The impact of low-frequency, low-force cyclic stretching of human bronchi on airway responsiveness

Low-frequency tomographic synthetic aperture radar (TomoSAR) techniques provide an opportunity for quantifying the dynamics of dense tropical forest vertical structures. Here, we compare the performance of different TomoSAR processing, Back-projection (BP), Capon beamforming (CB), and MUltiple SIgnal Classification (MUSIC), and compensation techniques for estimating forest height (FH) and forest vertical profile from the backscattered echoes. The study also examines how polarimetric measurements in linear, compact, hybrid, and dual circular modes influence parameter estimation. The tomographic analysis was carried out using P-band data acquired over the Paracou study site in French Guiana, and the quantitative evaluation was performed using LiDAR-based canopy height measurements taken during the 2009 TropiSAR campaign. Our results show that the relative root mean squared error (RMSE) of height was less than 10%, with negligible systematic errors across the range, with Capon and MUSIC performing better for height estimates. Radiometric compensation, such as slope correction, does not improve tree height estimation. Further, we compare and analyze the impact of the compensation approach on forest vertical profiles and tomographic metrics and the integrated backscattered power. It is observed that radiometric compensation increases the backscatter values of the vertical profile with a slight shift in local maxima of the canopy layer for both the Capon and the MUSIC estimators. Our results suggest that applying the proper processing and compensation techniques on P-band TomoSAR observations from space will allow the monitoring of forest vertical structure and biomass dynamics.

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Shift Detection in Hydrological Regimes and Pluriannual Low-Frequency Streamflow Forecasting Using the Hidden Markov Model

Water ◽

10.3390/w12072058 ◽

2020 ◽

Vol 12 (7) ◽

pp. 2058 ◽

Cited By ~ 2

Author(s):

Larissa Rolim ◽

Francisco de Souza Filho

Keyword(s):

Time Series ◽

Markov Model ◽

Hidden Markov Model ◽

Extreme Events ◽

Hidden Markov ◽

Low Frequency ◽

Streamflow Forecasting ◽

Hydrologic Time Series ◽

Low Frequency Variability ◽

The Impact

Improved water resource management relies on accurate analyses of the past dynamics of hydrological variables. The presence of low-frequency structures in hydrologic time series is an important feature. It can modify the probability of extreme events occurring in different time scales, which makes the risk associated with extreme events dynamic, changing from one decade to another. This article proposes a methodology capable of dynamically detecting and predicting low-frequency streamflow (16–32 years), which presented significance in the wavelet power spectrum. The Standardized Runoff Index (SRI), the Pruned Exact Linear Time (PELT) algorithm, the breaks for additive seasonal and trend (BFAST) method, and the hidden Markov model (HMM) were used to identify the shifts in low frequency. The HMM was also used to forecast the low frequency. As part of the results, the regime shifts detected by the BFAST approach are not entirely consistent with results from the other methods. A common shift occurs in the mid-1980s and can be attributed to the construction of the reservoir. Climate variability modulates the streamflow low-frequency variability, and anthropogenic activities and climate change can modify this modulation. The identification of shifts reveals the impact of low frequency in the streamflow time series, showing that the low-frequency variability conditions the flows of a given year.

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Polytetrafluoroethylene Films in Rigid Polyurethane Foams’ Dielectric Permittivity Measurements with a One-Side Access Capacitive Sensor

Polymers ◽

10.3390/polym13071173 ◽

2021 ◽

Vol 13 (7) ◽

pp. 1173

Author(s):

Ilze Beverte ◽

Ugis Cabulis ◽

Sergejs Gaidukovs

Keyword(s):

Dielectric Properties ◽

Dielectric Permittivity ◽

Low Frequency ◽

Capacitive Sensor ◽

Polyurethane Foams ◽

Active Area ◽

Ptfe Film ◽

Practical Applications ◽

Permittivity Measurements ◽

The Impact

As a non-metallic composite material, widely applied in industry, rigid polyurethane (PUR) foams require knowledge of their dielectric properties. In experimental determination of PUR foams’ dielectric properties protection of one-side capacitive sensor’s active area from adverse effects caused by the PUR foams’ test objects has to be ensured. In the given study, the impact of polytetrafluoroethylene (PTFE) films, thickness 0.20 mm and 0.04 mm, in covering or simulated coating the active area of one-side access capacitive sensor’ electrodes on the experimentally determined true dielectric permittivity spectra of rigid PUR foams is estimated. Penetration depth of the low frequency excitation field into PTFE and PUR foams is determined experimentally. Experiments are made in order to evaluate the difference between measurements on single PUR foams’ samples and on complex samples “PUR foams + PTFE film” with two calibration modes. A modification factor and a small modification criterion are defined and values of modifications are estimated in numerical calculations. Conclusions about possible practical applications of PTFE films in dielectric permittivity measurements of rigid PUR foams with one-side access capacitive sensor are made.

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Abstract P315: Increase in Stress May Contribute to Lower Heart Rate Variability in Healthy Young Subjects

Circulation ◽

10.1161/circ.125.suppl_10.ap315 ◽

2012 ◽

Vol 125 (suppl_10) ◽

Author(s):

Amanda C Costa ◽

Ana Gabriela C Silva ◽

Cibele T Ribeiro ◽

Guilherme A Fregonezi ◽

Fernando A Dias

Keyword(s):

Cardiovascular Disease ◽

Heart Rate ◽

Heart Rate Variability ◽

Healthy Volunteers ◽

Perceived Stress ◽

Low Frequency ◽

Statistical Correlation ◽

Total Power ◽

The Impact ◽

Nonparametric Correlation

Background: Stress is one of the risk factors for cardiovascular disease and decreased heart rate variability is associated to increased mortality in some cardiac diseases. The aim of the study was to assess the impact of perceived stress on cardiac autonomic regulation in young healthy volunteers. Methods: 35 young healthy volunteers (19 to 29 years old, 6 men) from a Brazilian population were assessed for perceived stress by the translated and validated Perceived Stress Scale (PSS, 14 questions) and had the R-R intervals recorded at rest on supine position (POLAR RS800CX) and analyzed (5 minutes, Kubius HRV software) by Fast-Fourier Transform for quantification of Heart Rate Variability (HRV). Results: Average data (±SD) for age, heart rate, BMI, waist circumference and percentage of body fat (%BF) were: 21.3±2.7 years; 65.5±7.9 bpm; 22.3±1.9 Kg/m 2 ; 76.0±6.1 cm and 32.1±6.6%; respectively. The mean score for the PSS-14 was 23.5±7.2 and for the HRV parameter as follow: SSDN=54.8±21.2ms; rMSSD=55.9±32.2ms; low-frequency (LF)= 794.8±579.7ms 2 ; High-frequency (HF)= 1508.0±1783.0 ms 2 ; LF(n.u.)= 41.1±16.2; HF(n.u.)= 58.9±16.2; LF/HF=0.89±0.80 and Total power (TP)= 3151±2570ms 2 . Spearman nonparametric correlation was calculated and there was a significant correlation of PSS-14 scores and LF (ms 2 ) (r=−0.343; p= 0.044). Other HRV variables did not shown significant correlation but also had negative values for Spearman r (TP r=−0.265, p=0.124; HF r=−0.158; SSDN r=−0.207; rMSSD r=−0.243, p=0.160). LF/HF and LF(n.u.) did not correlate to PSS-14 having Spearman r very close to zero (LF/HF r=−0.007, p=0.969; LF(n.u.) r=−0.005, p=0.976). No correlation was found for HRV parameters and BMI and there was a trend for statistical correlation of %BF and LF (ms 2 ) (r=−0.309, p=0.071). Conclusions: These data demonstrate a possible association of perceived stress level and HRV at rest. Changes in LF can be a consequence of both sympathetic and parasympathetic activity, however, analyzing the other variables HF, TP, SSDN and rMSSD (all negative Spearman r) and due to the lack of changes in LF/HF ratio and LF(n.u.) we interpret that increased stress may be associated to decrease in overall heart rate variability. These changes were seen in healthy individuals and may point out an important mechanism in cardiovascular disease development.

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Ceiling Construction Low-Frequency Noise Issues

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.649.277 ◽

2013 ◽

Vol 649 ◽

pp. 277-280

Author(s):

Petra Berková ◽

Pavel Berka

Keyword(s):

Spectral Analysis ◽

Low Frequency ◽

Sound Insulation ◽

Frequency Noise ◽

Low Frequency Noise ◽

Frequency Tone ◽

The Impact ◽

40 Hz

Through the use of a spectral analysis of the source of noise – person’s movement over the ceiling construction – it was found out that in this kind of noise distinctive low-frequency tone components occur (31,5 - 40 Hz) which is beyond the evaluation area of the impact sound insulation of the ceiling construction, s. [2], [3].

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Electric Vehicle Battery Performance Investigation Based on Real World Current Harmonics

Energies ◽

10.3390/en13020489 ◽

2020 ◽

Vol 13 (2) ◽

pp. 489 ◽

Cited By ~ 2

Author(s):

Sid-Ali Amamra ◽

Yashraj Tripathy ◽

Anup Barai ◽

Andrew D. Moore ◽

James Marco

Keyword(s):

Electric Vehicle ◽

Real World ◽

Low Frequency ◽

Single Frequency ◽

Current Harmonics ◽

Battery Systems ◽

Electric Vehicle Battery ◽

Dc Bus ◽

Dc Current ◽

The Impact

Electric vehicle (EV) powertrains consist of power electronic components as well as electric machines to manage the energy flow between different powertrain subsystems and to deliver the necessary torque and power requirements at the wheels. These power subsystems can generate undesired electrical harmonics on the direct current (DC) bus of the powertrain. This may lead to the on-board battery being subjected to DC current superposed with undesirable high- and low- frequency current oscillations, known as ripples. From real-world measurements, significant current harmonics perturbations within the range of 50 Hz to 4 kHz have been observed on the high voltage DC bus of the EV. In the limited literature, investigations into the impact of these harmonics on the degradation of battery systems have been conducted. In these studies, the battery systems were supplied by superposed current signals i.e., DC superposed by a single frequency alternating current (AC). None of these studies considered applying the entire spectrum of the ripple current measured in the real-world scenario, which is focused on in this research. The preliminary results indicate that there is no difference concerning capacity fade or impedance rise between the cells subjected to just DC current and those subjected additionally to a superposed AC ripple current.

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Making maps of cosmic microwave background polarization for B-mode studies: the POLARBEAR example

Astronomy and Astrophysics ◽

10.1051/0004-6361/201629467 ◽

2017 ◽

Vol 600 ◽

pp. A60 ◽

Cited By ~ 6

Author(s):

Davide Poletti ◽

Giulio Fabbian ◽

Maude Le Jeune ◽

Julien Peloton ◽

Kam Arnold ◽

...

Keyword(s):

Cosmic Microwave Background ◽

Time Domain ◽

Power Spectra ◽

Low Frequency ◽

Frequency Noise ◽

Spectrum Estimation ◽

Microwave Background ◽

Polarization Studies ◽

Ordered Data ◽

The Impact

Analysis of cosmic microwave background (CMB) datasets typically requires some filtering of the raw time-ordered data. For instance, in the context of ground-based observations, filtering is frequently used to minimize the impact of low frequency noise, atmospheric contributions and/or scan synchronous signals on the resulting maps. In this work we have explicitly constructed a general filtering operator, which can unambiguously remove any set of unwanted modes in the data, and then amend the map-making procedure in order to incorporate and correct for it. We show that such an approach is mathematically equivalent to the solution of a problem in which the sky signal and unwanted modes are estimated simultaneously and the latter are marginalized over. We investigated the conditions under which this amended map-making procedure can render an unbiased estimate of the sky signal in realistic circumstances. We then discuss the potential implications of these observations on the choice of map-making and power spectrum estimation approaches in the context of B-mode polarization studies. Specifically, we have studied the effects of time-domain filtering on the noise correlation structure in the map domain, as well as impact it may haveon the performance of the popular pseudo-spectrum estimators. We conclude that although maps produced by the proposed estimators arguably provide the most faithful representation of the sky possible given the data, they may not straightforwardly lead to the best constraints on the power spectra of the underlying sky signal and special care may need to be taken to ensure this is the case. By contrast, simplified map-makers which do not explicitly correct for time-domain filtering, but leave it to subsequent steps in the data analysis, may perform equally well and be easier and faster to implement. We focused on polarization-sensitive measurements targeting the B-mode component of the CMB signal and apply the proposed methods to realistic simulations based on characteristics of an actual CMB polarization experiment, POLARBEAR. Our analysis and conclusions are however more generally applicable.

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Monitoring the Impact of Electromagnetic Waves on Yield and Quality in Maize

Bulletin of University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca Agriculture ◽

10.15835/buasvmcn-agr:6437 ◽

2011 ◽

Vol 68 (1) ◽

Author(s):

Florin IMBREA ◽

Branko MARINCOVIC ◽

Valeriu TABĂRĂ ◽

PAUL PÎRŞAN ◽

Gheorghe DAVID ◽

...

Keyword(s):

Protein Content ◽

Quality Indicators ◽

Electromagnetic Waves ◽

Starch Content ◽

New Technology ◽

Low Frequency ◽

Cultivation Method ◽

Yield And Quality ◽

The Impact ◽

Starch Yield

Experimenting new technology of cultivating maize is an important step forward in order to optimise the yielding capacity if a crop that ranks second among crops cultivated worldwide and first among crops cultivated in Romania. Using low frequency radiations to stimulate yield and quality in maize allows increases in yield between 10 and 15% compared to the classical cultivation method and an improvement of the quality indicators (protein content increased with 6-11% determining an increase of the protein yield per ha; starch content increased with 7-14%, which also determined an increase of the starch yield per ha; while fat content, another indicator we monitored, increased with 2-6%).

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