Frequency Power Spectral Density Research Articles

Response of end tidal CO2pressure to impulse exercise

The purpose of the present study was to examine how end tidal CO(2) pressure (PETCO(2)) is controlled in impulse exercise. After pre-exercise at 25 watts for 5 min, impulse exercise for 10 sec with 200 watts followed by post exercise at 25 watts was performed. Ventilation (VE) significantly increased until the end of impulse exercise and significantly re-increased after a sudden decrease. Heart rate (HR) significantly increased until the end of impulse exercise and then decreased to the pre-exercise level. PETCO(2) remained constant during impulse exercise. PETCO(2) significantly increased momentarily after impulse exercise and then significantly decreased to the pre-exercise level. PETCO(2) showed oscillation. The average peak frequency of power spectral density in PETCO(2) appeared at 0.0078 Hz. Cross correlations were obtained after impulse exercise. The peak cross correlations between VE and PETCO(2), HR and PETCO(2), and VE and HR were 0.834 with a time delay of -7 sec, 0.813 with a time delay of 7 sec and 0.701 with a time delay of -15 sec, respectively. We demonstrated that PETCO(2) homeodynamics was interactively maintained by PETCO(2) itself, CO(2) transportation (product of cardiac output and mixed venous CO(2) content) into the lungs by heart pumping and CO(2) elimination by ventilation, and it oscillates as a result of their interactions.

Revealing the role of the autonomic nervous system in the development and maintenance of Goldblatt hypertension in rats

Despite extensive use of the renovascular/Goldblatt model of hypertension—2K-1C, and the use of renal denervation to treat drug resistant hypertensive patients, autonomic mechanisms that underpin the maintenance of this hypertension are important yet remain unclear. Our aim was to analyse cardiovascular autonomic function by power spectral density analysis of both arterial pressure and pulse interval measured continuously by radio telemetry for 6 weeks after renal artery clipping. Mean arterial pressure increased from 106 ± 5 to 185 ± 2 mm Hg during 5 weeks post clipping when it stabilized. A tachycardia developed during the 4th week, which plateaued between weeks 5 and 6. The gain of the cardiac vagal baroreflex decreased immediately after clipping and continued to do so until the 5th week when it plateaued (from − 2.4 ± 0.09 to − 0.8 ± 0.04 bpm/mm Hg; P < 0.05). A similar time course of changes in the high frequency power spectral density of the pulse interval was observed (decrease from 13.4 ± 0.6 to 8.3 ± 0.01 ms2; P < 0.05). There was an increase in both the very low frequency and low frequency components of systolic blood pressure that occurred 3 and 4 weeks after clipping, respectively. Thus, we show for the first time the temporal profile of autonomic mechanisms underpinning the initiation, development and maintenance of renovascular hypertension including: an immediate depression of cardiac baroreflex gain followed by a delayed cardiac sympathetic predominance; elevated sympathetic vasomotor drive occurring after the initiation of the hypertension but coinciding during its mid-development and maintenance.

A horizontal multiple-tip penetrometer for on-the-go soil mechanical resistance and acoustic failure mode detection

Soil mechanical resistance can be used as an indicator of soil compaction. For on-the-go mapping of spatial variability in soil compaction, single and multiple-tip horizontal penetrometers have been developed and used to measure the soil mechanical resistance. However, it has been reported that the measured soil resistance in different soil layers depends not only on the degree of soil compactness but also on soil failure mode induced by the shank of the sensor. It was hypothesized that the differences in sound signals collected by microphones during penetration tests could be used to differentiate the failure modes. In this research, an acoustic multiple-tip horizontal penetrometer was developed, with three 30° prismatic tips attached horizontally to S-shape load cells and worked at depths of 10, 20 and 30cm. The tips working at 10 and 30cm depths were also fitted with microphones. The sensor was tested in a field with a clay loam soil. The sound signal was first de-noised using wavelet method, and then frequency spectrum and power spectral density of the signals were obtained by fast Fourier transform and Welsh's method, respectively. When the prismatic tips were operated below the critical depth of the sensor (tips at depths of 20 and 30cm), there was a significant relationship between horizontal resistance index (HRI) and the cone index measured by a vertically-operated cone penetrometer; whereas for the shallower depth (10cm) the relationship was not significant. The power of the sound recorded of the tip passing through the disturbed soil above the critical depth (10cm) was much lower than when the tip was penetrating the undisturbed soil located below the critical depth (30cm). The increase in power of the acoustic signal with depth was in line with the increase in the measured HRI. It can be concluded that the developed combined acoustic penetrometer can both detect soil failure mode and measure soil horizontal resistance.

Autonomic dysfunction in different subtypes of post-acute ischemic stroke

ObjectivesCentral autonomic impairment is frequent in ischemic stroke at acute or chronic stages. The mechanism by which these symptoms occur in patients with ischemic stroke has not been elucidated. This study sought to investigate cardiovascular autonomic function in patients with different subtypes of post-acute ischemic stroke. Methods77 ischemic stroke patients [50 patients with large-artery atherosclerosis (LAA) and 27 patients with small-vessel occlusion (SVO), average 6months after stroke onset] and 37 elderly controls were recruited. All performed Ewing's battery autonomic function tests and power spectral analysis of heart rate variability (HRV). ResultsStroke patients with both LAA and SVO had significantly lower low frequency power spectral density than controls. The prevalence of autonomic dysfunction in both groups (82.0% patients with LAA and 63.0% with SVO) was higher than that in controls (21.6%). Patients with LAA showed impairment of all parasympathetic tests (all P<0.05) and one of the sympathetic tests (mean fall in systolic blood pressure on standing: P=0.058) and those with SVO only showed impairment in two parasympathetic tests (heart rate response to deep breathing: P=0.010; heart rate response to standing: P=0.004) in comparison with controls. Patients with LAA had significantly more impairment than those with SVO in some autonomic parameters (Valsalva ratio: P=0.039; mean fall in systolic blood pressure on standing: P=0.015). ConclusionsIrrespective of the subtype of the ischemia, post-acute stroke patients showed a parasympathetic cardiac deficit. Additionally, parasympathetic and sympathetic cardiovascular modulations were more severely impaired in patients with LAA.

Dynamic response of functional virtual prototyping of motorcycle under combined excitations

This paper developed 3D product models of motorcycle and engine by UGNX as well as virtual prototyping by ADAMS program with road roughness generated by MATLAB. Under the straight-line running condition, the dynamic responses of motorcycle multibody system to both road and engine excitations were compared with those to only road excitation in terms of vertical acceleration response, amplitude frequency response and power spectral density. The comparisons of simulation data showed that the response due to flat road excitation was around 20 Hz, while that to the combined excitations was in a wide frequency band, of which the major components focused on 10 Hz, 15 Hz, 35 Hz, 70 Hz, 100 Hz and even higher frequencies, reflecting the characteristics of engine excitation based on its unbalanced inertia force and torque. It is concluded that the high fidelity virtual prototyping can simulate the dynamics of motorcycle product well in investigating the vibration and ride comfort performance.

Force and slip detection with direct-write compliant tactile sensors using multi-walled carbon nanotube/polymer composites

A mechanically compliant tactile sensor has been developed through direct-write (DW) deposition of a flexible conductive nanocomposite embedded between flexible polyurethane materials. Dispersion of multi-walled carbon nanotubes (MWCNTs) in a flexible and photocurable monomer introduced electrical and piezoresistive properties to the polymer which was used for the flexible conductive nanocomposite. Dispensing experiments were performed using the developed DW system to precisely create and embed the sensor elements between polyurethane substrates. From the experimental results, several flexible sensors including highly stretchable sensor elements (wires) were fabricated. Experiments were also performed to show that the sensor could detect applied forces at distinct locations on the surface. Slip was detected by examining the frequency content of the signals; sliding contact was characterized by a greater presence of high frequency power spectral density caused by mechanical vibrations that occur during slip. A Chebyshev band pass filter was developed to amplify these vibrations to distinguish between slip and nonslip tactile events. Finally, it is concluded that the study demonstrated in this work provides compelling evidence that the suggested materials, and methods of fabrication and characterization are promising for compliant tactile sensors.

Comprehensive Assessment for Autonomic Dysfunction in Different Phases after Ischemic Stroke

Studies mostly use the analysis of heart rate variability to measure cardiovascular autonomic regulation in ischemic stroke. Besides power spectral analysis of heart rate variability, this study sought to determine whether autonomic function was impaired during different phases in ischemic stroke by Ewing's battery of autonomic function tests. Ninety-four patients with ischemic stroke (34 patients in acute phase and 60 patients in chronic phase, average six-months after stroke onset) and thirty-seven elderly controls were recruited. Ewing's battery autonomic function tests and power spectral analysis of heart rate variability were performed in all the subjects. From power spectral analysis of heart rate variability, stroke patients of both acute and chronic phases had significantly lower low frequency power spectral density than controls. From Ewing's battery of autonomic function tests, patients in acute phase showed impairment in two parasympathetic tests (Valsalva ratio: P = 0·002; heart rate response to deep breathing: P < 0·001) and those in chronic phase showed impairment in all parasympathetic tests (all P < 0·05) in comparison with controls. The comprehensive assessment indicates that autonomic dysfunction occurs in acute phase of ischemic stroke and may persist up to six-months after stroke. Parasympathetic dysfunction rather than sympathetic dysfunction is predominant after ischemic stroke.

Electronic heat transport across a molecular wire: Power spectrum of heat fluctuations

With this study we analyze the fluctuations of an electronic only heat current across a molecular wire. The wire is composed of a single energy level which connects to two leads which are held at different temperatures. By use of the Green function method we derive the finite frequency power spectral density (PSD) of the emerging heat current fluctuations. This result assumes a form quite distinct from the power spectral density of the accompanying electric current noise. The complex expression simplifies considerably in the limit of zero frequency, yielding the heat noise intensity. The heat noise intensity still depends on the frequency in the zero-temperature limit, assuming different asymptotic behaviors in the low- and high-frequency regimes. These findings evidence that heat transport across molecular junctions can exhibit a rich structure beyond the common behavior which emerges in the linear response limit.

The Evolution and Propagation of Quasigeostrophic Ocean Eddies*

Abstract The long-term evolution of initially Gaussian eddies is studied in a reduced-gravity shallow-water model using both linear and nonlinear quasigeostrophic theory in an attempt to understand westward-propagating mesoscale eddies observed and tracked by satellite altimetry. By examining both isolated eddies and a large basin seeded with eddies with statistical characteristics consistent with those of observed eddies, it is shown that long-term eddy coherence and the zonal wavenumber–frequency power spectral density are best matched by the nonlinear model. Individual characteristics of the eddies including amplitude decay, horizontal length scale decay, and zonal and meridional propagation speed of a previously unrecognized quasi-stable state are examined. The results show that the meridional deflections from purely westward flow (poleward for cyclones and equatorward for anticyclones) are consistent with satellite observations. Examination of the fluid transport properties of the eddies shows that an inner core of the eddy, defined by the zero relative vorticity contour, contains only fluid from the eddy origin, whereas a surrounding outer ring contains a mixture of ambient fluid from throughout the eddy’s lifetime.

Use of high-frequency peak in spectral analysis of heart rate increment to improve screening of obstructive sleep apnoea

Several studies have correlated the ratio of the very low frequency power spectral density of heart rate increment (%VLFI) with obstructive sleep apnoea syndrome (OSAS). However, patients with impaired heart rate variability may exhibit large variations of heart rate increment (HRI) spectral pattern and alter the screening accuracy of the method. To overcome this limitation, the present study uses the high-frequency increment (HFI) peak in the HRI spectrum, which corresponds to the respiratory influence on RR variations over the frequency range 0.2 to 0.4 Hz. We evaluated 288 consecutive patients referred for snoring, observed nocturnal breathing cessation and/or daytime sleepiness. Patients were classified as OSAS if their apnoea plus hypopnoea index (AHI) during polysomnography exceeded 15 events per hour. Synchronized electrocardiogram Holter monitoring allowed HRI analysis. Using a %VLFI threshold >2.4% for identifying the presence of OSAS, sensitivity for OSAS was 74.9%, specificity 51%, positive predictive value 54.9% and negative predictive value 71.7% (33 false negative subjects). Using threshold for %VLFI >2.4% and HFI peak position >0.4 Hz, negative predictive value increased to 78.2% while maintaining specificity at 50.6%. Among 11 subjects with %VLFI <2.4% and HFI peak >0.4 Hz, nine demonstrated moderate to severe OSAS (AHI >30). HFI represents a minimal physiological criterion for applying %VLFI by ensuring that heart rate variations are band frequency limited.

CHANNEL CAPACITY OF HIGH-SPEED POWERLINE COMMUNICATION IN VEHICLES

Powerline Communication (PLC) Systems intents to use the mains network in vehicles for high-speed data transmission. Carrier frequencies in the range of MHz are required to establish data rates of some megabits per second. In this paper, typical reference channels extracted from channel measurements are presented and computation results of their capacities according to Shannon’s theorem are presented. Furthermore, the effect of limitations of frequency range and power spectral density of transmitted signal on achievable capacity is investigated. This paper outlines an assessment for theoretical channel capacity and achievable data rates of vehicular PLC transmission schemes. Finally, EMC (Electromagnetics Compatibility) constraint according to CISPR 25 (Comite International Special des Perturbations Radioelectrique – The International Special Committee on Radio Interference) is deeply considered.

Carotid sinus hypersensitivity: disease state or clinical sign of ageing? Insights from a controlled study of autonomic function in symptomatic and asymptomatic subjects

This study sought to improve the currently limited understanding of the pathophysiology of carotid sinus hypersensitivity (CSH) by comparing autonomic function measured by heart rate variability (HRV) and baroreflex sensitivity inpatients with symptomatic CSH and asymptomatic individuals with and without CSH. Twenty-two patients with symptomatic CSH, 18 individuals with asymptomatic CSH, and 14 asymptomatic older individuals without CSH were recruited to our study. Non-invasive measurements of heart rate and blood pressure were obtained during 10 min of supine rest. Low frequency (LF), high frequency (HF), and total power spectral density (PSD) for HRV were determined using the autoregressive method. The baroreflex slope (BRS) and baroreflex effectiveness index (BEI) were determined using the sequence method for baroreflex sensitivity. There were significant increases in the LF-HRV (P = 0.014), total PSD (P = 0.031), LF:HF (P = 0.047), normalized (nu) LF-HRV (0.049), down ramp BEI (P = 0.017), and total BEI (P = 0.038) in the symptomatic CSH group compared with non-CSH controls. The asymptomatic CSH group had significantly higher LF-HRV (P = 0.001), total PSD (P = 0.002), nuLF-HRV (P = 0.026), and LF:HF (P = 0.030), as well as up, down, and total BRS (P = 0.012, P = 0.015, and P = 0.011, respectively) and BEI (P = 0.049, P = 0.001, and P = 0.006, respectively) than non-CSH control participants. This study has demonstrated an association between CSH with increased resting sympathetic activity and baroreflex sensitivity regardless of the presence of symptoms, indicating the presence of autonomic dysregulation in individuals with CSH. Our findings therefore suggest that CSH is part of a generalized autonomic disorder but do not differentiate between asymptomatic and symptomatic individuals.

Postural control and thigh muscle activity in men with knee osteoarthritis

The aim of this study was to examine the standing balance and the function of vastus medialis (VM) and biceps femoris (BF) muscles with surface electromyography (EMG). Fifty-four subjects with uni- or bilateral knee osteoarthritis (OA) (aged 50–69 years) and 53 age-matched randomly selected clinically and radiologically healthy men participated in this study. Postural control was assessed on a force platform with a bipedal stance with eyes open (EO) and closed (EC) and a monopedal stance with EO. The balance parameters, mean sway velocity, velocity along AP and ML axes, elliptical area, standard deviation of center of pressure, average radial displacement, mean frequency and frequency domain balance parameters and different power spectral density frequency bands were determined. Root mean square (RMS) for EMG amplitude, mean EMG frequency ( f EMG,mean) and median EMG frequency ( f EMG,med) of motor unit activity were calculated from the normalized EMG data. During bipedal stance with EC and EO, there were no significant differences in balance parameters between groups, but during bipedal stance with EO, the RMS in VM was about 56% higher ( p < 0.05) in subjects with knee OA than in the control subjects and the values of f EMG,mean and f EMG,med were about 48% higher ( p < 0.05) in control subjects than subjects with knee OA. It is concluded that subjects with knee OA do not have any standing balance deficit, but they do exhibit increased muscle activity in VM muscle compared to control subjects.

Revealing the role of the autonomic nervous system in the development and maintenance of Goldblatt hypertension in conscious rats

Despite the extensive use of the Goldblatt model of hypertension (two kidney one clip, 2K‐1C) autonomic nervous mechanisms responsible for both the development and maintenance of the hypertension remain unclear. The objective of this study was to analyse cardiovascular autonomic function by power spectral density analysis of arterial pressure and pulse interval measured by radio telemetry for 6 weeks after renal artery clipping. Mean arterial pressure increased from 106±5 to 185±2 mmHg five weeks post clipping (n=6; P&lt;0.05) remaining stable during the 6th week. A tachycardia developed during the 4th week from 406±7 bpm which plateaued by weeks 5 and 6 at 468±10 bpm. The gain of the parasympathetic component of the cardiac baroreflex decreased gradually until the 5th week (from ‐2.4±0.09 to ‐0.8±0.04 bpm/mmHg) when it plateaued, and high frequency power spectral density of the pulse interval decreased from 13.4±0.6 to 8.3±0.01 ms2. In addition, there was an increase in both the low frequency and very low frequency components of the spectra of systolic blood pressure that did not occur until 3 weeks after clipping. The results indicate that 2K‐1C hypertension is associated with: (i) an immediate alteration in cardiac autonomic control characterized by a sympathetic predominance and decreased baroreflex sensitivity; (ii) elevated sympathetic vasomotor drive occurring 3 weeks post clipping that persists into the 6th week. Supported by CAPES.

Response Spectral Density for Oscillators with Nonlinear Damping

The concept of equivalent nonlinearization is used to obtain approximate solutions for the frequency response function and power spectral density (PSD) function of the response for oscillators with nonlinear damping. When harmonic excitation is considered the energy of the response is assumed to oscillate around a mean energy level. Assuming that the response is harmonic with energy-dependent amplitude an approximate frequency response function is obtained. The PSD function of the response to white noise excitation at a given energy level is obtained by an expression similar to the expression for a linear system, where the damping is replaced by an energy-dependent damping function. The total PSD function is obtained as a weighted average of the damping at all energy levels, and the method can be considered an extension of the method of equivalent nonlinearization to the frequency domain. The accuracy of the methods is verified by numerical examples.

Self-phosphorylation modulates the gating of rat liver gap junction channels: A nonstationary noise analysis

The effect of phosphorylation on the gating of rat liver gap junction hemichannels (Cx 32) has been investigated. It has been shown that self-phosphorylation of rat liver Cx 32 protein reduces the permeability of proteoliposomes as well the current flowing through multichannels in lipid bilayer membrane (BLM). The low frequency power spectral density analyses of nonstationary noise evolved due to the gating of Cx 32 multichannels demonstrated that self-phosphorylation modulated the channel functioning. A clear change in the power spectrum slopes ( α) of the nonstationary noise profiles confirmed the modulation of the channel dynamics due to self-regulation.

Can heart rate variation rule out sleep-disordered breathing in heart failure?

In patients with obstructive sleep apnoea (OSA), the very low frequency power spectral density index (VLFI) derived from analysis of heart rate correlates with the severity of obstructive apnoeas. VLFI is also associated with Cheyne-Stokes respiration/central sleep apnoea (CSR/CSA) in congestive heart failure (CHF). The present authors have tested the hypothesis that per cent VLFI, derived from a standard Holter ECG recording, can be used to detect the presence of OSA and CSR/CSA in patients with mild-to-moderate CHF. In total, 60 CHF patients underwent polysomnography with monitoring of heart rate. Data from 33 patients were analysed for per cent VLFI. Of the 60 patients, 27 were excluded due to atrial fibrillation, extensive pacing or frequent ventricular extra systoles. Receiver operator characteristic curves were constructed to establish the per cent VLFI that would optimally identify the presence or absence of sleep-disordered breathing. Using an apnoea-hypopnoea index>20 events.h-1 and setting the per cent VLFI at 2.23% yielded a sensitivity of 85%, specificity of 65%, positive predictive value of 61% and a negative predictive value of 87%. The latter increased to 100% when using an apnoea-hypopnoea cut-off of 30 events.h-1. In conclusion, these results suggest that spectral analysis of heart rate may be useful as a "rule-out test" for sleep-disordered breathing in patients with mild-to-moderate congestive heart failure.

Flow Visualization and Flow Pattern Identification With Power Spectral Density Distributions of Pressure Traces During Refrigerant Condensation in Smooth and Microfin Tubes

This paper presents a flow pattern identifier of the prevailing flow regime during refrigerant condensation inside smooth- and microfin tubes. The power spectral density distribution of the fluctuating condensing pressure signal was used to identify the prevailing flow regime, as opposed to the traditional (and subjective) use of visual-only methods, and/or smooth-tube flow regime maps. The prevailing flow regime was observed by using digital cameras and was validated with the use of the conventional smooth-tube flow regime transition criteria, as well as a new flow regime map for microfin-tube condensation. Experimental work was conducted for condensing refrigerants R-22, R-407C, and R-134a at an average saturation temperature of 40°C with mass fluxes ranging from 300–800 kg/m2 s, and with vapor qualities ranging from 0.05–0.15 at condenser outlet to 0.85–0.95 at condenser inlet. Tests were conducted with one smooth-tube condenser and three microfin-tube condensers (with helix angles of 10°, 18°, and 37° respectively). The power spectral density distributions of the condensing pressure signals distinguish the annular and intermittent (slug and plug) flows. A very low resonant frequency (&lt;40 Hz) and low power spectral density amplitude of the pressure oscillation denoted stratified and wavy flows. As the annular flow regime was approached, the oscillations became larger and their frequencies increased (typically 40–120 Hz). Intermittent flow showed the most distinct character of all flow regimes. Its trace consisted of large amplitude pressure pulses occurring at fairly constant frequencies (approximately 50, 60, 80, 100, and 120 Hz). As the transition from intermittent to annular flow began, the pressure fluctuations became less regular and the amplitude dropped sharply.

A study on intermittency phenomena in the impeller stream via digital particle image velocimetry (DPIV)

To characterize intermittency phenomena in the impeller jet, digital particle image velocimetry (DPIV) was used to measure the near-instantaneous flow fields in baffled, stirred reactor, equipped with a Rushton turbine (RT) impeller of large impeller and reactor diameter ratio. From the transient velocity fields obtained by DPIV, characterized by a chaotic movement of the jet axis in a fan section in the plane of laser sheet, effective intermittency phenomena in the impeller stream were identified for lower rotational speed. To gain insight into the nature of the intermittency phenomena, the impeller discharge angle corresponding to the near-instantaneous velocity field was calculated and its time series were constructed and analyzed via frequency count and power spectral density function (PSD). The macro-instability (MI) behavior of the reactor was investigated and its presence in the bulk flow was verified via spectral analysis of time series of the spatially averaged vorticity for lower rotational speed (namely 30, 60 and 120 min −1). Coherent spectral analysis was introduced to determine the cause of the intermittency phenomenon in the impeller stream as well as the relationship between the intermittency phenomenon and MI in the bulk flow. Results show that intermittency in the impeller stream is linearly related to MI in the reactor. The influence of MI should not be neglected in study of impeller stream intermittency phenomena.

Instrumentation notes - Mathematical approach to tremor recognition in extrapyramidal disease

Tremor is rhythmic involuntary oscillatory movement of body parts. There have been attempts to separate tremors due to different extrapyramidal diseases with objective techniques by measuring the acceleration of hands and applying the features of conventional spectral description, peak value and peak frequency of power spectral density (PSD). However, no clear-cut separation has been found with these methods; none of the parameters helps to decide reliably which kind of pathological tremor is present. The task is then twofold: to exploit other PSD features and to apply descriptions extracting new information from existing data. This article shows that the features of this process, based on the application of cumulants and polyspectra, represent different types of tremor and may stand as the basis for recognition between them. The results of numerical experiments are presented and discussed.