results are stated for integer m and lifted to fractional orders α>0 through the same binomial structure and duality. Full article
(This article belongs to the Section Engineering)
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9 pages, 294 KB  
Article
Germanium-Based Temperonic Crystal
by Jesus Manzanares-Martinez, Diego Soto-Puebla and Gerardo Morales-Morales
Crystals 2025, 15(10), 899; https://doi.org/10.3390/cryst15100899 - 16 Oct 2025
Viewed by 222
Abstract
We propose a germanium-based temperonic crystal consisting of a two-layer unit cell designed to enable interference of thermal waves in the non-Fourier regime. Each layer features temperature-dependent properties, including thermal diffusivity D(T), thermal conductivity κ(T), [...] Read more.
We propose a germanium-based temperonic crystal consisting of a two-layer unit cell designed to enable interference of thermal waves in the non-Fourier regime. Each layer features temperature-dependent properties, including thermal diffusivity D(T), thermal conductivity κ(T), and relaxation time τ(T). Utilizing the Cattaneo-Vernotte model, we predict band gaps in the temperature oscillation frequencies. Our analysis reveals that band gaps emerge when one layer is maintained at 110 K and the other at 50 K; however, these gaps close rapidly as the temperature contrast diminishes or the overall temperature increases. Drawing from the temperonic-crystal paradigm and inspired by recent experimental observations of thermal waves in germanium, this design offers a promising pathway for on-chip control of ultrafast thermal pulses and thermal-management devices in semiconductors. Full article
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13 pages, 2225 KB  
Communication
Experimental Evaluation of Memristor-Enhanced Analog Oscillators: Relaxation and Wien-Bridge Cases
by Luis Manuel Lopez-Jimenez, Esteban Tlelo-Cuautle, Luis Fortino Cisneros-Sinencio and Alejandro Diaz-Sanchez
Dynamics 2025, 5(4), 43; https://doi.org/10.3390/dynamics5040043 - 1 Oct 2025
Viewed by 294
Abstract
This paper presents two classic analog oscillators: a relaxation oscillator and a Wien bridge one, where a memristor replaces a resistor. The circuits are simulated in TopSPICE 7.12 using a memristor emulation circuit and commercially available components to evaluate the memristor’s impact. In [...] Read more.
This paper presents two classic analog oscillators: a relaxation oscillator and a Wien bridge one, where a memristor replaces a resistor. The circuits are simulated in TopSPICE 7.12 using a memristor emulation circuit and commercially available components to evaluate the memristor’s impact. In the case of the relaxation oscillator, which includes the memristor, a notable increase in oscillation frequency was observed compared to the classical circuit, with a nearly 10-fold increase from 790 Hz to 7.78 kHz while maintaining a constant amplitude. This confirms the influence of the memristor’s dynamic resistance on the circuit time constant. On the other hand, the Wien-bridge oscillator exhibits variations in specific parameters, such as peak voltage, amplitude, and frequency. In this case, the oscillation frequency decreased from 405 Hz to 146 Hz with the addition of the memristor, a characteristic introduced by the proposed memristive element’s nonlinear interactions. Experimental results confirm the feasibility of incorporating memristors into classical oscillator circuits, enabling frequency changes while maintaining stable oscillations, allowing reconfigurable and adaptable analog designs that leverage the properties of memristive devices. Full article
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18 pages, 601 KB  
Article
Back-Reaction of Super-Hubble Fluctuations, Late Time Tracking, and Recent Observational Results
by Marco A. Alvarez, Leila L. Graef and Robert Brandenberger
Symmetry 2025, 17(9), 1507; https://doi.org/10.3390/sym17091507 - 10 Sep 2025
Viewed by 439
Abstract
Previous studies have suggested that the back-reaction of super-Hubble cosmological fluctuations on a symmetric background space-time, with respect to being homogeneous and isotropic, could behave like a dynamical relaxation of the cosmological constant. Moreover, this mechanism appears to be self-regulatory, potentially leading to [...] Read more.
Previous studies have suggested that the back-reaction of super-Hubble cosmological fluctuations on a symmetric background space-time, with respect to being homogeneous and isotropic, could behave like a dynamical relaxation of the cosmological constant. Moreover, this mechanism appears to be self-regulatory, potentially leading to oscillatory behavior in the effective DE. Such an effect would occur in any cosmological model with super-Hubble matter fluctuations, including the standard ΛCDM model. Apart from that, recent DESI data, which indicate that DE may be dynamical, have renewed interest in exploring scenarios leading to such an oscillatory behavior. In this study, we propose a parameterization to account for the impact of super-Hubble fluctuations on the background energy density of the Universe. We model the total effective cosmological constant as the sum of a constant and an oscillating contribution. We performed a preliminary comparison of the background dynamics of this model with recent radial BAO data from DESI. We also discuss the status of the H0 tension problem in this model. Full article
(This article belongs to the Special Issue Symmetry and Cosmology)
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12 pages, 1365 KB  
Article
On Standard Cell-Based Design for Dynamic Voltage Comparators and Relaxation Oscillators
by Orazio Aiello
Chips 2025, 4(3), 31; https://doi.org/10.3390/chips4030031 - 30 Jul 2025
Viewed by 684
Abstract
This paper deals with a standard cell-based analog-in-concept pW-power building block as a comparator and a wake-up oscillator. Both topologies, traditionally conceived as an analog building block made by a custom process and supply voltage-dependent design flow, are designed only by using digital [...] Read more.
This paper deals with a standard cell-based analog-in-concept pW-power building block as a comparator and a wake-up oscillator. Both topologies, traditionally conceived as an analog building block made by a custom process and supply voltage-dependent design flow, are designed only by using digital gates, enabling them to be automated and fully synthesizable. This further results in supply voltage scalability and regulator-less operation, allowing direct powering by an energy harvester without additional ancillary circuit blocks (such as current and voltage sources). In particular, the circuit similarities in implementing a rail-to-rail dynamic voltage comparator and a relaxation oscillator using only digital gates are discussed. The building blocks previously reported in the literature by the author will be described, and the common root of their design will be highlighted. Full article
(This article belongs to the Special Issue IC Design Techniques for Power/Energy-Constrained Applications)
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23 pages, 6299 KB  
Article
Multi-Valve Coordinated Disturbance Rejection Control for an Intake Pressure System Using External Penalty Functions
by Louyue Zhang, Duoqi Shi, Chao Zhai, Zhihong Dan, Hehong Zhang, Xi Wang and Gaoxi Xiao
Actuators 2025, 14(7), 334; https://doi.org/10.3390/act14070334 - 2 Jul 2025
Viewed by 414
Abstract
Altitude test facilities for aero-engines employ multi-chamber, multi-valve intake systems that require effective decoupling and strong disturbance rejection during transient tests. This paper proposes a coordinated active disturbance rejection control (ADRC) scheme based on external penalty functions. The chamber pressure safety limit is [...] Read more.
Altitude test facilities for aero-engines employ multi-chamber, multi-valve intake systems that require effective decoupling and strong disturbance rejection during transient tests. This paper proposes a coordinated active disturbance rejection control (ADRC) scheme based on external penalty functions. The chamber pressure safety limit is formulated as an inequality-constrained optimization problem, and an exponential penalty together with a gradient based algorithm is designed for dynamic constraint relaxation, with guaranteed global convergence. A coordination term is then integrated into a distributed ADRC framework to yield a multi-valve coordinated ADRC controller, whose asymptotic stability is established via Lyapunov theory. Hardware-in-the-loop simulations using MATLAB/Simulink and a PLC demonstrate that, under ±3 kPa pressure constraints, the maximum engine inlet pressure error is 1.782 kPa (77.1% lower than PID control), and under an 80 kg/s2 flow-rate disturbance, valve oscillations decrease from ±27% to ±5%. These results confirm the superior disturbance rejection and decoupling performance of the proposed method. Full article
(This article belongs to the Special Issue Actuation and Robust Control Technologies for Aerospace Applications)
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17 pages, 2350 KB  
Article
Acute Heterogeneous Changes in Muscle and Tendon Viscoelastic Properties Following a VO₂max Treadmill Test in High-Level Male Soccer Players
by Karol Skotniczny, Artur Terbalyan, Michał Krzysztofik, Robert Roczniok, Miłosz Drozd, Łukasz Radzimiński and Jakub Jarosz
Appl. Sci. 2025, 15(13), 6986; https://doi.org/10.3390/app15136986 - 20 Jun 2025
Viewed by 454
Abstract
Background: This study aimed to investigate the acute changes in muscle and tendon viscoelastic properties in response to a progressive treadmill VO2max test among professional male soccer players. Methods: Bilateral assessments at five sites—the Achilles tendon (AT), biceps femoris, semitendinosus, rectus [...] Read more.
Background: This study aimed to investigate the acute changes in muscle and tendon viscoelastic properties in response to a progressive treadmill VO2max test among professional male soccer players. Methods: Bilateral assessments at five sites—the Achilles tendon (AT), biceps femoris, semitendinosus, rectus femoris (RF), and sternocleidomastoid (SCM)—measured tone (oscillation frequency), dynamic stiffness, logarithmic decrement (elasticity), stress relaxation time, and creep. Each site was probed five times and values averaged. Repeated-measures ANOVA (Time × Side) with Bonferroni correction tested pre- to post-exercise changes; Pearson’s r examined associations with VO2max. Results: Significant Time effects (all p < 0.05) were observed for RF frequency (ηp2 = 0.226), RF creep (ηp2 = 0.144), AT stiffness (ηp2 ≈ 0.035), AT frequency (ηp2 = 0.035), and SCM frequency (ηp2 = 0.037). Post-exercise, right AT stiffness fell by 65 ± 14 N/m (p = 0.015), while left AT stiffness rose by 22 ± 9 N/m (p = 0.015). RF stiffness decreased by 28 ± 6 N/m (p < 0.001) and tone by 1.2 ± 0.3 Hz (p < 0.001), with creep (+0.08 ± 0.02; p < 0.001) and relaxation time (+1.5 ± 0.7 ms; p < 0.001) increasing. SCM tone declined by 0.8 ± 0.4 Hz (p = 0.010). Baseline RF properties—frequency (r = −0.597), stiffness (r = −0.59), relaxation time (r = 0.53), and creep (r = 0.48)—correlated moderately with VO2max (all p < 0.05). Conclusions: These findings suggest that viscoelastic adaptations to exhaustive aerobic exercise are tissue- and side-specific, and that rectus femoris viscoelastic properties may serve as potential indicators of endurance readiness. Full article
(This article belongs to the Special Issue Advances in Sport Physiology, Nutrition, and Metabolism)
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14 pages, 2712 KB  
Article
Research on Robust Adaptive Model Predictive Control Based on Vehicle State Uncertainty
by Yinping Li and Li Liu
World Electr. Veh. J. 2025, 16(5), 271; https://doi.org/10.3390/wevj16050271 - 14 May 2025
Cited by 1 | Viewed by 1280
Abstract
To address the performance degradation in model predictive control (MPC) under vehicle state uncertainties caused by external disturbances (e.g., crosswinds and tire cornering stiffness variations) and rigid constraint conflicts, we propose a robust MPC framework with adaptive weight adjustment and dynamic constraint relaxation. [...] Read more.
To address the performance degradation in model predictive control (MPC) under vehicle state uncertainties caused by external disturbances (e.g., crosswinds and tire cornering stiffness variations) and rigid constraint conflicts, we propose a robust MPC framework with adaptive weight adjustment and dynamic constraint relaxation. Traditional MPC methods often suffer from infeasibility or deteriorated tracking accuracies when handling model mismatches and disturbances. To overcome these limitations, three key innovations are introduced: a three-degree-of-freedom vehicle dynamic model integrated with recursive least squares-based online estimation of tire slip stiffness for real-time lateral force compensation; an adaptive weight adjustment mechanism that dynamically balances control energy consumption and tracking accuracy by tuning cost function weights based on real-time state errors; and a dynamic constraint relaxation strategy using slack variables with variable penalty terms to resolve infeasibility while suppressing excessive constraint violations. The proposed method is validated via ROS (noetic)–MATLAB2023 co-simulations under crosswind disturbances (0–3 m/s) and varying road conditions. The results show that the improved algorithm achieves a 13% faster response time (5.2 s vs. 6 s control cycles), a 15% higher minimum speed during cornering (2.98 m/s vs. 2.51 m/s), a 32% narrower lateral velocity fluctuation range ([−0.11, 0.22] m/s vs. [−0.19, 0.22] m/s), and reduced yaw rate oscillations ([−1.8, 2.8] rad/s vs. [−2.8, 2.5] rad/s) compared with a traditional fixed-weight MPC algorithm. These improvements lead to significant enhancements in trajectory tracking accuracy, dynamic response, and disturbance rejection, ensuring both safety and efficiency in autonomous vehicle control under complex uncertainties. The framework provides a practical solution for real-time applications in intelligent transportation systems. Full article
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13 pages, 3316 KB  
Article
Time Parameter Optimization for the Semiconductor Laser-Based Time-Delay Reservoir Computing System
by Qiudi Li, Yushuang Hou, Keqiang Li, Xiaoyu Guo, Chunxia Hu and Dianzuo Yue
Photonics 2025, 12(5), 455; https://doi.org/10.3390/photonics12050455 - 8 May 2025
Viewed by 665
Abstract
Time-delay reservoir computing (RC) systems, particularly those based on semiconductor lasers (SLs), have gained attention due to their low energy consumption, high response rates, and rich nonlinear dynamics. This work investigates the influence of key time parameters—virtual node interval (θ), delay [...] Read more.
Time-delay reservoir computing (RC) systems, particularly those based on semiconductor lasers (SLs), have gained attention due to their low energy consumption, high response rates, and rich nonlinear dynamics. This work investigates the influence of key time parameters—virtual node interval (θ), delay feedback (τ), and data injection period (T) on the performance of SL-based time-delay RC systems. Using the Santa Fe time series prediction task and memory capacity evaluation task, we analyze how these parameters affect prediction accuracy and memory capability. The results reveal that θ = 0.2Tro (where Tro is the relaxation oscillation period of the SLs) optimizes prediction performance, while θ = 0.5Tro maximizes memory capacity. Additionally, feedback delay τ significantly impacts system performance. Shorter τ values (e.g., τ = 0.54T) enhance prediction accuracy, whereas longer τ values (e.g., τ = 1.74T) improve memory capacity. These findings provide valuable insights for optimizing time-delay RC systems, enabling better task-specific performance and stability. Full article
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17 pages, 540 KB  
Article
Linear Stability of a Viscoelastic Liquid Film on an Oscillating Plane
by Jing Zhang, Quansheng Liu, Ruigang Zhang and Zhaodong Ding
Nanomaterials 2025, 15(8), 610; https://doi.org/10.3390/nano15080610 - 16 Apr 2025
Viewed by 555
Abstract
This paper investigates the linear stability of the liquid film of Oldroyd-B fluid on an oscillating plate. The time-dependent Orr–Sommerfeld boundary-value problem is formulated through the assumption of a normal modal solution and the introduction of the stream function, which is further transformed [...] Read more.
This paper investigates the linear stability of the liquid film of Oldroyd-B fluid on an oscillating plate. The time-dependent Orr–Sommerfeld boundary-value problem is formulated through the assumption of a normal modal solution and the introduction of the stream function, which is further transformed into the Floquet system. A long-wavelength expansion analysis is performed to derive the analytical solution of the Orr–Sommerfeld equation. The results indicate that long-wave instability occurs only within specific bandwidths related to the Ohnesorge number (Oh). Fixing the elasticity parameter (El) and increasing the relaxation-to-delay time ratio (λ˜) from 2 to 4 or fixing (λ˜) and increasing (El) from 0.001 to 0.01 decreases the number of unstable bandwidths while enhancing the intensity of unstable modes. Increasing the surface-tension-related parameter (ζ) from 0 to 100 suppresses the wave growth rate, stabilizing the system. Additionally, increasing (λ˜) from 2 to 4 reduces the maximum values of the coupling of viscoelastic, gravitational, and surface-tension forces, as well as the maximum value of the Floquet exponent, further stabilizing the system. These findings provide supplements to the theoretical research on the stability of viscoelastic fluids and also offer a scientific basis for engineering applications in multiple fields. Full article
(This article belongs to the Special Issue Trends and Prospects in Nanoscale Thin Films and Coatings)
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21 pages, 7692 KB  
Article
Enhanced DMA Test Procedure to Measure Viscoelastic Properties of Epoxy-Based Molding Compound: Multiple Oscillatory Strain Amplitudes and Monotonic Loading
by Sukrut Prashant Phansalkar, Roshith Mittakolu, Bongtae Han and Taehwa Kim
Micromachines 2025, 16(4), 384; https://doi.org/10.3390/mi16040384 - 27 Mar 2025
Cited by 1 | Viewed by 1317
Abstract
Dynamic mechanical analysis (DMA) is routinely practiced in the semiconductor industry to measure the viscoelastic properties of various thermosetting polymers. Modern commercial DMA test machines are highly-advanced systems which enable users to perform automatic testing and post-processing of the experimental data. When highly [...] Read more.
Dynamic mechanical analysis (DMA) is routinely practiced in the semiconductor industry to measure the viscoelastic properties of various thermosetting polymers. Modern commercial DMA test machines are highly-advanced systems which enable users to perform automatic testing and post-processing of the experimental data. When highly filled thermosets like epoxy-based molding compound (EMC) are tested, unique challenges are encountered during measurements due to the extremely large change in modulus over the testing temperature range. An advanced procedure is proposed to cope with these problems. The first part is the use of different oscillation strain amplitudes so that the variations in stress amplitudes across the testing domain remain consistent. The second part is the conducting of two monotonic tests at the lowest and highest temperatures to obtain the glassy modulus and equilibrium modulus, which can guide the master curve construction accurately. The results of the proposed procedure are presented. The relaxation modulus master curve is used to conduct a virtual testing to verify the accuracy of the generalized Maxwell model constants determined from the frequency data using the proposed procedure. Full article
(This article belongs to the Special Issue Advanced Packaging for Microsystem Applications, 3rd Edition)
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18 pages, 11051 KB  
Article
Methods for Designing High-Precision Relaxation Oscillator
by Zhibo Huang, Kunpeng Xu, Hongguang Dai, Zhanxia Wu, Xiaopeng Yu and Guoqiang Zhang
Micromachines 2025, 16(4), 364; https://doi.org/10.3390/mi16040364 - 22 Mar 2025
Cited by 1 | Viewed by 1118
Abstract
A novel low-power delay time cancellation (LPDTC) technique and a current ratio adjustment (CRA) method are proposed for designing high-precision relaxation oscillators. These methods effectively reduce the impacts of comparator delay time, offset voltage, and temperature-induced variations in resistors. To validate these methods, [...] Read more.
A novel low-power delay time cancellation (LPDTC) technique and a current ratio adjustment (CRA) method are proposed for designing high-precision relaxation oscillators. These methods effectively reduce the impacts of comparator delay time, offset voltage, and temperature-induced variations in resistors. To validate these methods, we have designed and simulated an 8 MHz open-loop relaxation oscillator using a 40 nm CMOS process. The oscillator, incorporating these advanced methods, achieves a line sensitivity of 0.38%/V and a temperature sensitivity of 43 ppm/°C over a temperature range of −40 °C to 125 °C. Full article
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12 pages, 2787 KB  
Article
Sub-Nanosecond, Room-Temperature, Mid-IR Fe:ZnSe Gain-Switched Laser: Experimental Characterization and Modeling
by Saugat Ghimire, Daniil Danilin, Dmitry Martyshkin, Vladimir Fedorov and Sergey Mirov
Photonics 2025, 12(3), 254; https://doi.org/10.3390/photonics12030254 - 12 Mar 2025
Cited by 1 | Viewed by 1695
Abstract
We present the modeling and experimental characterization of a room-temperature, sub-nanosecond, gain-switched (GS) Fe:ZnSe laser operating at 4.4–4.8 μm. As pump sources, we used a 2.79 µm Q-switched Cr:Er:YSGG laser with a pulse duration of 52 ns and the 2.98 μm idler of [...] Read more.
We present the modeling and experimental characterization of a room-temperature, sub-nanosecond, gain-switched (GS) Fe:ZnSe laser operating at 4.4–4.8 μm. As pump sources, we used a 2.79 µm Q-switched Cr:Er:YSGG laser with a pulse duration of 52 ns and the 2.98 μm idler of a Nd:YAG pumped KTA-OPO system with a pulse duration of 9 ns. The shortest pulse durations were measured to be 1.4 ns and 0.7 ns under excitation by the Cr:Er:YSGG laser and KTA-OPO system, respectively. The developed Fe:ZnSe laser model showed good agreement with the experimental results. Optimization of the laser parameters based on model simulations suggests that an Fe:ZnSe microchip laser configuration could be achieved with a pulse duration of ~250 ps and an efficiency of ~20%. Full article
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29 pages, 9619 KB  
Article
Rheological Properties of Polyethylene Color Masterbatches Containing Pigment RED 122 (2,9-Dimethylquinacridone) Modified by Silanes Using Pulverization Method
by Magdalena Kozłowska, Magdalena Lipińska and Michał Okraska
Polymers 2025, 17(5), 618; https://doi.org/10.3390/polym17050618 - 25 Feb 2025
Viewed by 1720
Abstract
Polyethylene color masterbatches containing pigment RED 122, 2,9-dimethylquinacridone, ((2,9-dimethyl-5,12-dihydroquinolino[2,3-b]acridine-7,14-dione) modified by the pulverization method in ball mills were obtained. As pigment-modifying agents, isobutyltrimethoxysilane IBTMS and octyltrietoxysilane OTES were used. The viscoelastic properties of the prepared masterbatches were investigated by using an oscillation rotational [...] Read more.
Polyethylene color masterbatches containing pigment RED 122, 2,9-dimethylquinacridone, ((2,9-dimethyl-5,12-dihydroquinolino[2,3-b]acridine-7,14-dione) modified by the pulverization method in ball mills were obtained. As pigment-modifying agents, isobutyltrimethoxysilane IBTMS and octyltrietoxysilane OTES were used. The viscoelastic properties of the prepared masterbatches were investigated by using an oscillation rotational rheometer. The impact of the 2 wt.% of coloring masterbatch on the rheological behavior of polyethylene during processing at 170 °C was analyzed. Storage shear modulus G′, loss shear modulus G″, complex viscosity η* and loss factor tan δ were analyzed. Modification prevents the agglomeration of modified pigment particles in the masterbatch, leading to a significant increase in the storage shear modulus G′, from 13.83 kPa (masterbatch containing pigment RED 122) to 58.74 kPa (pigment modified with 2 wt.% of IBTMS) and 49.67 kPa (pigment modified with 2 wt.% of OTES). The analysis of the continuous relaxation models showed that the modified pigment influenced the relaxation of melted polyethylene. The tendency of the silane-modified pigment to create its “own structure” in the polyethylene carrier via particle–particle interactions was estimated based on rotational tests at low and high shear rates. The larger area of viscosity loops was determined at 170 °C for the masterbatch containing 1 wt.% of OTES-modified pigment, 2574.44 Pas(1/s), as compared with the reference masterbatch, 464.88 Pas(1/s). The Carreau and Carreau–Yasuda viscosity models were applied to analyze the flow curve and the changes in viscosity as a function of the shear rate. After pigment modification, the zero shear viscosity µ0 of the mixtures of polyethylene/pigment masterbatch changed from 234.9 Pas (pigment RED 122) to 305.9 Pas (pigment modified with 1 wt.% of IBTMS). The influence of the modified pigments on the crystallization of polyethylene and its thermal stability was investigated. The temperatures of melting Tm were determined. Full article
(This article belongs to the Special Issue Advances in Rheology and Polymer Processing)
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18 pages, 5366 KB  
Article
Regenerative Structural Fatigue Testing with Digital Displacement Pump/Motors
by Win Rampen, Marek J. Munko, Sergio Lopez Dubon and Fergus Cuthill
Actuators 2025, 14(3), 103; https://doi.org/10.3390/act14030103 - 20 Feb 2025
Viewed by 1097
Abstract
Historically, a large fraction of fatigue testing of both components and structures has been performed using hydraulic actuators. These are typically driven by servo-valves, which are in themselves very inefficient. But, as most tests involve elastically stressing mechanical components, a lot of stored [...] Read more.
Historically, a large fraction of fatigue testing of both components and structures has been performed using hydraulic actuators. These are typically driven by servo-valves, which are in themselves very inefficient. But, as most tests involve elastically stressing mechanical components, a lot of stored energy could be recovered. Unfortunately, servo-valves are not regenerative—simply metering out fluid in order to relax the system prior to the start of the next cycle. There is much to be gained with a more intelligently controlled system. The FastBlade facility in Scotland uses a new type of regenerative test hydraulics. Digital displacement pump/motors (DDPMs), originated by Artemis Intelligent Power, now Danfoss Scotland, are used to load and unload the test structure directly via hydraulic rams. The DDPMs are driven by induction motors supplied by three-phase frequency converters, each with a very loose speed correction target, such that they can speed up or slow down according to the instantaneous torque exerted by the load. The rotating assembly of the induction motor and DDPM is designed to have sufficient inertia so as to function as a kinetic energy storage flywheel. The loading energy is then cyclically transferred between the rotating inertia of the motor/DDPM and the spring energy in the test structure. The electric motor provides sufficient energy to maintain the target average cyclical shaft speed of the DDPM whilst the bulk of the system energy oscillates between the two storage mechanisms. Initial tests (at low load) suggest that this technique requires only 30% of the energy previously needed. FastBlade is a unique facility built by the University of Edinburgh and Babcock, with support from the UK EPSRC, conceived as a means of testing and certifying turbine blades for marine current turbines. However, this approach can be used in any cyclical application where elastic energy is stored. Full article
(This article belongs to the Special Issue Actuation and Control in Digital Fluid Power)
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