Search Results (536)

In this study, a phase-generated carrier (PGC) demodulation algorithm combined with the extended Kalman filter (EKF) algorithm based on an electro-optic modulator (EOM) is proposed, which can achieve nonlinear distortion (such as modulation depth drift and carrier phase delay) suppression for high-frequency phase carrier modulation. The improved algorithm is implemented on a field-programmable gate array (FPGA) hardware platform. The experimental results by the PGC-EKF method show that total harmonic distortion (THD) decreases from −32.61 to −54.51 dB, and SINAD increases from 32.59 to 47.86 dB, compared to the traditional PGC-Arctan method. This indicates that the PGC-EKF demodulation algorithm proposed in this paper can be widely used in many important fields such as hydrophone, transformer, and ultrasound signal detection. Full article

This study delves into the dynamic behavior of ultra-high-speed rotor systems underpinned by helium hydrostatic gas bearings, with a focus on the impact of rotational velocity on system performance. We have formulated an integrative dynamic model that harmonizes the rotor motion equation with the transient Reynolds equation. This model has been meticulously resolved via the Finite Difference Method (FDM) and the Wilson-Θ technique. Our findings unveil intricate nonlinear dynamics, including 2T-periodic and multi-periodic oscillations, and underscore the pivotal role of first-order temporal fluctuations, which account for over 20% of the transient pressure at rotational speeds exceeding 95.0 krpm. Further, we have executed empirical studies to evaluate the system’s performance in practical settings. It is observed that when the ratio of low-frequency to fundamental frequency approaches 0.3 and the amplitude ratio exceeds 3, the vigilant monitoring of system stability and reliability is imperative. Collective insights from both computational simulations and experimental studies have enriched our understanding of the dynamic attributes of ultra-high-speed rotor systems. These revelations are crucial for the advancement of more efficacious and resilient rotor systems designed for high-speed applications. Full article

External-rotor dual-armature flux-switching PM (ER-DA-FSPM) machines have high torque density and decent fault tolerance, making them promising candidates for in-wheel machine applications in electric vehicles. The torque output and optimal design parameters of ER-DA-FSPM machines are affected by the stator/rotor torque ratio, which is the focus of this paper. Firstly, this paper analyzes airgap flux density harmonics of ER-DA-FSPM to provide a clear insight into the torque-generation mechanism. Then, this paper investigates the influence of torque ratio on average torque under the same copper loss. It is found that the average torque decreases with torque ratio increasing due to the reduction of the positive torque component generated by the sixth airgap field harmonics and the rise in the negative torque component from the eighth harmonics. Moreover, this paper also provides the optimal parameter recommendation to guide the machine design. The split ratio should increase, and the arc of PMs should decrease for a larger torque ratio, whilst the other parameters are hardly influenced. Next, this paper makes a comparison among the ER-DA-FSPM machine, external rotor flux-switching PM (ER-FSPM) machine, and surface-mounted PM (ER-SPM) machines. It shows that the ER-DA-FSPM machine, with the torque ratio being 2, can lead to a much larger total torque. In addition, in the event of rotor winding failure, which is more possible due to the existence of slip rings than stator winding failure, the stator can still provide an average torque larger than that of ER-SPM machine and 92.0% that of the ER-FSPM machine, respectively. Finally, the theoretical analysis is verified by the experiments. Full article

Proportions and canons of the human body have always been an area of research mainly through art, architecture, or construction, and today, they have a significant application in product design. Research confirms that body height in most cases corresponds to the canon (head–body ratio) of 7.5 to 8 head lengths. This paper investigates the ratio of the head length (HL) to the total body height (BH, stature) of kindergarten and school-aged children, aiming to define the children’s canon inspired by the idea of the harmonic circle theory and the biomechanical model. The data were collected from 1307 children (male 676, female 631) aged 2 to 16 years in the cities of Zagreb (Croatia), Sofia (Bulgaria), and Skopje (North Macedonia). A generalized ESD test (alpha-level 0.10) and Turkey’s 1977 test were used in order to detect outliers in distributions of heights and in the distribution of ratios. Statistical significance was set at 0.05, all p values were two-sided, and the MedCalc statistical tool (version 20.110) was used. The results confirm that canonical changes follow the historical research of artists throughout the centuries, but that they change according to contemporary secular trends in children’s growth and cover HL/BH canons from 5.59 and 5.72 (2-year-old girls and boys) to 7.50 and 7.60 (15-year-old boys and girls) depending on age and gender. HL/BH ratio was significantly higher among female examinees in all age groups where difference was significant (Student’s t test, p < 0.02). In conclusion, such a calculation based on the canon is important for interdisciplinary professions. Creating an anthropological–biomechanical model based on canons, instead of time-consuming measurement, could significantly simplify the long-term collection of anthropometric data used for designing children’s products. Future detailed research is proposed. Full article

The series-type 12-pulse rectifier generates a large amount of harmonics in the AC side current due to the strong nonlinearity of its rectifying diodes, causing serious harmonic pollution to the power grid. This article proposes a series 36-pulse rectifier based on a DC side dual passive frequency-doubling circuit to suppress the AC side current harmonics of a 12-pulse rectifier. The rectifier uses two symmetrical passive pulse multiplication circuits to regulate the circulation in the DC side circuit, increasing the output voltage and current state of the rectifier bridge, thereby increasing the number of pulses in the rectifier from 12 times to 36 times. Firstly, the working principle of the rectifier and the working mode of the dual passive frequency-doubling circuit were analyzed. Secondly, the harmonic suppression mechanism of the rectifier input current was revealed, and the frequency-doubling characteristics of the load voltage were analyzed. Finally, the correctness of the theoretical analysis was verified through a semi-physical platform. The verification and comparison results show that under the optimal conditions of the injecting transformer turns ratio, the DPPC can not only reduce the THD value of the input current by about 1/3 (from 14.87% to 4.78%) but can also increase the fluctuation frequency of the load voltage by 3 times (from 12 to 36), while improving the power quality of the AC/DC side rectifier and achieving the low harmonic operation of the rectifier. The proposed 36-pulse rectifier can effectively suppress harmonics; it has the advantages of simple structure, strong robustness, and high output voltage gain, and it is suitable for medium-voltage and high-voltage high-power rectification applications. Full article

This paper introduces a complete real-time algorithm, where the chatter is detected and eliminated by spindle speed manipulation via the chatter energy feedback calculated from the axis encoder measurement. The proposed method does not require profound knowledge of the machining dynamics; instead, the entire algorithm exploits the fact that milling vibrations consist of forced vibrations at spindle speed harmonics and chatter vibrations that are close to one of the natural modes, with sidebands which are spread at the multiples of spindle speed frequency above and below the chatter frequency. The developed algorithm is able to identify the amplitude, phase and frequency of all the harmonics constituting the periodic forced and chatter vibrations. The key challenge is to select dominant chatter frequencies for the calculation of a robust and accurate chatter energy ratio feedback; this is achieved by utilizing the frequency estimation variance of EKF as a novel chatter indicator. Based on the chatter energy ratio feedback, the controller overrides the spindle speed in order to suppress the chatter energy below a particular threshold value. The varying spindle speed challenge is handled by updating the state transition matrices of the Kalman filters and real-time calculation of the band-pass filter coefficients, based on the derived discrete time transfer functions. The developed algorithm is tested on a Deckel FP5cc CNC which is in-house retrofitted and has a PC-based controller for the real-time application of the proposed algorithm. It is shown that the real-time chatter frequency and amplitude estimates are compatible with off-line FFT analysis, and chatter can be successfully eliminated by energy feedback. Full article

To explore the potential application of concrete-filled double-skin steel tubular (CFDST) structures in wind turbine towers, this study carried out wind tunnel tests to explore the aerodynamic behavior of CFDST tower-based wind turbine systems. Two scaled models including traditional steel tower-based and CFDST tower-based wind turbine systems were designed and tested in the field of typhoons. Then, the vibration characteristics in both the downwind and crosswind directions were systematically investigated, in terms of acceleration and displacement response, motion trajectory, dynamic characteristics, etc. The findings demonstrate that CFDST structures can have significantly improved performance against both blade harmonic excitation and external environmental excitation. Compared to traditional steel towers, CFDST towers exhibit a substantial reduction in aerodynamic response. In particular, the reduction in the RMS value can be over five times in the resonance case and 457.69% in the non-resonance case. The CFDST towers predominantly exhibited converged motion trajectory and concentrated on lower vibration modes. The energy dissipation capability was remarkably enhanced, with the damping ratio increasing up to 40.98%. Overall, it was experimentally demonstrated that CFDST towers can efficiently address the dynamic problems of large-scale wind turbine towers in engineering. Full article

Piezoelectric c-axis oriented zinc oxide (ZnO) thin films, from 1.8 up to 6.6 µm thick, have been grown by the radio frequency magnetron sputtering technique onto fused silica substrates. A delay line consisting of two interdigital transducers (IDTs) with wavelength λ = 80 µm was photolithographically implemented onto the surface of the ZnO layers. Due to the IDTs’ split-finger configuration and metallization ratio (0.5), the propagation of the fundamental, third, and ninth harmonic Rayleigh waves is excited; also, three leaky surface acoustic waves (SAWs) were detected travelling at a velocity close to that of the longitudinal bulk wave in SiO₂. The acoustic waves’ propagation in ZnO/fused silica was simulated by using the 2D finite-element method (FEM) technique to identify the nature of the experimentally detected waves. It turned out that, in addition to the fundamental and harmonic Rayleigh waves, high-frequency leaky surface waves are also excited by the harmonic wavelengths; such modes are identified as Sezawa waves under the cut-off, hereafter named leaky Sezawa (LS). The velocities of all the modes was found to be in good agreement with the theoretically calculated values. The existence of a low-loss region in the attenuation vs. layer thickness curve for the Sezawa wave below the cut-off was theoretically predicted and experimentally assessed. Full article

Immunization through vaccines among children has contributed to improved childhood survival and health outcomes globally. However, vaccine coverage among children is unevenly distributed across settings and populations. The measurement of inequalities is essential for understanding gaps in vaccine coverage affecting certain sub-populations and monitoring progress towards achieving equity. Our study aimed to characterize the methods of reporting inequalities in childhood vaccine coverage, inclusive of the settings, data source types, analytical methods, and reporting modalities used to quantify and communicate inequality. We conducted a scoping review of publications in academic journals which included analyses of inequalities in vaccination among children. Literature searches were conducted in PubMed and Web of Science and included relevant articles published between 8 December 2013 and 7 December 2023. Overall, 242 publications were identified, including 204 assessing inequalities in a single country and 38 assessing inequalities across more than one country. We observed that analyses on inequalities in childhood vaccine coverage rely heavily on Demographic Health Survey (DHS) or Multiple Indicator Cluster Surveys (MICS) data (39.3%), and papers leveraging these data had increased in the last decade. Additionally, about half of the single-country studies were conducted in low- and middle-income countries. We found that few studies analyzed and reported inequalities using summary measures of health inequality and largely used the odds ratio resulting from logistic regression models for analyses. The most analyzed dimensions of inequality were economic status and maternal education, and the most common vaccine outcome indicator was full vaccination with the recommended vaccine schedule. However, the definition and construction of both dimensions of inequality and vaccine coverage measures varied across studies, and a variety of approaches were used to study inequalities in vaccine coverage across contexts. Overall, harmonizing methods for selecting and categorizing dimensions of inequalities as well as methods for analyzing and reporting inequalities can improve our ability to assess the magnitude and patterns of inequality in vaccine coverage and compare those inequalities across settings and time. Full article

Background/Objectives: Tracheoesophageal voice is the most commonly used voice rehabilitation technique after a total laryngectomy. The placement of the tracheoesophageal prosthesis can be performed at the same time as the total laryngectomy (primary placement) or in a second procedure after surgery (secondary placement). The purpose of this study is to analyze the substitution voice in patients with a tracheoesophageal prosthesis, considering the influence of radiotherapy and timing of prosthesis placement (primary or secondary) on voice quality. Methods: A retrospective analysis was conducted of all patients who received a tracheoesophageal phonatory prosthesis after a total laryngectomy was performed. We assessed whether patients received radiotherapy and whether they had a primary or secondary tracheoesophageal prosthesis. For the voice analysis, maximum phonation time (MPT), INFVo, SECEL, AVQI, CPPS, harmonic to noise ratio (HNR), unvoiced fraction (UVF), and number of voice breaks (NVB) were evaluated. Results: A total of 15 patients (14 males and 1 female) with a mean age of 71.8 years (SD ± 7.5) were enrolled. Eight had a primary prosthesis placement and five did not receive radiotherapy. INFVo parameters I and Vo were higher in patients with a primary placement of the phonatory prosthesis (p = 0.046 and p = 0.047). Patients who received the prosthesis secondarily had a higher mean CPPS and lower mean AVQI. Conclusions: A secondary placement of the prostheses seems to result in a minimal advantage in voice quality compared to a primary placement. Radiation therapy, on the other hand, has no effect on voice quality, according to these preliminary data. Full article

Low serum vitamin D levels have been associated with a variety of health conditions which has led the medical community but also the general population to evaluate vitamin D status quite liberally. Nevertheless, there remain questions about the efficacy and cost-effectiveness of such a broad and untargeted approach. This review therefore aims to summarize the current evidence and recommendations on when and how to evaluate vitamin D status in human health and disease. For the general population, most guidelines do not recommend universal screening but suggest a targeted approach in populations at risk. Also, some guidelines do not even recommend evaluating vitamin D status when vitamin D substitution is indicated anyway, such as in children or patients receiving anti-osteoporosis drugs. In those guidelines that recommend the screening of vitamin D status, serum 25(OH)D levels are universally proposed as the preferred screening tool. However, little attention is given to analytical considerations and almost no guidelines discuss the timing and frequency of screening. Finally, there is the known variability in diagnostic thresholds for defining vitamin D insufficiency and deficiency. Overall, the existing guidelines on the evaluation of vitamin D status differ broadly in screening strategy and screening implementation, and none of these guidelines discusses alternative screening modes, for instance, the vitamin metabolic ratio. Efforts to harmonize these different guidelines are needed to enhance their efficacy and cost-effectiveness. Full article

The active wave absorption method has been widely employed in numerical wave tanks. The wave absorption performance of active wave absorption methods is investigated within a numerical wave tank based on a lattice Boltzmann method. Specifically, two active wave absorption methods—the classical shallow water method and the extended range method—are compared. By analyzing the contributions of free and bound components in the harmonics of the reflected wave to the reflection coefficient, we found that the extended-range method is more effective than the shallow-water method in absorbing the reflection of the primary harmonic. Moreover, a wave absorption performance index is proposed to carry out rapid evaluation of active wave absorption method performance without resorting to numerical simulations. Our findings indicate that the performance index ratio of two active wave absorption methods closely mirrored their reflection coefficient ratio. Notably, the extended-range method significantly reduces the performance index in both shallow and deep waters, exhibiting superior active absorption performance within the lattice Boltzmann method-based numerical wave tank context compared to the shallow-water method. Full article

A new photonic scheme is proposed for the generation of a frequency 16-tupling millimeter wave (mm-wave) signal, based on four cascaded polarization modulators (PolMs). Firstly, through the precise control of these four PolMs, odd harmonics can be effectively suppressed sequentially. Next, combined with the modulation index of the PolMs, only the pure ± 8th-order optical harmonics are retained and enter the photodetector to beat the frequency. After multiple rounds of detailed, mathematical formula derivation and computer simulation, the accuracy and advantages of the proposed solution can be demonstrated. As a result, a 160 GHz mm-wave signal is obtained, which is produced from a 10 GHz radio frequency (RF) signal. By properly setting the modulation index and the angle of three phase differences, the optical suppression ratio (OSSR) and the radio frequency suppression ratio (RFSSR) of the acquired signal are 64.21 dB and 60.99 dB, respectively. Further, the impact of the variables on the OSSR and the RFSSR are analyzed and discussed. Full article

This paper investigates the influence of soil with finite depth on the vibrational behavior of a multi-span continuous beam resting on an elastic foundation. The simplified model of the Timoshenko beam supported on soil with finite depth is established, introducing the foundation displacement decay function. The numerical solution of the continuous beam’s vibration response on the elastic foundation is obtained by using the transfer matrix method (TMM) and fourth-order Runge-Kutta method (RK4). Taking a two-span continuous beam as an illustrative example, the validity of the calculation theory is validated by comparing it with the outcomes obtained from the finite element method (FEM). Utilizing numerical computation and parametric analysis, the vibration response of continuous beams is evaluated in terms of its influence by various factors such as soil thickness, viscous damping coefficient of the soil, subgrade reaction coefficient, and span ratio. The findings indicate that the inertial motion of the soil with a finite depth significantly reduces the continuous beam’s inherent frequency and enhances the structure’s resonance effect. The rise of the subgrade response coefficient increases the system’s resonant frequency while decreasing the displacement response amplitude. The ratio between the adjacent spans determines the effect of beam span vibration energy transfer to adjacent spans. In addition, compared with the span directly excited by a concentrated harmonic load, the impact of soil thickness, subgrade reaction coefficient, and viscous damping, the coefficient of the soil is more significant on the indirect influence span of a continuous beam. Full article

This paper proposes a method that combines window functions with compressed sensing for the detection of ultra-high harmonics in the frequency range of 2–150 kHz. By analyzing the sparsity of the signal, the Bruckmann window function, which is most suitable for the compressed sensing reconstruction process and the characteristics of ultra-high harmonics, is selected. Simulations indicate that, compared to existing methods, the proposed algorithm based on the fusion of the Bruckmann window and compressed sensing achieves a sparser post-observation signal with reduced fluctuations. The robustness and anti-interference capabilities are enhanced, while the harmonic detection accuracy and signal reconstruction performance are significantly improved. The reconstruction error reaches 4.15 × 10⁻⁶, the mean squared error percentage (MSE) reaches 4.13 × 10⁻⁶, and the signal-to-noise ratio (SNR) is as high as 97.69 dB, marking an increase of 54.11%. This study provides a new theoretical and methodological approach for the analysis and processing of ultra-high harmonics caused by a high proportion of power electronic devices. Full article