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Background The aim of this study is to quantify the frequency content of the blood velocity waveform in different body regions by means of phase contrast (PC) cardiovascular magnetic resonance (CMR) and Doppler ultrasound. The highest frequency component of the spectrum is inversely proportional to the ideal temporal resolution to be used for the acquisition of flow-sensitive imaging (Shannon-Nyquist theorem). Methods Ten healthy subjects (median age 33y, range 24–40) were scanned with a high-temporal-resolution PC-CMR and with Doppler ultrasound on three body regions (carotid arteries, aorta and femoral arteries). Furthermore, 111 patients (median age 61y) with mild to moderate arterial hypertension and 58 patients with aortic aregurgitation, atrial septal defect, or repaired tetralogy of Fallot underwent aortic CMR scanning. The frequency power distribution was calculated for each location and the maximum frequency component, fmax, was extracted and expected limits for the general population were inferred. Results In the healthy subject cohort, significantly different fmax values were found across the different body locations, but they were nonsignificant across modalities. No significant correlation was found with heart rate. The measured fmax ranged from 7.7 ± 1.1 Hz in the ascending aorta, up to 12.3 ± 5.1 Hz in the femoral artery (considering PC-CMR data). The calculated upper boundary for the general population ranged from 11.0 Hz to 27.5 Hz, corresponding to optimal temporal resolutions of 45 ms and 18 ms, respectively. The patient cohort exhibited similar values for the frequencies in the aorta, with no correlation between blood pressure and frequency content. Conclusions The temporal resolution of PC-CMR acquisitions can be adapted based on the scanned body region and in the adult population, should approach approximately 20 ms in the peripheral arteries and 40 ms in the aorta. Trial registration This study presents results from a restrospective analysis of the clinical study NCT01870739 (ClinicalTrials.gov).

Background: The evaluation of balance measures can help identify postural control processes, but traditional data collection for the center of pressure (COP) may not reveal differences in postural control mechanisms. This study aimed to evaluate the reliability of the frequency component of postural sway using wavelet analysis of COP signals. Methods: Fifteen healthy male subjects (average age: 39.16±7.2 years, average weight: 72±11.06 kg, average height: 171±6.31 cm) participated in this project. They were requested to perform three trials of single-leg and tandem stance conditions for 20-second with and without vision on a force plate. The frequency content of COP signals, including the energy, root mean square (RMS), and velocity of the COP in four frequency bandwidths of postural sway, was evaluated. The test-retest reliability of COP parameters was tested using the intraclass correlation coefficient (ICC). Results: Among different COP parameters, the energy of the COP within a moderate (1.56–6.25 Hz) frequency band (.79≤ ICC ≤.97) with standard error measurement (SEM) ranged from .14 to .23, the RMS of COP within low (.39–1.56Hz) (.79≤ ICC ≤.93) and ultralow (< .10 Hz) (SEM ranged from .000 to .002) (.78≤ ICC ≤.94) in a tandem stance and the RMS of COP in a bandwidth of < .10 Hz (SEM=.00) in a single-leg stance (.70≤ ICC ≤.99) with the eyes closed and open showed good to excellent reliability. Conclusion: The results of this study showed moderate to excellent reliability of wavelet-based COP measures; therefore, these parameters can be used for the identification of postural control mechanisms.

Time-frequency (TF) representations are very important tools to understand and explain circumstances, where the frequency content of non-stationary signals varies in time. A variety of biosignals such as speech, electrocardiogram (ECG), electroencephalogram (EEG), and electromyogram (EMG) show some form of non-stationarity. Considering Priestley's evolutionary (time-dependent) spectral theory for analysis of non-stationary signals, the authors defined a TF representation called evolutionary Slepian transform (EST). The evolutionary spectral theory generalises the definition of spectra while avoiding some of the shortcomings of bilinear TF methods. The performance of the EST in the representation of biosignals for the blind source separation (BSS) problem to extract information from a mixture of sources is studied. For example, in the case of EEG recordings, as electrodes are placed along the scalp, what is actually observed from EEG data at each electrode is a mixture of all the active sources. Separation of these sources from a mixture of observations is crucial for the analysis of recordings. In this study, they show that the EST can be used efficiently in the TF-based BSS problem of biosignals.

Dynamic testing of bridges has as target to establish their response on pulse forces between the wheels and unevenness of road surface. Generally, during the tests, real time accelerations or deformations are to be measured and which through successive processing methods lead to other data as velocities, displacements, dynamic impact factor, but also the damping ratio. In order to validate the bridge response following testing, the measured data are compared both with allowable limits existing in standards and with the results obtained using analytical or numerical models. In Romania, the dynamic testing of bridges is recommended by the current standards, only for important bridges, erected in complex or special solutions and also for large span bridges. The aim of this paper is to outline the results obtained from the on-site measurements during dynamic testing of a viaduct placed on the motorway A1, sector Orăştie-Sibiu. The bridge superstructure is a composite one, continuous girder on 12 spans: 40+10×60+40 m, the substructure consisting in 11 piers with lamellar elevations and variable height in the range 8.50-24m. In the paper a finite element model is also presented which was used for time-history analyses using an impulse type load. Finally, the results obtained on the site and using the numerical model are compared and discussed.

This study presents a newly developed modular system for control of power electronic amplifiers in high-power, high-frequency power hardware in the loop experiments. The proposed design comprises computational nodes connected via multi-gigabit fibre-optic links. Nodes are modular and reconfigurable, allowing interfacing with a range of sensors and actuators, typically voltage and current sensors, and switching converters. The system has been designed for scalability to permit arbitrarily high power ratings and fidelity to be achieved through paralleling and interleaving of multiple power converter modules, targeting an ultimate sample and control rate of 1 MHz. Experimental validation is presented using a two-node configuration to facilitate a power electronic experiment operating at 120 V(rms) and 10 A(rms), with a fundamental frequency of 50 Hz and frequency content up to the 11th harmonic.

On-stage sound field analysis of a traditional performance of the Javanese gamelan at Pendopo ISI Surakarta, Indonesia was conducted by analyzing the effective decay time of a normalized autocorrelation function called tau-e, τ e , during a performance of the Gambyong Pare Anom dance. The parameter tau-e is used to describe the richness of the frequency content, tempo, and types of gamelan instruments being played at a certain time and position on stage. The tau-e parameter is important for musicians in order to maintain communication between each other such that they can keep the performance in harmony. In order to determine the acoustic parameters heard by gamelan musicians on stage, sound measurements were conducted at 4 points on stage during a performance. Each position represents a specific group of gamelan instruments, which have different characteristics of loudness and frequency, different functions and different ways the instruments are played. The analysis showed that each of the four positions had a different value of τ e , which fluctuated throughout the performance. Overall, the dominant τ e at position 1 was 20 ms; at position 2 it was 50 ms; at position 3 it was 20 ms; and at position 4 it was 40 ms. The distribution of τ e on the stage shows that positions 1 and 3 had more frequency richness compared to positions 2 and 4.

This paper is concerned with the assessment of seismic drift demands in steel moment frames designed to comply with Eurocode 8 provisions, with due account for cyclic and in-cycle degradation. In addition to degradation effects, the main parameters examined include the ground motion frequency content as well as the level of constant relative strength or inelasticity. To represent a wide range of structural characteristics, a set of 54 multi-storey frames are considered, in which the number of stories, steel profiles, seismic hazard and compliance criteria are varied. Detailed incremental dynamic analyses are performed on the full set of frames using a suite of 56 far-field ground motion records, which are scaled appropriately to achieve different levels of inelastic demand or equivalent behaviour factors. The seismic performance is evaluated in terms of maximum global and local drifts as well as beam chord rotations. Characteristic results show that maximum response in terms of global deformations and inter-storey drifts is significantly affected by degradation phenomena, along with the ground motion frequency content and the level of inelastic demand. For medium rise typologies subjected to earthquakes with relatively high frequency content, concentration of seismic demand in terms of inter-storey drift is captured by the degrading models and leads to early development of plastic mechanisms. The seismic demand scenarios used in this study, through spectral acceleration-based scaling of ground motions, indicate that the influence of degradation can be significant not only at collapse levels but also at those associated with typical design situations. Finally, based on the extensive analyses carried out in this investigation, expressions for predicting the global and local demands are proposed and discussed.

This study deals with the seismic fragility of elastic structural systems equipped with single concave sliding (friction pendulum system (FPS)) isolators considering different soil conditions. The behavior of these systems is analyzed by employing a two-degree-of-freedom model, whereas the FPS response is described by means of a velocity-dependent model. The uncertainty in the seismic inputs is taken into account by considering artificial seismic excitations modelled as timemodulated filtered Gaussian white noise random processes of different intensity within the power spectral density method. In particular, the filter parameters, which control the frequency content of the random excitations, are calibrated to describe stiff, medium and soft soil conditions. The sliding friction coefficient at large velocity is also considered as a random variable modelled through a uniform probability density function. Incremental dynamic analyses are developed in order to evaluate the probabilities of exceeding different limit states related to both the reinforced concrete (RC) superstructure and isolation level, defining the seismic fragility curves within an extensive parametric study carried out for different structural system properties and soil conditions. The abovementioned seismic fragility curves are useful to evaluate the seismic reliability of base-isolated elastic systems equipped with FPS and located in any site for any soil condition.

A sample of healthy wind turbines from the same wind farm with identical sizes and designs was investigated to determine the average vibrational signatures of the drive train components during normal operation. The units were variable-speed machines with three blades. The rotor was supported by two bearings, and the drive train connected to an intermediate three-stage planetary/helical gearbox. The nominal 2 MW output power was regulated using blade pitch adjustment. Vibrations were measured in exactly the same positions using the same type of sensors over a six-month period covering the entire range of operating conditions. The data set was preliminary validated to remove outliers based on the theoretical power curves. The most relevant frequency peaks in the rotor, gearbox, and generator vibrations were detected and identified based on averaged power spectra. The amplitudes of the peaks induced by a common source of excitation were compared in different measurement positions. A wind speed dependency of broadband vibration amplitudes was also observed. Finally, a fault detection case is presented showing the change of vibration signature induced by a damage in the gearbox.

Near-fault ground motion with directivity or fling effects is significantly influenced by the rupture mechanism and substantially different from ordinary records. This class of ground motion has large amplitude and long period, exhibits unusual response spectra shapes, possesses high PGV/PGA and PGD/PGA ratios and is best characterized in the velocity and the displacement time-histories. Such ground motion is also characterized by its energy being contained in a single or very few pulses, thus capable of causing severe damage to the structures. This paper investigates the characteristics of near-fault pulse-like ground motions and their implications on the structural responses using new proposed measures, such as, the effective frequency range, the energy rate (in time and frequency domains) and the damage indices. The paper develops also simple mathematical expressions for modeling this class of ground motion and the associated structural responses, thus eliminating numerical integration of the equations of motion. An optimization technique is also developed by using energy concepts and damage indices for modeling this class of ground motion for inelastic structures at sites having limited earthquake data.

This discussion raises a few comments and questions on the paper by Cao and Friswell [Cao H, Friswell MI. The effect of energy concentration of earthquake ground motions on the nonlinear response of RC structures. Soil Dyn Earthquake Eng 2009; 29: 292?9.]. The authors consider an interesting problem on seismic response analysis of nonlinear structures. Specifically, the study examines the implication of the energy concentration of the adopted ground acceleration record on the nonlinear response of reinforced concrete structures. The paper employs the wavelet transform to characterize the energy content of the ground acceleration in time and frequency domains., Soil Dynamics and Earthquake Engineering, 29(7), pp. 1181-1183; 2009

Acoustic emission (AE) is a Non Destructive Inspection Technique, widely used for monitoring of structural condition of different materials like concrete, masonry and rock. It utilizes the transient elastic waves after each fracture occurrence, which are captured by sensors on the surface. Several parameters of the AE behavior enlighten the damage stage within the material. These may be the cumulative AE activity, which is connected to the density of cracks and the emission energy which is connected to the cracks’ intensity. Additionally, AE waveform parameters like duration and frequency content depend on the motion of the crack tip and therefore, carry information about the mode of the crack. Study of the AE indices enlightens the fracture process, enabling predictions on the remaining life. However, the experimental conditions crucially affect the waveforms captured by the sensors. Specimen size, as well as sensor type and sensors separation distance exercise strong influence in the acoustic emission parameters. Since AE features like amplitude and energy are used for characterization purposes in the framework of an energy density approach and frequency is used in cracking mode classification schemes, the influence of the above mentioned experimental parameters should be certainly taken into account in order to lead to more accurate results and increase reliability. This would help to expand the use of AE in situ which so far is hindered by geometric and other technical reasons that allow only a case-specific approach. In the present paper fracture experiments in different specimen sizes of cementitious and rock materials are described while the sensor location relatively to the cracking zone is altered. The aim of this study is to validate the use of cracking characterization in laboratory and check the extension for similar schemes in real size structures with a multiscale methodology.

This study aims to develop efficient tools for performance-based seismic design of soil-structure interaction (SSI) systems on soft soils. To simulate the SSI effects, linear and nonlinear 'equivalent fixed-base single-degree-of-freedom' (EFSDOF) oscillators as well as a sway-rocking SSI model were adopted. The nonlinear dynamic response of around 10,000 SSI models and EFSDOF oscillators having a wide range of fundamental periods, target ductility demands, and damping ratios were obtained under a total of 20 seismic records on soft soil sites. Based on the results of this study, a practical method is developed for estimating the base shear and maximum displacement demands of a nonlinear single-degree-of-freedom structure on soft soil deposits. In the proposed procedure, the effect of frequency content of ground motions is considered by normalising the period of vibration by the spectral predominant periods, while the nonlinear EFSDOF models are used to improve the computational efficiency.