Main Subbands Research Articles

Using machine learning methods and EEG to discriminate aircraft pilot cognitive workload during flight

Pilots of aircraft face varying degrees of cognitive workload even during normal flight operations. Periods of low cognitive workload may be followed by periods of high cognitive workload and vice versa. During such changing demands, there exists potential for increased error on behalf of the pilots due to periods of boredom or excessive cognitive task demand. To further understand cognitive workload in aviation, the present study involved collection of electroencephalogram (EEG) data from ten (10) collegiate aviation students in a live-flight environment in a single-engine aircraft. Each pilot possessed a Federal Aviation Administration (FAA) commercial pilot certificate and either FAA class I or class II medical certificate. Each pilot flew a standardized flight profile representing an average instrument flight training sequence. For data analysis, we used four main sub-bands of the recorded EEG signals: delta, theta, alpha, and beta. Power spectral density (PSD) and log energy entropy of each sub-band across 20 electrodes were computed and subjected to two feature selection algorithms (recursive feature elimination (RFE) and lasso cross-validation (LassoCV), and a stacking ensemble machine learning algorithm composed of support vector machine, random forest, and logistic regression. Also, hyperparameter optimization and tenfold cross-validation were used to improve the model performance, reliability, and generalization. The feature selection step resulted in 15 features that can be considered an indicator of pilots' cognitive workload states. Then these features were applied to the stacking ensemble algorithm, and the highest results were achieved using the selected features by the RFE algorithm with an accuracy of 91.67% (± 0.11), a precision of 93.89% (± 0.09), recall of 91.67% (± 0.11), F-score of 91.22% (± 0.12), and the mean ROC-AUC of 0.93 (± 0.06). The achieved results indicated that the combination of PSD and log energy entropy, along with well-designed machine learning algorithms, suggest the potential for the use of EEG to discriminate periods of the low, medium, and high workload to augment aircraft system design, including flight automation features to improve aviation safety.

First detection and analysis of an electronic spectrum of vanadium hydride: The D5Π-X5Δ (0,0) band.

The D5Π-X5Δ (0,0) band of vanadium hydride at 654nm has been recorded by laser excitation spectroscopy and represents the first analyzed spectrum of VH in the gas phase. The molecules were generated using a hollow cathode discharge source, with laser-induced fluorescence detected via the D5Π-A5Π (0,0) transition. All five main (ΔΩ = ΔΛ) subbands were observed as well as several satellite ones, which together create a rather complex and overlapped spectrum covering the region 15 180-15 500 cm-1. The D5Π state displays the effects of three strong local perturbations, which are likely caused by interactions with high vibrational levels of the B5Σ- and c3Σ- states, identified in a previous multiconfigurational self-consistent field study by Koseki et al. [J. Phys. Chem. A 108, 4707 (2004)]. Molecular constants describing the X5Δ, A5Π, and D5Π states were determined in three separate least-squares fits using effective Hamiltonians written in a Hund's case (a) basis. The fine structure of the ground state is found to be consistent with its assignment as a σπ2δ, 5Δ electronic state. The fitted values of its first-order spin-orbit and rotational constants in the ground state are A=36.537815cm-1 and B = 5.7579(13)cm-1, the latter of which yields a bond length of R0=1.72122 Å. This experimental value is in good agreement with previous computational studies of the molecule and fits well within the overall trend of decreasing bond length across the series of 3d transition metal monohydrides.

Improved double TQWT sparse representation using the MQGA algorithm and new norm for aviation bearing compound fault detection

The double tunable wavelet transform sparse representation realizes signal decomposition by constructing a basis function dictionary that match various characteristic waveforms of compound fault signal. However, the quality factor describing the resonance characteristic of the wavelet basis function can only be determined from practical experience, which is often subjective, and can significantly affect the matching degree between the wavelet basis function and the fault signal. To solve this problem, a new sparse representation method and a new norm are proposed. First, the multi-population quantum genetic algorithm (MQGA) is used to optimize the selected quality factor parameter combinations. The cross-correlated kurtosis of the periodic impact signal is established as the new norm and used to evaluate the optimized parameters. Then, according to the principle of energy entropy dominance, main sub-bands of the low resonance component are reconstructed to reduce noise interference and enhance the impact characteristics of the signal. Finally, Hilbert envelope demodulation analysis is performed on the reconstructed signal to obtain the instantaneous fault characteristic frequency. The proposed method was applied to diagnose compound faults of aviation bearings. The results show that the proposed method can effectively separate and extract the compound fault signal of a bearing in an aero-engine testbed. Furthermore, the compound fault of a damaged bearing in a helicopter transmission system was successfully decoupled, which verified the effectiveness and practicability of the proposed method.

Anomalous electron polarizability of HgTe quantum wells

The polarizability of electrons in CdTe/Cd x Hg 1− x Te/CdTe quantum wells is studied. It is shown that polarizability in the quantum well without cadmium is negative, i.e., the displacement of an electron and hole in the main subbands of spatial quantization in an electric field applied perpendicularly to the quantum well plane is opposite to the force acting on it. It is predicted that the negative polarizability can reduce the dielectric constant of quantum wells by up to 15% and manifest itself as the blue shift of the interband light absorption edge in an electric field.

Raman spectroscopy fingerprint of stainless steel-MWCNTs nanocomposite processed by ball-milling

Stainless steel 304L alloy powder and multiwalled carbon nanotubes were mixed by ball-milling under ambient atmosphere and in a broad range of milling times, which spans from 0 to 120 min. Here, we provided spectroscopic signatures for several distinct composites produced, to show that the Raman spectra present interesting splittings of the D-band feature into two main sub-bands, D-left and D-right, together with several other secondary features. The G-band feature also presents multiple splittings that are related to the outer and inner diameter distributions intrinsic to the multiwalled carbon nanotube samples. A discussion about the second order 2D-band (also known as G′-band) is also provided. The results reveal that the multiple spectral features observed in the D-band are related to an increased chemical functionalization. A lower content of amorphous carbon at 60 and 90 min of milling time is verified and the G-band frequencies associated to the tubes in the outer diameters distribution is upshifted, which suggests that doping induced by strain is taking place in the milled samples. The results indicate that Raman spectroscopy can be a powerful tool for a fast and non-destructive characterization of carbon nanocomposites used in powder metallurgy manufacturing processes.

Feature Extraction for Rolling Element Bearing Faults Using Resonance Sparse Signal Decomposition

Rolling element bearings are widely used in a variety of rotating machineries. If the rolling bearing elements are damaged, a cyclical impact transient signal and the vibration signal modulation phenomenon appears when the fault surface contacts other components of the rolling element bearing. To demodulate the cyclical impact signal and extract the bearing fault information, this paper proposes a new method based on resonance-based sparse signal decomposition (RSSD). First, the bearing vibration signal is decomposed into three components via RSSD. The high-resonance component contains a sustained oscillation cycle signal, the low-resonance component contains the impact transient signal, and the final component is the residual. The sub-bands near the natural bands are extracted for demodulation into two components. Two main sub-bands are obtained by summing these sub-bands. Next, these two main sub-bands are summed to obtain the original signal’s main sub-band. Finally, the auto power spectrum is extracted using envelope signal autocorrelation processing, and it reflects the degree and location of the fault in the rolling bearing. To verify its effectiveness in extracting fault information, the proposed method is applied to two practical application examples with an inner race fault and an outer race fault in a rolling bearing, respectively. Compared with envelope analysis and wavelet analysis, the results indicate that the spectra obtained with this method exhibit less burrs and a higher signal-noise ratio, and outperforms the other spectra in terms of revealing the amplitude modulation frequency of the fault impact response.

Investigation of the modulation between EEG alpha waves and slow/fast delta waves in children in different depths of Desflurane anesthesia

Objectives Investigation of the amplitude modulation of alpha-band EEG oscillations (i.e., grouping of alpha-band activities) by delta-band EEG activities in various depths of anesthesia (DOA). Methods This modulation, which is a sort of phase dependent amplitude modulation, is studied in 10 children in various depths of Desflurane anesthesia. Two parameters are defined to quantify the modulation: strength of modulation (SOM) and phase of modulation (POM). SOM indicates to what extent delta and alpha activities are related to each other, and POM is the delta phase in which the alpha amplitude is maximal. These parameters are analyzed in different DOA for various formations of delta sub-bands. Results The ability of POM and SOM were explored to characterize mechanisms contributing to delta activities and their correlation with the level of anesthesia. These parameters are influenced by DOA and frequency intervals of delta sub-bands. SOM takes higher values around certain frequency ranges of delta band. According to this, delta band comprises three main sub-bands in various unconsciousness levels. Although boundaries of these sub-bands change with DOA, they are almost in [0.1–0.5] Hz (very slow delta), [0.7–1.7] Hz (slow delta) and [2–4] Hz (fast delta) intervals. POMs relating to slow and fast delta bands increase with consciousness level. This is an indication that delta waves differently modulate alpha EEG activities (in terms of phase lag) in different DOA. In deep anesthesia, POM relating to fast delta correlates with DOA better than POM relating to slow delta does. In light anesthesia this correlation is inversed. Investigation regarding to different formations of delta sub-bands shows that POM relating to [1.8–4] Hz is a proper choice for distinguishing deep, moderate and light anesthesia. Conclusion SOM allows separating mechanisms underlying delta band activities, and POM can be seen as a complementary neurophysiologic-based parameter for quantifying DOA.

Acoustic wave propagating in one-dimensional Fibonacci binary composite systems

The acoustic or elastic wave transmission properties and the frequency spectra of Fibonacci binary composite systems consisting of water and mercury with different filling fractions are studied by the transfer matrix method. The numerical result shows that the transmitting band and the frequency spectra regularly split into several main sub-bands as the Fibonacci generation number increases. The splitting rule is influenced by the filling fraction of the studied systems. The corresponding relationship between the transmission coefficient and the eigenfrequency is also presented.

The A2E–X2A1 System of CaOCH3

We have recorded laser excitation spectra of the CaOCH3 free radical in a laser ablation molecular beam apparatus, at a spectral resolution of about 0.010 cm−1 and a rotational temperature estimated at 15 K. The two spin–orbit components of the A2E–X2A1 000 origin band between 625 and 630 nm have been analyzed. Five main subbands were revealed, with ΔK=+1 and K″=0,±1,±2. There was clear evidence of lambda-doubling in the A2E1/2–X2A1 000 (F′1) K′=+1←K″=0 component. A nonlinear least-squares fitting program based on the model developed by Endo et al. [Y. Endo, S. Saito, and E. Hirota, J. Chem. Phys.81, 122–135 (1984)] fit the experimental data (514 A–X lines, N″≤37) with a root mean square deviation of 0.003 cm−1, using known molecular constants of the ground state. The main vibronic (T0=15 925.1232(5) cm−1), spin–orbit (aζed=66.974 48(51) cm−1), Coriolis (Aζt=5.437 30(24)) cm−1, rotational (A=5.439 97(24) cm−1, B=0.117 884(2) cm−1), and fine structure constants (ε1=−8.208(14)×10−3 cm−1, h1=1.50(12)×10−4 cm−1, εaa=3.58(89)×10−3 cm−1, εbc=3.20(76)×10−3 cm−1) for the excited state have been obtained.

Spectroscopy and predissociation of the 3A 2 electronic state of ozone 16O 3 and 18O 3 by high resolution Fourier transform spectrometry

A high resolution Fourier transform spectrometry analysis of the rotational structure of the 2 0 1 absorption bands of the 3A 2← X ̃ 1 A 1 Wulf transition for the isotopomers 16O 3 and 18O 3 of the ozone molecule is presented. These bands are very intense compared to the 0 0 0 bands but the predissociation is so strong that the main sub-bands appear as continuous contours. Isolated lines and band contour methods are used together to analyse these two rovibrational bands. The lines corresponding to the F 2 component are generally the most intense and isolated. Our data sets for the (0 1 0) level of the 3A 2 state are limited to about 102 weakly or unperturbed rotational lines for the 2 0 1 of 16O 3 in the range 9620–10 140 cm −1 and 123 weakly or unperturbed rotational lines for the same band of 18O 3. Using for each of them the well-defined ground state parameters, we obtained a standard deviation of about 0.035 cm −1 in the fit to the lines for 16O 3 and 0.027 cm −1 in the case of 18O 3. The rotational constants A, B and C, the three rotational distortion terms Δ K , Δ JK and Δ J , the spin–rotation constants a 0, a and b have been successfully calculated for 16O 3 and 18O 3 while the spin–spin constants were fixed to their respective values obtained for the origin bands. As is the case for the 0 0 0 band, we have a partial agreement with the isotopic laws for the rotational constants. The geometrical parameters of the (0 1 0) level of 3A 2 state for the two isotopomers are close, r=1.357 Å, θ=100.7° for 18O 3 and r=1.352 Å and θ=100.0° for 16O 3. The origin of the 2 0 1 band of 18O 3 is red shifted by 7.06(4) cm −1 with respect to 16O 3 2 0 1 band and the two bending mode quanta are, respectively, 528.99(9) and 501.34(7) cm −1. A preliminary qualitative analysis of the predissociation is given in the particular case of the F 2 spin component of 16O 3 for 0 0 0 and 2 0 1 bands by the measurement of shifts of positions of some rovibrational levels and the evolution of predissociation broadenings in Q Q 2 branches. We justify the existence of perturbations in the rovibrational levels of 3A 2 state through different interaction types: with the dissociation continuum of the same electronic state or with high vibrational repulsive or weakly bound levels of the ground state.

Observation of TiF+by Velocity Modulation Laser Spectroscopy and Analysis of the [17.6]3Δ–X3Φ System

The molecular ion TiF+has been observed for the first time using high-resolution spectroscopy. The ions were produced in the positive column of an AC glow discharge with a gas mixture of He/TiF4. A single-mode cw dye laser along with the velocity modulation detection technique was used to record an absorption spectrum in the spectral region 16800–18600 cm−1. The observed system was assigned to the 0–0 and 1–1 bands of the [17.6]3Δ–X3Φ transition of TiF+. The rotational analysis of the main subbands has been performed up toJvalues equal to 77 and 56 for the 0–0 and 1–1 bands, respectively. Despite a careful search, no intercombination band was observed. A set of effective molecular parameters has been determined, characterizing thev= 0, 1 levels of the [17.6]3Δ andX3Φ states. The spin–orbit constantsAeand the vibrational constants ωe, ωexehave been estimated for both electronic states, as well as their equilibrium distancesRe(1.7509 and 1.7800) Å for the [17.6]3Δ andX3Φ states, respectively).

A subband approach to adaptive acoustic echo cancellation

In this paper a novel subband-based acoustic echo canceller (AEC) is proposed for teleconferencing applications. The proposed AEC consists of K non-overlapping main subbands and K auxiliary subbands. The auxiliary subbands are introduced in order to provide frequency coverage in the non-overlapping region between the neighboring main subbands. The main and auxiliary bands are constructed using the discrete Fourier transform (DFT) filter bank approach. Owing to the complex modulation feature implied in the DFT filter bank, the proposed structure consists of ( K 2 + 1) distinct main subbands and ( K 2 + 1) distinct auxiliary subbands. Central to computational efficiency of the proposed AEC is the down-sampling of the auxiliary bands by a factor of two compared to the main bands. The normalized mean squares algorithm (NLMS) is employed for updation of subband adaptive filter coefficients. The proposed subband AEC is implemented both in a real-time teleconferencing system employing a floating-point DSP chip and in simulation for the case of K = 16 i.e. nine distinct main bands and nine distinct auxiliary bands.

Novel infrared spectroscopic method for the determination of crystallinity of hydroxyapatite minerals

Biologically important apatite analogues have been examined by Fourier Transform Infrared Spectroscopy (FT-IR), and a method developed to quantitatively assess their crystalinity. Changes in the phosphate v1 and v3 regions, 900-1,200 cm-1, for a series of synthetic (containing hydroxide, fluoride, or carbonate ion) and biological apatites with crystal sizes of 100-200 A were analyzed with curve-fitting and second derivative spectroscopy. The v1,v3 contour was composed of three main subbands. Correlations were noted between two spectral parameters and crystal size as determined by x-ray diffraction. The percentage area of a component near 1,060 cm-1 decreased as the length of the c-axis of the hydroxyapatite (HA) compounds increased, while the frequency of a band near 1,020 cm-1 increased with increasing length of the apatite c-axis. These parameters are thus proposed as indices of crystallinity for biological (poorly crystalline) HA. The FT-IR spectra of highly crystalline apatitic compounds were also analyzed. For crystal sizes of 200-450 A, the percentage area of the phosphate v1 band (near 960 cm-1) decreased with increasing HA crystal size. IR indices of crystallinity have thus been developed for both well crystallized and poorly crystallized HA derivatives. The molecular origins of the various contributions to the v1,v3 contour are discussed, and a preliminary application of the method to a microscopic biological sample (rat epiphyseal growth plate) is illustrated.

High-resolution spectroscopy of refractory molecules at low temperature. The e3Π–a3Δ band system (β-system) of ZrO

The band origins of the e3Π–a3Δ system of ZrO have been investigated using the combined techniques of chemical reaction in laser-produced plasma, supersonic cooling and laser-induced fluorescence. Rotational temperatures of ca. 35–45 K have been observed. Each of the three main sub-bands, 3Π2–3Δ3, 3Π1–3Δ2 and 3Π0–3Δ1, has been fully analysed at a Doppler-limited resolution of 120 MHz. Lambda-type doubling has been observed for all three sub-bands, and nuclear hyperfine structure has been resolved for 91ZrO. Data for all five isotopic species are reported. Effective molecular constants (B″, D″, ν0–0,B′, D′) have been derived for (1) the e-and f-term series of each sub-band and (2) the entire system. In light of these results the multiplet splittings are re-assessed, the electronic configurations of ZrO in the a3Δ and e3Π states are discussed, and the nature and location of nearby perturbing states are predicted.

Comparison of enzymatic characteristics of creatine kinase BB from human healthy and tumor stomach tissues

Creatine kinase (ATP : creatine N-phosphotransferase, EC 2.7.3.2, CK) BB isoenzyme from stomach tumor tissue was partially purified and its characteristics were compared with those from healthy tissue. Molecular mass of tumor CK-BB was estimated to be 82000 by polyacrylamide gel electrophoresis. Tumor CK-BB was separated into 2 main subbands around pH 4.5 and 11, minor subbands around pH 5−7.5 by agarose isoelectric focusing. The isoenzyme reacted with anti-human brain CK-BB antibodies and formed a hybrid, CK-MB, with CK-MM prepared from healthy human skeletal muscle. The above physicochemical and immunological characteristics of tumor CK-BB were the same as those of normal CK-BB from normal stomach tissue. Optimum pH of tumor CK-BB was more acidic than that of normal CK-BB. Affinity for creatine phosphate and heat sensitivity of tumor CK-BB were slightly lower than those of normal CK-BB. Tumor CK-BB was more stable after iodoacetamide and urea treatments.