Dynamics Of Spectrum Research Articles

A Unified Framework for Investigating Aperiodic and Periodic Components in the Hearbeat Dynamics Spectrum: a Feasibility Study.

Heart Rate Variability (HRV) series is a widely used, non-invasive, and easy-to-acquire time-resolved signal for evaluating autonomic control on cardiovascular activity. Despite the recognition that heartbeat dynamics contains both periodic and aperiodic components, the majority of HRV modeling studies concentrate on only one component. On the one hand, there are models based on self-similarity and 1/f behavior that focus on the aperiodic component; on the other hand, there is the conventional division of the spectral domain into narrow-band oscillations, which considers HRV as a combination of periodic components. Taking inspiration from a recent parametrization of EEG power spectra, here we evaluate the applicability of a unified modeling framework to quantitatively assess heartbeat dynamics spectra as a mixture of aperiodic and periodic components. The proposed model is applied on publicly-available, real HRV series collected during postural changes from 10 healthy subjects. Results show that the proposed modeling effectively characterizes different experimental conditions and may complement HRV standard analysis defined in the frequency domain.

IRMPD spectroscopy of a PAH cation using FELICE: The infrared spectrum and photodissociation of dibenzo[a,l]pyrene

We present the experimental InfraRed Multiple Photon Dissociation (IRMPD) spectrum and fragmentation mass spectrum of the irregular, cationic PAH dibenzo[a,l]pyrene (C24H14+) in the 6–40μm/250–1650 cm−1 range. The use of the Free-Electron Laser for IntraCavity Experiments (FELICE) enabled us to record its Far-InfraRed (FIR) spectrum for the first time. We aim to understand how irregularity affects the infrared spectrum and fragmentation chemistry of PAHs. Dibenzo[a,l]pyrene is an asymmetric, non-planar molecule, for which all vibrational modes are in principle IR-active. Calculated harmonic Density Function Theory (DFT) and anharmonic Density Functional based Tight Binding Molecular Dynamics (DFTB-MD) spectra show a large wealth of bands, which match the experiment well, but with a few differences. The periphery of the molecule contains several edge geometries, but out of all possible modes in the 11–14μm out-of-plane CH bending region, only one band at 13.5μm is prominent. This fact and the richness of the CC stretching range make irregular PAHs a possible contributor to D-class interstellar spectra. The fragmentation mass spectra reveal facile 2H-loss and no [2C, 2H]-loss, which is attributed to the sterically hindered, non-planar cove region, which could protect irregular PAHs from radiation damage.

Path-integral dynamics of water using curvilinear centroids

We develop a path-integral dynamics method for water that resembles centroid molecular dynamics (CMD), except that the centroids are averages of curvilinear, rather than Cartesian, bead coordinates. The curvilinear coordinates are used explicitly only when computing the potential of mean force, the components of which are re-expressed in terms of Cartesian “quasicentroids” (so-called because they are close to the Cartesian centroids). Cartesian equations of motion are obtained by making small approximations to the quantum Boltzmann distribution. Simulations of the infrared spectra of various water models over 150–600 K show these approximations to be justified: for a two-dimensional OH-bond model, the quasicentroid molecular dynamics (QCMD) spectra lie close to the exact quantum spectra, and almost on top of the Matsubara dynamics spectra; for gas-phase water, the QCMD spectra are close to the exact quantum spectra; for liquid water and ice (using the q-TIP4P/F surface), the QCMD spectra are close to the CMD spectra at 600 K and line up with the results of thermostated ring-polymer molecular dynamics and approximate quantum calculations at 300 and 150 K. The QCMD spectra show no sign of the CMD “curvature problem” (of erroneous red shifts and broadening). In the liquid and ice simulations, the potential of mean force was evaluated on-the-fly by generalizing an adiabatic CMD algorithm to curvilinear coordinates; the full limit of adiabatic separation needed to be taken, which made the QCMD calculations 8 times more expensive than partially adiabatic CMD at 300 K, and 32 times at 150 K (and the intensities may still not be converged at this temperature). The QCMD method is probably generalizable to many other systems, provided that collective bead-coordinates can be identified that yield compact mean-field ring-polymer distributions.

About Spectral Structure Management of Gas Pressure Pulsations Signals in Nozzles with Deflector

Complex results in experimental and numerical flow dynamics research and spectra signals of gas pressure pulsations in annular and linear dual slotted nozzles are presented. Experiments are performed in a pulsed aerodynamic facility using acetylene-air mixture combustion products as working gas. Viscous flow calculations are based on the Navier-Stokes equations for multicomponent reactive gaseous medium using single-temperature chemical nonequilibrium model. As a result, the frequency Fourier spectrum of pressure pulsation at the thrust wall center is determined. Typical pulsed pressure signals obtained in the calculations and detected in the experiments are presented.

Spectra signals of gas pressure pulsations in annular and linear dual-slotted nozzles

ABSTRACTComplex results in experimental and numerical flow dynamics research and spectra signals of gas pressure pulsations in annular and linear dual-slotted nozzles are presented. Experiments are performed in a pulsed aerodynamic setup using acetylene–air mixture combustion products as working gas. Viscous flow calculations are based on the Navier–Stokes equations for multicomponent reactive gaseous medium using single-temperature chemical nonequilibrium model. As a result, the frequency Fourier spectrum of pressure pulsation at the thrust wall center is determined. Typical pulsed pressure signals obtained in the calculations and detected in the experiments are presented.

Dynamics and energy spectra of aperiodic discrete-time quantum walks.

We investigate the role of different aperiodic sequences in the dynamics of single quantum particles in discrete space and time. For this we consider three aperiodic sequences, namely, the Fibonacci, Thue-Morse, and Rudin-Shapiro sequences, as examples of tilings the diffraction spectra of which have pure point, singular continuous, and absolutely continuous support, respectively. Our interest is to understand how the order, intrinsically introduced by the deterministic rule used to generate the aperiodic sequences, is reflected in the dynamical properties of the quantum system. For this system we consider a single particle undergoing a discrete-time quantum walk (DTQW), where the aperiodic sequences are used to distribute the coin operations at different lattice positions (inhomogeneous DTQW) or by applying the same coin operation at all lattice sites at a given time but choosing different coin operation at each time step according to the chosen aperiodic sequence (time dependent DTQW). We study the energy spectra and the spreading of an initially localized wave packet for different cases, finding that in the case of Fibonacci and Thue-Morse tilings the system is superdiffusive, whereas in the Rudin-Shapiro case it is strongly subdiffusive. Trying to understand this behavior in terms of the energy spectra, we look at the survival amplitude as a function of time. By means of the echo we present strong evidence that, although the three orderings are very different as evidenced by their diffraction spectra, the energy spectra are all singular continuous except for the inhomogeneous DTQW with the Rudin-Shapiro sequence where it is discrete. This is in agreement with the observed strong localization both in real space and in the Hilbert space. Our paper is particularly interesting because quantum walks can be engineered in laboratories by means of ultracold gases or in optical waveguides, and therefore would be a perfect playground to study singular continuous energy spectra in a completely controlled quantum setup.

Upconversion luminescence properties and color tunability of 12CaO⋅7Al2O3:Ho3+/Yb3+ single crystal

Rear earth (RE) ions-doped 12CaO[Formula: see text]7Al2O3 single crystal has been successfully prepared by Czochralski method. Under 980 nm excitation, a strong green upconversion emission at 548 nm and a weaker red upconversion emission at 662 nm were observed. The green upconversion emission is corresponding to the transition of 5F 4/5S[Formula: see text]I8 of Ho[Formula: see text], and the red one is corresponding to the transition of 5F[Formula: see text]I8 of Ho[Formula: see text]. A much weaker NIR band at 762 nm is also observed, which corresponds to the 5F 4/5S[Formula: see text]I7 transition of Ho[Formula: see text]. The pump dependence and luminescence decay dynamics spectra show the green and red upconversion are populated by two-photon process, and the upconversion mechanisms are analyzed in detail. The color of the upconversion luminescence can be changed by simply adjusting the excitation power. RE ions-doped 12CaO[Formula: see text]7Al2O3 single crystal with these properties is expected to have broad application prospects in solid-state multicolor display and instrument integration. RE ions-doped 12CaO[Formula: see text]7Al2O3 single crystal has the ability to replace some traditional single crystals such as LiNbO3 in many applications.

Preparation and upconversion luminescence characterization of 12CaO·7Al2O3:Ho3+/Yb3+ polycrystals

The effect of Yb3+ concentration on the fluorescence of 12CaO·7 Al2O3:Ho3+/Yb3+ polycrystals is investigated. The Raman spectra of pure C12A7 under 633‐nm excitation show that the highest photon energy is 787.267 cm−1, which is not much bigger than general fluorides, so it can realize high efficiency upconversion. The upconversion emission spectra suggest that the green upconversion emission centered at 548 nm and the red upconversion emission at 662 nm correspond to the 5F4/5S2→5I8 and 5F5→5I8 transition of Ho3+ ions, respectively. The intensity of the upconversion luminescence and the ratio of red to green are changed with Yb3+ ion concentration. The pump dependence and luminescence decay dynamics spectra show the green and red upconversion emissions are populated by a two‐photon process, and the upconversion mechanisms are analyzed. The relative luminous efficiencies of green and red emissions are 2.035% and 0.7%, respectively. The normalized efficiency obtained for green emission of Ho3+ at RT when the sample is excited by 980‐nm light with an absorbed intensity of 7.5 W/cm2 is 0.27 cm2/W. This result is comparable to the values obtained in YF3 for the Yb3+, Er3+ green emission. The C12A7 with upconversion red and green light will be a promising luminous material.

Identification of 13- and 14-Coordinated Structures of First Hydrated Shell of [AuCl4]− Acid Aqueous Solution by Combination of MD and XANES

Molecular dynamics simulations combined with multiple scatting X-ray absorption spectral calculations have been employed to study the local geometry of an [AuCl4](-) cluster in acid aqueous solution. It is found that the previously assumed simple octahedral structure with two H atoms located in the axial position of the [AuCl4](-) plane fails to correctly reproduce the experimental X-ray absorption spectra. Molecular dynamics simulations have revealed a very complicated first hydrated water shell that mainly consists of 13 or 14 ligand water molecules. In general, the first hydrated water molecules are located in two orthogonal quasi-elliptic surfaces around [AuCl4](-) cluster. The water molecules' configuration in the first hydrated shell is further confirmed by the X-ray absorption spectral analysis, which gives a good agreement with the experiment when the 13-hydrated and 14-hydrated complexes are evenly mixed. It shows the power of the combined molecular dynamics simulations and spectra calculations in determining the local structure of molecular ligands around the metal center.

Interaction in the Ternary Complexes of HCl−Methanol−X, X = H2O or NH3: Ab Initio Calculations and On-the-Fly Molecular Dynamics

Dynamics, structures, energetics, and vibrational spectra of the ternary complexes of hydrogen chloride with either methanol and water or methanol and ammonia were investigated by on-the-fly molecular dynamics and ab initio and density functional theory (DFT) with aug-cc-pvDZ basis sets. Addition of CH3OH to the HCl-NH3 system catalyzes the proton transfer from HCl to NH3. However, the dynamics of the system show that the proton is not localized on NH3; rather, it is shared between N and Cl.

Modeling and Calculation of the Dynamics of Spectra with Allowance for Isomerization of Complex Molecules

A semiempirical parametric method for modeling of dynamic (time-resolved) electron-vibrational spectra of complex molecules with allowance for isomer-isomer transformations is proposed. It is based on the method developed earlier for construction of three-dimensional spectra of complex molecules without regard for isomer-isomer transformations. All the matrix elements necessary for calculation of spectra can be determined by the methods developed earlier. The time dependence of the population of a large number of vibronic levels has been determined using the iteration numerical method of integrating kinetic equations. Handy computational algorithms and a specialized software for a personal computer have been developed. The computer experiments conducted have shown that the method proposed can be used for modeling of dynamic spectra of complex molecules with allowance for their isomer-isomer transformations in the real-time scale.

Evolution of the dynamic susceptibility of paradigmatic glass formers below the critical temperature Tc as revealed by light scattering

We have studied the molecular glass formers toluene and picoline in the liquid and glassy state by quasi-elastic light scattering applying tandem Fabry–Perot interferometry. Also, we perform an analysis of the susceptibility spectra of the inorganic glasses calcium potassium nitrate (CKN) and silica at T< T g. At high temperatures the evolution of the susceptibility minimum in toluene and picoline is described by mode coupling theory (MCT), and the critical temperature T c can be determined consistently. Below T c the asymptotic laws of MCT fail, and the excess wing of the α process is rediscovered in a similar way as in the dielectric spectra. The wing contribution controls the evolution of the susceptibility minimum and is attributed to a secondary relaxation process different from the slow β process. The fast dynamics spectra exhibit a trend to white noise at low frequencies ( T< T c). We conclude, regarding the fast dynamics, that MCT predictions hold also below T c. In CKN the relaxation mechanism changes below T g and the fast relaxation in both CKN and silica is reproduced by assuming thermally activated transitions in asymmetric double well potentials, while this is not possible for picoline or toluene.

Subpicosecond dynamics spectra in [formula omitted] strained-layer and strained quantum well

The direct observation of refractive-index spectral hole burning in InGaAs GaAs strain layer, and asymmetric double quantum well(ADQW) are demonstrated. The spectral hole burning is believed to be related to nonthermal relaxation mechanism. The nonthermal relaxation time is estimated to be less than several hundred femtoseconds for InGaAs strained layer and InGaAs GaAs ADQWs samples, while the time is too short to be detected for InGaAs GaAs multiquantum-well(MQW) samples in our experiment, in which the one dimensionally confinement enhances the e-h wavefunction over lapping, and reduces the scattering time of nonthermal carriers.

Dynamics and noise spectra of a driven single flux line in superconductors.

We study the low temperature dynamics of a single flux line in a bulk type-II superconductor, driven by the Lorentz force acting near the sample surfaces, both near and above the depinning threshold. We find a novel instability of the flux line motion at large driving currents. The power spectrum of the voltage noise generated by the moving flux line in the presence of random pinning has a ${\mathrm{\ensuremath{\omega}}}^{0.5}$ and ${\mathrm{\ensuremath{\omega}}}^{\mathrm{\ensuremath{-}}0.5}$ form for \ensuremath{\omega}${\mathrm{\ensuremath{\omega}}}_{1}$ and \ensuremath{\omega}&gt;${\mathrm{\ensuremath{\omega}}}_{1}$, respectively, where ${\mathrm{\ensuremath{\omega}}}_{1}$\ensuremath{\rightarrow}0 at the depinning threshold.

Dynamics and optical spectra of an exciton in a deformable lattice

Abstract The dynamics of an exciton strongly interacting with phonons are studied by calculating the optical absorption and the secondary-emission spectra in a new effective-medium approximation which is an extension of the dynamical coherent potential approximation. Relations between spectral line shapes and dynamical relaxation processes are discussed in the case of a self-trapped state being separated from a metastable free state by a potential barrier. It is shown that quantum-mechanical configurational mixing between the free state and the self-trapped state causes sizable effects on the line shape of the absorption spectrum as well as on the excitation-energy dependence of the secondary-emission spectrum.

Dynamics and fluctuation spectra of electrostatic resistive interchange turbulence

The saturation mechanism for density and potential fluctuation spectra that evolve from linearly unstable electrostatic resistive interchange modes are investigated using particle simulations. Detailed comparisons of the nonlinear evolution, saturation levels, and resultant spectra between two- and three-dimensional sheared magnetic field configurations are made. Significant differences appear. The single rational surface, quasilinear-dominated evolution, fluctuation spectrum is adequately described using a density convection model. For the multiple rational surface case, the potential fluctuations are adequately represented by a balance between the nonlinearly modified source (curvature drive) and linear sink (parallel resistive field line diffusion). An accurate description of the density spectrum requires a mode coupling theory based on the two-point density correlation evolution equation.

Dynamics and emission spectra of semiconductor lasers

Dynamics and emission spectra of semiconductor lasers