Investigation of internal intermittency by way of higher-order spectral moments

The analysis of turbulence by way of higher-order spectral moments is uncommon, despite the relatively frequent use of such statistical analyses in other fields of physics and engineering. In this work, higher-order spectral moments are used to investigate the internal intermittency of the turbulent velocity and passive-scalar (temperature) fields. This study first introduces the theory behind higher-order spectral moments as they pertain to the field of turbulence. Then, a short-time Fourier-transform-based method is developed to estimate these higher-order spectral moments and provide a relative, scale-by-scale measure of intermittency. Experimental data are subsequently analysed and consist of measurements of homogeneous, isotropic, high-Reynolds-number, passive and active grid turbulence over the Reynolds-number range $35\leq R_{\lambda } \leq ~731$ . Emphasis is placed on third- and fourth-order spectral moments using the definitions formalised by Antoni (Mech. Syst. Signal Pr., vol. 20 (2), 2006, pp. 282–307), as such statistics are sensitive to transients and provide insight into deviations from Gaussian behaviour in grid turbulence. The higher-order spectral moments are also used to investigate the Reynolds (Péclet) number dependence of the internal intermittency of velocity and passive-scalar fields. The results demonstrate that the evolution of higher-order spectral moments with Reynolds number is strongly dependent on wavenumber. Finally, the relative levels of internal intermittency of the velocity and passive-scalar fields are compared and a higher level of internal intermittency in the inertial subrange of the scalar field is consistently observed, whereas a similar level of internal intermittency is observed for the velocity and passive-scalar fields for the high-Reynolds-number cases as the Kolmogorov length scale is approached.

A New Methodology to Characterise the Radar Bright Band Using Doppler Spectral Moments from Vertically Pointing Radar Observations

The detection and characterisation of the radar Bright Band (BB) are essential for many applications of weather radar quantitative precipitation estimates, such as heavy rainfall surveillance, hydrological modelling or numerical weather prediction data assimilation. This study presents a new technique to detect the radar BB levels (top, peak and bottom) for Doppler radar spectral moments from the vertically pointing radars applied here to a K-band radar, the MRR-Pro (Micro Rain Radar). The methodology includes signal and noise detection and dealiasing schemes to provide realistic vertical Doppler velocities of precipitating hydrometeors, subsequent calculation of Doppler moments and associated parameters and BB detection and characterisation. Retrieved BB properties are compared with the melting level provided by the MRR-Pro manufacturer software and also with the 0 °C levels for both dry-bulb temperature (freezing level) and wet-bulb temperature from co-located radio soundings in 39 days. In addition, a co-located Parsivel disdrometer is used to analyse the equivalent reflectivity of the lowest radar height bins confirming consistent results of the new signal and noise detection scheme. The processing methodology is coded in a Python program called RaProM-Pro which is freely available in the GitHub repository.

Serviceability Assessment of Footbridges via Improved Interval Analysis

This paper studies the propagation of uncertainties on serviceability assessment of footbridges in unrestricted traffic condition based on a non-deterministic approach. Multi-pedestrian loading is modeled as a stationary Gaussian random process through the Equivalent Spectral Model [1] which yields analytical expressions of the spectral moments of the footbridge dynamic response. The uncertain pedestrian-induced loading parameters and structural dynamic properties are modeled as interval variables. An approximate analytical procedure, based on the Improved Interval Analysis [2], is introduced as an efficient alternative to classical optimization in order to propagate interval uncertainties. The presented procedure allows us to derive closed-form expressions of the bounds of the spectral moments of the response, as well as of the expected value and cumulative distribution function of the maximum footbridge acceleration. Two strategies are proposed to assess footbridges' serviceability. The first one leads to the definition of a range of comfort classes. The second strategy enables us to estimate an interval of probability of reaching at least a suitable comfort level.

Спектральные моменты характеристик бинарных взаимодействий между линейными молекулами

A new approach to derive symmetrized expressions of leading classical moments of spectral distributions characterizing different anisotropic terms of the interaction potential for the case of two liear molecules is presented. The results allow to calculate diffuse shapes formed by transitions between continuous eigenstates of a molecular pair and open the way to account for the nonMarkov effects (due to finite collision durations) in the rotatonal relaxation matrix of an arbitrary rank. The approach is also applied to the spectral moments of vector and tensor characteristics determining the band intensities in the collision-induced spectra of linear molecules. Generally, the use of symmetrized expressions lead to considerably faster computer codes.

Acoustic Features of the Surgut Khanty Consonants

This paper deals with the acoustic features of the Surgut Khanty consonants. The research is based on the data gathered during fieldwork in Kogalym town (2018) and the Ugut village (2019). The audio samples are provided by three native speakers of the Tromjegan, Malyi Yugan, and Bolshoi Yugan idioms. The total size of the sample database numbers more than six thousand isolated consonant pronouncements. The data for the research was obtained using oscillographic and spectrographic methods, formant locus analysis, spectral moment analysis. The analysis was performed via Praat and Emu-SDMS software. Oscillograghy and spectrography methods reveal that voiceless fricative phonemes may be voiced in intervocalic distribution. It is common for the sonants to become devoiced in the final and preconsonantal positions. Moreover, due to devoicing, different phonemes may acquire low-obstruent and obstruent consonant features. For the fricative, lateral-fricative consonants, affricates spectral moment analysis has been carried out. The spectral moments technique gives an opportunity to represent complex noise data as a relatively small set of numbers that can be processed statistically. According to the data on spectral moments, four types of noise have been defined: high-frequency low-dispersion noise resembling /s/, medium-frequency low-dispersion noise resembling /ʃ/, /tʃ/, /cc/, low-frequency medium-dispersed noise for phonemes /ɫ/, / /, low-frequency dispersed noise for phonemes /w/, /γ/. The forman analysis is used o es ima e onsonan resonan frequen ies. As shown by he formant locus analysis, the smallest values of the second formant locus are associated with the labial and velar phonemes. Larger values are associated with the coronal phonemes. The largest ones are specific to the palatal phonemes. At the same time, the acoustic features make it possible to stably distinguish the nasal /n/ - /ɲ/, wherein the opposition of the middle and fron lingual ar i ula ions is observed only in some speakers’ re ordings for the pairs /ɫ/ - / /, /tʃ/ - /cc/.

Phase Codes for Mitigating Ambiguities in Range and Velocity

We review cubic phase codes for mitigating ambiguities in range and velocity before introducing two specific codes. The two have periodicities of 5 and 7 samples for both the transmitted and the modulation code sequences. The short periods are suitable for generating codes of arbitrary length starting with about 15. We abbreviate the two codes with L5 and L7 and describe generation of the codes starting with kernels (i.e., minimum length sequences which repeat to generate the codes of desired lengths). The L5 modulation code produces 5 spectral replicas of the coded signal and the L7 produces 7. We apply the L7 code to a sinusoid and reveal spectra of the modulated signals from several ambiguous range intervals. Through simulation, we show application to weather-like signals and construct examples whereby two weather signals and ground clutter are overlaid. Using theory, we define the operating region of the codes in the signal parameter space. The region covers a wide range of overlaid returned powers and spectrum widths; it is obtained from simulations involving the L codes and the SZ(8/64) code. The technique is effective in distinguishing the returns from two trip regions separated by no more than L-2 ambiguous range intervals and reconstructing the corresponding spectral moments. The L5 and L7 codes protect from trip returns, up to 5th and 7th making them suitable for short wavelength (3 and 5 cm) radars as their PRTs must be relatively short to accommodate the expected spread of velocities in storms.