Frequency Plots Research Articles

Vogel Fulcher analysis of electrical studies of NBT-CT ceramic composites

Impedance spectroscopy analyses of (1-x)Na0.5Bi0.5TiO3+(x) CaTiO3(NBT-CT) where x = 0.05, 0.10, 0.15, 0.20 are studied. The present samples reveal a non-Debye type relaxation phenomenon. The grain conduction effect is observed from complex impedance spectrum by the appearance of one semi-circular arc in Nyquist plot. Relaxation time of the samples is calculated by fitting Vogel-Fulcher law. DC conductivity is performed on samples and observed that resistance decreases with an increase in temperature showing a negative temperature coefficient of resistance (NTCR). The frequency-dependent AC conductivity at different temperatures indicates that conduction process is thermally activated. The activation energy has been calculated from Arrhenius plot of DC conductivity and relaxation frequency.

Vibrations of flexible pylons with time‐dependent mass attachments under ground induced motions

AbstractThis work examines how mass attachments that vary with time influence the motion of flexible pylons undergoing ground‐induced vibrations. Specifically, an analytical solution is derived for a time‐dependent, lumped mass attachment placed at the top of a cantilevered pylon undergoing time‐harmonic longitudinal vibrations. At first, the solution to the governing equation of motion entails the recovery of the eigenvalue problem in the presence of a fixed mass. This is then followed by a generalization of this solution to allow for mass variability with time. It is noted that modal analysis no longer yields an uncoupled system of equations for the generalized coordinates, this necessitating a second step modal analysis, which is complicated by the fact that the system matrices are now time dependent. Results are presented in terms of time histories and frequency plots for the pylon displacement amplitude at the top, resulting from harmonic base motion of unit amplitude. The aim is to identify the frequency range over which the presence of a time‐varying mass is either beneficial or detrimental in minimizing the pylon's kinematic response. Since the rate of change of the mass can be either positive or negative, the special cases of constant mass and of no mass can be recovered from the solution. Finally, this methodology can be generalized to include transverse and rotational vibrations of flexible pylons.

SEPIC converter in discontinuous conduction mode: Small signal modeling and analysis

AbstractIn this article, a new approach is applied to solve the small signal state space average (SSA) model for pulse width modulated (PWM) single ended primary inductor converter (SEPIC) under discontinuous conduction mode (DCM) of operation. Authors proposed a novel approach to get duty ratio constrains that is based on variation of current in inductor. The approach used a unique correction matrix (M) in the modeling process and obtained better results for DCM. To demonstrate the whole technique, the SEPIC‐based power supply of 75 W is designed and system loop gain is derived with the help of this new technique. The frequency response of the proposed system is captured with the help of linearization technique using MATLAB Simulink platform. The frequency plot from the proposed techniques is much closer to simulation results as compared to conventional method. This claims high predictions for dc–dc converter operating in DCM with wide range of input supply. The proposed model is analyzed with previous SSA small signal modeling for comparative results on the basis of frequency analysis and stability. The experiment results of designed power supply have shown good power quality performance at 220‐V AC mains for light‐emitting diode (LED) lighting application.

Association of Elevated Plasma Total Homocysteine With Dementia With Lewy Bodies: A Case-Control Study.

Background: Elevated plasma total homocysteine (tHcy) level, a known risk factor for vascular disease, is reported to be an independent risk factor for cognitive impairment and Alzheimer’s disease (AD) in most studies. tHcy may also be associated with dementia with Lewy bodies (DLB).Objective: To investigate the association between plasma tHcy levels and DLB or AD.Methods: This is a case-control study including 132 DLB patients, 264 AD patients, and 295 age-matched healthy controls. We used multivariate logistic regression model to analyze the data with adjustments for confounding variables.Results: The highest tHcy tertile (>13.9 μmol/L) was significantly independently associated with DLB [adjusted odds ratio (OR): 4.65, 95% confidence interval (CI): 1.95–11.10, P = 0.001] and AD (adjusted OR: 1.82, 95% CI: 1.02–3.23, P = 0.041) compared to the lowest tertile (<10.7 μmol/L). The cumulative frequency plots showed a shift in the distribution of the tHcy concentrations to higher values in patients with DLB compared to AD. The mean tHcy levels were stable and not altered by the duration of cognitive impairment prior to the collection of blood samples from DLB patients.Conclusion: Elevated plasma tHcy levels were independently associated with DLB, and the association was stronger for DLB than for AD. The lack of a relationship between tHcy levels and symptom duration may refute these observed associations being a consequence of DLB, and future longitudinal studies will be required to confirm whether tHcy plays a causative role in DLB.

Fracture analysis using Stoneley waves in a coalbed methane reservoir

ABSTRACTThe production of coalbed methane gas depends upon various factors such as permeability, gas content, gas saturation and seam thickness. The low permeability in coal is a constraint in the gas extraction process. However, the presence of natural fractures and cleats in coal increases the permeability; therefore, its identification is necessary to establish the prospectivity. Hence, a methodology is used to process the Stoneley waveform in the Bokaro coalfield located in India to obtain slowness magnitude from the semblance analysis. The separation of directly transmitted and reflected Stoneley waves determines the reflection coefficient and attenuation, and its analysis emphasizes the presence of fractures. In coal seams, the average reflection coefficient ranges from 0.42 to 2.44 and attenuation ranges from 0.2 dB to 12.68 dB. The Stoneley slowness versus frequency plot shows a constant slowness with increasing frequency in the non‐fractured seams, whereas a dispersive trend is observed in the fractured seams. Fractures are also distinguished from the cross‐plot of compressional/shear versus Stoneley velocity. The observation of higher reflection coefficient, attenuation and slowness‐frequency dispersion in coal seams indicates extensive fractures/cleats that corroborate with the resistivity image log correlation. Thus, the study helps to distinguish between fractured and non‐fractured coal seams from the integrated approach of reflection coefficient, attenuation and dispersion analysis of Stoneley waves supported by the identification of fractures from resistivity image log for optimization in coalbed methane production in the development phase.

An investigation of carboxylated chitosan hydrogel electrolytes for symmetric carbon-based supercapacitors at low temperatures

BackgroundChitosan (CS) is the most abundant cationic biopolymer on earth. However, the ionic conductivity performance of CS polymer electrolyte is relatively poor, restricting the application in energy storage devices. MethodsSubject to carboxylation at pH of 6. 8, and 10, CS turns into CCS6, CCS8, and CCS10 respectively with the DC of 100.9%, 20.0%, and 17.8%, respectively. Significant findingsFrom the Arrhenius plot, the activation energy of CS, CCS6, CCS8, and CCS10 electrolytes is estimated as 11.7, 2.5, 2.6, and 2.6 kJ/mol respectively. As for supercapacitor performance, CCS6 remains 57.2% capacitance but the others remain 0% with decreasing temperature from 25 °C to -7 °C. At -7 °C, only CCS6 supercapacitor shows relaxation peak in loss tangent versus frequency plot around 2 × 105 Hz according to dissociated ion pairs, being attributable to the existence of bound water. Three water states are examined by Differential Scanning Calorimetry (DSC) and Raman, verifying that CCS6 possesses high bound water proportion of 24.7%. With the highest DC, CCS6 possesses the almost equivalent amine and carboxyl groups in one glucosamine unit to play an important role to enhance dissociation, defer the breakpoints of ionic conductivity, and remain certain proportion of bound water for promising capacity at low temperature.

Electroanalysis with a single microbead of phosphate binding resin (FerrIX\u2122) mounted in epoxy film

Commercial resin microbeads are widely applied in ion exchange and extraction. Here, a single anion-selective and phosphate binding resin microbead (FerrIX™) is mounted into an epoxy membrane and investigated by 4-electrode membrane voltammetry and membrane impedance spectroscopy. Anion transport properties are observed to dominate associated with three distinct potential domains: (I) a low bias ohmic potential domain (dominant at high electrolyte concentration), (II) a concentration polarisation potential domain, and (III) an over-limiting potential domain. Voltammetric responses show transient diffusion-migration features at higher scan rates and quasi-steady state features at lower scan rates. Inherent microbead conductivity is shown to be linked to two resistive elements, electrolyte concentration dependent and independent, in series. The effects of phosphate binding are revealed as transient pattern in impedance spectroscopy data. Preliminary data suggest phosphate concentration-dependent peak features in the imaginary impedance versus frequency plot due to phosphate binding into the microbead.Graphical abstract

Oesophageal thermal protection during AF ablation: effect on left atrial myocardial ablation lesion formation and patient outcomes

Abstract Funding Acknowledgements Type of funding sources: Private company. Main funding source(s): Dr Leung has received research support from Attune Medical (Chicago, IL). Dr Gallagher has received research funding from Attune Medical (Chicago, IL). Background Randomized evidence has shown that controlled oesophageal cooling is effective at reducing oesophageal thermal injury during radiofrequency (RF) ablation for atrial fibrillation (AF) compared to standard care. The effect of oesophageal cooling on ablation lesion formation in left atrial myocardium and patient outcomes at 12-months had not been previously studied. Purpose To determine the effect of oesophageal cooling on the formation of RF lesions, the ability to achieve procedural endpoints and long-term patient outcomes compared to standard care ablations. Methods Ablation results and patient outcomes from a double-blind randomized controlled trial were analysed (IMPACT trial NCT03819946). AF ablation was guided by Ablation Index technology (30W at 350-400 AI posteriorly, 40W at 450 AI anteriorly). A blinded 1:1 randomization assigned patients to the use of an oesophageal temperature control device to keep oesophageal temperature at 4 degrees during ablation or standard practice using a single-sensor temperature probe. Ablation parameters and 12-month outcomes were analysed. Results We recruited 188 patients. Procedure and fluoroscopy times were similar. First pass pulmonary vein isolation and reconnection at the end of the waiting period were similar in both randomized groups (51/64 vs 51/68; p = 0.54 and 5/64 vs 7/68; p = 0.76, respectively). Posterior wall isolation was also similar: 24/33 vs 27/38; p = 0.88. Ablation effect on myocardial tissue, measured in impedance drop, was also similar: 8.6Ω (IQR: 6-11.8) vs 8.76Ω (IQR: 6-12.2; p = 0.25) and median catheter tip temperature was the same at 25.5 degrees. Arrhythmia recurrence was similar at 12 months (20.3% vs 26.8%, from 142 completed assessments; p = 0.66). Conclusions Oesophageal cooling has been shown to be effective in reducing ablation-related oesophageal thermal injury during RF ablation. Ablation data show that this protection does not make it any more difficult to achieve standard procedural endpoints or clinical success at 12-months. Abstract Figure. Pyramid frequency plots of AI values

Effect of varying road profile amplitude on the behavior of a nonlinear quarter car model

Vehicle suspensions are one of the most important equipment in an automobile which impart comfortable ride to the passengers. As the passive suspensions are most widely used in the automobiles, therefore this paper deals with the investigations of the suspension behavior at the different values of the road profile amplitude. The effects on the frequency plots are studied by using fast Fourier transform functions. The phase plots are also drawn to understand the periodic and quasi periodic transformations at the different values of road profile amplitude. It is seen that the natural frequency and its harmonics in the spectrum dies out with the rise in the values of the road profile amplitude and also the increase in the strength of forcing is observed. The in harmonics obtained is seen to be withdrawn with the increase in the road profile amplitude.

Visualization of user interactions with a pressure mapping mobile application for wheelchair users at risk for pressure injuries

ABSTRACT Pressure injuries for individuals with spinal cord injuries (SCI) are correlated with mortality and are a leading cause for rehospitalizations. The Assisted Weight Shift (AW-Shift©) is a mobile pressure mapping application designed to provide users with a live map view and reminders to perform weight shifts. Novel visualization techniques were used to understand daily distributions of user interaction with AW-Shift©. The date and time of system interactions were recorded for six participants with SCI over 7 days (five males/one female, five manual users/one power user, 55.3 ± 17.3 years old, 10.6 ± 6.5 years since injury). Circular frequency plots were created to visualize the time and frequency participants brought the app to the foreground of their phone and received alerts and reminders to complete weight shifts. While some participants used the system regularly throughout the day, others primarily used it before 8am; highlighting the system’s importance for regular spot checks and morning wheelchair setup. Participant adherence to weight shift reminders was low suggesting the live pressure map may be more useful. Circular frequency plots can be used by clinicians to more easily review large amounts of patient data. Future work will investigate raw pressure mat data and create a closed-loop weight shift detection algorithm.

An Improved Hilbert–Huang Transform for Vibration-Based Damage Detection of Utility Timber Poles

In this study, vibration based non-destructive testing (NDT) technique is adopted for assessing the condition of in-service timber pole. Timber is a natural material, and hence the captured broadband signal (induced from impact using modal hammer) is greatly affected by the uncertainty on wood properties, structure, and environment. Therefore, advanced signal processing technique is essential in order to extract features associated with the health condition of timber poles. In this study, Hilbert–Huang Transform (HHT) and Wavelet Packet Transform (WPT) are implemented to conduct time-frequency analysis on the acquired signal related to three in-service poles and three unserviceable poles. Firstly, mother wavelet is selected for WPT using maximum energy to Shannon entropy ratio. Then, the raw signal is divided into different frequency bands using WPT, followed by reconstructing the signal using wavelet coefficients in the dominant frequency bands. The reconstructed signal is then further decomposed into mono-component signals by Empirical Mode Decomposition (EMD), known as Intrinsic Mode Function (IMF). Dominant IMFs are selected using correlation coefficient method and instantaneous frequencies of those dominant IMFs are generated using HHT. Finally, the anomalies in the instantaneous frequency plots are efficiently utilised to determine vital features related to pole condition. The results of the study showed that HHT with WPT as pre-processor has a great potential for the condition assessment of utility timber poles.

Study of structural, morphological, Mössbauer and dielectric properties of NiFeCoO4 prepared by a sol gel method

A methodical study on structural, electrical and dielectric properties of NiFeCoO4 nanoparticles, synthesized via sol-gel technique has been reported in this article. X-ray diffractogram confirmed phase purity of the synthesized sample. Raman spectra show the five predicted Raman bands that appear around 600–720, 250–360, 500–590, 450–520 and 180–220 cm−1 corresponding to A1g, Eg, T2g (3), T2g (2) and T2g (1), respectively. From the dielectric measurements, we have determined the different dielectric parameters such as the conductivity σac, complex permittivity e*, complex impedance Z*, and the tangent loss (tanδ). The electrical properties strongly depend on temperature and frequency. The relaxation activation energy deduced from the Z” vs. frequency plots was similar to the conduction activation energy obtained from the conductivity. Hence, the same type of charge carriers are attributed to the relaxation process and the conduction mechanism. The complex impedance plots have revealed the presence of only one semicircular arc corresponding to grains and grain boundaries contributions at all the temperatures and an equivalent electric circuit was proposed as a model of the sample.

Frequency dependence of the dielectric properties of Au/(NG:PVP)/n-Si structures

The consequences of applying (Nanographite-PVP) interlayer on surface-states (Nss), series-resistance (Rs), and polarization effects on the real and imaginary parts of the complex dielectric constant (e* = e′-je″), loss-tangent {tanδ(= e″/e′)}, electrical-conductivity (σ), and complex electric-modulus (M* = M′ + jM″) have been investigated in wide range frequency (1 kHz/5 MHz) and voltage (-1 V/2 V) to get more information on them. Additionally, both the frequency-dependent profile of Rs and complex-impedance (Z* = Z′-jZ″) were extracted by using the e′ and e″ values. Whereas the e′ and e″ decline with incline frequency, but incline with positive applied voltage owing to restructure and reorganized of the charges at Nss, and polarization effect under electric field. While the increment in conductivity at high-frequencies was predicated on the increment in charge mobility, the increment in e′ and e″ at low-frequencies was attributed to increment in mobility of these charges. Hopping-carries from one traps to the other was also leads to an increment in the conductivity at high-frequencies. The observed peak characteristics in M″ and tanδ versus V and frequency plots was attributed to relaxation-time and spatial distribution of Nss located at interlayer/n-Si interface, interfacial/dipole polarization. High-dielectric value (6.5) shows that this organic interlayer may be good alternative to the conventional insulators which can be more charges/energy storage.

Tuning Magnetic Relaxation in Square-Pyramidal Dysprosium Single-Molecule Magnets Using Apical Alkoxide Ligands

Tuning Magnetic Relaxation in Square-Pyramidal Dysprosium Single-Molecule Magnets Using Apical Alkoxide Ligands

Effect of multifrequency, boundary conditions of Polyvinyl Alcohol (PVA) crosslinked with Glutaraldehyde (GA) using dynamic mechanical analyzer

ABSTRACT Due to rapid growth in global warming issues, researchers are focusing on alternative materials which will be replacing existing nonbiodegradable. This research article aims to study the mechanical and dynamic mechanical analysis of Polyvinylalcohol (PVA) crosslinked Glutaraldehyde (GA) polymer. The PVA-GA polymers are processed by using conventional compression moulding techniques by several volume fractions (Vf) from 5 to 40. The prepared PVA-GA polymer dipped in Sulphuric acid solution for 24 hours for better crosslinking. The result reveals that mechanical properties enhanced by adding up to 20 Vf GA in PVA, the tensile strength is maximum for 20 Vf GA in PVA, but flexural strength is maximum for 25 Vf GA in PVA. Further, thermo-mechanical properties are analysed from 20 to 140 °C at logarithmic frequency from 0.1 to 46 Hz for various boundary conditions like a dual cantilever, single cantilever, and three-point bending. The Time–Temperature Superposition (TTS) diagrams are plotted for various boundary conditions; additionally, storage modulus frequency plots are constructed by horizontal shifting called master curves.

Verifying and Redefining the Weather Prediction Center’s Excessive Rainfall Outlook Forecast Product

AbstractThe Weather Prediction Center’s Excessive Rainfall Outlook (ERO) forecasts the probability of rainfall exceeding flash flood guidance within 40 km of a point. This study presents a comprehensive ERO verification between 2015 and 2019 using a combination of flooding observations and proxies. ERO spatial issuance frequency plots are developed to provide situational awareness for forecasters. Reliability of the ERO is assessed by computing fractional coverage of the verification within each probabilistic category. Probabilistic forecast skill is evaluated using the Brier skill score (BSS) and area under the relative operating characteristic (AUC). A “probabilistic observation” called practically perfect (PP) is developed and compared to the ERO as an additional measure of skill. The areal issuance frequency of the ERO varies spatially with the most abundant issuances spanning from the Gulf Coast to the Midwest and the Appalachians. ERO issuances occur most often in the summer and are associated with the Southwestern monsoon, mesoscale convective systems, and tropical cyclones. The ERO exhibits good reliability on average, although more recent trends suggest some ERO-defined probabilistic categories should be issued more frequently. AUC and BSS are useful bulk skill metrics, while verification against PP is useful in bulk and for shorter-term ERO evaluation. ERO forecasts are generally more skillful at shorter lead times in terms of AUC and BSS. There is no trend in ERO area size over 5 years, although ERO forecasts may be getting slightly more skillful in terms of critical success index when verified against the PP.

Electrical studies on Na and Sm substituted strontium bismuth titanate (SBTi) ceramics

Single-phase Sodium (Na), Samarium (Sm) substituted Strontium Bismuth Titanate (SNSBTi I-V) ceramics were synthesized by solid-state double sintering approach via high energy planetary ball mill for 20 hours grinding. X-ray diffraction (XRD) study confirms the primary structure and orthorhombic distortion of crystal. Scanning electron microscopy (SEM) shows the grain orientation and densified plate-like grain structure of SNSBTi I-V. The complex impedance spectroscopy method was used to study the temperature and frequency dependent electric properties of the material using a high-frequency LCR meter. Z'' versus frequency plots have shown the peak shifting to higher frequencies with increasing concentration of Na, Sm. It is also found that the magnitude of the peaks decreases with increasing temperature. The grain and grain boundary relaxation mechanisms of SNSBTi I-V have been identified using Nyquist plots; the resistance, capacitance and relaxation times were obtained from Z-view software. It is seen that the grain and grain boundary resistances decreased with the increasing concentration of Na and Sm of SBTi ceramics.

Characterization of Multiphase Polypyrrole/Vanadium Oxide Nano Composites for a.c. Conductivity and Dielectric Properties

Vanadium oxide: Phase-1 and Phase-2 nano powers were synthesized from vanadium pentoxide in the presence of glucose using hydrothermal technique. The polypyrrole/vanadium oxide (PV P-1 and PV P-2) nano composites were synthesized with 15, 30, 45 and 60 weight percents of vanadium oxide: Phase-1 and Phase-2 in pyrrole, by the chemical polymerization (oxidation) method. The SEM micrographs of vanadium oxide: Phase-1 and Phase-2 nano powders have shown mixture of nano belts &amp; rods and PV P-1 &amp; PV P-2 nano composites indicate that the composites have cluster formation with almost spherical nature particles and form elongated chains at some places. Conductivity versus frequency plots shown that exponential increase for conductivity. The value of s increases to 1.13x10-3 S/cm for 15 wt. % of VO2 P-1 in polypyrrole &amp; to 2.43x10-3 S/cm for 30 wt. % of VO2 P-2 in polypyrrole at 1 MHz.

Moving beyond DSM5 and ICD11: Acoustic analysis for psychological stress on daily-wage workers in India during COVID19

AimTo observe psychological stress in the acoustic samples of daily-wage workers belonging to different states in India. MethodThe study was based on the observations obtained from prior work on detecting psychoacoustic detectors of psychological stress. Acoustic samples were obtained from interviews conducted by NDTV throughout March–May 2020. Spectrogram and Fundamental Frequency variations were used to identify psychological stress. ResultsStark differences existed in mean fundamental frequency plots by daily-wage workers and non-stressed individuals. Distinct density variations were also observed in the acoustic samples between the two groups. ConclusionPsychoacoustic detectors of psychological stress were confirmed in the acoustic samples of daily wage-workers, concluding that daily-wage workers are under dire psychological stress and are susceptible to stress-related disorders.

Investigation of dielectric behavior in Ni0.7-xZn0.3MxFe2O4 (M=Mn/Co/Cu) ferrites by impedance spectroscopy

The electrical characteristics of the Mn/Co/Cu-substituted Ni–Zn ferrites prepared using the citrate technique have been explored in detail by ac impedance spectroscopy. Measurements between temperatures (373K–523 K) were observed over a broad frequency range of 100 Hz–1 MHz. Maxwell and Wagner's model was used to analyze the frequency dependence of dielectric parameters. Dielectric loss tangent versus frequency plots show relaxation peaks due to the coincidence of the frequency of charge hopping between the localized state and the outer field. The Cole-Cole curve was designed to investigate the complex impedance of the current systems. Two semicircles corresponding to the grain and grain boundary were observed. The investigation of the electrical modulus includes the electrical relaxation of the non-Debye form. The substitution of Ni ions by Mn/Co/Cu ions indicates a major improvement in the dielectric characteristics of Ni − Zn ferrite. The Ni–Zn–Cu ferrite series displays the best dielectric properties suggesting the capability of this series to be suitable for high-frequency devices.