High Frequency Measurements Research Articles

On the Ability of Positron Emission Particle Tracking (PEPT) to Track Turbulent Flow Paths with Monte Carlo Simulations in GATE

Positron emission particle tracking (PEPT) has offered important insights into the internal dynamics of multiphase flows. High precision and frequency measurements of the location of the tracer particle are required to resolve individual eddies at the millimetre scale or smaller. To explore the potential of PEPT to perform these measurements, a model was developed of the Siemens ECAT “EXACT3D” HR++ positron emission tomography (PET) scanner at the PEPT Cape Town facility in South Africa with the software Geant4 Application for Tomographic Emission (GATE) and was used to generate Lagrangian tracks from simulations of moving tracer particles. The model was validated with measurements from both experiment and simulation and was extended to two virtual scenarios inspired by turbulent flows. The location data from the simulation accurately captured linear portions of an oscillating path up to high speeds of 25 m s−1; however, tracking tended to undercut the turning points due to the high tracer acceleration. For a particle moving on a spiral path of decreasing radius, the location data tracked the path above a radius of 2.0 mm with an uncertainty equivalent to the radius of the tracer particle, 300 μm. Improvements to the measurement are required to track sub-millimetre flow structures, such as the application of PET scanners with higher spatial resolution and upgrades to the sampling processes used in location algorithms.

A new procedure for autonomous acquisition of photosynthesis-irradiance curves on a microphytobenthic biofilm

Despite their high productivity and their key role in coastal processes, microphytobenthic biofilm studies remain relatively scarce because in situ, meteorological hazards make it difficult to acquire reproducible measurements, also due to difficulties in properly reproducing field conditions in the laboratory. Therefore, in order to better understand the processes of microphytobenthic primary production, we have developed an automated laboratory system and procedure with variable light intensity, with a large number of replicates. This article aims to provide a description of the creation of a P-I curve based on a total of 128 vertical profiles recorded on a sediment core taken in situ, placed in the automated system and studied under controlled conditions of temperature and air humidity while light intensity was varied automatically, thus allowing to work in standard and replicable conditions. With measured production levels of up to 14.68 ± 3.70 mmol O2.m-2.h-1 and a productivity of 0.06 ± 0.01 mmol O2.m-2.h-1 per gram of Chl a corresponding to what is generally found in temperate environments, we have shown that our system is suitable for high frequency measurements and, by combining surficial measurements of modulated fluorescence and oxygen microprofiling in sediments, complementary information from a large dataset on photosynthetic and microphytobenthic migratory activity may be obtained under standard conditions. The development of this tool has made it possible to highlight a stabilization time for oxygen fluxes. For our study conducted in a temperate environment, we observed a time lag of a few minutes that should be considered when acquiring PE curves in the laboratory to study microphytobenthic photosynthetic capacities. This tool also allowed to describe microphytobenthic migration in response to light exposure, with successive steps observed through fluorescence and oxygen profiles. First, microphytobenthos migrated towards the surface until the optimal intensity of production at 475 µmol photons.m-2.s-1, then from this intensity as well as towards 780 µmol photons.m-2.s-1, downwards migratory movements were detected. This system is a working basis which can open interesting perspectives for the study of the effect of other abiotic (or biotic) parameters.

121 Applying Low-Cost Particulate Matter Sensors for Characterizing Occupational Exposure; Findings from Field Studies in Different Industries

Abstract Low-cost particulate matter sensors are a up-and-coming technology for monitoring occupational exposure to hazardous substances in high spatial and temporal resolutions. Low costs, small sizes and high measurement frequencies offer the potential to continuously, automatically and remotely measure dust exposure and emission in the workplace. However, much remains unknown about how these devices can be successfully applied in occupational settings. TNO (the Netherlands) has, in collaboration with HSE (UK) and NIOSH (US), performed field studies at seven companies in the bakery, woodworking and welding industry to explore the use of sensors. A total of 145 full / half-shift measurements were collected for 37 workers and 15 static positions. Measurement data was obtained using four types of sensor and conventional respirable gravimetric and high-resolution reference devices. High-resolution contextual information was collected using additional sensors, including an ultrasound-based indoor positioning system, to investigate how these can further characterize exposure situations. Sensor accuracy compared to reference measurements ranged up to R2-values of 0.92, but large variations were observed within and between industries. Overall, stationary measurements showed less variation in performance compared to personal measurements. Different types of sensor seemed more accurate for specific industries. Contextual measurements provided additional information on when and where exposure occurred, for example by dynamic hazard maps based on indoor location and personal sensor measurements. Although performance of sensors remains lower than conventional methods, they may provide accurate measurements in specific situations. Additionally, sensors can provide new types of information that cannot be captured by time-integrated measurements.

Research on Germanium Photodetector with Multi-Mode Waveguide Input

In this work, a vertical N-I-P germanium (Ge) photodetector (PD) with a multi-mode waveguide input is presented. The fabricated devices exhibit a low dark current of 10 nA at bias of −1 V, and a high responsivity of exceeding 0.75 A/W over the wavelength range from 1270 to 1350 nm. High-frequency characteristics measurements show that the photodetector has a 3 dB opto-electrical (OE) bandwidth of 23 GHz under −3 V bias, which can be further improved by optimization of the photodetector configuration. A 50 Gb/s clear eye diagram with a non-return-to-zero (NRZ) modulation format is demonstrated. By using a single-mode excitation source, which is used to simulate light coming from the wavelength division multiplexing (WDM) devices, and sweeping its position, it is shown that the multi-mode input photodetector can be utilized in a WDM receiver to achieve both high responsivity and a flat-top passband.

Compressible viscoelasticity of cell membranes determined by gigahertz-frequency acoustic vibrations

Membrane viscosity is an important property of cell biology, which determines cellular function, development and disease progression. Various experimental and computational methods have been developed to investigate the mechanics of cells. However, there have been no experimental measurements of the membrane viscosity at high-frequencies in live cells. High frequency measurements are important because they can probe viscoelastic effects. Here, we investigate the membrane viscosity at gigahertz-frequencies through the damping of the acoustic vibrations of gold nanoplates. The experiments are modeled using a continuum mechanics theory which reveals that the membranes display viscoelasticity, with an estimated relaxation time of ca. 5.7+2.4/−2.7 ps. We further demonstrate that membrane viscoelasticity can be used to differentiate a cancerous cell line (the human glioblastoma cells LN-18) from a normal cell line (the mouse brain microvascular endothelial cells bEnd.3). The viscosity of cancerous cells LN-18 is lower than that of healthy cells bEnd.3 by a factor of three. The results indicate promising applications of characterizing membrane viscoelasticity at gigahertz-frequency in cell diagnosis.

Microwave Photonic Reconfigurable High Precision Instantaneous Frequency Measurement System Assisted by Stacking Ensemble Learning Method

This paper reports a microwave photonic reconfigurable high precision simple instantaneous frequency measurement system. With the first assistance of stacking ensemble learning method, it can achieve high measurement accuracy over a wide bandwidth. For introducing electrical and optical delays, the range and accuracy of the instantaneous frequency measurement method can be flexibly adjusted to suit the needs of various scenarios. Sufficient and systematic experimental results show that from 11 GHz to 17 GHz, the average measurement error is 4.39 MHz. This simple system acquits reconfigurability and on-chip integration possibilities without dispersion elements, which reveals great potential in the future integrated array radar, detection, and other fields.

Variations of Bottom Boundary Layer Turbulence under the Influences of Tidal Currents, Waves, and Raft Aquaculture Structure in a Shallow Bay

High-frequency measurements of tides, waves, and turbulence were made using the bottom-mounted tripod equipped with the Nortek 6-MHz acoustic Doppler velocimetry during 20–23 February 2016 (winter) and 12–26 June 2017 (summer) in Heini Bay, Yellow Sea. The synchro-squeezed wavelet transform was applied for wave-turbulence decomposition, and an iterative procedure was developed to identify the turbulence inertial subrange in the bottom boundary layer. The analysis results reveal the dependency of the inertial subrange on the tidal current and turbulence intensities. The flood-ebb tidal flows are different between the summer and winter seasons, without and with the presence of dense raft aquaculture for kelp, respectively. In summer, the turbulent kinetic energy (TKE), turbulent Reynolds stress (TRS), and dissipation rate (ε) of TKE increase smoothly with the increasing tidal flow magnitude, and ε is approximately in balance with TKE production related to the vertical shear. The presence of heavy kelp aquaculture in winter causes the reduction in flow speeds and TRS, while keeping TKE and ε at high levels.

Impact of asthma on heart rate variability in children and adolescents: Systematic review and meta-analysis.

Asthma is associated with abnormal autonomic function, and heart rate variability is considered a simple, accurate, and noninvasive tool for monitoring the autonomic system. Thus, the aim of this study was to investigate the impact of asthma on heart rate variability in children and adolescents. This systematic review of observational studies and clinical trials evaluated heart rate variability in children and adolescents with asthma compared to healthy controls. The data were extracted independently by two reviewers. The quality of the selected articles was assessed using Agency for Health Care Research and Quality indicators. Random effects meta-analysis was performed for each outcome, with the effect size reported as standardized mean difference. Fifteen studies were included, of which five were classified as having high methodological quality. In the meta-analysis, long-term recording of the standard deviation of all normal-to-normal sinus R-R intervals differed significantly between groups (standardized mean difference [SMD] = -0.46 [95% confidence interval {CI}: -0.79 to -0.14], p < 0.005, I2 = 0%). Moreover, R-R intervals (long-term) were significantly shorter in asthmatic children than controls (SMD = -0.47 [95% CI: -0.68 to -0.25], p < 0.0001, I2 = 0). There were no significant differences between adjacent normal R-R intervals that exceed 50 ms (long-term) and the root mean square of successive differences between normal sinus R-R intervals (short-term). Regarding frequency-domain variables, long-term low frequency measurements differed significantly between groups (SMD = -0.34 [95% CI: -0.58 to -0.10], p < 0.005, I2 = 15%). There were no differences in high frequency measurements or in the ratio between low/high frequency powers (short- or long-term) between groups. The results confirm the impact of asthma on heart rate variability in children and adolescents, indicating lower heart rate variability and sympathetic modulation.

Research on a method of high precision frequency measurement based on coordinate rotation digital computer algorithm and Kalman filter.

Frequency measurement is one of the key techniques in high-precision data acquisition technology of broadband signals. Generally, frequency measurement not only needs to deal with a large amount of data processing but also requires a high precision, but these two aspects are sometimes difficult to reconcile. Some algorithms are overly dependent on the accuracy of the to-be-measured data, which might not be the desired option for real projects since it is almost impossible to get ideal error-free data. This article adopts a frequency measurement method based on the coordinate rotation digital computer algorithm, differential algorithm, and Kalman filter. The use of these algorithms for the frequency measurement process would not only simplify the calculation but also reduce the effect of the measurement error. This method can measure all signals that satisfy the sampling theorem and can also measure multi-channel parallel signals. The experimental results of data simulation and actual measurement on the hardware platform show that the accurate frequency measurement algorithm has a strong data processing ability, stable measurement, and steady improvement in the accuracy of measurement results, which can meet the needs of most instruments for accurate frequency measurement. The measurement error could be reduced to the percentile by the Kalman filter and could be reduced to below the thousandth by the combining the algorithms.

Characterization and predictive modeling of a trajectory-oriented dual-mode scramjet combustor

Linear and nonlinear characteristics of a dual-mode scramjet combustor are investigated in ground-simulated acceleration and deceleration trajectory experiments. The experiments were conducted in the direct-connected transient flight trajectory simulator 1 at the Institute of Mechanics, Chinese Academy of Sciences. High-frequency pressure measurements, the schlieren, and CH* chemiluminescence high-speed imaging were applied for the diagnostics. Based on the quantitative analysis, the physical processes of acceleration and deceleration in general represent similar nonlinear characteristics. The linear characteristics are limited to the low-frequency oscillation period in the presence of physical governing mechanisms. A nonlinear predictive model of the dual-mode scramjet combustor based on historical measurements is proposed due to its generality for the acceleration and deceleration trajectory.

Traveling Wave-Based Primary Protection and Fault Localization Scheme for MTDC Grid Considering IEC 61869-9 Measurement Standard

Traveling wave (TW) based protection and fault localization requires high sampling frequency measurements (500 kHz - 1 MHz) and are non-compliant to the IEC 61869-9 measurement standards, which allows maximum sampling frequency of 96 kHz for DC application. This work proposes a novel low sampling frequency (50 kHz) TW based primary protection and real-time DC fault localization technique for multi terminal high voltage DC (MTDC) grid which is compliant with the aforementioned measurement standard. In the proposed MTDC protection scheme, a TW arrival time (TWAT) is estimated under low sampling frequency measurement using cascaded combination of modified mathematical morphology gradient (MMG), sobel operator and linear regression tool. Subsequently, the TWAT information at both DC link terminals is communicated via dedicated communication channel compliant to IEC-61850-9-2 standard. And if the TWAT difference between DC terminals is less than the TW propagation threshold for the protected DC line, then a DC trip signal is issued to the associated hybrid DC circuit breaker (HDCCB). For fast power system restoration, the same TWAT information is also used for real-time fault localization in the faulted DC line, which is also compliant with IEC 61869-9 measurement standards. Finally, the practical feasibility of the proposed algorithm is demonstrated through control hardware-in-loop testing with real-time digital simulation setup and TI TMS320F28379d digital signal processor card.

Dielectric Properties of Graphite Oxide Polymeric Composites Based on N-Vinylpirrolidone Copolymers with Different Topologies

The dielectric properties of graphite oxide composite materials based on a biocompatible branched copolymer of N-vinylpyrrolidone with 1,6-hexanediol dimethacrylate and a cross-linked copolymer of N‑vinylpyrrolidone with triethylene glycol dimethacrylate are studied. High-frequency (9.8 GHz) and low-frequency (25 Hz–1 MHz) measurements of the complex permittivity and electrical conductivity of polymer composites are carried out and their dependences on the polymer matrix topology and formation conditions are analyzed. Copolymers and composites based on them are characterized by IR, UV, and visible spectroscopy, dynamic light scattering, and the surface morphology of nanocomposite polymer matrices is characterized by optical microscopy. It is shown that the proposed electrophysical approach makes it possible to additionally characterize polymer matrices with carbon nanofillers.

A High-Frequency Measurement Method of Downhole Vibration Signal Based on Compressed Sensing Technology and Its Application in Drilling Tool Failure Analysis

A High-Frequency Measurement Method of Downhole Vibration Signal Based on Compressed Sensing Technology and Its Application in Drilling Tool Failure Analysis

Feature-Based Characterisation of Turned Surface Topography with Suppression of High-Frequency Measurement Errors.

Errors that occur when surface topography is measured and analysed can be classified depending on the type of surface studied. Many types of surface topographies are considered when frequency-based errors are studied. However, turned surface topography is not comprehensively studied when data processing errors caused by false estimation (definition and suppression) of selected surface features (form or noise) are analysed. In the present work, the effects of the application of various methods (regular Gaussian regression, robust Gaussian regression, and spline and fast Fourier Transform filters) for the suppression of high-frequency measurement noise from the raw measured data of turned surface topography are presented and compared. The influence and usage of commonly used available commercial software, e.g., autocorrelation function, power spectral density, and texture direction, which function on the values of areal surface topography parameters from selected (ISO 25178) standards, are also introduced. Analysed surfaces were measured with a stylus or via non-contact (optical-white light interferometry) methods. It was found that the characterisation of surface topography, based on the analysis of selected features, can be crucial in reducing measurement and data analysis errors when various filters are applied. Moreover, the application of common functions can be advantageous when feature-based studies are proposed for both profile and areal data processing.

Soft Computing Approach to Design a Triple-Band Slotted Microstrip Patch Antenna

The design process of antenna structures that meet up-to-date requirements takes a long time and brings a high computational load. In this paper, an approach based on Soft Computing (SC) techniques was used to shorten the design time and to achieve an antenna structure that yields performance characteristics as close as possible to the desired values. In order to obtain a microstrip patch antenna with the targeted characteristics and the best accuracy in a faster way, a Support Vector Machine (SVM)-based regression model was employed. A triple-band microstrip antenna with desired resonance frequencies and gain values was designed by using the Support Vector Regression (SVR) model by introducing multiple slots and arc-truncation to the patch antenna. Simulation results of the High-Frequency Structural Simulator (HFSS) and measurements of implementation of the designed antenna are given. Performance characteristics of the obtained antenna are also compared with those given in the literature, which have triple-band properties. In addition, the antenna was redesigned using the optimization tool in HFSS for comparison. The accuracy of the results and required time for design were compared for both the SVR model approach and the HFSS optimization tool.

High-frequency ultrasound-based thickness measurement of highly attenuating materials

This paper investigates an effective method for measuring the thickness of highly attenuating materials using the acoustic radiation-induced quasi-static component (QSC) of a primary longitudinal wave (PLW) at high frequency. The generated QSC features lower attenuation than the high-frequency PLW, so the generated QSC pulse with zero carrier frequency can propagate a longer distance at the same group velocity, even in highly attenuating materials. In addition, the method based on the QSC of a high-frequency PLW has better directivity than the low-frequency PLW-based method, making it more suitable for highly attenuated material local thickness measurement. The thickness of highly attenuating materials can be accurately measured by measuring the pulse-echo time-of-flight of the generated QSC pulse using an ultrasound pulse-echo technique. The experimental examinations conducted for highly attenuating silicone rubber blocks with different thicknesses demonstrate that their thicknesses can be accurately measured with the QSC-based method. This paper provides an effective method for thickness measurements of highly attenuating materials.

Characterizing the ramps and noise in solar power imbalances

The output of solar photovoltaic resources can be variable, with the power variability manifesting across multiple time scales. Several studies characterize the impacts of variability on system operations but there is limited literature available on how this variability needs to be modeled. This paper decomposes high resolution solar power measurements into metered average, ramp and noise components. With explicit consideration of average values and the imbalance power around the average, the proposed approach is able to consider the dispatch practices which use average values across dispatch intervals while the supply/demand changes continuously. The ramp component captures this disconnect while the noise reflects the natural variations in the solar output due to cloud transitions and other factors. The models proposed here allow us to identify the ramp components even when high frequency measurements are not available. A case study of actual field measurements of solar generation is presented to demonstrate how noise reduces with spatial aggregation while the ramp component persists in terms of magnitude across higher aggregations. A use case for the ramp component for balancing reserve sizing is also presented compared with the conventional one.

Correlation between amplitude and phase photothermal signals based on Kramers–Kronig relations: Application to the investigation of interfacial thermal resistance in multilayers

A general feature of frequency-domain photothermal (PT) experiments is that the signal phase follows the derivative of the log –log-amplitude. This is the consequence of the Kramers–Kronig (K–K) relations between real and imaginary parts of the thermal response of the system, represented by its thermal impedance. Simple expressions allow determining the phase from the amplitude, both theoretically and experimentally. They stem from the local Hilbert transform in differential form, instead of the traditional integral form which requires broadband information. These expressions are applied to the thermal impedance of a layered system. The measurements were performed in an earlier publication by photothermal radiometry (PTR) method to determine the interfacial thermal resistance between a 50 nm Ti layer and a steel or Si substrate. In this case, high frequency measurements are the most relevant, but they are also most prone to artifacts and background noise. It is concluded that the amplitude and phase results of Ti/steel samples are correctly linked to one another, but that the phase of Ti/Si samples violates the K–K relations at high frequency, probably due to a different signal generation mechanism than the PT one. The fact that PT phenomena are consistent with the K–K relations opens the possibility to check the self-consistency of the results obtained by PTR or by other related PT methods. It also reveals that the PT phase carries the same information as the signal amplitude, less a scaling factor that incorporates the thermal effusivity of a layer in the system.

Renewal of seasonally anoxic Saanich Inlet is temporally and spatially dynamic

Injection of oxygenated water into anoxic basins sets off a cascade of biogeochemical reactions and ecosystem shifts. The dynamic nature of these events can create spatial variability in the resulting water mass that strongly affects subsequent observations. Their irregularity can also make their prediction for experiment planning challenging. Our study focuses on Saanich Inlet, one of the most accessible and well-studied anoxic basins in the world. In the late summer and early fall, dense water can cross the sill into this fjord, in discrete events, bringing oxygen and nitrate to the deep waters of the inlet. We assess the potential strength of these renewal events using density measured at a bottom mooring on the sill. We find that the occurrence and potential strength of renewals is primarily controlled by tidal current speeds, which can be well predicted. However, the intensity of coastal upwelling, which brings dense water into the estuarine system, plays a significant secondary control, reducing predictability. We also demonstrate that renewals do not result in a homogeneous water mass filling the deep inlet. Instead, high frequency measurements from a profiling mooring in the centre of the inlet reveal that different densities intruding over the several-day renewal period create a complex layering of waters containing different proportions of new oxic and old anoxic waters. Finally, we show that not every instance of high density water observed over the sill results in flushing of the deepest waters inside the inlet. We hypothesize that each renewal improves the chance of a subsequent renewal in the same season by reducing the density contrast between waters entering and already inside the inlet. Consideration of the temporal and spatial complexity of these renewal dynamics is necessary to support studies using Saanich Inlet as a natural laboratory for exploring oxygen deficient systems.

Quantification of N and C cycling during aerobic composting, including automated direct measurement of N2, N2O, NO, NH3, CO2 and CH4 emissions

Closing the carbon (C) and nitrogen (N) balance has yet to be achieved in aerobic bioprocess due to current methodological drawbacks in the frequency of sampling and detection and the challenge in direct measurement of instantaneous N2 emission. To address this issue, a novel system was developed enabling simultaneous and online determination of gaseous C and N species (N2, N2O, NO, NH3, CO2 and CH4) from aerobic composting at a high frequency of 120 times·d−1. A helium‑oxygen gas mixture was used to replace the air in the system to enable direct measurement of N2 emission, and three different gas exchange methods were assessed in their ability to minimize atmospheric background N2: 1) the N2-free gas purging method; 2) one cycle of the evacuation-refilling procedure; 3) one cycle of evacuating and refilling followed by N2-free gas purging. Method 3 was demonstrated as an optimum N2-removal method, and background N2 concentrations decreased to ~66 μmol·mol−1 within 11.6 h. During the N2-free gas purging period, low temperature incubation at 15 °C reduced CO2, CH4, NO, N2O and NH3 losses by 80.5 %, 41-fold, 10-fold, 11,403-fold and 61.4 %, respectively, compared with incubation at 30 °C. Therefore, a fast and low-perturbation N2 removal method was developed, namely the evacuating/refilling-low temperature purging method. Notably, all C and N gases exhibited large within-day variations during the peak emission period, which can be addressed by high-frequency measurement. Based on the developed method, up to 97.8 % of gaseous C and 95.6 % of gaseous N losses were quantified over a 43-day compost incubation, with N2 emission accounting (on average) for 5.8 % of the initial total N. This system for high frequency measurement of multiple gases (including N2) provides a novel tool for obtaining a deeper understanding of C and N turnover and more accurate estimation of reactive N and greenhouse gas emissions during composting.