Frequency Energy Spectrum Research Articles

Small-Scale Potential Vorticity in the Upper-Ocean Thermocline

AbstractTwenty Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats in the upper-ocean thermocline of the summer Sargasso Sea observed the temporal and vertical variations of Ertel potential vorticity (PV) at 7–70-m vertical scale, averaged over O(4–8)-km horizontal scale. PV is dominated by its linear components—vertical vorticity and vortex stretching, each with an rms value of ~0.15f. In the internal wave frequency band, they are coherent and in phase, as expected for linear internal waves. Packets of strong, >0.2f, vertical vorticity and vortex stretching balance closely with a small net rms PV. The PV spectrum peaks at the highest resolvable vertical wavenumber, ~0.1 cpm. The PV frequency spectrum has a red spectral shape, a −1 spectral slope in the internal wave frequency band, and a small peak at the inertial frequency. PV measured at near-inertial frequencies is partially attributed to the non-Lagrangian nature of float measurements. Measurement errors and the vortical mode also contribute to PV in the internal wave frequency band. The vortical mode Burger number, computed using time rates of change of vertical vorticity and vortex stretching, is 0.2–0.4, implying a horizontal kinetic energy to available potential energy ratio of ~0.1. The vortical mode energy frequency spectrum is 1–2 decades less than the observed energy spectrum. Vortical mode energy is likely underestimated because its energy at vertical scales > 70 m was not measured. The vortical mode to total energy ratio increases with vertical wavenumber, implying its importance at small vertical scales.

A Single-Molecule Interaction Spectrum for Non-Covalent Interaction Inside Membrane Protein Channel

Dynamic non-covalent interactions of biomolecules are ubiquitous in almost all biological process. In particular, it underlies the successive transport of ions or target carriers by membrane protein, controlling many key cellular functions. However, few experimental approaches can directly define the multiple non-covalent interactions within the channel. Since all the dynamic non-covalent dynamic interaction inside membrane protein have been all recorded but hide in the traditional single-channel recording of ionic current, here, we present a rational strategy in the combination of experiments, MD simulations and frequency-energy spectra of ionic flow to quantify and quality a role of non-covalent interaction for membrane protein channel in transporting the carriers. We employed wild-type aerolysin transporting of methylcytosine and cytosine as a model to detailed explore the dynamic ionic signatures with the non-stationary and non-linear frequency analysis. The results demonstrate that The main frequency peak position in frequency-energy spectrum represents the main ion mobility inside membrane protein while its energy suggests the vibration amplitude of the related ions. The sudden spikes in the frequency-energy considered as the fingerprint spectra for potential characterization of non-covalent interaction. The frequency-energy spectrum of ions flowing inside membrane channels constituting a Single-Molecule Interaction Spectrum, which bridges the gap in-between traditional ionic current recording and the MD simulations, facilitating the qualitative and quantify describe the non-covalent interactions inside membrane channels.

Ultrasonic Testing Analysis of Concrete Structure Based on S Transform

Ultrasonic testing analysis is a crucial scientific component during the process and interpretation of the ultrasonic detection signal. Focusing on the ultrasonic testing characteristics, the time‐invariant spectral analysis method cannot meet the processing requirements of the detection signal fully. Thus, S transform, the time‐varying analysis method, was introduced into the ultrasonic testing data processing of the concrete structure. The acoustic wave phase velocity was derived based on the spectrum analysis, and the S transform time‐frequency analysis method was established. Finally, based on the method of concrete experimental data set, studies show that the frequency energy spectrum with S transform can realize flexible and effective identification of defects in the concrete structure. Definitely, this analysis method can significantly improve the resolution and practicality of ultrasonic testing.

Large Eddy Simulation study on the structure of turbulent flow in a complex city

Large Eddy Simulation (LES) of atmospheric flows has become an increasingly popular modelling approach within the last years, as it has the potential to provide deeper insight into unsteady flow phenomena. LES can be improved and validated using specifically designed and well documented wind tunnel datasets. In this work, we evaluate the performance of LES against a wind tunnel experiment in a semi-idealized city (“Michel-Stadt”; CEDVAL-LES database) and use the LES results to study the structure of the turbulent flow at the particular urban area. The first, second and third order statistics are presented, as well as velocity frequency distributions and energy spectra. The results compare well with the experimental values. Information about special features of the flow field is also provided. A particular focus of this work is put on the influence of grid resolution on the results. Five different grids are examined and the required resolution for turbulent flow within the canopy layer is evaluated. This study reveals the strong potential of LES for urban flow simulations. It is shown that LES can assess highly non-Gaussian flow behaviour in street canyons, which has implications for urban ventilation, wind comfort assessment and urban design.

Impact of dissipation on the energy spectrum of experimental turbulence of gravity surface waves

We discuss the impact of dissipation on the development of the energy spectrum in wave turbulence of gravity surface waves with emphasis on the effect of surface contamination. We performed experiments in the Coriolis facility which is a 13-m diameter wave tank. We took care of cleaning surface contamination as well as possible considering that the surface of water exceeds 100~m$^2$. We observe that for the cleanest condition the frequency energy spectrum shows a power law decay extending up to the gravity capillary crossover (14 Hz) with a spectral exponent that is increasing with the forcing strength and decaying with surface contamination. Although slightly higher than reported previously in the literature, the exponent for the cleanest water remains significantly below the prediction from the Weak Turbulence Theory. By discussing length and time scales, we show that weak turbulence cannot be expected at frequencies above 3 Hz. We observe with a stereoscopic reconstruction technique that the increase with the forcing strength of energy spectrum beyond 3~Hz is mostly due to the formation and strenghtening of bound waves.

EMD based Hilbert energy spectrum analysis of adventitious lung wave signals

The respiratory adventitious waves are analyzed effectively by time frequency analysis. In this paper, we present a new approach for rectifying the abnormality in adventitious wave. Basically, there are two types of respiratory sound waves and these are classified as wheezes and crackles. The proposed method utilizes the time frequency analysis using spectrum analysis method. The modified Empirical Mode Decomposition (EMD) called Ensemble Empirical Mode Decomposition (EEMD) to plot energy spectrum of adventitious wave is used in this work. The proposed method decomposes the respiratory adventitious wave into a different Intrinsic Mode Function (IMF). The long and short duration adventitious waves are present in a wheezing subject and this leads to production of non stationary and nonlinear sound waves. The empirical mode decomposition (EMD) decomposes such characteristic waves. The available spectrogram analyzes techniques related to additive expansions and explore amplitude wise time-frequency distribution. The methodology discussed in this context responding greatly even for correlative noise and explores energy spectra in addition to amplitude spectra. The various IMFs such produced are exhibits the fine details of adventitious wave and thus pattern can be predicted for final residual. The energy spectrum can be viewed as a diagnostic tool for accurate analysis of wheezing pattern. The decomposed frequency patterns indicate the physiological aspects. The instantaneous frequency and Hilbert energy spectrum based on above mentioned a method are employed by IMF to analyze and present the result in time-frequency distribution to explore the characteristics of inherent properties adventitious signals. The Hilbert marginal spectrum has been used to indicate overall energy distribution from each frequency component. Finally, the resultant EMD analysis along with EEMD energy spectrum is better for asthmatic subject and solves mode mixing problems.

Multi-Source Generation Mechanisms for Low Frequency Noise Induced by Flood Discharge and Energy Dissipation from a High Dam with a Ski-Jump Type Spillway.

As excess water is discharged from a high dam, low frequency noise (air pulsation lower than 10 Hz, LFN) is generated and propagated in the surrounding areas, causing environmental hazards such as the vibration of windows and doors and the discomfort of local residents. To study the generation mechanisms and key influencing factors of LFN induced by flood discharge and energy dissipation from a high dam with a ski-jump type spillway, detailed prototype observations and analyses of LFN are carried out. The discharge flow field is simulated and analyzed using a gas-liquid turbulent flow model. The acoustic response characteristics of the air cavity, which is formed between the discharge nappe and dam body, are analyzed using an acoustic numerical model. The multi-sources generation mechanisms are first proposed basing on the prototype observation results, vortex sound model, turbulent flow model and acoustic numerical model. Two kinds of sources of LFN are studied. One comes from the energy dissipation of submerged jets in the plunge pool, the other comes from nappe-cavity coupled vibration. The results of the analyses reveal that the submerged jets in the plunge pool only contribute to an on-site LFN energy of 0–1.0 Hz, and the strong shear layers around the high-velocity submerged jets and wall jet development areas are the main acoustic source regions of LFN in the plunge pool. In addition, the nappe-cavity coupled vibration, which is induced when the discharge nappe vibrates with close frequency to the model frequency of the cavity, can induce on-site LFN energy with wider frequency spectrum energy within 0–4.0 Hz. By contrast, the contribution degrees to LFN energy from two acoustic sources are almost same, while the contribution degree from nappe-cavity coupled vibration is slightly higher.

Spectral energy cascade in thermoacoustic shock waves

We have investigated thermoacoustically amplified quasi-planar nonlinear waves driven to the limit of shock-wave formation in a variable-area looped resonator geometrically optimized to maximize the growth rate of the quasi-travelling-wave second harmonic. Optimal conditions result in velocity leading pressure by approximately $40^{\circ }$ in the thermoacoustic core and not in pure travelling-wave phasing. High-order unstructured fully compressible Navier–Stokes simulations reveal three regimes: (i) modal growth, governed by linear thermoacoustics; (ii) hierarchical spectral broadening, resulting in a nonlinear inertial energy cascade, (iii) shock-wave-dominated limit cycle, where energy production is balanced by dissipation occurring at the captured shock-thickness scale. The acoustic energy budgets in regime (i) have been analytically derived, yielding an expression of the Rayleigh index in closed form and elucidating the effect of geometry and hot-to-cold temperature ratio on growth rates. A time-domain nonlinear dynamical model is formulated for regime (ii), highlighting the role of second-order interactions between pressure and heat-release fluctuations, causing asymmetry in the thermoacoustic energy production cycle and growth rate saturation. Moreover, energy cascade is inviscid due to steepening in regime (ii), with the $k$th harmonic growing at $k/2$-times the modal growth rate of the thermoacoustically sustained second harmonic. The frequency energy spectrum in regime (iii) is shown to scale with a $-5/2$ power law in the inertial range, rolling off at the captured shock-thickness scale in the dissipation range. We have thus shown the existence of equilibrium thermoacoustic energy cascade analogous to hydrodynamic turbulence.

A pseudo-coupled DEM–non-linear PBM approach for simulating the evolution of particle size during dry milling

A multi-scale modeling approach is formulated which combines the use of the discrete element method (DEM) and population balance model (PBM) to simulate the evolution of particle size distribution (PSD) in dry milling. As a major novelty, a pseudo-coupled DEM–non-linear PBM approach is proposed, in which the parameters of a non-linear PBM were calibrated using the DEM simulations of the microdynamic environment in a mill by using the DEM intermittently. To demonstrate the application of this approach, breakage dynamics of silica particles in a vibrating cylindrical vessel containing an alumina grinding ball was simulated numerically. DEM simulations were performed to obtain the collision frequency and impact energy spectra, calculate the first-order breakage rate parameters from short milling of mono-sized feeds, and calibrate the parameters of the effectiveness factor of the non-linear PBM. As another novelty, the form of the effectiveness factor chosen accounted for both acceleration effects and deceleration effects simultaneously, which have been observed in various experimental milling studies. By incorporating DEM input, the non-linear PBM with the effectiveness factor was used to simulate the evolution of the PSD. This study demonstrates that a non-linear PBM, whose parameters were calibrated using DEM at early milling times, could predict the PSD evolution during prolonged milling and potentially obviate the need for using computationally expensive DEM simulations for the whole milling duration.

Turbulence Measurements from Five-Beam Acoustic Doppler Current Profilers

AbstractTwo new five-beam acoustic Doppler current profilers—the Nortek Signature1000 AD2CP and the Teledyne RDI Sentinel V50—are demonstrated to measure turbulence at two energetic tidal channels within Puget Sound, Washington. The quality of the raw data is tested by analyzing the turbulent kinetic energy frequency spectra, the turbulence spatial structure function, the shear in the profiles, and the covariance Reynolds stresses. The five-beam configuration allows for a direct estimation of the Reynolds stresses from along-beam velocity fluctuations. The Nortek’s low Doppler noise and high sampling frequency allow for the observation of the turbulent inertial subrange in both the frequency spectra and the turbulence structure function. The turbulence parameters obtained from the five-beam acoustic Doppler current profilers are validated with turbulence data from simultaneous measurements with acoustic Doppler velocimeters. These combined results are then used to assess a turbulent kinetic energy budget in which depth profiles of the turbulent kinetic energy dissipation and production rates are compared. The associated codes are publicly available on the MATLAB File Exchange website.

Energy spectrum analysis of blast waves based on an improved Hilbert–Huang transform

Using the improved Hilbert–Huang transform (HHT), this paper investigates the problems of analysis and interpretation of the energy spectrum of a blast wave. It has been previously established that the energy spectrum is an effective feature by which to characterize a blast wave. In fact, the higher the energy spectra in a frequency band of a blast wave, the greater the damage to a target in the same frequency band. However, most current research focuses on analyzing wave signals in the time domain or frequency domain rather than considering the energy spectrum. We propose here an improved HHT method combined with a wavelet packet to extract the energy spectrum feature of a blast wave. When applying the HHT, the signal is first roughly decomposed into a series of intrinsic mode functions (IMFs) by empirical mode decomposition. The wavelet packet method is then performed on each IMF to eliminate noise on the energy spectrum. Second, a coefficient is introduced to remove unrelated IMFs. The energy of each instantaneous frequency can be derived through the Hilbert transform. The energy spectrum can then be obtained by adding up all the components after the wavelet packet filters and screens them through a coefficient to obtain the effective IMFs. The effectiveness of the proposed method is demonstrated by 12 groups of experimental data, and an energy attenuation model is established based on the experimental data. The improved HHT is a precise method for blast wave signal analysis. For other shock wave signals from blasting experiments, an energy frequency time distribution and energy spectrum can also be obtained through this method, allowing for more practical applications.

Rail Damage Detection Based on AE Technology and Wavelet Data Processing

In order to improve the accuracy and reliability of the defect recognition in rails, the new principle and methods of NDT should be explored, and the safety of railway operation and guiding the repair can be guaranteed. The study is aiming at comparing and analyzing the characteristics of destructive data signals with non-destructive ones. The damage and defect can be judged by the differences of the processed data in the frequency domain and energy spectrum. The location of the defect and damage can be obtained by the singularities of destructive signals using wavelet data processing method: continuous wavelet transform, Mallat algorithm and à Trous algorithm. Based on the above consequence, à Trous algorithm is found that its result is more similar to the real damage location, which proves that the method can be used in the real damage detection and provide us more precise defect location information for early warning.

Changes of snoring sound after relocation pharyngoplasty for obstructive sleep apnoea: the surgery reduces mean intensity in snoring which correlates well with apnoea–hypopnoea index

To investigate objective changes of snoring aftersurgery in patients with obstructive sleep apnoea (OSA) andcorrelate these with changes in the apnoea-hypopnoea index (AHI). Prospective case series. A novel measurement, Snore Map, was used to analyse full-night snore sounds in terms of the maximal/mean intensity, peak/mean frequency, snoring index and energy type (Snore Map type, 0-4). Snore sound was classified into three bands according to frequency energy spectrum: B1 (40-300Hz), B2 (301-850Hz) and B3 (851-2000Hz). Thirty-four male and two female OSA patients (mean age, 39years; mean AHI, 53.1/h; mean body mass index, 26.8kg/m(2) ) with favourable anatomic structure were consecutively enrolled. Parameters of polysomnographies and Snore Maps at baseline and six months after operation were compared. Statistical significance was set at P<0.05. Thirty-two patients completed this study. The mean reduction in the total-snoring index was insignificant but there were significant decreases in total mean intensity, total peak frequency, total mean frequency and Snore Map type after surgery. There were also significant decreases in the mean intensity in all three bands, the snoring index in B2/B3 and the mean frequency in B1 postoperatively. Changes in the total mean intensity, total mean frequency, B2 mean intensity and B3 snoring index positively correlated with change in the AHI. Relocation pharyngoplasty significantly decreases both the snoring sound intensity and snoring frequency. These reductions are directly proportional to the improvement of OSA.

THE VIOLATION OF THE TAYLOR HYPOTHESIS IN MEASUREMENTS OF SOLAR WIND TURBULENCE

Motivated by the upcoming Solar Orbiter and Solar Probe Plus missions, qualitative and quantitative predictions are made for the effects of the violation of the Taylor hypothesis on the magnetic energy frequency spectrum measured in the near-Sun environment. The synthetic spacecraft data method is used to predict observational signatures of the violation for critically balanced Alfv\'enic turbulence or parallel fast/whistler turbulence. The violation of the Taylor hypothesis can occur in the slow flow regime, leading to a shift of the entire spectrum to higher frequencies, or in the dispersive regime, in which the dissipation range spectrum flattens at high frequencies. It is found that Alfv\'enic turbulence will not significantly violate the Taylor hypothesis, but whistler turbulence will. The flattening of the frequency spectrum is therefore a key observational signature for fast/whistler turbulence.

Fingerprint Classification Method based on J-divergence Entropy and SVM

Fingerprint classification is one of the key technologies in Automatic Fingerp rint Identification System (AFIS). However, the performance of most recent fingerprint classification methods is lo w when the quality of the fingerprint image was low. To overcome this problem, a novel method based on j-divergence entropy and SVM (Support Vector Machine) classifier is proposed in this paper. Firstly, our method transforms the fingerprint images from spatial doma in to frequency domain and constructs the directional images according to frequency spectrum energy. Secondly, eigenvector around the core point is extracted. Thirdly, the dimension of eigenvector is reduced by j-divergence entropy. At last, the input image is classified by SVM classifier. Experimental results on NIST-4 database show the validity of our method, and the classification accuracy reaches 9 4.7% for four-class classification and 91.5% for five-class classification with zero rejection rate.

Quantification of the strength of inertial waves in a rotating turbulent flow

We quantify the strength of the waves and their impact on the energy cascade in rotating turbulence by studying the wave number and frequency energy spectrum, and the time correlation functions of individual Fourier modes in numerical simulations in three dimensions in periodic boxes. From the spectrum, we find that a significant fraction of the energy is concentrated in modes with wave frequency ω ≈ 0, even when the external forcing injects no energy directly into these modes. However, for modes for which the period of the inertial waves τω is faster than the turnover time \documentclass[12pt]{minimal}\begin{document}$\tau _\textrm {NL}$\end{document}τ NL , a significant fraction of the remaining energy is concentrated in the modes that satisfy the dispersion relation of the waves. No evidence of accumulation of energy in the modes with \documentclass[12pt]{minimal}\begin{document}$\tau _\omega = \tau _\textrm {NL}$\end{document}τω=τ NL is observed, unlike what critical balance arguments predict. From the time correlation functions, we find that for modes with \documentclass[12pt]{minimal}\begin{document}$\tau _\omega &amp;lt; \tau _\textrm {sw}$\end{document}τω&amp;lt;τ sw (with \documentclass[12pt]{minimal}\begin{document}$\tau _\textrm {sw}$\end{document}τ sw the sweeping time) the dominant decorrelation time is the wave period, and that these modes also show a slower modulation on the timescale \documentclass[12pt]{minimal}\begin{document}$\tau _\textrm {NL}$\end{document}τ NL as assumed in wave turbulence theories. The rest of the modes are decorrelated with the sweeping time, including the very energetic modes with ω ≈ 0.

Research of Adaptive Resolution Spectrum Sensing Method Based on Discrete Wavelet Packet Transform

Spectrum sensing is the precondition of the realization of cognitive radio. In order to achieve efficient multi-resolution spectrum sensing, and find the available spectrum hole quickly, it proposes a variable resolution adaptive frequency spectrum energy sensing method based on discrete wavelet packet transform (DWPT). The method applied hierarchical decomposition and threshold denoising characteristic of wavelet packet transform, and solved the problem of subband sort disorder in wavelet packet decomposition process; it can eliminate the influence of uncertainty noise on detection performance, effectively. It also can reduce the computational complexity according to demand of selection resolution and perception band. The simulation results and its analysis show that the proposed method has advantages of high precision, simple arithmetic and fine flexibility, etc. The method is adapted to fast sensing in the cognitive radio environment. DOI : http://dx.doi.org/10.11591/telkomnika.v12i2.3971

Emerging role of Color Doppler in Infertility Management: A Public Health perspective

Color Doppler is emerging as a valuable diagnostic imaging modality in the field of reproductive medicine, primarily infertility. Reproductive disorders, including infertility and spontaneous abortions/miscarriages, have emerged as major public health problem(s) worldwide. Color Doppler energy imaging is a high throughput technology based on the total integral of energy frequency spectrum. We extracted the most relevant articles (comprehensive reviews and original research articles) for inclusion in our review by performing a comprehensive literature search using the Pubmed (last accessed on 2015 April 28) scientific database. Color Doppler is a high-throughput, sophisticated imaging technique for the assessment of uterine anomalies, intrauterine pathology, tubal patency, polycystic ovaries, ovarian follicular monitoring, endometrial receptivity, failed and/or ectopic pregnancy, male infertility, and uterine, endometrial, and ovarian vascularity. Assessments of the uteroovarian pulsatility indices (PIs), resistance indices (RIs), and endometrial color signals are important determinants of in vitro fertilization (IVF) cycles and pregnancy rates. With our clinical/scientific research experience in the field of reproductive medicine, we strongly believe that an overall public health model needs to be designed in managing infertility patients; therefore, major issues such as cost-effectiveness and technical artifacts should be addressed so as to achieve an accurate clinical diagnosis, successful IVF outcome/pregnancy, and overall patient satisfaction in a clinical research setting. Simple, safe, efficient, and affordable diagnostic modalities should be incorporated at infertility clinics coupled with well-designed patient counseling sessions and community-based public health awareness campaigns conducted so as to reduce the morbidity and mortality rates associated with reproductive disorders.

Eulerian–Lagrangian bridge for the energy and dissipation spectra in isotropic turbulence

We study, numerically and analytically, the relationship between the Eulerian spectrum of kinetic energy, E E(k, t), in isotropic turbulence and the corresponding Lagrangian frequency energy spectrum, E L(ω, t), for which we derive an evolution equation. Our DNS results show that not only E L(ω, t) but also the Lagrangian frequency spectrum of the dissipation rate \({\varepsilon_{\rm L} (\omega, t)}\) has its maximum at low frequencies (about the turnover frequency of energy-containing eddies) and decays exponentially at large frequencies ω (about a half of the Kolmogorov microscale frequency) for both stationary and decaying isotropic turbulence. Our main analytical result is the derivation of equations that bridge the Eulerian and Lagrangian spectra and allow the determination of the Lagrangian spectrum, E L (ω) for a given Eulerian spectrum, E E (k), as well as the Lagrangian dissipation, \({\varepsilon_{\rm L}(\omega)}\), for a given Eulerian counterpart, \({\varepsilon_{\rm E} (k)=2\nu k^2 E_{\rm E}(k)}\). These equations were derived from the Navier–Stokes equations in the sweeping-free coordinate system (intermediate between the Eulerian and Lagrangian frameworks) which eliminates the effect of the kinematic sweeping of the small eddies by the larger eddies. We show that both analytical relationships between E L (ω) and E E (k) and between \({\varepsilon_{\rm L} (\omega)}\) and \({\varepsilon_{\rm E} (k)}\) are in very good quantitative agreement with our DNS results and explain how \({\varepsilon_{\rm L} (\omega, t)}\) has its maximum at low frequencies and decays exponentially at large frequencies.

A NEW MULTI-DIMENSIONAL GENERAL RELATIVISTIC NEUTRINO HYDRODYNAMICS CODE OF CORE-COLLAPSE SUPERNOVAE. III. GRAVITATIONAL WAVE SIGNALS FROM SUPERNOVA EXPLOSION MODELS

We present a detailed theoretical analysis of the gravitational-wave (GW) signal of the post-bounce evolution of core-collapse supernovae (SNe), employing for the first time relativistic, two-dimensional (2D) explosion models with multi-group, three-flavor neutrino transport based on the ray-by-ray-plus approximation. The waveforms reflect the accelerated mass motions associated with the characteristic evolutionary stages that were also identified in previous works: A quasi-periodic modulation by prompt postshock convection is followed by a phase of relative quiescence before growing amplitudes signal violent hydrodynamical activity due to convection and the standing accretion shock instability during the accretion period of the stalled shock. Finally, a high-frequency, low-amplitude variation from proto-neutron star (PNS) convection below the neutrinosphere appears superimposed on the low-frequency trend associated with the aspherical expansion of the SN shock after the onset of the explosion. Relativistic effects in combination with detailed neutrino transport are shown to be essential for quantitative predictions of the GW frequency evolution and energy spectrum, because they determine the structure of the PNS surface layer and its characteristic g-mode frequency. Burst-like high-frequency activity phases, correlated with sudden luminosity increase and spectral hardening of electron (anti-)neutrino emission for some 10ms, are discovered as new features after the onset of the explosion. They correspond to intermittent episodes of anisotropic accretion by the PNS in the case of fallback SNe. We find stronger signals for more massive progenitors with large accretion rates. The typical frequencies are higher for massive PNSs, though the time-integrated spectrum also strongly depends on the model dynamics.