The article deals with a research of acoustic emission induced by electromagnetic field. Experiments were focused on measurement of acoustic emission (sound waves) as a mechanical response to the excitation current. Surface displacement was detected by laser interferometer and arising surface waves were then observed. Maximal measured amplitude of mechanical displacement driven by excitation current with amplitude 120 mA is about 8 nm. and Článek se zabývá výzkumem akustické emise generované pomocí elektromagnetického pole. V experimentech se měří velikost mechanické odezvy akustické emise (mechanických vln) na budicí proud z generátoru. Výchylka povrchu byla snímána laserovým interferometrem, byla registrována přítomná povrchová vlna. Maximální amplituda výchylky je 8 nm při amplitudě budicího proudu 120 mA.
This paper contains the studies of the noise level in GPS (Global Positioning System) time series. As the data for this research the authors used changes of the geodetic coordinates of the ASG-EUPOS and associated (Slovak and Czech) sites. The method of precise GPS observations processing in short-time intervals was worked out in the Centre of Applied Geomatics, Military University of Technology. The authors focus on the diurnal and sub-diurnal frequency bands (tidal) as the tidal effects influence the sites’ positions at the most and the model used in the standard processing software does not contain geodetic coefficients. Thus the residual values of the geodetic coordinates time series should hold some information in the shape of coloured noise. The paper comprise short description of the Earth tides phenomenon, the concept of the tidal parameters determination, character of the white and coloured noise and the assessment of the noise estimation from GPS data. As the processed network contains 130 sites the spatial distribution of the noise’s parameters is also investigated., Janusz Bogusz and Bernard Kontny., and Obsahuje bibliografii
The paper deals with the measurement of coherent light power below the noise level of one detector. The method uses the optical arrangement of the Mach-Zehnder interferometer and the modified detector in the quadrature. Using correlated detection of signals in two quadrant detector channels, the measured power was 23 times weaker than the noise-equivalent power. and Článek se zabývá měřením výkonu koherentního světla pod úrovní šumu jednoho detektoru. Měřicí metoda využívá optického uspořádání Machova-Zehnderova interferometru a upraveného detektoru v kvadratuře. Pomocí korelované detekce signálů ve dvou kanálech detektoru v kvadratuře se podařilo naměřit výkon 23krát slabší, než je ekvivalentní šumový výkon.
Gearboxes and similar machines containing rotating parts are complex systems with complicated structure and couplings. Generally they can be decomposed into more simple subsystems. These subsystems are usually rotating shafts with gears joined
by gear couplings and housing coupled with rotating shafts by bearings. The paper is aimed at the mathematical modelling of gearboxes with spur helical gears considered including their interior rotating shaft system and housing. The used bearing model
respects real number of rolling elements and roller contact forces acting between the journals and the outer housing. The model of a complete gearbox is created using the modal synthesis method. The kinematic transmission errors in gear couplings are viewed as sources of excitation. Vibration and noise analysis of the gearbox housing is performed by means of the created model. Four types of objective functions suitable for optimization from the radiated noise point of view are proposed. The presented methodology is applied to the simple test-gearbox. and Obsahuje seznam literatury
With the evolution of GNSS technology, geodynamic activities can appropriately be modelled nowadays. GNSS derived time series from wdhich velocities and their uncertainties are derived, are vital derivatives in geodynamic modelling processes. Therefore, understanding all the stochastic properties is crucial. Assuming that GNSS coordinate time series is characterized by only white noise may lead to underestimation of velocity uncertainties. In this contribution, noise behaviour of NigNET tracking stations position time series was examined by adopting WN, FL+WN, WN+RW, WN+PL. Using the maximum likelihood estimate (MLE), Akaike Information Criteria (AIC) and Bayesian Information Criteria (BIC) the quality of stochastic model or the goodness of fit of a stochastic model is determined. The results of this study show that the combination of white plus flicker noise is the best model for describing the stochastic part of NigNET tracking stations position time series.
For a random vector (X,Y) characterized by a copula CX,Y we study its perturbation CX+Z,Y characterizing the random vector (X+Z,Y) affected by a noise Z independent of both X and Y. Several examples are added, including a new comprehensive parametric copula family (Ck)k∈[−∞,∞].
Impact of noise on hearing system, acoustic quantities, process of noise measurement and imaging of acoustic pressure at measurement surface by 3D graph are described in the article. Mentioned 3D graph is a new tool for noise reduction of large rotating machines. and V článku jsou popsány vlivy hluku na sluchové ústrojí, akustické veličiny, postup měření hluku a zobrazení akustického tlaku na měřicí ploše pomocí 3D grafu. Popsaný 3D graf je nový nástroj pro snižování hluku velkých točivých strojů.
Previous studies of physiological responses to music and noise showed the effect on the autonomic nervous system. The heart rate variability (HRV) has been used to assess the activation of the sympathetic and the parasympathetic nervous systems. The present study was aimed to examine HRV with exposure to four sine-wave pure tones (20 Hz, 50 Hz, 2 kHz and 15 kHz) in an environment where the sound intensity exceeded level 65 dB (A-weighted). The participants (20 adolescent girls) were lying in supine position during exposure protocol divided into 6 periods, the first time with generated sounds and the second time without sounds. In the protocol without sound exposure, the low frequency band of the HRV spectrum was increased compared to the basal state before examination (period_1: 6.05±0.29 ms2 compared to period_5: 6.56±0.20 ms2, p<0.05). The significant increase of root Mean Square of the Successive Differences (rMSSD, period_1: 4.09±0.16 s compared to period_6: 4.33±0.12 s, p<0.05) and prolongation of R to R peak (RR) interval (period_1: 889±30 ms compared to period_5: 973±30 ms, p<0.001) were observed in the protocol without sound exposure comparing to the protocol with sound exposure where only bradycardia was observed. Contrary to rather polemical data in literature our pilot study suggests that sounds (under given frequencies) have no impact on the heart rate variability and cardiac autonomic regulation., M. Veternik, I. Tonhajzerova, J. Misek, V. Jakusova, H. Hudeckova, J. Jakus., and Obsahuje bibliografii