Collectivity under random two-body interactions

In this paper we study collective motion under random two-body interactions in the fermion dynamical symmetry Model (FDSM). It is found that a Hamiltonian with the SO(8) symmetry of the FDSM does not give generic vibration and rotation under random interactions while that with the SP(6) symmetry does.     

Tracking problem under a time-varying topology

This paper studies the multi-agent tracking problem of a third-order maneuvering target under uncertain communication environments. Each tracking agent is assumed to be a third-order system and can only use its own and neighbors＇ position, velocity, and acceleration information to design its control input. In this work, the uncertain communication environments are modelled by a finite number of constant Laplacian matrices together with their corresponding scheduling functions. Sufficient conditions for the existence of a tracking strategy have been expressed in terms of the solvability of linear matrix inequalities. Finally, a numerical example is employed to demonstrate the effectiveness of the proposed tracking strategy.     

Partially Diffusive Helium-Silica Compound under High Pressure

Helium is the second most abundant element in the universe, and together with silica, they are important components of giant planets. Exploring the reactivity and state of helium and silica under high pressure is crucial for understanding of the evolution and internal structure of giant planets. Here, using first-principles calculations and crystal structure predictions, we identify four stable phases of a helium-silica compound with seven/eight-coordinated silicon atoms at pressure of 600–4000 ...     

Phase transitions in h-thiourea under electric‐field

Abstract

Dielectric constant, spontaneous polarization and pyroelectric response measurements were performed on thin samples (e < 100 μm) of H-thiourea as a function of temperature and applied electric field. Along with previous data obtained by optical birefringence, X-ray and neutron diffraction techniques, the results put in evidence three features in the modulated region between the ferroelectric state and the paraelectric one. The tricritical point is determined for E_tr ? 2075 V/mm and T_tr ? 192 K.     

L-α-alanine doped TGS under hydrostatic pressure

Abstract

A phenomenological model describing spontaneous polarization, pyroelectric, pressure-electric properties and dielectric permittivity of pure and 1-α-alanine doped TGS crystals is presented. Conclusions resulting from the model is illustrated by experimental data. Basic parameters of pressure-electric detectors and transducers made of doped or irradiated ferroelectric crystals can be estimated from the data determined for respective pure crystals.     

Half-life estimation under indefinite “mother-daughter” relation

An algorithm has been proposed to build an estimate of the half-life of a “daughter” nucleus in case, when it is unknown, which nucleus is its “mother” (“indefinite start time”). For a decay of the “mother” at an instant t we can determine P—a probability of such a decay, if we assume that each “mother”, which has been decayed before t has equal chances to be “mother” of this “daughter”:

Undulation instability under shear: A model to explain the different orientations of a lamellar phase under shear?

We study the effects of a dilation on a sheared smectic A phase. Through a linear analysis, we show that undulation may grow in the direction of the flow and of the vorticity as found in previous works. At higher shear rates, we evidence that the undulation along the flow disappears whereas it persists in the vorticity direction. We determine the stable or unstable zone as a function of the shear rate and of the lamellar spacing. This allows us to draw a theoretical shear diagram of the instability. Finally we compare our results with the orientations found experimentally in a lyotropic lamellar phase under shear. Our diagram describes qualitatively and quantitatively the transition observed at high shear rate. Received 18 October 1999     

Evolution of Spiral Waves under Modulated Electric Fields

Spirals generated from the excitable media within the Barkley model is investigated under the gradient electric fields by a numerical simulation. The spiral drift and spiral break up are observed when the amplitude of the electric fields is modulated by a constant signal or a chaotic signal. It is also verified that, even in the presence of the white noise, the whole system can reach homogeneous states after the spiral breakup, by using an adaptive strategy.     

Vehicle–bridge interaction analysis under high-speed trains

The dynamic interaction between high-speed train and simply supported girders is studied by theoretical analysis and field experiment in this paper. The dynamic interaction model of the train–bridge system is established, in which the rigid-body dynamics theory, finite element method and wheel–rail displacement corresponding assumption are adopted for the vehicle model, bridge model and wheel–rail interaction model, respectively. The measured track irregularities are taken as the system excitation. The responses of a 24 m-span PC box girder bridge are calculated. The proposed analysis model and the solution method are verified through the comparison between the calculated results and the measured results.     

Stability of Decoherence-Free Subspaces under Stochastic Phase Fluctuations

We study the stability of decoherence-free subspaces under stochastic phase fluctuations by analytically and numerically evaluating the fidelity of the corresponding decoherence-free subspace bases with stochastic phase fluctuations under the evolution of environment. The environment is modeled by a bath of oscillators with infinite degrees of freedom and the register-bath coupling is chosen to be a general dissipation-decoherence form. It is found that the decoherence-free subspaces take on good stability in the case of small dissipation and small phase fluctuations.     

Entanglement of Λ atoms under coherent population trapping

The entanglement of the internal states in ensembles of Λ atoms under coherent population trapping has been considered. The entanglement conditions for the pairs and triples of atoms have been derived in the form of inequalities for the correlation functions of the resonant optical field amplitudes. The fulfillment of these conditions requires the nonclassicality (the absence of positive definiteness) of the probability distribution of the amplitudes.

     

Excitonic Absorption of Semiconductor Nanorings under Terahertz Fields

The optical absorption of GaAs nanorings （NRs） under adc electric field and a terahertz （THz） ac electric field applied in the plane containing the NRs is investigated theoretically. The NRs may enclose some magnetic flux in the presence of a magnetic field perpendicular to the NRs plane. Numerical calculation shows that the excitonic effects are essential to correctly describe the optical absorption in NRs. The applied lateral THz electric field, as well as the dc field leads to reduction, broadening and splitting of the exciton peak. In contrast to the presence of a dc field, significant optical absorption peak arises below the zero-field bandgap in the presence ofa THz electric field at a certain frequency. The optical absorption spectrum depends evidently on the frequency and amplitude of the applied THz field and on the magnetic flux threading the NRs. This promises potential applications of NRs for magneto-optical and THz electro-optical sensing.     

Entanglement of Λ atoms under coherent population trapping

The entanglement of the internal states in ensembles of Λ atoms under coherent population trapping has been considered. The entanglement conditions for the pairs and triples of atoms have been derived in the form of inequalities for the correlation functions of the resonant optical field amplitudes. The fulfillment of these conditions requires the nonclassicality (the absence of positive definiteness) of the probability distribution of the amplitudes.     

Isostructural Phase Transition of TiN under High Pressure

In situ high-pressure energy dispersive x-ray diffraction experiments on polycrystalline powder TiN with NaCltype structure have been conducted with the pressure up to 30.1 GPa by using a diamond anvil cell instrument with synchrotron radiation at room temperature. The experimental results suggest that an isostructural phase transition might exist at about 7 GPa as revealed by the discontinuity of V/Vo with pressure.     

Resonance in Defect Turbulence under Periodic External Force

The periodically forced spatially extended Brusselator is investigated in the chaotic regime. We explore resonant or non-resonant patterns generated under various forcing frequencies and forcing amplitudes. Resonant spatially uniform oscillation and irregular structures are found. Furthermore two types of regular spatial patterns are generated under appropriate parameters. Our results of numerical simulations demonstrate that periodic force can give rise to resonant patterns in forced systems of spatiotemporal chaos similar to the situation of forced systems of regular oscillations.     

Liquid Water Structure from Anomalous Density under Ambient Condition

From discussion of the structure of liquid water, we deduce that water under ambient condition is mainly composed of ice Ih-like molecular dusters and clathrate-like molecular clusters. The water molecular dusters remain in a state of chemical equilibrium （reversible clustering reactions）. This structural model can be demonstrated by quantitative study on anomalous density with increasing temperature at ambient pressure.     

Processing of gadolinium–iron garnet under non-equilibrium conditions

We have investigated the mechanosynthesis of gadolinium iron garnet (GdIG) by high-energy ball-milling of 3.(Gd₂O₃)?+?10.(α-Fe) followed by thermal annealing conducted at moderate temperatures (1100 °C). The samples were characterized by X-ray diffraction and Mössbauer spectroscopy in order to determine the influence of the milling time on the final products. For as-milled samples the results revealed the enlargement of the magnetic component belonging to iron and a discrete paramagnetic component. The formation of a garnet phase was observed in all as-annealed samples treated at 1100 °C for 6 h in quantities proportional to the time of grinding the precursors. Evidently, high-energy ball milling of Gd₂O₃?+?α-Fe powders is an important step in GdIG synthesis by a ceramic method. Single-phase garnet is observed for the samples milled for 12 and 24 h treated at 1100 °C for 6 h.     

A Theoretical Scheme for Entanglement Transfer under Intensity-Dependent Couplings

We consider a theoretical scheme for entanglement transfer between a two-mode squeezed vacuum field and two initially separable atoms through intensity-dependent couplings. We find that the entanglement transfer between the field and the atoms has an exact period for any given squeezing. We also find that the maximum achievable entanglement of the atomic subsystem is a simple increasing function of r.For sufficiently large squeezing parameter r, it is possible for the atoms to be entangled into a Bell state at half the periodic time points.     

Target detection under sea background using constructed biorthogonal wavelet

A new technique is presented to detect targets under sea background. Focused on interested areas, the spatial and frequency distributions are first studied, then analytic expression of targets is set up by least square method (LSM). According to the shape, frequency, and analytic expression of targets, a matched biorthogonal wavelet is constructed to better enhance targets and eliminate noises. Results show the usefulness of this method for single frame detection (signal to noise ratio SNR≥1.25), which provides a better performance than classic wavelets and morphological filtering.