Average Power Spectral Density Research Articles

The Research of High-Level Modulation in Visible Light Communication

Visible light communication system using light emitting diode as light source, the system has the dual role of lighting and communication, thereby greatly saving energy .The bandwidth of LED modulation is a major obstacle to development of VLC technology. Researchers have put forward a variety of techniques to extend the modulation bandwidth and improve the transmission rate, such as Blu-ray filtering, equalization, multiple-input multiple-output (MIMO) technology, high ray modulation format, the wavelength division multiplexing technology, discrete multi-tone modulation and so on. The transmission rate of VLC system can be greatly improved by a combination of these techniques in a technical or several techniques. This paper analyzes the effect of OFDM technology each sub-carrier modulation with MQAM to visible light communication. It gives a brief introduction of the visible light communication system; it also shows the average power spectral density and error rate from SIMULINK simulation. It proves further the high-level quadrature amplitude modulation (MQAM) with higher bandwidth efficiency and smaller error rate, the bandwidth efficiency of 256QAM modulation is the twice of 16QAM modulation.

Integration method for directly analyzing interface statistics of periodic multilayers from X-ray scattering

An integration method is demonstrated for directly determining the average interface statistics of periodic multilayers from the X-ray scattering diagram. By measuring the X-ray scattering diagram in the out-of-plane geometry and integrating the scattered intensity along the vertical momentum transfer qz in an interval, which is decided by the thickness ratio Γ (ratio of sublayer's thickness to periodic thickness), the cross-correlations between different interfaces are canceled and only the autocorrelations are reserved. Then the multilayer can be treated as a `single interface' and the average power spectral density can be obtained without assuming any vertical correlation model. This method has been employed to study the interface morphology of sputter-deposited W/Si multilayers grown at an Ar pressure of 1-7 mTorr. The results show an increase in vertical correlation length and a decrease in lateral correlation length with increased Ar pressure. The static roughness exponent α = 0 and dynamic growth exponent z = 2 indicate the Edwards-Wilkinson growth model at an Ar pressure of 1-5 mTorr. At an Ar pressure of 7 mTorr, α = 0.35 and z = 1.65 indicate the Kardar-Parisi-Zhang growth model.

Effects of aging and propofol on the cardiovascular component of the autonomic nervous system

Study ObjectivesTo determine the combined effects of aging and propofol on autonomic nervous system activity using heart rate variability (HRV) analysis. DesignProspective, two-parallel group, repeated-measures study. SettingOperating room of an academic hospital. PatientsASA physical status 1, 2, and 3 patients, including 14 young (< 65 yrs) and 14 elderly (> 65 yrs) patients. All patients were scheduled for general surgical procedures with general anesthesia. InterventionsEach patient received two successive propofol doses during induction (0.5 mg/kg and 1.5 mg/kg) with a time interval allowing the return of Bispectral Index (BIS) to awake values. MeasurementsPrimary outcomes were HRV parameters, which included normalized power spectral density at low frequency (LFnorm) and high frequency (HFnorm) bands and the ratio LF/HF. Secondary outcomes were BIS values, blood pressure, heart rate, respiratory rate, and body temperature. Main ResultsThe interaction of age and propofol dose level was significant [multivariate analysis of variance, F (3,74) = 4.72, P = 0.005], representing a combined effect of age and propofol dose level on the mean HRV parameters. Propofol induction decreased the HFnorm component and enhanced LFnorm and LF/HF in the younger group, but had no significant effect in the older group. Such an effect was not associated with a significant difference in systolic blood pressure (SBP) decrements between the younger and older groups. Within each group, propofol caused significant decreases in SBP compared with preinduction values. Heart rate did not change significantly during propofol administration between groups or within groups. ConclusionsPropofol and aging act in synergy to depress the activity of the cardiovascular component of the autonomic nervous system. However, a compensatory increase in sympathetic outflow was seen in young patients. Such counterbalance was not observed in the older group.

Increased power spectral density in resting-state pain-related brain networks in fibromyalgia

Fibromyalgia (FM), characterized by chronic widespread pain, is known to be associated with heightened responses to painful stimuli and atypical resting-state functional connectivity among pain-related regions of the brain. Previous studies of FM using resting-state functional magnetic resonance imaging (rs-fMRI) have focused on intrinsic functional connectivity, which maps the spatial distribution of temporal correlations among spontaneous low-frequency fluctuation in functional MRI (fMRI) resting-state data. In the current study, using rs-fMRI data in the frequency domain, we investigated the possible alteration of power spectral density (PSD) of low-frequency fluctuation in brain regions associated with central pain processing in patients with FM. rsfMRI data were obtained from 19 patients with FM and 20 age-matched healthy female control subjects. For each subject, the PSDs for each brain region identified from functional connectivity maps were computed for the frequency band of 0.01 to 0.25Hz. For each group, the average PSD was determined for each brain region and a 2-sample t test was performed to determine the difference in power between the 2 groups. According to the results, patients with FM exhibited significantly increased frequency power in the primary somatosensory cortex (S1), supplementary motor area (SMA), dorsolateral prefrontal cortex, and amygdala. In patients with FM, the increase in PSD did not show an association with depression or anxiety. Therefore, our findings of atypical increased frequency power during the resting state in pain-related brain regions may implicate the enhanced resting-state baseline neural activity in several brain regions associated with pain processing in FM.

Chirped InAs/InP quantum-dash laser with enhanced broad spectrum of stimulated emission

We report on the demonstration of 50 nm (full-width at half-maximum) broadband stimulated emission from a chirped AlGaInAs barrier thickness multi-stack InAs/InP quantum dash (Qdash) laser. The 2 μm wide uncoated Fabry-Perot (FP) ridge-waveguide laser exhibits a total power of 0.18 W, corresponding to an average spectral power density of 3.5 mW/nm, under pulsed current conditions. Intentional extended inhomogeneity across the Qdash stacks have been attributed to the enhancement of broadband emission.

Analysis of the scalability of single-mode near-infrared supercontinuum to high average power

The scalability of single-mode near-infrared supercontinuum (SC) generation directly from a fiber amplifier is analyzed considering thermal and nonlinear effects, fiber end facet damage, pump as well as fiber combiner limits, and damage to the ytterbium-doped fiber. For fiber amplifiers with 3 ns input pulse width and gain fiber with 30 μm core diameter under optimized conditions, the safety temperature limit of the fiber coating prevents the average output power of the near-infrared SC from further scaling while the damage to the ytterbium-doped fiber restricts the scaling of the peak power of the near-infrared SC to a higher value. The results may provide some guidance on future work and the realization that kilowatt level near-infrared SC generation from a fiber amplifier with an average spectral power density of above 1 W nm−1 is possible.

Noise power spectral density of a fibre scattered-light interferometer with a semiconductor laser source

Spectral characteristics of the noise intensity fluctuations at the output of a scattered-light interferometer, caused by phase fluctuations of semiconductor laser radiation are considered. This kind of noise is one of the main factors limiting sensitivity of interferometric sensors. For the first time, to our knowledge, the expression is obtained for the average noise power spectral density at the interferometer output versus the degree of a light source coherence and length of the scattering segment. Also, the approximate expressions are considered which determine the power spectral density in the low-frequency range (up to ) and in the limiting case of extended scattering segments. The expression obtained for the noise power spectral density agrees with experimental normalised power spectra with a high accuracy.

Near-infrared supercontinuum generation in an all-normal dispersion MOPA configuration above one hundred watts

177.6 W near-infrared supercontinuum generation in a nonlinear fiber amplifier is first demonstrated. An all-normal dispersion master oscillator power amplifier (MOPA) configuration is adopted and an all-fiber structure is realized. The supercontinuum stretches from 1064 to 2000 nm with a 10 dB spectral width of 740 nm and 56% optical to optical conversion efficiency. The average spectral power density across the whole continuum is more than 150 mW nm−1 and the effective pulse energy is above 0.3 mJ, which paves the way for high-power supercontinuum generation at a level of hundreds of watts.

소형 고정익기의 신호기반 조종면 고장진단 알고리즘

본 논문에서는 소형 고정익기의 고장 발생시기와 부품 교체시기를 예측하여 유지보수 비용을 절감하고 정비 효율을 높이기 위하여 ANPSD와 PCA, 그리고 GC 방법을 이용하여 조종면의 고장에 대하여 이를 검출하고 위치와 정도를 분리하는 알고리즘을 제안하였다. 이때 ANPSD는 주파수 영역에서의 진동 분석을, PCA는 ANPSD의 중요 정보 추출을, GC는 고장 검출 및 분리 시의 오류 최소화를 위하여 사용되었다. 또한 모형 항공기에 가속도 센서를 부착하여 정상인 경우와 힌지 고장이 발생한 경우에 대하여 실제로 측정한 결과에 이와 같은 알고리즘을 적용한 결과 해당 알고리즘이 고장을 검출하고 분리하는 데에 적합함을 보였으며 제안된 알고리즘을 적용할 경우에 발생 가능한 문제들에 대하여 이를 완화할 수 있는 대응책을 함께 제시하였다. This paper presents a fault diagnosis algorithm of control surfaces of small fixed-wing aircraft to reduce maintenance cost or to improve repair efficiency by estimation of fault occurrence or part replacement periods. The proposed fault diagnosis algorithm consists of ANPSD (Averaged Normalized Power Spectral Density), PCA (Principle Component Analysis), and GC (Geometric Classifier). ANPSD is used for frequency-domain vibration testing. PCA has advantage to extract compressed information from ANPSD. GC has good properties to minimize errors of the fault detection and isolation. The algorithm was verified by the accelerometer measurements of the scaled normal and faulty ailerons and the test results show that the algorithm is suitable for the detection and isolation of the control surface faults. This paper also proposes solutions for some kind of implementation problems.

Measurement and validation of GHz-band whole-body average SAR in a human volunteer using reverberation chamber

The World Health Organization’s (WHO) recommendation on the need for further research for radio-frequency dosimetry has promoted studies on the whole-body average-specific absorption rate (WBA-SAR) in various kinds of anatomical-based numerical models. For experimental validation of GHz-band WBA-SARs in a real human, however, there have not so far been any published papers, despite the fact that, in 1982, Hill measured WBA-SARs at frequencies less than 40 MHz in human volunteers using a TEM-cell exposure system. In this study, we provide a measurement technique with a reverberation chamber for validating numerical dosimetry results on GHz-band WBA-SARs in living humans. We measured WBA-SARs at 1, 1.5 and 2 GHz for a 22 year old male volunteer, with a height of 173 cm and a weight of 73 kg, in the reverberation chamber, and compared the results with the finite-difference time-domain (FDTD) simulation. The reverberation chamber was excited by using a signal generator through an amplifier with an output power of 30–40 mW, which produced inside the chamber with the volunteer an average electric field strength of 5 V m−1 equivalent to an average power spectral density of 6.6 μW cm−2. The WBA-SARs were obtained from the measured S11 and S21 together with the power density. On the other hand, the WBA-SARs have been calculated using the FDTD method for an adult male model with almost the same physique as that of the volunteer exposed to the electromagnetic field in the reverberation chamber. From the comparison between the measured and the calculated WBA-SARs, we could confirm that the measured GHz-band WBA-SARs approximately agree with the FDTD calculated results.

Low-Frequency Noise Assessment of the Oxide Quality of Gate-Last High- $k$ pMOSFETs

The impact of wet versus dry dummy dielectric removal approaches on replacement metal gate (RMG) high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> last (RMG-HKL) pMOSFETs, with aggressively scaled high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> gate dielectric, has been studied by low-frequency noise. It is shown that excess generation-recombination noise, ascribed to random telegraph noise, causes a significant variability in the power spectral density (PSD). The best average PSD and the smallest device-to-device spread have been obtained by the remote-plasma dummy-gate removal followed by an in situ HF exposure prior to atomic layer deposition of HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> .

Universality classes of transport in time-dependent random potentials

The growth of the average kinetic energy of classical particles is studied for potentials that are random both in space and time. Such potentials are relevant for recent experiments in optics and in atom optics. It is found that for small velocities uniform acceleration takes place, and at a later stage fluctuations of the potential are encountered, resulting in a regime of anomalous diffusion. This regime was studied in the framework of the Fokker-Planck approximation. The diffusion coefficient in velocity was expressed in terms of the average power spectral density, which is the Fourier transform of the potential correlation function. This enabled to establish a scaling form for the Fokker-Planck equation and to compute the large and small velocity limits of the diffusion coefficient. A classification of the random potentials into universality classes, characterized by the form of the diffusion coefficient in the limit of large and small velocity, was performed. It was shown that one-dimensional systems exhibit a large variety of universality classes, contrary to systems in higher dimensions, where only one universality class is possible. The relation to Chirikov resonances, which are central in the theory of chaos, was demonstrated. The general theory was applied and numerically tested for specific physically relevant examples.

Spectral analysis of bilateral or alternate-site kindling-induced afterdischarges in the rabbit hippocampi

Kindling is one of the popular animal models of temporal lobe epilepsy. In the present study following the previous results obtained using unilateral hippocampal kindling (UK), we performed spectral analysis of bilateral or alternate-site kindling-induced afterdischarges (ADs) in the rabbit hippocampi. Eight and ten adult rabbits were used for bilateral kindling (BK) and alternate-site kindling (AK), respectively. Kindling stimuli consisted of a train of biphasic pulses (1ms duration each) of 50Hz for 1s, with suprathreshold intensity for AD. The stimulations were applied simultaneously to the bilateral hippocampi in the BK and were delivered to the right and left hippocampus once every 24h in the AK. Motor responses were classified into five stages according to the conventional criteria. All animals in BK as well as AK developed stage 5 convulsions. This contrasts to the result of UK (kindled: 50%; incomplete: 50%). We normalized power spectral density (PSD) and monitored the changes in the proportion of lower frequency band component (LFB: 0-9Hz) and the higher frequency band (HFB: 12-30Hz). BK animals showed a significantly large decrement (0.5 times, p<0.01) in LFB component at the final stage compared to the initial stage, but a very large increment (4.7 times) in HFB component. Likewise, AK animals exhibited a significantly large decrement (0.6 times, p<0.01) in LFB component at the final stage, but a very large increment (3.6 times) in HFB component. Correlation analyses were performed between the HFB component and AD duration, interictal discharge frequency, and behavioral stages during kindling progression. Very strong positive correlations were found in both kindling animals. Chronological spectral analysis of seizure discharges, resulting in a pattern of LFB decrement accompanied by HFB increment, is a convenient tool to investigate epileptic disorders and diagnose epileptic states.

Topographic power spectral density study of the effect of surface treatment processes on niobium for superconducting radio frequency accelerator cavities

Microroughness is viewed as a critical issue for attaining optimum performance of superconducting radio frequency accelerator cavities. The principal surface smoothing methods are buffered chemical polish (BCP) and electropolish (EP). The resulting topography is characterized by atomic force microscopy (AFM). The power spectral density (PSD) of AFM data provides a more thorough description of the topography than a single-value roughness measurement. In this work, one dimensional average PSD functions derived from topography of BCP and EP with different controlled starting conditions and durations have been fitted with a combination of power law, $K$ correlation, and shifted Gaussian models to extract characteristic parameters at different spatial harmonic scales. While the simplest characterizations of these data are not new, the systematic tracking of scale-specific roughness as a function of processing is new and offers feedback for tighter process prescriptions more knowledgably targeted at beneficial niobium topography for superconducting radio frequency applications.

Turbulent Radiation Statistics of Exhaust Plumes Exiting from a Subsonic Axisymmetric Nozzle

near the tip of the potential core and downstream. Axial and radial variation in radiation intensity fluctuations is similar to those reported for flames. Autocorrelation coefficients of the radiation intensity are approximated reasonably well by exponential curves. Integral time and length scales increase monotonically downstream of the core region and are consistent with Taylor’s hypothesis. The break frequency and slope of the normalized power spectral density function are comparable to those reported for turbulent jet flames. These findings suggest that reacting flows can be used to predict trends in turbulent radiation properties of exhaust plumes.

Subcutaneous adipose tissue blood flow and vasomotion in morbidly obese patients: Long term effect of gastric bypass surgery

Since recent findings suggest a relationship between reduction in adipose tissue blood flow (ATBF) and metabolic or vascular complications in obese patients (Ob-pts), increase in ATBF may be considered as a further goal in the treatment of obesity, besides fat mass reduction. Therefore, this preliminary study aimed at assess subcutaneous ATBF and vasomotion in morbidly obese patients and whether sustained weight loss induced by Roux-en-Y gastric bypass (RYGB) affects the same parameters. Using laser-Doppler flowmetry (LDF) and spectral Fourier analysis, subcutaneous ATBF was measured and subcutaneous ATBF oscillations (ATBF-O) were analyzed - within three frequency intervals related to vasomotion - in 16 Ob-pts, before and about one year after RYGB, and in 10 lean, healthy control subjects (CS). Before RYGB, Ob-Pts showed an important reduction in subcutaneous ATBF compared to CS (4.8 ± 2.7 PU vs 79.9 ± 34.5 PU, respectively; p < 0.0001), as well as higher normalized power spectral density (N-PSD) values of subcutaneous ATBF-O, - related to vasomotion. One year after RYGB, sustained weight loss in Ob-pts was associated with a slight but significant increase in subcutaneous ATBF (10.0 ± 6.6 PU, p < 0.05) and with almost complete normalization in N-PSD values of ATBF-O, related to vasomotion, compared to before RYGB. The slight subcutaneous ATBF increase, we observed in Ob-pts after sustained weight loss, moves toward a desirable goal. This finding suggests verifying whether an even more sustained weight loss in Ob-pts could determine a greater increase in subcutaneous ATBF and/or, more importantly, it could also determine a significant increase in visceral ATBF.

Evaluate laser needle effect on blood perfusion signals of contralateral hegu acupoint with wavelet analysis.

Our previous studies suggested that the MBF in contralateral Hegu acupoint (IL4) increased after ipsilateral Hegu acupoint was stimulated with manual acupuncture. In this study, twenty-eight (28) healthy volunteers were recruited and were randomly divided into Hegu acupoint stimulation group and Non-Hegu stimulation group. All subjects received the same model stimulation of the laser needle for 30 min in right Hegu acupoint and Non-Hegu acupoint, respectively. MBF of left LI4 was measured by the laser Doppler perfusion imaging system. The original data dealt with morlet wavelet analysis and the average amplitude and power spectral density of different frequency intervals was acquired. The results indicated that right Hegu stimulation with the laser needle might result in the increase of left Hegu acupoint MBF. 40 min later after ceased stimulation, the MBF is still increasing significantly, whereas the MBF has no significantly change in Non-Hegu stimulation group. The wavelet analysis result suggested that compared to Non-Hegu stimulation, stimulated to right Hegu acupoint might result in the increase of average amplitude in frequency intervals of 0.0095–0.02 Hz, 0.02–0.06 Hz, and 0.06–0.15 Hz, which might be influenced by the endothelial, neurogenic, and the intrinsic myogenic activity of the vessel wall, respectively.

Computational fluid dynamic simulation of small leaks in water pipelines for direct leak pressure transduction

Computational fluid dynamic simulation of small leaks in a pipe having 0.1m diameter has been performed under realistic velocities and pressures using a 3D turbulent flow model of well tested CFD code. The steady state simulations have shown clear signature in the pressure and pressure gradient variations along the pipe. For very small leaks (below 1l/min), this signature in not very strong in the pressure variation, but very clear in the pressure gradient. The averaged power spectral density (PSD) as well as FFT of the pressure fluctuations based on transient Detached Eddy Simulations (DESs) are presented for different locations around the leak position. These results show that the presence of a leak causes measurable differences in the magnitude and frequency of the pressure signal spectrum and also in the averaged PSD for the range of 220–500Hz frequency.

Broadband analysis of chaotic pulse trains generated by negative cloud-to-ground lightning discharge

[1] This paper presents direct broadband measurements of the electromagnetic radiation produced by so-called chaotic pulse trains (CPTs) in the frequency range from 0.1 to 40 MHz. We identify CPTs as a kind of pulse train with irregular pulse characteristics and erratic amplitudes, which are associated with the leader stage of subsequent strokes in negative cloud-to-ground lightning. The average duration of a CPT is 472 μs. In integrated E waveform, individual CPT pulse width varies in the range of 0.5–8 μs, and the most probable value is 1–2 μs. We find that 48% of subsequent strokes were preceded by a chaotic component. CPTs often produce strong HF radiation. From broadband waveforms, one can clearly see the intense radiation activity above the background noise level during the chaotic period. The average power spectral density (PSD) is used to measure the HF radiation intensity. The PSD distribution of CPTs shows substantially higher radiation power than that of “nonchaotic” subsequent leaders over the entire observation band. Two-site VHF interferometer data are recorded to investigate the fine structure of CPTs. The results of radiation source mapping indicate that CPTs during subsequent leaders occur with a channel propagation speed of 2 × 107 m/s. The data presented here suggest that it is proper to interpret CPTs as pulse activity associated with the dart phase of a subsequent leader.

Measuring and interpreting the temporal variability in the soundscape at four places in Sequoia National Park

The soundscape was recorded in four selected places in Sequoia National Park CA, to quantify and assess the diurnal and seasonal character of the park’s soundscape. The recording sites were selected to represent a combination of elevation and vegetation diversity. Hour-long sound recordings were made by four individuals at each place during fall, spring, summer and winter at dawn, midday, dusk, and midnight with identical recording instrumentation. The recordings of the soundscape were made in an old growth forest (Crescent Meadow), in a foothill oak savanna (Sycamore Spring), in an upland savanna chaparral (Shepherd Saddle) and in a foothill riparian location adjacent to the Kiawah River (Buckeye Flat). Sound recordings were analyzed using a normalized Power Spectral Density (PSD) algorithm and partitioned into 1 kHz intervals based on 12 subsamples from each of the 64 h-long sound recordings. Biological signals (biophony) were based on the highest PSD value within the range of 2–8 kHz. A multilevel analysis (MLA) was used to examine temporal patterns of biophony at four locations in Sequoia National Park. Unsupervised Landsat Thematic Mapper Satellite Imagery identified 25 vegetation regimes in Sequoia National Park. Satellite signatures of the habitat where recordings were made were extracted from the imagery to scale to the region.