High Power Spectral Density Research Articles

Large Eddy Simulation of near-bed pipelines in oscillatory flow

A series of unsteady, three-dimensional numerical simulations of the incompressible, oscillatory flow around a near-bed pipeline is presented. A flow at Reynolds number equal to Reαo=20,000 with respect to the oscillatory amplitude and maximum oscillation velocity is considered. The ratio of the pipeline diameter to the oscillatory amplitude examined is in the range of D/αo=0.1−1.0, with the pipeline located at a distance of G/D=0.0−1.0. The numerical simulations are conducted by means of Large Eddy Simulation (LES), using Cartesian grids. The presence of solid boundaries is taken into account by means of the Immersed Boundary method. For turbulence modelling, two different subgrid scale models are tested, the classical Smagorinsky and the Filtered Structure Function (FSF) models. The results in terms of vortex shedding are compared against previously reported data demonstrating very good agreement. Vortex shedding patterns are presented, indicating suppression of the boundary layer separation of the lower side of the pipeline for gap lengths G/αo≤1/20. The characteristic values of the hydrodynamic forcing in terms of the drag and lift coefficients and the three significant oscillation frequencies extracted from the temporal variation of the forcing signals are associated with the flow regimes and wall proximity. The pipeline experiences hydrodynamic loading which is found to oscillate with the external flow frequency along the direction of the flow. Along the wall-normal direction, the forces exerted on the pipe oscillate with several frequencies of high power spectral density. However, the three significant oscillation frequencies of the lift coefficient appear to have almost constant values. The presented results can provide trends for design purposes in similar flow conditions for a wide range of engineering applications.

Association between textural and morphological tumor indices on baseline PET-CT and early metabolic response on interim PET-CT in bulky malignant lymphomas.

We investigated whether metabolic, textural, and morphological tumoral indices evaluated on baseline PET-CT were predictive of early metabolic response on interim PET-CT in a cohort of patients with bulky Hodgkin and non-Hodgkin malignant lymphomas. This retrospective study included 57 patients referred for initial PET-CT examination. In-house dedicated software was used to delineate tumor contours using a fixed 30% threshold of SUV max and then to compute tumoral metabolic parameters (SUV max, mean, peak, standard deviation, skewness and kurtosis, metabolic tumoral volume (MTV), total lesion glycolysis, and area under the curve of the cumulative histogram), textural parameters (Moran's and Geary's indices, energy, entropy, contrast, correlation derived from the gray-level co-occurrence matrix, area under the curve of the power spectral density, auto-correlation distance, and granularity), and shape parameters (surface, asphericity, convexity, surfacic extension, and 2D and 3D fractal dimensions). Early metabolic response was assessed on interim PET-CT using the Deauville 5-point scale and patients were ranked according to the Lugano classification as complete or not complete metabolic responders. The impact of the segmentation method (alternate threshold at 41%) and image resolution (Gaussian postsmoothing of 3, 5, and 7mm) was investigated. The association of the proposed parameters with early response was assessed in univariate and multivariate analyses. Their added predictive value was explored using supervised classification by support vector machines (SVM). We evaluated in leave-one-out cross-validation three SVMs admitting as input features (a) MTV, (b) MTV+histological type, and (c) MTV+histology+relevant texture/shape indices. Features associated with complete metabolic response were low MTV (P=0.01), low TLG (P=0.003), high power spectral density AUC (P=0.007), high surfacic extension (P=0.006), low 2D fractal dimension (P=0.007), and low 3D fractal dimension (P=0.003). The prognostic value of these metrics was optimal with the 30% segmentation threshold and overall was progressively altered with decreasing image resolution. In cross-validation, the SVM accounting for texture and shape achieved the highest predictive value with ROC AUC of 0.82 and 80% accuracy (compared with 0.68 and 61% for MTV, and 0.65 and 68% for MTV+histology). The combination of usual prognostic factors with appropriately chosen textural and shape parameters evaluated on baseline PET-CT improves the prediction of early metabolic response in bulky lymphoma.

A fully integrated W‐band pulse compression radar CMOS transceiver

AbstractA fully integrated ultra‐wideband (UWB) W‐band pulse compression radar transceiver in a 65‐nm CMOS technology is presented. The transceiver adopts a pulse compression scheme for high power spectral density with low TX leakage. Two identical voltage controlled oscillators, which are coupled through the second harmonic, are designed to achieve high output power and low phase noise without buffers. A transformer‐based local oscillator distribution network is proposed to achieve both small chip area and high port‐to‐port isolation. The transceiver chip produces 7.5‐GHz UWB RF pulses with 14.5‐dBm peak output power in the tuning range of 75–81 GHz, while the receiver shows a dynamic range of above 60 dB. The radar module was realized with waveguide transitions from a micro‐strip to a WR‐10 waveguide, and was capable of differentiating two targets with 6.5‐cm separation within 30 m distance.

Marine soundscape as an additional biodiversity monitoring tool: A case study from the Adriatic Sea (Mediterranean Sea)

Acoustic monitoring can provide essential information on marine environments, including insights into ecosystem functioning and marine biodiversity monitoring. However, data on species acoustic behavior and ecoacoustics studies in the Mediterranean Sea are still extremely scarce and this limits our ability to use soundscape features in monitoring studies. Here we present the results of a soundscape investigation conducted on shallow hard bottoms of the Adriatic Sea (Central Mediterranean basin). We report the presence of diverse circadian rhythms recorded in two different months, July and September. A power spectral density (PSD) was used to assess the overall spectral composition over time, and the Acoustic Complexity Index (ACI), was identified as a proxy for marine sounds of biological origin. The dominant component of the biological soundscape was composed of snapping shrimps and fishes. Spectral characteristics varied significantly both daily and between the two months. For frequencies >620Hz (i.e., associated to snapping shrimp activity), both PSD and ACI were higher in July than in September. The same circadian rhythm was reported in both sampling periods, with the presence of snaps for 24h a day, but with significantly lower intensity during daylight hours and pitches at the beginning and ending of the night. At lower frequencies (i.e., <620Hz), fish vocalizations mostly occurred during the night. Higher values of ACI were recorded during the night in both months, whereas the presence of anthropogenic noise caused opposite results in PSD levels. Noise was associated with higher PSD and ACI at the peak frequency of the snaps, suggesting a stimulation in snapping activity. Our findings provide new insights on the marine biological soundscape and on the potential use of ecoacoustics in future monitoring programs.

Time and Frequency Characteristics of Pressure Fluctuations during Subcooled Nucleate Flow Boiling

ABSTRACTTime and frequency analyses methods including PDF (Probability Density Function), CDF (Cumulative Probability Function), FFT (Fast Fourier Transform) and PSD (Power Spectral Density) were used to investigate the pressure fluctuation characteristics during subcooled nucleate flow boiling and the effects of various parameters. The experimental conditions were heating currents to a high frequency induction heater of 200–720 A, liquid temperatures of 50–85°C, and flow rates of 0–290 L/h. The CDF and PSD methods were more effective than the PDF and FFT methods for the time-frequency analyses of the pressure fluctuations. Higher heating currents, lower liquid temperatures and lower flow rates result in wider frequency distributions and larger pressure fluctuation amplitudes in the time domain and wider frequency distributions and higher PSD of the pressure fluctuations in the frequency domain. The effects of the operating conditions on the Onset of Nucleate Boiling (ONB) were analyzed qualitatively by correlating the pressure fluctuation signals with visual images obtained from the experiments. A pressure drop occurs at the ONB regardless of the conditions with the pressure drop appearing earlier at higher heating currents and liquid temperatures and lower flow rates.

Generation of spectral clusters in a mixture of noble and Raman-active gases.

We report a novel scheme for the generation of dense clusters of Raman sidebands. The scheme uses a broadband-guiding hollow-core photonic crystal fiber (HC-PCF) filled with a mixture of H2, D2, and Xe for efficient interaction between the gas mixture and a green laser pump pulse (532 nm, 1 ns) of only 5 μJ of energy. This results in the generation from noise of more than 135 rovibrational Raman sidebands covering the visible spectral region with an average spacing of only 2.2 THz. Such a spectrally dense and compact fiber-based source is ideal for applications where closely spaced narrow-band laser lines with high spectral power density are required, such as in spectroscopy and sensing. When the HC-PCF is filled with a H2-D2 mixture, the Raman comb spans the spectral region from the deep UV (280 nm) to the near infrared (1000 nm).

Absolute Power Spectral Density Changes in the Magnetoencephalographic Activity During the Transition from Childhood to Adulthood.

The aim of this study was to define the pattern of reduction in absolute power spectral density (PSD) of magnetoencephalography (MEG) signals throughout development. Specifically, we wanted to explore whether the human skull's high permeability for electromagnetic fields would allow us to question whether the pattern of absolute PSD reduction observed in the human electroencephalogram is due to an increase in the skull's resistive properties with age. Furthermore, the topography of the MEG signals during maturation was explored, providing additional insights about the areas and brain rhythms related to late maturation in the human brain. To attain these goals, spontaneous MEG activity was recorded from 148 sensors in a sample of 59 subjects divided into three age groups: children/adolescents (7-14years), young adults (17-20years) and adults (21-26years). Statistical testing was carried out by means of an analysis of variance (ANOVA), with "age group" as between-subject factor and "sensor group" as within-subject factor. Additionally, correlations of absolute PSD with age were computed to assess the influence of age on the spectral content of MEG signals. Results showed a broadband PSD decrease in frontal areas, which suggests the late maturation of this region, but also a mild increase in high frequency PSD with age in posterior areas. These findings suggest that the intensity of the neural sources during spontaneous brain activity decreases with age, which may be related to synaptic pruning.

Supercontinuum Generation in an Ytterbium-Doped Photonic Crystal Fiber for CARS Spectroscopy

An optimized broadband source emitting from 1064 to 1600 nm was specially designed for coherent anti-Stokes Raman scattering spectroscopy. This source is based on the use of a ytterbium-doped photonic crystal fiber with a large core in which a supercontinuum is generated from a signal wave at 1064 nm regenerated by ytterbium ions pumping. A particularly flat spectrum with high spectral power density and perfectly synchronized spectral components is obtained.

GaAs-based superluminescent diodes with window-like facet structure for low spectral modulation at high output powers

We demonstrate a GaAs-based superluminescent diode (SLD) based on the incorporation of a window-like back facet into a self-aligned stripe structure in order to reduce the effective facet reflectivity. This allows the realisation of SLDs with low spectral modulation depth (SMD) at high power spectral density (PSD), without the application of anti-reflection coatings to either facet. This approach is therefore compatible with ultra-broadband gain active elements. We show that 30 mW output power can be attained in a narrow bandwidth, corresponding to 2.2 mW nm−1 PSD with only 5% SMD, centred about 990 nm. We discuss the design criteria for high power and low SMD and the deviation from a linear dependence of SMD on output power, resulting from Joule heating in the self-aligned stripe.

Advancements in quantum cascade laser-based infrared microscopy of aqueous media.

The large mid-infrared absorption coefficient of water frequently hampers the rapid, label-free infrared microscopy of biological objects in their natural aqueous environment. However, the high spectral power density of quantum cascade lasers is shifting this limitation such that mid-infrared absorbance images can be acquired in situ within signal-to-noise ratios of up to 100. Even at sample thicknesses well above 50 μm, signal-to-noise ratios above 10 are readily achieved. The quantum cascade laser-based microspectroscopy of aqueous media is exemplified by imaging an aqueous yeast solution and quantifying glucose consumption, ethanol generation as well as the production of carbon dioxide gas during fermentation.

An EEG study of turning freeze in Parkinson's disease patients: The alteration of brain dynamic on the motor and visual cortex.

Freezing of gait is a very debilitating symptom affecting many patients with Parkinson's disease, leading to a reduced mobility and increased risk for falls. Turning is known to be the most provocative trigger for freezing of gait. However, the underlying brain dynamic changes associated with a turning freeze remain unknown. This study therefore used ambulatory EEG to investigate the brain dynamic changes associated with freezing of gait during turning. In addition, this study aimed to determine the most suitable EEG sensor location to detect freezing of gait during turning using our classification system. Data from four Parkinson's disease patients with freezing of gait was analysed using power spectral density and brain effective connectivity, comparing periods of successful turning with freezing of gait during turning. Results showed that freezing of gait during turning is associated with significant alterations in the high beta and theta power spectral densities across the occipital and parietal areas. Furthermore, brain effective connectivity showed that freezing during turning was associated with increased connectivity towards the visual area, which also had the highest accuracy to detect freezing episodes in the O1 regions by using power spectral density in our classification analyses. This is the first study to show cortical dynamic changes associated with freezing of gait during turning, providing valuable information to enhance the performance of future freezing of gait detection systems.

High-power InGaAs/GaAs quantum-well laser with enhanced broad spectrum of stimulated emission

We report the demonstration of an InGaAs/GaAs quantum well (QW) broadband stimulated emission laser with a structure that integrated a GaAs tunnel junction with two QW active regions. The laser exhibits ultrabroad lasing spectral coverage of ∼51 nm at a center wavelength of 1060 nm with a total emission power of 790 mW, corresponding to a high average spectral power density of 15.5 mW/nm, under pulsed current conditions. Compared to traditional lasers, this laser with an asymmetric separate-confinement heterostructure shows broader lasing bandwidth and higher spectral power density.

6.8 W all-fiber supercontinuum source at 1.9–2.5 μm

We report a simple method of generating a spectrally flat and high average power spectral density (up to 14 mW/nm) optical supercontinuum in the 1.95–2.5 μm range covering a transparency window of the atmosphere. The supercontinuum was generated from the Tm-doped all-fiber MOPA lasers. The average output power of the picosecond linear-cavity SESAM mode-locked seed lasers operating at 46 and 77 MHz was as low as 6.7 and 2.6 mW, respectively. The corresponding one-stage silica-based fiber amplifier generated a supercontinuum with 5.06 and 6.83 W average power, 550 and 500 nm bandwidths at −10 dB level, and 5 and 8 dB spectral flatness, respectively.

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.

Broadly tunable quantum cascade laser in cantilever-enhanced photoacoustic infrared spectroscopy of solids

An external cavity quantum cascade laser (EC-QCL) is applied in the photoacoustic detection of solid samples. The EC-QCL used has a broad tuning range of 676 cm−1 (970–1,646 cm−1) in the mid-infrared region, which enables accurate broadband spectroscopy of large molecules. The high spectral power density of the EC-QCL is combined with an extremely sensitive optical cantilever microphone of the photoacoustic detector to achieve an ultimate sensitivity. The carbon black, polyethylene, and hair fiber samples were measured with the EC-QCL photoacoustic detection using electrical amplitude modulation to demonstrate the possibilities of the setup. The same measurements were repeated with a Fourier transform infrared (FTIR) spectrometer combined with a photoacoustic detector for a comparison. The EC-QCL photoacoustic setup yielded roughly a decade better signal-to-noise ratios than the FTIR setup with the same measurement time.

Power Spectral Density Analysis of WLAN based OFDM System

is a technique used in modern broadband wireless communications systems. OFDM has been adopted for wireless standards such as IEEE 802.11a. In this paper, different Power Spectral Density (PSD) curves of OFDM signal based on WLAN with various pulse shapes are presented. OFDM waveform is analyzed in frequency domain response for different modulation techniques such as BPSK, QPSK, 16-QAM, 64-QAM and different block sizes such as 50 and 2048. Power spectral density increases with increase in levels of modulation. For high power spectral density of transmitter higher levels of QAM modulation techniques are preferred.

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.

Type of Music Associated with Relaxation Based on EEG Signal Analysis

Music is the science and the art of tones, or the musical sounds. Music is also the art of combining tones in a manner to please the ear. Music therapy is the planned and creative use of music to attain and maintain health and well–being. There are a lot of experimental efforts to understand musical processing in the brain using electroencephalogram (EEG). It is accepted that listening to music increases the theta and alpha bands power that is associated to increase relaxation. In this study, we are interested to find the type of music that can produce such state of mind by analysing the EEG power spectrum in those frequency bands. 4 types of music were investigated, i.e. sound of instrumental piano, sound of wave, sound of birds and sound of nature. As the result, 71.4% of subjects were able to achieved highest power spectral density in theta and alpha frequency bands while listening to sound of instrumental piano and sound of nature while only 28.6–42.9% of subjects were able to produce the same while listening to sound of wave and sound of bird. From the finding, it can be concluded that sound of instrumental piano and sound of nature increase relaxation as indicated by the increase of PSD in the theta/alpha frequency bands compared to the sound of wave and sound of bird.

Reagent-free monitoring of multiple clinically relevant parameters in human blood plasma using a mid-infrared quantum cascade laser based sensor system

We present a semi-automated point-of-care (POC) sensor approach for the simultaneous and reagent-free determination of clinically relevant parameters in blood plasma. The portable sensor system performed direct mid-infrared (MIR) transmission measurements of blood plasma samples using a broadly tunable external-cavity quantum cascade laser source with high spectral power density. This enabled the use of a flow cell with a long path length (165μm) which resulted in high signal-to-noise ratios and a rugged system, insensitive to clogging. Multivariate calibration models were built using well established Partial-Least-Squares (PLS) regression analysis. Selection of spectral pre-processing procedures was optimized by an automated evaluation algorithm. Several analytes, including glucose, lactate, triglycerides, cholesterol, total protein as well as albumin, were successfully quantified in routinely taken blood plasma samples from 67 critically ill patients. Although relying on a spectral range from 1030cm(-1) to 1230cm(-1), which is optimal for glucose and lactate but rather unusual for protein analysis, it was possible to selectively determine the albumin and total protein concentrations with sufficient accuracy for POC application.

MEMS electrostatic energy harvesters with end-stop effects

In micro scale energy harvesting devices, end-stops that limit the proof mass motion are inevitable from reliability concerns and can even be exploited as a functional element to achieve a broadband response. To investigate how these can be modelled, both characterization and modelling of vibration energy harvesters with end-stop effects are presented in this paper. A Hertz contact model of the impact force between the proof mass and the end-stops is analysed and compared to a linear stiffness model. The resulting impact force model is then included into a SPICE model of an electrostatic harvester. The performance prediction of the model is validated by comparing simulations and measurements on two different prototypes, one with mechanical quality factor Qm = 5.7 and one with Qm = 203.5. The electromechanical coupling factors of the two devices are respectively k2 = 1.44% and 2.52%. Both devices display the well-known jump phenomenon and output voltage saturation during, respectively, frequency and amplitude sweeps. Under low-level broadband excitations, the high-Qm device performs in agreement with linear theory at an efficiency of 71.8%. For sufficiently high acceleration power spectral density (PSD), it displays a soft limit on the output power and a bandwidth increase, e.g. a factor 3.7 increase of 3 dB bandwidth when increasing the acceleration PSD from 0.34 × 10−3 to 0.55 × 10−3 g2 Hz−1. The end-stop effects reduce the device efficiency down to 35.4% at 1.69 × 10−3 g2 Hz−1. A comparison between model and experiment shows that a model with end-stop stiffness extracted from the contact analysis can adequately model the nonlinear end-stop effects both for narrow- and broadband accelerations.