Effects of Tau and Sampling Frequency on the Regularity Analysis of ECG and EEG Signals Using ApEn and SampEn Entropy Estimators

Electrocardiography (ECG) and electroencephalography (EEG) signals provide clinical information relevant to determine a patient’s health status. The nonlinear analysis of ECG and EEG signals allows for discovering characteristics that could not be found with traditional methods based on amplitude and frequency. Approximate entropy (ApEn) and sampling entropy (SampEn) are nonlinear data analysis algorithms that measure the data’s regularity, and these are used to classify different electrophysiological signals as normal or pathological. Entropy calculation requires setting the parameters r (tolerance threshold), m (immersion dimension), and τ (time delay), with the last one being related to how the time series is downsampled. In this study, we showed the dependence of ApEn and SampEn on different values of τ, for ECG and EEG signals with different sampling frequencies (F_s), extracted from a digital repository. We considered four values of F_s (128, 256, 384, and 512 Hz for the ECG signals, and 160, 320, 480, and 640 Hz for the EEG signals) and five values of τ (from 1 to 5). We performed parametric and nonparametric statistical tests to confirm that the groups of normal and pathological ECG and EEG signals were significantly different (p < 0.05) for each F and τ value. The separation between the entropy values of regular and irregular signals was variable, demonstrating the dependence of ApEn and SampEn with F_s and τ. For ECG signals, the separation between the conditions was more robust when using SampEn, the lowest value of F_s, and τ larger than 1. For EEG signals, the separation between the conditions was more robust when using SampEn with large values of F_s and τ larger than 1. Therefore, adjusting τ may be convenient for signals that were acquired with different F_s to ensure a reliable clinical classification. Furthermore, it is useful to set τ to values larger than 1 to reduce the computational cost.     

The a.c. susceptibility third harmonic component of NdO1−0.14F0.14FeAs: A flux dynamic magnetic analysis

In this contribution we present the analysis of the third harmonic susceptibility data of the new superconductor NdFeAs_1−0.14F_0.14. ‘Cole-Cole’ polar plots respect to the magnetic frequency of the exciting field are presented and discussed. Data show that NdFeAs_1−0.14F_0.14 exhibit a ‘bulk pinning’ with a 3D flux dynamic character. A comparison of the responses of high T_c materials and an evaluation of theoretical critical states is also presented.     

Frequency and phase synchronization in neuromagnetic cortical responses to flickering-color stimuli

In our earlier study dealing with the analysis of neuromagnetic responses (magnetoencephalograms—MEG) to flickering-color stimuli for a group of control human subjects (9 volunteers) and a patient with photosensitive epilepsy (a 12-year old girl), it was shown that Flicker-Noise Spectroscopy (FNS) was able to identify specific differences in the responses of each organism. The high specificity of individual MEG responses manifested itself in the values of FNS parameters for both chaotic and resonant components of the original signal. The present study applies the FNS cross-correlation function to the analysis of correlations between the MEG responses simultaneously measured at spatially separated points of the human cortex processing the red-blue flickering color stimulus. It is shown that the cross-correlations for control (healthy) subjects are characterized by frequency and phase synchronization at different points of the cortex, with the dynamics of neuromagnetic responses being determined by the low-frequency processes that correspond to normal physiological rhythms. But for the patient, the frequency and phase synchronization breaks down, which is associated with the suppression of cortical regulatory functions when the flickering-color stimulus is applied, and higher frequencies start playing the dominating role. This suggests that the disruption of correlations in the MEG responses is the indicator of pathological changes leading to photosensitive epilepsy, which can be used for developing a method of diagnosing the disease based on the analysis with the FNS cross-correlation function.     

Low temperature linear dynamical susceptibility of dipolar spin glasses

The dissipative part of the linear magnetic dynamic susceptibility of dipolar spin glasses is considered. Due to the transition of the system (at enough high concentration of the magnetic dipoles) from a paramagnetic phase to a magnetic dipolar one, an anomalous temperature dependence of the dissipative part of the magnetic susceptibility is found. Some considerations related to the experimental results for LiHo_xY _1?xF₄ are made.     

Antiferromagnetic Ordering of Magnetic Clusters Units in Nb6F15

We have studied the magnetic cluster compound Nb₆F₁₅ which has an odd number of 15 valence electrons per (Nb₆F₁₂)³⁺ cluster core, as a function of temperature using nuclear magnetic resonance, magnetic susceptibility, electron magnetic resonance and neutron powder diffraction. Nuclear magnetic resonance of the ¹⁹F nuclei shows two lines corresponding to the apical F^a?a nucleus, and to the inner Fⁱ nuclei. The temperature dependence of the signal from the Fⁱ nuclei reveals an antiferromagnetic ordering at T < 5 K, with a hyperfine field of ~2 mT. Magnetic susceptibility exhibits a Curie–Weiss behavior with T _N ~5 K, and μ _eff ~1.57 μ_B close to the expected theoretical value for one unpaired electron (1.73 μ_B). Electron magnetic resonance linewidth shows a transition at 5 K. Upon cooling from 10 to 1.4 K, the neutron diffraction shows a decrease in the intensity of the low-angle diffuse scattering below Q ~0.27 Å^?1. This decrease is consistent with emergence of magnetic order of large magnetic objects (clusters). This study shows that Nb₆F₁₅ is paramagnetic at RT and undergoes a transition to antiferromagnetic order at 5 K. This unique antiferromagnetic ordering results from the interaction between magnetic spins delocalized over each entire (Nb₆F ₁₂ ⁱ )³⁺ cluster core, rather than the common magnetic ordering.     

Effect of the encapsulation of Li atom on the electronic transport properties of C20F20 cage

Carrying out theoretical calculations using a self-consistent ab initio approach that combines the non-equilibrium Green′s function formalism with density functional theory, we investigate the effect of the center encapsulation of Li atom on the electronic transport properties of C₂₀F₂₀ cage sandwiched between two bulk gold electrodes. The results show that the electrical conductivity of the endohedral complex Li@C₂₀F₂₀ becomes better than that of the empty C₂₀F₂₀ in the bias voltages ranging from 0 to 1.2 V. The novel negative differential resistance behavior in the I-V characteristic curves can be observed by inserting Li atom into C₂₀F₂₀ cage. The mechanism for the negative differential resistance behavior of Li@C₂₀F₂₀ is suggested.     

Spectroscopic diagnostics of R.F. discharges at moderate pressure and chemical applications—I. Pure nitrogen

A vibro-rotational analysis has been performed of the second positive system (SPS) of N₂ and of the first negative system (FNS) of N⁺₂ emitted by 35 MHz discharges in flowing nitrogen operated at pressures of 5–50 torr and power densities of the order of 1–10 W-cm^-3. The distributions of the vibrational and of the rotational levels follow Boltzmann's law in both the SPS and the FNS with T_v = 4000°K and T_R = 2800°K for the N₂(C³Π_u) state and T_v = 5100°K and T_R = 5800°K for the N⁺₂(B²Σ⁺_g) state and independent of pressure. Kinetic gas temperatures are between 1200 and 2000°K and increase with pressure; electron temperatures are in the range 15,000–9,500°K. The reversal of line intensities of the SPS and of the FNS observed with increasing pressure has been tentatively interpreted. Possible chemical implications of these results have been examined.     

Studies on the optical and mechanical properties of organic nonlinear optical 1-(4-fluorostyryl)-4-nitrostilbene (FNS) single crystal

A new organic nonlinear optical material 1-(4-fluorostyryl)-4-nitrostilbene (FNS) has been synthesized and single crystals of FNS were grown using solvent evaporation solution growth technique (SESGT) by 2-butanon solvent. Single crystal x-ray diffraction analysis reveals the unit cell parameters of the grown crystal are a = 9.494(4) Å, b = 9.864(2) Å, c = 19.501(7) Å and it belongs to monoclinic system with noncentrosymmetric space group. Optical transmittance of the grown crystal has been studied by UV-Vis-NIR spectrum. The optical properties of FNS have been studied by means of optical transmittance measurements in the wavelength range of 190–1100 nm The optical constants were calculated from the optical transmittance (T) data such as refractive index (n), extinction coefficient (k) and reflectance (R). The optical band gap (E_g) of FNS is 3.27 eV with direct transition. The complex dielectric (?) constant of the grown FNS crystal was determined. The second harmonic generation (SHG) efficiency of the grown FNS crystal has been studied by using Kurtz-Perry powder technique and it shows 12 times relatively greater than KDP.     

Magnetic phase diagram of double-layered La2−2xCa1+2xMn2O7 manganite

Double-layered manganite La_2−2xCa_1+2xMn₂O₇ have been synthesized for compositions ‘x’=0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 by solid state reaction method. From X-ray diffraction study, their crystal structures were found to be tetragonal perovskite with lattice parameters decreasing with increasing ‘x’. The decreasing lattice parameters affect the balance between in-plane, intra-bilayer and inter-bilayer exchange interactions, which is reflected on magnetotransport properties. The metal-to-insulator transition temperature is found to vary with composition and peaked around ‘x’=0.3. From ac-susceptibility study, 2D-ferromagnetic ordering was observed at higher temperatures for all compositions whereas 3D-ferromagnetic ordering was observed at quite low temperatures. In low-temperature region, decreasing susceptibility shows antiferromagnetic state for all compositions. On the basis of electrical and magnetic properties, a magnetic phase diagram is given.     

Robust output synchronization of second-order systems

A technique to synchronize a network of dynamical systems described by second-order ordinary differential equations is presented. Each system can be driven by a coupling control signal, which is synthesized such that, at steady-state, the outputs of two given systems, say y _i and y _j , i ≠ j, satisfy a specified ratio, that is, y _i /y _j = α _i /α _j , α _i ≠ 0 ≠ α _j . Among others, this includes the cases where the outputs are synchronized in-phase or anti-phase. The proposed synchronization technique is robust; this means that a small synchronization error is preserved at steady-state, even if the systems were perturbed by external disturbances. Some level of parameter uncertainty can also be tolerated. The coupling control signals are synthesized based on a classical controller and a robust observer that estimates the generalized velocities and provides an estimation of the perturbation terms. Some experimental results, showing the performance of the proposed synchronization technique, are included.     

Collisional transfer of energy in ammonia investigated by infrared-microwave multiple-resonance experiments

Collisional transfer of energy in ammonia has been investigated by infrared-microwave, double-resonance, and triple-resonance experiments. The power modulated P(13) line of a N₂O laser was used to pump the $\text{ν}{}_2\text{[a}{}^{\mathrm{q}}\text{Q(8, 7)]}$ transition while various microwave transitions were observed. In the triple-resonance experiments a second microwave field was simultaneously applied to the (8, 7) inversion transition. Examination of the double-resonance signals observed at 25 microwave transitions showed that most of the signals could be explained as being mainly produced by heating effects and only in the case of the (7, 7) and (9, 7) transitions were direct collisional transitions occurring. From consideration of triple-resonance and phase-shift measurements it was concluded that the thermal signals consisted of at least two components with differing temporal characteristics.Relative intensity measurements of the double-resonance signals of the ΔF = ± 1 hyperfine components of the (8, 7) and (7, 7) gave information about the relative population reductions produced in the individual F levels. These observations and the reaction of the double-resonance signals to triple-resonance conditions may be explained by collisional transitions obeying the same F selection rules as radiative transitions.     

Magnetic susceptibility of titanium diselenide intercalated with copper

The temperature dependence of the magnetic susceptibility of Cu _x TiSe₂ polycrystalline samples has been measured. The electron density of states near the Fermi level N(E _F) in the Pauli model of paramagnetism has been calculated and discussed. The concentration dependences of the density of states N(E _F) and the unit cell parameter in the direction perpendicular to the layers in Cu _x TiSe₂ correlate with the concentration of centers V-Ti-Cu and Cu-Ti-V (V is the vacancy).     

Radiative lifetimes and tensor polarizabilities of 1s4f 1 F and 1s5f 1 F level of He I

He atoms have been excited by Ne⁺ ion impact and the depolarization of the fluorescence lines at 668 nm and 492 nm by magnetic and electric fields has been studied. The Ne⁺ ion energy could be chosen such that pure cascade level crossing signals were observed. From the widths of magnetic depolarization signals the radiative lifetimes τ(1s4f ¹ F)=74(2) ns and τ(1s5f ¹ F)=133(5) ns have been determined. By investigating the electric field splitting of the magnetic depolarization signals the tensor polarizabilities ¦α _ten(1s4f ¹ F)¦=0.58(1) kHz/(V/cm)² and ¦α _ten(1s5f ¹ F)¦=4.2(1) kHz/(V/cm)² have been deduced. From the latter value a mean frequencyv(1s5g?1s5f)=14.4 GHz of the transitions between the levels of the 1s5f configuration and those of the 1s5g configuration has been derived.α _ten(1s4f ¹ F) depends sensitively on the singlet-triplet mixing in the 1s4f configuration and thus a mixing coefficient could be deduced for this configuration.     

Mode-crossing signals of high order on the 4d 95s 2 2 D 5/2 state of Cd II isotopes

In the linearly polarized radiation field of a 442 nm He-Cd laser containing a natural isotope mixture, saturation-induced mode-crossing signals of the 4d ⁹5s ^{2 2} _5/2 state of Cd II are observed due to the even as well as the odd isotopes. The signal width of about 10^?4 T yields high resolution. Thus the signal splitting respective to the magnetic quantum number can be resolved. Theg _J - andg _F -factors of the² D _5/2 state are determined as follows:g _J=1.1980±0.0036,g _F(F=2)=1.397±0.008,g _F(F=3)=1.002±0.009.     

Cross-correlation markers in stochastic dynamics of complex systems

The neuromagnetic activity (magnetoencephalogram, MEG) from healthy human brain and from an epileptic patient against chromatic flickering stimuli has been earlier analyzed on the basis of a memory functions formalism (MFF). Information measures of memory as well as relaxation parameters revealed high individuality and unique features in the neuromagnetic brain responses of each subject. The current paper demonstrates new capabilities of MFF by studying cross-correlations between MEG signals obtained from multiple and distant brain regions. It is shown that the MEG signals of healthy subjects are characterized by well-defined effects of frequency synchronization and at the same time by the domination of low-frequency processes. On the contrary, the MEG of a patient is characterized by a sharp abnormality of frequency synchronization, and also by prevalence of high-frequency quasi-periodic processes. Modification of synchronization effects and dynamics of cross-correlations offer a promising method of detecting pathological abnormalities in brain responses.     

Discrete breathers and nonlinear normal modes in monoatomic chains

We consider a relation between discrete breathers (DBs) and nonlinear normal modes in some nonlinear monoatomic chains. The dependence of the breathers’ stability on the strength of interparticle interaction in the K₄ chain (the chain with uniform on-site and intersite potentials of the fourth order) is investigated. A general method for constructing DBs which provides the pair synchronization between the individual particles’ vibrations is discussed. Many-frequency breathers as DBs of a new type and quasibreathers [introduced in Physical Review E 74 (2006) 036608] are analyzed.     

Photoemission (XPS,UPS) studies of Pd-Si metallic glasses

The valence bands of glassy $\text{Pd}{}_{\mathrm{100?x}}\text{Si}{}_{\mathrm{x}}\text{(15?x?21)}$ and pure Pd were studied by XPS and UPS. The valence band spectra of the alloys show a strongly reduced density of states at the Fermi energy E_F compared to Pd. From the measured relative photoelectric cross sections for the different excitation energies we conclude that the electron states near E_F of the glassy alloys have mainly d-character. This is in good agreement with recent measurements of the low-temperature specific heat, the magnetic susceptibility and the optical reflectivity.     

Relaxationserscheinungen im 63 P 2-Zustand des Quecksilber-Isotops199Hg bei Stößen mit Quecksilberatomen im Grundzustand

The decay ofrf resonance signals (Δm _F =± 1, ΔF=0) in the hfs-states (F=3/2, 5/2) of the 6³ P ₂-state of¹⁹⁹Hg has been observed by means of a sampling method. By comparing the relaxation times to those of the even isotopes, the cross section σ₂(F) for the destruction of an alignment in the hfs-states by collisions with ground state Hg-atoms could be measured. The following ratios were obtained: σ₂(F=3/2)/σ₂=1.04±0.06 and σ₂(F=5/2)/σ₂=0.90± 0.03. The cross section σ₂ for the even isotopes was found to be (2.620±0.265) 10^?14cm². Assuming total decoupling of nuclear spinI and electronic angular momentumJ during the collision, the cross sections for the destruction of an orientation (σ₁) and an “octupolarisation” (σ₃) could be calculated. For the even isotopes the following ratios were derived: σ₁/σ₂=0.76 ± 0.07 and σ₃/σ₂=1.08 ± 0.09.     

Dynamics of plume and crater formation after action of femtosecond laser pulse

Using microinterferometric method, a transition in laser plume from the regime with spallation to the regime without spallation is experimentally studied for the first time. The transition occurs when the fluence F_inc of incident radiation exceeds a threshold of “evaporation” (F_inc)_ev. It has been shown previously that the spallation layer is formed at fluence above the ablation threshold (F_inc)_abl. Thus the spallation exists within the limits (F_inc)_abl<F_inc<(F_inc)_ev. A laser beam has a maximum fluence (F_inc)_c on the axis of the beam. The threshold F_ev separates two cases with qualitatively different morphology: (1) with unbroken shell covering the crater entirely if F_abl<F_c<F_ev, and (2) with the shell having an aperture in the center (like the volcano muzzle) if F_c>F_ev.