Summary
The concept of induction heating is slowly entrenching as it has the traits of homogeneous heating, zero pollution and higher power density. To achieve these traits convincingly in reality, ...there is a need to develop energy efficient converter topologies, which aid in achieving power regulation of soft switching and very high frequency operation. This paper presents the salient features of converter topologies used for domestic and industrial heating applications with a focus on its stage‐wise power conversion, power density, load handling capacity, soft switching, reliability and size. The performance of these topologies is analysed in terms of converter switching frequency, power rating, modulation techniques, flicker, user performance and efficiency. Moreover, this review paper predicts the future trends associated with the adaptation of wide band‐gap power semiconductor materials, multi‐output topologies, variable frequency control scheme with minimum losses and filter design to improve source‐side power factor. The detailed technology review will be extremely useful for researchers, designers and engineers in choosing the appropriate topology for the chosen application.
Electrical equivalent model for industrial application and domestic application
Anaesthesia for laryngeal surgery may be complex and associated with complications.
We conducted a national survey exploring airway management and ventilation during elective laryngeal surgery, ...focusing primarily on injector and jet ventilation (i.e. high-pressure source ventilation: HPSV).
Responses were received from 229 centres (75%). Several hospitals reported major complications during HPSV in the previous 5 yr, including three deaths. Complications during manual techniques led to seven discharge delays, three critical care admissions and three deaths. During the use of a high-frequency jet ventilation (HFJV), complications led to one discharge delay, two critical care admissions and no deaths. Complications were evenly spread between supraglottic, subglottic and transtracheal techniques. All deaths occurred in departments without HFJV. Three centres perform more than 100 transtracheal jet ventilation cases per year. None of these hospitals reported serious complications. Respondents in hospitals reporting serious complications were more likely to have plans to change practice (P=0.03). Elective laryngeal surgery is performed in 62% hospitals, of which 67% use HPSV. Supraglottic, subglottic and transtracheal techniques are used by 86, 50 and 35%, respectively. Manual ventilation devices are used widely. Only 17% of those using HPSV use an HFJV. Two-thirds of respondents initiate manual ventilation with pressures above 2 atm and only 6% start at ≤1 atm. I.V. cannulae are used for direct tracheal access by 18% and subcricoid insertion by 9%.
HPSV may cause serious complications and there are wide variations in clinical practice. This is an area where guideline development and examination of outcome data are warranted.
We report unusual Electromagnetic Ion Cyclotron (EMIC) waves with a very narrow frequency bandwidth, closely following and approaching the proton gyrofrequency. One interesting case analysis shows ...that magnetosonic waves, anisotropic suprathermal proton distributions, and high frequency EMIC waves are closely related. Magnetosonic waves potentially cause the resonant heating of suprathermal protons and the temperature anisotropy of suprathermal protons (10–100 eV) likely provides free energy for the excitation of high frequency EMIC waves. The statistical analysis shows that this type of EMIC waves has a typical wave amplitude of ~100 pT, left‐handed polarization, and small wave normal angles. Moreover, these low frequency EMIC waves typically occur near the equator in the low‐density regions from dawn to dusk. These newly observed high frequency EMIC waves provide new insights into understanding the generation of EMIC waves and the energy transfer between magnetosonic waves and EMIC waves.
Plain Language Summary
Electromagnetic Ion Cyclotron (EMIC) waves are commonly observed in the Earth's magnetosphere and play an important role in causing the loss of ring current ions and relativistic electrons due to pitch angle scattering. In this study, we report unusual high frequency EMIC waves with frequency very close to the proton gyrofrequency. An interesting case study clearly shows the correlation between magnetosonic waves, the enhancement of suprathermal protons, and high frequency EMIC waves. The protons at suprathermal energies could be heated by magnetosonic waves and the anisotropic distribution of suprathermal protons is likely responsible for the excitation of high frequency EMIC waves. The statistical analysis shows that this type of EMIC waves has a typical wave amplitude of ~100 pT, left‐handed polarization, and small wave normal angles. These newly observed high frequency EMIC waves provide new insights into understanding the generation of EMIC waves and the energy transfer between magnetosonic waves and EMIC waves.
Key Points
Unusually high frequency EMIC waves are observed near the proton gyrofrequency with a very narrow bandwidth
Temperature anisotropy of suprathermal protons in association with magnetosonic waves likely excites high frequency EMIC waves
Statistical results show that high frequency EMIC waves typically occur near the equator in the low‐density regions from dawn to dusk
Young healthy adults can hear tones up to at least 20 kHz. However, clinical audiometry, by which hearing loss is diagnosed, is limited at high frequencies to 8 kHz. Evidence suggests there is ...salient information at extended high frequencies (EHFs; 8 to 20 kHz) that may influence speech intelligibility, but whether that information is used in challenging listening conditions remains unknown. Difficulty understanding speech in noisy environments is the most common concern people have about their hearing and usually the first sign of age-related hearing loss. Digits-in-noise (DIN), a widely used test of speech-in-noise perception, can be sensitized for detection of high-frequency hearing loss by low-pass filtering the broadband masking noise. Here, we used standard and EHF audiometry, self-report, and successively higher cutoff frequency filters (2 to 8 kHz) in a DIN test to investigate contributions of higher-frequency hearing to speech-in-noise perception. Three surprising results were found. First, 74 of 116 “normally hearing,” mostly younger adults had some hearing loss at frequencies above 8 kHz. Early EHF hearing loss may thus be an easily measured, preventive warning to protect hearing. Second, EHF hearing loss correlated with self-reported difficulty hearing in noise. Finally, even with the broadest filtered noise (≤8 kHz), DIN hearing thresholds were significantly better (P < 0.0001) than those using broadband noise. Sound energy above 8 kHz thus contributes to speech perception in noise. People with “normal hearing” frequently report difficulty hearing in challenging environments. Our results suggest that one contribution to this difficulty is EHF hearing loss.
The design of power magnetic components for operation at high frequency (HF, 3-30 MHz) has been hindered by a lack of magnetic material performance data and by the limited design theory in that ...frequency range. To address these deficiencies, we have measured and present core loss data for a variety of commercially available magnetic materials in the HF range. In addition, we extend the theory of performance factor for appropriate use in the HF design. Since magnetic materials suitable for HF applications tend to have low permeability, we also consider the impact of low permeability on design. We conclude that, with appropriate material selection and design, increased frequencies can continue to yield improved power density well into the HF regime.
Objective
This study aimed to identify the sonographic features of pathologically confirmed onychopapilloma cases.
Methods
High‐frequency up to 24 MHz and ultra‐high frequency‐ultrasound up to 71 MHz ...examinations were performed and correlated with their clinical and pathologic presentations.
Results
Twenty‐two cases met the criteria. Clinical presentations revealed longitudinal erythronychia in 63.3% of cases. The ultrasound examinations identified a hypoechoic band in the nail bed (86.3%), nail plate abnormalities including upward displacement (68.2%) and thickening (68.1%), focal hyperechoic focal spots on the nail plate (50%) and irregularities of the ventral plate (33.3%).
Color Doppler imaging showed no hypervascularity of the nail bed in all studies. These findings correlate with histological characteristics of onychopapilloma, including nail bed acanthosis, papillomatosis, and layered hyperkeratosis. Recurrence occurred in two cases after surgery, with tumors showing proximal extension in the matrix region on ultrasound not evident during clinical examination.
Conclusion
High‐frequency and ultra‐high‐frequency can provide anatomical information in onychopapilloma that could enhance understanding and management.
Objective
New insights into high‐frequency electroencephalographic activity and network analysis provide potential tools to improve delineation of epileptic tissue and increase the chance of ...postoperative seizure freedom. Based on our observation of high‐frequency oscillations “spreading outward” from the epileptic source, we hypothesize that measures of directed connectivity in the high‐frequency range distinguish epileptic from healthy brain tissue.
Methods
We retrospectively selected refractory epilepsy patients with a malformation of cortical development or tumor World Health Organization grade I/II who underwent epilepsy surgery with intraoperative electrocorticography for tailoring the resection based on spikes. We assessed directed functional connectivity in the theta (4‐8 Hz), gamma (30‐80 Hz), ripple (80‐250 Hz), and fast ripple (FR; 250‐500 Hz) bands using the short‐time direct directed transfer function, and calculated the total, incoming, and outgoing propagation strength for each electrode. We compared network measures of electrodes covering the resected and nonresected areas separately for patients with good and poor outcome, and of electrodes with and without spikes, ripples, and FRs (group level: paired t test; patient level: Mann‐Whitney U test). We selected the measure that could best identify the resected area and channels with epileptic events using the area under the receiver operating characteristic curve, and calculated the positive and negative predictive value, sensitivity, and specificity.
Results
We found higher total and outstrength in the ripple and gamma bands in resected tissue in patients with good outcome (rippletotal: P = .01; rippleout: P = .04; gammatotal: P = .01; gammaout: P = .01). Channels with events showed lower total and instrength, and higher outstrength in the FR band, and higher total and outstrength in the ripple, gamma, and theta bands (FRtotal: P = .05; FRin: P < .01; FRout: P = .02; gammatotal: P < .01; gammain: P = .01; gammaout: P < .01; thetatotal: P = .01; thetaout: P = .01). The total strength in the gamma band was most distinctive at the channel level (positive predictive value PPVgood = 74%, PPVpoor = 43%).
Significance
Interictally, epileptic tissue is isolated in the FR band and acts as a driver up to the (fast) ripple frequency range. The gamma band total strength seems promising to delineate epileptic tissue intraoperatively.
•Iterative Adaptive Inverse Filtering extracts the glottal excitation information.•Excitation source information is extracted from high-frequency band.•CQCC algorithm is used to extract the feature ...from high-frequency band.•Gaussian mixture model is used as a classifier to detect replayed speech.•The experimental studies done on ASV spoof-2017 version 2.0 database.
Replay attack is most vulnerable to automatic speaker verification system, where the frauds get the access by replaying pre-recorded voice samples of the genuine speakers. In this proposed work, we mainly concentrated on glottal excitation and high frequency band. First, we demonstrate the importance of the glottal information of the speech signals to detect the replay attack for speaker verification system along with magnitude based discrimination power features set. Iterative Adaptive Inverse Filtering (IA-IF) technique is used to extract the glottal excitation information of the given speech spectrum which shows the difference in the characteristics of genuine and replayed speech sample. Using this technique the glottal information is gained by eliminating the lip radiation and vocal tract effect by applying the integration and inverse filtering respectively. Secondly, we have shown the prominence and discriminative information to detect the replayed attack which is present in high frequency band of the speech spectrums of genuine and replayed samples. Finally, Constant-Q Cepstral Coefficients (CQCC) is used to extract desired features set from the high-frequency bands of glottal excitation spectrum. From the experimental studies done on ASV spoof-2017 version 2.0 database it shows that the proposed method feature set significantly decreases the Equal Error Rate (EER) to 3.68% and 8.32% for development and evaluation set when compare to other state-of-art method feature set.
This paper reports a study to understand the radio spectrum of thunderstorm narrow bipolar events (NBEs) or compact intracloud discharges, which are powerful sources of high‐frequency (HF) and very ...high frequency (VHF) electromagnetic radiation. The radio spectra from 10 kHz to about 100 MHz are obtained for three NBEs, including one caused by fast positive breakdown and two by fast negative breakdown. The results indicate that the two polarities of fast breakdown have similar spectra, with a relatively flat spectrum in the HF and VHF band. The ratio of energy spectral densities in the very low frequency and HF bands is (0.9–5) × 105. We develop a statistical modeling approach to investigate if a system of streamers can explain the main features of fast breakdown. Assuming that the current moment peak and charge moment change of individual streamers vary in the ranges of 5–10 A‐m and 5–20 μC‐m, respectively, the modeling results indicate that a system of 107–108 streamers can reproduce the current moment, charge transfer, and radio spectrum of fast breakdown. The rapid current variation on a time scale of nanoseconds required for fast breakdown to produce strong HF/VHF emissions is provided by exponentially accelerating and expanding streamers. Our study therefore supports the hypothesis that fast breakdown is a system of streamers. Finally, suggestions are given regarding future streamer simulations and NBE measurements in order to further develop our understanding of NBEs and lightning initiation.
Key Points
The two polarities of fast breakdown have similar radio spectra, and the energy density ratio of VLF to HF bands is ∼105
A statistical modeling approach is developed to find the radio spectrum of a streamer ensemble
An ensemble of tens of million streamers can reproduce the current, charge transfer and radio spectrum of fast breakdown
Spinel ferrite ceramics of nominal composition Ni0.5Zn0.3Co0.2Fe2O4 (NiZnCo) with various BaO doping were successfully synthesized for applications as novel high‐frequency magneto‐dielectric ...materials. The influences of BaO doping on the crystal phase, density, microstructure, and magnetic and dielectric performances in the frequency range of 0.1 to 5 GHz were systematically studied. It is revealed that the doped Ba2+ ions aggregate to the grain‐boundary regions and lead to the formation of BaFe2O4 phase that significantly restrains the growth of NiZnCo ferrite grains. Correspondingly, permeability and permittivity are effectively tailored through the varied grain size and density, which is demonstrated by the magnetic circuit model and the modified effective medium theory proposed herein. As BaO content x = 1.2‐1.8 mol%, the NiZnCo ferrites reveal the excellent performance with almost equal values of μ′ and ε′, yielding a characteristic impedance to be nearly identical as that of free space over a wide frequency range of the VHF and UHF bands. Furthermore, the magnetic loss is effectively reduced at high frequencies, where the typical tan δμ at 0.5 GHz is decreased to ~0.043 with a reduction of up to 37% and the loss factor (tan δμ/μ′) is as low as ~0.006.
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