Additional Extrema Research Articles

Thermal effects on chemically induced Marangoni convection around A + B → C reaction fronts.

Chemical reactions can induce Marangoni flows by changing the surface tension of a solution open to the air, either by changing the composition and/or by modifying the temperature. We consider the case of a simple A + B → C reaction front propagating in a thin horizontal system open to air. The effect of the three chemical species on the surface tension of the aqueous solution is quantified by three solutal Marangoni numbers, while the effect of temperature changes is determined by the thermal Marangoni number. By integrating numerically the incompressible Navier-Stokes equations coupled to reaction-diffusion-convection equations for the chemical concentrations and temperature taking into account the Lewis number (ratio between heat and mass diffusivities), we emphasize the importance of thermal changes occurring due to the heat of reaction on the dynamics of chemically induced Marangoni convection. Based on the reaction-diffusion profiles of concentrations and temperature, asymptotic analytical solutions for the surface tension profiles are obtained and classified as a function of the Marangoni numbers and the Lewis number. This new classification allows for the prediction of the convective patterns in thermo-solutal Marangoni flows. The analytical predictions are further confirmed by numerical results and additional extrema in surface tension profiles induced by the thermal effects are found to affect the nonlinear dynamics.

The unsupervised pattern recognition for the ECG signal features detection

Smart devices and cloud-based technologies allow continuous non-invasive bio-signal recordings in daily life activities. There are many programs and applications that allow monitoring health condition and sharing that information with other people. However, bio-signals that are recorded in real nonstationary conditions are highly contaminated with noise that depends on various activities. Improper signal processing algorithms may lead to a faulty diagnosis or inaccurate decision-making results. Movement contaminated bio-signals require adaptive filtering and feature extraction algorithms because low frequency trends are mostly unstable, and the noise may cause higher impulses than the signal itself. That is why ordinary ECG signal parameters extraction algorithms fail in real time signal processing. In this research signals were filtered using two different methods: Butterworth filter for the high frequency noise reduction and BEADS algorithm for the low frequency noise removal. A new ECG feature extraction algorithm was proposed that is based on the unsupervised MTEO algorithm together with additional local extremum search. The proposed algorithm was compared with other methods on the MIT-BIH database. The additional comparison was made with Pan-Tompkins and k-TEO algorithms on ECG signals that were recorded in movement. Several examples are presented that show how each algorithm performs during training sessions with various intensity levels. The suggested method performed in linear time complexity that made it sufficient for the real time data processing. The obtained ECG parameter values could be used for diagnostics and fatigue recognition in health monitoring processes.

Электронные состояния и персистентные токи в кольцах с неоднородным спин-орбитальным взаимодействием Рашбы

The paper considers one-dimensional isolated quantum rings in a perpendicular magnetic field, in which Rashba spin-orbit coupling parameter changes along the ring. Electronic spectra and persistent currents of such ring structures are calculated for different values of the structure parameters and the magnitude of the magnetic flux. It is shown that the inhomogeneity of the Rashba parameter leads to anticrossing of energy levels and smoothing of the dependence of the persistent charge current on the flux. The influence of inhomogeneity on the spin persistent current turns out to be more significant: the projection of the spin current on the ring axis ceases to be preserved when moving along the ring; additional extrema or zeros appear on the dependence of the absolute value of the spin current on the magnetic flux for a given number of electrons in the ring.

CОНЯЧНО -ДОБОВІ ГЕОМАГНІТНІ ВАРІАЦІЇ: СЕЗОННІ ТА ДОВГОТРИВАЛІ ЗМІНИ SqY, SqZ НА ОБСЕРВАТОРІЇ AIA

The spatial ambiguity of the magnitude of centennial trends in the Sq variations diurnal amplitudes determined the investigation of this question in the region of negative century variations geomagnetic field. Objective. To study the characteristics (trends of diurnal amplitudes and shapes) of solar-diurnal Sq variations at the Antarctic observatory AIA. Methods. Analysis of geomagnetic field monitoring data at the observatory for the period 1958-1991. Exclusion of the effect of the dependence ofthe daily amplitude of Sq variations on the solar activity index F10.7 using the regression analysis residual method. Results. From the analysis of the shape of Sq variations, seasonal features of SqZ, SqY were obtained: autumn-spring asymmetry and an additional morning extremum in the daily course of Sq winter (April-September) type. Seasonal differences were found both in the mean monthly values of the daily amplitude of Sq variations and in the values of their long-term trend for 33 years. Conclusions. The revealed positive trends of the average annual daily amplitudes of Sq variations were 11% for the eastern SqY and 17-20% for the vertical SqZ variation. The observed variation in the trend value of the annual amplitudes Sq is apparently due to seasonal variations of the physical parameters that determine Sq.

Anisotropic mixed hole scattering mechanism in Sb2Te3–x Se x crystals (0 ≤ x ≤ 0.1) according to the data of the Nernst–Ettingshausen and seebeck effects

The temperature dependences of three independent coefficients of the Nernst–Ettingshausen tensor Qikl are investigated along with the electrical conductivity, thermal voltage, and Hall coefficients of layered p-Sb2Te3–xSex single crystals (0 ≤ x ≤ 0.1). It is established that all Qikl < 0 for the studied alloy crystals in the temperature range 77–400 K. Data on the Nernst–Ettingshausen effect and observed anisotropy of the Seebeck coefficient are indicative of the anisotropic mixed hole scattering mechanism at acoustic phonons and impurities and defects with the dominant contribution of scattering at lattice vibrations both in the crystal cleavage plane and in the trigonal axis direction. Estimation of the scattering parameters from four kinetic coefficients showed that they decrease with an increase in temperature due to phonon-scattering enhancement. They become negative at higher temperatures (T ≳ 200 K), which is apparently associated with bandto-band hole scattering to the additional valence-band extremum.

Tunneling density of states in quantum dots with anisotropic exchange

We reexamine the tunneling density of states in quantum dots and nanoparticles within the model which is extension of the universal Hamiltonian to the case of uniaxial anisotropic exchange. We derive the exact analytical result for the tunneling density of states in the case of arbitrary single-particle energy spectrum. We find that, similar to the case of the isotropic exchange, the tunneling density of states as a function of energy has the maximum due to a finite value of the total spin of the ground state near the Stoner instability. We demonstrate that there are no additional extrema which have been predicted on the basis of perturbative analysis [M.N. Kiselev and Y. Gefen, Phys. Rev. Lett. {\bf 96}, 066805 (2006)].

Electrostatic supersolitons in three-species plasmas

Superficially, electrostatic potential profiles of supersolitons look like those of traditional solitons. However, their electric field profiles are markedly different, having additional extrema on the wings of the standard bipolar structure. This new concept was recently pointed out in the literature for a plasma model with five species. Here, it is shown that electrostatic supersolitons are not an artefact of exotic, complicated plasma models, but can exist even in three-species plasmas and are likely to occur in space plasmas. Further, a methodology is given to delineate their existence domains in a systematic fashion by determining the specific limiting factors.

Band gap and type of optical transitions at the interband absorption edge in solid solutions based on bismuth telluride

The spectra of optical absorption in multicomponent n- and p-type solid solutions based on bismuth and antimony chalcogenides with substitutions in both sublattices of Bi2Te3 have been investigated. It has been found that, in all the solid solutions studied, just as in the parent compound Bi2Te3, direct allowed transitions occur at the interband absorption edge at T = 300 K. The band gap Eg in the n-Bi2 − xSbxTe3 − y − zSeySz solid solutions weakly increases with increasing number of substituted atoms in the Bi and Te sublattices. These atomic substitutions do not leads to an increase in Eg as compared to that of the n-Bi2Te2.7Se0.3 composition. An analysis of the optical absorption spectra suggests that the solid solutions under consideration are weakly degenerate, a conclusion supported by the earlier studies of the thermoelectric and galvanomagnetic properties. It has been established that, in the conduction band of the Bi1.8Sb0.2Te2.7Se0.15S0.15 solid solution, there is an additional extremum lying above the main extremum at a distance no more than 0.1 eV.

Ballistic conductance in kane type semiconductor quantum wire

The energy spectrum, ballistic conductance of an electron on the surface of a Kane type semiconductor hollow cylinder has been calculated by using the Kane equation with an additional term that takes into account the spin-orbit (SO) interaction. This term, known as Rashba term, occurs for asymmetric quantum wells, where two directions on the normal n are physically nonequivalent. If Rashba spin-orbital interaction is incorporated into energy spectrum, it leads to the emergence of new extrema. We obtained electron energy spectrum, which depends on the sign of the effective spin orbital constant. The energy spectrum of electrons has two branches when the magnetic field does not exist. One of these branches has only one minimum while the other branch has one maximum around k = 0 and two minima. The external magnetic field can control these extrema which occur in the event transport. The results were used to obtain the ballistic conductance at finite temperature of the Kane type hollow cylinder. It has been found that the presence of additional local extremum points in the subband of the electronic spectrum leads to a nonmonotonic dependence of the ballistic conductance of the system on the chemical potential. The g-factor of electrons was observed to depend on Rashba parameter in a linear manner. The effect of finite temperature smears out the sharp steps in the zero-temperature conductance.

Rashba spin–orbit coupling effect on a diluted magnetic semiconductor cylinder surface and ballistic transport

We have studied the Rashba spin–orbital effect on a diluted magnetic semiconductor (DMS) cylinder surface in the presence of a magnetic field parallel to the cylinder axis, taking into account the Zeeman coupling and the s–d exchange interaction between the carriers and the magnetic ions. We have obtained an analytical expression for the electron energy spectrum, which depends on the magnetic ion concentration, temperature and strength of magnetic field. The results are used to obtain the conductance of the cylinder at finite temperature. It is shown that the presence of additional local extremum points in the subbands of the electronic spectrum leads to a nonmonotonic dependence of the ballistic conductance of the system on the chemical potential and magnetic field. In the presence of anomalous Zeeman terms with taking into account the Rashba splitting, each minimum of subband contributes G 0 / 2 to conductance and each local maxima in the subband, actually reduce the conductance by G 0 / 2 compared with the value G 0 , without the anomalous Zeeman splitting. The effect of finite temperature on the DMS cylinder conductance is a smearing out the sharp steps in the zero-temperature conductance, and shifting the peaks due to the temperature dependence of the s–d exchange interaction term.

The effect of surface passivation on the intrinsic photoconductivity of gallium phosphide compensated with copper

The effect of passivation in sulfide solutions on the shape of the GaP:Cu photoconductivity spectra is studied. The position and shape of an additional extremum at energies above the fundamental-absorption threshold are related to the redistribution of nonequilibrium charge carriers in the surface-potential field.

Behavior of the dynamic magnetic susceptibility under spontaneous phase transitions in quasi-uniaxial ferromagnetic films

Behavior of the magnetic susceptibility of quasi-uniaxial ferromagnetic films in the vicinity of the Curie point was studied with allowance for a periodic spatial inhomogeneity in the distribution of the magnetization vector for an arbitrary frequency ω of an external magnetic field. In the presence of a constant bias magnetic field H0, the temperature dependence of the real and imaginary parts of the magnetic susceptibility exhibits, in the general case, both frequency-independent extrema and numerous additional extrema having shapes and positions dependent on frequency.

Acoustic emission caused by an edge dislocation breaking away and coming to rest in an isotropic medium

Acoustic emission produced by a moving edge dislocation in an isotropic crystal is investigated theoretically. It is shown that the acoustic-emission spectrum associated with a dislocation breaking away and coming to rest is similar to that associated with the annihilation of two dislocations. In the case where a linear defect breaks away and comes to rest periodically, additional extrema appear in the acoustic-emission spectrum and the frequencies corresponding to the maxima in the spectrum are multiples of the dislocation hopping frequency between minima of the potential-energy profile. Both cases of large and small distances of the acoustic-emission detection point from a dislocation array are considered. The latter case is exemplified by experimentally observed acoustic emission associated with electric-field-stimulated motion of edge dislocations in silicon.

B1359+154: A Six‐Image Lens Produced by az≃ 1 Compact Group of Galaxies

Hubble Space Telescope (HST) V- and I-band observations show that the gravitational lens B1359+154 consists of six images of a single zs = 3.235 radio source and its star-forming host galaxy, produced by a compact group of galaxies at zl ≃ 1. Very Long Baseline Array (VLBA) observations at 1.7 GHz strongly support this conclusion, showing six compact cores with similar low-frequency radio spectra. B1359+154 is the first example of galaxy-scale gravitational lensing in which more than four images are observed of the same background source. The configuration is due to the unique lensing mass distribution: three primary lens galaxies lying on the vertices of a triangle separated by 07 ≃ 4 h-1 kpc, inside the 17 diameter Einstein ring defined by the radio images. The gravitational potential has additional extrema within this triangle, creating a pair of central images that supplement the "standard" four-image geometry of the outer components. Simple mass models, consisting of three lens galaxies constrained by HST and VLBA astrometry, naturally reproduce the observed image positions but must be finely tuned to fit the flux densities.

A new type of peak effect in the magnetization of anisotropic superconductors

Experimental and theoretical studies of the magnetization curves M(H) obtained for plates of an anisotropic hard superconductor are performed. The samples are YBCO single-domain textured crystals with the c axis lying in the sample plane. It is shown that, for some orientations of the magnetic field in the sample plane, the magnetization curves contain additional extrema; at the same time, the virgin magnetization curve M(H) exhibits features characteristic of the peak effect. This proves that the anisotropy of the current-carrying ability can give rise to a new type of peak effect.

Optimal conditions for the generation of the third harmonic of focused radiation in a self-interaction regime

A method developed for the analysis of the interaction of wave beams in a self-interaction regime is used to determine the changes in the optimal conditions for third-harmonic generation with changes in the degree of focusing of the fundamental-frequency radiation in isotropic media. Conditions under which a redistribution of the intensities and phases of the interacting wave beams reduces the efficiency of third-harmonic generation are identified. It is shown that, under strong focusing conditions, there may be additional extrema in the dependence of the intensity of the harmonic on the density of the medium.

Band structure of TIGaSe2 ternary layered crystals

AbstractThe band structure in the high‐symmetry points of the TIGaSe2, Brillouin zone is calculated by the pseudopotential method. The top of the valence band is found to be located at the Γ point. The bottom of the conduction band is located at the line Γ–Y and the additional extremum of this band – at the point Γ of the Brillouin zone of TlGaSe2. The data obtained are compared with the results of previous band calculations and optical absorption data of TlGaSe2.

Band structure of TlGaSe2

AbstractA model of the TlGaSe2‐I band structure of the monoclinic modification is proposed. The monoclinic modification of TlGaSe2‐I is considered as a deformed tetragonal one. The band structure of the metastable tetragonal modification of TlGaSe2‐II is calculated by the pseudopotential method. The irreducible representations of the D184h group (TlGaSe2‐II) are expanded in irreducible representations of the C4s group (TlGaSe2‐I). It is found that the top of the valence band is located at the point Y (0,2π/bm, 0) of the TlGaSe2‐I Brillouin zone and is formed from band states N2, N4 of the tetragonal modification. The bottom of the conduction band is located at the point Γ of the TlGaSe4‐I Brillouin zone and is formed from T4 states. An additional extremum of the valence and conduction bands is located at the points Γ(A2) and Y(N6, N8), respectively. An interpretation of the absorption spectra of TlGaSe2‐I near the fundamental edge is proposed.

Thermopower of spin glasses

We calculate the thermopowerSd(T) of spin glasses on the basis of thesd exchange model with additional interactions between the impurity spins by means of time dependent perturbation theory. Similarly to the Kondo effect, the observed giant thermopower can only be explained if one also takes into account the spin independent interactionV between the magnetic impurities and the conduction electrons. We obtain a “Kondo” termSd(1)(T) (which reduces for vanishing spin interactions to the thermopower of Kondo systems) and in addition a “resonance” termSd(2)(T) of opposite sign which vanishes for vanishing interactions. The superposition of both terms leads to an additional extremum of the total thermopower and to a change of sign at a temperatureT0 which depends on the Kondo temperature and on the magnetic excitations of the spin glass and therewith on the freezing temperatureTf. We obtain at low temperatures for oscillating and relaxing spin glass modesSd(1)∝T2 andSd(2)∝T. At high temperaturesSd(1)(T) decreases as |lnT|−3 andSd(2) asT−1. A close relationship between the temperature dependent resistivity in Born approximation andSd(1)(T) is pointed out.

The magnetostriction of grain-oriented 3 percent silicon-iron strips

In the course of the polarization process a magnetostriction of Goss and cube-textured strips of silicon-iron is caused by the appearance of transverse domains (closure structures, influence of imperfect grain orientation). The elongation of the strips is measured by an interference method. In the case of annealed Goss samples, the static magnetostriction λ( H) as a function of the external magnetic field H deviates by two additional extrema from the familiar “butterfly” curve. This anomaly disappears after a plastic deformation of 0.1%. Cube-textured strips yield a negative magnetostriction up to a field of 85 Oe. But, after a plastic deformation (0.1%), the magnetostrictive strain is positive and the curve λ( H) is identical with that of the deformed Goss samples. The influence of an elastic stress is also investigated, and the magnetostriction is discussed with respect to special domain structures.