Low-frequency Terms Research Articles

Gender Differences in Autonomic Control of the Cardiovascular System.

The autonomic nervous system (ANS) is a key regulator of the cardiovascular system. The two arms of the ANS, sympathetic and parasympathetic (vagal) have co-regulatory effects on cardiac homeostasis. ANS modulation and dysfunction are also believed to affect various cardiac disease states. Over the past decade, there has been increasing evidence suggesting gender differences in ANS activity. In multiple previous studies, ANS activity was primarily assessed using heart rate variability, muscle sympathetic nerve activity, coronary blood flow velocity, and plasma biomarkers. Heart rate variability is a non-invasive measure, which can be analyzed in terms of low frequency and high frequency oscillations, which indicate the sympathetic and parasympathetic tone, respectively. These measures have been studied between women and men in states of rest and stress, and in cardiac disease. Studies support the concept of a significant gender difference in ANS activity. Further studies are indicated to elucidate specific differences and mechanisms, which could guide targeted therapy of various cardiovascular disease states.

Transient Electromagnetic Scattering by a Radially Uniaxial Dielectric Sphere: The Generalized Debye and Mie Series Solutions

In this paper, a theoretical study is carried out to determine the scattering of a transient electromagnetics wave by a radially uniaxial dielectric sphere. This is achieved by inverse Laplace transformation of the frequency-domain scattering solution. To improve understanding of the scattering mechanism from a uniaxial dielectric sphere, two different frequency-domain solutions are employed. In the first approach, the impulse and step responses of a uniaxial dielectric sphere are evaluated by the Mie series solution. Following the high-frequency (HF) scattering solution of a large uniaxial sphere, the Mie series summation is split into high-frequency (HF) and low-frequency terms where the HF term is replaced by its asymptotic expression allowing a significant reduction in computation time of the numerical Bromwich integral. In the second approach, the generalized Debye series solution is introduced, and the generalized Mie series coefficients are replaced by their equivalent Debye series formulations. The results are then applied to evaluate the transient response of each individual Debye term allowing the identification of impulse returns in the transient response of a uniaxial sphere. The effect of variation in permittivity on the arrival time as well as amplitudes of each impulse return is studied, and the results are compared with those computed using the Mie series solution. The numerical results obtained from both methods are in complete agreement.

External mechanical disturbances compensation with a passive differential measurement principle in nanoforce sensing using diamagnetic levitation

Nanoforce sensors using passive magnetic springs associated to a macroscopic seismic mass are known to be a possible alternative to force sensors based on elastic microstructures like Atomic Force Microscopes if the nanoforces that have to be measured are characterized by a bandwidth limited to a few Hertz. The estimation of the unknown force applied to the seismic mass is based on the deconvolution of the noisy measurement of the mass displacement which has an under-damped dynamic. Despite their high performances in terms of linearity, resolution and measurement range, such force sensors are extremely sensitive to low frequency environmental mechanical disturbances, like the angular variations of the anti-vibration table supporting the device or the residual seismic vibrations that are not filtered by the table. They are also sensitive to the temperature evolution of the ambient air. The evaluation, modeling and compensation of such environmental disturbances have to be specifically studied in the context of magnetic springs associated to a macroscopic seismic mass because of their important negative effects in terms of low frequency drifts and oscillatory disturbances. This article presents an estimation and a passive compensation strategy of the low frequency and non-stationary mechanical disturbances that is based on a differential principle. This approach is applied to a nanoforce sensor based on diamagnetic levitation developed in the last decade. It does not necessitate to add new types of sensors in the measurement chain such as very high resolution and low frequency inclinometers or accelerometers in order to estimate the mechanical disturbances. In term of performances, the force estimation error remains in the nanonewton level over periods of time of several minutes when external temperature remains constant.

Chinese Stock Index Futures Price Fluctuation Analysis and Prediction Based on Complementary Ensemble Empirical Mode Decomposition

Since the CSI 300 index futures officially began trading on April 15, 2010, analysis and predictions of the price fluctuations of Chinese stock index futures prices have become a popular area of active research. In this paper, the Complementary Ensemble Empirical Mode Decomposition (CEEMD) method is used to decompose the sequences of Chinese stock index futures prices into residue terms, low-frequency terms, and high-frequency terms to reveal the fluctuation characteristics over different time scales of the sequences. Then, the CEEMD method is combined with the Particle Swarm Optimization (PSO) algorithm-based Support Vector Machine (SVM) model to forecast Chinese stock index futures prices. The empirical results show that the residue term determines the long-term trend of stock index futures prices. The low-frequency term, which represents medium-term price fluctuations, is mainly affected by policy regulations under the analysis of the Iterated Cumulative Sums of Squares (ICSS) algorithm, whereas short-term market disequilibrium, which is represented by the high-frequency term, plays an important local role in stock index futures price fluctuations. In addition, in forecasting the daily or even intraday price data of Chinese stock index futures, the combination prediction model is superior to the single SVM model, which implies that the accuracy of predicting Chinese stock index futures prices will be improved by considering fluctuation characteristics in different time scales.

Spectral Decomposition of Soil Electrical and Dielectric Losses and Prediction of In Situ GPR Performance

The performance of high-frequency ground-penetrating radar (GPR) for high-resolution imaging of the near surface can essentially be controlled by the soil electromagnetic (EM) properties. One of these properties influencing sensing depth and image resolution of GPR is the intrinsic attenuation. We investigated the frequency-dependent electrical and dielectric properties of a broad range of soil samples. In order to derive the effective complex dielectric permittivity between 1 MHz and 10 GHz, we applied the coaxial transmission line (CTL) technique. A generalized dielectric response model, consisting of one Debye and one Cole-Cole type relaxation and a constant low-frequency conductivity term was used to analyze the dielectric relaxation behavior. Splitting the spectra into individual loss processes shows that dielectric relaxation mechanisms play a crucial role in most natural soils. Especially for high-frequency applications, attenuation cannot be described by a dielectric constant and dc-conductivity alone. Therefore, a simple conductivity-attenuation relation without dielectric losses can highly overestimate the GPR performance. As an alternative to the CTL technique in the lab, we suggest to use time-domain reflectometry (TDR) for the in Situ assessment of high-frequency electrical properties and deduced prediction of GPR performance.

Limiting factors for planar solid oxide fuel cells under different trace compound concentrations

The present work investigates the performance of anode supported solid oxide fuel cells under the influence of different trace compounds. EIS (Electrochemical impedance spectroscopy) has been used to deconvolute the impedance spectra of an SOFC (Solid Oxide Fuel Cell) in order to identify the main losses. The impact of single and double contaminants on the SOFC performance has also been investigated. Typical biogas trace contaminants, obtained after a clean-up stage, such as sulfur, chlorine, aromatic compounds and siloxanes, have been taken into consideration. The results show how the ohmic contribution is almost independent of the H2S concentration. H2S acts mainly on the polarization losses and especially on the mass transport resistance. The impact of HCl on the SOFC performance is mainly connected to the charge transfer process. D4, as the model compound for siloxanes, already acts on SOFC performance at ppb(v) levels. The polarization losses have been influenced the most, and the largest increase has been recorded for the low frequency term, Rlow, related to the mass transport resistance for naphthalene and toluene. H2S, introduced with other contaminants, causes the instantaneous deterioration of the SOFC performance and the more the types of contaminants co-fed to the SOFC, the larger the initial anode degradation.

TermFinder

The TermFinder project is a new kind of collaboration between academic specialists/teachers and applied linguists/terminographers in creating specialized online termbanks for pedagogical purposes. Although there are technical glossaries on the internet, their ad hoc definitions do not target the needs of novices in the discipline, or those with limited English. Specialized terminology remains a substantial barrier for tertiary students grappling with the foundation concepts, overshadowed by the recent emphasis on generic skills. TermFinder termbanks are customized for designated courses, and informed by a computerized corpus of lecture materials and reading texts used by the lecturer. The terminographer uses the corpus to identify the key terms by frequency and to source natural examples of their usage: their grammar as well as their technical sense(s) and connections with other terms in the discipline. The methodology is new for terminography (ie the description of terminology), though well established in general lexicography. This corpus-informed terminography is also pedagogically-informed, in that the selection and definitions of terms are reviewed in consultation with disciplinary teaching staff. It ensures that (a) necessary lower frequency terms are included; and (b) the definitions drafted by the terminographer are conceptually adequate for the level of student. Pilot testing of the statistics termbank confirms its pedagogical value. TermFinder pages contain verbal, audio and graphic elements to develop students’ understanding of disciplinary concepts through multiple cognitive channels.

Residual analysis using Fourier series transform in Fuzzy time series model

In this paper, we propose a new residual analysis method using Fourier series transform into fuzzy time series model for improving the forecast- ing performance. This hybrid model takes advantage of the high predictable power of fuzzy time series model and Fourier series transform to t the esti- mated residuals into frequency spectra, select the low-frequency terms, lter out high-frequency terms, and then have well forecasting performance. Two numerical examples are given to show that our proposed model can be applied with the best forecasting performance than the other models.

Everything Hertz: methodological issues in short-term frequency-domain HRV.

Frequency analysis of the electrocardiographic RR interval is a common method of quantifying autonomic outflow by measuring the beat-to-beat modulation of the heart (heart rate variability; HRV). This review identifies a series of problems with the methods of doing so—the interpretation of low-frequency spectral power, the multiple use of equivalent normalized low frequency (LFnu), high frequency (HFnu) and ratio (LF/HF) terms, and the lack of control over extraneous variables, and reviews research in the calendar year 2012 to determine their prevalence and severity. Results support the mathematical equivalency of ratio units across studies, a reliance on those variables to explain autonomic outflow, and insufficient control of critical experimental variables. Research measurement of HRV has a substantial need for general methodological improvement.

Self-Tuning Shape Control of Massively Actuated Adaptive Mirrors

This paper focuses on the design of the control system of massively actuated deformable mirrors for astronomical adaptive optics applications. The proposed solution is based on a high-frequency completely decentralized feedback combined with a hybrid low-frequency term, which is the sum of feedforward-feedback contributions. An appropriate in the field system identification procedure and an automatic gain optimization eventually lead to a complete self-tuning controller. The improvements of system performances are evaluated through high-fidelity simulations.

Improved Statistical Power with a Sparse Shape Model in Detecting an Aging Effect in the Hippocampus and Amygdala.

The sparse regression framework has been widely used in medical image processing and analysis. However, it has been rarely used in anatomical studies. We present a sparse shape modeling framework using the Laplace-Beltrami (LB) eigenfunctions of the underlying shape and show its improvement of statistical power. Traditionally, the LB-eigenfunctions are used as a basis for intrinsically representing surface shapes as a form of Fourier descriptors. To reduce high frequency noise, only the first few terms are used in the expansion and higher frequency terms are simply thrown away. However, some lower frequency terms may not necessarily contribute significantly in reconstructing the surfaces. Motivated by this idea, we present a LB-based method to filter out only the significant eigenfunctions by imposing a sparse penalty. For dense anatomical data such as deformation fields on a surface mesh, the sparse regression behaves like a smoothing process, which will reduce the error of incorrectly detecting false negatives. Hence the statistical power improves. The sparse shape model is then applied in investigating the influence of age on amygdala and hippocampus shapes in the normal population. The advantage of the LB sparse framework is demonstrated by showing the increased statistical power.

T-Test feature selection approach based on term frequency for text categorization

Feature selection techniques play an important role in text categorization (TC), especially for the large-scale TC tasks. Many new and improved methods have been proposed, and most of them are based on document frequency, such as the famous Chi-square statistic and information gain etc. These methods based on document frequency, however, have two shortcomings: (1) they are not reliable for low-frequency terms, that is, low-frequency terms will be filtered because of their smaller weights; and (2) they only count whether one term occurs within a document and ignore term frequency. Actually, high-frequency term (except stop words) occurred in few documents is often regards as a discriminators in the real-life corpus.Aimed at solving the above drawbacks, the paper focuses on how to construct a feature selection function based on term frequency, and proposes a new approach using student t-test. The t-test function is used to measure the diversity of the distributions of a term frequency between the specific category and the entire corpus. Extensive comparative experiments on two text corpora using three classifiers show that the proposed approach is comparable to the state-of-the-art feature selection methods in terms of macro-F1 and micro-F1. Especially on micro-F1, our method achieves slightly better performance on Reuters with kNN and SVMs classifiers, compared to χ2, and IG.

Multipath error mitigation based on wavelet transform in L1 GPS receivers for kinematic applications

GPS positioning issue has been experienced a surge of interest for multipath mitigation in the past few years. Multipath disturbance is a challenging error in high precision GPS positioning particularly in kinematic mode where the moving receiver undergoes different multipath circumstances. Diverse hardware and software approaches have been implemented to reduce this error in both static and kinematic modes. We have proposed an algorithm to alleviate C/A code multipath in kinematic mode. Our proposed scheme falls into software group where wavelet transform (WT) has been used as the main basis. Of course, we have used stationary wavelet transform (SWT) as the key idea of our proposed method that makes it possible to investigate all frequency sub-bands. Consequently, it would be possible to extract multipath disturbance since it is considered to be a low frequency term. After applying SWT to double difference (DD) residuals, the multipath error is extracted and used to correct DD observations. In this paper, we have designed three experiments to study our proposed method efficiency under different conditions in comparison with existing algorithms.

A new method to mitigate multipath error in single-frequency GPS receiver with wavelet transform

One of the major errors in high-precision GPS positioning is multipath. Multipath effect modeling and reduction have been a challenging issue in high-accuracy GPS positioning applications due to its special properties. Different methods have been employed to mitigate this error including hardware and software approaches. We reduce C/A code multipath error by adopting an efficient software method which uses wavelet transform as a basic data processing trend. The key idea of the proposed method is using stationary wavelet transform (SWT) in GPS signal data processing. Since we have used SWT, there is complete access to high-frequency and low-frequency terms in both time and frequency domains, and we can apply appropriated procedures to mitigate this error. The multipath error mostly is a low-frequency term. In our proposed method, the double difference (DD) residuals are applied to the SWT to identify the multipath disturbance. The extracted multipath is then used to correct DD observations. Our experiments include three data sets to investigate the proposed method and compare it with existing algorithms. We used simulations for two of these data sets. The results indicate the efficiency of the proposed method over existing algorithms.

Term extraction from sparse, ungrammatical domain-specific documents

Existing term extraction systems have predominantly targeted large and well-written document collections, which provide reliable statistical and linguistic evidence to support term extraction. In this article, we address the term extraction challenges posed by sparse, ungrammatical texts with domain-specific contents, such as customer complaint emails and engineers’ repair notes. To this aim, we present ExtTerm, a novel term extraction system. Specifically, as our core innovations, we accurately detect rare (low frequency) terms, overcoming the issue of data sparsity. These rare terms may denote critical events, but they are often missed by extant TE systems. ExtTerm also precisely detects multi-word terms of arbitrarily lengths, e.g. with more than 2 words. This is achieved by exploiting fundamental theoretical notions underlying term formation, and by developing a technique to compute the collocation strength between any number of words. Thus, we address the limitation of existing TE systems, which are primarily designed to identify terms with 2 words. Furthermore, we show that open-domain (general) resources, such as Wikipedia, can be exploited to support domain-specific term extraction. Thus, they can be used to compensate for the unavailability of domain-specific knowledge resources. Our experimental evaluations reveal that ExtTerm outperforms a state-of-the-art baseline in extracting terms from a domain-specific, sparse and ungrammatical real-life text collection.

Feasibility of digital image colorimetry—Application for water calcium hardness determination

Interpretation and relevance of basic RGB colors in Digital Image-Based Colorimetry have been treated in this paper. The studies were carried out using the chromogenic model formed by the reaction between Ca(II) ions and glyoxal bis(2-hydroxyanil). It produced orange–red colored solutions in alkaline media. Individual basic color data (RGB) and also the total intensity of colors, Itot, were the original variables treated by Factorial Analysis. Te evaluation evidenced that the highest variance of the system and the highest analytical sensitivity were associated to the G color. However, after the study by Fourier transform the basic R color was recognized as an important feature in the information. It was manifested as an intrinsic characteristic that appeared differentiated in terms of low frequency in Fourier transform. The Principal Components Analysis study showed that the variance of the system could be mostly retained in the first principal component, but was dependent on all basic colors.The colored complex was also applied and validated as a Digital Image Colorimetric method for the determination of Ca(II) ions. RGB intensities were linearly correlated with Ca(II) in the range 0.2–2.0mgL−1. In the best conditions, using green color, a simple and reliable method for Ca determination could be developed. Its detection limit was established (criterion 3s) as 0.07mgL−1. And the reproducibility was lower than 6%, for 1.0mgL−1 Ca. Other chromatic parameters were evaluated as dependent calibration variables. Their representativeness, variance and sensitivity were discussed in order to select the best analytical variable.The potentiality of the procedure as a field and ready-to-use method, susceptible to be applied ‘in situ’ with a minimum of experimental needs, was probed. Applications of the analysis of Ca in different real water samples were carried out. Water of the city net, mineral bottled, and natural-river were analyzed and results were compared and evaluated statistically. The validity was assessed by the alternative techniques of flame atomic absorption spectroscopy and titrimetry. Differences were appreciated but they were consistent with the applied methods.

The relationship between physical activity and heart rate variability in orthotopic heart transplant recipients

To investigate the relationship between physical activity and heart rate variability in orthotopic heart transplant recipients, to compare the difference in heart rate variability between patients one year after orthotopic heart transplant and healthy adults matched to the heart transplant recipients in terms of age, gender and physical activity levels. Although physical activity affects the heart rate variability in patients with heart disease, there is a paucity of literature discussing the correlation between physical activity and heart rate variability among heart transplant recipients. This was a descriptive and cross-sectional study. A total of 120 eligible subjects were divided into the orthotopic heart transplant recipient group (n = 60) and the healthy adult group (n = 60). The Seven-day Physical Activity Recall questionnaire was used to record the subjects' amount of physical activity per week. Heart rate variety parameters were determined by separate frequency domain components. Results indicated heart transplant recipients' heart rate variety was significantly lower than that of healthy adults in terms of mean, sdr, total power (ms(2)), low frequency (ms(2)), low frequency (nu), high frequency (ms(2)) and low frequency/high frequency. Heart transplant recipients' heart rate variety including total power (ms(2)), low frequency (ms(2)) and high frequency (ms(2)) was 18·2, 2 and 7·2% of healthy controls, respectively; the amount of absolutely and relatively moderate physical activity was positively related to high frequency (ms(2)) and high frequency (nu), but was negatively related to low frequency/high frequency. High frequency (nu) increases while the total amount of weekly physical activity increases. Results confirmed that the more the moderate physical activity performed, the better the patient's heart rate variability. We suggest that clinical care providers have to encourage heart transplant recipients to engage in moderate physical activity.

Parameter design of a parallax barrier based on the color moiré patterns in autostereoscopic display

We propose a parameter design of the parallax barrier (PB) based on the color moiré patterns in autostereoscopic displays. First, the display device and the PB are approximated as two corresponding binary gratings. In order to obtain different corresponding predominant Fourier low-frequency terms, the superposition of the equivalent grating for the display device and the special radial grating is analyzed, referring to the indicial equation method and Fourier theory. Moreover, the two transition regions are considered as the regions where moiré patterns vary gently. Finally, the appropriate parameter of the PB can be obtained. The validity of the proposed design is verified in the experiment.

Dielectric relaxation in hafnium oxide: A study of transient currents and admittance spectroscopy in HfO2 metal-insulator-metal devices

Dielectric relaxation is studied in 10 nm HfO2 thin films which are deposited by atomic layer deposition on TiN and Pt electrodes. Transient currents are recorded from 10−3 s to 10 s, as a function of bias (0.1 V to 1 V) and temperature (20 °C to 180 °C). A Curie-von Schweidler law is observed, I = Q0/tα. The power law exponent α is constant with bias and strongly depends on the temperature (varying in the 0.65–1.05 range, with a peak at 75 °C). The amplitude Q0 is described by a relation of the form Q0 = C0Vβ, where the factor C0 is weakly activated and the exponent β varies with temperature (in the 0.9–1.5 range as T varies). Transient currents are discussed along with tunneling based models from the literature. To complement transient current experiments, admittance spectroscopy (conductance G and capacitance C) is performed at low frequencies, from 0.01 Hz to 10 kHz. The dispersion law of the conductance is of the form G ∼ ωs. The capacitance is the sum of two terms, a non-dispersive term (C∞) and a low-frequency dispersive term, CLF ∼ ω−n. The critical exponents s and n verify s ≈ α and n ≈ 1−α. At room temperature, the dielectric constant is expressed as ɛ′ = Δɛ′ f−n + ɛ′∞, where ɛ′∞ = 11.1, n ≈ 0.2/0.3 (Pt/TiN), and Δɛ′ ≈ 1.5/0.7 (Pt/TiN).

The influence of galactic aberration on precession parameters determined from VLBI observations

The influence of proper motions of sources due to Galactic aberration on precession models based on VLBI data is determined. Comparisons of the linear trends in the coordinates of the celestial pole obtained with and without taking into account Galactic aberration indicate that this effect can reach 20 µ as per century, which is important for modern precession models. It is also shown that correcting for Galactic aberration influences the derived parameters of low-frequency nutation terms. It is therefore necessary to correct for Galactic aberration in the reduction of modern astrometric observations.