Oscillator Research Articles

On lattice oscillator equilibrium equation with positive infinite-range many-body potentials

The symmetrized lattice Kirkwood-Salsburg (KS) equation for the Gibbs grand canonical correlation functions of the lattice oscillators, interacting via positive infini te-range manybody potentials, is solved. The symmetrization is based on the superstability condition for the potentials.

Probing Hamiltonian dynamics by means of the 0–1 test for chaos

A recently proposed test for chaos (Gottwald G A and Melbourne I 2004 Proc. R. Soc. A 460 603–11) is employed to probe the Hamiltonian dynamics of a one-dimensional anharmonic oscillator lattice. For a homogeneous (uniform mass) lattice in the weakly chaotic regime and for a heavy impurity embedded in the lattice, the results stemming from the time record of the position and momentum of a single oscillator in the former case, and for that same variables corresponding to the impurity in the latter, are inconclusive to determine the dynamical regime of the system. This seemingly odd behavior has its origin in the insufficient time-series length employed. Nevertheless, for both cases the necessary time record length needed to obtain the correct result renders the test impractical. In particular, for the second case, specially in the large system size limit (which is the physically relevant one due to its connection with Brownian motion), the estimated length of the position time series required by the test to correctly classify the signal is beyond the reach of present-day computer capability. Thus, our results indicate that the proposed test, for the aforementioned cases of Hamiltonian chaos, affords no clear advantage over conventional phase-space reconstruction methods.

Anisotropic electrical and dispersive optical parameters in InS layered crystals

The anisotropy effect on the current transport mechanism and on the dispersive optical parameters of indium monosulfide crystals has been studied by means of electrical conductivity and polarized reflectance measurements along the a -axis and the b -axis, respectively. The temperature-dependent electrical conductivity analysis in the range 10–350 K for the a -axis and in the range 30–350 K for the b -axis revealed the domination of the thermionic emission of charge carriers and the domination of variable range hopping above and below 100 K, respectively. At high temperatures ( T > 100 K ) the conductivity anisotropy, s , decreased sharply with decreasing temperature following the law s ∝ exp ( − E s / k T ) . The anisotropy activation energy, E s , was found to be 330 and 17 meV above and below 220 K, respectively. Below 100 K, the conductivity anisotropy is invariant with temperature. In that region, the calculated hopping parameters are altered significantly by the conductivity anisotropy. The optical reflectivity analysis in the wavelength range 250–650 nm revealed a clear anisotropy effect on the dispersive optical parameters. In particular, the static refractive index, static dielectric constant, lattice dielectric constant, dispersion energy and oscillator energy exhibited values of 2.89, 8.39, 19.7, 30.02 eV and 4.06 eV, and values of 2.76, 7.64, 25.9, 22.26 eV and 3.35 eV for light polarized along the a -axis and the b -axis, respectively.

Observation of a coherent optical phonon in the iron pnictide superconductorBa(Fe1−xCox)2As2(x=0.06and 0.08)

We report the observation of a coherent lattice oscillation in a pnictide superconductor. A coherent fully symmetric optical phonon was detected in $\text{Ba}{({\text{Fe}}_{1\ensuremath{-}x}{\text{Co}}_{x})}_{2}{\text{As}}_{2}$ ($x=0.06$ and $x=0.08$) using time-resolved pump-probe reflectivity with 40 fs time resolution. The analysis of the phonon parameters for various excitation fluences reveals no evident difference below and above the critical temperature, suggesting that the ${A}_{1g}$ mode is not involved in the superconducting phase transition.

Absence of Slow Sound Modes in Supersolid 4He

Torsional oscillator experiments on solid 4He have been interpreted as showing mass decoupling similar to what one observes in a superfluid. Within the context of a two-component model for the supersolid one would expect the appearance of a second, slow acoustic mode. We have searched for this mode using an acoustic resonance technique. We have used porous membranes in bulk solid 4He analogous to a second sound experiment in the superfluid. We also investigated solid helium in Vycor using piezoelectrically driven titanium diaphragms (analogous to a fourth sound experiment in the liquid). Our measurements have shown no indication of an additional sound mode in the kHz range.

Bloch Oscillations in Complex Crystals withPTSymmetry

Bloch oscillations in complex lattices with PT symmetry are theoretically investigated with specific reference to optical Bloch oscillations in photonic lattices with gain or loss regions. Novel dynamical phenomena with no counterpart in ordinary lattices, such as nonreciprocal Bloch oscillations related to violation of the Friedel's law of Bragg scattering in complex potentials, are highlighted.

Propagation velocity of longitudinal and transverse acoustic waves and anharmonicity of lattice oscillations

A linear correlation between the Gruneisen parameter and ratio of the velocities of longitudinal (νl)and transverse (νt) acoustic waves in crystals is found. It is assumed that velocities νl and νt are severally harmonic parameters, while their ratio νl/νt is an anharmonic quantity and depends on the ratio between the shear and flexural rigidities of interatomic bonds.

Theoretical Temperature Dependence of the Charge-Carrier Mobility in Semiconducting Polymers

We present a theory of the temperature and electric field dependence on the mobility of polarons in conjugated polymers in terms of a tight-binding and stochastic approach. The polaron mobility is shown to have a strong dependence on the electric field, with two distinct regimes of temperature dependence. Lattice thermal oscillations enhance polaron mean velocity for electric fields of 1.0 mV/A or higher. In contrast, its mobility is damped by thermal oscillations under weaker electric fields. This semiconductor/metallic analogous behavior comes from the difference between the inertial content acquired by polarons under stronger/weaker electric fields. These new results and their analysis shed new light on several experimental controversies.

Periodic, quasiperiodic and chaotic discrete breathers in a parametrical driven two-dimensional discrete diatomic Klein–Gordon lattice

We study a two-dimensional (2D) diatomic lattice of anharmonic oscillators with only quartic nearest-neighbor interactions, in which discrete breathers (DBs) can be explicitly constructed by an exact separation of their time and space dependence. DBs can stably exist in the 2D discrete diatomic Klein–Gordon lattice with hard and soft on-site potentials. When a parametric driving term is introduced in the factor multiplying the harmonic part of the on-site potential of the system, we can obtain the stable quasiperiodic discrete breathers (QDBs) and chaotic discrete breathers (CDBs) by changing the amplitude of the driver. But the DBs and QDBs with symmetric and anti-symmetric profiles that are centered at a heavy atom are more stable than at a light atom, because the frequencies of the DBs and QDBs centered at a heavy atom are lower than those centered at a light atom.

Renormalization of oscillator lattices with disorder

A real-space renormalization transformation is constructed for lattices of nonidentical oscillators with dynamics of the general form dvarphi_{k}/dt=omega_{k}+g summation operator_{l}f_{lk}(varphi_{l},varphi_{k}) . The transformation acts on ensembles of such lattices. Critical properties corresponding to a second-order phase transition toward macroscopic synchronization are deduced. The analysis is potentially exact but relies in part on unproven assumptions. Numerically, second-order phase transitions with the predicted properties are observed as g increases in two structurally different two-dimensional oscillator models. One model has smooth coupling f_{lk}(varphi_{l},varphi_{k})=phi(varphi_{l}-varphi_{k}) , where phi(x) is nonodd. The other model is pulse coupled, with f_{lk}(varphi_{l},varphi_{k})=delta(varphi_{l})phi(varphi_{k}) . Lower bounds for the critical dimensions for different types of coupling are obtained. For nonodd coupling, macroscopic synchronization cannot be ruled out for any dimension D> or =1 , whereas in the case of odd coupling, the well-known result that it can be ruled out for D<3 is regained.

Periodic, Quasiperiodic and Chaotic Discrete Breathers in a Parametrical Driven Two-Dimensional Discrete Klein-Gordon Lattice

We study a two-dimensional lattice of anharmonic oscillators with only quartic nearest-neighbor interactions, in which discrete breathers can be explicitly constructed by an exact separation of their time and space dependence. DBs can stably exist in the two-dimensional Klein–Gordon lattice with hard on-site potential. When a parametric driving term is introduced in the factor multiplying the harmonic part of the on-site potential of the system, we can obtain the stable quasiperiodic discrete breathers and chaotic discrete breathers by changing the amplitude of the driver.

Experimental Observation of Rabi Oscillations in Photonic Lattices

We demonstrate spatial Rabi oscillations in optical waveguide arrays. Adiabatic transitions between extended Floquet-Bloch modes associated with different bands are stimulated by periodic modulation of the photonic lattice in the propagation direction. When the stimulating modulation also carries transverse momentum, the transition becomes indirect, equivalent to phonon-assisted Rabi oscillations. In solid state physics such indirect Rabi oscillations necessitate coherent phonons and hence they have never been observed. Our experiments suggest that phonon-assisted Rabi oscillations are observable also with Bose-Einstein condensates, as well as with other wave systems-where coherence can be maintained for at least one period of the Rabi oscillation.

Study on the adsorption of endotoxin and proinflammatory cytokines with HB-H-7 resin in vitro

To study the efficacy and safety of adsorption of endotoxin and proinflammatory cytokines with HB-H-7 resin in vitro. Static adsorption experiment: HB-H-7 resin was added into plasma of endotoxin-positive patients according to the ratio of 1;10. Then, they were put in a constant temperature water bath oscillator, and oscillated for 2 hours. Before and after the experiment, plasma endotoxin, proinflammatory cytokines, protein and electrolytes were detected, and the rate of 2-hour absorption was calculated. The experiment was repeated 10 times. Dynamic adsorption experiment: 5 ml resin was put into a self-made perfusion unit. Endotoxin-positive patients plasma (50 ml) was perfused for 2 hours. The flow rate of plasma was controlled at 4 ml/min with the infusion pump, and the plasma endotoxin was determined at 0, 30, 60 and 120 minutes after plasma hemoperfusion, and the absorption rates were calculated. The results were compared with static adsorption. The influence of temperature during adsorption was determined as follows. Perfusion method was similar with dynamic adsorption experiment. The perfusion units were either placed in a 37 centigrade water path or 25 centigrade (room temperature). Then, the plasma endotoxin was measured 2 hours after plasma perfusion, and the absorption rates were calculated. In static adsorption experiment, the plasma endotoxin and proinflammatory cytokines were significantly lower after adsorption with HB-H-7 resin adsorption (all P<0.05). The adsorption rates of endotoxin, tumor necrosis factor-alpha and interleukin-1, 6, 8 were 99.2%, 55.0%, 57.0%, 75.0%, 42.0%, respectively. Changes in protein were small (all P<0.05) , and there was no significant change in plasma electrolytes (all P>0.05). Dynamic adsorption rate was higher than that of static, but the differences were not significant (99.8% vs. 99.1%, P>0.05). There was no statistically significant difference between difference in temperature (37 centigrade vs. 25 centigrade, 99.8% vs. 99.9%, P>0.05). HB-H-7 resin effectively absorbs endotoxin and proinflammatory cytokines in vitro. Its adsorption rate for protein is lower, and it has no obvious effects on electrolytes.

Investigations on the Transient Mould Friction Force in Slab Continuous Casting based on Fast Fourier Transformation

In continuous casting, the friction forces in the mould reflect the lubrication between the mould and slab, moreover, they affect the slab surface quality and caster productivity. In the present research the friction force is calculated by measuring the difference of working forces during HOT and COLD tests, which are carried out on the slab continuous caster equipped with hydraulic oscillators. Through analysing the mould friction using the Fast Fourier Transformation (FFT) method, the effects of mould oscillation mode and casting speed on the mould friction force are evaluated. The characteristics of the friction signal in the frequency domain are also investigated. Especially, the characteristics of friction force fluctuations before breakouts are discussed. The experimental and analytical results may contribute to more clearly understand the transient lubrication behaviour not only in the time domain but also in the frequency domain, which is also useful for the application of FFT in data analysis of mould processes.

Analytical solution for estimation of temperature-dependent material properties of metals using modified morse potential

Summary An atomic-level analytical solution, together with a modified Morse potential, has been developed to estimate temperature-dependent thermal expansion coefficients (CTE) and elastic characteristics of bulk metals. In this study, inter-atomic forces are considered as a set of anharmonic oscillator networks which can be described by Morse potential, while the material properties can be defined by these inter-atomic forces; when temperature increases, the vibration of the anharmonic oscillator causes the phenomenon of temperature-dependent material properties. The results of analysis showed that the original Morse potential can give a reasonable prediction of the thermal expansion coefficients and elastic constants of metals at room temperature; however, it has difficulties in giving an accurate result at low and high temperatures. Therefore, to overcome the deficiency, a temperaturedependent modified Morse potential is developed and validated with various metals.

DESIGN AND ANALYSIS CONSIDERATIONS OF 4-GHZ INTEGRATED ANTENNA WITH NEGATIVE RESISTANCE OSCILLATOR

DESIGN AND ANALYSIS CONSIDERATIONS OF 4-GHZ INTEGRATED ANTENNA WITH NEGATIVE RESISTANCE OSCILLATOR

Vortex lattice oscillations in rotating neutron stars with quark “CFL” cores

Collective elastic oscillations of a lattice of nonabelian quark semisuperfluid vortex filaments in the superfluid core of a rotating neutron star are examined. It is shown that in the incompressible fluid approximation, transverse long wavelength oscillations (Tkachenko oscillations) owing to shear deformation of the vortex lattice propagate in a plane perpendicular to the axis of rotation. The periods of these oscillations are consistent with rotational variations on the order of 100-1000 days observed in the pulsars PSR B0531+21 and PSR B1828-11.

CMOS digitally programmable quadrature oscillators

CMOS digitally programmable quadrature oscillators based on digitally controlled current followers and voltage followers are proposed. The proposed designs provide the advantage of programmability ...

Traveling waves and compactons in phase oscillator lattices

We study waves in a chain of dispersively coupled phase oscillators. Two approaches—a quasicontinuous approximation and an iterative numerical solution of the lattice equation—allow us to characterize different types of traveling waves: compactons, kovatons, solitary waves with exponential tails as well as a novel type of semicompact waves that are compact from one side. Stability of these waves is studied using numerical simulations of the initial value problem.

The death of quasi-periodic regimes in a system of dissipatively coupled van der Pol oscillators under pulsed drive action

We have studied a system of coupled van der Pol oscillators under pulsed drive action. In the case where the coupled oscillators exhibit the death of oscillations, the introduction of a pulsed drive leads to the appearance of islands corresponding to quasi-periodic regimes in the drive period-amplitude plane, which are also dying with an increase in the frequency detuning.