地震事件自动检测新方法

地震事件的自动准确检测是地震速报的基础。本文基于地震信号所具有的非高斯性、非线性以及地震波的线偏振性特征并结合长短时平均比方法,提出了一种新的地震事件自动检测方法(EGLP)。基于山东数字化地震台网波形资料的研究结果表明,新方法(EGLP)能有效抑制高斯噪声、突出地震信号,提高了地震事件触发判断的准确性。

All-Optical Sampling Using Nonlinear Polarization Rotation in a Single Semiconductor Optical Amplifier

We propose a novel all-optical sampling method using nonlinear polarization rotation in a semiconductor optical amplifier. A rate-equation model capable of describing the all-optical sampling mechanism is presented in this paper. Based on this model, we investigate the optimized operating parameters of the proposed system by simulating the output intensity of the probe light as functions of the input polarization angle, the phase induced by the polarization controller, and the ori- entation of the polarization beam splitter. The simulated results show that we can obtain a good linear slope and a large linear dynamic range,which is suitable for all-optical sampling. The operating power of the pump light can be less than lmW. The presented all-optical sampling method can potentially operate at a sampling rate up to hundreds GS/s and needs low optical power.

UV-Polarizing Linear Polyyne Molecules Aligned in PVA

Electronic absorption bands of conjugated linear carbon chain molecules, namely polyynes H(C≡C)nH (n=5-7), are exploited to devise light-polarizing films applicable to the UV. Laser ablated polyynes are separated in size and dispersed in a film of polyvinyl alcohol (PVA), which is stretched to align the trapped linear polyyne molecules inside. As a nature of the structural anisotropy, transition dipole of the UV absorption for polyyne molecules is in parallel with the molecular axis and the absorption occurs only for the electromagnetic wave having the amplitude of its electric vector along the molecular axis. Aligned and fixed orientationally in the solid PVA film, polyyne molecules act as selective absorbers of one of the polarization components of incident light at particular wavelength. Using a light source of linearly polarized UV light, whose direction of polarization is rotatable, angular dependence of the absorption intensity is investigated for the stretched PVA film containing aligned polyyne molecules and analyzed in terms of an order parameter in the theory of linear dichroism.

Novel measurement scheme of peak separation of side-hole fiber grating

There are two peaks of different polarizations in the reflection spectrum of the side-hole fiber grating and their separation interval has a linear variation along with the pressure changing while it is insensitive to the temperature.We have proposed a novel measurement scheme based on polarization detection.The detection of peak separation is achieved by measuring the two peaks’ center wavelengths separately with all polarization maintaining fiber system.The side-hole fiber grating pressure sensing within the range of 0～3.5 MPa is realized successfully with the new scheme.

Experi mental study on a novel polarization state generator

In this letter,a new polarization state generator(PSG) is presented,which can generate an output with arbitrary state of polarization(SOP).This PSG consists of a linear polarizer,a rotatable quarter-waveplate,and a rotatable half-waveplate.The PSG can be used to study the polarization-related effects on optical components and on optical fiber communication systems.

Sensitivity Studies for Monitoring Tropospheric Ozone from Space Using the Ultraviolet,Visible,and Polarization Bands

The authors analyzed the retrieval sensitivity of tropospheric ozone using simulated the Global Ozone Monitoring Experiment-2 （GOME-2） measurements. The retrieval sensitivity was evaluated by the degree of free- dom for signal （DFS）. The combination of the ultraviolet （UV）, UV polarization （UVPOL）, and visible （VIS） bands enhances DFS of tropospheric ozone and improves the vertical resolution of the retrieved ozone profile. UVPOL reduces the dependence on solar zenith angle, mainly in- creases the sensitivity in upper troposphere. Polarization increased the DFS by 20% on the eastern side of the GOME-2 orbit, with little improvement on the western side because the increase in DFS due to polarization is depend- ent on the relative azimuth angle. The inclusion of the visi- ble band reduces significantly the dependence on viewing geometry, and mainly increases the DFS in the lower tro- posphere （0-6 kin） by a factor of two. It was possible to retrieve several independent pieces of tropospheric ozone information from GOME-2 UV/UVPOL/VIS measure- ments, especially in the lower troposphere.

Magnetic and Magneto-Optical Properties in Paramagnetic NdF3 Under High Magnetic Field

In this paper, we first theoretically report the magnetic and magneto-opticalproperties in paramagnetic media under high external magnetic field. Considering the action of theexternal magnetic Geld H_e and indirect exchange interaction H_v, the characteristic of the magneticsaturation and the property of the Faraday rotation to be nonlinear with external magnetic Geld arepresented in paramagnetic NdF_3. In terms of our theory, the indirect exchange interaction plays auimportant role in the magnetization M and the Faraday rotation θ in NdF_3 under high externalmagnetic Geld. The theory is in good agreement with experimental results. On the other hand, areasonable explanation for the temperature dependence of the ratio of the Verdet constant to themagnetic susceptibility V/x is obtained.

Study of Nonpolaritons in a Kerr Nonlinear Optical Resonator

We find that in a Kerr nonlinear optical resonator, the photon system possesses a new kind of quasiparticle, the nonpolariton. The existence of nonpolaritons should be testified by observing the energy density dependence of the velocity and squeezing of nonpolaritons. As we have investigated, the transition energy density of a Kerr nonlinear optical resonator is larger than that of a normal state.

Orientation Angle of Molecules at Hexadecane-Water Interface Studied with Total Internal Reflection Second Harmonic Generation

The orientation angle is an important parameter that reflects the structure of molecules at interfaces. In order to obtain this parameter, second order nonlinear spectroscopic techniques including second harmonic generation （SHG） and sum frequency generation-vibrational spec- troscopy （SFG-VS） have been successfully applied through analysis of the nonlinear signal from various polarizations. In some SHG and SFG-VS experiments, total internal reflection （TIR） configuration has been adopted to get enhanced signals. However, the reports on the detailed procedure of the polarization analysis and the calculation of the orientation angle of interracial molecules under TIR configuration are still very few. In this paper, we mea- sured the orientation angles of two molecules at the hexadecane-water interface under TIR and Non-TIR experimental configurations. The results measured from polarization analysis in TIR configuration consist with those obtained from Non-TIR configuration. This work demonstrates the feasibility and accuracy of polarization analysis in the determination of the orientation angle of molecules at the interfaces under TIR-SHG configuration.

Oscillation Theorems for Second Order Damped Nonlinear Differential Equations

Several oscillation criteria are given for the second order nonlinear differential equation with damped term of the form [α(t)(y'(t))σ]' +p(t)(y'(t))σ+ q(t)f(y(t)) = 0, where α∈C(R, (0,∞)), p(t) and q(t) are allowed to change sign on [t0, ∞), and f∈C1 (R, R) such that xf(x) > 0 for x ≠0. Our results improve and extend some known oscillation criteria. Examples are inserted to illustrate our results.

Oscillation of Nonlinear Impulsive Delay Hyperbolic Partial Differential Equations

In this paper,by making use of the calculous technique and some results of the impulsive differential inequality,oscillatory properties of the solutions of certain nonlinear impulsive delay hyperbolic partial differential equations with nonlinear diffusion coefficient are investigated.Sufficient conditions for oscillations of such equations are obtained.

Steric Effects in the Cl＋CHD3（v1=1） Reaction

A recent study has revealed a full 3-dimentional reactive scattering picture of the reaction CI＋CHD3（v1=1） as the C1 atoms attack CHD3 from various directions respective to the C-H stretching bond. The reported polarization-dependent differential cross sections provide the most detailed characterization of the influences of reagent alignments on reactivity. To convey the stereo-specific information more accessible to general chemists, we show here, by proper symmetry considerations, how to retrieve from the measurements the relative integral and differential cross sections of two most common collision geometries： the end-on versus side-on attacks. The results, albeit coarse-grained, provide an appealing picture that not only reinforces our intuition about chemical reactivity, but also sheds more light on the conventional （unpolarized） attributes.

Oscillation of Solutions for a Class of Nonlinear Neutral Partial Differential Equations with Continuous Distribution Delay

In this paper, some sufficient conditions are obtained for the oscillation of solutions for a class of second order nonlinear neutral partial differential equations with continuous distribution delay under Robin and Dirichlet＇s boundary value conditions.

Optical forces of focused femtosecond laserpulses on nonlinear optical Rayleigh particles

The principle of optical trapping is conventionally based on the interaction of optical fields with linear-induced polarizations. However, the optical force originating from the nonlinear polarization becomes significant when nonlinear optical nanoparticles are trapped by femtosecond laser pulses. Herein we develop the time-averaged optical forces on a nonlinear optical nanoparticle using high-repetition-rate femtosecond laser pulses, based on the linear and nonlinear polarization effects. We investigate the dependence of the optical forces on the magnitudes and signs of the refractive nonlinearities. It is found that the self-focusing effect enhances the trapping ability, whereas the self-defocusing effect leads to the splitting of the potential well at the focal plane and destabilizes the optical trap. Our results show good agreement with the reported experimental observations and provide theoretical support for capturing nonlinear optical particles.

Electron dynamics and wave activities associated with mirror mode structures in the near-Earth magnetotail

We report the observation of mirror mode structures by Cluster spacecraft at around X^-16 RE in the Earth’s magnetotail.The wavelength of the mirror structure is larger than 7000 km,corresponding to tens of ion gyroradii.Features of the mirror structures are similar to those detected in the magnetosheath:the anti-correlation between the magnetic field strength and plasma density,zero phase velocity in the plasma rest frame and linear polarization.The structures were observed in a region bounded by two dipolarizations during a substorm intensification.Thus,the dipolarization process may provide a plasma condition facilitating the growth of the mirror mode structures.Another interesting feature is the electron dynamics within the mirror structures.Thermal electron energy flux has an enhancement at 0°and 180°pitch angles inside the magnetic dips of the first three mirror structures and an enhancement at 90°pitch angle inside the magnetic dip of the last structure.The different electron distribution inside the mirror structures might be a result of different evolution stages of the mirror wave.The last structure may be in the nonlinear stage of the mirror instability,whereas the three others with quasi-sinusoidal waveforms may be in the linear stage.In addition,we found that intense whistler waves were confined within the magnetic dips.We conjecture that whistler waves observed in the first three dips were generated in a remote region,then they were trapped in the mirror mode troughs and transported toward the spacecraft;while the whistler wave detected in the last dip was excited locally by the electron anisotropy instability.

Angular momentum density of a Gaussian vortex beam

The Gaussian vortex beam is assumed to be linearly polarized.The analytical expression of the electric field of a linearly polarized Gaussian vortex beam propagating in free space is derived by using the vectorial Rayleigh-Sommerfeld integral formulae.The propagating magnetic field of the linearly polarized Gaussian vortex beam is presented by taking the curl of the electric field.By employing the electromagnetic field of the linearly polarized Gaussian vortex beam beyond the paraxial approximation,the analytical expression of the angular momentum density of the linearly polarized Gaussian vortex beam is derived.The three components of the angular momentum density of a linearly polarized Gaussian vortex beam are demonstrated in the reference plane.The effects of the linearly polarized angle and the topological charge on the three components of the angular momentum density are investigated.To acquire the more longitudinal angular momentum density requires such an optimal choice that the linearly polarized angle is set to be zero and the topological charge increases.This research is useful to the optical trapping,the optical guiding,and the optical manipulation.

Electron-Positron Pair Production in an Arbitrary Polarized Ultrastrong Laser Field

Electron-positron pair production in an arbitrary polarized ultrastrong laser field is investigated in the first order perturbation approximation in which the Volkov states are used for convenient calculation of scattering amplitude and cross section. It is found surprisingly that the optimal pair production depends strongly on the polarization. For some cases of field parameters, the optimal field is e11iptically polarized or evenly circularly polarized one, rather than the usual linear polarization as indicated by previous works interesting unexpected features are a/so discussed briefly. Some insights into pair generation are given and some

Transverse vibration of pre-tensioned nonlocal nanobeams with precise internal axial loads

This paper investigates the transverse vibration of a simply supported nanobeam with an initial axial tension based on the nonlocal stress field theory with a nonlocal size parameter. Considering an axial elongation due to transverse vibration, the internal axial tension is not precisely equal to the external initial tension. A sixth-order nonlinear partial differential equation that governs the transverse vibration for such nonlocal nanobeam is derived. Using a perturbation method, the relation between natural frequency and nonlocal nanoscale parameter is derived and the transverse vibration mode is solved. The external axial tension and nonlocal nanoscale parameter are proven to play significant roles in the nonlinear vibration behavior of nonlocal nanobeams. Such effects enhance the natural frequency and stiffness as compared to the predictions of the classical continuum mechanics models. Additionally, the frequency is higher if the precise internal axial load is considered with respect to that when only the approximate internal axial tension is assumed.

OSCILLATION OF A FORCED SECOND ORDER NONLINEAR EQUATION

This paper gives several criteria on the oscillatory behavior of solutions of the forced secondorder equation x″+ a(t)i(x) = g(t), where g(t) is oscillatory) by using a geometric idea. Asspecial cases these results include and improve some recent results, given by J. S. Wong. Thecriteria also solve the problem posed by H. Onose in Mathematical Reviews, 1986.

Self-error-rejecting photonic qubit transmission in polarization-spatial modes with linear optical elements

We present an original self-error-rejecting photonic qubit transmission scheme for both the polarization and spatial states of photon systems transmitted over collective noise channels. In our scheme, we use simple linear-optical elements, including half-wave plates, 50:50 beam splitters, and polarization beam splitters, to convert spatial-polarization modes into different time bins. By using postselection in different time bins, the success probability of obtaining the uncorrupted states approaches 1/4 for singlephoton transmission, which is not influenced by the coefficients of noisy channels. Our self-error-rejecting transmission scheme can be generalized to hyperentangled n-photon systems and is useful in practical high-capacity quantum communications with photon systems in two degrees of freedom.