Search Results (346)

Water availability is a major constraint on socioeconomic development in northeastern Mexico, highlighting the need for effective water resource planning that accounts for the variability and extremes of precipitation. In this study, seasonal precipitation reconstructions were developed using tree-ring chronologies from spruce species (Picea spp.). A representative chronology for Picea mexicana Martínez was developed from two populations and spans the period 1786–2020, while a chronology for Picea martinezii T.F. Patterson was established from three populations covering 1746–2020. Both species exhibited significant positive correlations with January–May precipitation (r = 0.65 and 0.71, respectively; p < 0.01) and negative correlations with maximum temperature over the same period (r = −0.52 and −0.59, respectively). Two January–May precipitation reconstructions were produced for periods with adequate sample depth (EPS > 0.85): 1851–2020 for P. mexicana and 1821–2020 for P. martinezii. Both reconstructions revealed pronounced interannual variability, with recurrent droughts and persistently dry conditions, particularly evident in the P. mexicana series. Spatial correlation analyses indicated a historical link between reconstructed precipitation and the El Niño–Southern Oscillation (ENSO). These results highlight the value of spruce species for dendroclimatic reconstruction and their sensitivity to precipitation variability, especially as rising maximum temperatures may compromise their persistence in the Sierra Madre Oriental. Full article

Capacitive micromachined ultrasonic transducers (CMUTs) have been developed for air-coupled applications to address key challenges such as noise, prolonged ringing, and side-lobe interference. This study introduces an optimized CMUT design that leverages the squeeze-film damping effect to achieve a low-quality factor, enhancing resolution and temporal precision for imaging as one of the suggested airborne application. The device was fabricated using the PolyMUMPs process, ensuring high structural accuracy and consistency. Finite element analysis (FEA) simulations validated the optimized parameters, demonstrating improved displacement, reduced side-lobe artifacts, and sharper main lobes for superior imaging performance. Experimental validation, including Laser Doppler Vibrometer (LDV) measurements of membrane displacement and mode shapes, along with ring oscillation tests to assess Q-factor and signal decay, confirmed the device’s reliability and consistency across four CMUT arrays. Additionally, this study explores the implementation of multi-frequency CMUT arrays, enhancing imaging versatility across different air-coupled applications. By integrating multiple frequency bands, the proposed CMUTs enable adaptable imaging focus, improving their suitability for diverse diagnostic scenarios. These advancements highlight the potential of the proposed design to deliver a superior performance for airborne applications, paving the way for its integration into advanced diagnostic systems. Full article

We present the first implementation of an FPGA-based PUF that leverages the usually contradictory requirements of stability and response time. Many state-of-the-art implementations of PUFs are either slow with a low error rate, like the ring oscillator-PUF, or fast with a higher error rate, like the arbiter-PUF. The presented implementation of an eye-opening PUF uses the phase-integrating effect of a ring oscillator to realize the shortest possible response for the required stability of the readout. This principle also allows for new automatic detection of unstable bits based on counting the number of oscillations required until an arbitration is conducted. This first implementation of an eye-opening PUF reduces the bit error rate to a number under our measurement limits, while the readout time is simultaneously kept as low as ≤1.54 μs, with an average of 0.85 μs. In addition, environmental temperature changes are evaluated, and methods for limiting these effects are discussed. Full article

The objective of this study was to identify surface geometric deviations that may adversely affect the operational properties of bearings, including vibration, noise, and service life. A comprehensive prediction model is presented that combines a fundamental trend expressed by a power function with periodic oscillations, whose influence gradually diminishes with exponential decay. The model was calibrated using the experimental data obtained from 17 industrial RA-608-338 rolling bearing rings manufactured from high-carbon, low-alloy 100Cr6 steel. An excellent goodness-of-fit (R² exceeding 0.98) and minimal root-mean-square error (RMSE) were achieved. The proposed procedure provides a clear physical interpretation of the model’s subcomponents, while facilitating straightforward implementation in real production processes for continuous quality control and predictive maintenance purposes. This paper also includes a detailed description of the methodology, data processing, experimental results, comparison of multiple model variants, interactive visualization of the results on a logarithmic scale, and recommendations for practical application. Full article

Traditional cryptographic systems face critical vulnerabilities posed by the rapid advancement of quantum computing, particularly concerning key exchange mechanisms and the quality of entropy sources for random number generation. To address these challenges, this paper proposes a multi-layered, quantum-resistant hybrid cryptographic architecture. First, to ensure robust data confidentiality and secure key establishment, the architecture employs AES-256 (Advanced Encryption Standard-256) for data encryption and utilizes the Kyber Key Encapsulation Mechanism (KEM), which is based on the Learning With Errors (LWE) problem, for secure key exchange. Second, to further bolster overall security by establishing a high-quality cryptographic foundation, we design a TRNG (true random number generator) system based on a multi-level Ring Oscillator (RO) architecture (employing 5, 7, 9, and 11 inverter stages), which provides a reliable and high-quality entropy source. Third, to enable intelligent and adaptive security management, we introduce FA-Kyber (Flow-Adaptive Kyber), a dual-trigger key exchange framework facilitating dynamic key management strategies. Experimental evaluations demonstrate that our implementation exhibits robust performance, achieving an encrypted data transmission throughput of over 550 Mbps with an average end-to-end latency of only 3.14 ms and a key exchange success rate of 99.99% under various network conditions. The system exhibits excellent stability under network congestion, maintaining 86% of baseline throughput under moderate stress, while adaptively increasing the key rotation frequency to enhance security. This comprehensive approach strikes an optimal balance between performance and post-quantum resilience for sensitive communications. Full article

This study investigates the influence of chirality on the dynamic susceptibility of concentric nanotori via micromagnetic simulations. The aim is to analyze the ferromagnetic resonance characteristics of coupled nanotori structures and compare them across various ring separation distances, thus providing an insight into how vortex configurations with identical or differing chiralities affect their dynamic properties. We analyze the energetic differences between the two vortex configurations and find them to be negligible; however, these minor differences suffice to explain the significant discrepancies in the demagnetization field observed between the nanotori. We examine the dynamic susceptibility spectrum and the spatial localization of the ferromagnetic resonance modes for different nanotori separations. Our findings demonstrate that the resonant oscillation frequencies are significantly influenced by the magnetostatic interactions between the nanotori, which can be effectively modulated by varying the distance between them. Furthermore, for smaller separations, the frequency peaks in the dynamic susceptibility markedly diverge between the two vortex configurations, demonstrating that the observed differences in the demagnetization field between the rings strongly influence the frequency response. In summary, our results indicate that both the inter-ring distance and the vortex configuration play a crucial role in determining the frequency response of the system. Full article

Understanding how regional and local climate variability drive radial growth in trees is necessary to assess the climate-warming mitigation potential of forests. However, tree species occurring in the same region differently respond to climate variability, including climate extremes such as droughts, depending on soil–moisture gradients (hydrological niche). We analyzed a tree-ring network built in a mountainous area (Sierra de Gredos, central Spain) to compare climate–growth responses between species and sites located along soil–moisture gradients. Tree-ring methods were applied to six tree species, and sampled in twelve sites, including conifers (Pinus pinaster) and broadleaves (Quercus pyrenaica, Quercus robur, Quercus ilex, Celtis australis, and Prunus lusitanica). Series of growth indices were correlated with climate variables and climate indices (NAO, North Atlantic Oscillation). The radial growth of most species was enhanced by high growing-season precipitation, linked to negative NAO phases. The influence of precipitation on growth variability strengthened as site elevation decreased, particularly in the case of C. australis and oak species. The topographical modulation of climate–growth couplings indicates that the hydrological niche drives species responses to water shortage. Tree-ring data could be used to refine time-dependent hydrological niches. Full article

We investigate 3D quantum dot–double quantum ring structures of GaAs/Al_0.3Ga_0.7As submitted to the combined action of a non-resonant intense laser and an axial magnetic field. We study three representative geometries with the dot height larger, comparable or lower than the ring height. The intense laser field can change the confinement potential of the dot–double ring into dot–triple-ring or –multiple-ring potentials. Also, depending on the dot height, it increases/decreases the absorption of the structure. Under magnetic field, the energy spectra display Aharonov–Bohm oscillations characteristic of a single effective ring covering almost both rings, with a period controlled by the dot height. For large and medium dot height, the magnetic field lowers the absorption and leads to splitting and/or the apparition of two peaks, one that goes to red and the other to blue. In the presence of both fields, the spectra show different characteristics. The dot height and the external fields are thus proved to be efficient tools in controlling the absorption spectra, a useful feature in designing dot–double ring-based devices. Full article

The Ring Oscillator Physical Unclonable Function (RO-PUF) is a hardware security innovation that creates a secure and distinct identifier by utilizing the special physical properties of ring oscillators. Their unique response, low hardware overhead, and difficulty of reproduction are some of the security benefits that make them valuable in safe authentication systems. Numerous developments, such as temperature adjustment methods, aging mitigation, and better architecture and layout, have been created to increase its security, dependability, and efficiency. However, achieving the sacrifice metric makes it challenging to implement with additional complex circuits. This work focuses on stability improvement in terms of the reliability of the RO-PUF in enhanced challenge and response (CRP) by exploiting existing on-chip hard processors. This work establishes only ROs and their counters inside the chip. The built-in microprocessor performs the remaining process using the intermediary process of a Q factor and new frequency mapping. As a result, the reliability improves significantly to 95.8% compared to previous methods. The proper use of resources due to the limitation of on-chip resources has been emphasized by considering that a hard processor exists inside the new FPGA chip. Full article

This work presents a current-controlled CMOS ring oscillator (CCRO) optimized for ultra-low-voltage applications in next-generation energy-constrained systems. Leveraging bulk voltage tuning in 22 nm FDSOI differential inverter stages, the topology enables frequency adjustment while operating MOSFETs in the subthreshold region—critical for minimizing power in sub-1 V environments. Simulations at 0.4 V supply demonstrate robust performance: a three-stage oscillator achieves a 537–800 MHz tuning range with bias current (I_BIAS) modulation from 30–130 nA, while a four-stage configuration spans 388–587 MHz. At 70 nA I_BIAS, the three-stage design delivers a nominal frequency of 666.8 MHz with just 10.23 µW power dissipation, underscoring its suitability for ultra-low-power IoT and biomedical applications. The oscillator’s linear frequency sensitivity (2.63 MHz/nA) allows precise, dynamic control over performance–power tradeoffs. To address diverse application needs, the design integrates three tunability mechanisms: programmable capacitor arrays for coarse frequency adjustments, configurable stage counts (three- or four-stage topologies), and supply voltage scaling. This multi-modal approach extends the operational range to 1 MHz–1 GHz, ensuring compatibility with low-speed sensor interfaces and high-speed edge-computing tasks. The CCRO’s subthreshold operation at 0.4 V—coupled with nanoampere-level current consumption—makes it uniquely suited for battery-less systems, wearable health monitors, and implantable medical devices where energy efficiency and adaptive clocking are paramount. By eliminating traditional voltage-controlled oscillators’ complexity, this topology offers a compact, scalable solution for emerging ultra-low-power technologies. Full article

Understanding precipitation changes over a long period of time can provide valuable insights into global climate change. Taking the forest–steppe ecotone of North China as the research area, based on the tree ring width index of Carya cathayensis Sarg (Carya cathayensis), the relationship between tree growth and climate factors is analyzed, and the annual precipitation is reconstructed from data from the nearest five weather stations from AD 1540 to 2019. The results show that the growth of trees was affected by the changes in precipitation. The precipitation was divided into three dry periods and three wet periods over 480 years, based on wavelet analysis. There were 328 years of precipitation within the mean plus or minus one standard deviation (SD) (accounting for 68.3% of 480 years), indicating that relatively stable climate conditions exist in the study area, which has become one of the main agricultural areas in China. Each period lasted 2–7 years according to the multi-taper method, indicating that precipitation change was closely related to the El Niño–Southern Oscillation (ENSO) on a short time scale and affected by the Atlantic Multidecadal Oscillation (AMO) on a medium time scale during the period of 60–80 years based on wavelet analysis. Full article

The residual magnetism of the iron core of power transformers can cause an excitation inrush current, posing a threat to the safe and stable operation of the power grid. This paper proposes a transformer remanence measurement method based on a demagnetization hysteresis loop to address the problems of large errors, complex operation, and poor universality in existing remanence measurement methods. This method is designed for off-grid transformers to avoid potential interference to the power grid caused by current pulses during the measurement process. This method constructs an RLC oscillation circuit that utilizes capacitor energy storage and iron core magnetic field energy conversion, combined with the dynamic characteristics of hysteresis loops, to achieve accurate measurement of residual magnetism and synchronous demagnetization. The effectiveness of this method has been verified through residual magnetism measurement experiments on ring transformers and large converter transformers, and it can be applied in specific engineering practice operations. Theoretical analysis shows that the charging range of energy storage capacitors is affected by the hysteresis characteristics of the iron core and the saturation magnetic flux, and the residual magnetization value can be directly calculated based on the difference in the intersection point of the longitudinal axis of the demagnetization hysteresis loop. Simulation and experimental results show that the measurement error of the proposed method is less than 5%—significantly better than traditional methods. This method does not require complex control strategies, has high precision and efficiency, and can provide reliable technical support for residual magnetism detection and suppression of off-grid power transformers. Full article

Oscillator networks display intricate synchronization patterns. Determining their stability typically requires incorporating the symmetries of the network coupling. Going beyond analyses that appeal only to a network’s automorphism group, we explore synchronization patterns that emerge from the phase-shift invariance of the dynamical equations and symmetries in the nodes. We show that these nonstructural symmetries simplify stability calculations. We analyze a ring-network of phase–amplitude oscillators that exhibits a “decoupled” state in which physically-coupled nodes appear to act independently due to emergent cancellations in the equations of dynamical evolution. We establish that this state can be linearly stable for a ring of phase–amplitude oscillators, but not for a ring of phase-only oscillators that otherwise require explicit long-range, nonpairwise, or nonphase coupling. In short, amplitude–phase interactions are key to stable synchronization at a distance. Full article

The design of heat and drag reduction systems for hypersonic vehicles has garnered widespread global attention. In this study, the Navier–Stokes equations and the SST k-ω turbulence model are employed to establish a simulation model for heat and drag reduction induced by a forward-facing cavity. The numerical methods are validated using existing experimental results. The oscillation characteristics of the bow shock wave at the head and the shock inside the cavity in hypersonic flows are investigated. The heat and drag reduction mechanisms of the forward-facing cavity are discussed. The effects of the diameter and depth of the cavity on drag and heat reduction are comprehensively analyzed. The obtained results show that a reduction in drag and heat is achieved when a forward-facing cavity is added to the vehicle. The main reasons for this heat reduction are the cold ring mechanism and the energy conversion mechanism. The size of the cold ring is significantly affected by the cavity diameter, whereas the energy conversion mechanism is more sensitive to variations in diameter. The maximum reduction in heat load is 2.2%, and the maximum reduction in the Stanton number is 25.3%. Increases in both diameter and depth enhance drag reduction, achieving an average drag reduction of approximately 1.65%. Full article

Although the harmonic oscillator model has found wide use in physics and chemistry, there are more interesting potential energy functions (PEFs) which can tell us a great deal about molecular structure and energetics. In the present work, we show that for selected systems simple one- and two-dimensional potential functions can be used to very accurately fit detailed spectroscopic data and provide extensive additional information. Results for molecular inversion, ring puckering, the anomeric effect, pseudorotation, triplet-state puckering, internal rotation, and π-type hydrogen bonding in ground and excited electronic states are presented. Full article