Phase Frequency Research Articles

Modeling Thermal Impedance of IGBT Devices Based on Fractional Calculus Techniques

The thermal impedance characteristics of insulated gate bipolar transistor (IGBT) modules are critical for the thermal management and design of electronic devices. This paper proposes a fractional-order equivalent thermal impedance model, which is inspired by the correlation between multi-time-scale dissipation characteristics of heat conduction processes and fractional calculus. The fractional-order equivalent thermal impedance model is derived based on the connection between fractional-order calculus and the Foster thermal network model in mathematical operations, with only two parameters to be identified: heat capacity C and fractional order α. Moreover, this paper provides a parameter identification method for the proposed fractional-order equivalent thermal impedance model based on the multi-objective particle swarm optimization (MOPSO) algorithm. In order to validate the effectiveness and superiority of this work, experiments and comparative works are provided in this paper. The results indicate that the fractional-order equivalent thermal impedance model can accurately describe the frequency domain characteristic curves of the thermal impedance of the Foster thermal network model for IGBT modules, with the difference between the amplitude frequency characteristics not exceeding 1 dB and the difference between the phase frequency characteristics not exceeding 1° within the operating frequency range of (1 kHz, 1 MHz).

Seeking the optimal SPOC-based blended learning approach to enhance deep learning from the community of inquiry perspective

To equip students with 21<sup>st</sup> century skills to be competent global citizens and succeed academically and professionally, information and communication technology tools are being utilized to facilitate deep learning in higher education. This study integrated a small private online course (SPOC) with face-to-face (F2F) classroom learning to design and implement a blended English as a foreign language (EFL) course for deep learning. A mixed-method design was employed to investigate the learning experiences and perceptions of EFL students in the SPOC-based blended learning (BL) environment. The primary objective was to examine whether and how the teaching, social and cognitive presences were established from the perspective of the community of inquiry (CoI) model. Participants were 60 students enrolled in an eight-week English communicative course in a Chinese college. Quantitative data was obtained from the CoI and BL surveys, while qualitative data was gathered through individual interviews with 10 students. The results showed that a CoI was established, and deep learning happened in both SPOC and F2F learning areas with a more salient teaching presence in the SPOC area, a stronger social presence and a higher frequency of resolution phase reached in the F2F area. Furthermore, learners expressed satisfaction with the BL course, perceiving it as effective for English language acquisition. Pedagogical implications were offered to assist educators and institutions in optimizing the use of SPOC-based BL to enhance deep learning.

Sinusoidal Fitting Decomposition for Instantaneous Characteristic Representation of Multi-Componential Signal.

The research on how to effectively extract the instantaneous characteristic components of non-stationary signals continues to be both a research hotspot and a very challenging topic. In this paper, a new method of multi-component decomposition is proposed to decompose a signal into finite mono-component signals and extract their Instantaneous Amplitude (IA), Instantaneous Phase (IP), and Instantaneous Frequency (IF), which is called Sinusoidal Fitting Decomposition (SFD). The proposed method can ensure that the IA extracted from the given signal must be positive, the IP is monotonically increasing, and the signal synthesized by both IA and IP must be mono-componential and smooth. It transforms the decomposition process into a synthesis iterative process and does not rely on any dictionary or basis function space or carry out the sifting operation. In addition, the proposed method can describe the instantaneous-frequency-amplitude characteristics of the signal very well on the time-frequency plane. The results of numerical simulation and the qualitative analysis of the amount of calculation show that the proposed method is effective.

LPI radar waveform design based on complementary phase and discrete chaotic frequency joint coding

In order to reduce the probability of radar radiation signals being detected by enemy passive detection systems, this paper proposes a phase and frequency joint coding low intercept Radar waveform design method. Based on the linear frequency modulation signal, this method uses complementary binary code and chaotic sequence to phase encode the intra-pulse modulation. Code and frequency coding. The numerical simulation results show that the designed waveform exhibits pseudo-random characteristics in the time-frequency domain, and the low recognition performance is improved; The signal has an extremely low peak sidelobe level after matched filtering, showing excellent low intercept performance; its three-dimensional ambiguity function diagram presents an ideal “graph”. Fishing type”, with good distance, speed resolution and anti-interference characteristics.

Infections Deaths in Acute Lymphoblastic Leukemia More Frequent in High Risk Leukemia

Abstract Background Acute lymphoblastic leukemia (ALL) in children currently has more than 90% survival in higher resource countries. However, in less resource countries, the survival rates are lower and infections are frequent causes. Risks for infections and poor outcomes vary during the chemotherapy phases. There is a paucity of data concerning the frequencies of the chemotherapy phase where the event is more probable. Our primary objective is to describe infections frequencies and outcomes of infection in children and also to look for association with risk factors. Methods Patients (Pts) were treated according to ALLIC-BFM-2010 protocol, a simpler branch of the BFM-AEIOP protocol and accrued prospectively. The main question is comparing outcomes of two randomizations using higher dose chemotherapy based on the leukemia risk. The risk severity was based on levels of measurable residual disease (<0.1, 0.1-10, >10 %,) and categorized in high (HR), intermediate (IR), and low (LR) risks. In SR Pts with B-cell-precursor ALL two doses of daunorubicin were prescribed in induction compared with four doses in all others. In consolidation, high-dose methotrexate was administered at 5g/m2 for SR/IR T-cell ALL and at 2g/m2 for SR/IR B-precursor-ALL. Consolidation for HR pts consisted of three intensive polychemotherapy blocks. Only T-ALL and HR pts age > 1 year received prophylactic cranial radiotherapy (12 Gy). Therapeutic cranial radiotherapy was reserved for pts with initial CNS. We performed a descriptive analysis, comparison of frequencies and proportions using Fisher test/Ji2. For time to event proportion we used Cox Analysis. Results 2232 de novo ALL pts were analyzed. Median age 5y (IQR 3-10), 56.3% were males. 2.1% had Down Syndrome; 24% categorized as HR, 56% as IR, and 20% as LR. The Immunophenotype analysis mostly B lineage (88.8%) and less T lineage (11.2%). The majority (96.7%) of pts achieved complete remission. Estimated mean time of survival was 8.8 years (ES 0.099, CI 95% 8.38-8.77) and the overall survival rate was 74 % (0.01). Trial wide, 518 (23.2%) pts died, 59 (2.6%) pts had criteria for clinical sepsis and 459 (20%) for not related sepsis causes. According to phase of the protocol, in less than one month from diagnosis, 21 events (35.6%) were observed; from 2-3 months 9 events (15.3%), from 4-6 months 6 events, (10.2%) and afterwards 23 events (39%) (p-value 0.000). No difference was found on T vs B immunophenotype, sex, age or Down syndrome. (P-value NS). However significant differences were found on risk groups 26/538 pts (4.8%) died on HR, 24/1248 (1.9%) in IR and 9/433 (2.1%) on standard risk (p-value 0.009). There was an association between the rates of sepsis and death on pts randomized to I and II protocols (p-value 0.007 and P-value 0.007). Conclusion In this large cohort of pts, we could demonstrate association between sepsis and mortality in those high-risk groups and in those pts randomized to higher chemotherapy doses. These results will allow to establish strategies to prevent infections or maximize medical interventions preventing poor infectious outcomes in high-risk groups.

PET imaging identifies anti-inflammatory effects of fluoxetine and a correlation of glucose metabolism during epileptogenesis with chronic seizure frequency

The serotonergic system has shown to be altered during epileptogenesis and in chronic epilepsy, making selective serotonin reuptake inhibitors interesting candidates for antiepileptogenic therapy. In this study, we aimed to evaluate disease-modifying effects of fluoxetine during experimental epileptogenesis.Status epilepticus (SE) was induced by lithium-pilocarpine, and female rats were treated either with vehicle or fluoxetine over 15 days. Animals were subjected to 18F-FDG (7 days post-SE), 18F-GE180 (15 days post-SE) and 18F-flumazenil positron emission tomography (PET, 21 days post-SE). Uptake (18F-FDG), volume of distribution (18F-GE180) and binding potential (18F-flumazenil) were calculated. In addition, hyperexcitability testing and video-EEG monitoring were performed.Fluoxetine treatment did not alter brain glucose metabolism. 18F-GE180 PET indicated lower neuroinflammation in the hippocampus of treated animals (−22.6%, p = 0.042), but no differences were found in GABAA receptor density. Video-EEG monitoring did not reveal a treatment effect on seizure frequency. However, independently of the treatment, hippocampal FDG uptake 7 days after SE correlated with seizure frequency during the chronic phase (r = −0.58; p = 0.015).Fluoxetine treatment exerted anti-inflammatory effects in rats during epileptogenesis. However, this effect did not alter disease outcome. Importantly, FDG-PET in early epileptogenesis showed biomarker potential as higher glucose metabolism correlated to lower seizure frequency in the chronic phase.

A low power low phase noise wide frequency range PLL

This paper presents a low-noise, low-power, wide output frequency range phase-locked loop (PLL) for WLAN/WiFi transceivers. By employing a dual-symmetric CMOS cross-coupled pair differential inductor voltage-controlled oscillator (VCO), the design achieves low phase noise. In addition, an improved phase frequency detector (PFD) and a programmable low-mismatch charge pump (CP) with feedback compensation bias control are used to mitigate bandwidth and noise variations caused by different reference frequencies. The improved charge pump PLL (CPPLL) is designed in 65 nm CMOS process, and the chip layout occupies an area of 0.28 mm2. Post-layout simulation results indicate that the PLL has a tuning range of 4.6 GHz to 6 GHz, a phase noise of 111.7 dBc/Hz at 1 MHz offset at 5 GHz, a total power consumption of 7.14 mW, and a lock time of about 9μs.

A robust time scale for space applications using the student’s t-distribution

Abstract In this article, the principles of robust estimation are applied to the standard basic time scale equation to obtain a new method of assigning weights to clocks. Specifically, the Student's t-distribution is introduced as a new statistical model for an ensemble of clocks that are experiencing phase jumps, frequency jumps or anomalies in their measurement links. The proposed robust time scale is designed to mitigate the effects of these anomalies without necessarily identifying them, but through applying a method of robust estimation for the parameters of a Student's t-distribution. The proposed time scale algorithm using the Student's t-distribution (ATST) is shown to achieve comparable robustness to phase jumps, frequency jumps, and anomalies in the measurements with respect to the AT1 oracle time scale. The AT1 oracle is a special realization of the AT1 time scale which corrects all anomalies by having prior knowledge of their occurrences. The similar performance of ATST and AT1 oracle suggests that the ATST algorithm is efficient for obtaining robustness with no prior knowledge or detection of the occurrences of anomalies.

Nonlinear Dynamics Induced by Coil Heat in the PMDC Motor and Control

In this paper, the interesting dynamics of chaos induced by the effect of the variation of internal average heat during operation in the DC motor control by the full bridge drive are analyzed. By using simple powerful tools of analyzing nonlinear dynamical systems like phase portraits, time traces and frequency spectrum in the MATLAB-SIMULINK environment, we showed that under certain conditions, the PMDC motor develops different behaviors so as periodic limited, and chaotic attractors, when the motor drive different form of external load torque and the windings resistance variation. This paper presents the first studies on the variation of the average heat of the motor and the amplitude of the triangular load torque to produce the strange phenomena like chaos as far as our knowledge go. A chaos control of the unstable regime is proposed to stabilize the PM DC motor in a desire regime. This contribution is very important in industry because some unexplained dynamical behaviors of the DC motor driven by a full bridge now can be avoided.

Three-phase balance relay using numerical techniques experimentally verified on synchronous machines

In this paper, a multifunction three-phase balance relay based on normalized correlation coefficients is proposed to detect and estimate imbalances and perturbations in synchronous machine output signals. Furthermore, fresh definitions of imbalance and disturbance indicators derived using the correlation estimators are introduced, taking into account the changes in the waveform phase displacement, frequency, amplitude, and shape of the machine three-phase waves. Experimental tests are performed on a motor–generator set connected to a three-phase load, which is used to identify and evaluate the imbalance and disturbance conditions of the voltage and current measurements. Extensive tests for different fault types have been presented. The practical results show that the proposed protection can respond quickly to faults, and assess online the level of the imbalance/disturbance with high accuracy. Its running time is within one cycle. In addition, the proposed algorithm’s reliability and accuracy are its most significant attributes, whose percentages exceed 96.6%. The present algorithm considers the impact of both negative and zero sequence components when measuring di-symmetry factors, while some conventional approaches merely rely on the negative sequence component computed for the machine voltages and currents.

Novel Power-Efficient Fast-Locking Phase-Locked Loop Based on Adaptive Time-to-Digital Converter-Aided Acceleration Compensation Technology

This paper proposes an adaptive acceleration lock compensation technology for phase-locked loops (PLLs) based on a novel dual-mode programmable ring voltage-controlled oscillator (ring-VCO). In addition, a time-to-digital converter (TDC) is designed to accurately quantify the phase difference from the phase frequency detector (PFD) in order to optimize the dead-zone effect while dynamically switching an auxiliary charge pump (CP) module to realize fast phase locking. Furthermore, a TDC-controlled three/five-stage dual-mode adaptively continuously switched VCO is proposed to optimize the phase noise (PN) and power efficiency, leading to an optimal performance tradeoff of the PLL. Based on the 180 nm/1.8 V standard CMOS technology, the complete PLL design and a corresponding simulation analysis are implemented. The results show that, with a 1 GHz reference signal as the input, the output frequency is 50–324 MHz, with a wide tuning range of 260 MHz and a low phase noise of −98.07 dBc/Hz@1 MHz. The key phase-locking time is reduced to 1.11 μs, and the power dissipation is lowered to 1.86 mW with a layout area of 66 μm × 128 μm. A significantly remarkable multiobjective performance tradeoff with topology optimization is realized, which is in contrast to several similar design cases of PLLs.

A hospital lipid-lowering protocol improves 2-year clinical outcomes in patients with acute coronary syndrome.

Although mortality after acute coronary syndrome (ACS) has improved in the acute phase, cardiovascular events occur at a certain frequency in the chronic phase. A hospital lipid-lowering protocol (HLP) could be effective in providing optimal lipid-lowering therapy to improve long-term clinical outcomes after ACS. This study investigated the impact of HLP on clinical outcomes in patients with ACS. We retrospectively analysed 1,114 ACS patients who had undergone successful percutaneous coronary intervention between November 2011 and June 2021. In December 2018, we introduced a HLP that included the prescription of the maximum tolerated dose of statin, ezetimibe, and eicosapentaenoic acid after ACS treatment. We compared 2-year clinical outcomes before (control group: 791 patients) and after the HLP's introduction (HLP group: 323 patients). The primary outcome was the non-target vessel revascularisation (non-TVR) rate. A multivariate Cox proportional hazard model and inverse probability weighting (IPW) based on the propensity score were used to evaluate the effect of HLP on the outcomes. The cumulative 2-year non-TVR incidence was significantly lower in the HLP group than in the control group (8.5% vs 13.8%; p=0.019). Multivariable analysis revealed non-TVR risk was significantly lower in the HLP group than in the control group (adjusted hazard ratio [aHR]: 0.637 [95% confidence interval [CI]: 0.416-0.975]; p=0.038). The IPW analysis confirmed a significant association between the HLP and a lower non-TVR risk (aHR: 0.544 [95% CI: 0.350-0.847]; p=0.007). Implementing HLP for ACS patients improved the 2-year clinical outcome.

High impedance fault detection method based on improved Mayr Arc model and fitting curve coefficients

To solve the problem of weak transient fault currents and significant nonlinear characteristics caused by arcs in resonant grounding systems, proposing a high-impedance fault (HIF) detection method based on an improved Mayr arc model and fitting curve coefficients. Firstly, to address the issue of low accuracy in simulating fault waveforms in existing HIF models, construct an improved arc model based on Mayr and control the parameter values under different feature dimensions, achieving accurate simulation of arc waveforms. Secondly, based on the impedance characteristics of the feeder, analyze the phase frequency characteristics, determine the first capacitive frequency band, and then determine the cutoff frequency of the Chebyshev filter to improve the ability of waveform feature extraction and fault recognition. Finally, by fitting the voltage and current geometric characteristic curve within the characteristic frequency band, using the least squares method and the quadratic coefficient values of the fitting curve to construct detection criteria, accurate detection of HIF is possible. Research shows that the improved arc model can fully characterize the current arc waveform under various working conditions. Simulations and real-world measurements verify that HIF can be accurately detected using the quadratic coefficient value of the fitting curve.

MTD precise jamming technology based on intra-pulse and inter-pulse frequency-phase joint modulation

For moving target detection (MTD) radar, existing jamming systems face problems such as poor controllability and strong regularity of two-dimensional false target characteristics. Time-frequency-phase modulation technology has great potential for active jamming and has received widespread attention. In this article, we propose a precise jamming method based on intra-pulse and inter-pulse frequency-phase joint modulation to control the two-dimensional distribution of false targets. First, construct periodic phase and segmented frequency modulation functions. Secondly, the intra-pulse phase modulation period Ts1 and frequency modulation amount ξl1 accurately control the positions of multiple false targets; the inter-pulse phase modulation period Ts2 and frequency modulation amount ξl2 accurately control the velocity of multiple false targets. Finally, the amplitude of the two-dimensional false target is accurately controlled by adjusting the phase modulation coefficient φi, phase modulation and frequency modulation duty cycles ηs, ηl. Compared with other jamming algorithms, the jamming distribution is more flexible and controllable, which verifies the superiority of this method.

The Challenges of Piezoelectric Actuators and Motors Application in a Space Environment

Piezoelectric actuators and motors are increasingly essential for space applications due to their precision, compactness, and efficiency. This review explores their advantages over traditional actuators, emphasizing their minimal electromagnetic interference, high responsiveness, and operational reliability in harsh space environments. This study highlights the challenges posed by space conditions such as vacuum, microgravity, extreme temperatures, and radiation, which require robust design and material considerations. A comprehensive review of missions using piezo actuators, including their operating principles, material advancements, and innovative designs tailored for space conditions. In addition, numerical calculations were performed by COMSOL Multiphysics 5.6 software with the aim of analyzing the impact of temperature variations typical of the low Earth orbit (LEO) on the electromechanical properties of the piezoelectric transducer. The results indicate significant variations in the characteristics of the resonant frequency, impedance, and phase frequency in a temperature range from −20 °C to 40 °C, emphasizing the importance of accounting for thermal effects in the design. The calculations show that advantages which are proposed by piezoelectric motion systems must be combined with adaptability to harsh environmental conditions and call for further research to enhance their robustness and performance for broader application in future space missions.

On mathematical analysis of synchronization of bidirectionally coupled Kuramoto oscillators under inertia effect

In this article, we analyze the phase synchronization and frequency synchronization for the bidirectionally coupled Kuramoto model under the effect of inertia. Unlike the classical Kuramoto model equipped with all-to-all coupled interaction, in the setting of this model, each oscillator θi only interacts directly with θi+1 and θi−1. The bidirectional interaction is a typical setting of the concatenation in power systems. Additionally, it is necessary to impose the effect of inertia in the Kuramoto model in the applications such as power systems and Josephson junction array. In this article, we first present a theory of the global convergence for frequency synchronization for the identical case. For the non-identical case, we prove that the second-order bidirectionally coupled Kuramoto model exhibits a frequency synchronization if the coupling strength is large, inertia is small, and all oscillators are initially confined to a sector. We emphasize that the arc length of this sector possesses a positive lower bound which is independent of the number of oscillators. If, in addition, all natural frequencies are identical, we further show that the phase synchronization emerges. Moreover, we demonstrate the numerical simulations to support the main results. On the other hand, we observe that the model equipped with large inertia can exhibit the synchronization. Exploring the synchronization theory for large inertia case is left as the future work.

Ultrasonic Sensor: A Fast and Non-Destructive System to Measure the Viscosity and Density of Molecular Fluids.

This study presents the design and development of an ultrasonic sensor as a fundamental tool for characterizing the properties of fluids and biofluids. The analysis primarily focuses on measuring the electrical parameters of the system, which correlate with the density and viscosity of the solutions, in sample volumes of microliters and with high temporal resolution (up to 1 data point per second). The use of this sensor allows the fast and non-destructive evaluation of the viscosity and density of fluids deposited on its free surface. The measurements are based on obtaining the impedance versus frequency curve and the phase difference curve (between current and voltage) versus frequency. In this way, characteristic parameters of the transducer, such as the resonance frequency, phase, minimum impedance, and the quality factor of the resonant system, can characterize variations in density and viscosity in the fluid under study. The results obtained revealed the sensor's ability to identify two parameters sensitive to viscosity and two parameters sensitive to density. As a proof of concept, the unfolding of the bovine albumin protein was studied, resulting in a curve that reflects its unfolding kinetics in the presence of urea.

Design and Implementation of PLL with Dead Zone-Less Low-Power Phase Frequency Detector

This project introduces a Phase-Frequency Detector (PFD) that includes a dedicated circuit for removing the dead zone. This design utilizes Pass Transistor Logic (PTL) and Delay Cells (DCs) to effectively address this issue. Additionally, a Low-Pass Filter is integrated into the system and connected with charge pump, employing a technique that replaces resistors with transistors, thereby significantly reducing the overall circuit area. Furthermore, a Phase-Locked Loop (PLL) serves to eliminate the dead zone and significantly reduce the circuit's size. This project aims to advance circuit design methodologies by enhancing performance and minimizing area requirements.

High-Accuracy Phase Frequency Detection Technology Based on BDS Time and Frequency Signals.

For the time and frequency signals of Beidou satellites, a high-accuracy phase frequency detection technology based on phase group synchronization is proposed. Using the Beidou receiver and satellite signals as the frequency standard and the measured signals, respectively. The Beidou receiver and the satellite signals are sent to the phase coincidence detector of the different frequencies to generate a phase coincidence point pulse, which is sent to the different frequency phase detector as a control signal to generate the phase differences between the Beidou receiver and satellite signals, and then complete the high-accuracy phase synchronization between the Beidou receiver and satellite signals. Experimental results show that when the delay resolution reaches ps level, the phase synchronization accuracy of the system can reach 10 ps, which has the characteristics of small phase noise, low development cost, simple circuit structure, and high synchronization accuracy compared with the traditional phase synchronization technologies. Therefore, it would be widely used in satellite positioning, astrometry, precision navigation, aerospace, satellite launch, power transmission, communications, radar, and other high-tech fields.

Technical note: Retrieval of the supercooled liquid fraction in mixed-phase clouds from Himawari-8 observations

Abstract. The supercooled liquid fraction (SLF) in mixed-phase clouds (MPCs) is an essential variable of cloud microphysical processes and climate sensitivity. However, the SLF is currently calculated in spaceborne remote sensing only as the cloud phase–frequency ratio of adjacent pixels, which results in a loss of the original resolution in observations of cloud liquid or ice content within MPCs. Here, we present a novel method for retrieving the SLF in MPCs based on the differences in radiative properties of supercooled liquid droplets and ice particles at visible (VIS) and shortwave infrared (SWI) channels of the geostationary Himawari-8. Liquid and ice water paths are inferred by assuming that clouds are composed of only liquid or ice, with the real cloud water path (CWP) expressed as a combination of these two water paths (SLF and 1-SLF as coefficients), and the SLF is determined by referring to the CWP from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). The statistically relatively small cloud phase spatial inhomogeneity at a Himawari-8 pixel level indicates an optimal scene for cloud retrieval. The SLF results are comparable to global SLF distributions observed by active instruments, particularly for single-layered cloud systems. While accessing the method's feasibility, SLF averages are estimated between 74 % and 78 % in Southern Ocean (SO) stratocumulus across seasons, contrasting with a range of 29 % to 32 % in northeastern Asia. The former exhibits a minimum SLF around midday in summer and a maximum in winter, while the latter trend differs. This novel algorithm will be valuable for research to track the evolution of MPCs and constrain the related climate impact.