Accurate Frequency Research Articles

An accurate interpolation-based iterative frequency estimator of 2D multi-frequency sinusoids

ABSTRACT There are many domains in which frequency estimation of two-dimensional (2D) multi-frequency sinusoids is of great concern. In this paper, based on 2D spectrum interpolation, an accurate and efficient method is proposed to estimate 2D multi-frequency in noise. The method estimates the order of the signal by adopting a coarse-fine strategy that effectively corrects frequency leakage and suppresses interference between frequency components. To obtain the coarse estimation, 2D spectrum interpolation and 2D discrete Fourier transform (2D-DFT) are adopted after the order of sinusoids has been estimated. The fine estimation, with subtraction strategies converting sinusoids into 2D single-frequency sinusoids, suppresses interference from other frequency components. Next, 2D spectrum interpolation is used to obtain an accurate frequency estimate, whose accuracy is further improved through iteration. Simulation results demonstrate that the proposed method is capable of achieving the Cramer-Rao lower bound (CRLB) and outperforms other recently proposed frequency domain methods for 2D multi-frequency sinusoids.

Metrology-grade spectroscopy source based on an optical parametric oscillator

Continuous-wave optical parametric oscillators (OPOs) are widely tunable and powerful sources of narrow-linewidth radiation. These properties make them suitable for a wide range of spectroscopic studies - but so far not at the metrological level. Indeed, although important technical OPO developments occurred more than two decades ago, and commercial devices have been available for nearly as long, the long-hoped-for the potential of these devices, providing simultaneously ultralow linewidth, ultrahigh frequency stability, ultrahigh frequency accuracy, and wide wavelength coverage has not yet become a reality. Here, we present an OPO metrology system suitable for optical spectroscopy with ultra-high resolution and accuracy in the 2.2 - 3.9 μm range. The system relies on the second-harmonic generation of the idler wave to bridge the gap to the near-infrared regime where frequency combs are readily available. By actively controlling the pump laser frequency, the idler radiation is phase-locked to an optically stabilized frequency comb, enabling a full transfer of the frequency comb’s spectral properties to the idler radiation and measuring the idler frequency with ultra-high precision. We reach fractional line widths and Allan deviations of the idler radiation at the level of 4 × 10−14 and 1 × 10−14, respectively. We also perform a thorough characterization of the stabilized OPO via a comparison with a second, independent optically stabilized frequency comb and thereby determine an overall idler frequency systematic uncertainty of less than 1.2 × 10−14. Sources of residual frequency noise are identified. The system delivered excellent results in high-accuracy spectroscopy.

Optimization of emergency frequency control strategy for power systems considering both source and load uncertainties

With the increasing integration of renewable energy sources and the presence of numerous controllable loads such as electric vehicles and energy storage in the modern power system, higher nonlinearities and uncertainty both sources and loads are introduced. These factors pose challenges in achieving fast and accurate emergency frequency control. Therefore, this paper addresses the issue of dual source-load uncertainties in power system and presents an optimization strategy based on the Soft Actor Critic (SAC) algorithm that involves the participation of controllable loads in emergency frequency control. Firstly, the spatio-temporal uncertainties of wind farm power output on power supply side and power demand on the load side are described using Weibull and normal probability distributions, respectively. Secondly, an improved Markov Decision Process (MDP) model for emergency frequency control is established, which considers the characteristics of the dual source-load uncertainties. Finally, an optimization of the SAC algorithm is conducted based on Deep Reinforcement Learning (DRL), aiming to achieve rapid system frequency recovery and minimize the cost of removing controllable loads. The presented approach in the paper enhances the emergency frequency control strategy for uncertain power systems and effectively addresses the issue of source-load uncertainty compounded by fault power shortages.

Home American Journal of Public Health (AJPH) July 2024 Computer Vision Syndrome Questionnaire (CVS-Q) Validation, Unidimensionality and Differential Item Functioning of Saudi Adult Population

Objectives. The CVS-Q, a self-administered research questionnaire, gauges the severity and frequency of 16 eye and vision issues linked to the utilization of digital devices. The study’s objective is to evaluate the computer vision syndrome questionnaire validation within the Saudi adult population. Methods. Responses to the CVS-Q from 634 participants. Rasch analysis used precision, separation index, and reliability for items and person, item and person fit statistics, the unidimensionality, and DIF stratified by age and gender. The reliability analysis, which evaluated the scale’s internal consistency, assisted the use of McDonald's ω, Cronbach's α coefficients, and item-rest correlations. It was carried out using the SPSS software to help analyze the severity of the symptoms. Results. The CVS-Q underwent analysis for both frequency and intensity items using a person separation index (PSI). The reliability measures were found to be robust, with values of 0.80 for frequency and 0.98 for intensity. The mean square infit and outfit statistics met acceptable criteria, demonstrating reliability in squared infit and outfit values. Principal component analysis (PCA) revealed an eigenvalue of 2.07 and a proportion of variance below 10% at 8.3%. Additionally, the first contrast in the PCA of unexplained variance exhibited an eigenvalue of 2.1 and a proportion of variance of 8.5%, below the 10% threshold. DIF analysis showed significant differences in DIF contrast for age groups (16-26 years) and (27-40 years) for questions 7, 11, 12, 13, and 15. The DIF contrast was also significant for questions 6, 12, and 16, and for questions 5, 6, 12, and 16, based on gender. Conclusion. Unidimensionality failed, and all goods displayed appropriate infit and outfits. The age-based CVS-Q frequency items DIF was significant for questions 7, 11, 12, 13, and 15. The age-based CVS-Q intensity DIF was significant for questions 7, 11, 12, and 13. For questions 6, 12, and 16, the CVS-Q frequency items based on gender DIF were significant, while the CVS-Q intensity DIF was significant for questions 5, 6, and 12. The CVS-Q frequency and intensity scale reliability data for Cronbach's scale show high internal consistency and reliability. This scale can be used confidently by academics and industry professionals as accurate and dependable CVS-Q frequency items. (Am J Public Health. 2024;114(3):139–148.

Free vibration analysis of damaged laminated piezoelectric plates and composite plates with piezoelectric patch based on the Extended Layerwise Method

The dynamic analytical models for a laminated piezoelectric plate and a laminated composite plate with piezoelectric patch containing the delamination, transverse crack and debonding damages are established by the Extended Layerwise Method (XLWM). The virtual kinetic energy is introduced into Hamilton’s principle, so resulting in mass matrices and displacement-dependent second mode derivatives in the finite element (FE) governing equations. Then, the FE governing equations for the laminated piezoelectric plate, and the characteristic equations of natural frequencies for the laminated piezoelectric plate with delamination and transverse crack are derived. The coupling model of the laminated composite plate and the piezoelectric patch is established by the displacement continuity and internal force equilibrium conditions at the nodes of the contact area. Based on the degrees of freedom (DoFs) in contact, the final governing equations is deduced, followed by the analysis of free vibration responses for both plates with various damages. The accuracy of natural frequencies for each plate is verified by comparing the results with those of FE simulation by ANSYS.

Appendectomy for suspected appendicitis during pregnancy– a retrospective comparative study of 99 pregnant and 1796 non-pregnant women

IntroductionSuspected appendicitis is the most common indication for non-obstetric surgery during pregnancy. Diagnosis and management of these patients can be challenging. Atypical clinical presentation has been described before, but the current literature consists mostly of small case series. Therefore, we conducted a large retrospective study to analyze the frequency and diagnostic accuracy of clinical signs, laboratory findings and imaging modalities in pregnant woman undergoing surgery for suspected appendicitis compared to a control group of non-pregnant women of childbearing age. We further describe intra- and postoperative findings in both groups.MethodsData from consecutive patients who underwent appendectomy for suspected appendicitis during pregnancy were retrieved from the electronic patient database and analyzed. Preoperative clinical, laboratory and imaging findings as well as intra- and postoperative characteristics were compared between pregnant and non-pregnant women.ResultsBetween January 2008 and June 2023, 99 pregnant woman and 1796 non-pregnant woman between the ages of 16 and 49 underwent emergency surgery for suspected appendicitis. Pregnant women were less likely to have right lower quadrant tenderness (p = 0.002), guarding (p = 0.011) and rebound tenderness (p = 0.097). A greater percentage of pregnant women had a symptom duration of more than 24 h before presentation (p = 0.003) Abdominal ultrasound showed a reduced diagnostic accuracy in pregnant women (p = 0.004). MRI was used in eight pregnant women and showed a diagnostic accuracy of 100%. Pregnant women had a longer operating time (p = 0.006), a higher rate of open appendectomies or conversion (p < 0.001) and a longer postoperative hospital stay (3.2 days vs. 2.2 days, p < 0.001). The perforation rate was also higher in pregnant women at 16% vs. 10% (p = 0.048).ConclusionThe diagnosis of acute appendicitis during pregnancy presents a challenge for the clinician. Our data confirm the paradigm of “atypical presentation” which should lead to an extended diagnostic workup. Ultrasound showed less diagnostic accuracy in pregnant women in our study. MRI is a useful tool to reduce uncertainty and the rate of negative appendectomies.

Solving the Puzzle of the Carbonic Acid Vibrational Spectrum - an Anharmonic Story.

Against the general belief that carbonic acid is too unstable for synthesis, it was possible to synthesize the solid[1,2] as well as gas-phase carbonic acid.[3] It was suggested that solid carbonic acid might exist in Earth's upper troposphere and in the harsh environments of other solar bodies,[4] where it undergoes a cycle of synthesis, decomposition, and dimerization.[5] To provide spectroscopic data for probing the existence of extraterrestrial carbonic acid,[2,6] matrix-isolation infrared (MI-IR) spectroscopy has shown to be essential.[3,4,6-8] However, early assignments within the harmonic approximation using scaling factors impeded a full interpretation of the rather complex MI-IR spectrum of H2CO3. Recently, carbonic acid was detected in the Galactic center molecular cloud,[9] triggering new interest in the anharmonic spectrum.[10] In this regard, we substantially reassign our argon MI-IR spectra based on accurate anharmonic calculations. We calculate a four-mode potential energy surface (PES) at the explicitly correlated coupled-cluster theory using up to triple-zeta basis sets, i. e., CCSD(T)-F12/cc-pVTZ-F12. On this PES, we perform vibrational self-consistent field and configuration interaction (VSCF/VCI) calculations to obtain accurate vibrational transition frequencies and resonance analysis of the fundamentals, first overtones, and combination bands. In total, 12 new bands can be assigned, extending the spectral data for carbonic acid and thus simplifying detection in more complex environments. Furthermore, we clarify disputed assignments between the cc- and ct-conformer.

A simple spectrogram model for high-accuracy spectral calibration of VIPA spectrometers.

The virtually imaged phased array (VIPA) spectrometer uses the orthogonal dispersion method and has the advantages of compact structure, high spectral resolution, and wide wavelength coverage. It has been widely used in different fields. However, due to the non-linear dispersion of the VIPA etalon and the cross-dispersion structure of the VIPA spectrometer, simple and high-accuracy wavelength calibration remains a challenge. In this paper, a new and simple five-parameter spectrogram model is developed by simplifying the phase-matching equation of the VIPA etalon and considering the angle between the camera and dispersion direction, which can achieve a frequency accuracy better than one pixel. The performance of the model is demonstrated by measuring the CO2 absorption spectrum in the range of 1.42 to 1.45 μm using a self-designed near-infrared VIPA spectrometer . The reported method is simple and easy to solve with high accuracy, which is conducive to promoting the application of VIPA spectrometers in precision measurement.

The next-generation of metaverse embodiment interaction devices: A self-powered sensing smart monitoring system

Wearable electronic devices collect user data to provide personalized experiences and real time interactions for the metaverse, thereby driving its development. This paper introduces an innovative self-powered sensing smart monitoring system (SSSMS) designed to harvest human low-frequency inertial energy and achieve gait recognition and fall monitoring (GR-FM) capabilities. The SSSMS enhances energy harvesting efficiency through Halbach electromagnetic enhancement mechanisms, achieving self-sustainability. Additionally, the conical roller triboelectric nanosensor (CR-TENS) accurately captures various human gaits, transmitting these states in the form of electrical signals to a computer via OpenBCI in real time. These signals are integrated with a deep learning-driven diagnostic module to achieve GR-FM. The experimental results demonstrate that under optimal external excitation, the output power is 2.27 mW, with a power density of 32 W/m3. After 100,000 cycles, both the EMG and CR-TENS modules still maintain good performance, sufficiently providing stable and continuous charging for the battery and offering a stable signal for signal processing. Both the EMG and CR-TENS modules exhibit robust feature capture capabilities, effectively sensing different excitation frequencies, amplitudes, and gait patterns. The SSSMS based on the GRU deep learning model achieves recognition accuracies of 96.13 %, 96.60 %, and 92.22 % for frequency, amplitude, and gait, respectively. Deployment experiments demonstrate high accuracy and sensitivity in frequency, amplitude, gait recognition, and fall monitoring, highlighting the advantageous design of EMG and CR-TENS for perceiving subtle motion state changes. The SSSMS demonstrates outstanding capabilities in self-sustainability and real time user embodiment information capture, showcasing its potential as a next-generation interaction device for the metaverse.

Comprehensive analysis of NGS-based expanded carrier screening and follow-up in southern and southwestern China: results from 3024 Chinese individuals.

This study aimed to screen southern and southwestern Chinese individuals using expanded carrier screening (ECS), which explores the carrier status of recessively inherited diseases in southern and southwestern China, evaluates the clinical effectiveness of ECS application, and helps recognize high-risk fetuses that may have genetic disorders early in pregnancy, to provide better reproductive guidance. ECS for 220 diseases based on next-generation sequencing was performed on 3024 southern and southwestern Chinese individuals (1512 couples). Carrier status was analyzed; genes and loci with high frequencies of variants and on high-risk couples (ARCs) were focused to evaluate the clinical utility of our ECS technology and provide them precise fertility guidance. In total, Pathogenic/likely pathogenic(P/LP) variants were found in 1885 individuals, so the carrier frequency was 62.3%, and 23.2% of the individuals were carriers of multiple diseases. furthermore, 2837 variants were detected, and the average number of P/LP variants carried per subject was 0.938. Additionally, 128 ARCs carried P/LP variants of the same gene, and the theoretical incidence rate in their offspring was as high as 2.12%. This study validated the application of our ECS technique for carrier screening in southern China, identifying carrier status and providing accurate carrier frequencies for hundreds of genetic diseases.

Aerodynamic Analysis of Blade Stall Flutter Prediction for Transonic Compressor Using Energy Method

In this study, stall flutter onset prediction in a transonic compressor is carried out using the (uncoupled) energy method with Fourier transform. As the study is conducted computationally using computational fluid dynamics (CFD)-based simulations, the energy method was employed due to its higher computational efficiency by implementing the one-way FSI (Fluid Structure Interaction) model. The energy method is relatively uncommon for determining the aerodynamic damping and flutter prediction, specifically in blade stall conditions for the 3D blade passages. The NASA Rotor 67 was chosen for the validation of the study due to the availability of a wide range of experimental data. A flutter prediction analysis was performed computationally using CFD for the two-blade passages of the rotor in the peak efficiency and stall regions. Prior to this, the modal analysis on the prestressed blade was conducted, considering the centrifugal effects. The modal analysis provided accurate blade frequency and amplitude, which were the inputs of the flutter analysis. The first three modes of blade resonance were studied with a range of nodal diameters within near-peak efficiency and stall regions. The energy method implemented in this study for the flutter analysis was successfully able to predict the aerodynamic damping coefficients of the first three modes for a range of nodal diameters from the periodic-unsteady solution of the defined blade oscillation within the regions of interest (peak efficiency and stall point). The results of the study confirm the rotor blade’s stability within the near-peak region and, most importantly, the prediction of the flutter onset in the stall region. The study concluded that the computationally inexpensive and time-efficient energy method is capable of predicting the stall flutter onset. In the future, further validations of the energy method and investigations related to flow mechanism of stall flutter onset are planned.

Vibration characteristics of a pretwisted multi-blade-shaft system with blade stiffness mismatch

The substructure mode synthesis method is employed to establish a mathematical model in this paper. The main body is represented by shaft, while the branching components are represented by blades. By solving this model, accurate frequency results of the rotating blade-shaft system are obtained at a high computational speed that meets engineering requirements. The resulting mode diagram aligns with that of the finite element model. Utilizing this model, the stiffness detuning of the rotating blade shaft system is investigated through a combination of surrogate modeling and ant colony algorithm, leading to several significant findings. It is observed that an increase in the standard deviation of stiffness detuning amplifies the length of frequency interval while minimally affecting the frequency mean value. Moreover, an increase in average stiffness expands the interval length for system frequencies. Additionally, higher rotational speeds reduce the interval length for blade-dominant vibrations but extend it for shaft-dominant vibrations.

Accurate calibration spectra for precision radial velocities

Astronomical spectrographs require calibration of their dispersion relation, for which external sources like hollow-cathode lamps or absorption-gas cells are useful. Laser frequency combs (LFCs) are often regarded as ideal calibrators because they provide the highest accuracy and dense sampling, but LFCs are facing operational challenges such as generating blue visual light or tunable offset frequencies. As an example of an external source, we aim to provide a precise and accurate frequency solution for the spectrum of molecular iodine absorption by referencing to an LFC that does not cover the same frequency range. We used a Fourier Transform Spectrometer (FTS) to produce a consistent frequency scale for the combined spectrum from an iodine absorption cell at 5200– 6200 Å and an LFC at 8200 Å. We used 17 807 comb lines to determine the FTS frequency offset and compared the calibrated iodine spectrum to a synthetic spectrum computed from a molecular potential model. In a single scan, the frequency offset was determined from the comb spectrum with an uncertainty of ∼1 cms−1. The distribution of comb line frequencies is consistent with no deviation from linearity. The iodine observation matches the model with an offset of smaller than the model uncertainties of ∼1 m s−1, which confirms that the FTS zero point is valid outside the range covered by the LFC, and that the frequencies of the iodine absorption model are accurate. We also report small systematic effects regarding the iodine model’s energy scale. We conclude that Fourier Transform Spectrometry can transfer LFC accuracy into frequency ranges not originally covered by the comb. This allows us to assign accurate frequency scales to the spectra of customized wavelength calibrators. The calibrators can be optimized for individual spectrograph designs regarding resolution and spectral bandwidth, and requirements on their long-term stability are relaxed because FTS monitoring can be performed during operation. This provides flexibility for the design and operation of calibration sources for high-precision Doppler experiments.

Nonlinear free vibrations of a structurally tailored anisotropic pre-twisted thin-walled beam subjected to large deformations

It is essential to understand the nonlinear free vibration behaviour of a thin-walled composite structure as they find their applications in harsher environments prone to large deformations. Further, these structures made of fibrous materials, have directional properties for different fibre orientations resulting in a diversified and a complex nonlinear behaviour. In this regard, present work provides a comprehensive mathematical formulation on nonlinear vibration of pre-twisted thin-walled anisotropic box beam. The mathematical model is derived as coupled (flap-lag-extension-torsion) model considering shear deformation and green's strain tensor for large displacements in order to study the influence of nonlinear couplings on the dynamic behaviour. The derived energy equations are presented depending on degree of nonlinearity. These nonlinear equations those derived are nondimensionalized and solved with in the frame work of energy method using classical Ritz approximation. An iterative method is used to solve the nonlinear equations pertaining displacement terms. This nonlinear behaviour is evaluated for two important types of structural tailoring techniques available for thin-walled composite beams namely Circumferentially Asymmetric Stiffness (CAS) and Circumferentially Uniform Stiffness (CUS). It is found that CAS layup experiences significantly severe nonlinear effects compared to CUS due to the presence of 3rd degree nonlinear coupling terms. The variation of nonlinear frequency ratios over different ply angles showing the influence of nonlinearity on fibres orientation is presented for the first time for the two ply lay ups. The influence of degree of nonlinearity on the accuracy of the nonlinear frequencies is evaluated and presented. Moreover, the impact of nonlinearity on the pre-twisted beam is presented for different pre-twist angles.

An in-phase filter-based flux observation strategy for sensorless control of PMSMs

Due to the complexity of determining the initial rotor flux and detecting errors, conventional rotor flux observation methods are easily affected by direct current (DC) components and harmonics. To address this issue, this paper proposes an in-phase filter (IPF)-based rotor flux observation strategy for sensorless control of permanent magnet synchronous machines (PMSMs). The core components of the IPF consist of a double second-order generalized integrator (DSOGI) and a phase angle compensation transfer function (PACTF). The DSOGI provides a accurate electrical angular frequency, while the PACTF implements a phase correction to the vq′ signals. By employing IPF structure, accurate observations for rotor flux, electronic speed, and rotor position are achieved, which can be effectively used in the sensorless control of PMSMs, eliminating the need for magnitude and phase compensations. Finally, the proposed observation strategy is applied to an experimental bench of a PMSM, and its effectiveness is illustrated by experimental results. From experimental results, it can be concluded that the IPF is significantly better than the LPF, and 5% more accurate than the observer based on cascade second-order generalized integral(CSOGI) overall.

Synchronous consistent integration for superconvergent isogeometric analysis of structural vibrations

A commonly used procedure to improve the frequency accuracy of isogeometric structural vibration analysis is the design of special superconvergent quadrature rules in accordance with the frequency error measure derived from the generic stencil equations. However, it is also numerically observed that such superconvergent quadrature rules may not consistently lead to the expected accuracy. The reason underlying this inconsistency is related to the failure of quadrature rules to meet the condition of variational integration consistency. Meanwhile, by means of the tensor product nature of isogeometric basis functions and quadrature rules, it is theoretically proved that in one- as well as multi-dimensional scenarios, the variational integration consistency of the isogeometric weak formulation necessitates the quadrature rules be exact through 2(p-m)th degree polynomials, where p is the complete degree of multi-dimensional basis functions or the degree of their correspondent one-dimensional basis functions, m is the order of differentiation in Galerkin weak form. A synchronous consistent superconvergent quadrature rule ensuring frequency superconvergence should simultaneously fulfill both the constraint of frequency error measure and the condition of variational integration consistency. Subsequently, the issues associated with certain quadrature rules that violate the variational integration consistency are examined for both second- and fourth-order problems, and the corresponding synchronous consistent quadrature rules are particularly elaborated.

Investigation of signal coupling circuit for NbN-based SIS mixer operated at 650 GHz

Superconductor-insulator-superconductor (SIS) mixers are the most sensitive coherent detectors in the terahertz region and are extensively utilized in astronomical research and atmospheric observation. In order to improve the detection accuracy of frequency, reduce the loss of signal in the transmission path, and reduce noise temperature, it is important to design a signal coupling circuit with high coupling efficiency. In this paper, with the help of a high-frequency structure simulator, a signal coupling circuit was designed based on a waveguide NbN-based SIS mixer at 650 GHz. The return loss and embedding impedance of this SIS mixer were investigated from 600 to 720 GHz. The effects of the SIS mixer chip’s bow-tie probe angle, substrate thickness, and chip slot height were calculated and analyzed. The results show that the return loss is lower than -16 dB in the 600 to 720 GHz band, and the embedding impedance is around 60 Ω, which can provide a good reference for the development of waveguide SIS mixers.

Design, development and multi-scenario application of portable multifunctional test master based on μM-PMU: The case study of Lingang new City Grid, Shanghai

With the large-scale access of new energy generation and electric vehicle charging piles to the grids, power generation and loads are characterized by random fluctuations and intermittency, which affect the stable operation of the distribution network. μM-PMU is capable of realizing the dynamic process monitoring of the grids. In order to solve the function and performance testing problems of multiple application scenarios of μM-PMU, this thesis develops a portable master station based on synchronous phasor measurement system to realize zero drift, voltage amplitude measurement accuracy, voltage phase angle accuracy, current amplitude measurement accuracy, current phase angle measurement accuracy, frequency measurement accuracy, voltage amplitude change with frequency accuracy, and voltage phase angle change with frequency accuracy, Accuracy of current amplitude with frequency change, accuracy of current phase angle with frequency change, active power accuracy, reactive power accuracy, amplitude step response, phase angle step response, frequency step response, a total of 15 test items. It can automatically calculate test results and generate test reports according to different equipment models, reducing the mistakes and calculation errors that may be caused by manually recording test data and improving the accuracy of test results and calculation precision.

Study on low-rank coal flotation collector screening and performance based on molecular polarity index.

Extensive studies using a trial-and-error approach have been conducted on low-rank coal flotation collectors. However, screening efficient collectors remains a considerable challenge due to the lack of suitable screening principles. It has proven that polar compounds such as carboxylic acids and esters are effective collectors for low-rank coal flotation. In this work, the effects of carboxylic acid, alcohol, and methyl ester on the floatability of low-rank coal were compared, the flotation performance of the polar collector was evaluated with theoretical calculations, a suitable evaluation parameter was determined and a screening principle based on this parameter was determined. The results show that the enhancement effects of polar collectors on low-rank coal floatability follow the order of methyl decanoate > methyl laurate > methyl octanoate > sec-octanol > methyl oleate (or methyl oleate > sec-octanol) > n-octanoic acid. Compared with the molecular polarity index, the hydrophobicity indices log P and dipole moment cannot be used to accurately evaluate different types of collectors and the same type of collectors, respectively. At room temperature, liquid polar compounds with molecular polarity indices in the range of 6.0 ~ 8.0kcal/mol effectively enhance the floatability of low-rank coal. The molecular polarity index of the collector is used for the first time to screen effective collectors of low-rank coal in this work. This parameter is anticipated to be highly important for the development and research of low-rank coal and other mineral collectors. To obtain reasonable and accurate molecular structure, geometry optimization and frequency calculations of the studied collectors were conducted via the Gaussian 09 software package based on density functional theory at the B3LYP/6-311 + G (d, p) level. The integral equation formalism for the polarizable continuum model (IEF-PCM) was utilized with water as the solvent (dielectric constant = 78.36, T = 298K) for all the calculations. Then, the atomic charge distributions (MPA and NPA) and electrostatic potential maps, the dipole moment and molecular polarity index, and the log P and water solubilities of studied collectors were shown or calculated by Gauss View 5.0, Mutiwfn program and website ( https://www.molsoft.com/mprop/mprop.cgi ), respectively.

Cycle-frequency content EEG analysis improves the assessment of respiratory-related cortical activity

Objective. Time-frequency (T-F) analysis of electroencephalographic (EEG) is a common technique to characterise spectral changes in neural activity. This study explores the limitations of utilizing conventional spectral techniques in examining cyclic event-related cortical activities due to challenges, including high inter-trial variability.Approach. Introducing the cycle-frequency (C-F) analysis, we aim to enhance the evaluation of cycle-locked respiratory events. For synthetic EEG that mimicked cycle-locked pre-motor activity, C-F had more accurate frequency and time localization compared to conventional T-F analysis, even for a significantly reduced number of trials and a variability of breathing rhythm.Main results. Preliminary validations using real EEG data during both unloaded breathing and loaded breathing (that evokes pre-motor activity) suggest potential benefits of using the C-F method, particularly in normalizing time units to cyclic activity phases and refining baseline placement and duration.Significance. The proposed approach could provide new insights for the study of rhythmic neural activities, complementing T-F analysis.