Optimal wavelet filter for suppression of coherent noise with an application to seismic data

Wavelet analysis is combined with the Karhunen-Loève (KL) transform into an innovative hybrid method for locally filtering coherent noise. In applying our method, the original time series is first decomposed with wavelet transform, the scales more contaminated with noise are reduced by an attenuation factor A_f, and the signal is reconstructed using the inverse wavelet transform. Then the KL transform is applied to the reconstructed signal and the behavior of the first energy modes is analyzed as a function of A_f. The point corresponding to a minimum in the first mode is identified with the maximum extraction of the coherent noise. Our methodology is applied with success to seismic data with the aim of locally extracting the relevant coherent noise, namely the ground roll noise. The procedure can be easily extended to other situations where an undesirable signal is associated with a specific set of energy modes.     

截断的有振幅调制和位相畸变光束的等效曲率半径

高功率激光通常具有振幅调制和相位畸变. 采用统计光学方法推导了截断的有振幅调制和位相畸变光束在大气湍流中传输 的等效曲率半径R的解析公式.研究表明:随着位相畸变参量、振幅调制参量和光 束截断参量的增大,光束在自由空间中的 R增大,但R受湍流的影响也会增大; 并且高斯光束在自由空间中的R最大, 但其受湍流影响也最大. 因此,在大气湍流中传输到足够远时, 截断的有振幅调制和位相畸变光束的R就要比高斯光束的大.特别地, 相对等效曲率半径R_r随传输距离为非单调变化, 存在一个最小值, 即在该位置处R受湍流的影响最大. 此外, 达到 R_r最小值所需传输距离随光束位相畸变和振幅调制的加剧而增大.     

Highly sensitive bend sensor based on Mach-Zehnder interferometer using photonic crystal fiber

Optical fiber bend sensor with photonic crystal fiber (PCF) based Mach-Zehnder interferometer (MZI) is demonstrated experimentally. The results show that the PCF-based MZI is sensitive to bending with a sensitivity of 3.046 nm/m⁻¹ and is independent on temperature with a sensitivity of 0.0019 nm/°C, making it the best candidate for temperature insensitive bend sensors. To that end, another kind of bend sensor with higher sensitivity of 5.129 nm/m⁻¹ is proposed, which is constructed by combining an LPFG and an MZI with zero offset at the second splice mentioned above.     

Solitary wave interactions in lattice systems with pure higher-order nonlinearity

In this paper, we investigate in detail the interactions of solitary waves in lattice systems with interaction potential V(q)=qⁿ/n, where n is 4,6,8…, through their all possible collision types, and establish a quantitative connection between the scattering property of solitary waves and the chaotic dynamics of the systems. Kink and antikink are excited in such lattice systems and the variation of their scattering effect with n is concerned. After a kink-antikink collision, the dominant interaction in the systems, if n is small, is that solitary waves pass through each other and the scattering effect increases with n; if n is large, solitary waves reflect back sometimes due to the influence of phase and this leads to a decrease of the scattering effect with n. The largest Lyapunov exponents of systems at fixed energy density first increase and then decrease with n, which is consistent with a variation of the scattering effect. The application of the special scattering behaviors between kink and antikink in information propagation is also discussed.     

Design and simulation of charge transport in single-electron transistor using TCAD numerical simulator

The ability to control the electron flow of a MOSFET is decreased due to the quantum mechanical effect when scaled down below 50 nm. Hence, A new field of device research is needed to complete this challenge. A device based on Tunneling phenomena is called a single-electron device. In this paper, the most fundamental single-electron device is a single-electron transistor (SET) designed using visual TCAD with a gate length and width of 2 nm. The channel is ultra-thin with a length of 2 nm and a width of 0.005 nm, and the channel thickness is 0.3 nm. Then a Si quantum dot of size 0.5 × 1.nm² is used between the island and the gate. Both the Devices are simulated using the Genius Simulator. And it is found that at room temperature, the device with Si dot is more efficient. The device with Si dot has less capacitance and higher charging efficiency than the device without the Quantum dot.     

Carbon doping induced giant low bias negative differential resistance in boron nitride nanoribbon

By applying nonequilibrium Green's function combined with density functional theory, we investigated the electronic transport properties of carbon-doped armchair boron nitride nanoribbons. Obvious negative differential resistance (NDR) behavior with giant peak-to-valley ratio up to the order of ${10}^4\text{–}{10}^6$ is found by tuning the doping position and concentration. Especially, with the reduction of doping concentration, NDR peak position can enter into mV bias range and even can be expected lower than mV bias. The negative differential resistance behavior is explained by the evolution of the transmission spectra and band structures with applied bias.     

Conversion of FexCo1–x Si and FexMn1–x Si Weak Band Magnetic Materials Caused by the Electron Concentration

The resistance of Fe_xCo_1–x Si and Fe_xMn_1–x Si weak band magnetic materials in the temperature interval 4.2–300 K is measured. Based on the experimental data, the conversion from semiconducting and submetallic materials with negative temperature resistance coefficients (TRC) to materials with positive TRC caused by the electron concentration is described. It is demonstrated that the main reason for the conversion of the electronic structure is splitting of s-, p- and d-electronic spectra in fluctuating exchange fields. As a result, the number of current carriers increases significantly with the temperature. The competition of this effect with electron-phonon scattering is the basic mechanism of forming resistive states with abnormally low TRC in the examined weak band magnetic materials.     

Semigroups of length increasing transformations

The semigroup of all operators T such that (Tx,Tx)?(x,x), for all elements of x of a finite-dimensional complex vector space with ( , ) a given, possibly indefinite Hermitian form on that space, is the object under study. It is shown that this semigroup is closed under the operation of taking adjoints with respect to the given form and that every semigroup element may be written as a product of a unitary and a self-adjoint operator (polar form), with the unitarity and self-adjointness defined with respect to the given form. It is further shown that the semigroup is generated by the group of isometries of the given form and the union of a finite family of semigroups, each of which is of an elementary nature. The intersection of the above semigroup with the complex symplectic group is also considered; all the above results have analogues in this case.     

Non-Equilibrium Dynamics of Dyson’s Model with an Infinite Number of Particles

Dyson’s model is a one-dimensional system of Brownian motions with long-range repulsive forces acting between any pair of particles with strength proportional to the inverse of distances with proportionality constant β/2. We give sufficient conditions for initial configurations so that Dyson’s model with β = 2 and an infinite number of particles is well defined in the sense that any multitime correlation function is given by a determinant with a continuous kernel. The class of infinite-dimensional configurations satisfying our conditions is large enough to study non-equilibrium dynamics. For example, we obtain the relaxation process starting from a configuration, in which every point of \mathbbZ{\mathbb{Z}} is occupied by one particle, to the stationary state, which is the determinantal point process with the sine kernel.     

Phthalocyanine-C60 composites as improved photoreceptor materials?

2 -Pc, in contact with C₆₀ is studied using photoelectron spectroscopy with ultraviolet and X-ray radiation (UPS and XPS, respectively), X-ray absorption near edge spectroscopy (XANES), and optical transmission spectroscopy. A possible improvement of the charge-carrier generation efficiency, which is essential for the performance as photoreceptor material, is thereby found for these materials upon doping with C₆₀. No ground-state charge transfer is detected for the Pcs in contact with C₆₀. The effect of an enhanced photoconductivity is demonstrated for τ-H₂-Pc when it is doped by 5% C₆₀. Received: 16 March 1998/Accepted: 16 March 1998     

Relation between space-charge-limiting current and electric field enhancement factor at curved surface cathode

A two-dimensional solution of space-charge-limiting current for a high current vacuum diode with a spherical cathode is presented. The relation between space-charge-limiting current and electric field enhancement factor at the cathode surface for the diode with a curved surface cathode is also discussed. It is shown that compared with the current given by the conventional Child—Langmuir law, which describes the one-dimensional space-charege-limiting current, the two-dimensional space-charge-limiting current in such a diode is enhanced due to the electric-field enhancement along the cathode surface. Among practical parameter ranges, enhancement factor η_b approximately satisfies η_b ≈ Aβⁿ, where β is the electric field enhancement factor at the cathode surface, and n is a constant between 1 and 2, which is confirmed to be universal for the diodes with curved surface cathodes.     

The impact of light polarization on imaging visibility of Nth-order intensity correlation with thermal light

The relationship between the imaging visibility of arbitrary Nth-order intensity correlation with thermal light and light’s degree of polarization is investigated. It is shown that for the same order correlation, the value of visibility with partially polarized light is greater than that with natural light but smaller than that with completely polarized light, and the visibility in all three cases is remarkably enhanced as N increases.     

Structural analysis, magnetic and electrical properties of samarium substituted lithium-nickel mixed ferrites

A series of Sm-doped Li-Ni ferrites with formula of (Li_0.5Fe_0.5)_0.4Ni_0.6Sm_yFe_2−yO₄, where 0.0≤y≤0.1 were prepared by double sintering ceramic technique. The structure was characterized by X-ray diffraction, which has confirmed the formation of single-phase spinel structure. The samarium concentration dependence of lattice parameters obeys Vegard's law. The octahedral site radii increased with Sm content while the tetrahedral site radii decreased. Deviation from the ideal crystal structure (Δ) is found to decrease with Sm substitution, and the hopping length on the octahedral site is found to increase with Sm content. Hall measurement confirmed p-type conductivity behavior for Sm-doped ferrite and the main charge transport mechanism is hopping of halls between Ni²⁺ and Ni³⁺. Sintering at 1300 °C resulted in low resistivity ferrite, which was found to increase with Sm content. Resistivity is governed by both charge carrier mobility and carrier concentration. It decreases with frequency, and this behavior with frequency is discussed according to Koop's theorem. The dielectric constant is found to decrease more rapidly at low frequencies than at higher frequencies while the dielectric constant increases with Sm content. The decrease in ε″ with frequency agrees with Deby's type relaxation process. Maximum in ε″ is observed when the hopping frequency is equal to the external electric field frequency. The variation in tan δ with frequency shows a similar nature to that of ε″ with frequency. The magnetization under applied magnetic field for the samples exhibits a clear hysteretic behavior. The scanning electron microscope (SEM) studies showed that the domain walls may tend to be trapped (pinned) by non-magnetic inclusions, precipitates and voids. The saturation magnetization (M_S) increases with the sintering temperature, while the coercivity (H_Ci) is found to decrease.     

A molecular dynamics study of fuel droplet evaporation in sub- and supercritical conditions

Evaporation processes of a fuel droplet under sub- and supercritical ambient conditions have been studied using molecular dynamics (MD) simulations. Suspended n-dodecane droplets of various initial diameters evaporating into a nitrogen environment are considered. Both ambient pressure and temperature are varied from sub- to supercritical values, crossing the critical condition of the chosen fuel. Temporal variation in the droplet diameter is obtained and the droplet lifetime is recorded. The time at which supercritical transition happens is determined by calculating the temperature and concentration distributions of the system and comparing with the critical mixing point of the n-dodecane/nitrogen binary system. The dependence of evaporation characteristics on ambient conditions and droplet size is quantified. It is found that the droplet lifetime decreases with increasing ambient pressure and/or temperature. Supercritical transition time decreases with increasing ambient pressure and temperature as well. The droplet heat-up time as well as subcritical to supercritical transition time increases linearly with the initial droplet size d₀, while the droplet lifetime increases linearly with ${\mathrm{d}}_0^2$. A regime diagram is obtained, which indicates the subcritical and supercritical regions as a function of ambient temperature and pressure as well as the initial droplet size.     

Experimental and numerical investigation of a stagnation pulverised coal flame

A multi-stream Flamelet Progress Variable (FPV) model, specifically developed for coal combustion, is proposed. The model accounts for the different fuel streams associated with the volatile and char burnout products. The applicability of the new FPV model is investigated in a laminar stagnation pulverized coal flame. The flame considered is a premixed mixture of CH₄, O₂ and N₂, carrying pulverized coal particles, stabilized in an impinging wall. Spontaneous emissions of OH*, CH* and C${}_2^{*}$ are measured to identify the flame. The 1D numerical simulations of the experimental conditions are able to reproduce the main features of the flame. The applicability of the multi-stream FPV model to coal combustion is further evaluated with the a posteriori analysis of the FPV results, comparing the results with a reference model, where the species are fully transported and the chemistry directly evaluated. Then, with the budget analysis, the influence of the control variables used to build the look-up table is assessed by examining the conditional contributions to the overall transport terms of scalar quantities (e.g. species, temperature). The results of both analyses show that the proposed multi-stream FPV model can accurately predict the main features of coal combustion, with only minor issues related to the manifold used to build the look-up table.     

A wide dynamic range laser rangefinder with cm-level resolution based on AGC amplifier structure

A pulsed time-of-flight (TOF) laser rangefinder with a pulsed laser diode and an avalanche photo diode (APD) receiver is constructed and tested. Trigged by an avalanche transistor, the laser diode can emit a periodic pulse with rise time of ～2 ns. A new structure with auto gain control (AGC) circuits both in the pre-amplifier and the post-amplifier is presented. Through this technology, not only the dynamic range of the receiver is extended, but also the walk error of timing discriminators is reduced. Large measurement range from 5 m to 500 m is achieved without any cooperative target. The single-shot precision is 3 cm for the weakest signal. Compared with previous laser rangefinders, the complexity of this system is greatly simplified.     

Microcanonical Analysis of Exactness of the Mean-Field Theory in Long-Range Interacting Systems

Classical spin systems with nonadditive long-range interactions are studied in the microcanonical ensemble. It is expected that the entropy of such a system is identical to that of the corresponding mean-field model, which is called “exactness of the mean-field theory”. It is found out that this expectation is not necessarily true if the microcanonical ensemble is not equivalent to the canonical ensemble in the mean-field model. Moreover, necessary and sufficient conditions for exactness of the mean-field theory are obtained. These conditions are investigated for two concrete models, the α-Potts model with annealed vacancies and the α-Potts model with invisible states.     

Fractional Klein-Gordon-Schrödinger equations with Mittag-Leffler memory

The main objective of the present investigation is to find the solution for the fractional model of Klein-Gordon-Schrödinger system with the aid of q-homotopy analysis transform method (q-HATM). The projected solution procedure is an amalgamation of q-HAM with Laplace transform. More preciously, to elucidate the effectiveness of the projected scheme we illustrate the response of the q-HATM results, and the numerical simulation is offered to guarantee the exactness. Further, the physical behaviour has been presented associated with parameters present the method with respect fractional-order. The present study confirms that, the projected solution procedure is highly methodical and accurate to solve and study the behaviours of the system of differential equations with arbitrary order exemplifying the real word problems.     

High power nonuniform linear vertical-cavity surface-emitting laser array with a Gaussian far-field distribution

A 980 nm bottom-emitting vertical-cavity surface-emitting laser (VCSEL) array with a nonuniform linear arrangement is reported to realize high power with a Gaussian far-field distribution. This array is composed of five symmetrically-arranged elements of 200 μm, 150 μm, and 100 μm diameters, with the center spacing of 300 μm and 250 μm respectively. This structure makes it possible to discriminate against the higher order array supermodes. The theoretical simulation of the far-field distribution is in good agreement with the experimental result. An output power of 880 mW with a power density of 1 KW/cm² is obtained. The divergence angle is below 20° in the range of operating current from 0 A to 4 A. The comparison between this nonuniform linear array and the conventional two-dimensional array is carried out to demonstrate the good performance of the linear array. A peak power of over 20 W is achieved under a short pulsed operation with a repetition frequency of 1 kHz.     

Noncolliding Squared Bessel Processes

We consider a particle system of the squared Bessel processes with index ν>−1 conditioned never to collide with each other, in which if −1<ν<0 the origin is assumed to be reflecting. When the number of particles is finite, we prove for any fixed initial configuration that this noncolliding diffusion process is determinantal in the sense that any multitime correlation function is given by a determinant with a continuous kernel called the correlation kernel. When the number of particles is infinite, we give sufficient conditions for initial configurations so that the system is well defined. There the process with an infinite number of particles is determinantal and the correlation kernel is expressed using an entire function represented by the Weierstrass canonical product, whose zeros on the positive part of the real axis are given by the particle-positions in the initial configuration. From the class of infinite-particle initial configurations satisfying our conditions, we report one example in detail, which is a fixed configuration such that every point of the square of positive zero of the Bessel function J _ν is occupied by one particle. The process starting from this initial configuration shows a relaxation phenomenon converging to the stationary process, which is determinantal with the extended Bessel kernel, in the long-term limit.